ECR-CVD方法生长a-SiNx:H薄膜的研究

使用微波电子回旋共振等离子体化学气相沉积(ECR-CVD)方法室温生长了非晶氢化的氮化硅薄膜,通过改变前驱气体(SiH4 80%Ar和NH3)的流量比,研究了薄膜的生长速率、等离子体的发射光谱和薄膜的红外特性.结果表明:随着NH3流量的增加,氮化硅薄膜的生长速率呈下降趋势,这主要是由于等离子体中的气相前驱成分之一硅基团浓度的不断下降所导致的;随着NH3流量的增加,薄膜中键合了较多的具有较高电负性的N原子是Si-N和Si-H伸缩振动发生蓝移的主要原因.红外光谱的定量计算表明所制备的氮化硅薄膜具有相对较低的H浓度,约15%左右.文中对氮化硅薄膜的生长机制也进行了讨论.     

High rate deposition of a-Si:H and a-SiNx:H by VHF PECVD

Very High Frequency (VHF) plasma enhanced chemical vapour deposition (PECVD) has been applied to hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (a-SiN_x:H) films for thin film transistors (TFTs) fabrication. The effect of the excitation frequency on the deposition rate and the film quality of both films has been investigated. The films were prepared by VHF (30 MHz∼50 MHz) and HF (13.56 MHz) plasma enhanced CVD.High deposition rates were achieved in the low pressure region for both a-Si:H and a-SiN_x:H depositions by the use of VHF plasma. The maximum deposition rates were 180 nm/min for a-Si:H at 50 MHz and 340 nm/min for a-SiN_x:H at 40 MHz. For a-SiN_x:H films deposited in VHF plasma, the optical bandgap, the hydrogen content and the [Si–H]/[N–H] ratio remain almost constant regardless of an increase in deposition rate. The increase of film stress could be limited to a lower value even at a high deposition rate. The TFTs fabricated with VHF PECVD a-Si:H and a-SiN_x:H films showed applicable field effect mobility. It is concluded that VHF plasma is useful for high rate deposition of a-Si:H and a-SiN_x:H films for TFT LCD application.     

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.     

Resonant Raman spectroscopy of nanotubes

Single and double resonances in Raman scattering are introduced and six criteria for the observation and identification of double resonances stated. The experimental situation in carbon nanotubes is reviewed in view of these criteria. The evidence for the D mode and the high-energy mode is found to be overwhelming for a double-resonance process to take place, whereas the nature of the radial breathing-mode Raman process remains undecided at this point. Consequences for the application of Raman scattering to the characterization of nanotubes are discussed.     

Hole-enhanced Raman scattering

Stokes and anti-Stokes non-resonant hole-enhanced Raman scattering (HERS) spectra with high signal-to-noise ratio (S/N) are reported for the first time for aqueous phase R6G molecules adsorbed onto random nanoholes in thin gold films. Compared to conventional surface-enhanced Raman scattering from nanometric gold colloid particles, HERS exhibits higher strength gain, exceptional reproducibility, simple and reliable substrate preparation, and excellent mechanical stability. By correlating the hole density with Raman scattering gain, we determined optimum HERS gain for 50 nm diameter holes at approximately 100 holes/microm(2). Providing a Raman substrate with uniform "hot spots", we expect that HERS will make the quantitative Raman analysis of biological molecules possible.     

Multiplex H2 coherent anti-Stokes Raman scattering thermometry with a modeless laser

The use of a modeless laser as the Stokes source for multiplex coherent anti-Stokes Raman scattering in molecular hydrogen is reported. The elimination of noise associated with mode competition in conventional standing wave lasers is shown to result in reliable and accurate single-shot thermometry of H(2) in a microwave-assisted diamond chemical vapor deposition plasma reactor. Single-shot temperatures are recorded with a precision of 7.3%. Possible improvements to this precision are discussed and applications of the technique for on-line process monitoring are briefly presented.     

