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  • 99351.
    Yan-Fang, Li
    et al.
    Tianjin University of Technology, China .
    Yang, Li-Ying
    Tianjin University of Technology, .
    Qin, Wen-Jing
    Tianjin University of Technology, .
    Yin, Shou-Gen
    Tianjin University of Technology, .
    Zhang, Feng-Ling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, The Institute of Technology.
    Efficiency Enhancement of MEH-PPV: PCBM Solar Cells by Addition of Ditertutyl Peroxide as an Additive2013In: Chinese Physics Letters, ISSN 0256-307X, E-ISSN 1741-3540, Vol. 30, no 1Article in journal (Refereed)
    Abstract [en]

    Improved power conversion efficiency (PCE) and stability of organic bulk heterojunction (BHJ) solar cells based on poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and methanofullerene [6,6]-phenyl C-61-butyric acid methyl ester (PCBM) blends are obtained by using ditert butyl peroxide (DTBP) as an additive. The effect of the DTBP contents on the performance of photovoltaic cells is investigated. The results reveal that efficiency enhancement of MEH-PPV: PCBM solar cells can be realized by carefully tuning the contents of DTBP. Compared to the control device, the optimized device with 0.5wt% DTBP additive exhibits enhanced performance with J(sc) of (3.51 +/- 0.21) mA/cm(2), FF of (44.45 +/- 0.71)%, and PCE of (1.31 +/- 0.08)%, increased by 9.3%, 8.0% and 22.4%, respectively. The stability of the device is found to be improved by adding 0.5wt% of DTBP.

  • 99352.
    Yang, Biao
    et al.
    Soochow University, Peoples R China.
    Björk, Jonas
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Chemistry. Linköping University, Faculty of Science & Engineering.
    Lin, Haiping
    Soochow University, Peoples R China.
    Zhang, Xiaoqing
    Soochow University, Peoples R China.
    Zhang, Haiming
    Soochow University, Peoples R China.
    Li, Youyong
    Soochow University, Peoples R China.
    Fan, Jian
    Soochow University, Peoples R China.
    Li, Qing
    Soochow University, Peoples R China.
    Chi, Lifeng
    Soochow University, Peoples R China.
    Synthesis of Surface Covalent Organic Frameworks via Dimerization and Cyclotrimerization of Acetyls2015In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, no 15, p. 4904-4907Article in journal (Refereed)
    Abstract [en]

    The formation of additional phenyl rings on surfaces is of particular interest because it allows for the building-up of surface covalent organic frameworks. In this work, we show for the first time that the cyclotrimerization of acetyls to aromatics provides a promising approach to 2D conjugated covalent networks on surfaces under ultrahigh vacuum. With the aid of scanning tunneling microscopy, we have systematically studied the reaction pathways and the products. With the combination of density functional theory calculations and X-ray photoemission spectroscopy, the surface-assisted reaction mechanism, which is different from that in solution, was explored.

  • 99353.
    Yang, Cha
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Municipal Solid Waste Management in an urban area of China: Case studies of Shanghai, China and Linköping, Sweden.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With the rapid and large increase of waste quantities, China, surpassed the USA as the world’s largest municipal solid waste (MSW) generator since 2004. The phenomena and critical issues of MSWM in China inspired this paper to investigate and analyse the MSWM in an urban area of China. Comparing with the increasing rates of MSW generation, little has been done concerning the municipal solid waste management (MSWM). Not only the local government and authorities are responsible for the MSWM, but also the individuals are playing a significant role in MSWM. An integrated waste management system should be built in order to improve the holistic MSW system and reduce the waste production. The aim of the study is to investigate and analyse the current status and problems of MSWM in an urban area of China and to analyse to what extent a viable reduction of the MSW can be implemented and management systems to be improved in the near future. In this study, two case studies of Shanghai and Linköping are employed and compared to explore the challenges and potentials for improving the MSWM system in China. The result indicated that inadequate facilities and infrastructure, less advanced technology, insufficient public participation, low awareness of environmental protection, problems in policy and laws are the major barriers for the improvement of MSWM. Involving international environmental cooperation activities, planning a sustainable and comprehensive policy and framework for MSWM, introducing economic incentive approaches, promoting the capacities of waste management technologies, raising public environmental awareness are believed to be viable solutions to improve the MSWM system in China.

  • 99354.
    Yang, Ching-Hsiang
    Linköping University, Department of Electrical Engineering, Communication Systems.
    Screen Content Coding in HEVC: Mixed Raster Content with Matching Pursuit2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Screen content coding is used to improve coding efficiency of synthetic contents in videos, such as text and UI elements, as opposed to contents captured using photo-graphic equipment, which most video codecs are optimized for. One way of improving screen content coding efficiency is to utilize mixed block coding with matching pursuit. By separating the prediction and transformation steps for overlay and background elements, better contrast and signal-to-noise ratio can be achieved. The paper describes the implementation of such algorithm within the HEVC reference encoder, and discusses the experimental results on several test images.

  • 99355. Yang, Dan-Hui
    et al.
    Andersson, Bertil
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Cell biology.
    Aro, Eva-Mari
    Ohad, Itzhak
    The redox state of the plastoquinone pool controls the level of the light-harvesting chlorophyll a/b binding protein complex II (LHC II) during photoacclimation.2001In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 68, p. 163-174Article in journal (Refereed)
  • 99356. Yang, Dan-Hui
    et al.
    Paulsen, Harald
    Andersson, Bertil
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Cell biology.
    The N-terminal domain of the light-harvesting chlorophyll a/b-binding protein complex (LHCII) is essential for its acclimative proteolysis2000In: FEBS Letters, ISSN 0014-5793, E-ISSN 1873-3468, Vol. 466, no 2-3, p. 385-388Article in journal (Refereed)
    Abstract [en]

    Variations in the amount of the light-harvesting chlorophyll a/b-binding protein complex (LHCII) is essential for regulation of the uptake of light into photosystem II. An endogenous proteolytic system was found to be involved in the degradation of LHCII in response to elevated light intensities and the proteolysis was shown to be under tight regulation [Yang, D.-H. et al. (1998) Plant Physiol. 118, 827-834]. In this study, the substrate specificity and recognition site towards the protease were examined using reconstituted wild-type and mutant recombinant LHCII. The results show that the LHCII apoprotein and the monomeric form of the holoprotein are targeted for proteolysis while the trimeric form is not. The N-terminal domain of LHCII was found to be essential for recognition by the regulatory protease and the involvement of the N-end rule pathway is discussed. (C) 2000 Federation of European Biochemical Societies.

  • 99357.
    Yang, Daobin
    et al.
    Yamagata Univ, Japan; Yamagata Univ, Japan.
    Wang, Yuming
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Sano, Takeshi
    Yamagata Univ, Japan; Yamagata Univ, Japan; Yamagata Univ, Japan.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Sasabe, Hisahiro
    Yamagata Univ, Japan; Yamagata Univ, Japan; Yamagata Univ, Japan.
    Kido, Junji
    Yamagata Univ, Japan; Yamagata Univ, Japan; Yamagata Univ, Japan.
    A minimal non- radiative recombination loss for efficient non- fullerene all- small- molecule organic solar cells with a low energy loss of 0.54 eV and high open- circuit voltage of 1.15 V+2018In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 28, p. 13918-13924Article in journal (Refereed)
    Abstract [en]

    Organic solar cells (OSCs) are considered as a promising next-generation photovoltaic technology because of their light weight, flexibility, and the potential of roll-to-roll fabrication. However, the relatively large energy loss (E-loss) from the optical bandgap (E-g) of the absorber to the open-circuit voltage (V-oc) of the device hinders further improvement of the PCEs of OSCs. Here, we report efficient non-fullerene all-small-molecule organic solar cells (NF all-SMOSCs), using DR3TBDTT and O-IDTBR as the donor and acceptor, respectively. We obtain a high electroluminescence yield (EQE(EL)) value of up to approximate to 4 x 10(-4) corresponding to a 0.21 eV non-radiative recombination loss, which is the smallest value for bulk-heterojunction (BHJ) OSCs so far. As a result, a low E-loss of 0.54 eV and a considerably high V-oc of 1.15 V are obtained for BHJ NF all-SMOSCs.

  • 99358.
    Yang, DH
    et al.
    Stockholm University.
    Andersson, Bertil
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Aro, EM
    University of Turku.
    Ohad, I
    The Hebrew University of Jerusalem.
    The redox state of the plastoquinone pool controls the level of the light-harvesting chlorophyll a/b binding protein complex II (LHC II) during photoacclimation - Cytochrome b(6)f deficient Lemna perpusilla plants are locked in a state of high-light acclimation2001In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 68, no 2, p. 163-174Article in journal (Refereed)
    Abstract [en]

    A cytochrome bf deficient mutant of Lemna perpusilla maintains a constant and lower level of the light-harvesting chl a/b-binding protein complex II (LHC II) as compared to the wild type plants at low-light intensities. Inhibition of the plastoquinone pool reduction increases the LHC II content of the mutant at both low- and high-light intensities but only at high-light intensity in the wild type plants Proteolytic activity against LHC II appears during high-light photoacclimation of wild type plants. However, the acclimative protease is present in the mutant at both light intensities. These and additional results suggest that the plastoquinone redox state serves as the major signal-transducing component in the photoacclimation process affecting both, synthesis and degradation of LHC II and appearance of acclimative LHC II proteolysis. The plastoquinol pool cannot be oxidized by linear electron flow in the mutant plants which are locked in a `high light acclimation state. The cytochrome bf complex may be involved indirectly in the regulation of photoacclimation via 1) regulation of the plastoquinone redox state; 2) regulation of the redox-controlled thylakoid protein kinase allowing exposure of the dephosphorylated LHC II to acclimative proteolysis

  • 99359.
    Yang, Fan
    et al.
    Chinese Academic Science, Peoples R China; University of Chinese Academic Science, Peoples R China.
    Qian, Deping
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Hesham Balawi, Ahmed
    KAUST, Saudi Arabia.
    Wu, Yang
    Xi An Jiao Tong University, Peoples R China.
    Ma, Wei
    Xi An Jiao Tong University, Peoples R China.
    Laquai, Frederic
    KAUST, Saudi Arabia.
    Tang, Zheng
    Technical University of Dresden, Germany.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Li, Weiwei
    Chinese Academic Science, Peoples R China.
    Performance limitations in thieno[3,4-c] pyrrole4,6-dione-based polymer: ITIC solar cells2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 35, p. 23990-23998Article in journal (Refereed)
    Abstract [en]

    We report a systematic study of the efficiency limitations of non-fullerene organic solar cells that exhibit a small energy loss (E-loss) between the polymer donor and the non-fullerene acceptor. To clarify the impact of Eloss on the performance of the solar cells, three thieno[3,4-c] pyrrole-4,6-dione-based conjugated polymers (PTPD3T, PTPD2T, and PTPDBDT) are employed as the electron donor, which all have complementary absorption spectra compared with the ITIC acceptor. The corresponding photovoltaic devices show that low Eloss (0.54 eV) in PTPDBDT: ITIC leads to a high open-circuit voltage (Voc) of 1.05 V, but also to a small quantum efficiency, and in turn photocurrent. The high Voc or small energy loss in the PTPDBDT-based solar cells is a consequence of less non-radiative recombination, whereas the low quantum efficiency is attributed to the unfavorable micro-phase separation, as confirmed by the steady-state and time-resolved photoluminescence experiments, grazing-incidence wide-angle X-ray scattering, and resonant soft X-ray scattering (R-SoXS) measurements. We conclude that to achieve high performance non-fullerene solar cells, it is essential to realize a large Voc with small Eloss while simultaneously maintaining a high quantum efficiency by manipulating the molecular interaction in the bulk-heterojunction.

