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Stehr, J. E., Balagula, R., Jansson, M., Yukimune, M., Fujiwara, R., Ishikawa, F., . . . Buyanova, I. A. (2020). Effects of growth temperature and thermal annealing on optical quality of GaNAs nanowires emitting in the near-infrared spectral range. Nanotechnology, 31(6), Article ID 065702.
Open this publication in new window or tab >>Effects of growth temperature and thermal annealing on optical quality of GaNAs nanowires emitting in the near-infrared spectral range
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2020 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 31, no 6, article id 065702Article in journal (Refereed) Published
Abstract [en]

We report on optimization of growth conditions of GaAs/GaNAs/GaAs core/shell/shell nanowire (NW) structures emitting at ~1 μm, aiming to increase their light emitting efficiency. A slight change in growth temperature is found to critically affect optical quality of the active GaNAs shell and is shown to result from suppressed formation of non-radiative recombination (NRR) centers under the optimum growth temperature. By employing the optically detected magnetic resonance spectroscopy, we identify gallium vacancies and gallium interstitials as being among the dominant NRR defects. The radiative efficiency of the NWs can be further improved by post-growth annealing at 680 °C, which removes the gallium interstitials.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2020
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-161947 (URN)10.1088/1361-6528/ab51cd (DOI)000502786100001 ()31658456 (PubMedID)
Note

Funding agencies:  Swedish Energy AgencySwedish Energy Agency [P40119-1]; Swedish Research CouncilSwedish Research Council [2015-05532]; Swedish Foundation for International Cooperation in Research and Higher Education (STINT) [JA2014-5698]; Swedish Government Strategic Res

Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2020-01-02Bibliographically approved
Bian, Q., Ma, F., Chen, S., Wei, Q., Su, X., Buyanova, I. A., . . . Inganäs, O. (2020). Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes. Nature Communications, 11(1)
Open this publication in new window or tab >>Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes
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2020 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 11, no 1Article in journal (Refereed) Published
Abstract [en]

Charge separation dynamics after the absorption of a photon is a fundamental process relevant both for photosynthetic reaction centers and artificial solar conversion devices. It has been proposed that quantum coherence plays a role in the formation of charge carriers in organic photovoltaics, but experimental proofs have been lacking. Here we report experimental evidence of coherence in the charge separation process in organic donor/acceptor heterojunctions, in the form of low frequency oscillatory signature in the kinetics of the transient absorption and nonlinear two-dimensional photocurrent spectroscopy. The coherence plays a decisive role in the initial ~200 femtoseconds as we observe distinct experimental signatures of coherent photocurrent generation. This coherent process breaks the energy barrier limitation for charge formation, thus competing with excitation energy transfer. The physics may inspire the design of new photovoltaic materials with high device performance, which explore the quantum effects in the next-generation optoelectronic applications.

Place, publisher, year, edition, pages
Nature Publishing Group, 2020
National Category
Other Physics Topics
Identifiers
urn:nbn:se:liu:diva-164232 (URN)10.1038/s41467-020-14476-w (DOI)32001688 (PubMedID)2-s2.0-85078713267 (Scopus ID)
Available from: 2020-03-10 Created: 2020-03-10 Last updated: 2020-03-16Bibliographically approved
Zhang, B., Huang, Y., Stehr, J. E., Chen, P., Wang, X. J., Lu, W., . . . Buyanova, I. A. (2019). Band structure of wurtzite GaBiAs nanowires. Nano letters (Print), 19, 6454-6460
Open this publication in new window or tab >>Band structure of wurtzite GaBiAs nanowires
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2019 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 19, p. 6454-6460Article in journal (Refereed) Published
Abstract [en]

