一个新的Si{001}2×1表面原子结构模型

本文提出了一个由低能电子衍射能带理论计算所确定的Si{001}2×1表面新的原子结构模型。新结构模型包括二聚键长l_d=2.387?,表面三个原子层间距d₁=0.50±0.01?,d₂=0.96±0.01?,d₃=1.17±0.01?和二聚原子的两个反对称移动。     

在强磁场中金属薄膜的超导电理论(Ⅰ)

本文研究了在接近转变温度T_c的区域内,超导薄膜在磁场中的性质。磁场是沿着超导膜的表面。在文章中,首先对Γорьков理论进行了分析,指出这个理论实际上是采用了局域近似,这个近似主要是隐含在他所采用的磁场中电子Green函数G_ω⁰(rr′)的表示式中。作者指出,Γорьков所采用的G_ω⁰(rr′)表示式对于本文研究的问题是不适用的,本文采用G_ω⁰(rr′)按矢势的微扰展开式。本文把Γорьков的补偿方程和电流方程推广到超导膜。对于d<δ₀(T)的膜,求出了这二个方程的解,得到超导薄膜的矢势、磁矩、能隙和临界电流的表达式,并研究了超导薄膜在磁场中的相变问题,求得超导薄膜的临界磁场。本文所得到的结果,对比较厚的膜(d?ξ₀)和ГЛ理论一致,而对比较薄的膜(d<ξ₀)和ГЛ理论有着显著不同(除了临界电流和超导膜在磁场中相变级数的判据外),二者的差异特别是表现在对厚度依赖关系上。由于本文所采用的近似,所得到的结果适用于δ₀(T)>d?d^*情形,其中2d^*=(1/(0.36)×ξ₀/p₀)^1/2,对于Sn,2d^*～10^-6cm。     

超薄栅超短沟LDD nMOSFET中栅电压对栅致漏极泄漏电流影响研究

本文研究了90nm CMOS工艺下栅氧化层厚度为1.4 nm沟道长度为100 nm的轻掺杂漏(LDD)nMOSFET栅电压V_G对栅致漏极泄漏 (GIDL)电流I_d的影响,发现不同V_G下ln (I_d/(V_DG-1.2))-1/(V_DG-1.2)曲线相比大尺寸厚栅器件时发生了分裂现象. 通过比较V_G变化下ln(I_d/(V_DG-1.2))的差值,得出V_G与这种分裂现象之间的作用机理,分裂现象的产生归因于V_G的改变影响了GIDL电流横向空穴隧穿部分所致. 随着|V_G|的变小,ln(I_d/(V_DG-1.2))曲线的斜率的绝对值变小.进一步发现不同V_G对应的ln (I_d/(V_DG-1.2))曲线的斜率c及截距d与V_G呈线性关系,c,d曲线的斜率分别为3.09和-0.77. c与d定量的体现了超薄栅超短沟器件中V_G对GIDL电流的影响,基于此,提出了一个引入V_G 影响的新GIDL电流关系式.     

Ⅲ-V族化合物半导体Λ轴光学声子形变势的研究

本文在LMTO-ASA能带计算中,采用冻结声子模型,系统地研究了Ⅲ-V族化合物半导体的Λ轴光学声子形变势随k值的变化关系,提供了9种Ⅲ-V族化合物在Λ轴不同k值情况下的光学声子形变势d₃₀(Λ), d₁₀(Λ,val)和d₁₀(Λ,con)的第一原理计算结果。     

R-宇称破缺的相互作用研究

在LHC上，最小超对称标准模型中R-宇称破缺相互作用使LHC上tt对的产生有两种过程，一种是交换slepton粒子的t道的d_Rd_R→t_Lt_L过程，一种是交换squark粒子的u道的d_Rd_R→t_Rt     

