高性能ZnO纳米块体材料的制备及其拉曼光谱学特征

利用六面顶高压设备制备了高密度、低脆性、纳米级的ZnO块体材料，用MDI/JADE5 X射线衍射仪(Cu靶)和XL30S-FEG场发射扫描电子显微镜对高压样品的相组成、晶粒尺寸及微观形貌进行了表征.利用E55+FRA106/5傅里叶变换激光拉曼光谱仪通过ZnO块体样品位于50—500cm^-1之内的拉曼光谱, 研究了极性半导体纳米材料的拉曼光谱学特征.发现在极性半导体ZnO纳米块体材料中，没有出现明显的尺寸限制效应. 关键词： ZnO纳米块体 拉曼光谱 尺寸限制效应     

若干低维材料的拉曼光谱学研究--2004年度国家自然科学二等奖获奖项目介绍

文章扼要介绍了2004年国家自然科学二等奖获奖项目：《若干低维材料的拉曼光谱学研究》．用拉曼光谱研究低维纳米材料,必须对传统拉曼光谱学进行改造,创建新的“低维拉曼光谱学”．该项目通过若干低维材料的研究,为创建低维拉曼光谱学作出了系统的创新性贡献,如最先鉴认出典型低维材料的拉曼指纹谱,发现拉曼光谱的两个基本特征出现“反常”,但证明拉曼散射基本原理在低维体系中依然成立．通过低维拉曼光谱和光发射谱的应用研究,发现了材料的许多新奇物性,如发现超晶格和碳纳米管是类缺陷结构,和极性半导体纳米晶材料具有非晶特性,并提出了多孔硅的“量子限制电化学”形成和“多源量子阱”光发射模型,促进了低维材料和半导体器件的制备．     

A Raman and dielectric study of ferroelectric ceramics

Dielectric and Raman scattering experiments were performed on various ceramics with composition Ba(Ti_1-xZr_x)O₃. Such lead-free, environmental-friendly materials were shown, from dielectric measurements, to exhibit behaviours extending from conventional to relaxor ferroelectrics on increasing the zirconium concentration. The evolution of the Raman spectra was studied as a function of temperature for various compositions, and the spectroscopic signature of the corresponding phases was determined. In the relaxor state, the variation of the integrated intensity of the Raman lines with temperature showed a plateau at low temperature. This anomaly was also detected as a peak in depolarization current measurements, and attributed to ergodicity breaking which characterizes usual relaxor systems. Raman results hint at locally rhombohedral polar nanoregions resulting from the random fields associated with Zr ions. Received 25 September 1998     

ZnO纳米管的拉曼光谱学研究

通过对ZnO纳米管样品的拉曼光谱研究,发现ZnO纳米管拉曼频率和体材料拉曼频率相同,在不同波长激发下,ZnO纳米管拉曼谱峰的频率也保持不变,从而得到了极性晶体拉曼谱不同于以往非极性拉曼谱的特性:在纳米体系中没有出现明显的尺寸限制效应。     

Investigation of structural phase transition in polycrystalline SrTiO3 thin films by Raman spectroscopy

Polycrystalline SrTiO₃ thin films were prepared by pulsed laser deposition technique. The phonon properties and structural phase transition were studied by Raman spectroscopy. The first-order Raman scattering, which is forbidden in SrTiO₃ single crystal, has been observed in the films, due to the structural distortion caused by strain effect and oxygen vacancies. The Fano-type line shape of TO₂ phonon reveals the existence of polar microregions in the STO thin films. The evolution of TO₂ and TO₃ phonons with temperature shows the occurrence of a structural phase transition at 120 K related to the formation of polar macroregions in the films.     

Dependence of vibrational density of states and Raman spectra on size in non-polar and polar nano-crystalline semiconductors

The vibrational density of states (VDOS) of Si, diamond, SiC, and InSb clusters has been calculated using the cluster model for various cluster sizes. The results show that the peak frequency of optical-like bands of VDOSs of non-polar nano-crystalline (NC) semiconductors varies with size, but that of polar NC semiconductors does not vary with size. We attribute the origin of this different behavior of non-polar and polar NC semiconductors to different interactions in the optical-like modes of them. That is, the deformation potentials for the non-polar NC semiconductors and electrostatic potentials for the polar NC semiconductors. According to the amorphous crystal (aC) model, Raman spectra are directly related to VDOS. In this Letter, it is verified that the aC model can be applied to NC semiconductors. Calculated VDOS are compared with observed Raman spectra of corresponding samples, which show agreement.     

