Raman active E2 modes in aluminum nitride films

The vibrational spectrum of AlN thin films has been studied in recent years by theoretical and experimental methods, but there is still a lack of full knowledge of the Raman shift of the active E₂ modes of this material. Early work by Carlone et al. [1] has indicated that the E₂ modes of AlN deposited on Si occur at frequencies of 303cm^-1 and 426cm^-1. In the present study, Raman spectra of AlN deposited by magnetron sputtering on polished Si, quartz and BK7 substrates and also the Raman spectrum of pure Si, were compared to show that these peaks can actually be assigned as Raman peaks of Si, instead of AlN Raman peaks. We show that the Raman lines at 240cm^-1 and 650cm^-1 are the true AlN E₂ Raman peaks in agreement with calculated and experimental works reported in the literature that indicate the occurrence of the low and high E₂ Raman modes of AlN in the ranges (228-252)cm^-1 and (631-665)cm^-1, respectively.     

真空还原制备的VO2热致相变薄膜Raman光谱和红外光谱研究

报道了利用真空还原制备的VO2薄膜的红外透射光谱和Raman光谱,并进行370－900nm波段的光透射测试以及900nm波长的热滞回线特性测试,表明所制备VO2薄膜具有优良的热致相变光学特性,结晶状态不同的薄膜其Raman谱位置有明显改变,室温时的红外光谱表现出较好的红外振动特性。讨论了薄膜结晶状态对Raman位移的影响以及VO2薄膜的红外光谱。     

The relation between zeolite framework structure and vibrational spectra

Using a general valence force field method, infrared and Raman spectra of pure silica zeolite crystals and molecular substructures of zeolites are calculated. Computed spectra of the substructures are directly compared with computed spectra of the crystal. Also, a comparison of the atomic displacement vectors of the vibrational modes is made. No general theoretical basis for a correlation between the presence of large structural elements and spectral features, sometimes reported, is found to exist. An extensive comparison between experimental and theoretical infrared and Raman spectra of the SiO₂ forms of sodalite and faujasite is made. Other applications of vibrational spectroscopy to zeolite structure research, such as the SiOSi angle distribution and the location of acid sites, are evaluated as well.     

Spectral and quantum chemical examination of the Si clusters nascent inside the SiO bulk

In the present communication the results of the synthesis, the quantum chemical (QC) and the spectral examination of the SiO thin film and powder are reported. The QC and Raman studies indicate the formation of the Si clusters inside the bulk of the SiO protoparticle at the very first stages of its gas-phase growth. Infrared, Raman, inelastic neutron scattering and electron spin resonance spectra for the synthesized SiO thin films and the commercial sample have been recorded and simulated in order to verify the theoretical model. The QC calculated radial distribution function and vibrational spectra reproduce well the experimental ones.     

Theoretical and experimental investigations of single- and multilayer structures with SiGe nanoislands

The influence of geometrical and physical parameters of self-assembled SiGe/Si nanoislands on their energy has been investigated theoretically. The island energy minimum was shown to depend on the growth temperature and Si content in the islands. The results of the theoretical calculations are compared with experimental data obtained by atomic force microscopy and Raman spectroscopy (RS).     

Raman scattering studies of ultrashallow Sb implants in strained Si

Sheet resistance (R _s) reductions are presented for antimony doped layers in strained Si. We use micro-Raman spectroscopy to characterise the impact of a low energy (2 keV) Sb implantation into a thin strained Si layer on the crystalline quality and resultant stress in the strained Si. The use of 325 nm UV laser light enables us to extract information from the top ∼9 nm of the strained Si layer. Prior to implantation the Si layer is fully strained with a tensile stress value ∼1.41 GPa, in agreement with the calculated theoretical maximum on a strain relaxed buffer with 17% Ge content. There is a clear decrease in the intensity of the Si Raman signal following Sb implantation. The lattice damage and lattice recovery achieved by subsequent rapid thermal anneal (RTA) is quantified using the amplitude and full width at half maximum (FWHM) of the crystalline Si peak. The shift of the Raman Si peak is a key parameter in the interpretation of the spectra. The ion-implanted sample is studied in terms of a phonon coherence length confinement model. Carrier concentration effects are seen to play a role in the Raman shift following electrical activation of the Sb atoms by RTA.     

