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1.	Adolph, David, 1971, et al. (författare) Impact of O2 flow rate on the growth rate of ZnO(0001) and ZnO(000-1) on GaN by plasma-assisted molecular beam epitaxy 2016 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 253:8, s. 1523-1528 Tidskriftsartikel (refereegranskat)abstract We studied the effects of a varying O$ flow rate on the growth of ZnO(0001) and ZnO(000-1) layers on GaN/Al2O3-templates by plasma-assisted molecular beam epitaxy. The O2 flow rate through the O-plasma source was varied between 0.25--4.5 standard cubic centimeters per minute corresponding to a growth chamber pressure between 3.0 x 10^-6 -- 5.0x10^-5 Torr. We found that the change of the O2 flow rate had a profound effect on the ZnO layer growth rate. A maximum growth rate was reached for an O2 flow rate of 1.0--2.0 standard cubic centimeters per minute. The same growth rate dependence on the O2 flow rate was observed for ZnO(0001) layers that were grown on GaN/4H-SiC buffer layers for verification. To assess the amount of active O contributing to the ZnO-growth, the spectral composition of the plasma was investigated with optical emission spectroscopy. The integrated optical emission line intensity reached a maximum for an O2 flow rate between 1.0--2.0 standard cubic centimeters per minute. Essentially all emission lines exhibited a maximum intensity for an O2 flow rate between 1.0--2.0 standard cubic centimeters per minute thus coinciding with the flow rate yielding the maximum growth rate.
2.	Barzegar, Hamid Reza, et al. (författare) Synthesis of graphene nanoribbons inside boron nitride nanotubes 2016 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 253:12, s. 2377-2379 Tidskriftsartikel (refereegranskat)abstract We report on bottom-up synthesis of graphene nanoribbons inside boron nitride nanotubes, using coronene molecules as building blocks. The synthesized ribbons are one or two coronene molecules wide, depending on the diameter of the host nanotube. The encapsulated carbon nanostructures can be eliminated from the inner cavity of the filled boron nitride nanotube via oxidation without any damage to the nanotube structure.
3.	Benavides, Vicente, et al. (författare) Raman and electron microscopy study of C60 collapse/transformation to a nanoclustered graphene-based disordered carbon phase at high pressure/temperature 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:11, s. 2626-2629 Tidskriftsartikel (refereegranskat)abstract Transformation of C60 polymers to a superelastic hard carbon (nanoclustered graphene phase (NGP)) occurring in metal matrix at 5 GPa in a temperature interval of 1000–1100 K was studied by optical, scanning electron microscopy (SEM), and Raman spectroscopy. Raman spectral scan across the sample surface allowed us to identify different stages of the structural transformation. The SEM and Raman spectroscopy data testify for the NGP appearance at the defects concentration sites in the parent fullerite structure. We propose that the buckyballs collapse/formation of the NGP is governed by nucleation and growth (diffusive) mechanism unlike earlier discussed in the literature possibility of the martensitic-type (displacive) character of this transformation.
4.	Bidermane, Ieva, 1984-, et al. (författare) Characterization of Gas Phase of Iron Phthalocyanine with X-ray Photoelectron and Absorption Spectroscopies 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:6, s. 1259-1265 Tidskriftsartikel (refereegranskat)abstract Despite the numerous studies dedicated to phthalocyanine molecules adsorbed on surfaces, in monolayer or thin film, very few works have been focused on the characterization of vapors of these molecules. In this article we present the C 1s, N 1s and Fe 2p photoemission results as well as N K-edge X-ray absorption data of iron phthalocyanine (FePc) in gas phase. Presented comparison of X-ray photoelectron spectroscopy and X-ray absorption spectroscopy spectra of FePc films show a great similarity with the gas phase results, confirming the molecular character of thick films. The Fe2p photoemission spectrum of the gas phase FePc, shown for the first time, can be considered as a fingerprint of the Fe(II) ionic state of the central metal of the iron phthalocyanine. The performed multiplet calculations for describing the Fe 2p XP spectrum indicate 3Eg (a1g2eg32g1) state as the most probable ground state for thick film of iron phthalocyanine.
5.	Bigdeli, Sedigheh, et al. (författare) New description of metastable hcp phase for unaries Fe and Mn: Coupling between first-principles calculations and CALPHAD modeling 2016 Ingår i: Physica Status Solidi B. - : John Wiley & Sons. - 1521-3951 .- 0370-1972. ; :9, s. 1830-1836 Tidskriftsartikel (refereegranskat)abstract The main focus in developing the third generation of CALPHADdatabases is to model thermodynamic properties of materialsby using models which are more physically based andvalid down to 0K. First-principles calculations are helpful tochoose and validate those models. Reliable calculation results,for example, at very low temperatures or on metastable systemsreveal physical facts which might be inaccessible by experiments.Following our earlierwork for modeling thermodynamicproperties of pure elements (i.e., Fe and Mn) in third-generationCALPHAD databases, the (hcp) phase was modeled as ametastable phase in the present work. Although hcp phase isjust observed in these two elements under ultra-high pressure, inthe binary Fe–Mn this phase is metastable at ambient temperaturesand pressures. Therefore, it should be properly modeled inunaries for later optimization of binary systems. Based on densityfunctional theory (DFT) calculations, the magnetic groundstate and the magnetic properties of -Fe, -Mn, and their binarysolution phase were calculated. It was found that -Fe is antiferromagnetic(type II) while -Mn has a paramagnetic groundstate. Accordingly, magnetic contributions to thermodynamicproperties were accurately modeled. Moreover, by means ofthe extrapolation of experimental data for the thermodynamicproperties of binary systems and high-pressure data for unaries,the metastable hcp phases at ambient pressure were modeledfor the third-generation CALPHAD database, consistently withother stable phases in the elements Fe and Mn.