相干和非相干合成光束对金属瑞利粒子的光学俘获

研究了两光束的合成方式(相干和非相干合成)对俘获金属瑞利粒子的辐射力和稳定性的影响,着重研究了辐射力与合成方式、离轴距离、相干参数和粒子半径的关系.结果表明,不同合成方式下,离轴距离和相干参数都分别存在临界值d_c和α_c,在0d_c或α>α_c时,焦面处光强呈中心凹陷分布,此时横向梯度力不能作为回复力俘获金属瑞利粒子.在0<d≤d_c时,与非相干合成光束比较,相干合成光束在焦面处光强、辐射力、俘获刚性和纵向俘获范围更大.因此,适当选择合成方式,较小离轴距离和较低相干参数可有利于合成光束对金属瑞利粒子的俘获.     

小动量转移区高扭曲效应对核子自旋结构函数的影响

利用夸克模型计算了核子的自旋相关结构函数随Q²的依赖关系.在小动量转移区研究高扭曲效应a₂(Q²),d₂(Q²)对结构函数的影响.计算结果和其它的一些模型理论计算做了比较.     

B介子稀有衰变与荷电PG玻色子企鹅图贡献

计算了荷电PG玻色子P^±和P^±₈对B介子稀有衰变过程B→X_s,dνν和B_s,d→1⁺1^－(l=e,μ,τ)的企鹅图和箱图贡献.计算表明:(a)荷电PG玻色子可以对B介子稀有衰变分枝比Br(B→X_s,dνν)和Br(B_s,d→1⁺1^－)给出3～5倍的增强;(b)在大部分参数空间内,色八重态PG玻色子P₈^±起主要作用.     

Electronic structures and magnetoelectric properties of tetragonal BaFeO3: an ab initio density functional theory study

First-principles calculations have been performed to investigate the ground state electronic properties of BaFeO₃ (BFO). Local spin density approximation (LSDA) plus U (LSDA+U) treatment modified the metallic behaviour to insulated one with a band gap of 4.12eV. The spontaneous polarization was found to be 89.3\muC/cm² with Berry phase scheme in terms of the modern theory of polarization. Fe-3d e_g were split into two singlet states (d_z² and d _x²-y²}), and Fe-3d t_2g were split into one doublet states(d_xz and d_yz) and one singlet states(d_xy) after Fe and O displaced along the c axis. Meanwhile the occupation numbers of d_z², d_yz, d_xz and O_T p_z (on the top of Fe) were increased at the expense of those in xy plane. Our results showed that it was the sensitivity of hybridization to ferroelectric distortions, not just the total change of hybridization, that produced the possibility of ferroelectricity. Moreover, the increasing occupation numbers of O_T p_z and Fe d_z² favoured the 180^o coupling between Fe-3d e_g and Fe-3d t_2g, leading to ferromagnetic ordering, which has been confirmed by the increase of magnetic moment by 0.13μ_B per formula unit in the polarized direction. Hence, the magnetization can be altered by the reversal of external electric field.     

铷原子初通道─末通道辐射跃迁矩阵元研究

在相对论性自洽场理论基础上，把量子亏损理论的一个初态到一个末通道的跃迁过程进行了推广：具有相同角动量特征的初态形成所谓的初通道，通过定义重整化矩阵元，统一处理了一个初通道激发到一个末通道的无数个光跃迁过程．作为例子，计算了你原子“s_1/2—p_1/2”，“p_1/2—d_3/2”，“d_3/2—f_5/2”通道之间的光吸收过程．     

GaAs和AlAs光学声子形变势的第一性原理研究

本文以冻结声子近似模型,采用空球随原子球位移的冻结势近似的LMTO-ASA计算方案,研究了GaAs和AlAs布里渊区Λ轴的光学声子形变势的计算,得到Γ点和Λ轴光学声子形变势d₀,d₃₀,d₁₀(val)和d₁₀(comd)的第一性原理的计算结果。研究中着重从GaAs和AlAs的Λ轴光学声子形变势随k点的变化趋势,从光学声子形变势在Γ点附近满足的关系,以及从不同计算方法对d₀的计算结果与实验结果的比 关键词：     