Raman scattering in air: four-dimensional analysis

Inertial confinement fusion requires propagation of high-intensity, pulse-shaped IR and UV laser beams through long air paths. Such beams are subject to energy losses and decreased beam quality as a result by stimulated rotational Raman scattering (SRRS). In this paper we describe how quantum fluctuations, stimulated Raman amplification, diffraction propagation, and optical aberrations interact during the propagation of short, high-power laser pulses using a four-dimensional (4-D) model of the optical beams and the medium. The 4-D model has been incorporated into a general optical-propagation computer program that allows the entire optical system to be modeled and that is implemented on high-end personal computers, workstations, and supercomputers. The numerical model is used to illustrate important phenomena in the evolution of the optical beams. In addition, the OMEGA Upgrade laser system is used as a design case to illustrate the various considerations for inertial confinement fusion laser design.     

Raman spectroscopy of crystals for stimulated Raman scattering

Raman frequency shift, line width, integral and peak Raman scattering cross sections were measured in various crystals using spontaneous Raman spectroscopy. The highest Raman gain coefficient in steady state Stimulated Raman Scattering (SRS) regime was proved to be in barium nitrate crystal; for transient SRS it is expected to be in lithium niobate and tungstate crystals. Barium molybdate crystal is proposed as a new highly efficient Raman material.OCIS: 300.6450; 290.5910; 190.2640     

Gas-phase thermometry using delayed-probe-pulse picosecond coherent anti-Stokes Raman scattering spectra of H2

We report the development and application of a simple theoretical model for extracting temperatures from picosecond-laser-based coherent anti-Stokes Raman scattering (CARS) spectra of H2 obtained using time-delayed probe pulses. This approach addresses the challenges associated with the effects of rotational-level-dependent decay lifetimes on time-delayed probing for CARS thermometry. A simple procedure is presented for accurate temperature determination based on a Boltzmann distribution using delayed-probe-pulse vibrational CARS spectra of H2; this procedure requires measurement at only a select handful of probe-pulse delays and requires no assumptions about sample environment.     

Stimulated Raman scattering of laser radiation in Raman crystals

Experimental study of stimulated Raman scattering (SRS) in barium nitrate and potassium gadolinium tungstate crystals are presented. Main features of crystalline single and multipass Raman shifters, Raman lasers with external and intracavity pumping are investigated and compared. Optimization of the optical schemes resulted in development of compact solid state Raman lasers for new important near infrared and eye safe spectral region of 1.2–1.5 μm.     

Surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS): a review of applications

Surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) can provide positive identification of an analyte or an analyte mixture with high sensitivity and selectivity. Better understanding of the theory and advances in the understanding of the practice have led to the development of practical applications in which the unique advantages of SERS/SERRS have been used to provide effective solutions to difficult analytical problems. This review presents a basic theory and illustrates the way in which SERS/SERRS has been developed for practical use.     

High-resolution Raman scattering in oligonucleotides

High-resolution Raman spectra have been obtained by a high-sensitivity nonresonant scattering technique for short single-strand oligonucleotides synthesized by the solid-state amidophosphite method on an automated synthesizer.     

Moving nanoparticles with Raman scattering

We show how to change optically the distance between two protein-linked gold nanoparticles by Raman-induced motion of the linker protein. Rayleigh scattering spectroscopy of the coupled-particle plasmon allows us to compare the inter-nanoparticle distance of individual protein-linked gold nanoparticle dimers before and after surface-enhanced Raman scattering (SERS). We find that low-intensity (50 microW/microm2) laser light in resonance with the nanoparticle-dimer plasmon provokes a change of the inter-nanoparticle distance on the order of 0.5 nm whenever SERS from the proteins connecting the nanoparticles can be observed.     

Resonant Raman spectroscopy of individual strained single-wall carbon nanotubes

Resonance Raman spectra of individual strained ultralong single-wall carbon nanotubes (SWNTs) are studied. Torsional and uniaxial strains are introduced by atomic force microscopy manipulation. Torsional strain strongly affects the Raman spectra, inducing a large downshift in the E2 symmetry mode in the G+ band, but a slight upshift for the rest of the G modes and also an upshift in the radial breathing mode (RBM). Whereas uniaxial strain has no effect on the frequency of either the E2 symmetry mode in the G+ band or the RBM, it downshifts the rest of the G modes. The Raman intensity change reflects the effect of these strains on the SWNT electronic band structure.