6.	Bigdeli, Sedigheh, et al. (författare) On the third-generation Calphad databases : An updated description of Mn 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:10, s. 2199-2208 Tidskriftsartikel (refereegranskat)abstract Aiming for better extrapolations and predictabilities of thermodynamic properties of materials, new thermodynamic models are implemented in the third-generation Calphad databases. In these models, each term contributing to the Gibbs energy has an explicit physical meaning. Furthermore, descriptions of thermodynamic properties of materials are valid from 0K up to high temperatures far above the melting point. As a starting point for the development of large self-consistent third-generation database, the new models in the present work are applied to the unary manganese system. Taking into account both the calculated first principles results and experimental data, thermodynamic model parameters are evaluated. Thermodynamic properties predicted using this description, agree very well with available data. The calculated properties vary smoothly in the whole temperature range, which is another important improvement compared to the second-generation databases.
7.	Borisov, Vladislav, et al. (författare) Microscopic Modeling of Correlated Systems Under Pressure : Representative Examples 2019 Ingår i: physica status solidi (b). - : Wiley. - 0370-1972 .- 1521-3951. ; 256:9 Tidskriftsartikel (refereegranskat)abstract The complex interplay between different order parameters in correlated systems can be finely tuned by mechanical pressure giving access to a variety of distinct phases and thereby providing new functionalities. This review addresses the challenges in the state-of-the-art theoretical simulations of pressure-induced phenomena on a few representative examples of correlated systems that are currently in the focus of on-going contemporary research. These include organic charge-transfer multiferroics, unconventional iron-based superconductors, frustrated quantum magnets, and candidate systems for Kitaev physics. All these systems show pronounced structural response to moderate pressures or even structural transitions to new phases which can be successfully addressed from first principles. The simulation techniques and general trends in pressure effects are discussed for each material class.
8.	Botella, Pablo, et al. (författare) Single-Walled Carbon Nanotubes Shock-Compressed to 0.5 Mbar 2017 Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 254:11 Tidskriftsartikel (refereegranskat)abstract Single-walled carbon nanotubes (SWCNTs) have been dynamically (shock) compressed to 0.5 Mbar, above the limit of their structural integrity. Two distinct types of material are identified by high-resolution transmission electron microscopy (HRTEM) and multi-wavelength Raman spectroscopy in the sample recovered after shock: multi-layer graphene (MLG) and a two-phase material composed of nano-clustered graphene and amorphous carbon whereas no diamond-like carbon or carbon nano-onions are found. Peak decomposition of the Raman spectra was used to estimate the coherent scatterers (clusters) size in MLG at 36 nm from the D- to G-band intensity ratio dependence on the photon excitation energy. Botella et al. (article no. 1700315) propose the peak fitting model for decomposition of the Raman spectra of highly disordered carbon material containing graphene nano-clusters and stress the importance of accounting for heptagonal- and pentagonal-ring defects in graphene layers for the analysis of such spectra. The cover image shows HRTEM images and the correspondent Raman spectra of the two types of material along with peak decomposition of the two-phase material with the peaks assigned to heptagons (a) and pentagons (b). Particulars of the SWCNTs transformation to other structural forms of carbon at high pressure/temperature are discussed
9.	Botella, Pablo, et al. (författare) Single-Walled Carbon Nanotubes Shock-Compressed to 0.5 Mbar 2017 Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 254:11 Tidskriftsartikel (refereegranskat)abstract Single-walled carbon nanotubes (SWCNTs) have been dynamically (shock) compressed to 0.5 Mbar, above the limit of their structural integrity. Two distinct types of material are identified by high-resolution transmission electron microscopy (HRTEM) and multi-wavelength Raman spectroscopy in the sample recovered after shock: multi-layer graphene (MLG) and a two-phase material composed of nano-clustered graphene and amorphous carbon whereas no diamond-like carbon or carbon nano-onions are found. Peak decomposition of the Raman spectra was used to estimate the coherent scatterers (clusters) size in MLG at 36 nm from the D- to G-band intensity ratio dependence on the photon excitation energy. Botella et al. (article no. 1700315) propose the peak fitting model for decomposition of the Raman spectra of highly disordered carbon material containing graphene nano-clusters and stress the importance of accounting for heptagonal- and pentagonal-ring defects in graphene layers for the analysis of such spectra. The cover image shows HRTEM images and the correspondent Raman spectra of the two types of material along with peak decomposition of the two-phase material with the peaks assigned to heptagons (a) and pentagons (b). Particulars of the SWCNTs transformation to other structural forms of carbon at high pressure/temperature are discussed
10.	Chen, Rongzhen, et al. (författare) Exploring the electronic and optical properties of Cu2Sn1-xGexS3 and Cu2Sn1-xSixS3 (x = 0, 0.5, and 1) 2017 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. Tidskriftsartikel (refereegranskat)abstract To accelerate environmental friendly thin-film photovoltaic technologies, earth-abundant, non-toxic, and low-cost materials are demanded. We study the compounds of Cu2Sn1−xGexS3 and Cu2Sn1−xSixS3 (x = 0, 0.5, and 1) employing first-principles method within the density functional theory. The compounds have comparable band dispersions. The band-gap energies Eg can be tailored by cation alloying the Sn atoms with Ge or Si. The gap energies of Cu2Sn1−xGexS3 and Cu2Sn1−xSixS3, with x = 0, 0.5, and 1, vary almost linearly from 0.83 to 1.43 eV and 2.60 eV, respectively. However, the gap energy of Cu2SiS3 does not follow the linear relation for x > 0.8. The effective electron masses at the Γ-point of the lowest conduction band are almost isotropic for all materials, which are between 0.15m0 and 0.25m0. On the other hand, the effective hole masses of the topmost valence band show very strong anisotropy for all compounds. In the (010) direction, the hole masses are estimated to be between 1.01m0 and 1.85m0, while between 0.11m0 and 0.41m0 in the (001) direction. Calculations reveal that all compounds have high absorption coefficients that are comparable with that of Cu2ZnSnS4. The absorptions in the energy region from Eg + 0.5 eV to Eg + 1.0 eV are even higher for Ge- and Si-alloying of Cu2SnS3, compared with Cu2ZnSnS4. The high-frequency dielectric constants of the compounds are between 6.8 and 8.9. Cu2Sn1−xGexS3 and Cu2Sn1−xSixS3 can be considered as potential candidates for absorber materials in thin-film solar cells.
