Xe(4d~(10))(e,2e)反应三重微分截面的理论研究

采用修正后的扭曲波玻恩近似理论,计算了共面不对称几何条件下Xe(4d~(10))(e,2e)反应的三重微分截面.散射电子能量为1000 eV,敲出电子能量为20 eV,散射电子角度分别固定在2°,4°和7.5°.理论计算与Avaldi等人的实验结果和扭曲波玻恩近似理论计算进行了比较,发现出射电子之间的后碰撞相互作用较弱,极化效应在反应过程中起着重要作用.     

氩原子近LⅡ,Ⅲ边结构和振子强度密度

在入射电子能量2500eV，平均散射角为0°的条件下测量了氩原子内壳层2p电子激发和电离的高分辨电子能量损失谱，确定了分立态的有效量子数和电离边的能量．同时确定了两组分立跃迁和电离连续区的振子强度密度． 关键词：     

1 500 eV入射下氦原子的电子碰撞双重微分散射截面测量

本工作使用高分辨快电子能量损失谱仪,在入射电子能量1 500 eV、能量分辨200 meV和散射角度0.5°～ 4.0°的实验条件下,测量了氦原子在电离连续区24.5～28.5 eV的双重微分散射截面.通过与理论及其它入射能量实验结果的比较,认为在入射电子能量为1 500 eV 时一阶Born近似成立.     

乙炔分子的低能电子弹性散射研究

本文采用R矩阵方法研究低能电子与乙炔分子的弹性散射截面及其动力学过程.研究采用静态交换势模型(SE)和静态交换加极化势模型(SEP)两种方法.结果显示当前SEP模型预测的弹性散射截面与已有的实验值和理论结果符合的很好.SE模型预测了一个位于4.75 eV,宽度为3.0 eV的π形状共振态.该共振态在SEP模型中的位置降低为2.65 eV,宽度为1.5 eV.它来自B_(2g)和B_(3g)对称性贡献,理论预测共振态位置与实验值符合的很好.我们讨论了考虑不同的虚轨道对共振态的影响,说明预测精确的共振态的位置需要准确的处理极化效应.基于SEP模型得到的K矩阵元,我们使用POLYDCS代码计算的散射微分截面(DCS),和实验值符合的较好.除此之外,我们还报道了2 eV时转动分辨的态-态微分截面.     

氮气在100 eV以下的绝对振子强度密度

在入射电子能量为2500 eV、能量分辨为100 meV的条件下，得到了氮气在100 eV以下的绝对光学振子强度密度和广义振子强度密度；得到了23 eV和31.4 eV两个超激发态的绝对广义振子强度、并讨论了它们的动量转移依赖特性。     

粒子(E≥45 MeV)核内级联Monte Carlo模拟程序研究

本文基于核内级联物理过程,采用Monte Carlo方法发展了一款质子、中子以及π介子的粒子输运程序.基本物理模型基于适当简化和核内级联Bertini模型,同时借鉴了INCL模型质心系下的角微分分布以克服Bertini模型之不足,即采用Monte Carlo方法模拟核子与核子、核子与π介子间的弹性散射、非弹性散射等过程,粒子相互作用时,核子密度随半径变化且作用截面参考Bertini模型22类实验截面数据,出射粒子散射角在质心系下的抽样遵从INCL模型所确定的微分分布.可模拟45—3500 MeV的中子、质子或2500 MeV以下π介子引起的核内级联过程.入射粒子能量在60—378 MeV范围内反应截面理论计算值与已有实验数据、以及在65—3000 MeV较宽能区范围内反应截面、出射粒子增殖比、微分截面和剩余核等计算结果与MCNPX,GEANT 4和PHITS模拟结果符合较好.     

低能电子与Kr、Xe弹性碰撞截面的计算

本文利用原子的解析波函数,导出了电子与第四,五周期元素原子相互作用势的解析形式,并用文献提出的物理模型与计算方法,对低能电子被Kr和Xe散射的截面进行了计算,得到了入射电子能量从0.01eV到100eV范围内弹性散射总截面,动量转移截面和微分散射截面的大量数据。计算结果与实验符合得很好。同时利用计算的结果,对低能电子被惰性气体原子散射的规律性进行了探讨。     

He光双电离末态波函数动量相关效应

在入射光子能量为79.6 eV～139 eV范围内,利用DS3C模型计算了不同碰撞几何条件下He光双电离的三重微分截面(TDCS),并与3C模型计算结果、CCC理论结果和实验数据做了比较.表明,末态波函数动量相关效应成功地修正了3C结果,特别当入射光子能量接近阈值时,明显改善了与实验结果的符合程度.     

