Zakir Jahangirli - Academia.edu (original) (raw)

Papers by Zakir Jahangirli

Research paper thumbnail of Infrared study of the multiband low-energy excitations of the topological antiferromagnet MnBi2Te4

Physical Review B, 2021

With infrared spectroscopy we studied the bulk electronic properties of the topological antiferro... more With infrared spectroscopy we studied the bulk electronic properties of the topological antiferromagnet MnBi2Te4 with TN ≃ 25 K. With the support of band structure calculations, we assign the intra-and interband excitations and determine the band gap of Eg ≈ 0.17 eV. We also obtain evidence for two types of conduction bands with light and very heavy carriers. The multiband free carrier response gives rise to an unusually strong increase of the combined plasma frequency, ω pl , below 300 K. The band reconstruction below TN , yields an additional increase of ω pl and a splitting of the transition between the two conduction bands by about 54 meV. Our study thus reveals a complex and strongly temperature dependent multi-band low-energy response that has important implications for the study of the surface states and device applications.

Research paper thumbnail of Ab initio calculations and experimental study of piezoelectric Y In1−N thin films deposited using reactive magnetron sputter epitaxy

Acta Materialia, 2016

By combining theoretical prediction and experimental verification we investigate the piezoelectri... more By combining theoretical prediction and experimental verification we investigate the piezoelectric properties of yttrium indium nitride (Y x In 1−x N). Ab-initio calculations show that the Y x In 1−x N wurtzite phase is lowest in energy among relevant alloy structures for 0 ≤ x ≤ 0.5. Reactive magnetron sputter epitaxy was used to prepare thin films with Y content up to x = 0.51. The composition dependence of the lattice parameters observed in the grown films is in agreement with that predicted by the theoretical calculations confirming the possibility to synthesize a wurtzite solid solution. An AlN buffer layer greatly improves the crystalline quality and surface morphology of subsequently grown Y x In 1−x N films. The piezoelectric response in films with x = 0.09 and x = 0.14 is observed using piezoresponse force microscopy. Theoretical calculations of the piezoelectric properties predict Y x In 1−x N to have comparable piezoelectric properties to Sc x Al 1−x N.

Research paper thumbnail of Crystal structure and Raman-active lattice vibrations of magnetic topological insulators MnBi2Te4·n(Bi2Te3) ( n=0 , 1,...,6)

Physical Review B

Further to the structure of the intrinsic magnetic topological insulators MnBi2Te4 n(Bi2Te3) with... more Further to the structure of the intrinsic magnetic topological insulators MnBi2Te4 n(Bi2Te3) with n<4, where index n is the number of quintuple Te-BiTe -BiTe building blocks inserted between the neighboring septuple Te-BiTe -Mn-Te-BiTe building blocks, the structure of the members with n=4, 5 and 6 was studied using X-ray powder diffraction. The unit cell parameters and atomic positions were calculated. The obtained and available structural data were summarized to show that the crystal structure of all members of MnBi2Te4 n(Bi2Te3) follows the cubic close packing principle, independently of the space group of the given member. Confocal Raman spectroscopy was then applied. Comparative analysis of the number, frequency, symmetry, and broadening of the vibration modes responsible for the lines in the Raman spectra of the systems with n=1,.. . ,6, as well as MnBi2Te4 (n=0) and Bi2Te3 (n=) has shown that lattice dynamics of MnBi2Te4 n(Bi2Te3) with n>0 overwhelmingly dominates by the cooperative atomic displacements in the quintuple building blocks. I.

Research paper thumbnail of Intercalation of p-Aminopyridine and p-Ethylenediamine Molecules into Orthorhombic In1.2Ga0.8S3 Single Crystals

Materials

A single crystalline layered semiconductor In1.2Ga0.8S3 phase was grown, and by intercalating p-a... more A single crystalline layered semiconductor In1.2Ga0.8S3 phase was grown, and by intercalating p-aminopyridine (NH2-C5H4N or p-AP) molecules into this crystal, a new intercalation compound, In1.2Ga0.8S3·0.5(NH2-C5H4N), was synthesized. Further, by substituting p-AP molecules with p-ethylenediamine (NH2-CH2-CH2-NH2 or p-EDA) in this intercalation compound, another new intercalated compound—In1.2Ga0.8S3·0.5(NH2-CH2-CH2-NH2) was synthesized. It was found that the single crystallinity of the initial In1.2Ga0.8S3 samples was retained after their intercalation despite a strong deterioration in quality. The thermal peculiarities of both the intercalation and deintercalation of the title crystal were determined. Furthermore, the unit cell parameters of the intercalation compounds were determined from X-ray diffraction data (XRD). It was found that increasing the c parameter corresponded to the dimension of the intercalated molecule. In addition to the intercalation phases’ experimental chara...

