Temperature-dependent sputtering of metals and insulators

The temperature dependence of the sputter yield and the energy spectrum of sputtered atoms have been investigated on the basis of a standard model for thermal spikes. A high-temperature and a low-temperature regime have been identified in the temperature spectrum making up the evaporation yield. The high-temperature component of the yield as well as the associated energy spectrum are only very weakly dependent on ambient target temperature. The relative variation is the less pronounced the higher the spike temperature. The low-temperature component is associated with the long-time behavior of the spike, and measurable evaporation takes place over time intervals where spikes overlap. The importance of time constants for macroscopic heat transport is pointed out. The results are shown to provide a framework within which experimental results on the temperature dependence of the sputter yield of metals can be explained. The results are also consistent with measured temperature dependences in the sputter yield of insulators.On leave from Instytut Fizyki, Uniwersytet Jagiellonski, PL-30-059 Krakow, Poland     

Hydrostatic pressure and temperature dependence of correlation energy in a spherical quantum dot

The combined effects of hydrostatic pressure and temperature on the ground state binding energy of two electrons in a GaAs spherical quantum dot have been studied by using a perturbation approach within the effective-mass approximation. Our results show that an increment in temperature results in a decrease of the correlation energy while an increment in the pressure for the same temperature increases the correlation energy at a particular dot size. In all cases, it is observed that there is a decrease in the correlation energy due to an increase in the dot size with a given temperature and pressure. The combined effects of hydrostatic pressure and temperature affect the correlation energies appreciably for narrower dots only. The correlation contributes 10%–30% to the binding energy. All the calculations have been carried out with finite barriers, and good agreement is obtained with the existing literature values.     

The hydrostatic pressure and temperature effects on donor impurities in GaAs/Ga1 − xAlxAs double quantum well under the external fields

The combined effects of hydrostatic pressure and temperature on donor impurity binding energy in GaAs/Ga_0.7Al_0.3As double quantum well in the presence of the electric and magnetic fields which are applied along the growth direction have been studied by using a variational technique within the effective-mass approximation. The results show that an increment in temperature results in a decrement in donor impurity binding energy while an increment in the pressure for the same temperature enhances the binding energy and the pressure effects on donor binding energy are lower than those due to the magnetic field.     

高功率速调管电子枪热形变分析与测试

 国产50 MW速调管需要脉冲功率为120 MW的电子枪，其阴极为皮尔斯型储备式阴极，扫描直径为85 mm。利用ANSYS 对该速调管电子枪的温度场分布及结构的热变形进行了模拟分析。对于电子枪复杂的内部结构形态以及能量转换方式,分析了热传导方式对温度场的影响。在此基础上进行了温度场与结构变形的耦合分析，利用EGUN对电子枪形变前后束流光学特性进行模拟分析，并对模拟结果与高功率测试结果进行了分析比较。     

长脉冲高能激光能量测试技术的研究

用锥形腔量热式激光能量计,测量了在不同脉冲宽度条件下,脉冲激光能量和激光吸收腔温升之间的关系,并用传统的方法得到不同激光能量对应的温升,并按照有关公式计算得到激光能量,结果表明实际激光能量和按传统方法计算得到的激光能量之间存在较大的差距;我们从理论上分析了由于热辐射、热传导影响,得出锥形吸收腔时间温度曲线关系的数学模型;用该数学模型对测量得到温度时间曲线进行最小二乘法拟合,拟合曲线和实际曲线非常吻合;通过该曲线我们对测量结果进行修正,和传统数据处理方法比较,该方法得到的结果更接近真值.     

Ferromagnetism of Electron Gas

We here investigate the density and temperature dependence of polarization using the relativistic formalism for the electron–electron interaction within the Fermi liquid model. The variational method has been used: the free energy has been minimized with respect to the effective mass and the polarization parameter. Then we obtained the equation of state and magnetic susceptibility of the system. The exact results for polarization and magnetic susceptibility have been obtained at zero temperature. It has been shown that for a given temperature (density) there is a critical density (temperature) at which the ferromagnetic phase can appear in an electron gas. The results are in agreement with previous work. Our results show that at nonzero temperatures and in very low and very high densities the ferromagnetism phase cannot exist.     