Characterization of fluorine-doped silicon dioxide films by Raman spectroscopy and Electron-spin resonance

We have measured Raman and Electron-spin resonance (ESR) spectra of fluorine-doped SiO₂ films deposited by two different methods. In high-density plasma (HDP) films, the Raman band at about 490 cm^− 1 becomes drastically stronger as the F/Si ratio increases, whereas the Raman band from threefold ring defect is independent of the F/Si ratio. The unusual increase of the intensity of the 490 cm^− 1 band in HDP films has been interpreted in terms of the existence of Si-Si clusters. From a comparison between Raman spectra of HDP film and plasma chemical vapor deposition using tetraethoxysilane (p-TEOS) film with the same F/Si ratios it has been found that HDP film has more Si-Si bonds and threefold ring defects than p-TEOS film. Furthermore, the polarized Raman spectra in the 810 cm^− 1 bands indicate that inhomogeneous SiO₂ clusters of various sizes should exist in the network structure of HDP film. The result of the ESR measurement shows that HDP films have fewer dangling bonds than p-TEOS films. It is considered that many Si-Si clusters, threefold ring defects, and inhomogeneous SiO₂ cluster sizes, and the few dangling bonds in HDP films give rise to the film properties of low stress, good adhesion with Si substrate, and low water permeation.     

Photoacoustic properties of softmagnetic amorphous Fe81B13Si4C2 ribbon

Photoacoustic properties of amorphous Fe81B13Si4C2 ribbons were investigated. The amplitude and phase photoacoustic spectra were measured as a function of the modulation frequency of an He–Ne laser beam. Thermal diffusivity was determined by comparison of obtained experimental results and calculated theoretical photoacoustic spectra for a non-annealed Fe81B13Si4C2 sample and an Fe81B13Si4C2 sample annealed at 600 °C. © 1998 Chapman & Hall     

Nanometer resolution stress measurement of the Si gate using illumination-collection-type scanning near-field Raman spectroscopy with a completely metal-inside-coated pyramidal probe

We have proposed an illumination-collection-type scanning near-field Raman spectroscopy (SNRS) with a completely gold metal-inside-coated (MIC) pyramidal probe without an optical aperture in order to detect the Raman spectra of fine Si devices for local stress measurements. The gold MIC pyramidal probe has been studied to act as a plasmon resonance near-field optical probe with high power using a finite differential time domain (FDTD) simulation and the prototyped SNRS. In the simulation, the propagated optical power can be made available for SNRS. In the experiments, it is clear that the prototyped SNRS enhanced the Si Raman peak signal by plasmon resonance and could measure the Si Raman peak shift by line scanning the Si gate region and the Si active layer. Furthermore, compressive and tensile stresses localized around the Si gate were demonstrated by the Si Raman peak shift with a resolution of about 10 nm. It is clarified that the proposed SNRS has the possibility of detecting the Raman spectra of a local area.     

常压化学气相沉积方法制备非晶硅薄膜及其光致发光性能研究

使用改进的常压化学气相沉积(APCVD)系统制备了非晶硅薄膜,测量了样品的光致发光特性,使用Raman光谱和X射线光电子能谱(XPS)谱测量了薄膜的微结构特征.样品在523 nm出现发光峰,Raman光谱和XPS谱表明制备的薄膜结构中存在富氧相和富硅相的分相现象,分析认为相界面的存在是产生发光的原因.Raman光谱分峰结果表明薄膜中存在纳米晶粒.     

Local Oscillations of Silicon–Silicon Bonds in Silicon Nitride

Raman spectra of films of nearly stoichiometric amorphous silicon nitride (a-Si₃N₄) reveal a contribution due to local oscillations of silicon–silicon (Si–Si) bonds. This observation directly confirms that the almost stoichiometric a-Si₃N₄ contains Si–Si bonds, which, according to theoretical predictions, act as electron and hole traps that are responsible for the memory effect in Si₃N₄.     