Research paper thumbnail of Bulk Modulus, Elastic Constants, and Force Constants of Interatomic Bonds of II–III2–VI4 Compounds

physica status solidi (b)

Ab initio density functional perturbation theory is used to calculate the elastic constants of Cd... more Ab initio density functional perturbation theory is used to calculate the elastic constants of CdGa2S4, CdGa2Se4, CdGa2Te4, and ZnGa2Se4 thiogallates. The values of the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio are determined. The force constants of interatomic bonds in CdGa2Te4 and ZnGa2Se4 compounds are calculated. Regularities in the dependence of the frequencies of Raman‐active phonons on the atomic masses are established.

Research paper thumbnail of Electronic structure of the Ge and Se vacancies in GeSe layered semiconductor

Turkish Journal of Physics

We report the results of a theoretical investigation of electronic properties of ideal cation and... more We report the results of a theoretical investigation of electronic properties of ideal cation and anion vacancies in GeSe. The calculations have been performed using self-consistent Green's function method. The bulk electronic structure is described by a tight-binding Hamiltonian ...

Research paper thumbnail of CSD 2116458: Experimental Crystal Structure Determination

Research paper thumbnail of Optical and Dynamic Properties of ZnGa 2 S 4

physica status solidi (b), 2021

Research paper thumbnail of Synthesis and characterization of new indium gallium selenides of the InSe-GaSe system

Journal of Solid State Chemistry, 2021

Abstract The new solid solution phases crystallized in the hexagonal and tetragonal system were r... more Abstract The new solid solution phases crystallized in the hexagonal and tetragonal system were revealed in the GaSe-InSe system, and a new orthorhombic phase with a new type of structural blocks has been proposed. The structural features of the In1-xGaxSe solid solutions (where 0 ​≤ ​x ​≤ ​1) were studied using X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), and Raman spectroscopy. The chemical interaction between Ga and In atoms in the hexagonal In1-xGaxSe phases was identified. The reversible phase transition from hexagonal to the tetragonal structure was found to occur in the In0.7Ga0.3Te phase. Using the Density Functional Theory (DFT) method, the electronic, optical, and vibrational properties for the Pnnm orthorhombic InGaSe2 phase were studied. Modified Becke-Johnson exchange potential and generalized gradient approximations (mBJ-GGA) were used to calculate the electronic band structure, dielectric function, and density of states (DOS) of InGaSe2, which solve the band-gap problem found within GGA approach. The InGaSe2 stoichiometric phase was found to be a direct band-gap semiconductor and the band gap of this compound can be tuned via the different stacking sequences of InSe/GaSe layers. The optical absorption edges which are observed in the visible light region make this compound promising material for photovoltaic applications. The calculated phonon spectra of the InGaSe2 revealed that the frequencies of the optic modes are close to frequencies of acoustic modes, which carry the heat flow, and in this case, the acoustic modes will be strongly scattered by low-frequency optic modes. The latter event may lead to a low lattice thermal conductivity that is important for thermoelectric applications. The phonon dispersion of this compound shows no imaginary modes, suggesting that it is dynamically stable.