11.	Chen, Xiren, et al. (författare) Bi-Induced Electron Concentration Enhancement Being Responsible for Photoluminescence Blueshift and Broadening in InAs Films 2019 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 256:5 Tidskriftsartikel (refereegranskat)abstract Photoluminescence (PL) study is conducted on InAs films molecular beam epitaxially grown on GaAs substrates with different Bi flux levels. A PL peak blueshift accompanied by linewidth broadening is found with the increase of Bi/As flux ratio, in contrast to the common Bi isoelectronic incorporation or surfactant effect. It is, with detailed lineshape analysis and the evidence of PL peak splitting in a magnetic filed, attributed to the electron concentration enhancement induced by Bi flux. The electron concentration in InAs film is evaluated, which is about 5-fold enhanced as Bi/As flux ratio rises up from 0 to 1x10(-3). The temperature dependence of the PL spectrum indicates that the carrier redistribution augments while the carrier-phonon Frohlich scattering weakens in InAs films with high Bi/As flux ratios. These findings reveal a novel Bi effect of electron concentration enhancement, and contribute to the basic knowledge of Bi in III-V semiconductors.
12.	Chen, Xingxing, et al. (författare) Control of fluorescence enhancement and directionality upon excitations in a thin-film system 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:10, s. 2222-2229 Tidskriftsartikel (refereegranskat)abstract Nanostructures with various configurations have been extensively used to engineer the emission properties of embedded fluorophores, but lack the flexibility to dynamically control fluorescence. Here we report a thin-film cavity system, comprising a quarter wavelength thick dye-doped dielectric coating on a reflecting surface, in which the fluorescence enhancement and directionality can be significantly modified by altering the illumination angle. The configuration of the cavity yields absorption properties that are highly dependent on illumination angles, due to the coupling between molecular absorption and Fabry-Perot resonances. Therefore the fluorescence intensity relating to the angle-dependent absorbing efficiency varies with illumination angles. In addition, as a result of synergy between intrinsic absorption of the reflecting surface, Fabry-Perot and surface-plasmon-polariton resonances and illumination-angle dependent excitation efficiencies for differently located molecules, the global emission intensity, including emission from dyes at all locations, can be directionally redistributed by altering the illumination angle.
13.	Doyle, Catherine M., et al. (författare) Surface Mediated Synthesis of 2D Covalent Organic Networks : 1,3,5-Tris(4-bromophenyl)benzene on Au(111) 2019 Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 256:2 Tidskriftsartikel (refereegranskat)abstract Covalent organic networks derived from surface-mediated self-assembly of 1,3,5-tris(4-bromophenyl)benzene into two-dimensional networks on Au(111) have been studied by scanning tunneling microscopy (STM) and by X-ray spectroscopic methods. High resolution soft X-ray photoemission spectroscopy (SXPS) using synchrotron radiation have been used to study the formation of the 1,3,5-tris(4-bromophenyl)benzene-derived 2D networks by observing temperature-dependent C 1s and Br 3d core level XPS spectra. X-ray absorption (XA) measurements of the formation of these 2D networks have been obtained at the C K-edge where their temperature and angular dependence are examined. The results of these XPS and XA spectroscopic measurements are compared to detailed ab initio electronic structure calculations of 1,3,5-tris(4-bromophenyl)benzene molecules to aid the interpretation of the features of these spectra.
14.	Duc Tran, Thien, et al. (författare) Electronic properties of defects in high-fluence electron irradiated bulk GaN 2016 Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 253:3, s. 521-526 Tidskriftsartikel (refereegranskat)abstract Using deep level transient spectroscopy, deep levels and capture cross sections of defects introduced by high-fluence electron irradiation of thick halide vapour phase epitaxy grown GaN has been studied. After irradiation with 2 MeV electrons to a high-fluence of 5×1016 cm-2, four deep trap levels, labelled T1 (EC – 0.13 eV), T2 (EC – 0.18 eV), T3 (EC – 0.26 eV) T4 and a broad band of peaks consisting of at least two levels could be observed. These defects, except T1 and T3, were annealed out after annealing at 650 K for 2 hours. The capture cross section is found to be temperature independent for T2 and T3, while T1 shows an decresing capture cross section with increasing temperature, suggesting that electron capturing to this deep level is governed by a cascade capturing process.
15.	Dunn, Gabriel, et al. (författare) Selective Insulation of Carbon nanotubes 2017 Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 254:11 Tidskriftsartikel (refereegranskat)abstract We demonstrate a method for the selective encapsulation of carbonnanotubes in thin parylene films using iron as a sacrificial lift-off layer. Theiron serves as an inhibitor of parylene deposition and prevents the parylenemolecules from linking, thus facilitating selective area coating after lift-off.
