Alexander P. Litvinchuk

A metastable germanium allotrope, Ge(oP32), was synthesized as polycrystalline powders and single crystals from the mild-oxidation/delithiation of Li7Ge12 in ionic liquids. Its crystal structure, from single crystal X-ray diffraction (Pbcm, a = 8.1527(4) Å, b = 11.7572(5) Å, c = 7.7617(4) Å), features a complex covalent network of 4-bonded Ge, resu...

Optical spectroscopy, x-ray diffraction measurements, density functional theory (DFT), density functional theory + embedded dynamical mean-field theory (DFT+eDMFT), and crystal-field calculations have been used to characterize structural and electronic properties of hexagonal M2Mo3O8 (M = Fe, Mn) polar magnets. Our experimental data are consistent...

Earth‐abundant and environmentally friendly semiconductors offer a promising path toward low‐cost mass production of solar cells. A critical aspect in exploring new semiconducting materials and demonstrating their enhanced functionality consists in disentangling them from the artifacts of defects. Nanowires are diameter‐tailored filamentary structu...

Ternary (I-III-VI) and quaternary (I-II-IV-VI) metal-chalcogenides like CuInS2 or Cu2ZnSn(S,Se)4 are among the materials currently most intensively investigated for various applications in the area of alternative energy conversion and light-emitting devices. They promise more sustainable and affordable solutions to numerous applications, compared t...

This work presents a comprehensive analysis of the structural and vibrational properties of the kesterite Cu2ZnSnS4 (CZTS, I4̅ space group) as well as its polymorphs with the space groups P4̅2c and P4̅2m, from both experimental and theoretical point of views. Multiwavelength Raman scattering measurements performed on bulk CZTS polycrystalline sampl...

High-pressure studies on elements play an essential role in superconductivity research, with implications for both fundamental science and applications. Here we report the experimental discovery of surprisingly low pressure driving a novel germanium allotrope into a superconducting state in comparison to that for α-Ge. Raman measurements revealed...

Bedding-parallel calcite layers (BPCLs) preserving a fibrous “beef” texture are common throughout the overmature Haynesville Formation shale. Their interfaces with the host shale contain radiating splays of anhydrite pseudomorphs after gypsum rosettes, suggesting either a primary evaporitic or an early burial origin. In places, the calcite layers c...

An erbium-doped β-GaLaS3 crystal has been grown by the solution-melt method, and the effect of γ-irradiation on their vibrational and radiative properties has been investigated. Experiments have demonstrated that the crystal is transparent in the near and mid-IR regions (transparency ∼62% in the range of 350 – 7100 cm-1), which allows it to be used...

Copper diphosphide (CuP2) is an emerging binary semiconductor with promising properties for energy conversion and storage applications. While functionality and possible applications of CuP2 have been studied, there is a curious gap in the investigation of its vibrational properties. In this work, we provide a reference Raman spectrum of CuP2, with...

AgGaGeS4 is an emerging material with promising nonlinear properties in the near- and mid-infrared spectral ranges. Here, the experimental phonon spectra of AgGaGeS4 single crystals synthesized by a modified Bridgman method are presented. The infrared absorption spectra are reported. They are obtained from the fitting of reflectivity to a model die...

Zn 3 P 2 is an excellent candidate for PV applications. However, the nature of intrinsic defects, as well as their ability to tune the optoelectronic properties is still unknown. How can Polarized Raman spectroscopy be used to effectively identify these defects and their position in the structure?

Predictive synthesis–structure–property relationships are at the core of materials design for novel applications. In this regard, correlations between the compositional stoichiometry variations and functional properties are essential for enhancing the performance of devices based on these materials. In this work, we investigate the effect of stoich...

Allotropes of an element can display drastically different properties depending on the fundamental chemical nature of the element. Because of the limited chemistry involved, synthetic allotropes of nonmolecular elemental structures are rare. A metastable germanium allotrope, oP32-structured Ge, was synthesized as polycrystalline powders and single...