Research paper thumbnail of Infrared spectroscopic ellipsometry and optical spectroscopy of plasmons in classic 3D topological insulators

Journal of Vacuum Science & Technology B, 2019

Research paper thumbnail of CrAs Monolayer: Low Buckled Two‐Dimensional Half‐Metal Ferromagnet

physica status solidi (RRL) – Rapid Research Letters, 2019

Ab-initio calculations based on density functional theory (DFT) are performed to study the struct... more Ab-initio calculations based on density functional theory (DFT) are performed to study the structural, electronic, and magnetic properties of two-dimensional (2D) free-standing honeycomb CrAs. We show that CrAs has low buckled stable structure. Magnetic CrAs has larger buckling than non-magnetic CrAs. 2D-CrAs is a ferromagnetic semiconductor for lattice constant a ≤ 3.71Å, and above this lattice constant CrAs is a half-metal ferromagnet. 2D-CrAs is shown to be half-metal ferromagnetic with magnetic moment of 3.0µB per unit cell, at equilibrium structure. The d 2 z orbital of eg band is completely empty in the spin-down state whereas it is almost occupied in the spin-up state, and the magnetic moment in the eg band is mainly dominated by the d 2 z orbital of Cr. The dzx/dzy and dxy orbitals of t2g band are partially occupied in the spin-up state and behaves as metal whereas they are insulator in the spin-down state. Phonon calculations confirm the thermodynamic stability of 2D-CrAs. The ferromagnetic (FM) and antiferromagnetic (AFM) interaction between the Cr atoms reveal that the FM state is more stable than the AFM state of 2D-CrAs.

Research paper thumbnail of Novel ternary layered manganese bismuth tellurides of the MnTe-Bi2Te3 system: Synthesis and crystal structure

Journal of Alloys and Compounds, 2019

Research paper thumbnail of Ellipsometric characterization of MoSe2 thin layers obtained by thermal treatment of molybdenum in selenium vapor

Applied Surface Science, 2017

 MoSe2 layers are obtained by thermal treatment of molybdenum in selenium vapor.  Spectroscopic... more  MoSe2 layers are obtained by thermal treatment of molybdenum in selenium vapor.  Spectroscopic ellipsometry is applied to the obtained layers and MoSe2 target.  Electronic band structure of MoSe2 is calculated and dielectric function is derived.  Calculated and ellipsometry-based data on dielectric function agree fairly well.  Excitonic transitions are assumed to form the dielectric function at around 1 eV.

Research paper thumbnail of First-principles lattice dynamics and Raman scattering in ionic conductor β-Ag2 S

physica status solidi (b), 2016

The phonon structure of the silver sulfide Ag2S was investigated, experimentally using Raman spec... more The phonon structure of the silver sulfide Ag2S was investigated, experimentally using Raman spectroscopy, and theoretically using the density‐functional perturbation theory for the first time. Seven Raman‐active modes were observed and identified at 23, 39, 42, 44, 62, 65, and 243 cm−1. Symmetry assignments of all the vibrational modes were derived from considerations of point group symmetry. The phonon band structure and the relative Raman intensities were also investigated by ab initio calculations and compared with the experimental data. The temperature, laser power, and illumination time dependencies of frequency, linewidth, and intensity of the Raman‐active modes are discussed. In the Raman spectra at higher frequencies 1300–1700 cm−1, additional broad Raman modes observed in all samples at higher laser powers 8–10 mW were ascribed to luminescence from β‐Ag2S. The phonon and Raman spectra of the β‐Ag2S provide a useful insight into the β‐Ag2S → α‐Ag2S phase transition. Finally, calculated infrared vibrational mode frequencies were compared with measured infrared mode frequencies.

Research paper thumbnail of Electronic Structure of Surfaces in GeSe Layered Semiconductor

Green´s function method in bases sets of Linear Combinations of Atomic Orbitals (LCAO) is used to... more Green´s function method in bases sets of Linear Combinations of Atomic Orbitals (LCAO) is used to calculate the electronic structure of the (010) surface of GeSe semiconductor. The energy states in energy gaps, their origin, orbital content, resonances and local changes in the density of states due to the surface are discussed.

Research paper thumbnail of DIRECT ELLIPSOMETRY TASK FOR ZnS/GaAs, ZnSe/GaAs and CuGaS2/GaP THIN FILM/SUBSTRATE SYSTEMS

In this work ellipsometric approach has been developed for ZnSlGaAs, ZnSelGaAs and CuGaS2/GaP fil... more In this work ellipsometric approach has been developed for ZnSlGaAs, ZnSelGaAs and CuGaS2/GaP film/substrate systems to solve direct ellipsometry task. The proposed approach allows to finding throifi eripsometric parameters the lattice mismatch effect on optical indicatrix of the considered stressed film.

