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Olsen, V. S., Bazioti, C., Baldissera, G., Azarov, A., Prytz, O., Persson, C., . . . Vines, L. (2019). Effects of Substrate and Post-Deposition Annealing on Structural and Optical Properties of (ZnO)(1-x)(GaN)x Films. Physica status solidi. B, Basic research, 256(6), Article ID 1800529.
Open this publication in new window or tab >>Effects of Substrate and Post-Deposition Annealing on Structural and Optical Properties of (ZnO)(1-x)(GaN)x Films
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2019 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 256, no 6, article id 1800529Article in journal (Refereed) Published
Abstract [en]

The structural and optical properties of magnetron sputtered thin films of (ZnO)(1-x)(GaN)(x) deposited on zinc oxide, sapphire, and silicon oxide are studied as a function of strain accumulation and postdeposition anneals at 600-800 degrees C. For the experimental conditions studied, we found that different amounts of tensile strain accumulated in the samples practically does not affect the strong bandbowing effect, that is, optical bandgap, observed in the asdeposited alloys. In its turn, postdeposition annealing results in a reduction of the tensile strain and dislocation density in the films, as measured by both X-ray diffraction and transmission electron microscopy, corroborating an increase in the crystal quality. In addition, the grain size is found to increase with annealing temperature, for example, mean values of 20 nm up to 50 nm were measured for the alloys with x=0.15. Meanwhile, the fullwidth at half maximum of the (0002) X-ray diffraction reflection increases with annealing temperature, but with only a small increase in bandgap energies for the x=0.15 sample. However, this observation was explained combining the experimental data and firstprinciples calculations based on density functional theory, showing that the increase in the amount of Ga-N bonds lowers the total energy of the system. As such, we conclude that the thermal treatments increase the Ga-N ordering, resulting in several contributions or a widening of the diffraction peaks.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2019
Keywords
alloying, annealing, density functional theory (DFT), magnetron sputtering, substrate dependency, thin films, NTON AR, 1991, PHYSICAL REVIEW A, V43, P3161 et Sudhakar, 2013, JOURNAL OF POWER SOURCES, V232, P74 u J., 2016, Phys. Rev. B, V93, P1 ngh D., 2017, MATERIALS RESEARCH EXPRESS, V4
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-255453 (URN)10.1002/pssb.201800529 (DOI)000473612400030 ()2-s2.0-85065034616 (Scopus ID)
Note

QC 20190822

Available from: 2019-08-22 Created: 2019-08-22 Last updated: 2019-08-22Bibliographically approved
Olsen, V. S., Baldissera, G., Zimmermann, C., Granerod, C. S., Bazioti, C., Galeckas, A., . . . Vines, L. (2019). Evidence of defect band mechanism responsible for band gap evolution in (ZnO)(1-x)(GaN)(x) alloys. Physical Review B, 100(16), Article ID 165201.
Open this publication in new window or tab >>Evidence of defect band mechanism responsible for band gap evolution in (ZnO)(1-x)(GaN)(x) alloys
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 16, article id 165201Article in journal (Refereed) Published
Abstract [en]

It is known that (ZnO)(1-x)(GaN)(x) alloys demonstrate remarkable energy band bowing, making the material absorb in the visible range, in spite of the binary components being classical wide band gap semiconductors. However, the origin of this bowing is not settled; two major mechanisms are under debate: Influence of the orbital repulsion and/or formation of a defect band. In the present work, we applied a combination of the absorption and emission measurements on the samples exhibiting an outstanding nanoscale level of (ZnO)(1-x)(GaN)(x) homogeneity as monitored by the high resolution electron microscopy equipped with the energy dispersive x-ray analysis and the electron energy loss spectroscopy; moreover the experimental data were set in the context of the computational analysis of the alloys employing density functional theory and quasiparticle GW approximation. A prominent discrepancy in the band gap values as deduced from the absorption and emission experiments was observed systematically for the alloys with different compositions and interpreted as evidence for the absorption gap shrinking due to the defect band formation. Computational data support the argument, revealing only minor variations in the bulk of the conduction and valence band structures of the alloys, except for a characteristic "tail" in the vicinity of the valence band maximum. As such, we conclude that the energy gap bowing in (ZnO)(1-x)(GaN)(x) alloys is due to the defect band formation, presumably at the top of the valence band maximum.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-262950 (URN)10.1103/PhysRevB.100.165201 (DOI)000489037500006 ()2-s2.0-85073711420 (Scopus ID)
Note