  • 99360.
    Yang, H
    et al.
    Linkoping Univ, Fac Hlth Sci, Dept Surg, Linkoping, Sweden Linkoping Univ, Fac Hlth Sci, Clin Res Ctr, Linkoping, Sweden Huddinge Univ Hosp, Karolinska Inst, Dept Surg, Stockholm, Sweden.
    Larsson, J
    Permert, J
    Linkoping Univ, Fac Hlth Sci, Dept Surg, Linkoping, Sweden Linkoping Univ, Fac Hlth Sci, Clin Res Ctr, Linkoping, Sweden Huddinge Univ Hosp, Karolinska Inst, Dept Surg, Stockholm, Sweden.
    Braaf, Ylva
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Surgery .
    Wiren, M
    Linkoping Univ, Fac Hlth Sci, Dept Surg, Linkoping, Sweden Linkoping Univ, Fac Hlth Sci, Clin Res Ctr, Linkoping, Sweden Huddinge Univ Hosp, Karolinska Inst, Dept Surg, Stockholm, Sweden.
    No effect of bolus glutamine supplementation on the postresectional adaptation of small bowel mucosa in rats receiving chow ad libitum2000In: Digestive Surgery, ISSN 0253-4886, E-ISSN 1421-9883, Vol. 17, no 3, p. 256-260Article in journal (Refereed)
    Abstract [en]

    Objective: Early postoperative enteral feeding has been reported to stimulate intestinal mucosa proliferation. Dietary components influence the intestinal adaptive response after resection and glutamine is a preferential nutrient to enterocytes. The purpose of this study was to evaluate the effects of bolus glutamine supplementation on intestinal adaptation. Methods: Male Wistar rats underwent a 65% small bowel resection, The rats were divided into three groups receiving glutamine 2 g/kg/day, isonitrogenous glycine or saline by gavage for 10 days. All the rats were provided with ordinary rat chow ad libitum. Sampling was done 10 days after resection, Animals fed ordinary rat chow without surgery or specific treatment served as control. Results: Mucosal wet weight, DNA, RNA, protein contents and sucrose activity, as well as villus height increased in the ileal remnant. No significant differences in any of these parameters or body weight could be found between the three groups. Conclusion: Postoperative enteral bolus glutamine supplementation at a dose of 2 g/kg b.w. did not enhance the adaptation of the residual intestine 10 days after massive intestinal resection in the rat. Copyright (C) 2000 S. Karger AG, Basel.

  • 99361. Yang, H.
    et al.
    Larsson, Jenny
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Experimental Pathology .
    Permert, J.
    Wiren, M.
    Bolus ornithine and arginine-ketoglutarate supplementation in distal intestine after 65% resection in rats2000In: Nutrition Research, ISSN 0271-5317, E-ISSN 1879-0739, Vol. 20, no 12, p. 1807-1816Article in journal (Refereed)
    Abstract [en]

    Introduction: Enteral feeding has been reported to increase intestinal mucosa proliferation after resection. Dietary components influence the intestinal adaptive response. The purpose of this study was to evaluate the effect of ornithine- (OKG) or arginine-ketoglutarate (AKG) bolus supplementation on intestinal postresectional adaptation in the rat. Methods: Male Wistar rats underwent 65% small-bowel resection and received either OKG 3 g/kg/day, isonitrogenous AKG or saline by gavage once daily. The animals had free access to rat chow. Sampling was done 10 days after resection. Fed animals without surgery or specific treatment served as controls. Results: Mucosal wet weight, DNA, RNA, protein content and sucrose activity of the mucosa, as well as villus height were significantly increased in all resected animals compared to controls. No significant differences in body weight or intestinal adaptation could be found between the three dietary groups. Conclusion: Postoperative enteral bolus feeding supplemented with OKG or AKG did not significantly enhance the adaptation of the remnant small bowel 10 days after massive intestinal resection when rats had free access to rat chow. © 2000 Elsevier Science Inc.

  • 99362.
    Yang, H
    et al.
    Linkoping Univ, Fac Hlth Sci, Dept Surg, S-58185 Linkoping, Sweden.
    Söderholm, Johan D
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Surgery . Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Surgery in Östergötland.
    Larsson, J
    Permert, J
    Linkoping Univ, Fac Hlth Sci, Dept Surg, S-58185 Linkoping, Sweden.
    Lindgren, Johan
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Surgery . Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Surgery in Östergötland.
    Wiren, M
    Linkoping Univ, Fac Hlth Sci, Dept Surg, S-58185 Linkoping, Sweden.
    Bidirectional supply of glutamine maintains enterocyte ATP content in the in vitro Ussing chamber model2000In: International Journal of Colorectal Disease, ISSN 0179-1958, E-ISSN 1432-1262, Vol. 15, no 5-6, p. 291-296Article in journal (Refereed)
    Abstract [en]

    Glutamine is the principal energy source for enterocytes, but it is not known whether parenteral or enteral supplementation is most beneficial to gut integrity. The aim of this study was to evaluate the effects of glutamine in uni- or bidirectional supply on the viability of intestinal mucosa of starved rats during incubation in Ussing chambers. Segments of jejunum from rats starved for 48 h were randomly mounted in Ussing chambers with three nutrient solutions: Krebs buffer without glutamine, 6 mM glutamine added to the mucosal side, 6 mM glutamine added to the mucosal side and 0.6 mM glutamine to the serosal side. ATP content of the mucosa, electrophysiology, and Cr-51-ethyl-enediaminetetraacetate (EDTA) permeability were studied during 180 min of incubation. The addition of glutamine to both sides of the stripped mucosa improved ATP levels compared to the Krebs solution (P<0.05), and the addition of glutamine resulted in an increase in short circuit current (P<0.05). No significant differences were seen in Cr-51-EDTA permeability or epithelial electrical resistance. Glutamine supplementation to both the luminal and serosal side in the Ussing chamber was more effective than luminal glutamine only in maintaining ATP levels of intestinal mucosa. Bidirectional supplementation of glutamine might improve intestinal energy metabolism and viability in in vitro studies.

  • 99363. Yang, H
    et al.
    Söderholm, Johan D
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Surgery. Östergötlands Läns Landsting, MKC-2, GE: Gastrokir.
    Larsson, J
    Kir klin Huddinge.
    Permert, J
    Kir klin Huddinge.
    Olaison, Gunnar
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Surgery. Östergötlands Läns Landsting, MKC-2, GE: Gastrokir.
    Lindgren, J
    Glutamine effects on permeability and APT content of jejunal mucosa in starved rat.1999In: Clinical Nutrition, ISSN 0261-5614, E-ISSN 1532-1983, Vol. 18, p. 301-306Article in journal (Refereed)
  • 99364.
    Yang, Hong
    et al.
    Nokia Bell Labs, NJ 07922 USA.
    Ngo, Hien Q.
    Queens Univ, North Ireland.
    Larsson, Erik G
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Multi-Cell Massive MIMO in LoS2018In: 2018 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    We consider a multi-cell Massive MIMO system in a line-of-sight (LoS) propagation environment, for which each user is served by one base station, with no cooperation among the base stations. Each base station knows the channel between its service antennas and its users, and uses these channels for precoding and decoding. Under these assumptions we derive explicit downlink and uplink effective SINR formulas for maximum-ratio (MR) processing and zero-forcing (ZF) processing. We also derive formulas for power control to meet pre-determined SINR targets. A numerical example demonstrating the usage of the derived formulas is provided.

  • 99365.
    Yang, J.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Politecn Cataluna, Spain; Pol Ind Les Fallulles, Spain.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Johansson-Joesaar, M. P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Esteve, J.
    University of Barcelona, Spain.
    Llanes, L.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Mechanical strength of ground WC-Co cemented carbides after coating deposition2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 689, p. 72-77Article in journal (Refereed)
    Abstract [en]

    Manufacturing of hardmetal tools often involves surface grinding, ion etching and final coating. Each stage throughout the manufacturing chain introduces surface integrity changes which may be critical for defining the final mechanical behavior of the coated tools. Within this context, an experimental test program has been developed to assess the influence of a coating (TiN) deposition on surface integrity and transverse rupture strength of a previously ground fine-grained WC-Co grade substrate. Four different substrate surface finish conditions (prior to ion etching and coating) were evaluated: as sintered (AS), ground (G), polished (P), and ground plus high temperature annealing (GTO. Surface integrity and fracture resistance characterization, complemented with a detailed fractographic analysis, were performed on both uncoated and coated samples. Results show that the surface integrity after grinding has been partly modified during the ion etching and film deposition processes, particularly in terms of a reduced compressive residual stress state at the substrate surface level. Consequently, the grinding induced strength enhancement in hardmetals is reduced for coated specimens. Main reason behind it is the change of nature, location and stress state acting on critical flaw: from processing defects existing at the subsurface (uncoated G specimens) to grinding-induced microcracks located close to the interface between coating and substrate, but within the subsurface of the latter (coated G specimens). This is not the case for AS and P conditions, where flexural strength does not change a result of ion etching and coating. Finally, fracture resistance increases slightly for GTT specimens after coating process, possibly caused by a beneficial effect of the deposited film on the residual stress state at the surface.

  • 99366.
    Yang, J.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology. Universitat Politècnica de Catalunya, Barcelona 08028, Spain.
    Roa, J. J.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Johansson-Jöesaar, Mats P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology. SECO Tools AB, Sweden.
    Esteve, J.
    University of Barcelona, Spain.
    Llanes, L.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Substrate surface finish effects on scratch resistance and failure mechanisms of TiN-coated hardmetals2015In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 265, p. 174-184Article in journal (Refereed)
    Abstract [en]

    In this study, the influence of substrate surface finish on scratch resistance and associated failure mechanisms is investigated in the case of a TiN-coated hardmetal. Three different surface finish conditions are studied: as-sintered (AS), ground (G), and mirror-like polished (P). For G conditioned samples, scratch tests are conducted both parallel and perpendicular to the direction of the grinding grooves. It is found that coated AS, G and P samples exhibit similar critical load for initial substrate exposure and the same brittle adhesive failure mode. However, the damage scenarios are different, i.e. the substrate exposure is discrete and localized to the scratch tracks for G samples while a more pronounced and continuous exposure is seen for AS and P ones. Aiming to understand the role played by the grinding-induced compressive residual stresses, the study is extended to coated systems where ground substrates are thermal annealed (for relieving stresses) before being ion etched and coated. It yielded lower critical loads and changes in the mechanisms for the scratch-related failure; the latter depending on the relative orientation between scratching and grinding directions. (C) 2015 Elsevier B.V. All rights reserved.

  • 99367.
    Yang, Jian
    et al.
    Drexel University, PA 19104 USA; Drexel University, PA 19104 USA; Nanjing Technical University, Peoples R China.
    Naguib, Michael
    Oak Ridge National Lab, TN 37381 USA.
    Ghidiu, Michael
    Drexel University, PA 19104 USA;.
    Pan, Li-Mei
    Nanjing Technical University, Peoples R China.
    Gu, Jian
    Nanjing Technical University, Peoples R China.
    Nanda, Jagjit
    Oak Ridge National Lab, TN 37381 USA.
    Halim, Joseph
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Drexel University, PA 19104 USA; Drexel University, PA 19104 USA.
    Gogotsi, Yury
    Drexel University, PA 19104 USA; Drexel University, PA 19104 USA.
    Barsoum, Michel W.
    Drexel University, PA 19104 USA; Drexel University, PA 19104 USA.
    Two-Dimensional Nb-Based M4C3 Solid Solutions (MXenes)2016In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 99, no 2, p. 660-666Article in journal (Refereed)
    Abstract [en]

    Herein, two new two-dimensional Nb4C3-based solid solutions (MXenes), (Nb-0.8,Ti-0.2)(4)C3Tx and (Nb-0.8,Zr-0.2)(4)C3Tx (where T is a surface termination) were synthesizedas confirmed by X-ray diffractionfrom their corresponding MAX phase precursors (Nb-0.8,Ti-0.2)(4)AlC3 and (Nb-0.8,Zr-0.2)(4)AlC3. This is the first report on a Zr-containing MXene. Intercalation of Li ions into these two compositions, and Nb4C3Tx was studied to determine the potential of those materials for energy storage applications. Lithiation and delithiation peaks at 2.26 and 2.35 V, respectively, appeared in the case of Nb4C3Tx, but were not present in Nb2CTx. After 20 cycles at a rate of C/4, the specific capacities of (Nb-0.8,Ti-0.2)(4)C3Tx and (Nb-0.8,Zr-0.2)(4)C3Tx were 158 and 132 mAh/g, respectively, both slightly lower than the capacity of Nb4C3Tx.