Research paper thumbnail of The Growth of Single Crystals of InGaSe2 Compounds, Their X-Ray-Phase Analysis, Electronic Structure and Optical Functions

Open Journal of Inorganic Non-metallic Materials, 2013

Growing of InGaSe 2 single crystals has been carried out by employing the Brijman-Stockbargor met... more Growing of InGaSe 2 single crystals has been carried out by employing the Brijman-Stockbargor methods. On the base of X-ray-analysis it has been found that the given phase is crystallized into tetragonal symmetry. The temperature dependence of electric conductivity has been studied. Band structure has been computed. Optical functions, effective masses of electrons and holes have been calculated. Origin of formation of valence and conductance bands as well as the width of forbidden band for InGaSe 2 have been determined.

Research paper thumbnail of Second-order phase transition in a SnS orthorhombic crystal under pressure

Physics of the Solid State, 2015

Research paper thumbnail of AB-INITIO AND HUBBARD-SHAM MODEL CALCULATIONS OF BAND STRUCTURE OF GeSe

Mathematical Physics - Proceedings of the XI Regional Conference, 2005

The band structure of the GeSe crystals has been calculated by the Density Functional Theory (DFT... more The band structure of the GeSe crystals has been calculated by the Density Functional Theory (DFT) in the Local Density Approximation and using the Hubbard-Sham model screening. The nonlocal pseudo-potentials constructed by procedure offered G.B. Bachelet et al. For the exchange-correlation energy and potentials we use the Ceperley-Alder results parametrized by Perdew and Zunger. The results received within the Hubbard-Sham

Research paper thumbnail of The pressure dependence of the phonon spectra and elastic modulus of orthorhombic: the method of local density functional

The IR-and Raman-active phonon frequencies, as well as the elastic constants of orthorhombic , we... more The IR-and Raman-active phonon frequencies, as well as the elastic constants of orthorhombic , were calculatedas a function of hydrostatic pressure using the method of density functional in the ABINIT software package. Comparison with the published results of theoretical calculations and experimental data of the pressure dependence of Raman-active phonons has been carried out. Our calculations show that at a pressure of about 29 GPa the crystal structure of GeSe undergoes a continuous transition from simple orthorhombic to base-centered orthorhombic lattice.

Research paper thumbnail of Infrared study of the multiband low-energy excitations of the topological antiferromagnet MnBi2Te4

Physical Review B, 2021

With infrared spectroscopy we studied the bulk electronic properties of the topological antiferro... more With infrared spectroscopy we studied the bulk electronic properties of the topological antiferromagnet MnBi2Te4 with TN ≃ 25 K. With the support of band structure calculations, we assign the intra-and interband excitations and determine the band gap of Eg ≈ 0.17 eV. We also obtain evidence for two types of conduction bands with light and very heavy carriers. The multiband free carrier response gives rise to an unusually strong increase of the combined plasma frequency, ω pl , below 300 K. The band reconstruction below TN , yields an additional increase of ω pl and a splitting of the transition between the two conduction bands by about 54 meV. Our study thus reveals a complex and strongly temperature dependent multi-band low-energy response that has important implications for the study of the surface states and device applications.

Research paper thumbnail of Ab initio calculations and experimental study of piezoelectric Y In1−N thin films deposited using reactive magnetron sputter epitaxy

Acta Materialia, 2016

By combining theoretical prediction and experimental verification we investigate the piezoelectri... more By combining theoretical prediction and experimental verification we investigate the piezoelectric properties of yttrium indium nitride (Y x In 1−x N). Ab-initio calculations show that the Y x In 1−x N wurtzite phase is lowest in energy among relevant alloy structures for 0 ≤ x ≤ 0.5. Reactive magnetron sputter epitaxy was used to prepare thin films with Y content up to x = 0.51. The composition dependence of the lattice parameters observed in the grown films is in agreement with that predicted by the theoretical calculations confirming the possibility to synthesize a wurtzite solid solution. An AlN buffer layer greatly improves the crystalline quality and surface morphology of subsequently grown Y x In 1−x N films. The piezoelectric response in films with x = 0.09 and x = 0.14 is observed using piezoresponse force microscopy. Theoretical calculations of the piezoelectric properties predict Y x In 1−x N to have comparable piezoelectric properties to Sc x Al 1−x N.

