Narrow Results

The electric field of incident light on metallic nanostructures goes through a dramatic increase in magnitude. This is because of the Surface Plasmon resonance. This change in the magnitude of the electric field takes place in a very short distance leading to a very high electric field gradient. This electric field gradient is very much capable of altering the Raman scattering as observed in our experiment performed on the Glycine in the presence of colloidal silver nano-prisms. We observed that new peaks at 560, 614 and 933 cm${}^{-1}$ appeared and the strength of peak 508 cm${}^{-1}$increased. Also, a few peaks at 1501 and 1580 cm${}^{-1}$disappeared. Further, an overall strength enhancement in peak is observed.

Raman scattering analysis revealed that the structure of carbon films prepared by pulsed laser deposition (PLD) at room temperature is predominantly amorphous and the structure of amorphous carbon nitride (a-CN_x) thin films can be changed with varying substrate temperatures (ST) from 20°C to 500°C. The deposited a-CN_x films are composed of C–N, C≡N and C–O bonded materials and the C–N and C≡N bonds are increased with ST. We have found that no other obvious peaks can be distinguished in the range 900–2300 cm^-1 in which several peaks always appear in a-CN_x films. The spectra were deconvoluted into Raman D and G peaks and the structural parameters are determined. The upward shifts of the Raman G peak towards 1592 cm^-1 shows the evidence of a progressive formation of crystallites in a-CN_x films upon increase of ST. While the upward shifts of the Raman D peak towards 1397 cm^-1 have been related to the decrease of bond-angle disorder and sp³ tetrahedral bonding in its structure. Raman FWHM and I_D/I_G also indicate that N incorporation with increase of ST caused an increase in the number and/or size of graphitic domains in the a-CN_x films.

The scattering intensity (SI) for an electron resonant Raman scattering (ERRS) process in a free-standing semiconductor quantum wire of cylindrical geometry associated with bulk longitudinal optical (LO) phonon modes or the surface optical (SO) phonon modes is calculated for T=0 K. The Fröhlich interaction is considered to illustrate the theory for a GaAs system. Electron states are confined within a free-standing quantum wire (FSW). Single parabolic conduction and valence bands are assumed. The selection rules are studied. Numerical results and a discussion are also presented for various radii of the cylindrical quantum wires.

The discovery of graphene, a single layer of covalently bonded carbon atoms, has attracted intense interest. Initial studies using mechanically exfoliated graphene unveiled its remarkable electronic, mechanical and thermal properties. There has been a growing need and rapid development in large-area deposition of graphene film and its applications. Chemical vapor deposition on copper has emerged as one of the most promising methods in obtaining large-scale graphene films with quality comparable to exfoliated graphene. In this paper, we review the synthesis and characterizations of graphene grown on copper foil substrates by atmospheric pressure chemical vapor deposition. We also discuss potential applications of such large-scale synthetic graphene.

Epitaxial grown Gallium nitride (GaN) thin film on sapphire was irradiated with Cu ions at various fluences (5×10¹⁴, 1 ×10¹⁵ and 5×10¹⁵cm^-2). The level of lattice disorder, as measured by Rutherford backscattering spectrometry and channeling (RBS/C), gradually increases with the increasing of ions fluence. Lattice amorphization is observed for the sample irradiated with fluence of 5×10¹⁵cm^-2 which is also confirmed by X-ray diffractometer (XRD) analysis. It was found that both Raman modes of GaN layer clearly shifted with Cu⁺ fluences. Both Raman and X-ray analyses explore that Cu atom substituted into Ga sites. Atomic force microscopy (AFM) images show the irradiated GaN surface roughness increases with the increasing ions fluence. The UV-visible transmittance spectrum and ellipsometric measurements show a decrease in the band gap value after irradiation of Cu ions in the GaN film. Moreover, the optical constants (n and k) of the films vary with the increasing of Cu ion fluences.

Effects of current density on nanostructure and light emitting properties of porous silicon (PS) samples were investigated by field emission scanning electron microscope (FE-SEM), gravimetric method, Raman and photoluminescence (PL) spectroscopy. FE-SEM images have shown that below 60 mA/cm², macropore and mesopore arrays, exhibiting rough morphology, are formed together, whose pore diameter, pore depth and porosity are about 265–760 nm, 58–63 μ m and 44–61%, respectively. However, PS samples prepared above 60 mA/cm² display smooth and straight macropore arrays, with pore diameter ranging from 900–1250 nm, porosity of 61–80% and pore depth between 63–69 μm. Raman analyses have shown that when the current density is increased from 10 mA/cm² to 100 mA/cm², Raman peaks of PS samples shift to lower wavenumbers by comparison to crystalline silicon (c-Si). The highest Raman peak shift is found to be 3.2 cm^-1 for PS sample, prepared at 90 mA/cm², which has the smallest nanocrystallite size, about 5.2 nm. This sample also shows a pronounced PL, with the highest blue shifting, of about 12 nm. Nanocrystalline silicon, with the smallest nanocrystallite size, confirmed by our Raman analyses using microcrystal model (MCM), should be responsible for both the highest Raman peak shift and PL blue shift due to quantum confinement effect (QCE).

