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A detailed comparison between theoretical and experimental LEED data for the Mo(001) surface, using the quantitative r-factor method of Zanazzi and Jona, yields a value for the surface layer contraction of 9.5 ± 2.0%, consistent with the 11.5% found previously by Ignatiev et al. Non-structural parameters are also in agreement, although the surface Debye temperature, 230 K, is slightly higher than found before. r-Factors were used to investigate the effects of all the parameters, and show that an energy-dependent inner potential gives better agreement than a fixed value and that the second layer is contracted by about 1% of the bulk layer spacing. The effect of using different ion core potentials is examined and discussed. A superposition potential which models the surface ion environment is found to have a significant effect on the layer displacement concluded.  相似文献   

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We investigate the microstructure of the reconstructed Au(001) surface using ultra-high vacuum transmission electron microscopy (UHV-TEM). Bulk single crystal Au(001) surfaces were prepared via standard metallographic techniques followed by repetitive cleaning of the surface with ion milling and annealing. After a clean surface was obtained, the (001) surface was found to reconstruct into two nearly orthogonal domains of dimensions (5 × n) where n ranges between 15 and 21. The unit cell vectors of the surface cell are parallel to the 110 directions of the unreconstructed fcc (001) surface. Analysis of the diffuse scattering and dark field micrographs indicates that the surface is sheared with a complicated domain and periodicity structure which depends upon the local geometry of the substrate.  相似文献   

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We have computed the electronic band structure for a model of the 2 × 1-reconstructed (111) surface of Si, based on 2 two-dimensional net of dangling bonds. A pairing of surface atoms is assumed, involving a displacement and a tilting of the dangling bonds towards each other. The energy gap that separates the two bands of surface states obtained increases with the degree of reconstruction, which is taken as a parameter. Experimental data, particularly surface optical absorption, find a satisfactory explanation in terms of this calculation, which indicates in Si (111) 2 × 1 a shift of the surface atoms by about 8% of their ideal distance.  相似文献   

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The experimental band structure of Mo(112) and the effects by temperature and adsorbate are presented. A surface resonance, identified as crossing the Fermi level at about 1/3 from to of surface Brillouin zone, was observed to be very sensitive to both contamination and temperature. We find evidence of adsorbate and temperature induced reconstruction of the Mo(112) surface. Examination of low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) data provides evidence for an adsorbate induced reconstruction of the Mo(112) surface with periodicities consistent with the Fermi level crossing of the surface resonance. The reconstruction is found to occur at coverages as low as 0.03 Langmuirs of oxygen or carbon. The reconstruction and/or adsorbate affects the density of states and bands near the Fermi level of a 1 symmetry. Received 3 March 1999 and Received in final form 1 October 1999  相似文献   

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(001)面任意方向单轴应变硅材料能带结构   总被引:1,自引:0,他引:1       下载免费PDF全文
马建立  张鹤鸣  宋建军  王冠宇  王晓艳 《物理学报》2011,60(2):27101-027101
首先计算了(001)晶面单轴应变张量,在此基础上采用结合形变势理论的K ·P微扰法建立了在(001)晶面内受任意方向的单轴压/张应力作用时,应变硅材料的能带结构与应力(类型、大小)及晶向的关系模型,进而分析了不同单轴应力(类型、大小)及晶向对应变硅材料导带带边、价带带边、导带分裂能、价带分裂能、禁带宽度的影响.研究结果可为单轴应变硅器件应力及晶向的选择设计提供理论依据. 关键词: 单轴应变硅 K ·P法 能带结构  相似文献   

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We present the results of a theory of electronic energy bands of superlattices using an application of a recent novel empirical tight binding method. The theory is applied to GaAs-AlAs (001) superlattices with very good agreements with available experimental results for both the direct and indirect energy gaps.  相似文献   

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The band structure for a Mo (001) surface covered with a saturated monolayer of hydrogen is calculated self-consistently using the pseudopotential method in a mixed-basis representation. Two adsorbate bands are found below the bottom of the molybdenum bulk bands. Most of the intrinsic surface states of the clean (001) surface also exist on the hydrogen covered surface at lower energies. The results are used to identify H induced structures observed in recent photoemission studies of hydrogen on W (001).  相似文献   

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采用密度范函理论计算了金属化合物MgB2(001)薄膜结构的电子能带结构和状态密度,计算的交换相关能分别采用LDA和GGA。规范保守赝势的计算结果表明,晶格常数与实验值误差在很小的范围内,分析了引起MgB2(001)面结构超导转变时电子浓度和偏态密度的变化情况,发现构成该超导体结构的成键有三种,着重从结构的电子浓度变化分析了其超导特性,六角蜂窝状结构中硼原子间相互作用为sp2杂化的共价键,镁原子和硼原子之间是离子键结合,镁原子层是金属键结合,镁原子的价电子部分转移到硼原子的pz轨道,部分电子为镁原子层共用。MgB2的超导机制为强烈的电子-声子耦合,为B原子间强烈的共价作用形成,是传统S波超导体。对Mg元素同一主族的其它硼化物进行布居分析,发现MgB2中Mg原子电子转移明显强于BeB2和CaB2,说明电子浓度是引起超导转变的一个重要因素。  相似文献   

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Using spin-polarized scanning tunneling microscopy with ring electrodes, the in-plane spin polarization of Mn on Fe(001) was measured. A large (square root 10 x 2 square root 10)R18.4 degrees reconstruction with a noncollinear spin structure was found. By combining maps of the spin polarization for two orthogonal in-plane directions, the vector field of the polarization in the unit cell could be constructed. The complex behavior is explained on the basis of the tendency of Mn to form antiferromagnetically coupled surface dimers.  相似文献   

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We report the observation of a peak in the region of the sp band for 4 < hν < 10 eV in the normal emission UPS spectrum of the Cs-reconstructed Ag(110) surface. It disperses over ~ 2.5 eV and its therefore not due to the alkali itself, but rather to a bulk excitation which becomes visible because of surface umklapp. Using the appropriate reciprocal lattice vector, we have mapped the dispersion along the original direction in the three dimensional Brillouin zone and find good agreement with theory.  相似文献   

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The structure of the clean, reconstructed W(001) surface has been studied by MeV ion back-scattering channeling. We extract quantitative information on the number of displaced surface atoms (~ 12 monolayer) and the magnitude of the lateral component of their displacement (~ 0.23 Å) by measuring the energy dependence of the surface peak.  相似文献   

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