共查询到19条相似文献,搜索用时 484 毫秒
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用同步辐射光电子能谱测量了Si/ZnS(111)及(100)异质结的价带偏移ΔEv.对于Si/ZnS(111)及(100)两界面,ΔEv的实验结果均为(1.9±0.1)eV,与已有理论预期值相当符合,但与Maierhofer所报告的ZnS/Si(111)异质结测量结果之间则存在明显差别.该实验结果表明对于Si/ZnS极性界面,互逆性规则(commutativity rule)可能不成立,就此进行了讨论.
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本文采用改进了的核散射函数计算了12种离子在非晶Al2O3,SiO2,20/25/Nb不锈钢、UO2和LiNbO3等材料中的投影射程分布一次至三次矩。给出了能量范围从5keV至1MeV的离子在上述材料中的理论计算结果。将计算值与近几年的实验测量结果及Gibbons等人和Winterbon的理论计算进行了比较。结果表明,我们得到了与实验符合得更好的理论值。文中较详细地介绍了化合物和合金材料中射程分布矩的计算方法,并对改进计算精度等问题进行了简要的讨论。
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采用LMTO能带方法,对两种不同应变状态下(自由形变和以InP为衬底),应变层超晶格(InAs)1(InP)1(001)和与应变层超晶格的分子层相对应的应变体材料,以及无应变的体材料进行了第一原理计算,并采用冻结势方法求出了两种超晶格各分子层的平均键能。结果表明,能存在应变的情况下,异质界面两边的平均键能非常一致,且这种一致性受应变状态的影响很小,因而可以把它用来作为确定应变层超晶格价带边不连续值(△Ev)的普遍适用的参考能级。研究了应变对
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采用平面波赝势密度泛函理论方法计算了PtN2的坐标、平衡态的晶格常数、体弹模量、剪切模量和弹性常数,计算结果与已有的实验值和理论值符合较好.通过能量与体积曲线,可知STAA结构比黄铁矿结构具有更低的能量.根据计算结果和Pugh提出的经验判据,PtN2是易脆的硬物质,随着压强增加PtN2的脆性逐渐过渡到延性.两种结构的能带结构和态密度表明了黄铁矿结构的PtN2是半导体而STAA
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2')" href="#">PtN2
第一性原理
力学性质 相似文献
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分别用PW91,B3LYP两种密度泛函方法和全电子高斯基组对β-Si3N4的几何结构进行全优化(包括晶格参数和原子坐标),结果和实验值符合良好. 同时计算了能带结构和态密度.在此基础上分别用上述两种方法计算了Γ点拉曼振动频率,并按对称性进行分类,将得到的11种拉曼活性模式的频率值与实验值以及其他文献值进行了比较,进一步确定了Ag模式为中等频率,值约459cm-1. 计算结果表明
关键词:
振动频率
密度泛函理论
电子结构
3N4')" href="#">β-Si3N4 相似文献
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介绍了几种计算纳米金属颗粒镶嵌于陶瓷基体中而形成的复合纳米金属陶瓷薄膜渗透阈的理论方法,分析了理论方法中所运用模型的特点及其精度.并将Landauer有效介质理论和Priou渗透阈理论应用于Ag-MgF2复合纳米金属陶瓷薄膜的渗透阈计算,所得值分别为0.08和0.14(Ag的体积分数),按Priou渗透阈理论计算的结果与实验结果相符.最后讨论了影响复合金属陶瓷薄膜体系渗透阈的主要因素.
