Study of lattice vibrational modes in CuGaS2 by using fourier transform spectroscopy

The lattice dynamics of a single crystal of CuGaS₂, grown by iodine transport technique, have been studied by using far IR absorption spectroscopy. All the absorption maxima caused by the phonon excitation are compared with the lattice vibrational modes obtained by Raman spectroscopy and by IR reflection techniques. An absorption maximum located at 175 cm^?1 cannot be explained with the help of phonon excitation; however this peak can be attributed to the defect frequency originating from the replacement of gallium atom by sulphur in the v₁₇ mode of vibration. The frequency of this defect-induced vibrational mode is calculated by taking a modified molecular model approach, and is found to be 166.9 cm^?1, which is in reasonably good agreement with the experimentally observed value of 175 cm^?1.     

GaP的缺陷随温度变化的PAT研究

我们对LEC法制成的掺S的GaP单晶,从室温至1000℃,每隔50℃恒温30分钟,在Ar气保护下进行热处理。用正电子湮没技术(PAT)对样品中的缺陷进行了分析研究。结果指出,随着热处理温度的升高,GaP中的点缺陷组态发生变化。测试结果表明,正电子湮没寿命可分解为两个寿命。其中捕获态寿命τ2随热处理温度的升高,由310ps变为330ps;进而在高温下变为280ps.相应地捕获强度I2随温度而发生变化,它反映出GaP单晶中的空位浓度也在随温度发生变化。     

Infrared absorption of interstitial oxygen in silicon at low temperatures

Localized modes of oxygen incorporated interstitially in the silicon lattice are the origin of infrared absorption lines in the wavelength region between 29 and 1750 cm^–1. The occupancy of the excited states of the lowest energy normal mode of this center determines the relative strength of absorption lines of the highest energy mode in a band around 1136 cm^–1 at low temperatures. The ratio of the strength of the different lines can be used as an intrinsic thermometer of the system. Exact knowledge of this temperature then allows the precise determination of the concentration of interstitial oxygen with high sensitivity.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

Photoionization of electrons and holes at oxygen donors in gallium phosphide

The spectral dependence of the photoionization cross-section for the oxygen donor in GaP is studied in the temperature range between 90 and 410°K by steady state photocurrent measurements using two different radiation sources. From a fit of Lucovsky's model to the experimental results, accurate information is obtained about the energy position of the oxygen donor at all temperatures. It is found that the oxygen level is pinned to the valence band for temperatures above 295 K and that at these temperatures the Franck-Condon shift is very small. This may indicate that there is little interaction between the impurity level and the surrounding lattice.     

Accelerated oxygen precipitation in fast neutron irradiated Czochralski silicon

Annealing effect of the oxygen precipitation and the induced defects have been investigated on the fast neutron irradiated Czochralski silicon （CZ-Si） by infrared absorption spectrum and the optical microscopy. It is found that the fast neutron irradiation greatly accelerates the oxygen precipitation that leads to a sharp decrease of the interstitial oxygen with the annealing time. At room temperature （RT）, the 1107cm^-1 infrared absorption band of interstitial oxygen becomes weak and broadens to low energy side. At low temperature, the infrared absorption peaks appear at 1078cm^-1, 1096cm^-1, and 1182cm^-1, related to different shapes of the oxygen precipitates. The bulk microdefects, including stacking faults, dislocations and dislocation loops, were observed by the optical microscopy. New or large stacking faults grow up when the silicon self-interstitial atoms are created and aggregate with oxygen precipitation.     

Tuning and mode characteristics of the C.W. InSb spin-flip Raman laser determined by use of a Fabry-Perot interferometer

A simple variable length (10–50 cm) air-spaced Fabry-Perot interferometer has been used to calibrate the tuning characteristics of a c.w. InSb spin-flip Raman laser (SFRL). The SFRL output frequency is determined by competition between the spontaneous spin-flip resonance line and the cavity axial modes of the InSb crystal. Over several cavity modes the SRFL is found to tune linearly within ±250 MHz and inside a single mode to ±50 MHz. The tuning rate over several modes is found to be 2.35 cm^-1/kgauss and within a single mode the tuning rate is 1.80 cm^-1/kgauss. Frequency jumps of ≈500 MHz between modes are inferred. Used in conjunction with the observation of known molecular absorption lines as frequency standards, the interferometer provides a calibration of the SFRL suitable for infra-red Doppler limited spectroscopy. of gases. The observed frequency asymmetry in the SFRL output power and the non-linear tuning rate (variable from ≈70-40 MHz/gauss) over a single axial mode show plane-wave cavity theory to be inadequate. These effects can be explained by considering gain controlled refraction induced by a pump beam of gaussian profile. The near resonant dispersion of the refractive index of InSb is inferred from a measurement of the spacing between adjacent peaks in the SFRL output.     