The electronic band structure, the optical properties, and the lattice dynamics of the quaternary Cu2ZnSnTe4 (CZTTe) semiconductor with kesterite crystallographic structure are calculated within first principles. The analysis of the phonon partial density of states shows that the highest frequency phonon modes involve mostly heavy Sn and Te atoms d...

Zinc phosphide (Zn3P2) is a II-V compound semiconductor with promising photovoltaic and thermoelectric applications. Its complex structure is susceptible to facile defect formation, which plays a key role in further optimization of the material. Raman spectroscopy can be effectively used for defect characterization. However, the Raman tensor of Zn3...

We combined optical spectroscopy and first-principles electronic structure calculations to reveal the charge gap in the polar magnet Fe2Mo3O8. Iron occupation on the octahedral site draws the gap strongly downward compared to the Zn parent compound, and subsequent occupation of the tetrahedral site creates a narrow resonance near the Fermi energy t...

Cu-Zn-Sn-Te (CZTTe) is an inexpensive quaternary semiconductor that has not been investigated so far, unlike its intensively studied CZTS and CZTSe counterparts, although it may potentially have desirable properties for solar energy conversion, thermoelectric, and other applications. Here, we report on the synthesis of CZTTe nanocrystals (NCs) via...

Band Structure Determination In article number 2105426, Mirjana Dimitrievska, Anna Fontcuberta i Morral, and co-workers demonstrate how nanowires can be effectively used for direct determination of the band structure by means of valence electron energy-loss spectroscopy. This work opens the path for characterizing the band structure of new compound...

Two-dimensional (2D) MoS2 possesses unique optical and electrical properties and has many practical applications in nano-optoelectronics. Raman spectroscopy allows readily identify monolayer of MoS2, but the unambiguous determination of the number of layers in a few-layer structure remains a challenging task. In this work, the modification of frequ...

The subject of this paper is to study the influence of anharmonicity and weak interlayer interaction on the Raman scattering of mono- and few-layer MoS2. In this work, we theoretically and experimentally studied the Raman scattering in MoS2 layered crystals, in particular, the change of intensity and wavenumber position of the in-plane and out-of-p...

There is currently an emerging drive to computational materials design and fabrication of the predicted novel materials. One of the keys for developing appropriate fabrication methods is determination of the composition and phase. Here we explore the FeGe system and establish reference Raman signatures for the distinction between the FeGe hexagonal...

The synthesis of (Cu,Ag)-Zn-Sn-S (CAZTS) and Ag-Zn-Sn-S (AZTS) nanocrystals (NCs) by means of “green” chemistry in aqueous solution and their detailed characterization by Raman spectroscopy and several complementary techniques are reported. Through a systematic variation of the nominal composition and quantification of the constituent elements in C...

The variation of the cationic composition in I2-II-IV-VI4 semiconductor compounds is an effective tool for altering their properties in a controlled manner. In particular, a partial substitution of Cu for Ag in kesterite Cu2ZnSnS4 was proposed to suppress Cu-Zn antisite defects and the improve photovoltaic performance. However, the efficiency of th...

Cu2ZnSnS4 (CZTS) is one of the promising materials for absorber layers of new-generation thin film solar cells. Various synthetic routes of materials preparation and structural characterization have been explored so far. Further tuning of the CZTS properties is realized via partial substitution of the cations. Here we have used an affordable and sc...

Magnetic and crystallographic transitions in the Cairo pentagonal magnet Bi2Fe4O9 are investigated by means of infrared synchrotron-based spectroscopy as a function of temperature (20-300 K) and pressure (0-15.5 GPa). One of the phonon modes is shown to exhibit an anomalous softening as a function of temperature in the antiferromagnetic phase below...

Magnetic and crystallographic transitions in the Cairo pentagonal magnet Bi2Fe4O9 are investigated by means of infrared synchrotron-based spectroscopy as a function of temperature (20 - 300 K) and pressure (0 - 15.5 GPa). One of the phonon modes is shown to exhibit an anomalous softening as a function of temperature in the antiferromagnetic phase b...

