Transverse Optical Research Articles

Simultaneous Generation of Two Orthogonally Polarized Terahertz Waves by Stimulated Polariton Scattering with a Periodically Poled LiNbO3 Crystal

We present a theoretical investigation of the simultaneous generation of two orthogonally polarized terahertz (THz) waves by stimulated polariton scattering (SPS) with a periodically poled LiNbO3 (PPLN) crystal. The two orthogonally polarized THz waves are generated from SPS with A1 and E symmetric transverse optical (TO) modes in a LiNbO3 crystal, respectively. The parallel polarized THz wave is generated from A1 symmetric TO modes with type-0 phase-matching of e = e + e, and the perpendicular polarized THz wave is generated from E symmetric TO modes with type-I phase-matching of e = o + o. The two types of phase-matching of e = e + e and e = o + o can be almost satisfied simultaneously by accurately selecting the poling period of the PPLN crystal. We calculate the photon flux density of the two orthogonally polarized THz waves by solving the coupled wave equations. The calculation results indicate that the two orthogonally polarized THz waves can be efficiently generated, and the relative intensities between the two orthogonally polarized THz waves can be modulated.

Structural, Optical and Magnetic Properties of NiO Nanopowders.

Nickel oxide (NiO) nanopowders were synthesized without using surfactant by chemical reduction technique. NaBH4 influence on structural, optical and magnetic properties of NiO product was investigated. XRD results revealed the formation of dominant single phase, cubic face centered nickel oxide. Raman peaks depicts the characteristic first-order transverse optical (TO) phonon, two phonon excitation (TO + LO), excitation (2LO) Raman mode vibrations of face centered cubic NiO. PL studies revealed the presence of strong emission band which is in good agreement with the intrinsic NiO product. FTIR studies explored metal oxygen vibrations of the obtained product. TEM results revealed the nanoscale product with spherical shape structures. VSM studies explored weak ferromagnetic behavior of the obtained product. High concentration of NaBH4 increases magnetization value and exhibits the typical weak ferromagnetic curve. Reducing agent played a vital role in the structural, optical and magnetic properties of the obtained NiO product.

Anharmonic phonon decay in polycrystalline CdTe thin film

The anharmonic decay of both the longitudinal optical phonon (LO) and its overtone (2LO) was found to decay asymmetrically into a transverse optical (TO) and a transverse acoustic (TA) phonon, both of which are at the L point along the Γ-L direction of the Brillouin zone. For the LO and its overtone 2LO, both the Raman shift and Raman linewidth were decreased/increased almost linearly with the temperature in the range of 78–523 K. This temperature-dependent phonon decay characteristics were induced by LO anharmonic decay to the TA phonon with an energy of only ∼29 cm−1. A TA phonon mode with such low energy is readily excited, and its phonon density is almost linearly increased with increased temperature. Strong multi-phonon scatterings, which involved the LO, the surface optical mode, and the TO, were funded to contribute to the anharmonic decay of the 1LO, especially at temperature higher than room temperature.

Characterization of Inhomogeneity in Thermal Oxide SiO<sub>2</sub> Films on 4H-SiC Epitaxial Substrates by a Combination of Fourier Transform Infrared Spectroscopy and Cathodoluminescence Spectroscopy

We measured Fourier transform infrared (FT-IR) and cathodoluminescence (CL) spectra of SiO2 films with a various thickness, grown on 4H-SiC substrates. The peak frequency of the transverse optical (TO) phonon mode was blue-shifted by about 5 cm−1 as the oxide-layer thickness decreased from 50-60 nm to 10 nm. The blue shift of the TO mode is considerd to be caused by interfacial compressive stresses in the oxide-layer. On the other hand, the TO phonon mode was found to dramatically decrease as the oxide-layer thickness decreased from 10 nm to 1.7 nm. The CL measurement indicates that the intensity of the CL peaks at about 460 and 490 nm attributed to oxygen vacancy centers (OVCs) for No.2 become stronger than that for No.1. From a comparison between FT-IR and CL measurements, we concluded that the red-shift of the TO phonon with decreasing the oxide-layer thickness can mainly be attributed to an increase in inhomogeneity at the SiO2/SiC interface with decreasing oxide-layer thickness.

