Papers by Keyword: Raman Scattering

Abstract: We have investigated Raman spectra of p-type 4H-SiC crystals with hole concentration ranging from 3×10¹⁶ to 1×10²¹ cm^-3. For folded transverse acoustic (FTA) doublet modes, Fano interference profiles were analyzed, and the frequency shift due to Fano interference was obtained as a function of hole concentration. We demonstrated that the shift of the FTA doublet modes is a quantitative measure for evaluating of hole concentration of p-type 4H-SiC. Spectral features of transverse optical (TO) and longitudinal optical phonon-plasmon coupled (LOPC) modes were also studied for various carrier concentrations. The results show that the full width at half maximum of the LOPC and relative intensity of TO and the LOPC can be used as other calibration measures for hole concentration.

Abstract: RF magnetron sputtering of two separate silicon and oxide (SiO₂ or Al₂O₃) targets in pure argon plasma was used for deposition of Si_x(SiO₂)_1-x and Si_x(Al₂O₃)_1-x films with x=0.15-0.7 on long fused quarts substrate. The effect of post-fabrication treatments on structural and light emitting properties of the films with different x values was investigated by means of Raman scattering, electron paramagnetic resonance and X-ray diffraction as well as by photoluminescence (PL) methods. The formation of amorphous Si clusters upon deposition process was found for the both types of films. The annealing treatment at 1150°C during 30 min results in formation of Si nanocrystallites (Si-ncs). The latter were found to be larger in Si_x(Al₂O₃)_1-x films than that in Si_x(SiO₂)_1-x counterparts with the same x values and are under tensile stresses. The investigation of photoluminescence properties of annealed films of both types revealed the appearance of visible-near infrared light emission. The Si_x(SiO₂)_1-x films demonstrated one broad PL band which peak position shifts gradually to from 1.4 eV to 1.8 eV with the x decrease. Contrary to this, for the Si_x(Al₂O₃)_1-x films two overlapped PL bands were observed in the 1.4-2.4 eV spectral range with peak positions at ~2.1 eV and ~1.7 eV accompanied by near-infrared tail. Comparative analysis of PL spectra of both types samples showed that the main contribution to PL spectra of Si_x(SiO₂)_1-x films is given by exciton recombination in the Si-ncs whereas PL emission of Si_x(Al₂O₃)_1-x films is caused mainly by carrier recombination either via defects in matrix or via electron states at the Si-ncs/matrix interface.

Abstract: The effect of calcination temperature for Fe₂O₃/MgO catalysts on the formation of carbon nanotubes (CNTs) was examined. CNTs were synthesized over Fe₂O₃/MgO catalysts calcined at different temperatures by catalytic decomposition of methane at 1000°C. The synthesized CNTs were investigated by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The results show that the effect of calcination temperatures greatly governed the diameter and the quality of the SWCNTs formed. The catalysts calcined at 500, 600 and 700°C produced CNTswith the diameters of 1.53, 1.95 and 2.97nm, respectively. Generally, an increase in the calcination temperature increases the average diameter and decreases the quality of the CNTs produced.

Abstract: In this work, we study the photoluminescence and the Raman scattering behavior of Si rich silicon oxynitride films obtained by plasma enhanced chemical vapor deposition as a result of thermal anneals during 1 hour in the temperature range from 400^O to 1100^OC and discuss the ways of the transformation of structure in them.

Abstract: laser radar is a kind of modern active optical remote sensing device and is the outcome of the combination of the traditional radar technology and the modern laser technology. It takes laser as the light source and senses remotely the target through the radiation signal generated when the detecting laser and the target interact. This paper summarizes the structure and classification of the laser radar for the purpose of atmosphere composition detection, and also discusses the existing problems and development trends.