We report on the first successful growth of wurtzite (WZ) GaBiAs nanowires (NWs) and reveal the effects of Bi incorporation on the electronic band structure by using polarization-resolved optical spectroscopies performed on individual NWs. Experimental evidence of a decrease in the band-gap energy and an upward shift of the topmost three valence subbands upon the incorporation of Bi atoms is provided, whereas the symmetry and ordering of the valence band states remain unchanged, that is, Γ9, Γ7, and Γ7 within the current range of Bi compositions. The extraordinary valence band structure of WZ GaBiAs NWs is explained by anisotropic hybridization and anticrossing between p-like Bi states and the extended valence band states of host WZ GaAs. Moreover, the incorporation of Bi into GaAs is found to significantly reduce the temperature sensitivity of the band-gap energy in WZ GaBiAs NWs. Our work therefore demonstrates that utilizing dilute bismide alloys provides new avenues for band-gap engineering and thus photonic engineering with NWs.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160735 (URN)10.1021/acs.nanolett.9b02679 (DOI)000486361900080 ()2-s2.0-85072133061 (Scopus ID)
Note

Funding agencies: Linkoping University; Swedish Research CouncilSwedish Research Council [2016-05091]; Swedish Energy AgencySwedish Energy Agency [P40119-1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [20

Available from: 2019-10-04 Created: 2019-10-04 Last updated: 2019-11-06Bibliographically approved
Stehr, J. E., Chen, S., Chen, W., Cai, L., Shen, S. & Buyanova, I. A. (2019). Effects of N implantation on defect formation in ZnO nanowires. Paper presented at 7th International Symposium on Transparent Conductive Materials (TCM). Thin Solid Films, 687, Article ID UNSP 137449.
Open this publication in new window or tab >>Effects of N implantation on defect formation in ZnO nanowires
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2019 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 687, article id UNSP 137449Article in journal (Refereed) Published
Abstract [en]

One-dimensional ZnO nanowires are a promising material system for a wide range of optoelectronic and photonic applications. Utilization of ZnO, however, requires high-quality ZnO with reliable n-type and p-type conductivity, with the latter remaining elusive, so far. In this work we report on effects of N doping via ion implantation on defect formation in ZnO nanowires studied by optically detected paramagnetic resonance (ODMR) spectroscopy complemented by photoluminescence spectroscopy. After N implantation, zinc interstitial shallow donors, which are formed as a result of ion implantation, are observed in addition to effective mass type shallow donors. Additionally, ODMR signals related to oxygen vacancies can be observed. Implantation also causes formation of a new nitrogen related defect center, which acts as an acceptor. The present findings are of importance for understanding impacts of different defects and impurities on electronic properties of nanostructured ZnO and achieving p-type conductivity via nitrogen doping.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Zinc oxide; Optically detected magnetic resonance; Photoluminescence; Defects; Nitrogen
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160580 (URN)10.1016/j.tsf.2019.137449 (DOI)000485255100006 ()
Conference
7th International Symposium on Transparent Conductive Materials (TCM)
Note

Funding Agencies|Swedish Energy AgencySwedish Energy Agency [43522-1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]; AForsk Foundation [15-433]

Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2019-10-17Bibliographically approved
Zhang, P., Sadeghimeresht, E., Chen, S., Li, X.-H., Markocsan, N., Joshi, S., . . . Peng, R. L. (2019). Effects of Surface Finish on the Initial Oxidation of HVAF-sprayed NiCoCrAlY Coatings. Surface & Coatings Technology, 364, 43-56
Open this publication in new window or tab >>Effects of Surface Finish on the Initial Oxidation of HVAF-sprayed NiCoCrAlY Coatings
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2019 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Journal of Surface and Coatings Technology, ISSN 0257-8972, Vol. 364, p. 43-56Article in journal (Refereed) Published
Abstract [en]

Oxide scale formed on HVAF-sprayed NiCoCrAlY coatings and the effect of surface treatment were investigated by a multi-approach study combining photo-stimulated luminescence, microstructural observation and mass gain. The initial oxidationbehaviour of as-sprayed, polished and shot-peened coatings at 1000 °C is studied. Both polished and shot-peened coatings exhibited superior performance due to rapid formation of α-Al2O3 fully covering the coating and suppressing the growth of transient alumina, assisted by a high density of α-Al2O3 nuclei on surface treatment induced defects. Moreover, the fast development of a two-layer alumina scale consisting of an inward-grown inner α-Al2O3 layer and an outer layer transformed from outward-grown transient alumina resulted in a higher oxide growth rate of the as-sprayed coating.