  • 99368.
    Yang, Jianming
    et al.
    East China Normal Univ, Peoples R China.
    Hong, Qiuming
    Soochow Univ, Peoples R China.
    Yuan, Zhongcheng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Xu, Ruipeng
    Soochow Univ, Peoples R China.
    Guo, Xuewen
    East China Normal Univ, Peoples R China.
    Xiong, Shaobing
    East China Normal Univ, Peoples R China.
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Braun, Slawomir
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Li, Yanqing
    Soochow Univ, Peoples R China.
    Tang, Jianxin
    Soochow Univ, Peoples R China.
    Duan, Chungang
    East China Normal Univ, Peoples R China; Shanxi Univ, Peoples R China.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Bao, Qinye
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. East China Normal Univ, Peoples R China; Shanxi Univ, Peoples R China; Soochow Univ, Peoples R China.
    Unraveling Photostability of Mixed Cation Perovskite Films in Extreme Environment2018In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 6, no 20, article id 1800262Article in journal (Refereed)
    Abstract [en]

    Organometal halide perovskites exhibit a bright future for applications in solar cells, as efficiency has achieved over 22%. The long-term stability remains a major obstacle for commercialization. Here, it is found that three cationic compositional engineered perovskites, MAPb(I0.83Br0.17)(3), FA(0.83)MA(0.17)Pb(I0.83Br0.17)(3), and Cs-0.1(FA(0.83)MA(0.17))(0.9)Pb(I0.83Br0.17)(3), undergo severe degradation under white-light illumination in ultrahigh vacuum (UHV) environment, but the rate of degradation is significantly lower for the mixed cation perovskites. This is attributed to the defect-induced trap states that trigger the strong coupling between the photoexcited carriers and the crystal lattice. The observed behavior supports the view of the mixed cations suppressing the photoinduced degradation. It is further demonstrated that UHV environment remarkably accelerates the degradation of the perovskite films under illumination, which delivers a very important message that the current hybrid perovskite materials and their optoelectronic devices are not suitable for application in outer space. Moreover, the applied UHV environment can be an accelerated test method to estimate the photostability of the perovskites.

  • 99369.
    Yang, Jianming
    et al.
    East China Normal Univ, Peoples R China.
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Zhang, Yuexing
    Soochow Univ, Peoples R China.
    Zheng, Xuerong
    Zhejiang Univ, Peoples R China.
    He, Xiaoxiao
    East China Normal Univ, Peoples R China.
    Wang, Han
    East China Normal Univ, Peoples R China.
    Yue, Fangyu
    East China Normal Univ, Peoples R China.
    Braun, Slawomir
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Chen, Jinquan
    East China Normal Univ, Peoples R China.
    Xu, Jianhua
    East China Normal Univ, Peoples R China.
    Li, Yanqing
    Soochow Univ, Peoples R China.
    Jin, Yizheng
    Zhejiang Univ, Peoples R China.
    Tang, Jianxin
    Soochow Univ, Peoples R China.
    Duan, Chungang
    East China Normal Univ, Peoples R China; Shanxi Univ, Peoples R China.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Bao, Qinye
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. East China Normal Univ, Peoples R China; Shanxi Univ, Peoples R China.
    Comprehensive understanding of heat-induced degradation of triple-cation mixed halide perovskite for a robust solar cell2018In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 54, p. 218-226Article in journal (Refereed)
    Abstract [en]

    The triple-cation mixed halide perovskite Cs-0.05(MA(0.17)FA(0.83))(0.95)Pb(I0.83Br0.17)(3) emerges as one of the most promising candidates for photovoltaics due to superior optoelectronic properties, but the thermal stability is still a major challenge for the viability of perovskite solar cells towards commercialization. Herein, we firstly explore the thermal response of the photovoltaic performances to access device physical changes. It is shown that the efficiency loss originates from decreased charge mobility, increased trap density and generation of PbI2 charge recombination centers near the interface. In-depth analysis of evolutions in morphology, chemical composition, dynamic and electronic structure of the perovskite layer at the nanometer scales indicates that it is initial dangling bonds and vacancies on the imperfect surfaces decrease the activation energy and cause the perovskite decomposition in a layer-by-layer pathway sequentially from the film surface to bulk. Based on the results, a strategy of surface passivation to improve the thermal stability is demonstrated and discussed. This work for the first time provides insights into the physical and chemical change of such triple-cation perovskite and indicates that more effort should be invested in surface treatment for enhancing perovskite device stability.

    The full text will be freely available from 2020-10-13 14:30
  • 99370.
    Yang, Jianming
    et al.
    East China Normal Univ, Peoples R China.
    Xiong, Shaobing
    East China Normal Univ, Peoples R China.
    Qu, Tianyi
    Soochow Univ, Peoples R China.
    Zhang, Yuexing
    Soochow Univ, Peoples R China.
    He, Xiaoxiao
    East China Normal Univ, Peoples R China.
    Guo, Xuewen
    East China Normal Univ, Peoples R China.
    Zhao, Qiuhua
    East China Normal Univ, Peoples R China.
    Braun, Slawomir
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Chen, Jinquan
    East China Normal Univ, Peoples R China.
    Xu, Jianhua
    East China Normal Univ, Peoples R China.
    L, Yanqing I
    Soochow Univ, Peoples R China.
    Liu, Xianjie
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Duan, Chungang
    East China Normal Univ, Peoples R China; Shanxi Univ, Peoples R China.
    Tang, Jianxin
    Soochow Univ, Peoples R China.
    Fahlman, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering.
    Bao, Qinye
    Linköping University, Department of Physics, Chemistry and Biology, Surface Physics and Chemistry. Linköping University, Faculty of Science & Engineering. East China Normal Univ, Peoples R China; Shanxi Univ, Peoples R China.
    Extremely Low-Cost and Green Cellulose Passivating Perovskites for Stable and High-Performance Solar Cells2019In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 14, p. 13491-13498Article in journal (Refereed)
    Abstract [en]

    The fast evolution of metal halide perovskite solar cells has opened a new chapter in the field of renewable energy. High-quality perovskite films as the active layers are essential for both high efficiency and long-term stability. Here, the perovskite films with enlarged crystal grain size and decreased defect density are fabricated by introducing the extremely low-cost and green polymer, ethyl cellulose (EC), into the perovskite layer. The addition of EC triggers hydrogen bonding interactions between EC and the perovskite, passivating the charge defect traps at the grain boundaries. The long chain of EC further acts as a scaffold for the perovskite structure, eliminating the annealing-induced lattice strain during the film fabrication process. The resulting devices with the EC additive exhibit a remarkably enhanced average power conversion efficiency from 17.11 to 19.27% and an improvement of all device parameters. The hysteresis index is found to decrease by three times from 0.081 to 0.027, which is attributed to suppressed ion migration and surface charge trapping. In addition, the defect passivation by EC significantly improves the environmental stability of the perovskite films, yielding devices that retain 80% of their initial efficiency after 30 days in ambient air at 45% relative humidity, whereas the pristine devices without EC fully degrade. This work provides a low-cost and green avenue for passivating defects that improves both the efficiency and operational stability of perovskite solar cells.

  • 99371.
    Yang, Jie
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Shenzhen Univ, Peoples R China.
    Bao, Chunxiong
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Shenzhen Univ, Peoples R China.
    Ning, Weihua
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Nanjing Tech Univ, Peoples R China.
    Wu, Bo
    Nanyang Technol Univ, Singapore.
    Ji, Fuxiang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Yan, Zhibo
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Nanjing Univ, Peoples R China.
    Tao, Youtian
    Nanjing Tech Univ, Peoples R China.
    Liu, Jun-Ming
    Nanjing Univ, Peoples R China.
    Sum, Tze Chien
    Nanyang Technol Univ, Singapore.
    Bai, Sai
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Jianpu
    Nanjing Tech Univ, Peoples R China.
    Huang, Wei
    Nanjing Tech Univ, Peoples R China.
    Zhang, Wenjing
    Shenzhen Univ, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Stable, High-Sensitivity and Fast-Response Photodetectors Based on Lead-Free Cs2AgBiBr6 Double Perovskite Films2019In: Advanced Optical Materials, ISSN 2162-7568, E-ISSN 2195-1071, Vol. 7, no 13, article id 1801732Article in journal (Refereed)
    Abstract [en]

    Solution-processed metal halide perovskites (MHPs) have demonstrated great advances on achieving high-performance photodetectors. However, the intrinsic material instability and the toxicity of lead still hinder the practical applications of MHPs-based photodetectors. In this work, the first highly sensitive and fast-response lead-free perovskite photodetectors based on Cs2AgBiBr6 double perovskite films are demonstrated. A convenient solution method is developed to deposit high-quality Cs2AgBiBr6 film with large grain sizes, low trap densities, and long charge carrier lifetimes. Incorporated within a photodiode device architecture comprised of optimized hole- and electron-transporting layers, lead-free perovskite photodetectors are achieved exhibiting a high detectivity of 3.29 x 10(12) Jones, a large linear dynamic range of 193 dB, and a fast response time of approximate to 17 ns. All the key figures of merit of the devices are comparable with the reported best-performing photodetectors based on lead halide perovskites. In addition, the resulting devices exhibit excellent thermal and environmental stability. The nonencapsulated devices show negligible degradation after thermal stressing at 150 degrees C and less than 5% degradation in the photoresponsivity after storage in ambient air for approximate to 2300 h. The results demonstrate the great potential of the lead-free Cs2AgBiBr6 double perovskite in applications for environmentally friendly and high-performance photodetectors.

  • 99372.
    Yang, Jie
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. University of Politecn Cataluna, Spain.
    Roa, J. J.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Schwin, M.
    SECO Tools AB, Sweden.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Llanes, L.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Grinding-induced metallurgical alterations in the binder phase of WC-Co cemented carbides2017In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 134, p. 302-310Article in journal (Refereed)
    Abstract [en]

    The metallic binder phase dictates the toughening behavior of WC-Co cemented carbides (hardmetals), even though it occupies a relative small fraction of the composite. Studies on deformation and phase transformation of the binder constituent are scarce. Grinding represents a key manufacturing step in machining of hardmetal tools, and is well-recognized to induce surface integrity alterations. In this work, metallurgical alterations of the binder phase in ground WC-Co cemented carbides have been assessed by a combination of electron back scattered diffraction and transmission electron microscopy techniques. The Co-base binder experiences a martensitic phase transformation from fcc to hcp crystal structure, predominantly in the first 5 mu m below the surface. The hcp fraction decreases gradually along a depth of 10 mu m. Surface Co displays severe plastic deformation under the highest strain, resulting in formation of nanocrystalline grains in the first micrometer below the surface. Microstructural refinement within the binder phase is observed even at greater depth. Stacking faults were detected in most of the refined grains. The metallurgical alterations of the binder phase modify the local stress distribution during grinding, which affects the discerned subsurface microcracking. The resulting residual stress profile is the sum of multiple subsurface changes, such as phase transformation, severe plastic deformation and grain refinement, where it is discerned that the depth profile of the transformed hcp-Co fraction coincides with the grinding-induced residual stress profile.

  • 99373.
    Yang, Jie
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. University of Politecn Cataluna, Spain.
    Roa, J. J.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Schwind, M.
    SECO Tools AB, Sweden.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Johansson-Jõesaar, Mats P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Esteve, J.
    University of Barcelona, Spain.
    Llanes, L.
    University of Politecn Cataluna, Spain.
    Thermally induced surface integrity changes of ground WC-Co hardmetals2016In: 3RD CIRP CONFERENCE ON SURFACE INTEGRITY, Elsevier, 2016, Vol. 45, p. 91-94Conference paper (Refereed)
    Abstract [en]

    Ground hardmetals are exposed to high temperatures during both processing (e.g. coating deposition) and use (e.g. as a cutting tool). However, studies on thermally induced changes of surface integrity are limited. Here we address this by means of FIB/FESEM and EBSD investigation, with special focus on the binder phase characterization. Our findings indicate that thermal treatment causes two main surface modifications. First, an unexpected microporosity appears in the binder within the subsurface layer when ground surfaces are heated. Second, the metallic phase underneath the ground surface experiences metallurgical changes, in terms of grain and crystallographic phase structures. The mechanisms responsible for these modifications of the binder are discussed in terms of grinding-induced and thermally-reversed phase transformation as well as recrystallization phenomena. We also note that no additional heat treatment related changes such as microcracking and carbide fragmentation in the subsurface layer, are discerned. (C) 2016 The Authors. Published by Elsevier B.V.