QC 20191203

Available from: 2019-12-03 Created: 2019-12-03 Last updated: 2019-12-12Bibliographically approved
David, D., Alnoor, H., Silva Santana, V. M., Bargiela, P., Nur, O., Willander, M., . . . Silva, A. F. (2019). Optical properties from photoelectron energy-loss spectroscopy of low-temperature aqueous chemically synthesized ZnO nanorods grown on Si. Semiconductor Science and Technology, 34(4), Article ID 045019.
Open this publication in new window or tab >>Optical properties from photoelectron energy-loss spectroscopy of low-temperature aqueous chemically synthesized ZnO nanorods grown on Si
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2019 (English)In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 34, no 4, article id 045019Article in journal (Refereed) Published
Abstract [en]

The optical properties of zinc oxide (ZnO) nanorods (NRs) synthesized by the low-temperature aqueous chemical method on top of silicon (Si) substrate have been investigated by means of photoelectron energy loss spectroscopy (PEELS). The ZnO NRs were obtained by the low temperature aqueous chemical synthesis on top of Si substrate. The measured valence band, the dynamical dielectric functions and optical absorption of the material show a reasonable agreement when the trending and shape of the theoretical calculations are considered. A first-principle calculation based on density functional theory (DFT) was performed using the partially self-consistent GW approximation (scGW(0)) and compared to the experimental results. The application of these two techniques brings a new analysis of the electronic properties of this material. The experimental results regarding the density of states (DOS) obtained for the valence band using x-ray photoelectron spectroscopy (XPS) was found to be consistent with the theoretical calculated value. Due to this consistency, the same wavefunctions was then employed to calculate the dielectric function of the ZnO NRs. The experimentally extracted dielectric function was also consistent with the calculated values.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
Keywords
ZnO nanorods, optical properties, density of states, dielectric function, density functional theory
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-248324 (URN)10.1088/1361-6641/ab0bc4 (DOI)000461940800007 ()
Note

QC 20190409

Available from: 2019-04-09 Created: 2019-04-09 Last updated: 2019-04-09Bibliographically approved
Huang, D., Jiang, J.-W., Guo, J., Zhao, Y.-J., Chen, R. & Persson, C. (2018). General rules of the sub-band gaps in group-IV (Si, Ge, and Sn)-doped I-III-VI2-type chalcopyrite compounds for intermediate band solar cell: A first-principles study. Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, 236, 147-152
Open this publication in new window or tab >>General rules of the sub-band gaps in group-IV (Si, Ge, and Sn)-doped I-III-VI2-type chalcopyrite compounds for intermediate band solar cell: A first-principles study
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2018 (English)In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 236, p. 147-152Article in journal (Refereed) Published
Abstract [en]

In this work, we have investigated Si, Ge and Sn doped at III-site(Ga or Al) in CuGaSe2, CuAlSe2, AgGaSe2, and AgAlSe2 as the candidates for intermediate band solar cell (IBSC), and demonstrated that the absolute energy levels of the intermediate band from a given group IV dopant in various Se-based chalcopyrite hosts do not show remarkable changes. This is resulted from the fact that the intermediate band originates from the same anti-bonding state of IV-s and Se-p states. The intermediate bands sequence of Ge* < Sn* < Si* from the different dopants in the same chalcopyrite host is explained by a simple model based on the atomic orbital energy and bond interaction. Furthermore, Sn-doped CuAlSe2 with the suitable main-gap and sub-gaps has been selected out as a potential candidate for IBSC, and alloying with isovalent cations to adjust to proper sub-band gaps has been demonstrated in Ge-doped (Ag,Cu)AlSe2 and Ag(Ga,Al)Se-2.( )