We combined optical spectroscopy and first principles electronic structure calculations to reveal the charge gap in the polar magnet Fe$_2$Mo$_3$O$_8$. Iron occupation on the octahedral site draws the gap strongly downward compared to the Zn parent compound, and subsequent occupation of the tetrahedral site creates a narrow resonance near the Fermi...

We combine optical spectroscopy and first-principles electronic structure calculations to reveal the microscopic character of the charge gap in polar magnet Fe2Mo3O8. Iron occupation on the octahedral site draws the gap strongly downward compared to the Zn parent compound, whereas occupation on the tetrahedral site creates a narrow resonance near t...

Results of Electrochemical Impedance Spectroscopy (EIS) are reported for lithium-niobium-titanium-oxide (LNTO) ceramics synthesized by a solid-state reaction method with two functional additives (MoO3 or ZnO) in the temperature range 323 K - 573 K and frequencies between 10⁻¹ Hz and 10⁷ Hz. Scanning electron microscopy (SEM) reveals a textured morp...

Earth-abundant and low-cost semiconductors, such as zinc phosphide (Zn3P2), are promising candidates for the next generation photovoltaic applications. However, synthesis on commercially available substrates, which favors the formation of defects, and controllable doping are challenging drawbacks that restrain device performance. Better assessment...

Lattice dynamic properties of the tetragonal modification of ZnP2 and CdP2 crystals (space group P41212, no. 92) are calculated within the density functional theory. Theoretical results are shown to compare favorably with available Raman scattering and infrared reflection/transmission experimental data, which allows assignment of Raman-and infrared...

Theoretical and experimental vibrational spectra of ReSe2 nanocrystals, synthesized by self‐limited chemical vapor deposition (CVD), are reported. Scanning electron microscopy reveals that the nanocrystals have the shape of polygon nanoplates (NPs), 20 nm thick and about 100–300 nm wide. X‐ray diffraction studies determined their triclinic structur...

A skyrmion state in a non-centrosymmetric helimagnet displays topologically protected spin textures with profound technological implications for high density information storage, ultrafast spintronics, and effective microwave devices. Usually, its equilibrium state in a bulk helimagnet occurs only over a very restricted magnetic-field-temperature p...

A skyrmion state in a non-centrosymmetric helimagnet displays topologically protected spin textures with profound technological implications for high density information storage, ultrafast spintronics, and effective microwave devices. Usually, its equilibrium state in a bulk helimagnet occurs only over a very restricted magnetic-field--temperature...

Supplemental information

Significance Skyrmion materials hold great promise for information technology due to the extremely low current needed to modify the spin configurations and the small size of magnetic domains. To facilitate their application, one great challenge is to break the magnetic field–temperature phase space restriction for the skyrmion state. We found that...

Phonon spectra of two novel nonlinear optical crystals, PbGa2GeSe6 and PbGa2GeS6, are studied experimentally by Raman and infrared reflection spectroscopy and theoretically by density functional theory (DFT) lattice dynamics calculations. The experimental peak frequencies are compared to calculated vibration frequencies, and a very reasonable agree...

Bi2Fe4O9 is a common by-product in the synthesis of the multiferroic compound BiFeO3 and has been claimed itself to display multiferroic properties [1]. The lattice formed by the two different sites of four iron Fe 3+ magnetic atoms is quite remarkable as it materializes the first analogue of a magnetic pentagonal lattice [2]. For its peculiar latt...

Optical properties and lattice dynamics of hexagonal M2Mo3O8 (M = Fe, Mn) single crystals are studied in a wide temperature range by means of infrared (IR) reflectivity and Raman scattering at the temperatures above and below the magnetic transitions. Experimental data for optical phonons are compared to group theoretical mode analysis and complime...