16.	Fleischer, K., et al. (författare) Formation of plasmonic nanoparticle arrays -rules and recipes for an ordered growth 2016 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 253:2, s. 198-205 Tidskriftsartikel (refereegranskat)abstract We review a self-assembled growth method for plasmonic nanoparticle arrays, based on glancing angle deposition. We produced ordered Ag, Au, and Cu nanoparticle arrays over large areas on different stepped oxide templates. Precise control over the final geometry can be difficult and we provide recipes to obtain macroscopically ordered structures. We discuss the influence of the adsorbate diffusion length and facet termination on the shape and size distributions of metallic nanoparticle arrays and show that an increased ad-atom mobility leads to more regular arrays of spherical nanoparticles. We also show how in-situ Reflectance Anisotropy Spectroscopy (RAS) can be used to extract indirect information on the nucleation and ripening the nanoparticles, as well as measure the plasmonic resonance. Schematics of the RAS setup used to in-situ monitor the growth of plasmonic nanoparticle arrays on stepped oxide templates.
17.	Jago, Roland, 1990, et al. (författare) Recombination channels in optically excited graphene 2015 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 252:11, s. 2456-2460 Tidskriftsartikel (refereegranskat)abstract We present a theoretical study on the efficiency of non-radiative recombination channels in optically excited graphene on a substrate. We find that depending on the strength of the excitation pulse and the dielectric constant of the applied substrate, either Auger or phonon-induced recombination prevails. The favorable conditions for Auger recombination are (i) strong excitation regime providing a large number of scattering partners and (ii) low-dielectric substrates, which only weakly screen the Coulomb interaction. The gained insights are important for achieving a population inversion in graphene that is temporally limited by the presented recombination channels.
18.	Jayathilaka, K. M. D. C., et al. (författare) Annealing effects of the untreated and sulfur-treated electrodeposited n-type and p-type cuprous oxide thin films 2016 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 253:4, s. 765-769 Tidskriftsartikel (refereegranskat)abstract The n-type and p-type cuprous oxide thin films were electrodeposited potentiostatically in acetate and lactate baths, respectively. Sulfur treatment of n-type and p-type cuprous oxide surfaces were achieved using gaseous (NH4)(2)S. Sulfur-treated Cu2O films were annealed in air at 100, 150, 200, 250, 350, and 450 degrees C for unique times to obtain the best photocurrent. Unannealed and annealed samples of sulfur-treated and untreated cuprous oxide were then investigated using high-energy X-ray diffraction (HEXRD). The HEXRD measurements and the pair distribution function (PDF) analysis revealed that the sulfur treatment leads to the formation of crystalline CuS on Cu2O film surfaces. The present study also shows that the sulfur treatment causes minor structural changes in Cu2O samples due to the formation of CuS. It was observed that the sulfur-treated cuprous oxide samples retarded the formation of CuO at higher temperatures showing good thermal stability and enhancement of the photoactivity of the n-type and p-type cuprous oxides.
19.	Jayathilaka, K. M. D. C., et al. (författare) Effect of chlorine doping on electrodeposited cuprous oxide thin films on Ti substrates 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:6, s. 1300-1305 Tidskriftsartikel (refereegranskat)abstract Highly photoactive Cl-doped Cu2O films were electrodeposited potentiostatically on Ti substrates. Optimum deposition potential was determined by Linear-Sweep Voltammetry measurements. The influence of chlorine doping on grain size, crystallite shape and orientation was examined using scanning electron microscopy and X-ray diffraction. X-ray photoelectron spectroscopy confirmed the presence of Cl due to doping. Mott-Schottky electrochemical impedance analysis showed the p-type conductivity for undoped Cu2O films and n-type conductivity for Cl-doped Cu2O films. Analysis also showed that the carrier concentration of Cu2O thin films varied with Cl concentration of the deposition bath. Spectral responses of the resulting films were investigated in a photo-electrochemical cell to optimize the CuCl2 concentration of the deposition bath to obtain highly photoactive films. Photocurrent measurements further confirmed that the conductivity of these Cl-doped Cu2O films was n-type while undoped films showed p-type conductivity at a bath pH 9.3. The resistivity of Cu2O films decreased with the Cl concentration and the resistivity obtained for the Cl-doped Cu2O films with the highest photoactivity was about 10(2)cm at 30 degrees C. The low resistance and high photoactivity of Cl-doped cuprous oxide thin films make them more suitable for solar cell and other applications.
20.	Kamata, N., et al. (författare) Spectral change of intermediate band luminescence in GaP:N due to below-gap excitation: Discrimination from thermal activation 2017 Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 254:2 Tidskriftsartikel (refereegranskat)abstract As an intermediate band (IB) originating from discrete nitrogen (N) levels is formed in GaP:N with increasing N concentration, GaP1-xNx alloy is considered to be a promising candidate for IB-type solar cells. We studied the IB luminescence of a GaP1-xNx with 0.56% N and detected carrier recombination (CR) levels by superposing a below-gap excitation (BGE) light of 1.17eV. We resolved a high-energy component of 2.15eV in the IB luminescence, I-high, from total luminescence intensity I-all. With increasing the BGE density at fixed temperature of 5K, the amount of decrease in I-high was distinctly smaller than that of simple temperature rise without the BGE at the same I-all value. We conclude that the observed intensity change of the IB luminescence due to the BGE comes not from thermal activation, but from optical excitation among the IB, conduction band, and CR levels in GaP1-xNx. It is of primal importance to understand CR levels toward determining their origins and eliminating them for realization of efficient IB-type solar cells.