Research paper thumbnail of Crystal structure and Raman-active lattice vibrations of magnetic topological insulators MnBi2Te4·n(Bi2Te3) ( n=0 , 1,...,6)

Physical Review B

Further to the structure of the intrinsic magnetic topological insulators MnBi2Te4 n(Bi2Te3) with... more Further to the structure of the intrinsic magnetic topological insulators MnBi2Te4 n(Bi2Te3) with n<4, where index n is the number of quintuple Te-BiTe -BiTe building blocks inserted between the neighboring septuple Te-BiTe -Mn-Te-BiTe building blocks, the structure of the members with n=4, 5 and 6 was studied using X-ray powder diffraction. The unit cell parameters and atomic positions were calculated. The obtained and available structural data were summarized to show that the crystal structure of all members of MnBi2Te4 n(Bi2Te3) follows the cubic close packing principle, independently of the space group of the given member. Confocal Raman spectroscopy was then applied. Comparative analysis of the number, frequency, symmetry, and broadening of the vibration modes responsible for the lines in the Raman spectra of the systems with n=1,.. . ,6, as well as MnBi2Te4 (n=0) and Bi2Te3 (n=) has shown that lattice dynamics of MnBi2Te4 n(Bi2Te3) with n>0 overwhelmingly dominates by the cooperative atomic displacements in the quintuple building blocks. I.

Research paper thumbnail of Intercalation of p-Aminopyridine and p-Ethylenediamine Molecules into Orthorhombic In1.2Ga0.8S3 Single Crystals

Materials

A single crystalline layered semiconductor In1.2Ga0.8S3 phase was grown, and by intercalating p-a... more A single crystalline layered semiconductor In1.2Ga0.8S3 phase was grown, and by intercalating p-aminopyridine (NH2-C5H4N or p-AP) molecules into this crystal, a new intercalation compound, In1.2Ga0.8S3·0.5(NH2-C5H4N), was synthesized. Further, by substituting p-AP molecules with p-ethylenediamine (NH2-CH2-CH2-NH2 or p-EDA) in this intercalation compound, another new intercalated compound—In1.2Ga0.8S3·0.5(NH2-CH2-CH2-NH2) was synthesized. It was found that the single crystallinity of the initial In1.2Ga0.8S3 samples was retained after their intercalation despite a strong deterioration in quality. The thermal peculiarities of both the intercalation and deintercalation of the title crystal were determined. Furthermore, the unit cell parameters of the intercalation compounds were determined from X-ray diffraction data (XRD). It was found that increasing the c parameter corresponded to the dimension of the intercalated molecule. In addition to the intercalation phases’ experimental chara...

Research paper thumbnail of Bulk Modulus, Elastic Constants, and Force Constants of Interatomic Bonds of II–III2–VI4 Compounds

physica status solidi (b)

Ab initio density functional perturbation theory is used to calculate the elastic constants of Cd... more Ab initio density functional perturbation theory is used to calculate the elastic constants of CdGa2S4, CdGa2Se4, CdGa2Te4, and ZnGa2Se4 thiogallates. The values of the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio are determined. The force constants of interatomic bonds in CdGa2Te4 and ZnGa2Se4 compounds are calculated. Regularities in the dependence of the frequencies of Raman‐active phonons on the atomic masses are established.

Research paper thumbnail of Electronic structure of the Ge and Se vacancies in GeSe layered semiconductor

Turkish Journal of Physics

We report the results of a theoretical investigation of electronic properties of ideal cation and... more We report the results of a theoretical investigation of electronic properties of ideal cation and anion vacancies in GeSe. The calculations have been performed using self-consistent Green's function method. The bulk electronic structure is described by a tight-binding Hamiltonian ...

