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Nizami Gasanly

Bio: Nizami Gasanly is an academic researcher from Middle East Technical University. The author has contributed to research in topics: Band gap & Thermoluminescence. The author has an hindex of 22, co-authored 362 publications receiving 2539 citations. Previous affiliations of Nizami Gasanly include Atılım University & Russian Academy of Sciences.


Papers
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TL;DR: In this article, the polarized Raman spectra of InSe and InS crystals are obtained, the assignment of frequencies is given, and atomic displacements are found at all normal vibrations.
Abstract: Polarized Raman spectra of InSe and InS crystals are obtained, the assignment of frequencies is given, and atomic displacements are found at all normal vibrations. In the InSe crystal, force constants of interaction of In-Se and In-In atomic planes are evaluated. It is shown that the Raman spectrum of InS has a doublet nature typical for layer crystals. The frequencies of rigid-layer modes forbidden in the Raman spectrum are calculated in the InS crystal. It is found that interlayer force constants in the InS crystal are only 5 to 10 times smaller than the intralayer covalentbond force constants. [Russian Text Ignored].

50 citations

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TL;DR: In this article, a simple model calculation indicates that the recombination centers are most likely located at the nearest neighbor lattice or interstitial sites and that all of them originate from close donor-acceptor pair recombination processes.
Abstract: Low temperature photoluminescence of GaS single crystals shows three broad emission bands below 2.4 eV. Temperature and excitation light intensity dependencies of these bands reveal that all of them originate from close donor–acceptor pair recombination processes. Temperature dependence of the peak energies of two of these bands in the visible range follow, as expected, the band gap energy shift of GaS. However, the temperature dependence of the peak energy of the third band in the near infrared shows complex behavior by blueshifting at low temperatures followed by a redshift at intermediate temperatures and a second blueshift close to room temperature, which could only be explained via a configuration coordinate model. A simple model calculation indicates that the recombination centers are most likely located at the nearest neighbor lattice or interstitial sites.

50 citations

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TL;DR: In this article, the polarization properties of bands in Raman scattering and IR reflection spectra are studied experimentally in TlGaS2, Tl GaSe2, and TlInS2 layer single crystals and in solid solutions based on them.
Abstract: The polarization properties of bands in Raman scattering and IR reflection spectra are studied experimentally in TlGaS2, TlGaSe2, and TlInS2 layer single crystals and in solid solutions based on them. Additionally the angular dependence of IR-active modes on the angle between the phonon wave vector and the direction of the optical axis c of single crystals is investigated. It is shown that the observed phonon spectra can be interpreted on the basis of a primitive cell which contains two tetragonal-symmetry layers bonded to each other by an inversion operation. Bands corresponding to cells with a mixed composition are observed in the Raman spectra of the solid solutions. [Russian Text Ignored].

49 citations

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TL;DR: In this paper, the photoluminescence (PL) spectra of AgIn5S8 single crystals were investigated in the 1.44-1.91 eV energy region and in the 10-170 K temperature range.
Abstract: Photoluminescence (PL) spectra of AgIn5S8 single crystals were investigated in the 1.44–1.91 eV energy region and in the 10–170 K temperature range. The PL band was observed to be centered at 1.65 eV at 10 K and an excitation intensity of 0.97 W cm−2. The redshift of this band with increasing temperature and with decreasing excitation intensity was observed. To explain the observed PL behavior, we propose that the emission is due to radiative recombination of a donor-acceptor pair, with an electron occupying a donor level located at 0.06 eV below the conduction band, and a hole occupying an acceptor level located at 0.32 eV above the valence band.

44 citations


Cited by
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TL;DR: This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility.
Abstract: This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), en...

636 citations

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TL;DR: In this article, the preparation, isolation and rapid unambiguous characterization of large size ultrathin layers of MoS2, GaS, and GaSe deposited onto SiO2/Si substrates is reported.
Abstract: There has been emerging interest in exploring single-sheet 2D layered structures other than graphene to explore potentially interesting properties and phenomena. The preparation, isolation and rapid unambiguous characterization of large size ultrathin layers of MoS2, GaS, and GaSe deposited onto SiO2/Si substrates is reported. Optical color contrast is identified using reflection optical microscopy for layers with various thicknesses. The optical contrast of these thin layers is correlated with atomic force microscopy (AFM) and Raman spectroscopy to determine the exact thickness and to calculate number of the atomic layers present in the thin flakes and sheets. Collectively, optical microscopy, AFM, and Raman spectroscopy combined with Raman imaging data are analyzed to determine the thickness (and thus, the number of unit layers) of the MoS2, GaS, and GaSe ultrathin flakes in a fast, non-destructive, and unambiguous manner. These findings may enable experimental access to and unambiguous determination of layered chalcogenides for scientific exploration and potential technological applications.