Modeling of the absorption profile of the 60 GHz band of atmospheric oxygen using the memory function formalism

The profile of the oxygen absorption band centered at 60 GHz is modeled using the formalism of memory functions. The memory function determines the relation between the initial and final states of a molecule after its collision. The model profile takes into account the spectral exchange and contains two parameters, which depend on temperature and pressure. These parameters characterize the probabilities of spectral exchange between series of lines (branches) corresponding to molecular transitions of different types. To describe the absorption profile in the frequency range of 0–120 GHz in terms of the model proposed, the “+” and “?” branches of fine structure transitions and the series of nonresonance lines with frequencies on the order of 10^?3–10^?5 GHz are taken into account. The values of the parameters that take into account the spectral exchange are found from the condition of the best fit between the developed model profile and the profile calculated according to the millimeter-wave propagation model. The parameters found have physically substantiated and smooth temperature dependences, which confirms the adequacy of the model. The difference between these models does not exceed 2–3%, which corresponds to the declared uncertainty.     

Complete identification of the Ti-related levels in GaP

A complete understanding of the electrical and optical properties of all the Ti-related levels is deduced from a number of different characterization techniques performed on several types of Ti-doped GaP materials (n-type, p-type and semi-insulating) grown by LEC. The Ti³⁺ /Ti⁴⁺ donor level and the Ti²⁺ /Ti³⁺ acceptor level are found at E_v + 0.92 and about E_c - 0.56 eV, respectively. Likewise, a comprehensive scheme of the two internal transitions ³T₂→³A₂ of the Ti²⁺ charge state and ²T₂→²E of the Ti³⁺ charge state is given.     

氧气A带吸收系数的温度依赖关系研究

氧气A带是理想的大气要素反演通道,吸收系数是重要的参数之一,它影响到反演结果的精度.结合HITRAN2012数据库和大气温度廓线图,分析氧气A带吸收系数的影响因素,推出各因素与温度的依赖关系,确定吸收系数随温度的变化.结果表明,氧气A带谱线半宽度受温度依赖系数影响较小,而受温度影响较大.线型因子随温度产生了两种变化,在谱线半宽度以外的谱线位置上,随温度的增大,函数值减小,而在中心频率到谱线半宽度的谱线位置上,随温度的升高而增大.谱线线强对温度具有强依赖关系.利用逐线积分算法计算氧气A带吸收系数,同时考虑了谱线半宽度的压力展宽效应和谱线线强及半宽度对温度的依赖关系,得出氧气A带吸收系数对温度的依赖关系主要来源于线强的温赖关系,尤其是中心频率处温度影响较大;而Lorentzian线型函数的温赖关系不明显.利用布鲁克光谱仪在1 cm-1下测量63 m处氧气A带的吸收光谱,与理论模型在同等条件下的透过率比较,误差小于0.83%,验证了温度校正模型的正确性.     

氧在GaP(111)上的初级吸附阶段

采用多种表面分析手段,系统地研究了氧在GaP(111)上的吸附,发现氧的初级吸附在1×10⁴L时就已饱和,获得了有关这一阶段表面电子结构的变化、表面能带弯曲、化学吸附反应等方面的信息,发现这一吸附阶段与表面缺陷有关,适当地加热处理则可能将缺陷和氧一同去除,因此这有可能成为一种有效的、去除缺陷的表面工程手段。 关键词：     

吸附于纳米磷化镓粉体表面碱性品红的拉曼光谱(英文)