Nickel silicides are widely used as contact materials for electronic devices based on silicon (Si). However, they have been predominantly fabricated by annealing separate Ni and Si phases which leads to phase and structural complexity. In this letter, direct epitaxial growth of a single-phase nickel disilicide (NiSi 2 ) thin film by sputter deposit...

Optical spectroscopy, X-ray diffraction measurements, density functional theory (DFT) and density functional theory + embedded dynamical mean field theory (DFT+eDMFT) have been used to characterize structural and electronic properties of hexagonal $M_2$Mo$_3$O$_8$ ($M$=Fe, Mn) polar magnets. Our experimental data are consistent with the room temper...

Optical and vibrational properties of a novel allotrope of elemental germanium Ge(oP32), which crystallizes in the structure corresponding to the orthorhombic space group Pbcm, are studied experimentally by means of absorption and polarized Raman scattering measurements and theoretically using the first principles Density Functional Theory. Materia...

In this report, we describe a unique roll-to-roll plasma-enhanced chemical vapor deposition (R2RPECVD) technique to grow high-quality single-crystalline-like Ge films on flexible metal foils, an important advancement towards scalable processing of epitaxial Ge films at low-cost. Ion-beam assisted deposition was used to create single-crystalline-lik...

The results of a comprehensive experimental and theoretical study of Raman scattering of Tl4HgI6, Tl4HgBr6, and TlHgCl3 ternary chalcogenides are presented. Phonon mode assignment to the specific lattice eigenmodes is achieved via comparison of experimental data with the results of first principle lattice dynamics calculations. Both experimental da...

Raman scattering spectroscopy is used to monitor the transition of reduced niobium oxyfluoride Nb2O2F3 single crystals from their high-temperature monoclinic (I2/a) into the low-temperature triclinic (P-1) phase at Tc = 90 K due to charge disproportionation of (Nb-Nb)7+ dimers and creation of crystallographically non-equivalent dimers with a long a...

Experimental Raman scattering study of mixed AgxGaxGe1−xSe2 (0.167 ≤ x ≤ 0.333) single crystals is reported. The spectra transformation upon composition variation exhibits the two-mode type of behavior, with lines of the end-member compounds of the solid solution (AgGaSe2 and GeSe2) dominating in the spectra, whose relative intensities vary with co...

High pressure vibrational spectroscopy is a powerful tool for exploring the properties of materials. In this work, we bring together diamond anvil cell techniques, synchrotron-based infrared and Raman spectroscopies, and complementary lattice dynamics calculations to reveal the pressure−temperature phase diagram of Co[N(CN)2]2 and how local lattice...

Despite comparatively uniform petrophysical and geomechanical rock properties, significant variations in Estimated Ultimate Recovery (EUR) are observed in many wells in the Haynesville shale gas play, NW Louisiana. Some of the differences may be attributable to differences in completion practices and Sw. However, these differences do not fully expl...

The Utica and Point Pleasant Fms. comprise over-mature Ordovician-age organic-rich shales, with reported VRE values of ~3 to 3.5%: In this paper, we present the results of a FI study on inclusions trapped in calcite from calcite veins that were sampled in core from the discovery well. Homogenization temperatures from primary 2 phase aqueous inclusi...

Single crystals of orthorhombic wurtzstannite Cu2ZnSiS4 (space group Pmn2_1 or C_2v^7 ) were synthesized by the chemical vapor transport method. Lattice dynamics of these crystals is studied experimentally by the low temperature polarized Raman scattering. Mode assignment to the specific lattice eigenmodes is performed based on a detail comparison...

Spectrally-selective solar absorber is required to be thermally stable at high operational temperature. However the currently available absorbers aren't stable beyond 700 °C. Here we explore a new absorber with cermet of TiN in SiO2 on LaAlO3 substrate that can be used for long term at 700 °C. The optimized cermets contain TiN with volume fraction...

The structures of two trigonal-rhombohedral CaSi2 polymorphs (space group R3m) were studied by X-ray diffraction and polarized Raman scattering spectroscopy. Raman-active even parity vibrational modes of A1g and Eg symmetry are unambiguously identified and assigned to the specific lattice eigenmodes. Experimental data are found to be in very good a...