Effect of particle size on the optical properties of lead zirconate titanate nanopowders

AbstractNanopowder samples of lead zirconate titanate (Pb1.1Zr0.52Ti0.48O3 or PZT) were prepared by the sol‐gel method with controlled pH values. The samples were characterized using FTIR spectroscopy, XRD, FE‐SEM, and TEM techniques. Most of the peaks in the XRD pattern were related to the coexistence of tetragonal‐rhombohedral phases and confirmed the formation of PZT with a perovskite structure. Also, the crystallite size of PZT nanopowders was in a range of 17‐28 nm. FTIR spectroscopy revealed a longitudinal optical (LO) and transverse optical (TO) phonon modes corresponding to the stretching vibration of Ti‐O and Zr‐O bonds. The influence of pH values on the LO and TO phonon modes, LO‐TO splitting, refractive index n(ω), extinction coefficient k(ω), and the real ɛ1(ω) and imaginary ɛ2(ω) parts of dielectric function was discussed. These properties were investigated in the mid‐infrared region (450‐750 cm−1). The energy loss function Im[−1/(ɛ)] of PZT nanopowders was obtained by Kramers‐Kronig dispersion relations. The TO phonon frequency decreases with increasing crystallite size of the PZT samples. This effect does not happen at pH 8 to pH 9. As the crystallite size increased from 17.26 nm (at pH 5) to 27.25 nm (at pH 7), the LO‐TO splitting increased as well. This result showed that the optimum pH for absorption of IR radiation and optical application was at pH 7.

Soft phonon modes and diffuse scattering in Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 relaxor ferroelectrics

0.29Pb(In1/2Nb1/2)O3-0.45Pb(Mg1/3Nb2/3)O3-0.26PbTiO3 single crystals have been studied using triple-axis based elastic and inelastic neutron scattering. Elastic diffuse scattering reveals the presence of polar nano-regions (PNR's) in this system, which emerge at the Burns temperature (TB ∼630 K) and then grow continuously in population and correlation size down to 100 K. At 300 K, characteristic “butterfly” and ellipsoid shaped diffuse scattering patterns are observed in the HK0 scattering plane. Electrical poling along the [110] direction produces a marked asymmetry in the diffuse scattering patterns, with the parallel-to-the-field components enhanced while the perpendicular-to-the-field components suppressed. Several low-energy phonon branches along the [100] and [110] directions have been measured. Most significantly, the PNR-acoustic phonon coupling is confirmed for the [110] transverse acoustic (TA) phonons polarized along the [1-10] real space direction and the [100] TA phonons. This coupling appears to be anisotropic and correlated with the PNRs' distribution, and also affected by the relative length scales of the PNRs and phonon wave vectors. The well-known “waterfall” phenomenon is observed on the [100] and [110] transverse optical (TO) branches, near the zone center. The optical phonons exhibit a lowest-energy, zone center soft TO mode, whose squared energy increases linearly with decreasing temperature below TB.

Charge transfer dynamical processes at graphene-transition metal oxides/electrolyte interface for energy storage: Insights from in-situ Raman spectroelectrochemistry

Hybrids consisting of supercapacitive functionalized graphene (graphene oxide; GO reduced graphene oxide; rGO multilayer graphene; MLG, electrochemically reduced GO; ErGO) and three-dimensional graphene scaffold (rGOHT; hydrothermally prepared) decorated with cobalt nanoparticles (CoNP), nanostructured cobalt (CoO and Co3O4) and manganese (MnO2) oxide polymorphs, assembled electrochemically facilitate chemically bridged interfaces with tunable properties. Since Raman spectroscopy can capture variations in structural and chemical bonding, Raman spectro-electrochemistry in operando i.e. under electrochemical environment with applied bias is employed to 1) probe graphene/metal bonding and dynamic processes, 2) monitor the spectral changes with successive redox interfacial reactions, and 3) quantify the associated parameters including type and fraction of charge transfer. The transverse optical (TO) and longitudinal optical (LO) phonons above 500 cm−1 belonging to Co3O4, CoO, MnO2 and carbon-carbon bonding occurring at 1340 cm-1, 1590 cm−1 and 2670 cm-1 belonging to D, G, and 2D bands, respectively, are analyzed with applied potential. Consistent variation in Raman band position and intensity ratio reveal structural modification, combined charge transfer due to localized orbital re-hybridization and mechanical strain, all resulting in finely tuned electronic properties. Moreover, the heterogeneous basal and edge plane sites of graphene nanosheets in conjunction with transition metal oxide ‘hybrids’ reinforce efficient surface/interfacial electron transfer and available electronic density of states near Fermi level for enhanced performance. We estimated the extent and nature (n− or p−) of charge transfer complemented with Density Functional Theory calculations affected by hydration and demonstrate the synergistic coupling between graphene nanosheets and nanoscale cobalt (and manganese) oxides for applied electrochemical applications.

