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Magnfält, D., Fillon, A., Boyd, R., Helmersson, U., Sarakinos, K. & Abadias, G. (2016). Compressive intrinsic stress originates in the grain boundaries of dense refractory polycrystalline thin films. Journal of Applied Physics, 119(5), 055305.
Open this publication in new window or tab >>Compressive intrinsic stress originates in the grain boundaries of dense refractory polycrystalline thin films
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2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 5, 055305- p.Article in journal (Refereed) Published
Abstract [en]

Intrinsic stresses in vapor deposited thin films have been a topic of considerable scientific and technological interest owing to their importance for functionality and performance of thin film devices. The origin of compressive stresses typically observed during deposition of polycrystalline metal films at conditions that result in high atomic mobility has been under debate in the literature in the course of the past decades. In this study, we contribute towards resolving this debate by investigating the grain size dependence of compressive stress magnitude in dense polycrystalline Mo films grown by magnetron sputtering. Although Mo is a refractory metal and hence exhibits an intrinsically low mobility, low energy ion bombardment is used during growth to enhance atomic mobility and densify the grain boundaries. Concurrently, the lateral grain size is controlled by using appropriate seed layers on which Mo films are grown epitaxially. The combination of in situ stress monitoring with ex situ microstructural characterization reveals a strong, seemingly linear, increase of the compressive stress magnitude on the inverse grain size and thus provides evidence that compressive stress is generated in the grain boundaries of the film. These results are consistent with models suggesting that compressive stresses in metallic films deposited at high homologous temperatures are generated by atom incorporation into and densification of grain boundaries. However, the underlying mechanisms for grain boundary densification might be different from those in the present study where atomic mobility is intrinsically low. (C) 2016 AIP Publishing LLC.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-125810 (URN)10.1063/1.4941271 (DOI)000369900600028 ()
Note

Funding Agencies|COST Action "Highly Ionized Pulsed Plasmas" [MP0804]; Swedish Research Council VR [621-2014-4882]; Linkoping University via the "LiU Research Fellows" program.

The previous status of this article was Manuscript and the working title was Atom insertion into grain boundaries generates compressive intrinsic stress in polycrystalline thin films.

Available from: 2016-03-08 Created: 2016-03-04 Last updated: 2017-11-30Bibliographically approved
Eriksson, J., Puglisi, D., Strandqvist, C., Gunnarsson, R., Ekeroth, S., Ivanov, I. G., . . . Lloyd Spetz, A. (2016). Modified Epitaxial Graphene on SiC for Extremely Sensitive andSelective Gas Sensors. Paper presented at ICSCRM 2015, The International Conference on Silicon Carbide and Related Materials, 4-9 October 2015, Giardini Naxos, Italy. Materials Science Forum, 858, 1145-1148.
Open this publication in new window or tab >>Modified Epitaxial Graphene on SiC for Extremely Sensitive andSelective Gas Sensors
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2016 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 858, 1145-1148 p.Article in journal (Refereed) Published
Abstract [en]

Two-dimensional materials offer a unique platform for sensing where extremely high sensitivity is a priority, since even minimal chemical interaction causes noticeable changes inelectrical conductivity, which can be used for the sensor readout. However, the sensitivity has to becomplemented with selectivity, and, for many applications, improved response- and recovery times are needed. This has been addressed, for example, by combining graphene (for sensitivity) with metal/oxides (for selectivity) nanoparticles (NP). On the other hand, functionalization or modification of the graphene often results in poor reproducibility. In this study, we investigate thegas sensing performance of epitaxial graphene on SiC (EG/SiC) decorated with nanostructured metallic layers as well as metal-oxide nanoparticles deposited using scalable thin-film depositiontechniques, like hollow-cathode pulsed plasma sputtering. Under the right modification conditions the electronic properties of the surface remain those of graphene, while the surface chemistry can betuned to improve sensitivity, selectivity and speed of response to several gases relevant for airquality monitoring and control, such as nitrogen dioxide, benzene, and formaldehyde.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2016
Keyword
Epitaxial graphene, graphene hybrid materials, gas sensor
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-128078 (URN)10.4028/www.scientific.net/MSF.858.1145 (DOI)
Conference
ICSCRM 2015, The International Conference on Silicon Carbide and Related Materials, 4-9 October 2015, Giardini Naxos, Italy
Available from: 2016-05-16 Created: 2016-05-16 Last updated: 2017-11-30
Shimizu, T., Villamayor, M. M., Lundin, D. & Helmersson, U. (2016). Process stabilization by peak current regulation in reactive high-power impulse magnetron sputtering of hafnium nitride. Journal of Physics D: Applied Physics, 49(6), 065202.
Open this publication in new window or tab >>Process stabilization by peak current regulation in reactive high-power impulse magnetron sputtering of hafnium nitride
2016 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 49, no 6, 065202- p.Article in journal (Refereed) Published
Abstract [en]

