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Publications (10 of 144) Show all publications
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
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 >104 cm−1 was only obtained at E > 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 > 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-Björkman, 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 E0 (∼1-1.5 eV) and the next following transition energy E1 (∼2-3 eV) were identified and found to blue-shift with increasing sulfur anion content, while keeping the energy separation E1−E0 almost constant, ∼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 Eg determined on samples prepared on Mo and soda lime glass substrate showed a positive linear relationship between x and bandgap Eg. The bandgap bowing factor determined from the theoretical data is 0.09 eV. 

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
Keywords
Calculations, Copper, Ellipsometry, Energy gap, Optical properties, Semiconducting selenium compounds, Spectroscopic ellipsometry, Substrates, Sulfur, Ab initio calculations, Dielectric functions, Dielectric response, Energy separations, Interband transition energies, Linear relationships, Soda lime glass substrate, Thin-film absorbers, Solar absorbers
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-202228 (URN)10.1063/1.4973353 (DOI)000392835300025 ()2-s2.0-85009359176 (Scopus ID)
Note

Correspondence Address: Li, S.-Y.; Ångström Solar Center, Solid State Electronics, Uppsala UniversitySweden; email: shuyi.at.uu@gmail.com. QC 20170320

Available from: 2017-03-20 Created: 2017-03-20 Last updated: 2017-11-29Bibliographically 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
Baldissera, G. & Persson, C. (2016). Understanding the optical properties of ZnO1-xSx and ZnO1-xSex alloys. Journal of Applied Physics, 119(4), Article ID 045704.
Open this publication in new window or tab >>Understanding the optical properties of ZnO1-xSx and ZnO1-xSex alloys
2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 4, article id 045704Article in journal (Refereed) Published
Abstract [en]

ZnO1-xYx with chalcogen element Y exhibits intriguing optoelectronic properties as the alloying strongly impacts the band-gap energy E-g(x). In this work, we analyze and compare the electronic structures and the dielectric responses of Zn(O,S) and Zn(O, Se) alloys by means of the density functional theory and the partially self-consistent GW approach. We model the crystalline stability from the total energies, and the results indicate that Zn(O, S) is more stable as alloy than Zn(O, Se). We demonstrate also that ion relaxation strongly affects total energies, and that the band-gap bowing depends primarily on local relaxation of the bonds. Moreover, we show that the composition dependent band-gap needs to be analyzed by the band anti-crossing model for small alloying concentration, while the alloying band-bowing model is accurate for strong alloying. We find that the Se-based alloys have a stronger change in the band-gap energy (for instance, Delta E-g(0.50) = E-g(ZnO) -(E)g(x = 0.50) approximate to 2.2 eV) compared with that of the S-based alloy (Delta E-g(0.50) = 1.2 eV), mainly due to a stronger relaxation of the Zn-anion bonds that affects the electronic structure near the band edges. The optical properties of the alloys are discussed in terms of the complex dielectric function epsilon(omega) = epsilon(1)(omega) + i epsilon(2)(omega) and the absorption coefficient alpha(omega). While the large band-gap bowing directly impacts the low-energy absorption spectra, the high-frequency dielectric constant epsilon(infinity) is correlated to the intensity of the dielectric response at energies above 4 eV. Therefore, the dielectric constant is only weakly affected by the non-linear band-gap variation. Despite strong structural relaxation, the high absorption coefficients of the alloys demonstrate that the alloys have well-behaved optoelectronic properties.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-183334 (URN)10.1063/1.4940700 (DOI)000369896300047 ()2-s2.0-84956618463 (Scopus ID)
Note

QC 20160308

Available from: 2016-03-08 Created: 2016-03-07 Last updated: 2017-11-30Bibliographically approved
Malyi, O. I., Bostroem, M., Kulish, V. V., Thiyam, P., Parsons, D. F. & Persson, C. (2016). Volume dependence of the dielectric properties of amorphous SiO2. Physical Chemistry, Chemical Physics - PCCP, 18(10), 7483-7489
Open this publication in new window or tab >>Volume dependence of the dielectric properties of amorphous SiO2
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2016 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 10, p. 7483-7489Article in journal (Refereed) Published
Abstract [en]