Research paper thumbnail of CSD 2116458: Experimental Crystal Structure Determination

Research paper thumbnail of Optical and Dynamic Properties of ZnGa 2 S 4

physica status solidi (b), 2021

Research paper thumbnail of Synthesis and characterization of new indium gallium selenides of the InSe-GaSe system

Journal of Solid State Chemistry, 2021

Abstract The new solid solution phases crystallized in the hexagonal and tetragonal system were r... more Abstract The new solid solution phases crystallized in the hexagonal and tetragonal system were revealed in the GaSe-InSe system, and a new orthorhombic phase with a new type of structural blocks has been proposed. The structural features of the In1-xGaxSe solid solutions (where 0 ​≤ ​x ​≤ ​1) were studied using X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), and Raman spectroscopy. The chemical interaction between Ga and In atoms in the hexagonal In1-xGaxSe phases was identified. The reversible phase transition from hexagonal to the tetragonal structure was found to occur in the In0.7Ga0.3Te phase. Using the Density Functional Theory (DFT) method, the electronic, optical, and vibrational properties for the Pnnm orthorhombic InGaSe2 phase were studied. Modified Becke-Johnson exchange potential and generalized gradient approximations (mBJ-GGA) were used to calculate the electronic band structure, dielectric function, and density of states (DOS) of InGaSe2, which solve the band-gap problem found within GGA approach. The InGaSe2 stoichiometric phase was found to be a direct band-gap semiconductor and the band gap of this compound can be tuned via the different stacking sequences of InSe/GaSe layers. The optical absorption edges which are observed in the visible light region make this compound promising material for photovoltaic applications. The calculated phonon spectra of the InGaSe2 revealed that the frequencies of the optic modes are close to frequencies of acoustic modes, which carry the heat flow, and in this case, the acoustic modes will be strongly scattered by low-frequency optic modes. The latter event may lead to a low lattice thermal conductivity that is important for thermoelectric applications. The phonon dispersion of this compound shows no imaginary modes, suggesting that it is dynamically stable.

Research paper thumbnail of Infrared spectroscopic ellipsometry and optical spectroscopy of plasmons in classic 3D topological insulators

Journal of Vacuum Science & Technology B, 2019

Research paper thumbnail of CrAs Monolayer: Low Buckled Two‐Dimensional Half‐Metal Ferromagnet

physica status solidi (RRL) – Rapid Research Letters, 2019

Ab-initio calculations based on density functional theory (DFT) are performed to study the struct... more Ab-initio calculations based on density functional theory (DFT) are performed to study the structural, electronic, and magnetic properties of two-dimensional (2D) free-standing honeycomb CrAs. We show that CrAs has low buckled stable structure. Magnetic CrAs has larger buckling than non-magnetic CrAs. 2D-CrAs is a ferromagnetic semiconductor for lattice constant a ≤ 3.71Å, and above this lattice constant CrAs is a half-metal ferromagnet. 2D-CrAs is shown to be half-metal ferromagnetic with magnetic moment of 3.0µB per unit cell, at equilibrium structure. The d 2 z orbital of eg band is completely empty in the spin-down state whereas it is almost occupied in the spin-up state, and the magnetic moment in the eg band is mainly dominated by the d 2 z orbital of Cr. The dzx/dzy and dxy orbitals of t2g band are partially occupied in the spin-up state and behaves as metal whereas they are insulator in the spin-down state. Phonon calculations confirm the thermodynamic stability of 2D-CrAs. The ferromagnetic (FM) and antiferromagnetic (AFM) interaction between the Cr atoms reveal that the FM state is more stable than the AFM state of 2D-CrAs.

Research paper thumbnail of Novel ternary layered manganese bismuth tellurides of the MnTe-Bi2Te3 system: Synthesis and crystal structure

Journal of Alloys and Compounds, 2019

Research paper thumbnail of Ellipsometric characterization of MoSe2 thin layers obtained by thermal treatment of molybdenum in selenium vapor

Applied Surface Science, 2017

 MoSe2 layers are obtained by thermal treatment of molybdenum in selenium vapor.  Spectroscopic... more  MoSe2 layers are obtained by thermal treatment of molybdenum in selenium vapor.  Spectroscopic ellipsometry is applied to the obtained layers and MoSe2 target.  Electronic band structure of MoSe2 is calculated and dielectric function is derived.  Calculated and ellipsometry-based data on dielectric function agree fairly well.  Excitonic transitions are assumed to form the dielectric function at around 1 eV.