  • 99374.
    Yang, Jie
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Univ Politecn Cataluna, Spain; AMES Sintered Met Components, Spain.
    Roa, J. J.
    Univ Politecn Cataluna, Spain; Univ Politecn Cataluna, Spain.
    Schwind, M.
    SECO Tools AB, Sweden.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Johansson-Jöesaar, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Esteve, J.
    Univ Barcelona, Spain.
    Llanes, L.
    Univ Politecn Cataluna, Spain; Univ Politecn Cataluna, Spain.
    Implementation of advanced characterisation techniques for assessment of grinding effects on the surface integrity of WC-Co cemented carbides2018In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 61, no 2, p. 100-105Article in journal (Refereed)
    Abstract [en]

    Grinding is a key step on the manufacturing process of WC-Co cemented carbides (hardmetals). In this work, an investigation of grinding effects on the surface integrity of hardmetals is conducted. It is done by combining diverse advanced characterisation techniques: X-ray diffraction, field emission-scanning electron microscopy, electron back scatter diffraction, focused ion beam - 3D tomography and transmission electron microscopy. The study is carried out in a fine-grained WC-Co grade. Besides ground state, polished surface finish condition is assessed for comparison purposes. It is evidenced that grinding induces significant alterations: 3D tomography illustrates microcracking exists down to 2.5 mu m depth with a highly anisotropic distribution at the subsurface, large compressive residual stresses extending until subsurface levels of about 12 mu m, and phase transformation of binder from the original fcc phase into the hcp one, as well as severe plastic deformation observed within the binder at the surface level.

  • 99375.
    Yang, Jing
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Grinding effects on surface integrity, flexural strength and contact damage resistance of coated hardmetals2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The tribological and mechanical behavior of coated tools depends not only on intrinsic properties of the deposited film but also on substrate surface and subsurface properties – such as topography and residual stress state – as well as on interface adhesion strength. It is particularly true in the case of coated tools based on WC-Co cemented carbides (backbone materials of the tool manufacturing industry, and simply referred to as hardmetals in practice) as substrates. Manufacturing of hardmetals often involves grinding, and in the case of cutting tools also edge preparation, etching and coating. The quality of the shaped components is influenced by how the surface integrity evolves through the different process steps. In this regard, substrate grinding and coating deposition represent key steps, as they are critical for defining the final performance and relative tool manufacturing cost. Within this framework, it is the main objective of this thesis to assess the influence of substrate surface integrity on different mechanical (flexural strength and contact damage resistance under spherical indentation) and tribological (scratch resistance as well as cracking and delamination response under Brale indentation) properties for a TiN-coated fine-grained hardmetal grade (WC-13 wt.%Co). In doing so, three different surface finish conditions are studied: as-sintered (AS), ground (G), and mirror-like polished (P). Moreover, aiming for an in-depth analysis of surface integrity evolution from grinding to coating, a relevant part of the work is devoted to document and understand changes induced by grinding in nude hardmetal substrates. The study is also extended to a fourth surface finish variant (GTT), corresponding to a ground substrate which is thermal annealed before being ion etched and coated. Because residual stress induced by grinding are effectively relieved after this high temperature thermal treatment, GTT condition allows to separate grinding-induced effects associated with surface texture and surface/subsurface damage changes (inherited from the G surface finish) from those related to the referred residual stresses.

    Surface integrity was characterized in terms of roughness, residual stresses (prior and after coating deposition), and damage at the subsurface level. It was found that grinding induces significant alterations in the surface integrity of cemented carbides. Main changes included relevant roughness variations; emergence of a topographic texture; anisotropic distribution of microcracks within a subsurface layer of about 1 micron in depth; severe deformation, microstructure refinement and phase transformation of binder regions, down to 5 microns in depth; and large compressive residual stresses, gradually decreasing from the surface to baseline values at depths of about 10-12 microns.

    Additional changes in surface integrity are induced during subsequent ion etching and coating deposition. In general, removal of material from the surface during sputter cleaning and extended low-temperature (during film deposition) treatment resulted in a significant residual stresses decrease (about half its original value). However, damage induced by grinding was not completely removed, and some microcracks were still left on the substrate surface (close to the interface). On the other hand, and as expected, high temperature annealing (GTT condition) resulted in a complete relief of the referred residual stresses, but without inducing any additional change in terms of existing microcracks and depth of damaged layer. This was not the case for the metallic binder phase where thermal treatment induced an unexpected microporosity, development of a recrystallized subgrain structure, and reversion of grinding-induced phase transformation.

    Flexural strength was measured on both uncoated and coated hardmetals, and complemented with extensive fractographic analysis. It was found that grinding significantly enhances the strength of hardmetals, as compared to AS and P conditions. However, such beneficial effect was partly lost in the corresponding coated specimens. On the other hand, film deposition increases strength measured for GTT surface variant. These findings were analyzed on the basis of the changes on nature and location of critical flaws, induced by the effective residual stress field resulting at the surface and subsurface after each manufacturing stage.

    The influence of substrate surface finish on scratch resistance of coated hardmetals and associated failure mechanisms was investigated. It was found that coated AS, G and P samples exhibit similar critical load for initial substrate exposure and the same brittle adhesive failure mode. However, damage scenario was discerned to be different. Substrate exposure was discrete and localized to the scratch tracks for G samples, while a more pronounced and continuous decohesion was seen for AS and P ones. Relieving of the substrate compressive residual stresses (GTT condition) yielded lower critical loads and changes in the mechanisms for the scratch-related failure, the latter depending on the relative orientation between scratching and grinding directions.

    The cracking and delamination of TiN-coated hardmetals when subjected to Brale indentation was studied while varying the microstructure and surface finish of the substrate. In this case, another fine-grained WC-Co cemented carbide with lower binder content (6 wt.%Co) was included in the investigation. It was found that polished and coated hardmetals exhibit more brittleness (radial cracking) and lower adhesion strength (coating delamination) with decreasing binder content. Such a response is postulated on the basis of the influence of intrinsic hardness/brittleness of the hardmetal substrate on both cracking at the subsurface level and effective stress state, particularly regarding changes in shear stress component. On the other hand, grinding was discerned to promote delamination, compared to the polished condition, but strongly inhibits radial cracking. This was the result of the interaction between elastic-plastic deformation imposed during indentation and several grinding-induced effects: remnant compressive stress field, pronounced surface texture, and microcracking within a thin microcracked subsurface layer. It is then concluded that coating spallation prevails over radial cracking as the main mechanism for energy dissipation in ground and coated hardmetals.

    Contact damage resistance of coated hardmetals with different substrate surface finish conditions was investigated by means of spherical indentation under increasing monotonic loads. It was found that grinding enhanced resistance against both crack nucleation at the coating surface and subsequent propagation into the hardmetal substrate. Hence, crack emergence and damage evolution was effectively delayed for the coated G condition, as compared to the reference P one. The observed system response was discussed on the basis of the beneficial effects associated with compressive residual stresses remnant at the subsurface level after grinding, ion-etching and coating. The influence of the stress state was further corroborated by the lower contact damage resistance exhibited by the coated GTT specimens. Finally, differences observed on the interaction between indentation-induced damage and failure mode under flexural testing pointed in the direction that substrate grinding also enhances damage tolerance of the coated system when exposed to contact loads.

    List of papers
    1. Grinding effects on surface integrity and mechanical strength of WC-Co cemented carbides
    Open this publication in new window or tab >>Grinding effects on surface integrity and mechanical strength of WC-Co cemented carbides
    2014 (English)In: 2ND CIRP CONFERENCE ON SURFACE INTEGRITY (CSI), ELSEVIER SCIENCE BV , 2014, Vol. 13, p. 257-263Conference paper, Published paper (Refereed)
    Abstract [en]

    In this study, the correlation existing among grinding, surface integrity, and flexural strength is investigated for WC-Co cemented carbides (hardmetals). A fine-grained WC-13 wt % Co grade and three different surface conditions: (1) ground, (2) mirror-like polished (reference), and (3) ground plus high-temperature annealed, are investigated. Surface integrity and mechanical characterization is complemented with fractography. The grinding strongly affects both surface integrity and flexural strength. During grinding, a damaged thin layer together with high compressive residual stresses is introduced. The layer results in considerable strength enhancement compared to the reference polished surface condition. Fractography reveals that the improved strength mainly stems from grinding-induced changes on effective location, from surface into subsurface levels, of the strength-controlling flaw.

    Place, publisher, year, edition, pages
    ELSEVIER SCIENCE BV, 2014
    Series
    Procedia CIRP, ISSN 2212-8271 ; 13
    Keywords
    Grinding; Surface integrity; Cemented Carbides
    National Category
    Manufacturing, Surface and Joining Technology
    Identifiers
    urn:nbn:se:liu:diva-122089 (URN)10.1016/j.procir.2014.04.044 (DOI)000360720300044 ()
    Conference
    2nd CIRP Conference on Surface Integrity (CSI)
    Available from: 2015-10-19 Created: 2015-10-19 Last updated: 2016-04-21
    2. Substrate surface finish effects on scratch resistance and failure mechanisms of TiN-coated hardmetals
    Open this publication in new window or tab >>Substrate surface finish effects on scratch resistance and failure mechanisms of TiN-coated hardmetals
    Show others...
    2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 265, p. 174-184Article in journal (Refereed) Published
    Abstract [en]

    In this study, the influence of substrate surface finish on scratch resistance and associated failure mechanisms is investigated in the case of a TiN-coated hardmetal. Three different surface finish conditions are studied: as-sintered (AS), ground (G), and mirror-like polished (P). For G conditioned samples, scratch tests are conducted both parallel and perpendicular to the direction of the grinding grooves. It is found that coated AS, G and P samples exhibit similar critical load for initial substrate exposure and the same brittle adhesive failure mode. However, the damage scenarios are different, i.e. the substrate exposure is discrete and localized to the scratch tracks for G samples while a more pronounced and continuous exposure is seen for AS and P ones. Aiming to understand the role played by the grinding-induced compressive residual stresses, the study is extended to coated systems where ground substrates are thermal annealed (for relieving stresses) before being ion etched and coated. It yielded lower critical loads and changes in the mechanisms for the scratch-related failure; the latter depending on the relative orientation between scratching and grinding directions. (C) 2015 Elsevier B.V. All rights reserved.

    Place, publisher, year, edition, pages
    Elsevier, 2015
    Keywords
    Scratch resistance; Substrate surface finish; Grinding; Coated hardmetal; Scratch failure mechanisms
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-117805 (URN)10.1016/j.surfcoat.2015.01.038 (DOI)000352669700022 ()
    Note

    Funding Agencies|Spanish MINECO [MAT 2012-34602]; Erasmus Mundus joint European Doctoral Programme DocMASE

    Available from: 2015-05-11 Created: 2015-05-08 Last updated: 2018-01-03
    3. Contact damage resistance of TiN-coated hardmetals: Beneficial effects associated with substrate grinding
    Open this publication in new window or tab >>Contact damage resistance of TiN-coated hardmetals: Beneficial effects associated with substrate grinding
    Show others...
    2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 275, p. 133-141Article in journal (Refereed) Published
    Abstract [en]

    Contact loading is a common service condition for coated hardmetal tools and components. Substrate grinding represents a key step within the manufacturing chain of these coated systems. Within this context, the influence of surface integrity changes caused by abrasive grinding of the hardmetal substrate, prior to coating, is evaluated with respect to contact damage resistance. Three different substrate surface finish conditions are studied: ground (G), mirror-like polished (P) and ground plus heat-treated (GTT). Tests are conducted by means of spherical indentation under increasing monotonic load and the contact damage resistance is assessed. Substrate grinding enhances resistance against both crack nucleation at the coating surface and subsequent propagation into the hardmetal substrate. Hence, crack emergence and damage evolution is effectively delayed for the coated G condition, as compared to the reference P one. The observed system response is discussed on the basis of the beneficial effects associated with compressive residual stresses remnant at the subsurface level after grinding, ion-etching and coating. The influence of the stress state is further corroborated by the lower contact damage resistance exhibited by the coated GTT specimens. Finally, differences observed on the interaction between indentation-induced damage and failure mode under flexural testing points in the direction that substrate grinding also enhances damage tolerance of the coated system when exposed to contact loads.