Доповідь є коротким оглядом сьогоднішнього стану фізичних досліджень сімейства четверних напівпровідникових халькогенідів металів, які в останні 5-6 років розглядаються як перспективні матеріали нового покоління тонкоплівкових фотоелектричних перетворювачів сонячного випромінювання, а також як потенційні матеріали для термоелектрики і нелінійної оп...

Доповідь є коротким оглядом сьогоднішнього стану фізичних досліджень сімейства четверних напівпровідникових халькогенідів металів, які в останні 5-6 років розглядаються як перспективні матеріали нового покоління тонкоплівкових фотоелектричних перетворювачів сонячного випромінювання, а також як потенційні матеріали для термоелектрики і нелінійної оп...

The crystal structure of Cu2ZnSiSe4 semiconductor, grown by the chemical vapor transport method, was determined by the powder and single-crystal X-ray diffraction and shown to be orthorhombic wurtzstannite (space group Pmn21). Lattice dynamics of Cu2ZnSiSe4 is studied by the low-temperature off resonant polarized and resonant Raman scattering. Out...

This frontispiece illustrates high-performance, mechanically flexible thin film transistors based on single-crystal-like Ge on flexible glass using biaxially textured CeO2 as a buffer layer, as described by M. Asadirad et al. in article number 1600041. High field-effect mobility and saturation current levels are achieved, significantly higher than...

Nanocrystalline Zn2SnO4 powders doped with Eu3+ ions were synthesized via a mechanochemical solid-state reaction method followed by post annealing in air at 1200 oC. X-ray diffraction (XRD), energy-dispersive X-ray (EDX), Raman and photoluminescence (PL) spectroscopies provide convincing evidence for the incorporation of Eu3+ ions into the host mat...

The transformation of the vibrational spectrum of Cu2Zn(Sn1-xGex)S4 single crystals over entire composition range (0 < x < 1) is studied experimentally by the low-temperature Raman scattering and photoluminesce spectroscopies, as well as theoretically in the framework of density functional theory (DFT). It is shown that, unlike "classic" mixed bina...

Thin-film transistors (TFTs) grown on a flexible glass substrate using single-crystal-like germanium (Ge) channel to simultaneously achieve high carrier mobility, high performance characteristics, mechanical flexibility, and cost-effective large-area manufacturing are reported. High-crystalline-quality materials of biaxially textured CeO2 deposited...

Cu2ZnGeS4 (CZGS) and mixed Cu2Zn(Ge,Sn)S4 (CZGTS) semiconductors attract considerable interest for the development of cost efficient photovoltaic devices with suitable band gap engineering. Development of these materials requires a deeper knowledge of their fundamental properties, which have been very little explored for these Ge-based compounds. I...

Single crystals of the new title compounds are hydrothermally synthesized from aqueous mixtures of NH4VO3 dissolved in concentrated NH4OH, CuX2 (X: Cl, Br), Ba(OAc)2, and LiX (autoclave, pH 8—10, 220 °C, 2—4 d, 25 and 55% yield for X: Cl and Br, resp.).

Optical properties of multiferroic orthoferrites RFeO3 (R=Tb,Dy) bulk crystals have been studied in the far-infrared range from 50 to 1000 cm-1 and temperatures from 7 K to 300 K. Mueller matrix and rotating analyzer ellipsometry measurements were carried out at the U4IR beamline of the National Synchrotron Light Source at Brookhaven National Lab....

We combined synchrotron-based infrared spectroscopy, Raman scattering, and diamond anvil cell techniques with complementary lattice dynamics calculations to reveal local lattice distortions in Mn[N(CN)2]2 under compression. Strikingly, we found a series of transitions involving octahedral counter-rotations, changes in the local Mn environment, and...