新型THz波超平坦色散光子晶体光纤

设计出一种新型的渐变空气孔径THz波超平坦色散光子晶体光纤.应用时域有限差分方法(finite-difference time-domain,FDTD)计算光纤色散,所得结果表明渐变空气孔径光子晶体光纤比孔直径不变光子晶体光纤控制色散的能力更强;且当第三层与第四层空气孔直径相同时,孔直径渐变的光子晶体光纤的色散更趋于平坦,而当空气孔直径取d₁=0.85d₄, d₂=0.95d₄,d₃=d₄(d₁,d₂,d₃,d₄分别为包层从内到外空气孔的直径)时,此种光子晶体光纤可以在波长60—65 μm(4.61—5 THz)范围内将波导色散值控制在-0.1±0.3 ps/(km·nm)范围内,得到趋于超平坦色散的、具有很好的束缚THz波的能力和良好的损耗特性的新型THz波光子晶体光纤. 关键词： THz波光子晶体光纤 时域有限差分方法 超平坦色散     

Measured and predicted band model parameters of BF3(v3) at high temperatures

Two experimental techniques were used to determine the high temperature infrared absorption coefficients of the v₃ band of BF₃. A high temperature flow tube fitted with a multipass infrared absorption cell was used to determine the BF₃ absorption coefficients at 295, 585, 870, 1150, and 1440K. BF₃ was also used in a flame emission-absorption apparatus to determine the BF₃ absorption coefficients at 2400 K.A generalized formulation for predicting the S/d and 1/d band model parameters of symmetric top perpendicular bands of MX₃ molecules is presented. The effect of including nuclear spin statistics in computing the S/d and 1/d band model parameters is considered. It is shown that nuclear spin statistic?s effect only the 1/d parameter and are significant only for the case of zero nuclear spin. A number of practical considerations, which arise in designing a computer algorithm to calculate the S/d and 1/d parameters, are discussed.Comparisons of the theoretical and experimental BF₃ absorption coefficients are made. Good agreement between theory and experiment at all temperatures was obtained by adjusting only two vibrational energy coupling constants, _χ23 and _χ34. Predicted S/d and 1/d band model parameters at 300, 600, 900, 1200, 1500, 2000, 2500, and 3000 K are presented.     

Piezoelectric coefficients of cross-linked polypropylene films stretched at elevated temperatures

Cross-linked polypropylene (XPP) foams are modified by a hot-stretching process and charged to be piezoelectric. The results show that a piezoelectric d₃₃ -coefficient of 308pC/N is obtained for sample with an elongation ratio of 200%. The dynamic d₃₃ value is smaller than the quasi-static value, which is probably due to the rise of Young’s modulus with increasing frequency. All the samples show pressure-independent d₃₃ in the range up to 30 kPa. Improved d₃₃ was obtained in the sample rough surface exposed to the corona during charging. Compared to linear PP, the stretched XPP shows pressure independence of d₃₃ in larger range.     

The proximity effect for weak itinerant ferromagnets

The Curie temperature T_c of a proximity sample composed of a thin film of a weak itinerant ferromagnet of thickness d_f in contact with a thick film of an enhanced parmagnetic metal is calculated using the Hubbard model in the Hartree-Fock approximation. The sample is paramagnetic for values of d_f less than a critical thickness d_f⁰ of the order of the coherence length. The shape of the curve of T_c vs. d_f for d_f > d_f⁰ depends on whether the bulk ferromagnet exhibits a Curie-Weiss or a Pauli susceptibility above the bulk Curie temperature. The letter is concluded by comments on the experimental situation.     