Using first principles calculations, the analysis of the dielectric properties of amorphous SiO2 (am-SiO2) was performed. We found that the am-SiO2 properties are volume dependent, and the dependence is mainly induced by the variation of nanoporosity at the atomic scale. In particular, both ionic and electronic contributions to the static dielectric constants are functions of volume with clear trends. Moreover, using the unique parameterization of the dielectric function provided in this work, we predict dielectric functions at imaginary frequencies of different SiO2 polymorphs having similar band gap energies.

National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-184522 (URN)10.1039/c5cp06775h (DOI)000371608600062 ()26902661 (PubMedID)2-s2.0-84960146396 (Scopus ID)
Note

QC 20160406

Available from: 2016-04-06 Created: 2016-04-01 Last updated: 2017-11-30Bibliographically approved
Malyi, O. I., Thiyam, P., Boström, M. & Persson, C. (2015). A first principles study of CO2 adsorption on alpha-SiO2(001) surfaces. Physical Chemistry, Chemical Physics - PCCP, 17(31), 20125-20133
Open this publication in new window or tab >>A first principles study of CO2 adsorption on alpha-SiO2(001) surfaces
2015 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 31, p. 20125-20133Article in journal (Refereed) Published
Abstract [en]

In this work, using first principles calculations, an analysis of CO2 interaction with cleaved and reconstructed alpha-SiO2(001) surfaces was performed. We showed that CO2 could strongly interact with a cleaved surface forming CO3-like configurations. Here, the binding energy per CO2 molecule depends strongly on CO2 surface coverage and can reach -2.35 eV. Despite this, even with CO2 molecules, the cleaved surface has a substantially higher surface energy than that of the reoptimized "dense'' surface. This observation is also consistent with molecular dynamics simulations. Because of this, for thermodynamically stable system, the interaction of CO2 molecules with a alpha-SiO2(001) surface should be treated as the physisorption of CO2 molecules on the reoptimized "dense'' surface with the binding energy varying from -0.26 eV for single CO2 molecule adsorption to -0.32 eV per molecule for monolayer coverage.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-173190 (URN)10.1039/c5cp02279g (DOI)000358729300009 ()26174090 (PubMedID)
Note

QC 20150911

Available from: 2015-09-11 Created: 2015-09-07 Last updated: 2017-12-04Bibliographically approved
Kulish, V. V., Malyi, O. I., Persson, C. & Wu, P. (2015). Adsorption of metal adatoms on single-layer phosphorene. Physical Chemistry, Chemical Physics - PCCP, 17(2), 992-1000
Open this publication in new window or tab >>Adsorption of metal adatoms on single-layer phosphorene
2015 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 2, p. 992-1000Article in journal (Refereed) Published
Abstract [en]

Single- or few-layer phosphorene is a novel two-dimensional direct-bandgap nanomaterial. Based on first-principles calculations, we present a systematic study on the binding energy, geometry, magnetic moment and electronic structure of 20 different adatoms adsorbed on phosphorene. The adatoms cover a wide range of valences, including s and p valence metals, 3d transition metals, noble metals, semiconductors, hydrogen and oxygen. We find that adsorbed adatoms produce a rich diversity of structural, electronic and magnetic properties. Our work demonstrates that phosphorene forms strong bonds with all studied adatoms while still preserving its structural integrity. The adsorption energies of adatoms on phosphorene are more than twice higher than on graphene, while the largest distortions of phosphorene are only similar to 0.1-0.2 angstrom. The charge carrier type in phosphorene can be widely tuned by adatom adsorption. The unique combination of high reactivity with good structural stability is very promising for potential applications of phosphorene.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-160060 (URN)10.1039/c4cp03890h (DOI)000346236000031 ()2-s2.0-84916618801 (Scopus ID)
Note

QC 20150305

Available from: 2015-03-05 Created: 2015-02-13 Last updated: 2017-12-04Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-9050-5445

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