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2复合纳米金属陶瓷薄膜')" href="#">Ag-MgF2复合纳米金属陶瓷薄膜
渗透阈理论
渗透阈 相似文献
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The complex permittivities of poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) blends have been measured under variation of temperature T(20°-60°C), frequency v(5 Hz-300 kHz), and hydrostatic pressure p (0-260 MPa). The values can be represented by a master curve with the shift factors △p/△ log (v/Hz) = ?140 MPa at room temperature and △ (1 /T) /△ log (v/Hz) = ?2. 10?4 K?1 at atmospheric pressure. The dependence of the activation energy △E A on pressure p is then given by △E A=(100 + 0.02 MPa?1 p) kJ/mol. Furthermore, the results indicate that the β-relaxation of PVDF is due to motions in the crystal-amorphous interphase. The interactions between the two polymers, which are miscible at all compositions, disturb the correlations between the PVDF monomer units at that location as well as the mobility of the PMMA side group. 相似文献
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An earlier study of the thermal quenching of luminescence using the single-configurational-coordinate model is extended from Condon-approximation overlap integrals 〈un|vm〉2 to the linear and derivative integrals 〈un|zv|vm〉2 and 〈un|?/?zv|vm〉2. For non-radiative transitions, the thermally weighted nuclear factor in the transition rate is, for the linear and derivative integrals, the corresponding factor for 〈un|vm〉2 integrals multiplied by 2EXv/?ωv and , respectively. EXv is the energy of the crossover above the initial- v-parabola minimum, and EpU(T) is the single activation energy fitted to the nuclear factor's temperature dependence for 〈un|vm〉2 integrals. These multiplying factors are exact for equal parabola force constants and good approximations for unequal force constants. These multiplying factors will be difficult to distinguish experimentally. The more important considerations for fitting the model to thermal-quenching data are the parabola placement and the Condon-approximation integrals described previously. 相似文献
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Annealing behaviors of the activation energy for the electrical conduction Eσ, that for the thermoelectric power Es, the optical gap Eoptg, and the spin density in evaporated amorphous Ge are investigated. Eσ is independent of Es and Eoptg, and the rates of variation of Eoptg and Es with annealing temperature are connected by △Eoptg = 2.5△Eopts. It is suggested that the position of the Fermi level does not change with annealing in contrast with amorphous Si, and the edge of the localized tail state shifts with annealing. 相似文献
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J.J. Aubert G. Bassompierre K.H. Becks C. Best E. Böhm X. de Bouard F.W. Brasse C. Broll S. Brown J. Carr R.W. Clifft J.H. Cobb G. Coignet F. Combley G.R. Court J.M. Crespo P.F. Dalpiaz S.J. Wimpenny 《Physics letters. [Part B]》1980,95(2):306-310
The transverse momenta of charged hadrons produced in high energy muon-proton scattering have been studied. The average squared transverse momentum 〈p2⊥〉 shows a strong dependence on z = Eh/v characteristic of intrinsic momentum effects and a significant rise as a function of s = W2. The W2, q2, x and z dependences of the data are compared with the predictions of a perturbative QCD model. 相似文献
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本文报道了对分子束外延(MBE)生长的In0.25Ga0.75As-GaAs应变层量子阱结构在77K下的压力光荧光(PL)研究的结果。流体静压力从0到50kbar.,给出了In0.25Ga0.75As-GaAs应变层量子阱的Γ谷压力系数,实验观察到了量子阱中能级与势垒GaAs中X谷的能级交叉。通过对其压力行为的分析,给出了In0.25Ga0.75As-GaAs异质结的导带与价带跃变比:Qc=△Ec:△Ev=0.68:0.32。对(InGa)As-GaAs应变量子阱常压下的理论分析与实验符合很好。本文也对Al0.3Ga0.70As-GaAs量子阱进行了讨论。
关键词: 相似文献
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The well-known Bragg-Kleeman rule R
CSDA = A ⋅ E has become a pioneer work in radiation physics of charged particles and is still a useful tool to estimate the range R
CSDA of approximately monoenergetic protons with initial energy E
0 in a homogeneous medium. The rule is based on the continuous-slowing-down-approximation (CSDA). It results from a generalized
(nonrelativistic) Langevin equation and a modification of the phenomenological friction term. The complete integration of
this equation provides information about the residual energy E(z) and dE(z)/dz at each position z(0 ≦ z ≦ R
CSDA). A relativistic extension of the generalized Langevin equation yields the formula R
CSDA = A ⋅ (E
0 + E/2M ⋅ c
2)p. The initial energy of therapeutic protons satisfies E
0 ≪ 2M ⋅ c
2(M ⋅ c
2 = 938.276 MeV), which enables us to consider the relativistic contributions as correction terms. Besides this phenomenological
starting-point, a complete integration of the Bethe-Bloch equation (BBE) is developed, which also provides the determination
of R
CSDA, E(z) and dE(z)/dz and uses only those parameters given by the BBE itself (i.e., without further empirical parameters like modification of friction).