456 citations

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TL;DR: In this article, a non-crystalline thin films of chalcogenide Cd 50 S 50−x Se x system were obtained by thermal evaporation technique onto a pre-cleaned glass substrate at a vacuum of 8.2 × 10 −4 ǫ.

412 citations

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TL;DR: This work utilizes Raman spectroscopy and X-ray absorptionSpectroscopy as a tool to elucidate the structure and function of an amorphous cobalt sulfide (CoSx) catalyst and surmise that these CoS2-like clusters form under cathodic polarization and expose a high density of catalytically active sulfur sites for the HER.
Abstract: The generation of chemical fuel in the form of molecular H2 via the electrolysis of water is regarded to be a promising approach to convert incident solar power into an energy storage medium. Highly efficient and cost-effective catalysts are required to make such an approach practical on a large scale. Recently, a number of amorphous hydrogen evolution reaction (HER) catalysts have emerged that show promise in terms of scalability and reactivity, yet remain poorly understood. In this work, we utilize Raman spectroscopy and X-ray absorption spectroscopy (XAS) as a tool to elucidate the structure and function of an amorphous cobalt sulfide (CoSx) catalyst. Ex situ measurements reveal that the as-deposited CoSx catalyst is composed of small clusters in which the cobalt is surrounded by both sulfur and oxygen. Operando experiments, performed while the CoSx is catalyzing the HER, yield a molecular model in which cobalt is in an octahedral CoS2-like state where the cobalt center is predominantly surrounded by a first shell of sulfur atoms, which, in turn, are preferentially exposed to electrolyte relative to bulk CoS2. We surmise that these CoS2-like clusters form under cathodic polarization and expose a high density of catalytically active sulfur sites for the HER.

302 citations

Journal ArticleDOI
Xin Zhang1, Qing-Hai Tan1, Jiang-Bin Wu1, Wei Shi1, Ping-Heng Tan1 
TL;DR: A unified method based on symmetry analysis and polarization measurements to assign the observed Raman modes and characterize the crystal structure of different types of LMs is introduced, and the recent advances on Raman spectroscopy in the characterization of anisotropic LMs, such as black phosphorus and rhenium diselenide are reviewed.
Abstract: Two-dimensional layered materials, such as graphene and transition metal dichalcogenides (TMDs), have been under intensive investigation. The rapid progress of research on graphene and TMDs is now stimulating the exploration of different types of layered materials (LMs). Raman spectroscopy has shown its great potential in the characterization of layer numbers, interlayer coupling and layer-stacking configurations and will benefit the future explorations of other LMs. Lattice vibrations or Raman spectra of many LMs in bulk have been discussed since the 1960s. However, different results were obtained because of differences or limitations in the Raman instruments at early stages. The developments of modern Raman spectroscopy now allow us to revisit the Raman spectra of these LMs under the same experimental conditions. Moreover, to the best of our knowledge, there were limitations in detailed reviews on the Raman spectra of these different LMs. Here, we provide a review on Raman spectra of various LMs, including semiconductors, topological insulators, insulators, semi-metals and superconductors. We firstly introduce a unified method based on symmetry analysis and polarization measurements to assign the observed Raman modes and characterize the crystal structure of different types of LMs. Then, we revisit and update the positions and assignments of vibration modes by re-measuring the Raman spectra of different types of LMs and by comparing our results to those reported in previous papers. We apply the recent advances on the interlayer vibrations of graphene and TMDs to these various LMs and obtain their shear modulus. The observation of the shear modes of LMs in bulk facilitates an accurate and fast characterization of layer numbers during preparation processes in the future by a robust layer-number dependency on the frequencies of the shear modes. We also summarize the recent advances on the layer-stacking dependence on the intensities of interlayer shear vibrations. Finally, we review the recent advances on Raman spectroscopy in the characterization of anisotropic LMs, such as black phosphorus and rhenium diselenide. We believe that this review will benefit the future research studies on the fundamental physics and potential applications of these various LMs, particularly when they are reduced down to monolayers or multilayers.

289 citations