分子束外延PbTe单晶薄膜的反常拉曼光谱研究

采用分子束外延(MBE)方法在BaF₂(111)衬底上生长了高质量的PbTe单晶薄膜， 拉曼光谱测量观察到了表面氧化物的振动模、布里渊区中心(q≈0)纵光学(LO)声子振动模以 及声子-等离子激元耦合模振动.随着显微拉曼光谱仪激光光斑聚焦深度的改变，各拉曼散射 峰的峰位、积分强度、半高宽等都表现出不同的变化趋势. 随着激光光斑聚焦位置从样品表 面上方3μm处变化到表面下方3μm处，PbTe外延薄膜的LO声子频率从119cm^-1移 动到124cm^{-1关键词： PbTe外延薄膜 拉曼散射 纵光学声子}     

利用拉曼光谱对短链烷烃的相变过程及旋转相的研究

利用激光拉曼光谱研究了二十六烷的凝结相变过程。在冷却过程中,二十六烷经历了从液相→旋转相→固态单斜晶相的相变过程。主要研究了烷烃分子碳链上CH₂弯曲振动、CH₂剪式振动、C—C伸展振动和CH₃平面摇摆等振动模式的变化过程,包括这些模的频率、半宽和强度变化等,研究在相变过程中不同振动模式的的演变顺序和过程,反映各种振动模式与分子结构的相关性,并了解反式构象和歪曲构象在相变过程中的变化,从而更深入的理解烷烃等非晶体物质的相变过程。此外,通过分析800～1 500 cm-1波段各个拉曼波峰在降温过程中的变化过程,得到了二十六烷的旋转相的温度区间,证明可以利用拉曼光谱来观察烷烃相变过程中出现的旋转相。     

掺Er/Er+O的GaN薄膜光学性质的研究

利用Raman散射谱研究了GaN注Er以及Er+O共注样品的振动模，并讨论了共注入O对Er离子发光的影响. 在Raman散射谱中，对于注Er的GaN样品出现了300 cm^-1和670 cm^-1两个新的Raman峰，而对于Er+O共注样品，除了上述两个峰外，在360 cm^-1处出现了另外一个新的峰，其中300 cm^-1峰可以用disorder-activated Raman scattering (DARS)来解释，670 cm^-1峰是由于与N空位相关的缺陷引起的，而360 cm^-1峰是由O注入引起的缺陷络合物产生的. 由于360 cm^-1模的缺陷出现，从而导致Er+O共注入GaN薄膜红外光致发光(PL)强度的下降. 关键词： GaN Er Raman散射 光致发光     

用布里渊散射研究晶体相变

在研究相变和临界现象中,光散射实验起着十分重要的作用.在晶体的结构相变研究中,高分辨的喇曼和布里渊散射谱能够提供有关“软模”的许多知识.软模是一种对温度有着很强依赖性的晶格振动,其振动频率在相变点变为零.软模的凝聚导致自发对称破缺. 当晶体发生相变时,弹性性质通常表现出反常.由于布里渊散射实验能够探测长波声学模行为,因此在过去的十六年中,布里渊散射光谱学被广泛地应用来研究固体相变.它有力地补充了与此紧密相近的声共振和超声传播测量手段所获得资料.这些实验结果,与喇曼散射、非弹性中子散射和X射线测量结果综合起来,使…     

过渡金属原子与一氧化碳作用对C—O伸缩振动的红外和拉曼光谱强度的影响

采用杂化密度泛函方法计算了过渡金属M-CO分子的基态几何结构和谱学性质。计算结果表明C—O伸缩振动的红外强度明显比M-C和弯曲振动模的红外强度大;C—O伸缩振动有最大的拉曼散射因子,且第四周期和Cu族金属的M-CO分子的C—O伸缩振动的拉曼散射因子明显比其他过渡金属的大。     