21.	Karpus, V., et al. (författare) Interband optical transitions of Zn 2016 Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 253:3, s. 419-428 Tidskriftsartikel (refereegranskat)abstract Experimental results of an optical study of single-crystal zinc are presented. Components of the Zn dielectric function tensor were measured by spectroscopic ellipsometry in the 0.1-5 eV spectral range. In the NIR-VIS range, the dielectric function spectra show two clearly resolved, polarization-dependent optical features located at about 1 and 1.7 eV. The optical features were analyzed in a framework of parallel-band optical transitions. The performed theoretical calculations of the optical conductivity spectra well reproduce the experimental data with respect to positions, intensities, and polarization dependencies of the observed interband absorption peaks. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
22.	Landström, Anton, et al. (författare) Thermal Defect Modulation and Functional Performance : A Case Study on ZnO–rGO Nanocomposites 2019 Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 256:12 Tidskriftsartikel (refereegranskat)abstract Herein, a reduced graphene oxide–zinc oxide (rGO–ZnO) hybrid nanocomposite (1 wt% rGO) is synthesized and heat treated at different temperatures, aimed at modulating the intrinsic bulk/surface defects naturally present in nano‐ZnO. The correlation of both the dispersion of rGO within the metal oxide scaffold and the defects present on the semiconductor crystalline lattice with the photocatalytic performance toward the degradation of a molecular dye in water is investigated and discussed. It is shown that several processes compete to determine the catalytic skill of the nanocomposite, which can be enhanced by a simple thermal treatment at moderate temperatures.
23.	Li, Mingkai, et al. (författare) Magnetic order and phase diagram of magnetic alloy system : MgxNi1-xO alloy 2017 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 254:9 Tidskriftsartikel (refereegranskat)abstract The antiferromagnetic phase diagram of MgxNi1-xO alloy was reexamined theoretically by multicomponent cluster expansion method. It predicts antiferromagnetic state in the alloy with high Mg content, instead of a mixture of antiferromagnetic and paramagnetic states, which was deduced previously from neutron diffraction results. The theoretically found intermediate antiferromagnetic ground states at Mg contents of x(Mg) = 0.25 and 0.75 exhibit very low neutron diffraction intensities, which leads to confusion with paramagnetic state. Our approach here reduced remarkably the computation time in searching the intermediate ground states as well as calculating the magnetic phase diagram.
24.	Li, Zhou, et al. (författare) Thermodynamic evaluation of pure Co for the third generation of thermodynamic databases 2016 Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. Tidskriftsartikel (refereegranskat)abstract An updated thermodynamic description of pure Co was obtained by applying new models for the third generation of Calphad databases. In these models, different contributions to the heat capacity, especially the vibrational part, were treated separately, each with a clear physical meaning. More importantly, the phase stabilities of the various allotropes are now physically well defined. Thus, the derived thermodynamic properties vary more reasonably and smoothly from 0K and up. Calculated thermodynamic properties were compared with experimental data and good agreement was obtained.
25.	Lilja, Louise, et al. (författare) In-grown stacking-faults in 4H-SiC epilayers grown on 2 degrees off-cut substrates 2015 Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 252:6, s. 1319-1324 Tidskriftsartikel (refereegranskat)abstract 4H-SiC epilayers were grown on 2 degrees off-cut substrates using standard silane/propane chemistry, with the aim of characterizing in-grown stacking faults. The stacking faults were analyzed with low temperature photoluminescence spectroscopy, room temperature photoluminescence mappings, room temperature cathodoluminescence and synchrotron white beam X-ray topography. At least three different types of in-grown stacking faults were observed, including double Shockley stacking faults, triple Shockley stacking faults and bar-shaped stacking faults. Those stacking faults are all previously found in 4 degrees and 8 degrees off-cut epilayers; however, the geometrical size is larger in epilayers grown on 2 degrees off-cut substrates due to lower off-cut angle. The stacking faults were formed close to the epilayer/substrate interface during the epitaxial growth. (C) 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim
26.	Malic, Ermin, 1980, et al. (författare) Review on carrier multiplication in graphene 2016 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 253:12, s. 2303-2310 Tidskriftsartikel (refereegranskat)abstract The remarkable gapless and linear band structure of graphene opens up new carrier relaxation channels bridging the valence and the conduction band. These Auger scattering processes change the number of charge carriers and can give rise to a significant multiplication of optically excited carriers in graphene. This is an ultrafast many-particle phenomenon that is of great interest both for fundamental many-particle physics as well as technological applications. Here, we review the research on carrier multiplication in graphene and Landau-quantized graphene including theoretical modeling and experimental demonstration. Illustration of the electronic band structure of graphene including Auger scattering channels that can lead to a carrier multiplication (CM). Figure adapted from Ref. [2].
27.	Moskalenko, S. A., et al. (författare) Landau quantization, Rashba spin-orbit coupling and Zeeman splitting of two-dimensional heavy-hole gases 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:4, s. 730-742 Tidskriftsartikel (refereegranskat)abstract The origin of the g-factor of two-dimensional (2D) electrons and holes moving in the periodic crystal lattice potential with perpendicular magnetic and electric fields is discussed. The Pauli equation describing the Landau quantization accompanied by the Rashba spin-orbit coupling (RSOC) and Zeeman splitting (ZS) for 2D heavy holes with nonparabolic dispersion law is solved exactly. The solutions have the form of pairs of the Landau quantization levels due to the spinor-type wave functions. The energy levels depend on the amplitudes of the magnetic and electric fields, on the g-factor g(h), and on the parameter of nonparabolicity C. The dependences of two energy levels in any pair on the Zeeman parameter Z(h) = g(h)m(h) = 4m(0), where m(h) is the hole effective mass, are nonmonotonous and without intersections. The smallest distance between them at C = 0 takes place at the value Z(h) = n/2, where n is the order of the chirality terms determined by the RSOC and is the same for any quantum number of the Landau quantization.