    Place, publisher, year, edition, pages
    Elsevier, 2015
    Keywords
    Substrate grinding; Contact damage resistance; Coated hardmetal; Surface integrity
    National Category
    Manufacturing, Surface and Joining Technology
    Identifiers
    urn:nbn:se:liu:diva-120327 (URN)10.1016/j.surfcoat.2015.05.028 (DOI)000357753900020 ()
    Note

    Funding Agencies|Spanish MINECO [2012-34602]; Erasmus Mundus joint European Doctoral Programme DocMASE

    Available from: 2015-07-31 Created: 2015-07-31 Last updated: 2018-01-03
    4. Influence of substrate microstructure and surface finish on cracking and delamination response of TiN-coated cemented carbides
    Open this publication in new window or tab >>Influence of substrate microstructure and surface finish on cracking and delamination response of TiN-coated cemented carbides
    2016 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 352-353, p. 102-111Article in journal (Refereed) Published
    Abstract [en]

    The cracking and delamination of TiN-coated hardmetals (WC-Co cemented carbides) when subjected to Brale indentation were studied. Experimental variables were substrate microstructure related to low (6 wt% Co) and medium (13 wt% Co) binder content, and surface finishes associated with grinding and polishing stages before film deposition. Brale indentation tests were conducted on both coated and uncoated hardmetals. Emphasis has been placed on assessing substrate microstructure and subsurface finish effects on load levels at which cracking and delamination phenomena emerge, the type of cracking pattern developed, and how fracture mechanisms evolve with increasing load. It is found that polished and coated hardmetals are more brittle (radial cracking) and the adhesion strength (coating delamination) diminishes with decreasing binder content. Such a response is discussed on the basis of the influence of intrinsic hardness/brittleness of the hardmetal substrate on both cracking at the subsurface level and effective stress state, particularly regarding changes in shear stress component. Grinding promotes delamination compared to the polished condition, but strongly inhibits radial cracking. This is a result of the interaction between elastic-plastic deformation imposed during indentation and several grinding-induced effects: remnant compressive stress field, pronounced surface texture and micro cracking within a thin altered subsurface layer. As a consequence, coating spallation prevails over radial cracking as the main mechanism for energy dissipation in ground and coated hardmetals. (C) 2016 Elsevier B.V. All rights reserved.

    Place, publisher, year, edition, pages
    ELSEVIER SCIENCE SA, 2016
    Keywords
    Coated hardmetal; Brale indentation technique; Cracking; Delamination; Substrate microstructure; Substrate surface finish
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-127252 (URN)10.1016/j.wear.2016.02.004 (DOI)000372722000012 ()
    Note

    Funding Agencies|Spanish MINECO [MAT 2012-34602]; Erasmus Mundus joint European Doctoral Programme DocMASE

    Available from: 2016-04-20 Created: 2016-04-19 Last updated: 2018-03-23
  • 99376.
    Yang, Jing
    et al.
    University of Politecn Cataluna, Spain.
    Garcia Marro, F.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Trifonov, T.
    University of Politecn Cataluna, Spain.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Johansson-Jöesaar, Mats P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Llanes, L.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Contact damage resistance of TiN-coated hardmetals: Beneficial effects associated with substrate grinding2015In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 275, p. 133-141Article in journal (Refereed)
    Abstract [en]

    Contact loading is a common service condition for coated hardmetal tools and components. Substrate grinding represents a key step within the manufacturing chain of these coated systems. Within this context, the influence of surface integrity changes caused by abrasive grinding of the hardmetal substrate, prior to coating, is evaluated with respect to contact damage resistance. Three different substrate surface finish conditions are studied: ground (G), mirror-like polished (P) and ground plus heat-treated (GTT). Tests are conducted by means of spherical indentation under increasing monotonic load and the contact damage resistance is assessed. Substrate grinding enhances resistance against both crack nucleation at the coating surface and subsequent propagation into the hardmetal substrate. Hence, crack emergence and damage evolution is effectively delayed for the coated G condition, as compared to the reference P one. The observed system response is discussed on the basis of the beneficial effects associated with compressive residual stresses remnant at the subsurface level after grinding, ion-etching and coating. The influence of the stress state is further corroborated by the lower contact damage resistance exhibited by the coated GTT specimens. Finally, differences observed on the interaction between indentation-induced damage and failure mode under flexural testing points in the direction that substrate grinding also enhances damage tolerance of the coated system when exposed to contact loads.

  • 99377.
    Yang, Jing
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Politecn Cataluna, Spain.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Johansson-Joesaar, M. P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Llanes, L.
    University of Politecn Cataluna, Spain.
    Grinding effects on surface integrity and mechanical strength of WC-Co cemented carbides2014In: 2ND CIRP CONFERENCE ON SURFACE INTEGRITY (CSI), ELSEVIER SCIENCE BV , 2014, Vol. 13, p. 257-263Conference paper (Refereed)
    Abstract [en]

    In this study, the correlation existing among grinding, surface integrity, and flexural strength is investigated for WC-Co cemented carbides (hardmetals). A fine-grained WC-13 wt % Co grade and three different surface conditions: (1) ground, (2) mirror-like polished (reference), and (3) ground plus high-temperature annealed, are investigated. Surface integrity and mechanical characterization is complemented with fractography. The grinding strongly affects both surface integrity and flexural strength. During grinding, a damaged thin layer together with high compressive residual stresses is introduced. The layer results in considerable strength enhancement compared to the reference polished surface condition. Fractography reveals that the improved strength mainly stems from grinding-induced changes on effective location, from surface into subsurface levels, of the strength-controlling flaw.

  • 99378.
    Yang, Jing
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Politecn Cataluna, Spain.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Johansson-Joesaar, Mats P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Llanes, L.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Influence of substrate microstructure and surface finish on cracking and delamination response of TiN-coated cemented carbides2016In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 352-353, p. 102-111Article in journal (Refereed)
    Abstract [en]

    The cracking and delamination of TiN-coated hardmetals (WC-Co cemented carbides) when subjected to Brale indentation were studied. Experimental variables were substrate microstructure related to low (6 wt% Co) and medium (13 wt% Co) binder content, and surface finishes associated with grinding and polishing stages before film deposition. Brale indentation tests were conducted on both coated and uncoated hardmetals. Emphasis has been placed on assessing substrate microstructure and subsurface finish effects on load levels at which cracking and delamination phenomena emerge, the type of cracking pattern developed, and how fracture mechanisms evolve with increasing load. It is found that polished and coated hardmetals are more brittle (radial cracking) and the adhesion strength (coating delamination) diminishes with decreasing binder content. Such a response is discussed on the basis of the influence of intrinsic hardness/brittleness of the hardmetal substrate on both cracking at the subsurface level and effective stress state, particularly regarding changes in shear stress component. Grinding promotes delamination compared to the polished condition, but strongly inhibits radial cracking. This is a result of the interaction between elastic-plastic deformation imposed during indentation and several grinding-induced effects: remnant compressive stress field, pronounced surface texture and micro cracking within a thin altered subsurface layer. As a consequence, coating spallation prevails over radial cracking as the main mechanism for energy dissipation in ground and coated hardmetals. (C) 2016 Elsevier B.V. All rights reserved.

  • 99379.
    Yang, Jinghai
    et al.
    Jilin Normal University.
    Yang, Lili
    Jilin Normal University.
    Zhang, Yongjun
    Jilin Normal University.
    Wang, Dandan
    Jilin Normal University.
    Lang, Jihui
    Jilin Normal University.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Investigation on the origin of green light emission in ZnO bulk materials2009In: INTERNATIONAL JOURNAL OF MATERIALS and PRODUCT TECHNOLOGY, ISSN 0268-1900, Vol. 34, no 3, p. 360-368Article in journal (Refereed)
    Abstract [en]

    ZnO bulk materials were implanted by O and Zn with different concentration and their photoluminescence (PL) properties were investigated in detail. The results clearly show that O and Zn implantation indeed have great influence on the green light emission. By comparing the PL spectra for the samples with different implantations, O-i, Zn-i and Cu-related defects have been excluded from the possibility of the origin of green light emission step by step. Finally, it can be concluded that V-Zn is responsible to the observed green light emission, which has good agreement with the theoretical results from first principle calculation.

  • 99380.
    Yang, Junyu
    et al.
    Jinan Univ, Peoples R China.
    Lin, Yuanbao
    Jinan Univ, Peoples R China.
    Zheng, Wenhao
    Jinan Univ, Peoples R China.
    Liu, Alei
    Jinan Univ, Peoples R China.
    Cai, Wanzhu
    Jinan Univ, Peoples R China.
    Yu, Xiaomin
    Jinan Univ, Peoples R China.
    Zhang, Fengling
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Jinan Univ, Peoples R China.
    Liang, Quanbin
    South China Univ Technol, Peoples R China.
    Wu, Hongbin
    South China Univ Technol, Peoples R China.
    Qin, Donghuan
    South China Univ Technol, Peoples R China.
    Hou, Lintao
    Jinan Univ, Peoples R China.
    Roll-to-Roll Slot-Die-Printed Polymer Solar Cells by Self-Assembly2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 26, p. 22485-22494Article in journal (Refereed)
    Abstract [en]

    Extremely simplified one-step roll-to-roll slot-die-printed flexible indium tin oxide (ITO)-free polymer solar cells (PSCs) are demonstrated based on the ternary blends of electron-donor polymer thieno[3,4-b]thiophene/benzodithiophene, electron-acceptor fullerene [6,6]-phenyl-C-71-butyric acid methyl ester, and electron-extracting polymer poly[(9,9-bis(3-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) at room temperature (RT) in ambient air. The flexible ITO-free PSC exhibits a comparable power conversion efficiency (PCE) with the device employing complicated two-step slot-die printing (5.29% vs 5.41%), which indicates that PFN molecules can migrate from the ternary nanocomposite toward the Ag cathode via vertical self-assembly during the one-step slot-die printing process in air. To confirm the migration of PFN, the morphology and elemental analysis as well as charge transport of different active layers are investigated by the in situ transient film drying process, transmission electron microscopy, atomic force microscopy, contact angle and surface energy, X-ray photoelectron spectroscopy, scanning electron microscopy, impedance spectroscopy, transient photovoltage and transient photocurrent, and laser-beam-induced current. Moreover, the good air and mechanical stability of the flexible device with a decent PCE achieved in 1 cm(2) PSCs at RT in air suggests the feasibility of energy-saving and time-saving one-step slot-die printing to large-scale roll-to-roll manufacture in the future.

  • 99381.
    Yang, Lei
    et al.
    Univ Chinese Acad Sci, Peoples R China; Imperial Coll London, England.
    Qin, Linqing
    Univ Chinese Acad Sci, Peoples R China.
    Xu, Yunxiao
    Univ Chinese Acad Sci, Peoples R China.
    Zhang, Huotian
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Lv, Lei
    Univ Chinese Acad Sci, Peoples R China.
    Chen, Kepeng
    Dalian Univ Technol, Peoples R China.
    Sui, Xinyu
    Natl Ctr Nanosci and Technol, Peoples R China.
    Zhong, Yangguang
    Natl Ctr Nanosci and Technol, Peoples R China.
    Guo, Yuan
    Chinese Acad Sci, Peoples R China.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Zhao, Jianzhang
    Dalian Univ Technol, Peoples R China.
    Li, Yuhao
    Chinese Univ Hong Kong, Peoples R China.
    Liu, Xinfeng
    Natl Ctr Nanosci and Technol, Peoples R China; Univ Chinese Acad Sci, Peoples R China.
    Yi, Yuanping
    Chinese Acad Sci, Peoples R China.
    Lu, Xinhui
    Chinese Univ Hong Kong, Peoples R China.
    Peng, Aidong
    Univ Chinese Acad Sci, Peoples R China.
    Huang, Hui
    Univ Chinese Acad Sci, Peoples R China.
    Sulfur vs. tellurium: the heteroatom effects on the nonfullerene acceptors2019In: Science in China Series B: Chemistry, ISSN 1674-7291, E-ISSN 1869-1870, Vol. 62, no 7, p. 897-903Article in journal (Refereed)
    Abstract [en]

    The effect of chalcogen heteroatom variation on donor materials has been systematically investigated. However, this effect on acceptors has rarely been explored. Herein, nonfullerene acceptors BFPSP and BFPTP were reported by simply changing the chalcogen atoms from S to Te. The differences between BFPSP and BFPTP in light absorption, energy levels, excited-state lifetimes, energy loss, charge mobilities, morphology, and photovoltaic properties were systematically investigated to understand the heteroatom effects. More importantly, the electroluminescence spectra, external quantum efficiency of photovoltaics and TD-DFT calculations revealed that the triplet excited state (T-1) in energy of BFPTP equals to the charge transfer (CT) state in PBDB-T:BFPTP, which allows T-1 excitons, generated by intersystem crossing, to split into free charges to contribute to the efficiency. This contribution provides a strategy for tuning the photophysical properties of nonfullerene acceptors and designing high performance triplet materials for OSCs.