末态电子的关联在氢原子(e,2e)反应中的影响(英文)

在共面非对称几何条件下,利用双势公式解析计算了电子碰撞电离氢原子的三重微分截面.对快电子采用平面波近似,跃迁矩阵元可以表示成两个因子乘积的形式,即结构散射因子和出射道两电子的关联因子.在计算过程中对关联因子采取了最简单的近似,当入射能量为150 eV和54.4 eV时,计算结果与实验结果的符合说明对于这些入射能量该关联近似是有效的;而对于入射能量为27.2 eV时,计算结果与实验结果的较大差异说明这种关联近似是无效的.     

反质子与核的电荷交换反应和非弹性散射

在扭曲波冲量近似下,讨论了反质子与核的电荷交换反应A(p,n)B和非弹性散射A(p,p′)*A.并具体地计算能量为E_p=179.7MeV和46.8MeV下¹²C(p,n)¹²B,¹⁸O(p,n)¹⁸N和¹⁸O(p,p′)¹⁸O的微分截面.用严格的分波法处理扭曲波.非弹性散射的微分截面能符合实验.同时预示了在这些能量下,反质子与核发生电荷交换反应可能出现的微分截面理论结果.     

First-principles study of ground- and metastable-state properties of XO (X = Be,Mg, Ca,Sr, Ba,Zn and Cd)

The evolution of the local atomic order of an amorphous Ni₄₆Ti₅₄ alloy produced by mechanical alloying as a function of temperature was studied by synchrotron X-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. XRD measurements at several temperatures (25 °C, 350 °C, 412 °C, 430 °C, 450 °C and 515 °C) were performed and analyzed using the reverse Monte Carlo (RMC) simulations method or the Rietveld refinement procedure. The experimental total structure factor for samples at 25 °C and 350 °C, which are amorphous in nature, were simulated by using the RMC method, and the local structures of the alloy at both temperatures were determined, indicating a decrease in its density as the temperature increases. At 412 °C, the XRD pattern shows a partially crystalline sample, indicating that the crystallization process is in progress. At 430 °C, 450 °C and 515 °C, the XRD measurements indicate the presence of two crystalline phases, NiTi and NiTi₂, whose structural parameters (lattice parameters, coherently diffracting domains (CDD) sizes, microstrains and relative amount of phases) were determined using the Rietveld refinement procedure. DSC measurements at different heating rates furnished the crystallization temperature, enthalpy and activation energy of the crystallization process, and these values are similar to those found in other amorphous alloys of the Ni-Ti system. They also showed the existence of a second exothermic process, which was related to diffusive processes in the crystalline phases, which could be associated with the changes in the CDD sizes happening from 450 °C to 515 °C.     

Dielectric properties of Bi<Subscript>2</Subscript>PbNb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics prepared by different techniques

Different techniques for the synthesis of Bi₂PbNb₂O₉, namely the mixed oxide technique, molten salt synthesis, hydrothermal synthesis, co-precipitation and the tartaric acid gel method were investigated and the results on the dielectric properties are reported. The heat-treatment of the precursor powders was the same for all precursor powders. Sintering at 1040 °C under ambient pressure resulted in polycrystalline specimens, while hot-forging at 1040 °C with a pressure of 20 MPa produced c-axis aligned samples. Phase composition and crystallite orientation of the sintered bodies were analyzed by X-ray diffraction. Single-phase material was obtained in all cases. Hot-forging not only yielded c-axis orientation, but also increased the relative densities above 99.4%. The relative permittivity decreased for c-axis oriented material compared to polycrystalline ceramics. Values for the relative permittivity for the hot-forged specimens at 100 °C at 100 kHz varied between 165 and 250, depending on the fabrication method. The Curie temperature for the c-axis aligned samples was 568 °C, independent of the nature of the precursor powders. PACS 77.22.-d; 77.84.-s     

