SSSvetoslav Stankov

Svetoslav Stankov

Karlsruhe Institute of Technology
*This is an algorithmically generated author record based on publicly available information.
See Latest Publications
See Most Cited Publications
SciProfiles
ORCID Profile
Google Scholar

Current Organizations / Institutes

The organizations/institutes from the scholar's latest article

Svetoslav Stankov has a total of 221 co-authors. Here are the top co-authors by number of shared publications:

Latest Publications

  • Website
    Google Scholar

    Ab initio study of the anharmonic properties and thermal conductivity in β-FeSi2

    by Svitlana Pastukh, Małgorzata Sternik, Paweł T. Jochym, Jan Łażewski, Andrzej Ptok, Svetoslav Stankov, Przemysław Piekarz

  • Website
    Google Scholar
    Open Access

    Phonons in Epitaxial DySi 2 : From the Bulk to Self-Organized Nanoislands and Nanowires

    by Svetoslav Stankov, Przemysław Piekarz, Anja Seiler, Dániel G. Merkel, Olga Bauder, Ramu Pradip, Tilo G. Baumbach, Aleksandr I. Chumakov, Rudolf Rüffer

    Using nuclear inelastic scattering on Dy 161 , we determined the Dy-partial phonon density of states of epitaxial DySi 2 in bulk and self-organized nanoislands and nanowires (NWs) on vicinal Si(001) surface. Compared to the bulk, the nanoislands exhibit softening of the crystal lattice, which is further enhanced in the NWs and significantly affects their thermodynamic and elastic properties. Our calculations reveal that the origin of this effect is the vibrations of Dy atoms located at the surfaces of the nanoislands and the NWs as well as forming a ( 2 × 4 ) reconstruction on the Si(001) surface between the NWs. The results demonstrate that, opposite to the widely accepted anisotropic lattice mismatch model, the NWs form with their length along the [0001] direction of the strained hexagonal unit cell with lattice parameters close to the Si(001) surface.

  • Website
    Google Scholar
    Open Access

    Lattice Dynamics of Cu2ZnSn(Sx,Se1–x)4 Kesterite Thin-Film Solar Cells Studied by Nuclear Inelastic Scattering

    by Raju Edla, David Nowak, Dirk Hauschild, Ilya Sergueev, Devendra Pareek, Levent Gütay, Clemens Heske, Lothar Weinhardt, Svetoslav Stankov

    Phonons play a crucial role in thermalization and non-radiative recombination losses in semiconductors, impacting the power conversion efficiency of solar cells. To shed light on the lattice dynamics in Cu2ZnSn(S x ,Se1-x )4 (CZTSSe) thin-film solar cells and validate the extensive number of theoretical studies, we determine the 119Sn-partial phonon density of states (Sn-PDOS) by nuclear inelastic X-ray scattering. CZTSSe-based devices, one with near-stoichiometric and two with off-stoichiometric compositions, are investigated, and the results are correlated with the corresponding power conversion efficiencies (PCEs) of 3.2, 7.6, and 10.6%, respectively. Compared to the near-stoichiometric cell, the main Sn-PDOS peak of the off-stoichiometric cells broadens and slightly shifts to higher energy; this effect is correlated with the type and concentration of the characteristic defects in the studied samples. Furthermore, the Sn-PDOS of the 10.6% device is also obtained under operando (maximum power point) and open-circuit conditions. A comparison of the Sn-PDOS before and after the operando measurements suggests structural changes, likely due to the formation of metastable defects. In agreement with the theoretical studies, the Sn-PDOS of the CZTSSe absorber shows additional peaks compared to CZTSe attributed to coupling of Sn to the vibrations of Se and S atoms. This work paves the way for a further understanding of the lattice dynamics and subsequent enhancement of the PCEs of thin-film solar cells as well as other applied materials and devices containing elements that are Mössbauer-active and hence suitable for nuclear inelastic scattering.

    Cited by 2
  • Website
    Google Scholar

    Lattice dynamics of β−FeSi2 nanorods

    by J. Kalt, M. Sternik, I. Sergeev, M. Mikolasek, D. Bessas, J. Göttlicher, B. Krause, T. Vitova, R. Steininger, O. Sikora, et al.