Density functional calculations of the electronic band structure, optical properties and lattice dynamics of kesterite Cu2ZnGeSe4 semiconductor (space group I4) are reported. Theoretical optical properties of the material are shown to agree quantitatively with available spectroscopic ellipsometry experimental data that allows detail interpretation...

A comprehensive vibrational analysis of the kesterite Cu2ZnGeS4 semiconductor (space group I4 ) is reported, which includes experimental in-plane rotation polarized Raman scattering measurements from the (101)-single crystal facet as well as first principle lattice dynamic calculations. 17 out of the 27 expected vibrational modes of the kesterite s...

The experimental resonant and non-resonant Raman scattering spectra of the kesterite structural modification of Cu2ZnGeS4 single crystals are reported. The results are compared with those calculated theoretically within the density functional perturbation theory. For the majority of lines a good agreement (within 2 – 5 cm−1) is established between...

Optical properties and lattice dynamics of hexagonal 2H−BaMnO3 single crystals are studied experimentally in a wide temperature range by means of rotating analyzer ellipsometry and Raman scattering. The magnitude of the direct electronic band gap is found to be Eg=3.2eV. At room temperature the far-infrared (IR) ellipsometry spectra reveal six IR-a...

Spectrally-selective solar absorbers are widely used in solar hot water and concentrating solar power (CSP) systems. However, their performance at high temperatures (445C) is still not satisfactory due to high infrared (IR) emittance and lack of long-term thermal stability. Here, we explore yttria-stabilized zirconia (YSZ) cermet-based spectrally-s...

The new title compound is synthesized by reaction of Nb, SnF2, and SnO in Sn flux (4:4:3:8 molar ratio; welded Nb containers, 600 C, 7 d). Nb2O2F3 is characterized by powder and single crystal XRD, Raman spectroscopy, magnetic and transport measurements, and DFT calculations. At 296 K the compound crystallizes in the monoclinic space group I2/a wi...

Dark-red crystals of the title compound are hydrothermally synthesized from aqueous mixtures of MnCl2, NH4VO3, Ba(OAc)2, and LiCl (autoclave, 220 °C, 3—4 d, 55% yield).

BaMn9[VO4]6(OH)2 was synthesized by hydrothermal methods. We evaluated the crystal structure based on the two possible space groups P213 and Pa3̅ [a = 12.8417(2) Å] using single-crystal and powder X-ray diffraction techniques. The structure contains three-dimensionally linked Mn9 units of a chiral "paddle-wheel" type. Experimental IR and Raman spec...

A new niobium oxyfluoride, Nb2O2F3, synthesized through the reaction of Nb, SnO and SnF2 in Sn flux, within welded Nb containers, crystallizes in a monoclinic crystal structure (space group: I2/a; a=5.7048(1)Å, b= 5.1610(1)Å, c = 12.2285(2)Å, β = 95.751(1)Å). It features [Nb2X10] units (X = O, F), with short (2.5739(1) Å) Nb−Nb bonds, that are link...

We report the results of a Raman spectroscopy study of lattice vibrations in colloidal Cu3SnS4 nanocrystals (NCs) in a broad spectral range between 70 and 1200 cm-1. The crystallographic structure and lattice symmetry of NCs is confirmed by the X-ray diffraction data. The three most intensive Raman features in the spectra obtained in this work coin...

The dielectric function of orthorhombic Cu2CdGeS4 and Cu2CdSiS4 single crystals (space group Pmn21) is measured experimentally in the spectral range of 0.7–5.2 eV, and the results are interpreted via comparison with ab initio calculations. Polarized Raman-scattering measurements of both semiconductors are reported. All observed vibrational modes ar...

Optical properties of hexagonal multiferroic oxides RMnO3, where R = Ho, Er, Tm, Yb, and Lu, have been studied in the far-infrared spectral range between 100 and 2000 cm(-1) and temperatures between 1.5 and 300 K by means of several experimental techniques: Mueller matrix spectroscopic ellipsometry, rotating analyzer ellipsometry, and optical trans...