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Intermediate band solar cell, Chalcopyrite compound, First-principles calculation, Doping
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-244563 (URN)10.1016/j.mseb.2018.11.006 (DOI)000457506500018 ()2-s2.0-85057261236 (Scopus ID)
Note

QC 20190312

Available from: 2019-03-12 Created: 2019-03-12 Last updated: 2019-03-12Bibliographically approved
Thiyam, P., Fiedler, J., Buhmann, S. Y., Persson, C., Brevik, I., Bostrom, M. & Parsons, D. F. (2018). Ice Particles Sink below the Water Surface Due to a Balance of Salt, van der Waals, and Buoyancy Forces. The Journal of Physical Chemistry C, 122(27), 15311-15317
Open this publication in new window or tab >>Ice Particles Sink below the Water Surface Due to a Balance of Salt, van der Waals, and Buoyancy Forces
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 27, p. 15311-15317Article in journal (Refereed) Published
Abstract [en]

According to the classical Archimedes' principle, ice floats in water and has a fraction of its volume above the water surface. However, for very small ice particles, other competing forces such as van der Waals forces due to fluctuating charge distributions and ionic forces due to salt ions and charge on the ice surface also contribute to the force balance. The latter crucially depends on both the pH of the water and the salt concentration. We show that a bulge in the air-water interface due to interaction of surface tension with the rising ice particle becomes significant when the particle radius is greater than 50-100 mu m. The role of these forces in governing the initial stages of ice condensation has never been considered. Here, we show that small ice particles can only form below an exclusion zone, from 2 nm (in high salt concentrations) up to 1 mu m (in pure water at pH 7) thick, under the water surface. This distance is defined by an equilibrium of upward buoyancy forces and repulsive van der Waals forces. Ionic forces due to salt and ice surface charge push this zone further down. Only after growing to a radius larger than 10 pm, will the ice particles eventually float toward the water surface in agreement with the simple intuition based on Archimedes' principle. Our result is the first prediction of observable repulsive van der Waals forces between ice particles and the water surface outside a laboratory setting. We posit that it has consequences on the biology of ice water as we predict an exclusion zone free of ice particles near the water surface which is sufficient to support the presence of bacteria.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-232902 (URN)10.1021/acs.jpcc.8b02351 (DOI)000439003600030 ()2-s2.0-85048664682 (Scopus ID)
Note

QC 20180808

Available from: 2018-08-08 Created: 2018-08-08 Last updated: 2018-08-08Bibliographically approved
Zamulko, S., Berland, K. & Persson, C. (2018). Optical Properties of Cu2ZnSn(SxSe1-x)(4) by First-Principles Calculations. Paper presented at European Congress and Exhibition on Advanced Materials and Processes (Euromat), SEP 17-22, 2017, Thessaloniki, Greece. Physica Status Solidi (a) applications and materials science, 215(17), Article ID 1700945.
Open this publication in new window or tab >>Optical Properties of Cu2ZnSn(SxSe1-x)(4) by First-Principles Calculations
2018 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 215, no 17, article id 1700945Article in journal (Refereed) Published
Abstract [en]

Structural, electronic, and optical properties of Cu2ZnSn(SxSe1-x)(4) semiconductors are studied theoretically for different concentration of S and Se anions. The optical properties are calculated at three levels of theory, in the generalized gradient approximation (GGA), meta-GGA, and with a hybrid functional. The GGA and meta-GGA calculations are corrected with an on-site Coulomb U-d term. Lattice constants, dielectric constants, and band-gaps are found to vary almost linearly with the concentration of S. The authors also show that a dense sampling of the Brillouin zone is required to accurately account for the shape of the dielectric function, which is hard to attain with hybrid functionals. This issue is resolved with a recently developed kp based interpolation scheme, which allows us to compare results of the hybrid functional calculations on an equal footing with the GGA and meta-GGA results. We find that the hybrid functionals provide the overall best agreement with the experimental dielectric function.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2018
Keywords
Cu2ZnSnS4 (CZTS), dielectric function, electronic structure, optical properties, solar cell materials
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-235887 (URN)10.1002/pssa.201700945 (DOI)000444080000002 ()2-s2.0-85052986822 (Scopus ID)
Conference
European Congress and Exhibition on Advanced Materials and Processes (Euromat), SEP 17-22, 2017, Thessaloniki, Greece
Note