A simple and cost effective approach to stabilize the sputtering process in the transition zone during reactive high-power impulse magnetron sputtering (HiPIMS) is proposed. The method is based on real-time monitoring and control of the discharge current waveforms. To stabilize the process conditions at a given set point, a feedback control system was implemented that automatically regulates the pulse frequency, and thereby the average sputtering power, to maintain a constant maximum discharge current. In the present study, the variation of the pulse current waveforms over a wide range of reactive gas flows and pulse frequencies during a reactive HiPIMS process of Hf-N in an Ar-N2 atmosphere illustrates that the discharge current waveform is a an excellent indicator of the process conditions. Activating the reactive HiPIMS peak current regulation, stable process conditions were maintained when varying the N-2 flow from 2.1 to 3.5 sccm by an automatic adjustment of the pulse frequency from 600 Hz to 1150 Hz and consequently an increase of the average power from 110 to 270 W. Hf-N films deposited using peak current regulation exhibited a stable stoichiometry, a nearly constant power-normalized deposition rate, and a polycrystalline cubic phase Hf-N with (1 1 1)-preferred orientation over the entire reactive gas flow range investigated. The physical reasons for the change in the current pulse waveform for different process conditions are discussed in some detail.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2016
Keyword
reactive sputtering; HiPIMS; hafnium nitride; process control
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-124621 (URN)10.1088/0022-3727/49/6/065202 (DOI)000368099600016 ()
Note

Funding Agencies|Swedish Research Council (VR) [VR 621-2014-4882]; Japan Society for the Promotion of Science (JSPS) [26820327]; AMADA foundation [AF-2013028]; Bases Conversion Development Authority (BCDA), Philippines

Available from: 2016-02-09 Created: 2016-02-08 Last updated: 2017-11-30
Vermang, B., Timo Watjen, J., Fjallstrom, V., Rostvall, F., Edoff, M., Gunnarsson, R., . . . Flandre, D. (2015). Highly reflective rear surface passivation design for ultra-thin Cu(In,Ga) Se-2 solar cells. Thin Solid Films, 582, 300-303.
Open this publication in new window or tab >>Highly reflective rear surface passivation design for ultra-thin Cu(In,Ga) Se-2 solar cells
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2015 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 582, 300-303 p.Article in journal (Refereed) Published
Abstract [en]

Al2O3 rear surface passivated ultra-thin Cu(In,Ga)Se-2 (CIGS) solar cells with Mo nano-particles (NPs) as local rear contacts are developed to demonstrate their potential to improve optical confinement in ultra-thin CIGS solar cells. The CIGS absorber layer is 380 nm thick and the Mo NPs are deposited uniformly by an up-scalable technique and have typical diameters of 150 to 200 nm. The Al2O3 layer passivates the CIGS rear surface between the Mo NPs, while the rear CIGS interface in contact with the Mo NP is passivated by [Ga]/([Ga] + [In]) (GGI) grading. It is shown that photon scattering due to the Mo NP contributes to an absolute increase in short circuit current density of 3.4 mA/cm(2); as compared to equivalent CIGS solar cells with a standard back contact.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Ultra-thin films; Copper Indium Gallium Selenide; Aluminum oxide; Surface passivation layer; Molybdenum; Nanoparticles; Local contacts; Solar cells
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-117642 (URN)10.1016/j.tsf.2014.10.050 (DOI)000352225900064 ()
Note

Funding Agencies|European Commission via FP7 Marie Curie IEF [300998]; Knut and Alice Wallenberg Foundation [2012.0083]; Swedish Research Council via the Linkoping Linnaeus Environment LiLi-NFM [2008-6572]; European and Wallonia Region FEDER [ECP12020011678F]

Available from: 2015-05-12 Created: 2015-05-06 Last updated: 2017-12-04
Gunnarsson, R., Helmersson, U. & Pilch, I. (2015). Synthesis of titanium-oxide nanoparticles with size and stoichiometry control. Journal of nanoparticle research, 17(9), 353.
Open this publication in new window or tab >>Synthesis of titanium-oxide nanoparticles with size and stoichiometry control
2015 (English)In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 17, no 9, 353- p.Article in journal (Refereed) Published
Abstract [en]

Ti-O nanoparticles have been synthesized via hollow cathode sputtering in an Ar-O-2 atmosphere using high power pulsing. It is shown that the stoichiometry and the size of the nanoparticles can be varied independently, the former through controlling the O-2 gas flow and the latter by the independent biasing of two separate anodes in the growth zone. Nanoparticles with diameters in the range of 25-75 nm, and with different Ti-O compositions and crystalline phases, have been synthesized.