  • 99382.
    Yang, Li
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    A unified model of optical and physical dot gain in print color reproduction2004In: Journal of Imaging Science And Technology, ISSN 8750-9237, Vol. 48, no 4, p. 347-353Article in journal (Refereed)
    Abstract [en]

    A unified model coping with both physical and optical dot gains on print color tone reproduction is proposed. The physical dot gain, is approximated by a quadratic function of nominal dot percentages. The function, for each color, is characterized by a single parameter depending on printing technologies as well as ink-paper interactions, and has a symmetric form around where the nominal dot percentage is 50%. The parameter can be derived from the best fit for the model to measured data, such as spectral reflectance values or CIEXYZ tristimulus values. Applications to a color laser printer (on office copy paper) reproduces the experimental dot gain curves fairly well. Dependence on physical dot percentage, a summation of the nominal dot percentage and the corresponding physical dot gain, results in the optical dot gain and in turn the overall dot gain asymmetric forms, plotted against the nominal dot percentages. Furthermore, theoretical analysis reveals fundamental differences between physical and optical dot gains. Therefore, effects of optical dot gain can not be accurately represented by any physical extension in printing practices.

  • 99383.
    Yang, Li
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Characterization of inks and ink application for ink-jet printing: model and simulation2003In: Journal of the Optical Society of America A, ISSN 0740-3232, Vol. 20, no 7, p. 1149-1154Article in journal (Refereed)
    Abstract [en]

    Ink-jet printing quality is determined primarily by, among other factors, the printing engine and its inks. The printing engine controls the process of ink application and the scheme of ink mixing for the generation of secondary and tertiary colors. The inks selectively absorb different wavelengths from the illumination and result in the visible color output. Therefore characterizations of the output print in terms of ink distribution and volume, the scheme of ink mixing, light absorption, and light scattering are of essential importance in controlling and understanding the quality of the color reproduction. I present a method to characterize the ink volume and the properties of the ink by means of spectral reflectance measurements and simulations. The simulations are based on the Kubelka-Munk theory, whose applicability to ink-jet printing is also discussed. (C) 2003 Optical Society of America.

  • 99384.
    Yang, Li
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ink-paper interaction: a study in ink-jet color reproduction2003Doctoral thesis, monograph (Other academic)
    Abstract [en]

    An ink jet printing system consists of three fundamental parts: inks, printing engine, and substrates. Inks are materials creating color by selectively absorbing and scattering the visible illumination light. The printer acts as an ink distributor that governs the ink application. Finally, the substrate acts as a receiver of the inks and forms the images. Ink setting on the substrate is a complex process that depends on physical and chemical properties of the inks and the substrates, and their bilateral interactions. For a system consisting of dye based liquid inks and plain paper, the ink moves together with the liquid carrier before the pores absorb the liquid. This process contributes to serious ink spreading on the surface along the paper fibers. At the same time the ink spreads down into the pore structure. This causes severe dot deformation, physical dot gain and ink penetration. Understanding the consequences of these phenomena and above all being able to characterize their impact on color reproduction is of great importance. Moreover this knowledge is fundamental for finding solutions to ink-penetration related problems. This thesis presents studies of some important issues concerning image reproduction quality for dye based ink-jet printing on ordinary plain paper (office copy paper), such as ink penetration, optical dot gain, and even physical dot gain. The thesis begins with theoretical developments to the Kubelka-Munk theory, which allows one to study even non-uniform ink penetration into the substrate. With the knowledge of scattering and absorption coefficients and ink thickness, reflectance can be computed by solving differential equations. Three forms of ink penetration, uniform, linear, and exponential have been studied. A method is then presented for obtaining fundamental properties of the inks from spectral reflectance measurements, like the scattering- and absorption-power of inks, ink layer thickness, and ink mixing scheme for the generation of secondary colors. The method is further developed for modelling the ink penetration in printing systems consisting of dye based liquid inks and plain paper. By combining the spectral reflectance measurements with theoretical simulations, quantities like the depth of ink penetration is determined. These quantities, in turn, are used to predict the spectral reflectance of prints. Simulated spectral reflectance values have been in fairly good agreement with experimental results. Models dealing with light scattering inside the substrate resulting in optical dot gain for halftone printing, in the case of existing ink penetration, have been developed for both mono- and multi-color printing. It is shown that the optical dot gain leads to higher color saturation than predications from Murray-Davis approximation Additionally, tentative studies for physical dot gain were made. Finally, an evaluation of the chromatic effects of the ink penetration for printing on office copy paper has been carried out based on both experimental data and simulations. It is found that ink penetration has a dramatic impact on chroma and hue of the color, and the col or saturation is significantly reduced by the ink penetration. Consequently, the capacity for color representation, or the color gamut, is dramatically reduced by the ink penetration.

  • 99385.
    Yang, Li
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Qualifying the arguments used in the derivation of the revised Kubelka-Munk theory: reply2007In: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION, ISSN 1084-7529, Vol. 24, no 2, p. 557-560Other (Other academic)
    Abstract [en]

    The fundamental assumptions made in the revised Kubelka-Munk (KM) model of light propagation in scattering and absorptive media, recently proposed [J. Opt. Soc. Am. A 21, 1942 (2004), 22, 866 (2005)], are critically reviewed and analyzed. The authors argue that the model, now questioned by Edstrom [J. Opt. Soc. Am. A 24, 548 (2007)] is well founded on physical grounds and consistent with the original KM model, which has been the cornerstone of light propagation studies and utilized for more than half a century. (c) 2007 Optical Society of America

  • 99386.
    Yang, Li
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Spectral model of halftone on a fluorescent substrate2005In: Journal of Imaging Science And Technology, ISSN 8750-9237, Vol. 49, no 2, p. 179-184Article in journal (Refereed)
    Abstract [en]

    The color rendition of a halftone image depends on, among other things, physical and optical dot gains and fluorescence of substrates. A unified model describing spectral reflectance of a print is proposed with consideration of these effects. In this model the effects of either physical or optical dot gain are characterized by a single parameter, while those of fluorescence by two sets of spectral parameters, one for fluorescence of bare paper and one for fluorescence of a print solid. This model is tested and further illustrated with applications to images generated by a laser color printer on ordinary office papers. © 2005, IS&T - The Society for Imaging Science and Technology.

  • 99387.
    Yang, Li
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Fogden, Andrew
    Institute for Surface Chemistry, Stockholm.
    Pauler, Nils
    Mid Sweden University.
    Saevborg, Oerjan
    Stora Enso Research Center.
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Studying ink penetration with microscopic and spectroscopic techniques2006In: Journal of Imaging Science and Technology, ISSN 1062-3701, E-ISSN 1943-3522, Vol. 50, no 4, p. 327-332Article in journal (Refereed)
    Abstract [en]

    Distribution of ink jet ink in paper substrates and the consequences of ink penetration for printing color reproduction have been studied by combining microscopic image processing with spectroscopic analysis. The study focused on the effects of the composition of uncoated paper, for five laboratory papers plus two commercial products, all consisting of similar pulps but with different combinations of additives. In particular, it was observed that hydrophobizing internal size agents significantly reduced ink penetration, while their effect on paper optical properties was negligible. This observation thus made it possible to study experimentally the pure effects of ink penetration. Pairwise comparisons of prints on such laboratory papers with identical optical properties revealed remarkable impacts of ink penetration on optical density, causing color saturation reduction and color shift. These experimental observations confirmed the theoretical predictions.

  • 99388.
    Yang, Li
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Fogden, Andrew
    Pauler, Nils
    Sävborg, Örjan
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    A novel method for studying ink penetration of a print2005In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, no 4, p. 423-429Article in journal (Refereed)
    Abstract [en]

    A method combining microscopy with image analysis for studying ink penetration of ink-jet prints has been proposed. Prints on paper substrates of various material compositions have been microtomed, imaged with optical microscopy, and analyzed with image processing. The penetration depth and distribution of the ink-jet dye in the paper, which depend on the material compositions of the substrates and printed ink volumes, are then obtained by means of statistical analysis. The study focuses on uncoated fine papers, including five types of hand-sheets and two commercial papers. It is observed that ink penetration can be significantly reduced by adding internal sizing (hydrophobizing) chemicals in the hand-sheet making, while it is relatively less affected by addition of filler and fluorescent whitening agent (FWA). Ink volume obviously influences the depth of its penetration, with depth increasing linearly for higher ink volumes but displaying a disproportionately shallow penetration for smaller applied volumes.

  • 99389.
    Yang, Li
    et al.
    Karlstad University.
    Gooran, Sasan
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Eriksen, Magnus
    Johansson, Tobias
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Color Based Maximal GCR for Electrophotography2006In: IS&T Int. Conf. on Digital Printing Technologies (NIP22), The Society for Imaging Science and Technology , 2006, p. 394-397Conference paper (Other academic)
    Abstract [en]

    The underline idea of grey component replacement (GCR) is to replace a mixture of primary colors (cyan, magenta, and yellow) by a black. Current algorithms of GCR are mainly based on the concept of equal-tone-value-reduction or mixing equal amount (tone value) of primary colors generating gray, which in turn can be represented by the same amount of black. As the colors used are usually non-ideal, such a replacement can result in remarkable color deviation.    

    We proposed an algorithm of maximal GCR based on color matching, i.e. the black is introduced in a way that preserves the color (before and after GCR). In the algorithm, the primary with smallest tonal value is set to be zero (tone value) while the other two are reduced according to the color matching calculations. To achieve a real color matching of print, dot gain effects have been considered in the calculation. The proposed algorithm has been tested successfully for FM halftoning using an electrophotographic printer.   

  • 99390.
    Yang, Li
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Gooran, Sasan
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Simulation of optical dot gain in multichromatic tone production2001In: Journal of Imaging Science And Technology, ISSN 8750-9237, Vol. 45, no 2, p. 198-204Article in journal (Refereed)
    Abstract [en]

    Optical dot gain (light scattering or Yule-Nielsen effect) is an important effect influencing the quality of tone reproductions. Based on probability descriptions on the light scattering, a framework is established for describing this effect on the reflectance and color appearance of a chromatic halftone image. General expressions for the reflectance and CIEXYZ tristimulus values have been derived. Simulations for images printed with 2 inks have been carried out by applying Gaussian type of point spread function (PSF). Dependence of the optical dot gain on the optical properties of substrate and inks, the dot geometry etc., have been studied in detail.

  • 99391.
    Yang, Li
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Gooran, Sasan
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Kruse, Björn
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Yule-Nielsen Effect and Ink-penetration in Multi-chromatic Tone Reproduction2000In: IS & T's NIP16: International Conference on Digital Printing Technologies, 2000, p. 363-366Conference paper (Other academic)
    Abstract [en]

    A framework describing influences of ink penetration and Yule-Nielsen effect on the reflectance and tristimulus values of a halftone sample has been proposed. General expressions of the reflectance values and CIEXYZ tristimulus values have been derived. Simulations for images printed with two inks have been carried out by applying Gaussian type of point spread function (PSF). Dependence of Yule-Nielsen effect on the optical properties of substrate, inks, the dot geometry, ink penetration etc., have been discussed.

