Raman scattering study of zinc blende and wurtzite ZnS
TL;DR: In this article, the first and second-order Raman scattering of zinc blende and wurtzite ZnS was studied and the origins of these vibration modes in the second order Raman spectra from these two polymorphs were identified for the first time.
Abstract: We have conducted an experimental and theoretical study on first- and second-order Raman scattering of zinc blende and wurtzite ZnS. Based on the calculated phonon band structure, phonon density of states, and symmetry selection rules, we have clearly identified for the first time the origins of these vibration modes in the second-order Raman spectra from these two polymorphs. For zinc blende ZnS, it is found that the previously estimated frequency of the LA mode at X point in the Brillouin-zone boundary is much smaller than the value obtained from other experiments and our calculation. Considering the involvement of LA phonon at X point, we reassign the second-order Raman active modes and some other modes which have not yet been understood so far. This work clarifies some of the controversial Raman mode assignments in zinc blende and wurtzite ZnS.
Citations
More filters
TL;DR: In this article, zinc vacancy defects are successfully introduced into zinc sulfide (ZnS) via adding sodium sulfide as sulfur source during the hydrothermal reaction, and the defective ZnS with different amount of zinc vacancies were employed as catalysts for the examination of vacancy-dependent catalytic activity toward photocatalytic hydrogen evolution under visible light irradiation.
Abstract: Zinc sulfide is a superior photocatalyst for H 2 evolution, whereas the wide bandgap restricts its performance to only UV region. In this work, zinc vacancy (V Zn ) defects are successfully introduced into ZnS via adding sodium sulfide as sulfur source during the hydrothermal reaction. The defective ZnS with different amount of zinc vacancies were employed as catalysts for the examination of vacancy-dependent catalytic activity toward photocatalytic hydrogen evolution under visible light irradiation. Fluorescence emission spectra and XPS results confirm that existence of abundant zinc vacancies on ZnS. These zinc vacancies exhibit remarkable effects on modifying the electronic structure of ZnS as shown in UV–visible absorption spectra and Mott–Schottky plots. Zinc vacancies can raise valence band (VB) position that weaken the oxidative capacity of the holes to protect Zn-deficient ZnS from photocorrsion. And electrochemical and photo-electrochemical experiments also demonstrate that the charge separation and the electrons transfer are more efficient with the introduction of the Zn vacancies in ZnS. The zinc-deficient ZnS-2.5 with optimum amount of Zn vacancies shows superior photocatalytic activity for H 2 evolution that reaches 337.71 ± 3.72 μmol h −1 g −1 under visible-light irradiation and also exhibits a much higher photostability. The intrinsic modify by self-defects might be a potential strategy for design novel photocatalysts with photocorrosion stability and visible-light activity in photocatalysis proton reduction.
391 citations
TL;DR: In this article, confocal Raman spectroscopy and imaging can distinguish between CZTS and the other binary and ternary metal sulfides, which is a potential candidate for next generation thin film solar cells.
Abstract: Copper zinc tin sulfide (Cu2ZnSnS4 or CZTS) is a potential candidate for next generation thin film solar cells because it contains abundant and nontoxic elements and exhibits high light absorption. Thin films of CZTS are typically synthesized by sulfidizing a stack of zinc, copper, and tin films. In addition to CZTS, a variety of binary and ternary metal sulfides can form and distinguishing among phases with similar crystal structure can be difficult. Herein, the authors show that confocal Raman spectroscopy and imaging can distinguish between CZTS and the other binary and ternary sulfides. Specifically, Raman spectroscopy was used to detect and distinguish between CZTS (338 cm−1), Cu2SnS3 (298 cm−1), and Cu4SnS4 (318 cm−1) phases through their characteristic scattering peaks. Confocal Raman spectroscopy was then used to image the distribution of coexisting phases and is demonstrated to be a useful tool for examining the heterogeneity of CZTS films. The authors show that, during sulfidation of a zinc/copp...
242 citations
TL;DR: The synthesis of alloyed quaternary and quinary nanocrystals based on copper chalcogenides with tunable chemical composition were characterized by optical spectroscopy and cyclic voltammetry, which demonstrated tunability of their light absorption characteristics as well as their electrochemical band gaps.
Abstract: We report the synthesis of alloyed quaternary and quinary nanocrystals based on copper chalcogenides, namely, copper zinc selenide–sulfide (CZSeS), copper tin selenide–sulfide (CTSeS), and copper zinc tin selenide–sulfide (CZTSeS) nanoplatelets (NPLs) (∼20 nm wide) with tunable chemical composition. Our synthesis scheme consisted of two facile steps: i.e., the preparation of copper selenide–sulfide (Cu2–xSeyS1–y) platelet shaped nanocrystals via the colloidal route, followed by an in situ cation exchange reaction. During the latter step, the cation exchange proceeded through a partial replacement of copper ions by zinc or/and tin cations, yielding homogeneously alloyed nanocrystals with platelet shape. Overall, the chemical composition of the alloyed nanocrystals can easily be controlled by the amount of precursors that contain cations of interest (e.g., Zn, Sn) to be incorporated/alloyed. We have also optimized the reaction conditions that allow a complete preservation of the size, morphology, and crysta...
128 citations
TL;DR: In this article, the area ratios between the first, second, and third order peaks of ZnS identified as the T2(LO) mode decrease with increasing grain size, attributed to changes in the bandgap energy from quantum confinement due to the varying grain size between the films/particles.