    Here we present a combined experimental and ab initio lattice dynamics study of the semiconducting β phase of FeSi2. A polycrystalline β−FeSi2 film was prepared on Si(111) and single-crystalline, self-assembled β−FeSi2 nanorods were grown on Si(110) by molecular beam epitaxy. Both types of nanostructures were obtained by annealing of precursor structures, an epitaxial Fe film in the case of the film and high-aspect-ratio α−FeSi2 nanowires in the case of the nanorods. The morphology and crystalline structure of the samples were investigated by reflection high-energy electron diffraction, atomic force microscopy, as well as x-ray diffraction and x-ray absorption spectroscopy. The Fe-partial phonon density of states (PDOS) was obtained from nuclear inelastic scattering. The PDOS of the film was investigated in the temperature range of 296 K down to 11 K and shows an excellent agreement with the ab initio calculations. In the PDOS of the nanorods, a shift in the number of states in the main features and an additional vibrational mode at 20 meV are observed. While the first effect can fully be explained by the specific orientation of the β−FeSi2 unit cell on the Si(110) surface, the second effect is attributed to the formation of an α−FeSi2 interlayer at the β−FeSi2/Si interface. Furthermore, the thermoelastic properties of the film show a harmonic behavior in the investigated temperature range. For the nanorods, no significant deviation from the film is observed, except for a small decrease of the sound velocity.

    Cited by 4
  • Website
    Google Scholar
    Open Access

    Phonon confinement and interface lattice dynamics of ultrathin high-k rare earth sesquioxide films: the case of Eu2O3 on YSZ(001)

    by Svetoslav Stankov, Dániel G. Merkel, Jochen Kalt, Jörg Göttlicher, Jan Łażewski, Małgorzata Sternik, Paweł T. Jochym, Przemysław Piekarz, Tilo Baumbach, Aleksandr I. Chumakov, et al.

    The spatial confinement of atoms at surfaces and interfaces significantly alters the lattice dynamics of thin films, heterostructures and multilayers. Ultrathin films with high dielectric constants (high-k) are of paramount interest for applications as gate layers in current and future integrated circuits. Here we report a lattice dynamics study of high-k Eu2O3 films with thicknesses of 21.3, 2.2, 1.3, and 0.8 nm deposited on YSZ(001). The Eu-partial phonon density of states (PDOS), obtained from nuclear inelastic scattering, exhibits broadening of the phonon peaks accompanied by up to a four-fold enhancement of the number of low-energy states compared to the ab initio calculated PDOS of a perfect Eu2O3 crystal. Our analysis demonstrates that while the former effect reflects the reduced phonon lifetimes observed in thin films due to scattering from lattice defects, the latter phenomenon arises from an ultrathin EuO layer formed between the thin Eu2O3 film and the YSZ(001) substrate. Thus, our work uncovers another potential source of vibrational anomalies in thin films and multilayers, which has to be cautiously considered.

    Cited by 4
  • Website
    Google Scholar

    Chiral phonons in the honeycomb sublattice of layered CoSn-like compounds

    by Andrzej Ptok, Aksel Kobiałka, Małgorzata Sternik, Jan Łażewski, Paweł T. Jochym, Andrzej M. Oleś, Svetoslav Stankov, Przemysław Piekarz

    Honeycomb and kagome lattices exhibit extraordinary electronic properties. It is a natural consequence of additional discrete degree of freedom associated with a valley or the occurrence of electronic flat bands. The combination of both types of lattices, observed in CoSn-like compounds, leads not only to the topological electronic behavior, but also to the emergence of chiral phonon modes. We study CoSn-like compounds and show that chiral phonons are realized here. Previous theoretical studies demonstrated that the chiral phonons can be found in ideal two-dimensional honeycomb or kagome lattices. Recent experimental results support such a prediction as the chiral phonons were observed in the transition metal dichalcogenide WSe2. It turns out that in the case of CoSn-like systems with the P6/mmm symmetry, the kagome lattice formed by d-block element is decorated by the additional p-block atom. As a result one finds a two-dimensional triangular lattice of atoms with nonequal masses and the absence of chiral phonons in the kagome plane. Contrary to this, the interlayer honeycomb lattice of p-block atoms is preserved and allows for the realization of chiral phonons. In this paper we discuss the properties of such chiral phonons in seven CoSn-like compounds and demonstrate that they do not depend on the atomic mass ratio or the presence of intrinsic magnetic order. The chiral phonons of d-block atoms can be restored by removing the inversion symmetry. The latter is possible in the crystal structure of CoGe and RhPb with the reduced symmetry (P6¯2m) and in distorted-kagome-like lattice.

    Cited by 50
  • Website
    Google Scholar
    Open Access

    Lattice Dynamics and Structural Phase Transitions in Eu2O3

    by Jan Łażewski, Małgorzata Sternik, Paweł T. Jochym, Jochen Kalt, Svetoslav Stankov, Aleksandr I. Chumakov, Jorg Göttlicher, Rudolf Rüffer, Tilo Baumbach, Przemysław Piekarz

    Using the density functional theory, we study the structural and lattice dynamical properties of europium sesquioxide (Eu2O3) in the cubic, trigonal, and monoclinic phases. The obtained lattice parameters and energies of the Raman modes show a good agreement with the available experimental data. The Eu-partial phonon density of states calculated for the cubic structure is compared with the nuclear inelastic scattering data obtained from a 20 nm thick Eu2O3 film deposited on a YSZ substrate. A small shift of the experimental spectrum to higher energies results from a compressive strain induced by the substrate. On the basis of lattice and phonon properties, we analyze the mechanisms of structural transitions between different phases of Eu2O3.