Place, publisher, year, edition, pages
Elsevier: Elsevier, 2019
Keywords
Oxidation, Transient ot alpha transformation, Surface treatment, Polishing, Shot-peening, Photo-stimulated liminescence spectroscopy
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-154936 (URN)10.1016/j.surfcoat.2019.02.068 (DOI)000463302800006 ()2-s2.0-85062231529 (Scopus ID)
Note

Funding agencies: Siemens Industrial Turbomachinery AB (Finspang, Sweden) [KME-703]; Swedish Energy Agency through KME consortium [KME-703]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [SFO-Mat-LiU 2009-00

Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2019-11-04Bibliographically approved
Stehr, J. E., Hofmann, D., Schörmann, J., Becker, M., Chen, W. & Buyanova, I. A. (2019). Electron paramagnetic resonance signatures of Co2+ and Cu2+ in β-Ga2O3 [Letter to the editor]. Applied Physics Letters, 115(24), Article ID 242101.
Open this publication in new window or tab >>Electron paramagnetic resonance signatures of Co2+ and Cu2+ in β-Ga2O3
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2019 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 115, no 24, article id 242101Article in journal, Letter (Refereed) Published
Abstract [en]

Gallium oxide (β-Ga2O3) is a wide-bandgap compound semiconductor with a bandgap of ∼4.9 eV that is currently considered promising for a wide range of applications ranging from transparent conducting electrodes to UV optoelectronic devices and power electronics. However, all of these applications require a reliable and precise control of electrical and optical properties of the material, which can be largely affected by impurities, such as transition metals commonly present during the growth. In this work, we employ electron paramagnetic resonance (EPR) spectroscopy to obtain EPR signatures of the 3d-transition metals Co2+ and Cu2+ in β-Ga2O3 bulk crystals and powders that were unknown so far. Furthermore, we show that both Co2+ and Cu2+ preferentially reside on the octahedral gallium lattice site.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-162638 (URN)10.1063/1.5127651 (DOI)000505734100009 ()
Note

Funding agencies:  Linkoping University; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]

Available from: 2019-12-12 Created: 2019-12-12 Last updated: 2020-01-22Bibliographically approved
Stehr, J. E., Chen, W., Pearton, S., Uecker, R., Hofmann, D. & Buyanova, I. A. (2019). Electron paramagnetic resonance signatures of defects and impurities in β-Ga2O3. In: : . Paper presented at 30th International Conference on Defects in Semiconductors, Seattle, Washington, USA, July 21-26, 2019.
Open this publication in new window or tab >>Electron paramagnetic resonance signatures of defects and impurities in β-Ga2O3
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2019 (English)Conference paper, Oral presentation with published abstract (Refereed)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160096 (URN)
Conference
30th International Conference on Defects in Semiconductors, Seattle, Washington, USA, July 21-26, 2019
Available from: 2019-09-05 Created: 2019-09-05 Last updated: 2019-09-12Bibliographically approved
Stehr, J. E., Chen, S., Chen, W., Cai, L., Shen, S. & Buyanova, I. A. (2019). Identification of a N-related acceptor in ZnO nanowires. In: : . Paper presented at 30th International Conference on Defects in Semiconductors, Seattle, Washington, USA, July 21-26, 2019.
Open this publication in new window or tab >>Identification of a N-related acceptor in ZnO nanowires
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2019 (English)Conference paper, Poster (with or without abstract) (Refereed)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160099 (URN)
Conference
30th International Conference on Defects in Semiconductors, Seattle, Washington, USA, July 21-26, 2019
Available from: 2019-09-05 Created: 2019-09-05 Last updated: 2019-09-13Bibliographically approved
Goransson, D. J., Borgstrom, M. T., Huang, Y., Messing, M. E., Hessman, D., Buyanova, I. A., . . . Xu, H. Q. (2019). Measurements of Strain and Bandgap of Coherently Epitaxially Grown Wurtzite InAsP-InP Core-Shell Nanowires. Nano letters (Print), 19(4), 2674-2681
Open this publication in new window or tab >>Measurements of Strain and Bandgap of Coherently Epitaxially Grown Wurtzite InAsP-InP Core-Shell Nanowires
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2019 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 19, no 4, p. 2674-2681Article in journal (Refereed) Published
Abstract [en]