Deformation parameter changes in fission mass yields within the systematic statistical scission-point model

The fission fragment mass-yields are evaluated for pre-actinide and actinide isotopes using a systematic statistical scission point model. The total potential energy of the fissioning systems at the scission point is presented in approximate relations as functions of mass numbers,deformation parameters and the temperature of complementary fission fragments. The collective temperature, Tcoll, and the temperature of fission fragments, Ti, are separated and the effect of collective temperature on mass yields results is investigated. The fragment temperature has been calculated with the generalized superfluid model. The sum of deformation parameters of complementary fission fragments has been obtained by fitting the calculated results with the experimental data. To investigate the transitions between symmetric and asymmetric modes mass yields for pre-actinide and heavy actinides are calculated with this model. The transition from asymmetric to symmetric fission is well reproduced using this systematic statistical scission point model. The calculated results are in good agreement with the experimental data with Tcoll= 2 Me V at intermediate excitation energy and with T_(coll)= 1MeV for spontaneous fission.Despite the Langevin model, in the scission point model, a constraint on the deformation parameters of fission fragments has little effect on the results of the mass yield.     

Adsorption of carbon monoxide on the molybdenum (100) surface

The interaction of CO with Mo(100) has been studied by means of thermal desorption spectrometry, work function measurements and electron stimulated desorption, in conjunction with LEED and AES. Results have been obtained for adsorption at room temperature and at temperatures down to 200 K. The study confirms previous results, showing that the β-states formed at room temperature are atomic. The thermal desorption data for the β-states are analyzed to give directly the desorption activation energy as a function of coverage. This energy is found to vary smoothly from an initial value of 3.7 to a final value of 2.9 eV molecule, indicating an average repulsive interaction between a pair of adjacent adatoms of 0.2 eV. The data at low temperature indicate that a molecular state, virgin-CO, is produced in competition with β-CO and probably one other state, from a common precursor. The step leading to virgin-CO has both a low activation energy and a low pre-exponential factor, suggesting that a reorientation of the molecule is required.     

Hydrostatic pressure and temperature effects on the electronic energy levels of a spherical quantum dot placed at the center of a nano-wire

The effect of pressure and temperature on the electronic structure of an InAs spherical quantum dot located at the center of a GaAs cylindrical nano-wire have been determined using finite element method, within the effective mass approximation. The energy levels and transition energies are numerically calculated as a function of the dot radius, pressure and temperature. It is shown that the pressure and temperature effects are significant and should be considered in the study of low-dimensional semiconducting systems. The results show that; energy levels (i) decrease as the dot radius increases (ii) decrease as the pressure increases and (iii) increase as the temperature increases. For very small dot radii, the energy levels show unusual behavior, such that the energy levels increase as the pressure increases. We also found that the transition energy (i) increases as the dot size decreases (ii) increases as the pressure increases and (iii) decreases as the temperature increases.     

Modeling cohesive energy and melting temperature of nanocrystals

A model has been developed to account for the size dependent cohesive energy and melting temperature of nanocrystals. This model can deal with the thermodynamic properties of nanoparticles (spherical and non-spherical), nanowires and nanofilms with free surface or non-free surface (embedded in a matrix). The cohesive energy depression of nanocrystals has been predicted, and the conditions of superheating are obtained. It is found that the present theoretical results are consistent with the available experimental values.     

Positron beam studies of void swelling in ion irradiated Ti-modified stainless steel

The void swelling behavior of heavy ion irradiated D9 steel has been investigated using variable low energy positron beam. The normalized defect-sensitive S-parameter shows up a large increase in the depth region corresponding to the maximum radiation damage as a function of irradiation temperature. From the variation of S-parameter as a function of irradiation temperature, the peak swelling temperature has been deduced and the results are discussed.     

Growth and characterization of single crystals of the quaternary TlGaSeS compound

The electrical conductivity and Hall effect for TlGaSeS crystals have been investigated over a wide temperature range. The crystals we used are grown by a modified Bridgman technique and possess p-type conductivity. The energy gap has been found to be 1.63 eV, whereas the ionization energy is 0.25 eV. The variations of the Hall mobility as well as the carrier concentration with temperature have been investigated. The scattering mechanisms of the carrier are checked over the whole investigated temperature range. Furthermore, the diffusion coefficient, relaxation time, and diffusion length of holes are estimated.     

Nuclear Level Density with Non-zero Angular Momentum

The statistical properties of interacting fermions have been studied for various angular momentum with the inclusion of pairing interaction. The dependence of the critical temperature on angular momentum for several nuclei,have been studied. The yrast energy as a function of angular momentum for 28 Si and 24Mg nuclei have been calculated up to 60.0 MeV of excitation energy. The computed limiting angular momenta are compared with the experimental results for 26Al produced by 12C 14N reaction. The relevant nuclear level densities for non-zero angular momentum have been computed for 44Ti and l36Ba nuclei. The results are compared with their corresponding values obtained from the approximateformulas.     