With the help of temperature dependence, Raman scattering anharmonic effect of various modes of layered semiconductor InSe over temperature range of 20–650 K has been studied. It was found that with an increase in temperature, anharmonicity will increase. Two and three phonons coupling with optical phonon, are used to describe temperature-induced anharmonicity in the linewidth of Raman modes. It was found that the temperature variation of the phonon parameter can be accounted for well by the cubic term in anharmonic model. To describe line-center shift of Raman modes, a model not considering independently cubic and quartic anharmonicity was used. A similar study has been done for InSe doped with different concentration of GaS dopant. The result of temperature study of InSe doped with GaS revealed that in this case anharmonicity increases with an increase in dopant and an increase in temperature.

Nanostructured ZnS films of various molar concentrations have been deposited using chemical bath deposition (CBD) method on glass substrates in the matrix of polyvinyl alcohol (PVA). Structural analysis of the samples with the help of X-ray diffraction (XRD) shows that the films are of cubic phase structure and diffraction peaks shift toward higher diffraction angle with the increase of molar concentration. Crystallite size is obtained using Scherrer’s formula, Williamson–Hall (WH) plot as well as size–strain plot (SSP), and reveals decrease in size with increasing molar concentration. Surface morphology and surface texture of the samples are observed with the help of atomic force microscopy (AFM) and high-resolution transmission electron microcopy (HRTEM) which exhibit the roughly spherical shape of the particles as well as formation of cluster by a large number of ZnS nanoparticles. Observation from selected area electron diffraction (SAED) pattern also confirms the cubic phase of nanostructured ZnS samples. Surface topographic study using scanning electron microscopy (SEM) also shows particle agglomeration forming nanoclusters and energy-dispersive X-ray spectroscopy observation reveals that the films are composed of zinc and sulfur. With the increase of molar concentration, the optical bandgap energy increases whereas the refractive index as well as dielectric constant decrease, and in comparison to ZnS bulk counterpart, the samples are found to be blue-shifted. Samples exhibit blue emission photoluminescence (PL) band and second-order Raman scattering. Fourier-transform infrared (FTIR) technique is utilized to detect the presence of stabilizing agent.

The Biswas–Arshed equation (BAE) with space–time dispersion was currently considered in the literature. Optical phenomena embedded in this equation are self-steepening, self-phase modulation and Raman scattering. Here, we consider BAE with gain or loss. It is worth mentioning that the gain or loss has an impact on blowup or decaying solitons propagation in optical fibers, which is novel. Our objective is to find optical soliton solutions of BAE and the aforementioned physical phenomena are investigated in some details. The conditions for the dominance of a phenomenon are predicted. This is physically important to inspect the behavior of solitons prpagation. To this issue, exact solutions of the model equation are derived by using the unified method. The solutions obtained are displayed graphically. Dark soliton, bright soliton, M-shaped soliton, rhombus soliton (which is novel) and chirped soliton with tunneling are observed. The modulation instability is studied and it is found that it triggers when the coefficients of the space–time dispersions are positive.

A survey of recent Raman scattering studies on the interstitial hydrogen molecule (H₂) in Si and GaAs is presented. It is shown that properties of H₂ strongly depend on the nuclear spin state I. In either material, para-H₂ (I=0) is unstable against irradiation with band gap light. In the case of Si, para-H₂ also preferentially disappears from the Raman spectra in the course of storage at room temperature in the dark. Possible explanations for this surprising behavior are discussed and compared with the latest infrared absorption studies.

Based on dynamical diffraction theory, we study nonlinear processes in the hard X-ray region. First, we consider the process of frequency doubling in perfect crystals in the general case where the process of Bragg rescattering of the generated harmonic field should be taken into account. The optimum conversion conditions for the Bragg and Laue interaction geometry are determined and the efficiency is calculated. Secondly, we consider the modulation of X-ray diffraction by a wave of coherent optical phonons produced by an intense laser pulse. We show that in the optimum regime the modulation period of the X-ray beam may be even shorter than the period of the excited optical phonons, as a result of higher order Raman scattering. Generation of extremely short X-ray pulses using this technique is discussed. Our results suggest that synchronous interaction schemes analogous to the schemes long known in nonlinear optics can significantly increase the efficiency of nonlinear processes in the hard X-ray region.

Powder X-ray diffraction, Raman scattering and infrared spectra at different doping (x = 0 ~ 0.5) on polycrystalline Pr_1-xSr_1+xCoO₄ were performed. With increasing x, the shift of Raman scattering spectra is due to the enhancement of electron–phonon interaction along the c-axis. The contrary variation of infrared in wavenumber comes from the weakening electron–phonon interactions in the ab plane. There is a dramatic variation in resistivity as x increases, which is also caused by increasing carrier concentration and is related to the band shift. For Pr_1-xSr_1+xCoO₄, both A_1g bands shift to low frequency and reach a minimum when x = 0.3 and the resistivity of Pr_0.7Sr_1.3CoO₄ is the smallest at room temperature.