  • 99392.
    Yang, Li
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Evaluation of the effects of ink penetration in ink jet printing: Experiments and simulation2004In: Journal of Imaging Science And Technology, ISSN 8750-9237, Vol. 48, no 3, p. 260-264Article in journal (Refereed)
  • 99393.
    Yang, Li
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Revised Kubelka-Munk theory. I. Theory and application2004In: Journal of the Optical Society of America A: Optics and Image Science, and Vision, ISSN 1084-7529, Vol. 21, no 10, p. 1933-1941Article in journal (Refereed)
    Abstract [en]

    Using a statistical analysis of light propagation in media, we propose a revision to Kubelka-Munk (K-M) theory by taking into account the effect of scattering on the path length of light propagation (path variation). This leads to new relationships between the K-M scattering S and absorbing K coefficients and the intrinsic scattering s and absorbing a coefficients of a material that indicate that the S and K coefficients depend nonlinearly on both a and s. The additivity law that bridges K-M S and K coefficients of a composite medium, such as dye-dispersed paper (dyed paper) and those of its material components (dye and paper), is also revised. It is further shown that experimental findings on dyed paper that the original K-M theory failed to explain can be clearly understood and accommodated by the new K-M theoretical framework (two-flux approach). Numerical simulations with the revised theory on model ink, paper, and dyed paper have been carried out.

  • 99394.
    Yang, Li
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Miklavcic, Stan
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Revised Kubelka-Munk theory. II. Unified framework for homogeneous and inhomogeneous optical media2004In: Journal of the Optical Society of America A: Optics and Image Science, and Vision, ISSN 1084-7529, Vol. 21, no 10, p. 1942-1952Article in journal (Refereed)
    Abstract [en]

    We extend the applicability of the recently revised Kubelka-Munk (K-M) theory to inhomogeneous optical media by treating inhomogeneous ink penetration of the substrate. We propose a method for describing light propagation in either homogeneous or inhomogeneous layers using series representations for the K-M scattering and absorption coefficients as well as for intensities of the upward and downward light streams. The conventional and matrix expressions for spectral reflectance and transmittance values of optically homogeneous media in the K-M theory are shown to be special cases of the present framework. Three types of ink distribution - homogeneous, linear, and exponential - have been studied. Simulations of spectral reflectance predict a depression of reflectance peaks and reduction of absorption bands characteristic of hue shifts and significant reduction of saturation and, in turn, color gamut.

  • 99395.
    Yang, Li
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Lenz, Reiner
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Kruse, Björn
    Linköping University, Department of Science and Technology, Digital Media. Linköping University, The Institute of Technology.
    Light scattering and ink penetration effects on tone reproduction2001In: Journal of the Optical Society of America A, ISSN 0740-3232, Vol. 18, no 2, p. 360-366Article in journal (Refereed)
    Abstract [en]

    Light scattering, or the so-called Yule-Nielsen effect, and ink penetration into the substrate paper play important roles in tone reproduction. We develop a framework in which the influences of both of these effects on the reflectance and tristimulus values of a halftone sample are investigated. The properties of the paper and the ink and their bilateral interaction can be parameterized by the reflectance R-p(0) of the substrate paper, the transmittance T-i of the ink layer, the parameter gamma describing the ink penetration, and (p) over bar describing the Yule-Nielsen effect. We derive explicit expressions that relate the reflectance of the ink dots (R-i), the paper (R-p) and the halftone image (R) as functions of these parameters, We also describe the optical dot gain as a function of these parameters. We further demonstrate that ink penetration leads to a decrease in optical dot gain and that scattering in the paper results in the printed image's being viewed as more saturated in color. (C) 2001 Optical Society of America. OCIS codes: 100.7810, 290.7050.

  • 99396.
    Yang, Li Li
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Synthesis and Characterization of ZnO Nanostructures2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    One-dimensional ZnO nanostructures have great potential applications in the fields of optoelectronic and sensor devices.  Therefore, it is very important to realize the controllable growth of one-dimensional ZnO nanostructures and investigate their properties. The main points for this thesis are not only to successfully realize the controllable growth of ZnO nanorods (ZNRs), ZnO nanotubes (ZNTs) and ZnMgO/ZnO heterostructures, but also investigate the structure and optical properties in detail by means of scanning electron microscope (SEM), transmission electron microscope (TEM), resonant Raman spectroscopy (RRS), photoluminescence (PL), time resolved PL (TRPL), X-ray photoelectron spectroscopy (XPS) and Secondary ion mass spectrometry (SIMS).

    For ZNRs, on one hand, ZNRs have been successfully synthesized by a two-step chemical bath deposition method on Si substrates. The diameter of ZNRs can be well controlled from 150 nm to 40 nm through adjusting the diameter and density of the ZnO nanoparticles pretreated on the Si substrates. The experimental results indicated that both diameter and density of ZnO nanoparticles on the substrates determined the diameter of ZNRs. But when the density is higher than the critical value of 2.3×108cm-2, the density will become the dominant factor to determine the diameter of ZNRs.

    One the other hand, the surface recombination of ZNRs has been investigated in detail. Raman, RRS and PL results help us reveal that the surface defects play a significant role in the as-grown sample. It is the first time to the best of our knowledge that the Raman measurements can be used to monitor the change of surface defects and deep level defects in the CBD grown ZNRs. Then we utilized TRPL technique, for the first time, to investigate the CBD grown ZNRs with different diameters. The results show that the decay time of the excitons in ZNRs strongly depends on the diameter. The altered decay time is mainly due to the surface recombination process. A thermal treatment under 500°C can strongly suppress the surface recombination channel. A simple carrier and exciton diffusion equation is also used to determine the surface recombination velocity, which results in a value between 1.5 and 4.5 nm/ps. Subsequently, we utilized XPS technique to investigate the surface composition of as-grown and annealed ZNRs so that we can identify the surface recombination centers. The experimental results indicated that the OH and H bonds play the dominant role in facilitating surface recombination but specific chemisorbed oxygen also likely affect the surface recombination. Finally, on the basis of results above, we explored an effective way, i.e. sealing the beaker during the growth process, to effectively suppress the surface recombination of ZNRs and the suppression effect is even better than a 500oC post-thermal treatment.

    For ZNTs, the structural and optical properties have been studied in detail. ZNTs have been successfully evolved from ZNRs by a simple chemical etching process. Both temperature-dependent PL and TRPL results not only further testify the coexistence of spatially indirect and direct transitions due to the surface band bending, but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their strong enhancement of luminescence intensity.

    For ZnMgO/ZnO heterostructures, the Zn0.94Mg0.06O/ZnO heterostructures have been deposited on 2 inch sapphire wafer by metal organic chemical vapor deposition (MOCVD) equipment. PL mapping demonstrates that Mg distribution in the entire wafer is quite uniform with average concentration of ~6%. The annealing effects on the Mg diffusion behaviors in Zn0.94Mg0.06O/ZnO heterostructures have been investigated by SIMS in detail. All the SIMS depth profiles of Mg element have been fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn0.94Mg0.06O layer deposited at 700 oC is two orders of magnitude lower than that of annealing samples, which clearly testifies that the deposited temperature of 700 oC is much more beneficial to grow ZnMgO/ZnO heterostructures or quantum wells.

    This thesis not only provides the effective way to fabricate ZNRs, ZNTs and ZnMgO/ZnO heterostructures, but also obtains some beneficial results in aspects of their optical properties, which builds theoretical and experimental foundation for much better understanding fundamental physics and broader applications of low-dimensional ZnO and related structures.

    List of papers
    1. Size-controlled growth of well-aligned ZnO nanorod arrays with two-step chemical bath deposition method
    Open this publication in new window or tab >>Size-controlled growth of well-aligned ZnO nanorod arrays with two-step chemical bath deposition method
    2009 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 469, no 1-2, p. 623-629Article in journal (Refereed) Published
    Abstract [en]

    Well-aligned ZnO nanorod arrays (ZNAs) with different sizes in diameter were fabricated on Si substrates by two-step chemical bath deposition method (CBD), i.e. substrate pre-treatment with spin coating to form ZnO nanoparticles layer and CBD growth. The effects of substrate pre-treatments, pH, angel (θ) between substrate and beaker bottom and growth time (t) on the structure of ZNAs were investigated in detail by X-ray diffraction (XRD), field emission scan electronic microscope (SEM) and photoluminescence (PL). The results show that substrate pre-treatment, pH, θ and t indeed have great influence on the growth of ZNAs, and their influence mechanisms have been, respectively, explained in detail. The introduction of a ZnO nanoparticle layer on the substrate not only helps to decrease the diameter but also has a strong impact on the orientation of ZNAs. Under the growth condition of pH 6, θ = 70° and t = 2 h, the well-aligned ZnO nanorod arrays with 50 nm diameter was obtained on the pre-treated Si substrates. And only a strong UV peak at 385 nm appears in room temperature PL spectrum for this sample, which indicates that as-synthesized ZnO nanorods have a perfect crystallization and low density of deep level defects.

    Keywords
    ZnO nanorods, Chemical bath deposition, Optical properties
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:liu:diva-15532 (URN)10.1016/j.jallcom.2008.08.002 (DOI)
    Note
    Original Publication:LiLi Yang, Qingxiang Zhao and Magnus Willander, Size-controlled growth of well-aligned ZnO nanorod arrays with two-step chemical bath deposition method, 2009, Journal of Alloys and Compounds, (469), 1-2, 623-629.http://dx.doi.org/10.1016/j.jallcom.2008.08.002Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com/Available from: 2009-03-27 Created: 2008-11-14 Last updated: 2017-12-14Bibliographically approved
    2. Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition
    Open this publication in new window or tab >>Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition
    2009 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 311, no 4, p. 1046-1050Article in journal (Refereed) Published
    Abstract [en]

    The diameter of well-aligned ZnO nanorod arrays (ZNAs) grown on Si substrates has been well controlled from 150nm to 40nm by two-step chemical bath deposition method (CBD), i.e. substrate pretreatment with spin coating to form ZnO nanoparticles seed layer and CBD growth. The effects of ZnO nanoparticles density and diameter on size and alignment of ZNAs were investigated in detail by atomic force microscope (AFM), X-ray diffraction (XRD), scan electronic microscope (SEM), transmission electron microscope (TEM) and photoluminescence (PL). The results indicate that both diameter and density of ZnO nanoparticles which were pre-coated on the substrates will influence the size and alignment of ZNAs, but the density will play a key role to determine the diameter of ZNAs when the density is higher than the value of 2.3×108cm-2. Moreover, only a strong UV peak at 385 nm appears in room temperature PL spectrum for these samples, which indicates that  as-synthesized ZnO nanorods have a perfect crystallization and low density of deep level defects.

    Keywords
    ZnO nanorods arrays, CBD, Size-controlled growth
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:liu:diva-15533 (URN)10.1016/j.jcrysgro.2008.12.028 (DOI)
    Note
    Original Publication: Li-Li Yang, Qingxiang Zhao, Magnus Willander and J.H. Yang, Effective way to control the size of well-aligned ZnO nanorod arrays with two-step chemical bath deposition, 2009, Journal of Crystal Growth, (311), 4, 1046-1050. http://dx.doi.org/10.1016/j.jcrysgro.2008.12.028 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2008-11-14 Created: 2008-11-14 Last updated: 2017-12-14
    3. Annealing effects on optical properties of low temperature grown ZnO nanorod arrays
    Open this publication in new window or tab >>Annealing effects on optical properties of low temperature grown ZnO nanorod arrays
    Show others...
    2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 5, p. 053503-Article in journal (Refereed) Published
    Abstract [en]

    Vertically well-aligned ZnO nanorods on Si substrates were prepared by a two-step chemical bath deposition method. The structure and optical properties of the grown ZnO nanorods were investigated by Raman and photoluminescence spectroscopy. The results showed that after an annealing treatment at around 500 degrees C in air atmosphere, the crystal structure and optical properties became much better due to the decrease in surface defects. The resonant Raman measurements excited by 351.1 nm not only revealed that the surface defects play a significant role in the as-grown sample, which was supported by low temperature time-resolved photoluminescence measurements, but also suggested that the strong intensity increase in some Raman scatterings was due to both outgoing resonant Raman scattering effect and deep level defect scattering contribution for ZnO nanorods annealed from 500 to 700 degrees C.