Analysis of semiconductor surface phonons by Raman spectroscopy

Only recently Raman spectroscopy (RS) has advanced into the study of surface phonons from clean and adsorbate-covered semiconductor surfaces. RS allows the determination of eigenfrequencies as well as symmetry selection rules of surface phonons, by k-conservation limited to the Brillouin zone-center, and offers a significantly higher spectral resolution than standard surface science techniques such as high-resolution electron energy loss spectroscopy. Moreover, surface electronic states become accessible via electron–phonon coupling. In this article the fundamentals of Raman scattering from surface phonons are discussed and its potential illustrated by considering two examples, namely Sb-monolayer-terminated and clean InP(110) surfaces. Both are very well understood with respect to their atomic and electronic structure and thus may be regarded as model systems for heteroterminated and clean semiconductor surfaces. In both cases, localized surface phonons as well as surface resonances are detected by Raman spectroscopy. The experimental results are compared with surface modes predicted by theoretical calculations. On InP(110), due to the high spectral resolution of Raman spectroscopy, several surface modes predicted by theory can be experimentally verified. Surface electronic transitions are detected by changing the energy of the exciting laser light indicating resonances in the RS cross section. Received: 7 April 1999 / Accepted: 25 June 1999 / Published online: 16 September 1999     

Understanding as well as characterization of erratic interspike dynamics in semiconductor devices

The understanding of the origin of electronic noise would be very important in semiconductor devices. Detecting time characteristics via statistical approaches has been known to be useful in complex systems. In this study, the ensemble Monte Carlo particle method is used to simulate electron transport in a layered III-V semiconductor at room temperature. Nonlinear/erratic spiking fluctuations are predominant at the onset of current instabilities. To explore time characteristics detrended fluctuation analysis is used to analyze interspike intervals in different scales. Interestingly, multifractal behaviors are responsible for this kind of electronic noise. Therefore, it indicates that many extra time-characteristic would emerge in semiconductor devices, which would be strongly related to polar optical phonon scattering for intervalley transfer.     

Electron Raman scattering in cylindrical quantum wires

Electron Raman scattering (ERS) is investigated in a free-standing semiconductor quantum wire of cylindrical geometry for two classes of materials CdS and GaAs. The differential cross section (DCS) involved in this process is calculated as a function of a scattering frequency and the radius of the cylinder. Electron states are considered to be confined within a free-standing quantum wire (FSW). Single parabolic conduction and valence bands are assumed. The selection rules are studied. Singularities in the spectra are found and interpreted for various radii of the cylinder.     

不同晶向SrTiO3上外延GaAs薄膜的光谱研究

利用MBE生长技术,成功地在不同晶向SrTiO3(100)(111)(110)衬底上生长了GaAs薄膜,利用显微Raman和荧光光谱（PL）对此进行了研究。实验结果表明,在不同晶向SrTiO3上生长的GaAs薄膜有不同的晶向和应力状态。荧光光谱（PL）研究表明在SrTiO3(100)(111)晶面上生长的GaAs薄膜的PL峰发生明显的蓝移。研究表明在SrTiO3(110)面上生长的GaAs薄膜和体单晶基本上一致,有更好的光学质量。     

Control of Schottky barrier heights on high-K gate dielectrics for future complementary metal-oxide semiconductor devices

The calculated Schottky barrier heights of polar and nonpolar interfaces of many metals on HfO2 high dielectric constant gate oxide have been found to vary strongly with the metal work function and also with oxide termination, with relatively little Fermi level pinning. This indicates that the choice of metal gate materials will not limit the continued scaling of metal-oxide semiconductor devices.     

近年国内非弹性光散射研究的一些进展

本文介绍了近二年来我国在用喇曼散射和布里渊散射研究半导体、金属及半导体超晶格,高温超导体、磁性物质和介电晶体等方面的进展,以及表面增强喇曼和受激光散射研究的进展情况。     

Excimer laser-induced crystallization of CdSe thin films

We have investigated ArF (λ=193 nm) excimer laser-induced crystallization of amorphous CdSe semiconductor thin films. The crystallization has been monitored by a related photoluminescence emission in the free-exciton and defect-band transition regions. For different irradiation conditions, we have observed formation of nanorods, up to 2 μm long, as well as the formation of arrays of CdSe nanobeads with a narrow size distribution and characteristic dimensions corresponding to λ/2 and λ/8. The successful crystallization has also been confirmed by confocal Raman spectroscopy.     

拉曼光谱技术在食品质量安全检测中的应用

拉曼光谱技术具有样品无需前处理、操作简便、时间短、灵敏度高等优点,可获得样品的物理化学及深层结构信息,已广泛应用于石油化工、生物医学、地质考古、刑事司法、宝石鉴定等领域。拉曼光谱对水等极性物质极其不敏感,在食品质量安全检测方面具有良好的应用前景。论文简述了拉曼光谱技术的检测原理、分类以及系统的组成,综述了拉曼光谱技术在食品成分分析和农药残留检测中的最新研究进展,指出了该技术在食品质量安全检测中的关键技术并对今后的研究进行了展望。     

A Semiconductor Laser of the Visible Range as an Exciting Source of Raman Scattering

A possibility of application of semiconductor lasers of the visible range as exciting sources for Raman spectroscopy is studied. An experimental set-up for measuring Raman spectra of polycrystalline dielectrics and broad-gap semiconductors excited by a semiconductor laser with a wavelength of 640 nm was created. The conditions under which the spectral width of the lasing line of a semiconductor laser was within 10^-3 cm^-1 in the continuous mode with a power of 10 mW are realized. The characteristics of various types of exciting sources used in Raman spectroscopy are compared. The results of studies of the characteristic Raman spectra excited with a semiconductor laser in polycrystalline sulfur are presented.     