QC 20181012

Available from: 2018-10-12 Created: 2018-10-12 Last updated: 2018-11-12Bibliographically approved
Davydova, A., Eriksson, J., Chen, R., Rudisch, K., Persson, C. & Scragg, J. J. (2018). Thio-olivine Mn2SiS4 thin films by reactive magnetron sputtering: Structural and optical properties with insights from first principles calculations. Materials & design, 152, 110-118
Open this publication in new window or tab >>Thio-olivine Mn2SiS4 thin films by reactive magnetron sputtering: Structural and optical properties with insights from first principles calculations
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2018 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 152, p. 110-118Article in journal (Refereed) Published
Abstract [en]

Thio-olivines such as (Fe,Mn)2(Si,Ge)S4 have been proposed as candidate earth-abundant materials for single and multi-junction solar cells. In this work we present the first investigation of Mn2SiS4thin films prepared by reactive magnetron sputtering deposition, using a composition grading approach. Precursor instability in ambient conditions is observed, revealing the oxidation/hydrolysis of Si–S bonds from the as-deposited film as a blocking mechanism for the ternary compound formation. Structural, morphological and optical properties of the annealed Mn2SiS4 films are reported for the first time. Resulting Mn2SiS4 films have orthorhombic Pnma structure and are polycrystalline. Raman active modes at 325 nm excitation are observed at 262, 320, 400 and 464 cm−1. From room temperature photoluminescence at 532 nm excitation the band gap is estimated to be about 1.9 eV, but a high optical absorption coefficient of &gt;104 cm−1 was only obtained at E &gt; 2.8 eV. First principles calculations are used for better understanding of opto-electronic properties. From the calculations, Mn2SiS4 is suggested to have a band gap of about 1.73–1.86 eV depending on the magnetic configuration of Mn and slight indirect nature. The slow absorption onset is interpreted by strong anisotropy due to one of the components of the dielectric function.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Compositional grading, Magnetron sputtering deposition, Mn2SiS4, Thin films, Thio-olivines
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-228708 (URN)10.1016/j.matdes.2018.04.080 (DOI)000433213300011 ()2-s2.0-85046641086 (Scopus ID)
Funder
Swedish Energy AgencySwedish Research CouncilStandUp
Note

QC 20180530

Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2018-06-19Bibliographically approved
Fiedler, J., Thiyam, P., Kurumbail, A., Burger, F. A., Walter, M., Persson, C., . . . Buhmann, S. Y. (2017). Effective Polarizability Models. Journal of Physical Chemistry A, 121(51), 9742-9751
Open this publication in new window or tab >>Effective Polarizability Models
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2017 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 121, no 51, p. 9742-9751Article in journal (Refereed) Published
Abstract [en]

Theories for the effective polarizability of a small particle in a medium are presented using different levels of approximation: we consider the virtual cavity, real cavity, and the hard-sphere models as well as a continuous interpolation of the latter two. We present the respective hard-sphere and-cavity radii as obtained from density-functional simulations as well as the resulting effective polarizabilities at discrete Matsubara frequencies. This enables us to account for macroscopic media in van der Waals interactions between molecules in water and their Casimir-Polder interaction with an interface.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-221368 (URN)10.1021/acs.jpca.7b10159 (DOI)000419263900010 ()29185741 (PubMedID)2-s2.0-85038816623 (Scopus ID)
Note