    Keywords
    annealing, crystal structure, deep levels, II-VI semiconductors, liquid phase deposition, nanostructured materials, nanotechnology, photoluminescence, Raman spectra, time resolved spectra, wide band gap semiconductors, zinc compounds
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-17508 (URN)10.1063/1.3073993 (DOI)
    Note
    Original Publication:Lili Yang, Qingxiang Zhao, Magnus Willander and Ivan Gueorguiev Ivanov , Annealing effects on optical properties of low temperature grown ZnO nanorod arrays, 2009, JOURNAL OF APPLIED PHYSICS, (105), 5, 053503.http://dx.doi.org/10.1063/1.3073993Copyright: American Institute of Physicshttp://www.aip.org/Available from: 2009-04-07 Created: 2009-03-27 Last updated: 2017-12-13Bibliographically approved
    4. Surface recombination in ZnO nanorods grown by chemical bath deposition
    Open this publication in new window or tab >>Surface recombination in ZnO nanorods grown by chemical bath deposition
    Show others...
    2008 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 104, no 7, p. 073526-Article in journal (Refereed) Published
    Abstract [en]

    Verticallywell-aligned ZnO nanorods on Si substrates were prepared by atwo-step chemical bath deposition (CBD) method. The optical properties ofthe grown ZnO nanorods were investigated by time resolved photoluminescencespectroscopy. It was found that the effective decay time ofthe near bandgap recombination in the CBD grown ZnO nanorodsstrongly depends on the diameter of the ZnO nanorods. Typically,the decay curves obtained from these ZnO nanorods show acombination of two exponential decays. The experimental results show thatthe fast exponential decay is related to the surface recombinationand the slow decay is related to the “bulk” decay.The measured decay time of the effective surface recombination decreaseswith decreasing diameter, while the bulk decay time remains unchanged.The results also show that an annealing treatment around 500 °Csignificantly reduces the surface recombination rate. A simple carrier andexciton diffusion equation is also used to determine the surfacerecombination velocity, which results in a value between 1.5 and4.5 nm/ps.

    Keywords
    Annealing, excitons, II-VI semiconductors, nanostructured materials, nanotechnology, photoluminescence, semiconductor growth, surface recombination, time resolved spectra, wide band gap semiconductors, zinc compounds
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:liu:diva-15425 (URN)10.1063/1.2991151 (DOI)
    Note

    Original publication: Q. X. Zhao, L. L. Yang, M. Willander, B. E. Sernelius and P. O. Holtz, Surface recombination in ZnO nanorods grown by chemical bath deposition, 2008, Journal of Applied Physics, (104), 073526.http://dx.doi.org/10.1063/1.2991151. Copyright: Institute of Physics and IOP Publishing Limited, http://www.iop.org/EJ/journal/PM

    Available from: 2008-11-06 Created: 2008-11-06 Last updated: 2017-12-14Bibliographically approved
    5. Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy
    Open this publication in new window or tab >>Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy
    Show others...
    2010 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, no 11, p. 3592-3597Article in journal (Refereed) Published
    Abstract [en]

    The surface composition of as-grown and annealed ZnO nanorods arrays (ZNAs) grown by a two-step chemical bath deposition method has been investigated by X-ray photoelectron spectroscopy (XPS). XPS confirms the presence of OH bonds and specific chemisorbed oxygen on the surface of ZNAs, as well as H bonds on (1 0 (1) over bar 0) surfaces which has been first time observed in the XPS spectra. The experimental results indicated that the OH and H bonds play the dominant role in facilitating surface recombination but specific chemisorbed oxygen also likely affect the surface recombination. Annealing can largely remove the OH and H bonds and transform the composition of the other chemisorbed oxygen at the surface to more closely resemble that of high temperature grown ZNAs, all of which suppresses surface recombination according to time-resolved photoluminescence measurements.

    Place, publisher, year, edition, pages
    Amsterdam, Netherlands: Elsevier, 2010
    Keywords
    ZnO nanorods, Optical properties, Surface recombination, X-ray photoelectron spectroscopy
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-54620 (URN)10.1016/j.apsusc.2009.12.160 (DOI)000275515100042 ()
    Note

    Original Publication: Li-Li Yang, Qingxiang Zhao, Magnus Willander, Xianjie Liu, Mats Fahlman and J H Yang, Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy, 2010, APPLIED SURFACE SCIENCE, (256), 11, 3592-3597. http://dx.doi.org/10.1016/j.apsusc.2009.12.160 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/

    Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2017-12-12
    6. Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process
    Open this publication in new window or tab >>Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process
    Show others...
    2010 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 10, no 4, p. 1904-1910Article in journal (Refereed) Published
    Abstract [en]

    ZnO nanorods arrays are respectively prepared under different vapor pressures with opening (OZN) or sealing (SZN) of the beaker. The results from time-resolved photoluminescence measurements indicate that sealing the beaker during the growth process can effectively suppress the surface recombination of ZnO nanorods, and the suppression effect is even better than a 500 degrees C post-thermal treatment or OZN samples. The results from X-ray photoelectron spectroscopy measurements reveal that the main reason for this phenomenon is that the surfaces of the SZN samples are attached by groups related to NH3 instead of the main surface recombination centers such as OH and groups in the OZN samples. The ammonia surface treatment on both OZN and SZN samples further testifies that the absorption of the groups related to NH3 does not contribute to the surface recombination on the ZnO nanorods.

    Place, publisher, year, edition, pages
    American Chemical Society (ACS), 2010
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-54866 (URN)10.1021/cg100017b (DOI)000276234500068 ()
    Note

    This document is the Accepted Manuscript version of a Published Work that appeared in final form in CRYSTAL GROWTH and DESIGN, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see: Li-Li Yang, Qingxiang Zhao, Magnus Willander, Xianjie Liu, Mats Fahlman and J H Yang, Effective Suppression of Surface Recombination in ZnO Nanorods Arrays during the Growth Process, 2010, CRYSTAL GROWTH and DESIGN, (10), 4, 1904-1910. http://dx.doi.org/10.1021/cg100017b Copyright: The American Chemical Society http://pubs.acs.org/

    Available from: 2010-04-16 Created: 2010-04-16 Last updated: 2017-12-12Bibliographically approved
    7. Indirect optical transition due to surface band bending in ZnO nanotubes
    Open this publication in new window or tab >>Indirect optical transition due to surface band bending in ZnO nanotubes
    Show others...
    2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 10Article in journal (Refereed) Published
    Abstract [en]

    ZnO nanotubes (ZNTs) have been successfully evolved from ZnO nanorods (ZNRs) by a simple chemical etching process. Two peaks located at 382 nm and 384 nm in the UV emission region has been observed in the room temperature photoluminescence (PL) spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending, but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity.

    Place, publisher, year, edition, pages
    American Institute, 2010
    Keywords
    Zinc Oxide, Nanotube, Surface band bending, Indirect transition, Temperature-dependent photoluminescence
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-60853 (URN)10.1063/1.3511345 (DOI)000285005000053 ()
    Note
    Original Publication: Li Li Yang, Qingxiang Zhao, Muhammad Qadir Israr, Jamil Rana Sadaf, Magnus Willander, Galia Pozina and J. H. Yang, Indirect optical transition due to surface band bending in ZnO nanotubes, 2010, Journal of Applied Physics, (108), 10, 103513. http://dx.doi.org/10.1063/1.3511345 Copyright: American Institute of Physics http://www.aip.org/ Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12
    8. Mg diffusion in Zn0.94Mg0.06O/ZnO heterostructures grown by MOCVD
    Open this publication in new window or tab >>Mg diffusion in Zn0.94Mg0.06O/ZnO heterostructures grown by MOCVD
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Zn0.94Mg0.06O/ZnO heterostructures were grown on 2 inch sapphire wafer by MOCVD equipment. Photoluminescence mapping demonstrated that Mg uniformly distributed on the entire wafer with average concentration of ~6%. The annealing effects on the Mg diffusion behaviors were investigated by secondary ion mass spectrometry (SIMS). All Mg SIMS depth profiles were fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn0.94Mg0.06O layer deposited at 700 oC was two order of magnitude lower than that of annealed samples, which indicated that the deposition temperature of 700 oC is much more beneficial to grow ZnMgO/ZnO heterostructures or quantum wells.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-60854 (URN)
    Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2014-01-15
  • 99397.
    Yang, Li Li
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Israr, Muhammad Qadir
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Sadaf, Jamil Rana
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Pozina, Galia
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yang, J. H.
    Institute of Condensed State Physics, Jilin Normal University, Siping, 136000, People's Republic of China.
    Indirect optical transition due to surface band bending in ZnO nanotubes2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 10Article in journal (Refereed)
    Abstract [en]

    ZnO nanotubes (ZNTs) have been successfully evolved from ZnO nanorods (ZNRs) by a simple chemical etching process. Two peaks located at 382 nm and 384 nm in the UV emission region has been observed in the room temperature photoluminescence (PL) spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending, but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity.

  • 99398.
    Yang, Li Li
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Zhao, Qingxiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Xing, G. Z.
    Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, NanyangTechnological University, Singapore.
    Wang, D. D.
    Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, NanyangTechnological University, Singapore.
    Wu, T.
    Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, NanyangTechnological University, Singapore.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Yang, J. H.
    Institute of Condensed State Physics, Jilin Normal University, Siping, 136000, People's Republic of China.
    Mg diffusion in Zn0.94Mg0.06O/ZnO heterostructures grown by MOCVDManuscript (preprint) (Other academic)
    Abstract [en]

    Zn0.94Mg0.06O/ZnO heterostructures were grown on 2 inch sapphire wafer by MOCVD equipment. Photoluminescence mapping demonstrated that Mg uniformly distributed on the entire wafer with average concentration of ~6%. The annealing effects on the Mg diffusion behaviors were investigated by secondary ion mass spectrometry (SIMS). All Mg SIMS depth profiles were fitted by three Gaussian distribution functions. The Mg diffusion coefficient in the as-grown Zn0.94Mg0.06O layer deposited at 700 oC was two order of magnitude lower than that of annealed samples, which indicated that the deposition temperature of 700 oC is much more beneficial to grow ZnMgO/ZnO heterostructures or quantum wells.

  • 99399.
    Yang, Li
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Lundström, Niclas
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Physical dot gain of offset: Understanding and determination2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 3, p. 388-393Article in journal (Refereed)
    Abstract [en]

    This report consists of two parts. In the first, a methodology for estimating physical dot gain from scanned images of test patches is proposed. Mathematical relationships bridging the image intensities with the physical dot coverage have been worked out, taking into consideration of light scattering inside the paper substrate and the light reflection at air-paper and air-ink interfaces. In the second part, the possible causes for the physical dot gain in the light of ink-transfer and ink-setting are discussed. The physical dot gain obtained reveals significant differences in the light tones compared to the middle and dark tones. This indicates differences in ink-transfer and ink-setting between the prints consisting of well isolated dots in the light tones and those of overlapping dots in the middle and dark tones. A tentative explanation based on process-competition between press, ink spreading, and free ink-splitting, is given.

  • 99400.
    Yang, Li
    et al.
    Graphical Technology/Package Printing Group, Department of Chemical Engineering Karlstad University.
    Miklavcic, Stan
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Revised Kubelka-Munk theory. III. A general theory of light propagation in scattering and absorptive media2005In: Journal of the Optical Society of America A: Optics and Image Science, and Vision, ISSN 1084-7529, Vol. 22, no 9, p. 1866-1873Article in journal (Refereed)
    Abstract [en]

    A generally applicable theoretical model describing light propagating through turbid media is proposed. The theory is a generalization of the revised Kubelka-Munk theory, extending its applicability to accommodate a wider range of absorption influences. A general expression for a factor taking into account the effect of scattering on the total photon path traversed in a turbid medium is derived. The extended model is applied to systems of ink-dyed paper sheets - mixtures of wood fibers with dyes - which represent examples of systems that have thus far eluded the original Kubelka-Munk model. The results of simulations of the spectral dependence of Kubelka-Munk coefficients of absorption and scattering show that they compare very well with those derived from experimental results. © 2005 Optical Society of America.

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  • rtf