28.	Nilsson, Daniel, et al. (författare) On the behavior of the silicon donor in conductive AlxGa1-xN (0.63≤x≤1) layers 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 252:6, s. 1306-1310 Tidskriftsartikel (refereegranskat)abstract We have studied the silicon donor behavior in intentionally silicon doped AlxGa1-xN (0.63≤x≤1) grown by hot-wall metal-organic chemical vapor deposition. Efficient silicon doping was obtained for lower Al contents whereas the conductivity drastically reduces for AlGaN layers with Al content in the range x~0.84-1. Degradation of the structural quality and compensation by residual O and C impurities were ruled out as possible explanations for the reduced conductivity. By combining frequency dependent capacitance-voltage and electron paramagnetic resonance measurements we show that the Si donors are electrically active and that the reduced conductivity can be explained by the increased activation energy caused by the sharp deepening of the Si DX– state..
29.	Nilsson, Johan O., et al. (författare) Modeling Kinetics of Water Adsorption on the Rutile TiO2 (110) Surface: Influence of Exchange-Correlation Functional 2018 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 255:3 Tidskriftsartikel (refereegranskat)abstract The accuracy of the theoretical description of materials properties in the framework of density functional theory (DFT) inherently depends on the exchange-correlation (XC) functional used in the calculations. Here we investigate the influence of the choice of a XC functional (PBE, RPBE, PW91, and PBE0) on the kinetics of the adsorption, diffusion and dissociation of water on the rutile TiO2(110) surface using a combined Kinetic Monte Carlo (KMC) - DFT approach, where the KMC simulations are based on the barriers for the aforementioned processes calculated with DFT. We also test how the adsorption energy of intact and dissociated water molecules changes when dispersion interactions are included into the calculations. We consider the beginning of the water layer formation varying coverage up to 0.2 monolayer (ML) at temperatures up to 180K. We demonstrate that the dynamics of the simulated water-titania system is extremely sensitive to the choice of the XC functional.
30.	Olsen, Vegard S., et al. (författare) Effects of Substrate and Post-Deposition Annealing on Structural and Optical Properties of (ZnO)(1-x)(GaN)x Films 2019 Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 256:6 Tidskriftsartikel (refereegranskat)abstract 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.
31.	Pozina, Galia, et al. (författare) Nonlinear behavior of the emission in the periodic structure of InAs monolayers embedded in a GaAs matrix 2017 Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 254:4 Tidskriftsartikel (refereegranskat)abstract We report time-resolved photoluminescence (TRPL) measurements performed at different temperatures for the Bragg structure containing 60 InAs monolayer-based quantum wells (QWs) periodically arranged in a GaAs matrix. TRPL data reveal an appearance of the additional superradiant (SR) mode originated from coherent collective interaction of QWs. The SR mode is not manifested in the case if a small number of QWs is excited, then only an exciton emission related to the InAs QWs dominates the PL spectrum. The SR mode demonstrates a superlinear dependence of the intensity and radiative decay rate on the excitation power and its intensity increases at elevated temperatures compared to the excitonic emission. The photoluminescence delay time is much shorter for the SR mode indicating that the relaxation of hot excitons can occur via stimulated scattering processes. The specific behavior of the SR emission can have a strong potential for different applications such as optical logic devices, superluminescent diodes, optical switches, and low-threshold lasers. Time-resolved photoluminescence image at low temperature for the Bragg structure consisting of InAs monolayer-based quantum wells (inset).
32.	Pozina, Galia, et al. (författare) Optical Cavity Based on GaN Planar Nanowires Grown by Selective Area Metal-Organic Vapor Phase Epitaxy 2019 Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 256:6 Tidskriftsartikel (refereegranskat)abstract GaN planar nanowires (NWs) are fabricated by selective area metal-organic vapor phase epitaxy using focused ion beam etching of trench pattern in the Si3N4 mask. Two crystallographic orientations of NWs along [1120] and [1010] directions are investigated. The coherent growth is confirmed for both directions; however, the best morphology, crystalline and optical properties are found in the GaN planar NWs fabricated along the [1010] axis. Cathodoluminescence (CL) at 5K reveals a presence of Fabry-Perot modes in the region of 1.8-2.5 eV for the NWs fabricated in the [1010] direction. The position and intensity of the Fabry-Perot peaks vary depending on measured point within the NW, which is explained by the model based on the Purcell coefficient calculations. It is shown that small fluctuations in the NW thickness cause a noticeable shift of the Fabry-Perot modes energies, while the enhancement or reduction of the emission intensity for the Fabry-Perot peaks depend on the position of the emitter inside the planar NW.
33.	Rudisch, Katharina, et al. (författare) Structural and Electronic Properties of Cu2MnSnS4 from Experiment and First-Principles Calculations 2019 Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 256:7 Tidskriftsartikel (refereegranskat)abstract Cu2MnSnS4 shares several promising properties with the widely investigated Cu2ZnSnS4 for photovoltaic applications such as containing only earth abundant and non-toxic elements, and suitable absorption characteristics for absorber materials. Thin film Cu2MnSnS4 samples with various cation compositions are co-sputtered reactively followed by a high temperature anneal. Formation of Cu2MnSnS4 and co-existence of several secondary phases is verified by XRD and Raman. Our investigation of the crystal structure based on first-principles DFT confirms that stannite crystal structure is preferred over kesterite, although, further verification considering cation disorder is needed. The direct band gap of Cu2MnSnS4 is calculated as 1.52 eV (1.62 eV) for stannite (kesterite), which coincides with the range of the measured band gaps from spectrophotometry of 1.42-1.59 eV. After further annealing treatments below 240 degrees C, the absorption shows reversible changes: the band gap blue-shifts and the Urbach tail energy is reduced. It is concluded that, just like Cu2ZnSnS4, disorder also occurs in Cu2MnSnS4. The implications of our findings are discussed and related to the current understanding of cation disorder in Cu2ZnSnS4 and related compounds. Furthermore, for the first time first-principles DFT investigations are presented for the thiospinel Cu2MnSn3S8 which is observed experimentally as a secondary phase in Sn-rich Cu2MnSnS4 thin films.