Research paper thumbnail of First-principles lattice dynamics and Raman scattering in ionic conductor β-Ag2 S

physica status solidi (b), 2016

The phonon structure of the silver sulfide Ag2S was investigated, experimentally using Raman spec... more The phonon structure of the silver sulfide Ag2S was investigated, experimentally using Raman spectroscopy, and theoretically using the density‐functional perturbation theory for the first time. Seven Raman‐active modes were observed and identified at 23, 39, 42, 44, 62, 65, and 243 cm−1. Symmetry assignments of all the vibrational modes were derived from considerations of point group symmetry. The phonon band structure and the relative Raman intensities were also investigated by ab initio calculations and compared with the experimental data. The temperature, laser power, and illumination time dependencies of frequency, linewidth, and intensity of the Raman‐active modes are discussed. In the Raman spectra at higher frequencies 1300–1700 cm−1, additional broad Raman modes observed in all samples at higher laser powers 8–10 mW were ascribed to luminescence from β‐Ag2S. The phonon and Raman spectra of the β‐Ag2S provide a useful insight into the β‐Ag2S → α‐Ag2S phase transition. Finally, calculated infrared vibrational mode frequencies were compared with measured infrared mode frequencies.

Research paper thumbnail of Electronic Structure of Surfaces in GeSe Layered Semiconductor

Green´s function method in bases sets of Linear Combinations of Atomic Orbitals (LCAO) is used to... more Green´s function method in bases sets of Linear Combinations of Atomic Orbitals (LCAO) is used to calculate the electronic structure of the (010) surface of GeSe semiconductor. The energy states in energy gaps, their origin, orbital content, resonances and local changes in the density of states due to the surface are discussed.

Research paper thumbnail of DIRECT ELLIPSOMETRY TASK FOR ZnS/GaAs, ZnSe/GaAs and CuGaS2/GaP THIN FILM/SUBSTRATE SYSTEMS

In this work ellipsometric approach has been developed for ZnSlGaAs, ZnSelGaAs and CuGaS2/GaP fil... more In this work ellipsometric approach has been developed for ZnSlGaAs, ZnSelGaAs and CuGaS2/GaP film/substrate systems to solve direct ellipsometry task. The proposed approach allows to finding throifi eripsometric parameters the lattice mismatch effect on optical indicatrix of the considered stressed film.

Research paper thumbnail of The Growth of Single Crystals of InGaSe2 Compounds, Their X-Ray-Phase Analysis, Electronic Structure and Optical Functions

Open Journal of Inorganic Non-metallic Materials, 2013

Growing of InGaSe 2 single crystals has been carried out by employing the Brijman-Stockbargor met... more Growing of InGaSe 2 single crystals has been carried out by employing the Brijman-Stockbargor methods. On the base of X-ray-analysis it has been found that the given phase is crystallized into tetragonal symmetry. The temperature dependence of electric conductivity has been studied. Band structure has been computed. Optical functions, effective masses of electrons and holes have been calculated. Origin of formation of valence and conductance bands as well as the width of forbidden band for InGaSe 2 have been determined.

Research paper thumbnail of Second-order phase transition in a SnS orthorhombic crystal under pressure

Physics of the Solid State, 2015

Research paper thumbnail of AB-INITIO AND HUBBARD-SHAM MODEL CALCULATIONS OF BAND STRUCTURE OF GeSe

Mathematical Physics - Proceedings of the XI Regional Conference, 2005

The band structure of the GeSe crystals has been calculated by the Density Functional Theory (DFT... more The band structure of the GeSe crystals has been calculated by the Density Functional Theory (DFT) in the Local Density Approximation and using the Hubbard-Sham model screening. The nonlocal pseudo-potentials constructed by procedure offered G.B. Bachelet et al. For the exchange-correlation energy and potentials we use the Ceperley-Alder results parametrized by Perdew and Zunger. The results received within the Hubbard-Sham

Research paper thumbnail of The pressure dependence of the phonon spectra and elastic modulus of orthorhombic: the method of local density functional

The IR-and Raman-active phonon frequencies, as well as the elastic constants of orthorhombic , we... more The IR-and Raman-active phonon frequencies, as well as the elastic constants of orthorhombic , were calculatedas a function of hydrostatic pressure using the method of density functional in the ABINIT software package. Comparison with the published results of theoretical calculations and experimental data of the pressure dependence of Raman-active phonons has been carried out. Our calculations show that at a pressure of about 29 GPa the crystal structure of GeSe undergoes a continuous transition from simple orthorhombic to base-centered orthorhombic lattice.