Revisiting PbTe to identify how thermal conductivity is really limited

Due to the long range interaction in lead telluride (PbTe), the transverse optical (TO) phonon becomes soft around the Brillouin zone center. Previous studies have postulated that this zone-center softening causes the low thermal conductivity of PbTe through either enlarged phonon scattering phase space and/or strengthened lattice anharmonicity. In this work, we reported an extensive sensitivity analysis of the PbTe thermal conductivity to various factors: range and magnitude of harmonic and anharmonic interatomic force constants, and phonon wavevectors in the three-phonon scattering processes. The analysis reveals that the softening by long range harmonic interaction itself does not reduce thermal conductivity and it is the large magnitude of the anharmonic (cubic) force constants that realizes low thermal conductivity, however, not through the TO phonons around the zone center but dominantly through the ones with larger wavevectors in the middle of Brillion zone. The work clarifies that local band softening cannot be a direct finger print for low thermal conductivity and the entire Brillion zone needs to be characterized on exploring low thermal conductivity materials.

Optical gain coefficients of silicon: a theoretical study

A theoretical model is presented and an explicit formula is derived for calculating the optical gain coefficients of indirect band-gap semiconductors. This model is based on the second-order time-dependent perturbation theory of quantum mechanics by incorporating all the eight processes of photon/phonon emission and absorption between the band edges of the conduction and valence bands. Numerical calculation results are given for Si. The calculated absorption coefficients agree well with the existing fitting formula of experiment data with two modes of phonons: optical phonons with energy of 57.73 meV and acoustic phonons with energy of 18.27 meV near (but not exactly at) the zone edge of the X-point in the dispersion relation of phonons. These closely match with existing data of 57.5 meV transverse optical (TO) phonons at the X4-point and 18.6 meV transverse acoustic (TA) phonons at the X3-point of the zone edge. The calculated results show that the material optical gain of Si will overcome free-carrier absorption if the energy separation of quasi-Fermi levels between electrons and holes exceeds 1.15 eV.

Investigation of Protective Coatings for Bronze Using Combined Techniques

Bronze is a metal alloy that is commonly used for statuary, but also as decorative element in architecture. Naturally, the surface of bronze monuments tends to passivation and formation of patina. This acts as protection, but can also have a decorative value. Anyhow, in certain conditions an artificial protection of bronze sculptures is also desired. Waxes and polymeric protection (Incralac, Sotter, …), also in combinations of layers, are mostly used nowadays. However, in order to prepare more effective solutions for protection, there have been performed some studies on possibilities for application of organic coatings (benzotriazole [1,2]) and various polymeric protective coatings like acrylate/methacrylate [3], fluoropolymers [1], polyurethanes [4] and sol-gel [5,6]. Since conservators demand that the coatings have to be removable, sol-gel coatings are often overlooked. Various strippers, for example on the basis of benzyl alcohol, can be applied to remove polymeric coatings from bronze surfaces. From environmental point of view, the studies of polymeric coatings are not prepared only from solvent-born formulations, but are shifted also to water-born formulations and comparison of both types of coatings [3]. Herein is reported the investigation of fluoropolymer and polyurethane protective coatings for bronze. The characterization of these coatings was made by using different analytical techniques. For structural determination, infrared (IR) and Raman vibrational spectroscopies were applied. Surface characteristics were determined by scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements. Protective efficiency was analyzed using electrochemical techniques like potentiodynamic polarization and electrochemical impedance spectroscopy. As more advanced analytical techniques, there were applied ex situ IR reflection-absorption (IR RA) and in situ Raman spectroelectrochemistry. The analyzed coating is in both spectroelectrochemical techniques gradually chronocoulometrically charged at more and more positive anodic potentials to follow the eventual degradation processes that are analyzed spectroscopically after each charging. IR RA spectra are measured in near grazing incidence angle assembly using an angle of 80° and P polarized IR radiation. In such spectra longithudinal optical (LO) modes appear that are commonly shifted towards higher wavenumbers compared to usual transversal optical (TO) modes from absorbance IR spectra. The disadvantage is the contact of electrochemically treated protective coating with atmosphere. This circumstance is overcome in in situ Raman spectroelectrochemical technique. The coating on bronze is mounted in a custom-made Tephlon in situ three-electrode cell. The counter electrode is platinum grid and the reference electrode Ag/AgCl. All electrochemical experiments are performed in 0.5 M sodium chloride. Fluoropolymer coatings are prepared from resins on the basis of fluoroethylene/vinyl ether (FEVE) alternating copolymers (Asahi Glass Company, Japan). The building unit of FEVE compounds is -CF2-CFX-. Solvent- and water- born formulations are made from appropriate resins, by applying corresponding poly(isocyanate) hardener, defoamer, light stabilizers, surfactants and co-solvents. Results confirm that the higher contact angles for water are achieved for solvent-born coatings (> 100°) than for water-born coatings (< 80°). Potentiodynamic polarization measurements are in accordance with these values, suggesting higher protective effectivity of solvent-born coatings. The use of water-born coatings for outside long-term protection of bronze is questionable, since the ex situ IR RA measurements showed that after treatment at high anodic potential the coating becomes much thinner. Consequently, the band at 565 cm-1 appeared in the IR RA spectrum and can be assigned to Cu2O of the bronze substrate. Similarly, also the in situ Raman spectra showed that after application of long anodic chronocoulometric pulse the coating burned and detached from the bronze substrate. Solvent-born coatings reveal more stable behavior through in situ Raman spectroelectrochemical measurements. Solvent-born polyurethane protective coatings show hydrophobic properties and the contact angle of 110°. Relatively good protective properties are confirmed through potentiodynamic polarization curves, impedance spectroscopy and ex situ IR RA measurements. The latter technique shows quite stable response during forced degradation at high anodic potentials. The activity is carried out within the framework of the NANORESTART project which has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 646063.