    Cited by 45
  • Website
    Google Scholar

    Origin of a Simultaneous Suppression of Thermal Conductivity and Increase of Electrical Conductivity and Seebeck Coefficient in Disordered Cubic Cu 2 ZnSnS 4

    by Eleonora Isotta, Binayak Mukherjee, Carlo Fanciulli, Narges Ataollahi, Ilya Sergueev, Svetoslav Stankov, Raju Edla, Nicola M. Pugno, Paolo Scardi

    The parameters governing the thermoelectric efficiency of a material, Seebeck coefficient, electrical, and thermal conductivities, are correlated and their reciprocal interdependence typically prevents a simultaneous optimization. Here, we present the case of disordered cubic kesterite Cu2ZnSnS4, a phase stabilized by structural disorder at low temperature. With respect to the ordered form, the introduction of disorder improves the three thermoelectric parameters at the same time. The origin of this peculiar behavior lies in the localization of some Sn lone pair electrons, leading to “rattling” Sn ions. On one hand, these rattlers remarkably suppress thermal conductivity, dissipating lattice energy via optical phonons located below 1.5 THz; on the other, they form electron-deficient Sn—S bonds leading to a p-type dopinglike effect and highly localized acceptor levels, simultaneously enhancing electrical conductivity and the Seebeck coefficient. This phenomenon leads to a 3 times reduced thermal conductivity and doubling of both electrical conductivity and the Seebeck coefficient, resulting in a more than 20 times increase in figure of merit, although still moderate in absolute terms.

    Cited by 30
  • Website
    Google Scholar

    Lattice dynamics of endotaxial silicide nanowires

    by J. Kalt, M. Sternik, B. Krause, I. Sergueev, M. Mikolasek, D. Merkel, D. Bessas, O. Sikora, T. Vitova, J. Göttlicher, et al.

    Self-organized silicide nanowires are considered as building blocks of future nanoelectronics and have been intensively investigated. In nanostructures, the lattice vibrational waves (phonons) deviate drastically from those in bulk crystals, which gives rise to anomalies in thermodynamic, elastic, electronic, and magnetic properties. Hence a thorough understanding of the physical properties of these materials requires a comprehensive investigation of the lattice dynamics as a function of the nanowire size. We performed a systematic lattice dynamics study of endotaxial FeSi2 nanowires, forming the metastable, surface-stabilized α phase, which are in-plane embedded into the Si(110) surface. The average widths of the nanowires ranged from 24 to 3 nm, and their lengths ranged from several micrometers to about 100 nm. The Fe-partial phonon density of states, obtained by nuclear inelastic scattering, exhibits a broadening of the spectral features with decreasing nanowire width. The experimental data obtained along and across the nanowires unveiled a pronounced vibrational anisotropy that originates from the specific orientation of the tetragonal α−FeSi2 unit cell on the Si(110) surface. The results from first-principles calculations are fully consistent with the experimental observations and allow for a comprehensive understanding of the lattice dynamics of endotaxial silicide nanowires.

    Cited by 3
  • Website
    Google Scholar
    Open Access

    Lattice dynamics of endotaxial silicide nanowires

    by J. Kalt, M. Sternik, B. Krause, I. Sergueev, M. Mikolasek, D. Merkel, D. Bessas, O. Sikora, T. Vitova, 8 J. Göttlicher, et al.

    Self-organized silicide nanowires are considered as main building blocks of future nanoelectronics and have been intensively investigated. In nanostructures, the lattice vibrational waves (phonons) deviate drastically from those in bulk crystals, which gives rise to anomalies in thermodynamic, elastic, electronic, and magnetic properties. Hence, a thorough understanding of the physical properties of these materials requires a comprehensive investigation of the lattice dynamics as a function of the nanowire size. We performed a systematic lattice dynamics study of endotaxial FeSi$_2$ nanowires, forming the metastable, surface-stabilized $\alpha$-phase, which are in-plane embedded into the Si(110) surface. The average widths of the nanowires ranged from 24 to 3 nm, their lengths ranged from several $\mu$m to about 100 nm. The Fe-partial phonon density of states, obtained by nuclear inelastic scattering, exhibits a broadening of the spectral features with decreasing nanowire width. The experimental data obtained along and across the nanowires unveiled a pronounced vibrational anisotropy that originates from the specific orientation of the tetragonal $\alpha$-FeSi$_2$ unit cell on the Si(110) surface. The results from first-principles calculations are fully consistent with the experimental data and allow for a comprehensive understanding of the lattice dynamics of endotaxial silicide nanowires.

Show all