One-phonon-assisted resonant electron Raman scattering of GaAs quantum dots in an AlAs matrix

We have presented a theoretical calculation of the differential cross section (DCS) for the electron Raman scattering (ERS) process associated with the bulk-like longitudinal optical (LO) and interface optical (IO) phonon modes in semiconductor quantum dots (QDs). Electron states are considered to be confined within the QDs. We consider the Fröhlich electron-phonon interaction in the framework of the dielectric continuum approach. We study selection rules for the processes. Some singularities in the Raman spectra are found and interpreted. A discussion of the phonon behavior for QDs with large and small size is presented. The numerical results are also compared with that of experiments.     

Surface-enhanced Raman spectroscopy of semiconductor nanostructures

We review our recent results concerning surface-enhanced Raman scattering (SERS) by confined optical and surface optical phonons in semiconductor nanostructures including CdS, CuS, GaN, and ZnO nanocrystals, GaN and ZnO nanorods, and AlN nanowires. Enhancement of Raman scattering by confined optical phonons as well as appearance of new Raman modes with the frequencies different from those in ZnO bulk attributed to surface optical modes is observed in a series of nanostructures having different morphology located in the vicinity of metal nanoclusters (Ag, Au, and Pt). Assignment of surface optical modes is based on calculations performed in the frame of the dielectric continuum model. It is established that SERS by phonons has a resonant character. A maximal enhancement by optical phonons as high as 730 is achieved for CdS nanocrystals in double resonant conditions at the coincidence of laser energy with that of electronic transitions in semiconductor nanocrystals and localized surface plasmon resonance in metal nanoclusters. Even a higher enhancement is observed for SERS by surface optical modes in ZnO nanocrystals (above 10⁴). Surface enhanced Raman scattering is used for studying phonon spectrum in nanocrystal ensembles with an ultra-low areal density on metal plasmonic nanostructures.     

Theory of the effect of a DC magnetic field on surface space-charge-wave/optical phonon instabilities in semiconductor media

A theoretical investigation has been carried out on the effect of a DC magnetic field on surface space-charge-wave instabilities caused by a drift current parallel to the surface of a doped polar semiconductor. The magnetic field is taken as perpendicular to the semiconductor surface. The dispersion relation is obtained using a generalization of the Kliewer-Fuchs specular-reflection boundary conditions. Calculated results are obtained in the non-retarded limit for two cases: (1) where a current-carrying, nonpolar semiconductor interfaces a polar insulator half-space and (2) where a current-carrying, polar semiconductor interfaces a nonpolar insulator half-space. Convective or amplifying instabilities arise because of the presence of optical phonons. Numerical results are presented for the gain as a function of frequency and magnetic field.     

Raman spectroscopy of graphene and carbon nanotubes

This paper reviews progress that has been made in the use of Raman spectroscopy to study graphene and carbon nanotubes. These are two nanostructured forms of sp² carbon materials that are of major current interest. These nanostructured materials have attracted particular attention because of their simplicity, small physical size and the exciting new science they have introduced. This review focuses on each of these materials systems individually and comparatively as prototype examples of nanostructured materials. In particular, this paper discusses the power of Raman spectroscopy as a probe and a characterization tool for sp² carbon materials, with particular emphasis given to the field of photophysics. Some coverage is also given to the close relatives of these sp² carbon materials, namely graphite, a three-dimensional (3D) material based on the AB stacking of individual graphene layers, and carbon nanoribbons, which are one-dimensional (1D) planar structures, where the width of the ribbon is on the nanometer length scale. Carbon nanoribbons differ from carbon nanotubes is that nanoribbons have edges, whereas nanotubes have terminations only at their two ends.     

Tapered waveguide semiconductor raman laser

Semiconductor Raman laser can act as a heterodyne demodulator of terahertz-band modulated light wave signals in wideband optical communication systems. We have been developing the semiconductor Raman laser with a waveguide structure composed of a GaP core and Al_xGa_1–xP cladding layers. The tapered waveguide structure can reduce the threshold pump power by increasing the internal pump power density. Fabricated tapered waveguide semiconductor Raman laser have shown the threshold pump power of 160 mW. Discussion is made on the origin of losses as well as the limit of the low pump power operation.