基于群论的PAHs分子偏振拉曼去噪

利用群论理论研究16种多环芳烃(polycyclic aromatic hydrocarbons,PAHs)分子振动规律,并对PAHs指纹区特征拉曼峰进行偏振去噪,减少非特征拉曼峰对特征拉曼峰的干扰,增强16种PAHs之间的拉曼辨识度。群论分析发现16种PAHs分别属于C_s,C_2v,C_2h,D_2h点群,四个点群中的A′,A₁,A_g,A_g类对称振动属于全对称振动,其余对称振动为非全对称振动,其中全对称振动均具有拉曼活性。Gaussian 09杂化密度泛函理论计算与群论分析相结合,发现16种PAHs全对称振动分布拉曼位移全区域,涵盖16种PAHs基团振动模式;全对称振动产生的波动性小,具有一定的抗外部环境干扰能力,稳定性相对较高,并且其产生的拉曼峰更强。根据全对称振动具有代表性、稳定性、显著性的特征,本文将16种PAHs的全对称振动作为特征拉曼振动。此外,研究发现,拉曼偏振效应与振动模对称性直接相关,拉曼光谱的偏振效应具有增强PAHs特征拉曼峰、降低PAHs非特征峰强度的作用。16种PAHs通过拉曼光谱的偏振效应选择性调节作用后,PAHs特征拉曼峰信噪比可提高6.52%~182%,说明利用拉曼偏振效应去除非特征拉曼峰的作用显著,可有效降低特征峰的噪声干扰。因此,所建立的基于群论的PAHs分子拉曼偏振去噪方法可以改善其拉曼光谱信号质量,提高PAHs同步拉曼光谱分析效率,为实现16种PAHs同步拉曼光谱检测提供了理论依据。     

铝硅酸盐Raman活性分子振动解析

分别测定了蓝晶石、红柱石和硅线石三种铝硅酸盐天然矿物晶体以及K₂O-Al₂O₃-SiO₂三元铝硅酸盐玻璃的Raman光谱。构建了一组硅铝四面体聚集体结构模型,采用量子化学自洽场分子轨道从头计算的方法计算了其Raman振动频率。分析研究了上述Raman光谱振动特征,确定了特征谱峰的归属,解析了铝对铝硅酸盐Raman活性分子振动特征的影响。结果表明,随四配位铝的增加,导致800～1 200 cm-1波数区间内谱峰频率降低,该区间的谱峰是Si—O_nb间非桥氧对称伸缩振动引起的,其中不含Al—O振动;700～800 cm-1区间内出现的谱峰归属于Al—O_nb间非桥氧的对称伸缩振动。     

溴乙烷分子的质量分辨阈值光谱

利用单色双光子(1C2P)技术得到了高精度的溴乙烷分子的质量分辨阈值(MATI)光谱，精确给出了溴乙烷分子的绝热电离势和离子振动频率.从中性基态到离子基态两个自旋-轨道分量X₁ ²E_1/2和X₂ ²E_1/2的绝热电离势分别为83097±3 cm^-1和85452±3 cm^-1，离子基态两个自旋-轨道分量的间隔为2355±6 cm^-1，这些值与文献报道值符合得较好，且精度更高.溴乙烷分子的单色双光子质量分辨阈值光谱展现出丰富的振动结构，这是在溴乙烷分子相继吸收两个光子的过程中波包在解离态势能面上演化的结果.以已有的离子振动谱标识为参考，以中性分子的振动频率为基础，标识了溴乙烷分子的质量分辨阈值光谱，发现观测到的振动模几乎都和溴乙烷分子的解离运动有关，其中还包括一些非全对称模. 关键词： 质量分辨阈值光谱 振动模 单色双光子零动能光谱技术 溴乙烷     

InGaN合金中LO声子-等离子激元耦合模的研究

分别采用532,488 nm可见光和325 nm紫外光激发,对金属有机化学气相沉积法在蓝宝石衬底上生长的六方相InGaN/GaN薄膜样品在室温和78 K低温下的拉曼散射谱进行了研究。在可见光激发时,E₂模和A₁(LO)模的散射信号主要来自GaN层;采用紫外光激发时,A₁(LO)模向低频方向移动且共振增强,此散射信号来自InGaN层。在可见光激发的情况下,在A₁(LO)模的高频方向观察到一个宽峰,此宽峰为InGaN的LO声子-等离子激元耦合模,根据耦合模频率得到InGaN层中的电子浓度为n_ｅ＝1.61×1018 cm-3。紫外光激发时,没有观察到耦合模,A₁(LO)模散射信号主要来自样品表面耗尽层,由此估算样品中的耗尽层宽度大约在40 nm。此外,还对比分析了在室温和78 K低温下LO声子-等离子激元耦合模的散射强度的变化规律,计算了不同温度下等离子激元的屏蔽波矢。这些结论对于了解InGaN材料的基本性质以及氮化物光电器件的开发利用都有重要参考价值。     