Place, publisher, year, edition, pages
Springer Verlag (Germany), 2015
Keyword
Titanium dioxide; TiO2; Reactive sputtering; Size control; Composition control; Gas flow sputtering; Aerosols
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-121300 (URN)10.1007/s11051-015-3158-3 (DOI)000360245300002 ()
Note

Funding Agencies|Knut and Alice Wallenberg foundation [KAW 2014.0276]; Swedish Research Council via the Linkoping Linneaus Environment LiLi-NFM [2008-6572]

Available from: 2015-09-16 Created: 2015-09-14 Last updated: 2017-12-21
Boyd, R., Gunnarsson, R., Pilch, I. & Helmersson, U. (2014). Characterisation of Nanoparticle Structure by High Resolution Electron Microscopy. In: Electron Microscopy and Analysis Group Conference  (EMAG2013): . Paper presented at Conference of the Electron-Microscopy-and-Analysis-Group (EMAG) (pp. 012065). Institute of Physics Publishing (IOPP), 522(012065).
Open this publication in new window or tab >>Characterisation of Nanoparticle Structure by High Resolution Electron Microscopy
2014 (English)In: Electron Microscopy and Analysis Group Conference  (EMAG2013), Institute of Physics Publishing (IOPP), 2014, Vol. 522, no 012065, 012065- p.Conference paper, Published paper (Refereed)
Abstract [en]

Whilst the use of microscopic techniques to determine the size distributions of nanoparticle samples is now well established, their characterisation challenges extend well beyond this. Here it is shown how high resolution electron microscopy can help meet these challenges. One of the key parameters is the determination of particle shape and structure in three dimensions. Here two approaches to determining nanoparticle structure are described and demonstrated. In the first scanning transmission electron microscopy combined with high angle annular dark field imaging (HAADF-STEM) is used to image homogenous nanoparticles, where the contrast is directly related to the thickness of the material in the electron beam. It is shown that this can be related to the three dimensional shape of the nano-object. High resolution TEM imaging, combined with fast Fourier transform (FFT) analysis, can determine the crystalline structure and orientation of nanoparticles as well as the presence of any defects. This combined approach allows the physical structure of a significant number of nano-objects to be characterised, relatively quickly.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2014
Series
Journal of Physics Conference Series, ISSN 1742-6588 ; 522
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-110717 (URN)10.1088/1742-6596/522/1/012065 (DOI)000340969200065 ()
Conference
Conference of the Electron-Microscopy-and-Analysis-Group (EMAG)
Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2014-11-05Bibliographically approved
Sønderby, S., Aijaz, A., Helmersson, U., Sarakinos, K. & Eklund, P. (2014). Deposition of yttria-stabilized zirconia thin films by high power impulse magnetron sputtering and pulsed magnetron sputtering. Surface & Coatings Technology, 240, 1-6.
Open this publication in new window or tab >>Deposition of yttria-stabilized zirconia thin films by high power impulse magnetron sputtering and pulsed magnetron sputtering
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2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 240, 1-6 p.Article in journal (Refereed) Published
Abstract [en]

Yttria-stabilized zirconia (YSZ) thin films were reactively sputter-deposited by high power impulse magnetron sputtering (HiPIMS) and pulsed direct current magnetron sputtering (DCMS). The use of substrate bias voltage was studied in both modes of deposition as a process parameter to promote the growth of dense and less columnar films. Films were deposited on both Si(100) and NiO-YSZ fuel cell anodes. The texture, morphology and composition of the deposited films were investigated with regard to their application as thin electrolytes for solid oxide fuel cells (SOFCs). Independent of the deposition mode the films were found to be stoichiometric. The application of substrate bias voltage had opposite effects on texture and crystallinity of films deposited by pulsed DCMS and HiPIMS. Films deposited by pulsed DCMS became highly crystalline and <220> textured at high bias voltage whereas bias applied to HiPIMS deposited films disrupted crystal growth leading to deterioration of crystallinity. Comparing film morphology, it was found that pulsed DCMS films were columnar and contained voids regardless of the applied substrate bias. When depositing by HiPIMS a window of operation at a bias voltage of -25 V to -50 V was found in which it is possible to deposit non-columnar thin films without voids and cracks as desired for SOFC applications. 