Silicon nanocrystals synthesized by electron-beam co-evaporation method and their application for nonvolatile memory

In this paper, the silicon nanocrystals (Si NCs)/SiO₂ hybrid films designed for nonvolatile memory applications are prepared by electron-beam co-evaporation of Si and SiO₂. Transmission electron microscopy images and Raman spectra verify the formation of Si NCs. Metal-oxide-semiconductor capacitor structure with Si NCs embedded in the gate oxide is fabricated to characterize the memory behaviors. High-frequency capacitance-voltage and capacitance-time measurements further demonstrate the memory effect of the structure resulting from the charging or discharging behaviors of Si NCs. It is found that the memory window can be changed by adjusting the Si/SiO₂ wt. ratio in source material. The memory devices with Si NCs/SiO₂ hybrid film as floating gate yield good retention characteristics with small charge loss.     

Comparison of discrete and continuous motion in scanning probe microscopy monitored via confocal Raman microspectroscopy

Confocal Raman imaging is a relatively new analytical technique that combines the strengths of Raman microspectroscopy and confocal optics. The images collected by the microscope are obtained by monitoring specific bands in the Raman spectra that are collected at many points in a sample, with the number of spectra usually numbering in the hundreds or thousands. Some commercially available systems acquire data while the sample is continuously moving with respect to the microscope objective. The distance that the stage moves during a single acquisition is a parameter that can be set prior to data acquisition. Data in this report was acquired with both a static and continuously moving sample for comparison, utilizing the 520 cm(-1) Si phonon of a silicon wafer to monitor an edge. Scattering collected from each discrete step, i.e., no motion during spectral acquisition, showed excellent precision of location, but a loss in resolution was observed as the pixel size was increased beyond the maximum theoretical resolution of the instrument. A continuously moving stage contributed to erroneous position data as the pixel size was increased beyond the maximum theoretical resolution of the instrument.     

Fiber Raman background study and its application in setting up optical fiber Raman probes

Fiber Raman background spectra of different types of fused-silica fibers are studied and compared. The results show the following: (a) all the background spectra are very similar and comparable with Raman spectra of fused silica, regardless of the difference in the cladding and buffer materials; (b) the overall background intensity increases with the fiber numerical aperture but has no obvious relation with the core diameter. Both experimental evidence and theoretical explanation have been provided for these views. A simple and unfiltered fiber probe for surface-enhanced Raman scattering detection with low fiber Raman background interference is constructed, and the optimum configuration of the probe is suggested and discussed based on the results of the background study.     

Resonant Raman and micro-Raman scattering from Si matrix with unburied beta-FeSi2 nanolayers

Samples, representing Si matrix with nanolayers of the semiconducting beta-FeSi2 silicide are studied by Raman scattering. The unpolarized Raman spectra of the samples are measured in two different configurations. It is found that the characteristic beta-FeSi2 Raman modes are seen in the spectra, taken at incident angle of about 45 degrees , while only comparatively intensive broad feature is detected in a back-scattering geometry. The difference in the spectra is interpreted with the appearance of surface polariton modes of the optical phonons in the nanosized layers in near back-scattering geometry. The resonant Raman scattering is investigated at incident light angle of about 45 degrees and the energies of the interband transitions in the investigated energy range are determined. It is known that the resonant Raman scattering appears to be even more precise method for the determination of the interband transitions energies than the modulation spectroscopy. Thus we claim that the energies determined here are firstly determined with such a precision.     