QC 20180117

Available from: 2018-01-17 Created: 2018-01-17 Last updated: 2018-01-17Bibliographically approved
Zamulko, S., Chen, R. & Persson, C. (2017). Investigation of the structural, optical and electronic properties of Cu2Zn(Sn,Si/Ge)(S/Se)4 alloys for solar cell applications. Physica status solidi. B, Basic research, 254(6), Article ID e201700084.
Open this publication in new window or tab >>Investigation of the structural, optical and electronic properties of Cu2Zn(Sn,Si/Ge)(S/Se)4 alloys for solar cell applications
2017 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 254, no 6, article id e201700084Article in journal (Refereed) Published
Abstract [en]

The crystalline structural, electronic and optical properties of the alloys Cu2ZnSn1−xGexS4, Cu2ZnSn1−xSixS4, Cu2ZnSn1−xGexSe4 and Cu2ZnSn1−xSixSe4 are calculated by first-principles using both the generalized gradient approximation and a hybrid functional approach. We find that the electronic band structures are qualitatively very similar for these alloys. The band-gap energy Eg(x) (for x = 0, 0.125, 0.25, 0.5, 0.75, 0.875 and 1) increases almost linearly with Ge and Si substitution. However, for very Si rich Cu2ZnSn1−xSixS4 alloys (but not for Cu2ZnSn1−xSixSe4) there is an abrupt increase of Eg(x) for x &gt; 0.96. We therefore analyse this effect by calculating the electronic structures for x = 0.93, 0.96 and 1. We find that the Sn-like states form localised density-of-states below the conduction band edge in Cu2ZnSn1−xSixS4, while corresponding states resonate more with the conduction bands in Cu2ZnSn1−xSixSe4. The effect in S-based alloys is a direct consequence of the energetically high conduction band edge for Cu2ZnSiS4 in combination with energetically low Sn-like states. Furthermore, the calculated dielectric constants are relatively similar for all alloy configurations. Overall however, our results suggest that it is possible to use Si and Ge as alloying element in quaternary Cu2ZnSnS4 to improve the photovoltaic properties.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2017
Keywords
alloys, band gap, first-principles calculations, kesterites
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-209892 (URN)10.1002/pssb.201700084 (DOI)000403292300007 ()2-s2.0-85020424311 (Scopus ID)
Funder
Swedish Foundation for Strategic Research
Note

QC 20170627

Available from: 2017-06-27 Created: 2017-06-27 Last updated: 2018-02-28Bibliographically approved
Li, S.-y., Zamulko, S., Persson, C., Ross, N., Larsen, J. K. & Platzer-Bjorkman, C. (2017). Optical properties of Cu2ZnSn(SxSe1-x)(4) solar absorbers: Spectroscopic ellipsometry and ab initio calculations. Applied Physics Letters, 110(2), Article ID 021905.
Open this publication in new window or tab >>Optical properties of Cu2ZnSn(SxSe1-x)(4) solar absorbers: Spectroscopic ellipsometry and ab initio calculations
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2017 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 110, no 2, article id 021905Article in journal (Refereed) Published
Abstract [en]

Dielectric functions of Cu2ZnSn(SxSe1-x)(4) thin film absorbers with varied x were determined by spectroscopic ellipsometry and ab initio calculations. From the combination of experimental and theoretical studies, the fundamental interband transition energy E-0 (similar to 1-1.5 eV) and the next following transition energy E-1 (similar to 2-3 eV) were identified and found to blue-shift with increasing sulfur anion content, while keeping the energy separation E-1 - E-0 almost constant, similar to 1.4 eV from experiments, and 1 eV from theory. In addition, the average dielectric responses were found to decrease with sulfur anion content from both theoretical and experimental results. The Tauc optical bandgap value E-g determined on samples prepared on Mo and soda lime glass substrate showed a positive linear relationship between x and bandgap E-g. The bandgap bowing factor determined from the theoretical data is 0.09 eV.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-202435 (URN)10.1063/1.4973353 (DOI)000392835300025 ()2-s2.0-85009359176 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilSwedish Foundation for Strategic Research
Note

QC 20170306

Available from: 2017-03-06 Created: 2017-03-06 Last updated: 2017-11-29Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-9050-5445

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