Investigating the Electron–Phonon Coupling of Molecular Beam Epitaxy-Grown Hg1−xCdxSe Semiconductor Alloys

Using spectroscopic ellipsometry, the temperature-dependence of the dielectric functions of a series of Hg1−xCdxSe thin films deposited on both ZnTe/Si(112) and GaSb(112) substrates were investigated. Initially, for each sample, room-temperature ellipsometric spectra were obtained from 35 meV to 6 eV using two different ellipsometers. Subsequently, ellipsometry spectra were obtained from 10 K to 300 K by incorporating a cryostat to the ellipsometer. Using a standard inversion technique, the spectroscopic ellipsometric data were modeled in order to obtain the temperature-dependent dielectric functions of each of the Hg1−xCdxSe thin films. The results indicate that the E1 critical point blue-shifts as a function of Cd-alloy concentration. The temperature-dependence of E1 was fitted to a Bose–Einstein occupation distribution function, which consequently allowed us to determine the electron–phonon coupling of Hg1−xCdxSe alloys. From the fitting results, we obtain a value of 17 ± 2 meV for the strength of the electron–phonon coupling for Hg1−xCdxSe alloy system, which compares nominally with the binary systems, such as CdSe and CdTe, which have values around 38 meV and 16 meV, respectively. This implies that the addition of Hg into the CdSe binary system does not significantly alter its electron–phonon coupling strength. Raman spectroscopy measurements performed on all the samples show the HgSe-like transverse optic (TO) and longitudinal optic (LO) phonons (∼ 130 cm−1 and ∼ 160 cm−1, respectively) for all the samples. While there is a slight red-shift of the HgSe-like TO peak as a function of the Cd-concentration, HgSe-like LO peak does not significantly change with the alloy concentration.

First-principles calculation of the structural, electronic, dynamical, and thermodynamic properties of Li4TiO4

The compound Li4TiO4 (Tetralithium Titanium) has attracted widespread scholarly interest for its sharp nose about carbon dioxide and high lithium density in the atmosphere and tritium breeder materials. At present, the structural, electronic, dynamical and thermodynamic properties of Li4TiO4 are studied by means of density functional theory (DFT) and phonon lattice dynamics. The calculated structural parameters and available experimental measurements are corresponding to each other, with the deviation being less than 1.5%. The obtained electronic band structure and density of states manifest that Li4TiO4 is an insulator with the indirect gap of 4.23 eV. Furthermore, the vibrational properties of Li4TiO4 are investigated usi ng the linear-response method from ab initio calculation. The calculation of phonon spectrum cures, the Born effective charges, the longitudinal optical (LO)-transverse optical (TO) splitting and optical-modes (IR- and Raman-active) are achieved in the first place. Additionally, the thermodynamic properties (F, S, Cv and E) are firstly evaluated ground on the phonon dynamics contribution. The formation of this paper will benefit the characterization of Li4TiO4, which may be subservient to further experimental researches in some degree.