34.	Schmitz, Detlef, et al. (författare) Soft X-Ray Magnetic Circular Dichroism of Vanadium in the Metal-Insulator Two-Phase Region of Paramagnetic V2O3 Doped with 1.1% Chromium 2019 Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. Tidskriftsartikel (refereegranskat)abstract V2O3 doped with 1.1% Cr is investigated at its isostructural correlation-driven metal-insulator transition near room temperature in its paramagnetic state with X-ray magnetic circular dichroism (XMCD) spectroscopy in external magnetic fields. A relative XMCD amplitude of about 2 permille is observed at the L-2,L-3 absorption edges of vanadium as expected for magnetic moment per mass values of the order of 1 J T-1 kg(-1) from magnetometry and the literature. Across the metal-insulator transition, the vanadium XMCD spectral shape significantly changes. According to atomic multiplet simulations, these changes are due to a changing orbital occupation indicating a changing phase composition. According to estimates used in this study, the dipole moment of the spin density distribution 7⟨Tz⟩ in the bulk increases such that the effective vanadium spin moment increases by a few percent with temperature in the two-phase region. Thereby, it partially compensates for the decrease in the relative XMCD amplitude due to a decreasing alignment of the paramagnetic moments. After a few minor temperature cycles, the sample is in a two-phase state in which the XMCD and X-ray linear dichroism spectra hardly depend on the temperature, and the specific electrical resistance is intermediate, showing only a weak sign of the metal-insulator transition.
35.	Scragg, Jonathan, 1983-, et al. (författare) Cu–Zn disorder and band gap ﬂuctuations in Cu2ZnSn(S,Se)4 : Theoretical and experimental investigations 2016 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 253:2, s. 247-254 Tidskriftsartikel (refereegranskat)abstract Cu2ZnSn(S,Se)4 (CZTS(e)) solar cells suffer from low-open-circuit voltages that have been blamed on the existence of band gap fluctuations, with different possible origins. In this paper, we show from both theoretical and experimental standpoints that disorder of Cu and Zn atoms is in all probability the primary cause of these fluctuations. First, quantification of Cu–Zn disorder in CZTS thin films is presented. The results indicate that disorder is prevalent in the majority of practical samples used for solar cells. Then, ab initio calculations for different arrangements and densities of disorder-induced [CuZn + ZnCu] defect pairs are presented and it is shown that spatial variations in band gap of the order of 200 meV can easily be caused by Cu–Zn disorder, which would cause large voltage losses in solar cells. Experiments using Raman spectroscopy and room temperature photoluminescence combined with in situ heat-treatments show that a shift in the energy of the dominant band-to-band recombination pathway correlates perfectly to the order-disorder transition, which clearly implicates Cu–Zn disorder as the cause of band gap fluctuations in CZTS. Our results suggest that elimination or passivation of Cu–Zn disorder could be very important for future improvements in the efficiency of CZTS(e)-based solar cells.
36.	Shubina, T. V., et al. (författare) III-nitride microcrystal cavities with quasi whispering gallery modes grown by molecular beam epitaxy 2016 Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 253:5, s. 845-852 Tidskriftsartikel (refereegranskat)abstract This paper analyzes current trends in fabrication of III-nitride microresonators exploiting whispering gallery modes. Novel cup-cavities are proposed and their fabrication from GaN and InN by molecular beam epitaxy on patterned substrates is described. These cup-cavities can concentrate the mode energy in a subwavelength volume. Their mode energies are stable up to room temperature, being identical in large microcrystals. In these cavities, mode switching can be realized by means of refractive index variation. Cup-cavity modes, being inferior to plasmonic resonances in the respect of integral emission enhancement, have advantages for spectrally selective amplification of quantum transitions in site-controlled nano-emitters. (C) 2016 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim
37.	Shubina, T. V., et al. (författare) Recombination dynamics in arrays of II-VI epitaxial quantum dots with Forster resonance energy transfer 2017 Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 254:4 Tidskriftsartikel (refereegranskat)abstract We report on time-resolved photoluminescence (TR PL) studies of Forster resonance energy transfer (FRET) between epitaxial CdSe/ZnSe quantum dots (QDs). To prove the existence of FRET, we use two sheets of QD arrays, formed from CdSe insertions of different nominal thicknesses, which are separated by a ZnSe barrier of a variable width. The FRET mechanism manifests itself as acceleration of the PL decay of the energy-donating QD sheet when the barrier width is decreased. The Forster radius of about 10.5nm is determined by fitting TR PL data. Besides, our findings exhibit the inhomogeneous distribution of QD sizes within the QD arrays and the influence of FRET efficiency on recombination dynamics of forbidden exciton states. TR PL images showing the acceleration of PL decay of the energy-donating QD array with decreasing the barrier width.