本文中,对吸附于纳米磷化镓(GaP)粉体表面的碱性品红拉曼光谱进行了研究。通过将吸附碱性品红与纯碱性品红晶体样品的拉曼光谱进行对比、分析可知,碱性品红在纳米GaP粉体表面发生了化学吸附。在吸附碱性品红样品的拉曼光谱中,位于1200~1320cm-1范围内的光谱特征表明可能有新的化学键(P-O-C+或Ga-O-C+)形成。碱性品红分子的中央碳正离子(C+)与GaP表面具有孤对电子的氧原子形成配位键。红外光谱结果表明,氧原子与纳米GaP粉体表面的磷原子或镓原子键合,以P-O,Ga-O或P-O-Ga形式存在于GaP表面。碱性品红分子的呼吸振动,N-苯环伸缩振动,以及苯环C-C伸缩振动散射强度与纯碱性品红晶体样品相比皆有所增强。N-苯环伸缩振动散射强度增加意味着N原子是除C+离子以外的另一个可以与GaP表面发生化学作用的活性中心,这种化学作用是由N原子与GaP表面存在共轭效应造成的。     

Ultrafast dephasing of light in strongly scattering GaP nanowires

We demonstrate ultrafast dephasing in the random transport of light through a layer consisting of strongly scattering GaP nanowires. Dephasing results in a nonlinear intensity modulation of individual pseudomodes which is 100 times larger than that of bulk GaP. Different contributions to the nonlinear response are separated by using total transmission, white-light frequency correlation, and statistical pseudomode analysis. A dephasing time of 1.2±0.2 ps is found. Quantitative agreement is obtained with numerical model calculations which include photoinduced absorption and deformation of individual scatterers. Nonlinear dephasing of photonic eigenmodes opens up avenues for ultrafast control of random lasers, nanophotonic switches, and photon localization.     

Dynamique de reseau et frequences des modes de vibration pour des impuretes substitutionnelles dans InP,GaP et ZnS

The model used is a rigid-ion model with an effective ionic charge including general interactions for nearest and next nearest neighbours and long range Coulomb interactions. It provides a good fit with available neutron data and with IR absorption results for InP. In this model, no hypothesis is made apriori on the interatomic forces and the eleven parameters given by the model are used. A mathematical model which employs a Green's function technique in the mass defect and the nearest neighbour force constant defect approximation is used to calculate the lattice dynamics of the imperfect crystal. The frequencies of the local modes, the gap modes and the band modes, are given for isolated substitutional impurities. The same calculation is achieved for GaP and ZnS and the results are compared with IR data.     

Impurity absorption in gallium phosphide doped with zinc and oxygen

The extrinsic optical properties were investigated in homogeneous GaP crystals at room temperature. The transmission of extrinsic light is influenced by a simultaneous illumination of an additional light of different frequency. This light changes the occupancy of an impurity level. A simple theory is given, which relates this change in transmission of the extrinsic light to the optical cross sections of the impurity level. We had to use steady light because of the large relaxation time, but still obtained a resolution of 2 × 10⁻⁵ in the relative transmission change. The spectral dependence of the optical cross sections for an impurity level 0·9 eV below the conduction band were calculated. Another level approximately 1·85 eV from a band edge was also seen in these measurements, but it had complex optical properties. Both levels were seen in a direct measurement of the absorption coefficient.     

PbWO4晶体中的填隙氧及其对晶体光学性质的影响

运用GULP计算软件模拟计算了PbWO₄(PWO)晶体中不同位置的填隙氧原子点缺陷的生成能，计算结果表明：当填隙氧原子存在于(WO₄)^2-的周围时，填隙氧原子点缺陷的生成能最低；进一步运用基于密度泛函理论的全数值自洽DV-Xα方法计算了包含填隙氧原子的PWO晶体的态密度，计算结果表明：当填隙氧处在(WO₄)^2-的周围时，容易与(WO₄)^2-上的一个或两个氧离子相互作用形成分子离子O₂^2-或O₃^4-，通过分析这些计算结果，认为PWO晶体中350 nm吸收带的出现很可能与晶体中的氧分子离子有关.     