Nanocrystalline CeO₂ with different particle sizes has been studied under high pressure using Raman spectroscopy techniques and diamond anvil cell at room temperature. The pressure shift of the first-order Raman frequency for each particle sizes was measured. Linear dependence of the first order Raman frequency on pressure for each particle sizes has been observed. We found that the first order Raman frequency decreases with the decreasing particle sizes under ambient condition and the lattice constant increases with the decreasing particle size. The increasing molar fraction of oxygen vacancies with the decreasing particle size is responsible for the lattice expansion.

Iron-based superconducting layered compounds have the second highest transition temperature after cuprate superconductors. Their discovery is a milestone in the history of high-temperature superconductivity and will have profound implications for high-temperature superconducting mechanism as well as industrial applications. Raman scattering has been extensively applied to correlated electron systems including the new superconductors due to its unique ability to probe multiple primary excitations and their coupling. In this review, we will give a brief summary of the existing Raman experiments in the iron-based materials and their implications for pairing mechanism in particular. And we will also address some open issues from the experiments.

Since the discovery of cuprate superconductors, the mechanism of high temperature superconductivity is still a mystery. Among the investigation tools, the electronic Raman scattering is a powerful one to probe electronic excitations in different regions of the Fermi surface of cuprate superconductors by a simple choice of the incident and scattered polarization vectors. Thus the symmetry of the superconducting Cooper pairs can be indicated. In this article we review our investigations of electronic Raman scattering in cuprate superconductors based on the t–J model within the kinetic energy driven superconductivity. The theory of electronic Raman response in cuprate superconductors is presented together with an overview of the charge-spin separation fermion-spin theory to handle the t–J model. Some theoretical results of electronic Raman response are presented in comparison with the experimental results. Special emphasize is given to the doping and temperature dependent of electronic Raman spectra.

In this paper, the interface phonons in a core-shell quantum dot are theoretically studied by a resonant Raman scattering (RRS) process. Fröhlich electron–phonon interaction is considered in the framework of the dielectric continuum approach. The Raman peaks are found to be sensitive to the size of strongly confined shell. The shift of the Raman resonant peaks is a consequence of the change of observed dispersion of the phonon frequency. The Raman intensity changes in the system with shell thickness, originating from the competition between the spacial distribution of electron wave function and the number of phonons joining in the RRS process. The analysis of the Raman spectra gives a physical explanation to the size-selective nature of the Raman process and some experimental results.

In this study, Nb₂O₅ was prepared by the sol–gel method. Crystallization process was investigated by thermal analysis (TG–DSC), X-ray diffraction (XRD), UV–vis spectra and Raman spectra. TG–DSC results indicated that amorphous Nb₂O₅ appeared at 460${}^{\circ }$C. XRD results indicated that amorphous Nb₂O₅ transformed into pseudo-hexagonal phase and crystallization degree has an increasing trend with an increase of temperature. UV–vis and Raman spectra results reflected the significant variations of optical property and atomic structure in this process. Nb₂O₅ atomic arrangement transforms from short-range order to medium-range order, then to long-range order. Atoms transform into long-range ordered structure through connection of structural units with increasing temperature. Additionally, crystallization degree, optical property and atomic arrangement all are mutually connected in the crystallization process.

The generation of ultrashort pulses is the key to exploring the dynamic behaviors of matter on ever-shorter timescales. Sub-femtosecond pulses can be used to explore atomic-scale electron motion which can reveal the nature of changes in chemical reactions and the function of biological systems. Recent developments have shown that sub-2-fs pulse trains can be produced in an experiment through molecular modulation. In this paper, we experimentally demonstrate the potential of yielding sub-femtosecond pulse trains with eight or more high-order stimulated Raman scattering components; and report the current bottleneck of generating sub-femtosecond pulse trains via molecular modulation.

The optical properties of the ZnGa₂Se₄ are investigated by infrared (IR) reflectivity, Raman scattering, photoluminescence and DFT simulations. We have analyzed pairs of lines of FL corresponding to 1.24eV and 1.22eV at low energy excitations, about these FL maxima haven’t any information in other works. Studies show that depending on the temperature, the intensity of luminescence decreases and formed new third maximum. The energy difference between each of these peaks is 0.02eV, which corresponds to the energy of the most intense phonon in the Raman spectrum.

We study a semiclassical modelization of the interaction of a laser with a mono-atomic gas. The Maxwell equations are coupled with a three-level version of the Bloch equations. Taking into account the specificities of the laser pulse and of the gas, we introduce small parameters and a dimensionless form of the equations. To describe stimulated Raman scattering, we perform a three-scale WKB expansion in the weakly nonlinear regime of geometric optics. The limit system is of Schrödinger–Bloch type. We prove a global existence result for this system and the convergence of its solution toward the solution of the initial Maxwell–Bloch equations, as the parameter of the WKB expansion goes to 0. We put in evidence Raman instability in the one-dimensional case, both theoretically and numerically.