38.	Slomski, Michael, et al. (författare) Thermal conductivity of bulk GaN grown by HVPE: Effect of Si doping 2017 Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 254:8 Tidskriftsartikel (refereegranskat)abstract The thermal conductivity of bulk GaN grown by Hydride Phase Vapor Epitaxy with intentional Si doping was measured using the 3 method. The effect of Si concentration ranging from 1.6x10(16) to 7x10(18)cm(-3) on the thermal conductivity was studied over the temperature range of 295-470K. The room temperature thermal conductivity was found to decrease with increasing Si doping from 245 to 210W/m.K. Also, for each Si doped sample the thermal conductivity decreases with increasing temperature. The experimental data were analysed by a modified Callaway model and the contribution of different resistive phonon scattering process was examined. It was found that in n-type GaN the phonon-free-electron scattering became an important resistive process that leads to a reduction of the thermal conductivity at high temperatures. At the highest free electron concentrations, electronic thermal conduction was found to play a role in addition to lattice thermal conduction and compete with the effects of phonon-free-electron scattering. (C) 2017 WILEY-VCH Verlag GmbH amp; Co. KGaA, Weinheim
39.	Szabó, T., et al. (författare) Generating photocurrent by nanocomposites based on photosynthetic reaction centre protein 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 252:11, s. 2614-2619 Tidskriftsartikel (refereegranskat)abstract An optoelectronic device, which converts light energy to electric potential, was designed and fabricated by using photosynthetic reaction centre (RC) proteins of purple bacterium Rhodobacter sphaeroides R-26, based on the structure and function of the dye sensitised organic solar cells. First, an electrochemical cell with three electrodes was created especially for this measurement. ITO covered by the MWCNT-RC containing sample served as the working electrode and the counter and the reference electrodes were platinum and Ag\AgCl, respectively. Water soluble ubiquinone-0 and ferrocene, in some experiments were used as mediators. In another experiment, the presence of the RCs in the active layer under dried conditions assured tuneable wavelength sensitivity, in general in the visible, but specially, in the near infrared (700-1000 nm) spectral range. The lifetime of the primary charge separation is in the ps time scale and that of the charge stabilisation can be modulated (at least theoretically) between ps and seconds. A successful combination of RC protein with a light energy converter device in spectroelectrochemical cell (wet conditions in buffered electrolyte) and in dried multilayer structure will be presented here.
40.	Talyzin, Alexandr V., et al. (författare) High-temperature transformations of coronene-based graphene nanoribbons encapsulated in SWNTs 2015 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 252:11, s. 2491-2495 Tidskriftsartikel (refereegranskat)abstract Coronene-based graphene nanoribbons encapsulated inside single-walled carbon nanotubes (SWNTs) were prepared 440 degrees C under Ar and annealed at temperatures up to 825 degrees C. The structural modifications of coronene/SWNT samples were studied using Raman spectroscopy and transmission electron microscopy. Coronene and coronene-based graphene nanoribbons are hydrogen terminated and annealing at temperatures above the stability limit of C-H bonds were expected to result in formation of new products. Indeed, Raman spectroscopy revealed the appearance of new sharp peaks after annealing of samples above 650 degrees C. The possible nature of encapsulated products produced by annealing of hydrogen terminated nanoribbons inside SWNTs is discussed.
41.	Thallapaka, Satya K., et al. (författare) Magneto-Structural Properties of the Layered Quasi-2D Triangular-Lattice Antiferromagnets Cs2CuCl4-ˆ’xBrx for x€ = €‰0, 1, 2, and 4 2019 Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 256:9 Tidskriftsartikel (refereegranskat)
42.	Vanherck, Joren, 1993, et al. (författare) Relaxation of quantum dots in a magnetic field at finite bias - charge, spin and heat currents 2017 Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 254:3 Tidskriftsartikel (refereegranskat)abstract We perform a detailed study of the effect of finite bias and magnetic field on the tunneling-induced decay of the state of a quantum dot by applying a recently discovered general duality [PRB 93, 81411 (2016)]. This duality provides deep physical insight into the decay dynamics of electronic open quantum systems with strong Coulomb interaction. It associates the amplitudes of decay eigenmodes of the actual system to the eigenmodes of a so-called dual system with attractive interaction. Thereby, it predicts many surprising features in the transient transport and its dependence on experimental control parameters: the attractive interaction of the dual model shows up as sharp features in the amplitudes of measurable time-dependent currents through the actual repulsive system. In particular, for interacting quantum dots, the time-dependent heat current exhibits a decay mode that dissipates the interaction energy and that is tied to the fermion parity of the system. We show that its decay amplitude has an unexpected gate-voltage dependence that is robust up to sizable bias voltages and then bifurcates, reflecting that the Coulomb blockade is lifted in the dual system. Furthermore, combining our duality relation with the known Iche-duality, we derive new symmetry properties of the decay rates as a function of magnetic field and gate voltage. Finally, we quantify charge- and spin-mode mixing due to the magnetic field using a single mixing parameter.
43.	Viñas Boström, Emil, et al. (författare) Steering Magnetic Skyrmions with Currents : A Nonequilibrium Green's Functions Approach 2019 Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. Tidskriftsartikel (refereegranskat)abstract Magnetic skyrmions, topologically protected vortex-like configurations in spin textures, are of wide conceptual and practical appeal, notably in relation to the making of so-called race-track memory devices. Skyrmions can be created, steered, and destroyed with magnetic fields and/or (spin) currents. Here the authors focus on the latter mechanism, analyzed via a microscopic treatment of the skyrmion–current interaction. The system considered is an isolated skyrmion in a square-lattice cluster, interacting with electron spins in a current-carrying quantum wire. For the theoretical description, a quantum formulation of spin-dependent currents via nonequilibrium Green's functions (NEGF) within the generalized Kadanoff–Baym ansatz (GKBA) is employed. This is combined with a treatment of skyrmions based on classical localized spins, with the skyrmion motion described via Ehrenfest dynamics. With the mixed quantum–classical scheme, the authors assess how time-dependent currents can affect the skyrmion dynamics, and how this in turn depends on electron–electron and spin–orbit interactions in the wire. This study shows the usefulness of a quantum–classical treatment of skyrmion steering via currents, as a way for example to validate/extract an effective, classical-only, description of skyrmion dynamics from a microscopic quantum modeling of the skyrmion–current interaction.
44.	Zamulko, S., et al. (författare) Investigation of the structural, optical and electronic properties of Cu2Zn(Sn,Si/Ge)(S/Se)4 alloys for solar cell applications 2017 Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 254:6 Tidskriftsartikel (refereegranskat)abstract 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.

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