Abstract: Near-resonant Raman scattering measurements of zinc sulfide nanoparticles and thin films have been made and correlated to grain and particle size, respectively, using a 325 nm wavelength excitation source. The area ratios between the first, second, and third order peaks of ZnS identified as the T2(LO) mode decrease with increasing ZnS grain size. This is an effect attributed to changes in the bandgap energy from quantum confinement due to the varying grain size between the films/particles, as noted by a shift in the room temperature photoluminescence emission corresponding to the free exciton emission energy. While Raman scattering spectroscopy is typically limited to identification of phases and their crystalline properties, it is possible to attain more than such straightforward information by calibrating the spectral features to variations between sets of samples. These results open the possibility of making a quantitative grain size estimation in ZnS thin films and nanostructures, as well as in other material systems where ZnS may be expected as a secondary phase, such as Cu2ZnSnS4. Additionally, more commonly used excitation wavelengths for Raman scattering, such as 514 and 532 nm, are shown to be of limited use in characterizing ZnS thin films due to the extremely low Raman scattering efficiency of ZnS in films with sub-micron thicknesses.
115 citations
108 citations
References
More filters
TL;DR: In this paper, the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method, is reviewed.
Abstract: This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudopotential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long-wavelength vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.
6,917 citations
TL;DR: In this paper, a Raman scattering study of wurtzite was carried out over a temperature range from 80 to 750°C, where the second-order Raman features were interpreted in the light of recent ab initio phonon density of states calculations.
Abstract: We present a Raman scattering study of wurtzite $\mathrm{ZnO}$ over a temperature range from 80 to $750\phantom{\rule{03em}{0ex}}\mathrm{K}$ Second-order Raman features are interpreted in the light of recent ab initio phonon density of states calculations The temperature dependence of the Raman intensities allows the assignment of difference modes to be made unambiguously Some weak, sharp Raman peaks are detected whose temperature dependence suggests they may be due to impurity modes High-resolution spectra of the ${E}_{2}^{\mathrm{high}}$, ${A}_{1}(\mathrm{LO})$, and ${E}_{1}(\mathrm{LO})$ modes were recorded, and an analysis of the anharmonicity and lifetimes of these phonons is carried out The ${E}_{2}^{\mathrm{high}}$ mode displays a visibly asymmetric line shape This can be attributed to anharmonic interaction with transverse and longitudinal acoustic phonon combinations in the vicinity of the $K$ point, where the two-phonon density of states displays a sharp edge around the ${E}_{2}^{\mathrm{high}}$ frequency The temperature dependence of the linewidth and frequency of the ${E}_{2}^{\mathrm{high}}$ mode is well described by a perturbation-theory renormalization of the harmonic ${E}_{2}^{\mathrm{high}}$ frequency resulting from the interaction with the acoustic two-phonon density of states In contrast, the ${A}_{1}(\mathrm{LO})$ and ${E}_{1}(\mathrm{LO})$ frequencies lie in a region of nearly flat two-phonon density of states, and they exhibit a nearly symmetric Lorentzian line shape with a temperature dependence that is well accounted for by a dominating asymmetric decay channel
1,217 citations
TL;DR: In this article, first and second-order Raman scattering in cubic and hexagonal boron nitride using excitation energies in the visible and in the UV was measured.
Abstract: We measured first- and second-order Raman scattering in cubic and hexagonal boron nitride using excitation energies in the visible and in the UV. The nonresonant first-order Raman susceptibilities for cubic and hexagonal BN are 1 and $10\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{2}$, respectively. Raman scattering is thus very powerful in detecting the hexagonal phase in mixed thin boron nitride films. In cubic BN the constant Raman sucseptibility in the visible and the UV is due to its indirect band gap. For hexagonal BN a Raman enhancement is found at $5.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. It is well explained by the energy dependence of the dielectric function of hexagonal BN. The second-order spectrum of cubic boron nitride is in excellent agreement with first-principles calculations of the phonon density of states. In hexagonal BN the overbending of the LO phonon is $\ensuremath{\approx}100\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, five times larger than in graphite.
358 citations
TL;DR: The signature of 3- and 4-membered rings in the Raman spectra of several polymorphs of SiO2, including a zeolite having 102 atoms per unit cell is studied.
Abstract: We present an approach for the efficient calculation of vibrational Raman intensities in periodic systems within density functional theory. The Raman intensities are computed from the second order derivative of the electronic density matrix with respect to a uniform electric field. In contrast to previous approaches, the computational effort required by our method for the evaluation of the intensities is negligible compared to that required for the calculation of vibrational frequencies. As a first application, we study the signature of 3- and 4-membered rings in the Raman spectra of several polymorphs of SiO2, including a zeolite (H-ZSM-18) having 102 atoms per unit cell.
314 citations
TL;DR: In this paper, the second-order Raman-scattering experiments on hexagonal and cubic GaN covering the acoustic and the optical overtone spectral region were presented, and the observed structures were assigned to particular phonon branches and determined the points in the Brillouin zone from which the scattering originates.
Abstract: We present results of second-order Raman-scattering experiments on hexagonal and cubic GaN covering the acoustic and the optical overtone spectral region. Based on a comparison of the experimental scattering data with the calculated phonon-dispersion curves as well as the group-theoretically derived selection rules, we were able to assign the observed structures to particular phonon branches and determined the points in the Brillouin zone from which the scattering originates. Our measurements reveal the energies of acoustic zone-boundary phonons in hexagonal GaN.
284 citations