Keyword
HiPIMS, HPPMS, pulsed DCMS, SOFC, YSZ, Substrate bias
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-102516 (URN)10.1016/j.surfcoat.2013.12.001 (DOI)000331989900001 ()
Available from: 2013-12-12 Created: 2013-12-12 Last updated: 2017-12-06
Tal, A., Münger, P., Abrikosov, I., Brenning, N., Pilch, I. & Helmersson, U. (2014). Molecular dynamics simulation of the growth of Cu nanoclusters from Cu ions in a plasma. Physical Review B. Condensed Matter and Materials Physics, 90(16), 165421.
Open this publication in new window or tab >>Molecular dynamics simulation of the growth of Cu nanoclusters from Cu ions in a plasma
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2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 16, 165421- p.Article in journal (Refereed) Published
Abstract [en]

A recently developed method of nanoclusters growth in a pulsed plasma is studied by means of molecular dynamics. A model that allows one to consider high-energy charged particles in classical molecular dynamics is suggested, and applied for studies of single impact events in nanoclusters growth. In particular, we provide a comparative analysis of the well-studied inert gas aggregation method and the growth from ions in a plasma. The importance to consider of the angular distribution of incoming ions in the simulations of the nanocluster growth is underlined. A detailed study of the energy transfer from the incoming ions to a nanocluster, as well as the diffusion of incoming ions on the cluster surface, is carried out. Our results are important for understanding and control of the nanocluster growth process.

Place, publisher, year, edition, pages
American Physical Society, 2014
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-112305 (URN)10.1103/PhysRevB.90.165421 (DOI)000343699900005 ()
Note

Funding Agencies|Knut and Alice Wallenberg Foundation [2012.0083]; Swedish Foundation for Strategic Research (SSF) [10-0026]; Russian Federation Ministry for Science and Education [14.Y26.31.0005]

Available from: 2014-11-24 Created: 2014-11-24 Last updated: 2017-12-05
Aijaz, A., Sarakinos, K., Raza, M., Jensen, J. & Helmersson, U. (2014). Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films. Diamond and related materials, 44, 117-122.
Open this publication in new window or tab >>Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films
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2014 (English)In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 44, 117-122 p.Article in journal (Refereed) Published
Abstract [en]

In the present study we contribute to the understanding that is required for designing sputtering-based routes for high rate synthesis of hard and dense amorphous carbon (a-C) films. We compile and implement a strategy for synthesis of a-C thin films that entails coupling a hydrocarbon gas (acetylene) with high density discharges generated by the superposition of high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). Appropriate control of discharge density (by tuning HiPIMS/DCMS power ratio), gas phase composition and energy of the ionized depositing species leads to a route capable of providing ten-fold increase in the deposition rate of a-C film growth compared to HiPIMS Ar discharge (Aijaz et al. Diamond and Related Materials 23 (2012) 1). This is achieved without significant incorporation of H (< 10 %) and with relatively high hardness (> 25 GPa) and mass density (~2.32 g/cm3). Using our experimental data together with Monte-Carlo computer simulations and data from the literature we suggest that: (i) dissociative reactions triggered by the interactions of energetic discharge electrons with hydrocarbon gas molecules is an important additional (to the sputtering cathode) source of film forming species and (ii) film microstructure and film hydrogen content are primarily controlled by interactions of energetic plasma species with surface and sub-surface layers of the growing film.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Hydrogenated amorphous carbon, DLC, HiPIMS, reactive sputtering
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-104261 (URN)10.1016/j.diamond.2014.02.014 (DOI)000335272800017 ()
Available from: 2014-02-13 Created: 2014-02-13 Last updated: 2017-12-06Bibliographically approved
Pilch, I., Söderström, D., Lundin, D. & Helmersson, U. (2014). The use of highly ionized pulsed plasmas for the synthesis of advanced thin films and nanoparticles. Kona: Powder and Particle, 31(1), 171-180.
Open this publication in new window or tab >>The use of highly ionized pulsed plasmas for the synthesis of advanced thin films and nanoparticles
2014 (English)In: Kona: Powder and Particle, ISSN 0288-4534, E-ISSN 2187-5537, Vol. 31, no 1, 171-180 p.Article in journal (Refereed) Published
Abstract [en]

Pulsed plasma processes open up the possibility of using very high plasma densities and modulated deposition in the synthesis of thin films and nanoparticles. The high plasma densities lead to a high degree of ionization of the source material, which creates new possibilities for surface engineering. Ions can, in contrast to atoms, be easily controlled with regard to their energy and direction, which is beneficial for thin film growth. Furthermore, ions can also increase the trapping probability of material on nanoparticles growing in the gas phase. The pulsed sputter ejection of source material also has other consequences: the material in the plasma and the material arrival on the growth surface will fluctuate strongly resulting in high level of supersaturation during pulse-on time. In this paper, an overview of the generation and properties of highly ionized pulsed plasmas is given. In addition, the use and importance of these types of discharges in the fields of thin-film and nanoparticle growth are also summarized. ©2014 Hosokawa Powder Technology Foundation.

Place, publisher, year, edition, pages
Hosokawa Powder Technology Foundation, 2014
Keyword
HiPIMS; HPPMS; IPVD; Nanoparticle synthesis; Sputtering; Thin films
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-116406 (URN)10.14356/kona.2014008 (DOI)2-s2.0-84897712230 (Scopus ID)
Available from: 2015-03-27 Created: 2015-03-26 Last updated: 2017-12-04
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1744-7322

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