现场用激光能量计校准方法的实验研究

在激光功率能量测量当中,军用激光现场检测环境温度和实验室环境温度相差很大,而激光能量计的传感器灵敏度与环境温度条件有关,不对激光能量计进行温度灵敏度校准,将严重影响测量结果。针对目前存在的问题,本文提出将激光能量计放置于温控制箱中,脉冲激光器输出的激光经过分光镜分束后分为2束激光,其中透射光由标准能量计或现场激光能量计接收,反射光由参考能量计接收,在-50℃～70℃的温度范围内进行校准的一种新方法,并进行原理性的验证实验及结果分析,得到了能量计灵敏度系数关于环境温度的函数关系,使得能量计在非标准环境下进行准确测量成为可能。为激光能量计现场测试校准技术的研究提供了一种可靠的新途径。     

Ionization potentials and partition functions of ions in a semiclassical model

The characteristics of an isolated ion (its radius, energy, ionization potential, bound-state energy, and excitation spectrum), which appear in the chemical plasma model, are calculated via the Thomas-Fermi statistical model. The expression for the partition function of the ion excitation at a given temperature and plasma density has been derived. A comparison with the empirical results is performed.     

亚皮秒脉冲激光辐照硅薄膜热效应的模拟研究

基于Boltzmann方程,采用了Chen J K等人建立的自相关模型,考虑了Si薄膜的热容、热导率、弛豫时间等热力学参量随温度非线性变化的影响.采用有限差分法,数值求解了脉宽为500 fs的激光脉冲辐照2 μm厚硅膜的自相关模型.分析了膜表面载流子浓度、载流子温度、晶格温度等随入射激光功率和脉宽等的变化规律.结果表明：在脉冲辐照初期（t<0.68 ps）,载流子和晶格之间存在着明显的非热平衡性,之后通过相互之间的弛豫碰撞,逐渐达到热平衡,载流子热容是引起载流子温度在早期迅速上升的原因;载流子温度速率方程中单光子吸收、载流子-晶格能量交换和载流子能流变化率对载流子温升影响较大,而多光子吸收、双极能流和带隙能量变化率对载流子温升的影响较小,可以忽略;较高脉冲激光能量（Ф＞0.02 J·cm－2）辐照Si膜,会引起载流子密度方程中的俄歇复合项增大,从而使载流子密度下降率增大,导致载流子温度出现双峰.     

Josephson Currents and Gap Enhancement in Graph Arrays of Superconductive Islands

Evidence is reported that topological effects in graph-shaped arrays of superconducting islands can condition superconducting energy gap and transition temperature. The carriers giving rise to the new phase are couples of electrons (Cooper pairs) which, in the superconducting state, behave as predicted for bosons in our structures. The presented results have been obtained both on star and double comb-shaped arrays and the coupling between the islands is provided by Josephson junctions whose potential can be tuned by external magnetic field or temperature. Our peculiar technique for probing distribution on the islands is such that the hopping of bosons between the different islands occurs because their thermal energy is of the same order of the Josephson coupling energy between the islands. Both for star and double comb graph topologies the results are in qualitative and quantitative agreement with theoretical predictions.     

Determination of temperature dependence of energy gap in HgTe by oscillatory magnetotransmission measurements

Interband Γ₆ → Γ₈ magnetotransmission measurements have been performed of HgTe for ten values of temperature, between 8 K and 92 K, in the magnetic field up to 60 kG. The results are interpreted using the many-level model of Pidgeon and Brown. The energy gap dependence versus temperature has been found. The others kp parameters show no systematic temperature variation within the experimental uncertainty.     

Modeling the cohesive energy and melting point of nanoparticles by their average coordination number

We present a relation between the average coordination number and the cohesive energy for nanoparticles that shows that the ratio of nanoparticles cohesive energy to the bulk value is equal to the ratio of the nanoparticles average coordination number to that of the bulk. We consider the effect of lattice and surface packing factors on the average coordination numbers of the atoms in the nanoparticle. The melting temperature of nanoparticles has been calculated from the obtained relation for cohesive energy, and predictions for the cohesive energy and melting temperature of the nanoparticles have been compared with other theoretical models and available experimental data and the results of molecular dynamics simulations.     

量子点中束缚极化子性质的温度依赖性

采用线性组合算符和幺正变换方法研究抛物量子点中弱耦合束缚极化子性质的温度依赖性,导出了弱耦合束缚极化子的振动频率、基态能量和声子平均数随温度的变化关系。取ZnS晶体为例进行数值计算,结果表明:量子点中弱耦合束缚极化子的振动频率、基态能量和声子平均数随温度的升高而增大。