Thermal conductivity of binary,ternary and quaternary mixtures of rare gases

The thermal conductivity data of the Ne-Ar, Ne-Kr, Ar-Xe and Kr-Xe systems are reported as a function of composition and at temperatures 40°, 65° and 90°c. Similar results are also presented for the ternary systems Kr-Ar-Ne, Xe-Kr-Ar and a quaternary system Xe-Kr-Ar-Ne. A conductivity cell of the thick hot-wire type is used. The thermal conductivity values for the binary mixtures are compared with those obtained from rigorous theory and such procedures as approximate, semi-theoretical, empirical, linear mixing, reciprocal mixing, combination of linear and reciprocal mixing and quadratic equations. A similar study is also made for ternary and quaternary mixtures and some interesting conclusions are drawn concerning the relative appropriateness of different methods for computing thermal conductivity of multi-component gas mixtures.     

Laser-induced periodic surface structures formed on the sidewalls of microholes trepanned by a femtosecond laser

Laser-induced periodic surface structures (LIPSSs) were observed on the sidewalls of 300-μm-diameter holes trepanned on cemented tungsten carbide using femtosecond laser pulses at a wavelength of 800 nm. For a circularly polarized beam, LIPSSs were formed at a period of 300 nm and oriented perpendicularly to the plane of incidence on the sidewalls. For a linearly polarized beam, LIPSS formation was dependent on the relative angle α between the polarization direction and the plane of incidence. For relative angles α from 0° to 70° and from 110° to 180°, LIPSS spacing was 300 nm. However, there were two types of LIPSSs coexisting from 70° to 110°. One had a spacing of 120 nm and the other had a spacing that varied from 500 to 760 nm. It was found that the orientation angle of LIPSSs measured between the LIPSS orientation and the plane of incidence had a nonlinear dependence on α. To understand this dependence, a model was proposed in which LIPSSs are assumed to align perpendicularly to the direction of the absorbed electric field lying in the tangent plane of the sidewall of a drilled hole. The calculated results from this model showed good agreement with the experimental results.     

Effect of thermal annealing on disorder and optical properties of Cr/Si bilayer thin films

Chromium/silicon bilayers are deposited by sequential electron beam evaporation on quartz substrates. The bilayers consisting of Cr and Si layers of 50 and 400 nm thicknesses, respectively, are subjected to post-deposition annealing at temperatures from 200 to 700 °C. The thermal annealing results in the interdiffusion between Cr and Si, as evidenced by cross-section scanning electron micrographs and the line profiles obtained from energy-dispersive X-ray spectroscopy. It is inferred from the compositional line profiles that the films are a combination of silicon-rich oxide, chromium oxide and unreacted Cr up to 500 °C. Chromium disilicide forms at temperatures greater than 500 °C with decrease in chromium oxide content. The refractive index value and extinction coefficient values are 2.1 and 0.12 in the as-deposited case which increase to 3.5 and 0.24 at 400 °C. These values decrease to 2.1 and 0.12 at 500 °C. At the same temperatures, the band gap values are 2.21, 2.40 and 2.28, respectively. Thus, the refractive index, absorption coefficient and the optical band gap of the films peak at an annealing temperature of 400 °C and decrease thereafter. Significantly, this is accompanied by increase in Urbach energy which is an indication of increase in disorder in the system. There is decrease in Urbach energy as well as the optical constants at temperatures >400 °C.     

Investigation of the lateral spread of erbium ions implanted in silicon crystal

The erbium ions at energy of 400 keV and dose of 5×10 15 ions/cm 2 were implanted into silicon single crystals at room temperature at the angles of 0,45 and 60.The lateral spread of 400 keV erbium ions implanted in silicon sample was measured by the Rutherford backscattering technique.The results show that the measured values were in good agreement with those obtained from the prediction of TRIM’98 (Transport of Ions in Matter) and SRIM2006 (Stopping and Range of Ions in Matter) codes.     