Synthesis and photoluminescence enhancement of pure CdO: Annealing effect study

The effect of post-preparation annealing on the structure and photoluminescence of CdO samples prepared by precipitation method are described. The particle size was shifted towards higher values in nanometer range as examined by particle size analyzer upon annealing at higher temperatures. While X-ray diffraction pattern revealed phase pure CdO with cubic crystal structure for the annealed sample. The scanning electron microscopy with energy dispersive X-ray analysis confirmed the origin of defects due to the presence of chlorine (CdCl). Furthermore, the Raman bands obtained at 400 and 450 cm−1 confirmed the isolation of pure CdO, which correspond to two-phonon combinations such as longitudinal optical (LO) mode and transverse optical (TO) + transverse acoustic (TA) combination at the CdO Brillouin zone. Both the as-prepared and annealed CdO samples exhibited blue emission at about 430 nm upon excitation at 320 nm. Decay-associated spectra (DAS) were extracted from global analysis of time-resolved emission spectra of CdO powders. It reveals switching of emission decays from bi-exponential to mono-exponential (0.9 ns) in the annealed CdO powder at 600 °C. The enhancement in photoluminescence with the concomitant mono-exponential emission decay as induced by annealing should have potential implication for advancing the technology of optoelectronic micro/nano devices.

Optical phonon modes and polaron related parameters in GaxIn1−xP

Based on a pseudopotential approach under the virtual crystal approximation that includes the effect of compositional disorder, the optical lattice vibration frequencies and polaron related parameters in zinc-blende GaxIn1−xP have been studied. Our findings showed generally reasonably good accord with data in the literature. Other case, our results are predictions. The composition dependence of longitudinal optical (LO) and transverse optical (TO) phonon modes, LO-TO splittings, Frӧhlich coupling parameter, Debye temperature of LO phonon frequency, and polaron effective mass has been analyzed and discussed. While a non-monotonic behavior has been noticed for the LO and TO phonon frequencies versus Ga concentration x, a monotonic behavior has been observed for the rest of the features of interest. The information derived from this investigation may be useful for optoelectronic technological applications.

Physical model of the infrared dielectric function of zinc sulfide

We apply the Gaussian-oscillator model of the infrared dielectric function of ZnS materials prepared by hot pressing (HP) and chemical vapor deposition (CVD). Chemical factor analysis of the 700 to 1300 cm−1 spectral range shows 3 oscillators in the HP material and 4 in that prepared by CVD. The origin of these oscillators is identified. In both materials, high-order transverse-optical (TO) and longitudinal-acoustic (LA) vibration modes are excited. In HP-ZnS, the four oscillators are related to the 3TO, 1TO + 2LA, 3LA, and 4LA modes. Only the first three are found in the CVD material. These results clarify the physical mechanisms of lattice absorption of ZnS in this spectral range.

The properties of spray-deposited zinc sulfide thin films using trisodium citrate complexant

Zinc sulfide thin films were deposited on soda-lime glass substrates by chemical spray pyrolysis technique using trisodium citrate complexant. The films were deposited at substrate temperatures of 300 to 400 °C using 0.1 M zinc chloride, 0.1 M thiourea, and 0.01 M trisodium citrate. The thin films’ transmittance is between 40.83 and 50.86% at 550 nm, and energy band gap varied between 3.52 and 3.72 eV. The films have very high refractive indices in the range of 3.07 to 4.02 at 550 nm. The X-ray diffraction (XRD) analyses of the films revealed hexagonal structure. The crystallite size changed between 7.030 and 45.486 nm. The surface morphology is flower-like, dense, and contains rectangular nanorod-like particles and cracks. Raman spectroscopy revealed the presence of first-order (transverse optic (TO) and longitudinal acoustic), second-order (2TO and 2LO), and third-order (3LO) Raman phonons. The Fourier transform infrared spectra indicate the presence of chemical bonds in the thin films, while photoluminescence indicates near band edge emissions. The contact angle revealed hydrophilic nature of the deposited ZnS thin films.