Abstract: We present a study on five Mg_xZn_1-xO samples with varied x (x = 0, 0.01, 0.06, 0.10 and 0.14), grown on sapphire substrate by Metalorganic Chemical Vapor Deposition (MOCVD). Combined photoluminescence (PL) and Raman scattering studies were carried out over a temperature range of 80K-470K, under the excitation of UV 325 nm. Temperature dependence of the PL for MgZnO with x = 0, 0.01 and 0.06 are shown. The resonance Raman longitudinal optical (LO) multiple modes are exhibited for MgZnO with x = 0.06, 0.10 and 0.14 over all temperature range. Raman shifts exhibit a quadratic dependence on temperature in the measured temperature range. These dependences can be calculated, based upon a model involving three-and four-phonon coupling. We attribute both the thermal expansion and four-phonon terms in the four-phonon anharmonic processes to describe the change of Raman shift with temperature.

Abstract: We reported on a study upon a Surface-enhanced Raman Scattering (SERS) substrate produced from a large area multi-walled carbon nanotube (MWCNT) films decorated with Au nanoparticles. The morphology and spectrum of the MWCNTs/Au composite structure was characterized with scanning electron microscopy and spectrophotometer. The SERS signals of Rhodamine 6G (R6G) absorbed on the substrate were improved, which could contribute to the enlarged surface area for adsorption of molecules and Localized Plasmon Resonance Effect. The results indicated that it is potential to produce sensitive SERS substrates via further fine-tuning of size, shape of the nanostructure.

Abstract: Properties of Au nanoparticles (NPs) caused by various sizes (5-12 nm) were studied in this article. Au NPs capped with citrate of various sizes were synthesized by two methods including trisodium citrate dihydrate reduction of chloroauric acid tetrahydrate and sodium borohydride reducion of chloroauric acid tetrahydrate. Au NPs were characterized and measured by using transmission electron microscope (TEM), UV-vis-NIR absorption spectroscopy, and surface Raman scattering. The results of experiment indicated that the size of Au NPs was related to the type of reducing agent and molar ratio of reducing agent and chloroauric acid. The weaker the reducing capacity of the reducing agent or the lower the molar ratio, the bigger the size of Au NPs is. The max wavelength of absorption peak for the citrate-capped Au NPs is red-shifted with the increase of particle diameter. Raman scattering observed from Au NPs of various sizes is found to be NP size-dependent. It is clear that the bigger Au NPs are more apparent in the Raman scattering determination. Size-tunable Au NPs should be crucial for biosensors, particularly as Raman-tag particles.

Abstract: Raman spectrum is a kind of characteristic spectrum. The information of molecular vibration and rotation can be obtained by studying Raman spectrum. Raman spectrum will be changed because of molecular interaction under effect of different solvent. We selected zinc gluconate as the object of research. Zinc gluconate is dissolved respectively in ethyl chloride, benzene, ring of ethane，chloroform, acetic acid, ethylene oxide, n-propanol, n-butanol solution, and Raman spectra were tested. The change of molecular internal structure and the interaction of molecular functional groups are studied by means of measuring Raman frequency shift, bandwidth, and light intensity. Thus, the information of solute structure change can be obtained. Experiments show that when zinc gluconate dissolved in the organic solvent, molecular gap became larger, its velocity increased, and stretching vibration of associating OH key group became strong. Methylenes in polar and non-polar molecule interact, and the polarization changed. In different polar solvents, Raman spectra had different changes. When the bond length increases，the stretching vibration frequency of molecules moves to the direction of low frequency. It produces red shift instead of blue shift. The results of this paper provide a basis to study molecular interactions further.

Abstract: Few-layers graphene films (FLG) were grown by local solid phase epitaxy on a semi-insulating 6H-SiC substrate by annealing Ni films deposited on the Si and C-terminated faces of the SiC. The impact of the annealing process on the final quality of the FLG films is studied using Raman spectroscopy. X-ray photoelectron spectroscopy was used to verify the presence of graphene on the sample surface. We also demonstrate that further device fabrication steps such as dielectric deposition can be carried out without compromising the FLG films integrity.