The results obtained in the context of the aforementioned methods are compared with Monte-Carlo calculations (GEANT4); this
Monte-Carlo code is also used with regard to further topics such as lateral scatter, nuclear interactions, and buildup effects.
In the framework of the CSDA, the energy transfer from protons to environmental atomic electrons does not account for local
fluctuations. Based on statistical quantum mechanics, an analysis of the Gaussian convolution and the Landau-Vavilov distribution
function is carried out to describe these fluctuations. The Landau tail is derived as Hermite polynomial corrections of a
Gaussian convolution. It is experimentally confirmed that proton Bragg curves with E
0 ≧ 120 MeV show a buildup, which increases with the proton energy. This buildup is explained by a theoretical analysis of
impinging proton beamlets. In order to obtain a complete dose calculation model for proton treatment planning, some further
aspects have to be accounted for: the decrease of the fluence of the primary protons due to nuclear interactions, the transport
of released secondary protons, the dose contribution of heavy recoil nuclei, the inclusion of lateral scatter of the primary
and secondary protons based on Molière’s multiple-scatter theory, and the scatter contributions of collimators. This study
also presents some results which go beyond proton dose calculation models; namely, the application of the relativistic generalization
of the Bragg-Kleeman rule to electrons and, in an appendix, a method to determine inelastic cross-sections of therapeutic
protons in media of therapeutic interest. 相似文献
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A method is given for the analysis of the rotational spectrum in the ground and excited states of C3v molecules; it consists in a direct diagonalization of the energy matrix including all elements whose contribution can become significant for the analysis up to the sixth order of approximation.The method of factoring the energy matrix into four submatrices A1, A2, E, E, according to the symmetry species of the full point group C3v, is given. The programm enables the calculation of the rotational frequencies and also carries out by a least-squares method the fitting of the molecular constants for vibrational states v = 0 (ground state) and vE = 1, 2, 3, and 4, separately or simultaneously over several of these states.The analysis of the rotational spectrum of CH3C15N in the v8 = 0, 1, 2 states is given as an example. 相似文献
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本文从描述光激射器工作的基本方程出发,讨论了光激射器光束线宽的“短期”(short-time)部分。通常都以下式描写这部分线宽:△vs=(8πhv(△v′)2)/P,(1)其中△v′是谐振腔电磁模的半宽度;v为光束频率;P为输出功率。我们的主要结论可以归结为以下三点:(1)线宽主要是由与电磁模耦合的耗散体系引起的,与分子耦合的耗散体系的贡献是可以忽略的;(2)在单模近似下,只要分子的线宽比电磁模的线宽大得多,则(1)式是正确的;(3)如果多模谐振腔中激发模与其他模之间的相互作用是强的,则式(1)将被推广为 △vs=(8πhv(△v′)2)/P+(4hv(△v′))/P somefromn=(λ′≠λ)(rλλ′2/(rλ′),(2) 其中rλλ′是相关弛豫系数;rλ′是模λ′的线宽。在某些情况下,式(2)中第二项可以比其第一项还大。所以,这可能是目前关于线宽的实验结果与由式(1)计算结果不相符合的原因之一。 相似文献