Dynamical mean-field study of the Mott transition in thin films

The correlation-driven transition from a paramagnetic metal to a paramagnetic Mott-Hubbard insulator is studied within the half-filled Hubbard model for a thin-film geometry. We consider simple-cubic films with different low-index surfaces and film thickness d ranging from d=1 (two-dimensional) up to d=8. Using the dynamical mean-field theory, the lattice (film) problem is self-consistently mapped onto a set of d single-impurity Anderson models which are indirectly coupled via the respective baths of conduction electrons. The impurity models are solved at zero temperature using the exact-diagonalization algorithm. We investigate the layer and thickness dependence of the electronic structure in the low-energy regime. Effects due to the finite film thickness are found to be the more pronounced the lower is the film-surface coordination number. For the comparatively open sc(111) geometry we find a strong layer dependence of the quasi-particle weight while it is much less pronounced for the sc(110) and the sc(100) film geometries. For a given geometry and thickness d there is a unique critical interaction strength U _c2 (d) at which all effective masses diverge and there is a unique strength U _c1 (d) where the insulating solution disappears. U _c2 (d) and U _c1 (d) gradually increase with increasing thickness eventually approaching their bulk values. A simple analytical argument explains the complete geometry and thickness dependence of U_c2. U_c1 is found to scale linearly with U_c2. Received 19 August 1998     

Probing meson spectral functions with double differential dilepton spectra in heavy-ion collisions

The double differential dilepton spectrum d/(d ² d _⊥ ²) at fixed transverse mass M _⊥ allows a direct access to the vector meson spectral functions. Within a fireball model the sensitivity of d/(d ² d _⊥ ²) against variations of both the in-medium properties of mesons and the dynamics of the fireball is investigated. In contrast to the integrated invariant-mass spectrum d/d ², in the spectrum d/(d ² d _⊥ ²) with fixed M _⊥ the ω signal is clearly seen as bump riding on the ρ background even in case of strong in-medium modifications.[3mm] Received: 16 November 2000 / Accepted: 16 January 2001     

Ga1-xAlxAs光学声子形变势研究

本文用LMTO-ASA能带技术结合新的虚晶近似处理方法和冻结声子模型,计算了三元合金Ga_1-xAl_xAs Γ点的光学声子形变势(ODP)do及A轴上ODP的d₃₀,d₁₀(val)和d₁₀(cond),预言了它们作为Al组分x的函数关系,发现这些ODP都可用x的二次方程表示,其中d₀随x增加而减小的弯曲参数很小,是近乎线性的,理论预言了x≈0.65处d₁₀关键词：     

Fe/SnO2非晶多层膜的磁特性

研究了高频溅射制备的Fe/SnO₂非晶多层膜的磁特性.当SnO₂层厚度d_s固定为5nm时，样品的饱和磁化强度M_s随Fe层厚度d_m的减小而降低，这主要受样品的死层效应和维度效应的影响.另外，在d_m很小时，样品呈现准二维磁性.样品居里温度T_C随d_m的减小单调下降.样品矫顽力H_c随d_m的变化呈现 关键词：     

Early transition metal dopants in cuprous oxide: To spin or not to spin

We present a trend study of a large variety of dopants at the cation site in Cu₂O (i.e. substituting Cu), focussing largely on the early 3d-, 4d-, and 5d-transition metals (TMs) in which many of them are known to be non-magnetic. We also include s-, sp- and d¹⁰-metals for comparison. We find that doping with sp-elements results in zero spin moment while dopants with a partially filled d-band show a stronger tendency to magnetize and 3d-TM dopants exhibit a larger magnetic moment than most of the 4d- and 5d-TM dopants. From this trend study, we also find a correlation between their substitution enthalpy and associated interatomic relaxations. In particular, Ti-doped Cu₂O appears to be an interesting system, given its “peculiar” ability to exhibit a spin moment when doped with a non-magnetic substituent like Ti. We also find that the interaction between two doped Ti atoms in Ti₂:Cu₂O is predominantly antiferromagnetic, and interestingly (and unexpectedly), this interaction rapidly declines as a function of inter-dopant distance, as in the case for the magnetic late-TM dopants like Co₂:Cu₂O.