Intrinsic recombination radiation from GaP

Intrinsic recombination radiation has been detected in GaP crystals grown by vapour transport on GaAs and GaP substrates and in the form of needles, using 50 KeV electron beam excitation in the temperature range 25°K to 80°K. The three major components of the radiation are associated with the decay of free excitons with the emission of the transverse acoustic, longitudinal acoustic and transverse optic phonons which conserve momentum for transitions across the indirect energy gap. Structure has also been observed associated with the emission of two phonons, and for T > 77 >K a phonon absorption component can also be detected. In crystals grown on GaAs substrates, a no-phonon component has been observed with a threshold at the intrinsic exciton energy gap. This is thought to be associated with the presence of arsenic and there is a corresponding shift in the band gap to lower energy. close agreement is observed between the measured shapes of the emission components and those computed by the principle of detailed balance from the intrinsic edge absorption spectrum, when the broadening associated with the crystal imperfections and anomalous structure in the absorption spectrum are taken into account. The phonon energies derived from the emission spectra are in good agreement with the values determined from intrinsic edge absorption measurements.     

First-principles study on superconductivity of solid oxygen

The superconductivity of solid oxygen in ζ phase was investigated by first-principles calculations based on the density functional theory. Using a monoclinic C2/m structure, we calculated the superconducting transition temperature by the Allen–Dynes formula and obtained 2.4 K at 100 GPa for the effective screened Coulomb repulsion constant μ* of 0.13. The transition temperature slowly decreases with increasing pressure and becomes 1.3 K at 200 GPa. The phonon analysis shows that the electron–phonon coupling is dominantly enhanced by the intermolecular vibrations of O₂ rather than the intramolecular ones. The phonon modes showing the strong electron–phonon coupling were found to be concentrated in the phonon frequency range of 100–150 cm^?1 at around the M-point in the Brillouin zone.     

基于大气氧光谱吸收特性的单目单波段被动测距

根据目标红外辐射在大气中传输衰减的特性探测传感器与目标的距离, 隐身无源, 难于被敌方探测, 发展了一种基于大气氧组分光谱吸收特性的单目单波段被动测距方法.引入视线路径的概念, 将氧物性分布场离散化, 寻找辐射积分路径; 利用离散传递法基本思想, 得到目标窄带辐射强度分布.基于氧分子吸收发射谱独立、吸收系数恰当, 饱和可测范围大等特性, 分析氧吸收波段内谐振频带和远谐振频带辐射强度谱线分布的相对关系, 得到其与积分路径(即距离)的关联. 采用分辨率为0.75 nm半高宽的窄带高分辨率光谱仪, 实地校准氧物性分布场, 实现了测距实验范围75–200 m, 模型测算相对误差最大为7.56%的样机. 关键词： 被动测距 单目测距 单波段测距 氧光谱     

Change of the stoichiometry and electrocoloration due to the injection of Li and O ions into lithium niobate crystals

Congruently grown LiNbO₃ single crystals show both high oxygen and lithium ion conductivity at temperatures above 500 °C. The high oxygen ion conductivity can be understood in terms of a certain amount of oxygen vacancies already present in congruently grown LiNbO₃ single crystals. Thermal treatment of LiNbO₃ produces additional oxygen vacancies. The absorption bands introduced by this procedure are investigated. It is found that the electrons which are generated during the reduction process are homogeneously distributed among all oxygen vacancies in the LiNbO₃ single crystals. The electrocoloration phenomenon in LiNbO₃ single crystals is due to the process of injection of lithium ions and electrons into LiNbO₃ by a double charge mechanism. Investigations of the optical and electrical properties of electrocolored LiNbO₃ crystals are reported. It is shown that the absorption spectra of thermally and electrochemically reduced samples are identical and that the origin of the absorption processes has to be therefore the same in both cases. That means, additional electrons produced by the double charge injection of lithium ions and electrons are also homogeneously distributed among the oxygen vacancies. This supports our hypothesis that a certain amount of oxygen vacancies has to be present already in as-grown LiNbO₃ single crystals.     

Two-phonon absorption in InP and GaP

Far-infrared absorption in crystals of GaP and InP was investigated using a high-resolution Fourier-transform spectrometer. The two-phonon absorption was found to be very similar in these two materials. Van Hove singularities on the GaP spectrum were identified with the aid of calculated two-phonon sum and overtone density-of-states curves. The analysis of the InP spectrum was based on its homology to GaP. Many of the prominent features of the absorption spectra are assigned to pairs of phonons on the hexagonal face of the Brillouin zone while phonon pairs at Γ, X and L generally contribute only minor features to the spectra.