GaN和GaN:Mg外延膜低温拉曼谱的对比研究

对液氮温度下六方相GaN和掺Mg的P型GaN薄膜的拉曼谱进行了对比研究。除对两个样品中主晶格振动模进行了对比分析外,着重讨论了位于247 cm-1的散射峰的产生机制。结果表明GaN:Mg的谱中该峰的散射强度随温度升高先增大再减小,在500K以上消失且对样品重新降温到78K观察此峰不再出现,因此认为它是缺陷产生的振动模。而GaN样品中经同样加热降温的过程此峰仍然存在,说明两个样品中该峰的产生机制不同。此外,在GaN:Mg的谱中还观察到Mg诱导的局域振动模。     

Comparison of the Raman pressure shift and the Raman temperature shift of benzene and diamond with the ruby soale

Abstract

In order to serve as substitute for the pressure ruby scale at high temperature, the breathing mode of bemsens (990 cm^?1) and the first order Raman mode of diamond (1333 cm^?1) have been studied as a function of pressure and temperature in the range of 0–15 GPa and 25–400°C. The diamond and bensene Raman frequency shifts are shoft to be of valuable use as a pressure scale at high temperature. A further advantage of bensene is to remain a suitable pressure transmitting medium up to 350°C and 15 GP.     

Raman and DFT study of hydrogen‐bonded 2‐ and 3‐chloropyridine with methanol

Precise polarized Raman measurements of 2‐chloropyridine (2Clpy) in the region 560–1060 cm⁻¹ and 3‐chloropyridine (3Clpy) in the region 680–1080 cm⁻¹ at different concentrations in mole fraction of methanol were made to calculate the isotropic part of the Raman spectra, which has contributions only from vibrational dephasing. A detailed analysis of the Raman spectra was carried out to see the variation of peak position and linewidth. The dephasing is mode specific. The trigonal bending mode of 3Clpy has two components when it is mixed with methanol. The relative intensities of these two bands are used to calculate the equilibrium constants. The ring‐breathing mode of 3Clpy, on the other hand, remains single in the mixture. The appearance of a new band corresponding to the trigonal bending mode, as well as the nonappearance of that of the ring‐breathing mode, is also shown by the density functional theory (DFT) study of gas phase and methanol‐solvated complexes. The vibrational dephasing time for the hydrogen‐bonded ring‐breathing mode is calculated from the linear Raman linewidth and peak position data. For other modes, it was not possible to calculate the dephasing time because of the nonavailability of a suitable theoretical model. Contrary to 3Clpy, in 2Clpy the ring‐breathing mode becomes a doublet but the trigonal bending mode remains single. It is seen that the hydrogen‐bonding capacity of chloropyridines is highly influenced by the position of the Cl atom. Single and double components of these modes are also explained by DFT calculations. We obtained excellent match of the experimental and theoretical spectra with the B3LYP/6‐31 + G (d,p) method. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of hydrostatic pressure on the Raman spectrum of anatase (TiO2)

Raman spectra of anatase have been investigated under pressures up to 60 kbar and at room temperature. A pressure-induced phase transition is observed at pressures above 25.6 kbar. The 197 cm^-1 mode (at 1 atm.) of six Raman active modes exhibits anomalous pressure dependence in which the frequency decreases with increasing pressure. This mode may be significant in the phase transition. The remaining modes show usual behavior.     

Evidence for a metastable mode of superfluid 3HeA

A metastable mode of ³HeA has been observed using pulsed NMR techniques. The frequency of the mode is related to the previous cw NMR observation of a transverse satellite resonance.     