Thin film of aluminum oxide through pulsed laser deposition: a micro-Raman study

Successful use of micro-Raman spectroscopy to characterize the surface of the thin Al₂O₃ films deposited on Si(010) substrate through pulsed laser ablation is presented. The micro-Raman spectra have been recorded on several spots (sized ≈1 μm) over the length and the breadth of the films in a systematic fashion. The as-deposited films are inhomogeneous from spot-to-spot over the surface. The variation in characteristic properties of 521 cm⁻¹ line of crystalline Si (c-Si) have been used to estimate the thickness of the Al₂O₃ films. The thickness of the films has been found to depend on the position of the substrate with respect to the plume boundaries produced by the laser pulse after hitting the Al target. The thickness also depends on the position of the spot on a film placed at a fixed distance from the target surface. The thickness profiling of the deposited films on the basis of micro-Raman spectroscopic investigations corroborates the theoretical prediction of the model of the plume formation and the formation of the shock-front region in the pulsed laser deposition technique. All the seven Raman active modes (2A_1g+5E_g) observable in single crystals of sapphire (c-Al₂O₃) powder have been identified in the complex spectra obtained from deposited film surfaces under varying experimental conditions. The intensity variation of an isolated line (750 cm⁻¹) of Al₂O₃ corroborates the deposition profiling obtained from c-Si line parameters. The most intense Raman lines in the micro-Raman spectra of the deposited films are two infrared active modes around 450 and 600 cm⁻¹. The strong presence of these infrared active modes in the micro-Raman spectra suggests a highly distorted micro-crystalline structure of the films. The local micro-stress created by the micro-crystals on the Si-substrate is maximum near the stopping distance of the plume. Largest micro-crystal of Al₂O₃ are also seen over the spot near the stopping distance of the plume.     

Strain measurement in diacetylene-containing copolymers using Raman spectroscopy

Rigid diacetylene-containing block copolymers are shown to have Raman spectra similar to those of polydiacetylene single crystals. The vibrational frequencies of certain main-chain Raman-active modes of the copolymers are sensitive to deformation which enables strain measurement to be made by following the shift in the Raman band positions. Measurements of the stress concentrations around defects in copolymer specimens during deformation have been carried out using Raman spectroscopy and they have been compared with theoretical analyses of stress concentrations. There is good agreement between the theoretical and experimental measurements and it has been demonstrated that the use of Raman spectroscopy allows the measurement of stress or strain in complex situations for which no theoretical solutions exist.     

On the band diagram of Mg2Si/Si heterojunction as deduced from optical constants dispersions

The optical constant dispersions of ion-beam-synthesized Mg₂Si phase in Si matrix are obtained from the transmittance and reflectance spectra. Two types of samples are studied - one of them with Mg₂Si phase embedded in n-type (100)Si and the other with Mg₂Si phase embedded in p-type (100)Si. The formation of the phase is proved by Raman scattering and infrared transmittance measurements. From the interpretation of the optical constant dispersions, the energies of the transitions nearby the material band edge are determined. As a result the band diagram of the heterojunction Mg₂Si/Si is obtained. The results about the Mg₂Si band gap value are compared with the theoretically predicted and experimentally determined ones. The value of the conduction band offsets of Mg₂Si and Si is not reported by now.     

Raman spectroscopy of graphite

We present a review of the Raman spectra of graphite from an experimental and theoretical point of view. The disorder-induced Raman bands in this material have been a puzzling Raman problem for almost 30 years. Double-resonant Raman scattering explains their origin as well as the excitation-energy dependence, the overtone spectrum and the difference between Stokes and anti-Stokes scattering. We develop the symmetry-imposed selection rules for double-resonant Raman scattering in graphite and point out misassignments in previously published works. An excellent agreement is found between the graphite phonon dispersion from double-resonant Raman scattering and other experimental methods.     

Thickness of diamond-like carbon coatings quantified with Raman spectroscopy

A model is developed for quantifying the thickness of thin coatings and wear scars using Raman spectroscopy. The model, which assumes that both incident and Raman light obey Beer's law, was applied to Raman spectra from a diamond-like carbon (DLC) coating containing Si and O, known as DLN (diamond-like nanocomposite). The coatings ranged in thickness from 10 nm to 2 μm, according to stylus profilometry. Systematic variations in the Raman carbon (G band) and Si (1st order) peak intensities vs. thickness were found. Fits to the model gave an optical mean free path of λ250 nm for DLN. This value is in good agreement with optical absorption coefficient values of other DLC films. Thickness profiles of wear tracks in the coatings determined by the model compared well with depths determined by profilometry.