Auger spectroscopic study of the surface composition of Pt/Sn alloys in ultrahigh vacuum and in the presence of oxygen and hydrogen

The surface composition of two Pt/Sn alloys, viz. PtSn and Pt₃Sn, has been followed by means of AES, as a function of annealing in ultrahigh vacuum, oxygen chemisorption and reduction with hydrogen.The results, which were quantitatively interpreted with the aid of a novel calibration technique, reveal the following features: - The surface of PtSn and Pt₃Sn becomes enriched with tin by annealing in vacuum. Ultimate values of 68±5 at% Sn for PtSn and 41±5 at% Sn for Pt₃Sn were attained after annealing at 500°C. - The adsorption of oxygen on the annealed surface of PtSn and Pt₃Sn causes a further enrichment with tin, while severe oxidation of PtSn at 500°C leads to complete disappearance of Pt from the surface. - Oxygen is more strongly and differently bound on a surface containing about 40 at% Sn than on a surface containing about 70 at% Sn. Activated adsorption of oxygen takes place only on the latter. The results suggest the formation of SnO₂ surface complexes on the exposed surface of Pt₃Sn. - Reduction of the alloys at 500°C carries the excess of tin into the bulk and reduces its surface concentration to 35±5 at% for Pt₃Sn and 64±5 at% for PtSn, which is an enrichment of the surface with platinum relative to the annealed state.     

Influence of thermal stress on the relative permittivity of the AlGaN barrier layer in an AlGaN/GaN heterostructure Schottky contacts

Ni Schottky contacts on AlGaN/GaN heterostructures were fabricated. Some samples were thermally treated in a furnace with N₂ ambience at 600 °C for different times (0.5 h, 4.5 h, 10.5 h, 18 h, 33 h, 48 h, and 72 h), the others were thermally treated for 0.5 h at different temperatures (500 °C, 600 °C, 700 °C, and 800 °C). With the measured current—voltage (I—V) and capacitance—voltage (C—V) curves and by self-consistently solving Schrodinger's and Poisson's equations, we found that the relative permittivity of the AlGaN barrier layer was related to the piezoelectric and the spontaneous polarization of the AlGaN barrier layer. The relative permittivity was in proportion to the strain of the AlGaN barrier layer. The relative permittivity and the strain reduced with the increased thermal stress time until the AlGaN barrier totally relaxed (after 18 h at 600 °C in the current study), and then the relative permittivity was almost a constant with the increased thermal stress time. When the sample was treated at 800 °C for 0.5 h, the relative permittivity was less than the constant due to the huge diffusion of the contact metal atoms. Considering the relation between the relative permittivity of the AlGaN barrier layer and the converse piezoelectric effect, the conclusion can be made that a moderate thermal stress can restrain the converse piezoelectric effect and can improve the stability of AlGaN/GaN heterostructure devices.     

Thermal and optical properties of Cd2SnO4 thin films using photoacoustic spectroscopy

Cadmium stannate (Cd₂SnO₄) thin films were prepared by the RF magnetron sputtering technique on glass substrates with substrate temperatures of room temperature (RT), 100°C, 200°C and 300°C. Photoacoustic analyses were made to obtain the thermal diffusivity and the optical bandgap values of the Cd₂SnO₄ thin films. The change in thermal diffusivity of the films with the substrate temperature was analyzed. The optical bandgap values obtained from the photoacoustic spectroscopy were compared with the values obtained from the optical transmittance spectra. X-ray photoelectron spectroscopic (XPS) studies confirm the formation of stoichiometric films. Surface morphological studies by atomic force microscopy (AFM) revealed the crystalline nature of the films deposited at 100°C.     

Optical testing of star sensor (II): Alignment of star sensor from off-line pictures taken in orbital test

Alignment error of an image sensor relative to the optical axis of a star sensor head and alignment errors between four heads were calculated from pictures taken in an orbital experiment. When comparing the image sensor alignment parameters in the orbital test and a ground test, both values matched well. By determining the relative relationship of the four heads using four pictures taken at the same moment in orbit and uploading the parameters to the star sensor system in orbit, the estimated attitude error was improved from 0.29 to 0.17°, though the accuracy was limited by the ±0.2° determination accuracy of the satellite itself. We estimated the attitude determination accuracy from separation angles between boresights of the four heads, calculated from pattern matching between downloaded pictures and a star catalogue. The estimated accuracy, in terms of potential optical performance, was 0.60 arcmin at 3σ, which is sufficient to satisfy the specification of 1 arcmin.