The adsorption of cyclic hydrocarbons on Ru(001): I. Cyclopropane

The adsorption of cyclopropane on Ru(001) at 90 K has been investigated by high-resolution electron energy loss spectroscopy, He I photoelectron spectroscopy, low-energy electron diffraction and thermal desorption mass spectrometry. The results indicate that the molecule adsorbs nondissociatively without long-range order and that no opening of the carbon ring occurs. The adsorption bond is weak, and multilayers form at 90 K only in the presence of a relatively high c-C₃H₆ equilibrium pressure. The vibrational spectrum is characterized by strong, dipole-active ring deformation modes and an additional mode at 570 cm^?1, which is due to a frustrated translation of the admolecule perpendicular to the surface with some ring deformation character. The photoelectron spectrum is characterized by a Jahn-Teller splitting of the 3e' molecular orbital, which is observed also in the gas phase. With the exception of a uniform relaxation shift, no other shifts could be observed in comparison with the gas phase. The results are discussed in relation to possible bonding mechanisms.     

Synchrotron radiation for long wavelength spectroscopy

A fundamental radiometric measurement has been carried out in the spectral region 1–140 cm^–1 which demonstrates the higher brightness of the synchrotron radiation source at Daresbury Laboratory over a high pressure mercury arc lamp source. Comparison of the output powers from the SRS and the mercury lamp revealed that the SRS has a particular advantage in the region where the wavelength of the emitted photon becomes very longer. The gain factor of the SRS at 10 cm^–1 was at least 10 times of the mercury lamp at a storage ring current of about 90 mA.A single period wiggler is considered to be a favorable device which will provide a higher level of photon fluxes from an electron storage ring in the long wavelength region.     

Spectroscopic study ofβ-Ni(OH)2 under pressure

Infrared absorption and Raman study ofβ-Ni(OH)₂ has been carried out up to 25 GPa and 33 GPa, respectively. The frequency ofA _2u internal antisymmetric stretching O-H mode decreases linearly with pressure at a rate of −0.7 cm⁻1/GPa. The FWHM of this mode increases continuously with pressure and reaches a value of ∼ 120 cm⁻¹ around 25 GPa. There was no discernible change observed in the frequency and width of the symmetric stretchingA _1g O-H Raman mode up to 33 GPa. The constancy of the Raman mode is taken as a signature of the repulsion produced by H-H contacts in this material under pressure. Lack of any discontinuity in these modes suggests that there is no phase transition in this material in the measured pressure range.     

Pressure dependence of the radial breathing mode of carbon nanotubes: the effect of fluid adsorption

The pressure dependence of shifts in the vibrational modes of individual carbon nanotubes is strongly affected by the nature of the pressure transmitting medium as a result of adsorption at the nanotube surface. The adsorbate is treated as an elastic shell which couples with the radial breathing mode (RBM) of the nanotube via van der Waal interactions. Using analytical methods as well as molecular simulation, we observe a low frequency breathing mode for the adsorbed fluid at approximately 50 cm-1, as well as diameter dependent upshifts in the RBM frequency with pressure, suggesting metallic nanotubes may wet more than semiconducting ones.     

Light scattering from E-symmetry amplitudon in the incommensurate phase of quartz

Low frequency depolarized Raman spectra of quartz were investigated in the incommensurate phase near the α-β transition at T_c = 573°C. A weak mode, but underdamped in the temperature region close to the commensurate α phase, was observed at about 8 cm^-1 with an intensity proportional to the square of the order parameter. The mode is assigned as the E-symmetry amplitudon which has been predicted to exist in the “3-k state” of the incommensurate phase, in addition to a totally symmetric A-amplitudon.     

Anomalous properties of optical lattice vibrations in HgTe: A double-well model of the lattice potential for a Hg atom

A double-well potential model has been proposed for a Hg atom in the HgTe crystal lattice in which the Hg atom either occupies the center of the anion tetrahedron or is located at the off-center position. The fundamental TO mode of the Hg-Te vibrations at a frequency of ∼120 cm⁻¹ corresponds to the vibrations of the off-center Hg atom, and the additional mode is associated with the vibrations of the Hg atom located at the center of the anion tetrahedron. The model has made it possible to explain both the strong increase in the intensity of the additional mode with increasing temperature, which, at T = 300 K, is comparable to the intensity of the fundamental mode, and the anomalous change (decrease) in the damping parameter of the fundamental TO mode with increasing pressure, which corresponds to a more ordered crystal structure.