We report on experimental determination of the strain and bandgap of InAsP in epitaxially grown InAsP-InP core-shell nanowires. The core-shell nanowires are grown via metal-organic vapor phase epitaxy. The as-grown nanowires are characterized by transmission electron microscopy, X-ray diffraction, micro-photoluminescence (mu PL) spectroscopy, and micro-Raman (mu-Raman) spectroscopy measurements. We observe that the core-shell nanowires are of wurtzite (WZ) crystal phase and are coherently strained with the core and the shell having the same number of atomic planes in each nanowire. We determine the predominantly uniaxial strains formed in the core-shell nanowires along the nanowire growth axis and demonstrate that the strains can be described using an analytical expression. The bandgap energies in the strained WZ InAsP core materials are extracted from the mu PL measurements of individual core-shell nanowires. The coherently strained core-shell nanowires demonstrated in this work offer the potentials for use in constructing novel optoelectronic devices and for development of piezoelectric photovoltaic devices.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
Strain; core-shell nanowire; wurtzite; InAsP; InP; mu PL; mu-Raman
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-157241 (URN)10.1021/acs.nanolett.9b00644 (DOI)000464769100066 ()30908918 (PubMedID)2-s2.0-85064175484 (Scopus ID)
Note

Funding Agencies|Myfab; Swedish Research Council (VR); Ministry of Science and Technology of China through the National Key Research and Development Program of China [2017YFA0303304, 2016YFA0300601]; National Natural Science Foundation of China [11874071, 91221202, 91421303]

Available from: 2019-06-13 Created: 2019-06-13 Last updated: 2019-06-18Bibliographically approved
Rudko, G., Vorona, I. P., Dzhagan, V. M., Raevskaya, A. E., Stroyuk, O. L., Fediv, V. I., . . . Buyanova, I. A. (2019). Optically detected magnetic resonance study of relaxation/emission processes in the nanoparticle-polymer composite. SPQEO, 22(3), 310-318
Open this publication in new window or tab >>Optically detected magnetic resonance study of relaxation/emission processes in the nanoparticle-polymer composite
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2019 (English)In: SPQEO, ISSN 1605-6582, Vol. 22, no 3, p. 310-318Article in journal (Refereed) Published
Abstract [en]

Two nanocomposites containing CdS nanoparticles in polymeric matrices were studied using the photoluminescence (PL) and optically detected magnetic resonance (ODMR) methods. Due to equal sizes of NPs in the composites (~5 nm) but different matrices – the oxygen-containing polymer PVA (polyvinyl alcohol) and oxygen-free polymer PEI (polyethyleneimine) – differences of nanocomposites properties are predominantly caused by different interfacial conditions. ODMR spectra have revealed five types of centers related to the PL emission – four centers involved in radiative recombination and one center related to non-radiative recombination processes. The oxygen-related interfacial center in CdS/PVA (LK1-center) and sulfur vacancy center in CdS/PEI (Vs-center) were identified.

Place, publisher, year, edition, pages
Kiev, Ukraine: Natsional'na Akademiya Nauk Ukrainy * Instytut Fizyky Napivprovidnykiv, 2019
Keywords
CdS nanoparticles, polymer, composites, photoluminescence, optically detected magnetic resonance
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-160736 (URN)10.15407/spqeo22.03.310 (DOI)000485820300006 ()
Available from: 2019-10-04 Created: 2019-10-04 Last updated: 2020-03-27Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7155-7103

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