Electronic properties and the phonon band structure of PbTe

Electronic properties of PbTe in its Rock-Salt (B1) phase have been investigated using density functional theory (DFT) as well as the Phonon Band Structure of PbTe using density functional perturbation theory (DFPT). The lattice parameter, bulk modulus and pressure derivative are calculated as 6.608 Å, 36.00 GPa and 3.39 respectively; The density of states (DOS) has a maximum peak of 3.2 states/eV at −3.00 eV, the spherical charge distributions between the Pb+2 and Te−2 ions depict that the system is an ionic compound; From the band structure, a direct band gap of 0.7968 eV was obtained which agreed well with other calculations. We observed a large splitting value of 2.16 THZ between the longitudinal optic (LO) and the transverse optic (TO) phonon branches along the Γ-point. The vibrational density of states (VDOS) has a maximum peak of 0.185 states/eV at 1.53 THZ. The values obtained for electronic properties and the phonon band structure PbTe are essentially important for PbTe energy applications such as thermoelectric, solar cells, biological imaging electroluminescent, infrared photodetectors and optoelectronic devices.

Coordinated EDX and micro‐Raman analysis of presolar silicon carbide: A novel, nondestructive method to identify rare subgroup SiC

AbstractWe report the development of a novel method to nondestructively identify presolar silicon carbide (SiC) grains with high initial 26Al/27Al ratios (&gt;0.01) and extreme 13C‐enrichments (12C/13C ≤ 10) by backscattered electron‐energy dispersive X‐ray (EDX) and micro‐Raman analyses. Our survey of a large number of presolar SiC demonstrates that (1) ~80% of core‐collapse supernova and putative nova SiC can be identified by quantitative EDX and Raman analyses with &gt;70% confidence; (2) ~90% of presolar SiC are predominantly 3C‐SiC, as indicated by their Raman transverse optical (TO) peak position and width; (3) presolar 3C‐SiC with 12C/13C ≤ 10 show lower Raman TO phonon frequencies compared to mainstream 3C‐SiC. The downward shifted phonon frequencies of the 13C‐enriched SiC with concomitant peak broadening are a natural consequence of isotope substitution. 13C‐enriched SiC can therefore be identified by micro‐Raman analysis; (4) larger shifts in the Raman TO peak position and width indicate deviations from the ideal 3C structure, including rare polytypes. Coordinated transmission electron microscopy analysis of one X and one mainstream SiC grain found them to be of 6H and 15R polytypes, respectively; (5) our correlated Raman and NanoSIMS study of mainstream SiC shows that high nitrogen content is a dominant factor in causing mainstream SiC Raman peak broadening without significant peak shifts; and (6) we found that the SiC condensation conditions in different stellar sites are astonishingly similar, except for X grains, which often condensed more rapidly and at higher atmospheric densities and temperatures, resulting in a higher fraction of grains with much downward shifted and broadened Raman TO peaks.

Raman spectroscopy and atomic force microscopy study of interfacial polytypism in GaP/Ge(111) heterostructures

Abstract Effects of lattice and polar/nonpolar mismatch between the GaP layer and Ge(111) substrate are investigated by spatially resolved Raman spectroscopy. The red shifted transverse optical (TO) and longitudinal optical (LO) phonons due to residual strain, along with asymmetry to TO phonon ∼358 cm −1 are observed in GaP/Ge(111). The peak intensity variation of mode ∼358 cm −1 with respect to TO phonon across the crystallographic morphed surface of GaP micro structures is associated with the topographical variations using atomic force microscopy mapping and Raman spectroscopy performed on both in plane and cross-sectional surface. Co-existence of GaP allotropes, i.e. wurtzite phase near heterojunction interface and dominant zinc-blende phase near surface is established using the spatially resolved polarized Raman spectroscopy from the cross sectional surface of heterostructures. This consistently explains effect of surface morphology on Raman spectroscopy from GaP(111). The study shows the way to identify crystalline phases in other advanced semiconductor heterostructures without any specific sample preparation.

Fabrication of ZnSe nanoparticles: Structural, optical and Raman Studies

In this work, a simple, effective, reproducible and green fabrication process for the production of high-quality, pure ZnSe nanoparticles at low temperature is presented. The structural and optical properties of these nanoparticles have been examined by transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), Ultraviolet-Visible spectroscopy (UV–vis), photoluminescence (PL), and Raman spectroscopy. TEM analysis confirms that the formed products are ZnSe particles with size less than 10nm, respectively. Strong blue shift absorption with energy band gap of 3.85eV is observed from UV–vis spectrophotometry. Photoluminescence measurements showed that the nanoparticles exhibit a strong UV emission peak at 380nm. The blue emission could be attributed to the quantum size effect of ZnSe nanocrystals. Raman spectroscopy of the ZnSe NPs showed a clear shift of transverse optical (TO) and longitudinal optical (LO) phonon modes, as well as a broadening of the LO phonon mode.