c-axis-textured LiNbO3 thin films on Si (111) substrates

We have successfully prepared highly c-axis-textured LiNbO₃ films on hydrogen-terminated Si (111) substrate using sol-gel spin-coating and rapid thermal annealing. These highly c-axis-textured films were obtained with a preheating at 300 °C for 15 min followed by a rapid thermal annealing at 500–700 °C for 120 s. The c-axis orientation of the LiNbO₃ film is due to a weak effect caused by the 3-fold symmetry match between the film and the Si (111) substrate. The c-axis orientation of LiNbO₃ films is very useful in integrated optics devices and metal–ferroelectric–semiconductor nonvolatile memory applications. Received: 15 September / Accepted: 4 December / Published online: 3 April 2001     

Molecular dynamics simulation of graphene on Cu (111) with different Lennard-Jones parameters

The interaction between graphene and copper (111) surface have been investigated using the molecular dynamics simulations. The range of Lennard-Jones parameters which correspond to the binding energies and the binding distances calculated via ab initio methods was found. The dependencies of the binding energy, the binding distance and the graphene thickness on the parameters of the potential and the rotational angle are presented. We have found minima of the binding energy which can be related to experimentally observed Moiré superstructures.     

KTP(001)晶体分光性能研究

根据同步辐射光源对软X射线分光晶体的性能要求,分析了软X射线能区常用分光晶体的性能优劣,指出对于晶格常数值大的分光晶体,KTP(KTiOPO₄)(011)是该能区比较理想的分光晶体. 同时提出了一种利用同步辐射光源测量晶体衍射效率的实验方法,指出光源的发散度与晶体的衍射效率密切相关. 测量了KTP(011)晶体的晶格常数,给出了KTP(011)晶体的实测衍射效率. 关键词： 同步辐射 KTP(011)晶体 衍射效率 光源发散度     

InAs(001)表面脱氧动力学分析

利用反射式高能电子衍射(RHEED)实时监控对InAs衬底进行两步完全脱氧的过程, 对比了有低(高)砷等效束流压强保护下采用两步法对InAs衬底缓慢长时间的高温脱氧过程. InAs衬底两步完全脱氧法的第一步为传统的缓慢升温脱氧方法, 第二步为高温In束流辅助脱氧方法. 衬底高温脱氧的RHEED衍射图样说明了高温In束流辅助脱氧最终完全清除传统的缓慢升温法无法去掉的残留氧化物, 通过脱氧完成同质外延生长后的扫描隧道显微镜图像, 说明高砷等效束流压强保护下的脱氧方法是可行的; 分析了高温In束流能完全清除衬底表面残余In氧化物的原理. 关键词： 热分解 Ⅲ-V族半导体 反射式高能电子衍射     

Si(001)表面稀土金属硅化物纳米结构

稀土金属元素的硅化物在n型硅衬底上具有高电导率和低肖特基势垒的特点，在大规模集成的微电子器件领域具有很好的应用价值．文章系统介绍了在Si（001）表面自组装生长的稀土金属硅化物纳米结构的研究进展，较全面地讨论了退火温度、退火时间以及稀土金属表面覆盖度等生长条件对纳米结构生长的影响作用，并在此基础上分析了纳米线、纳米岛的晶化结构，衬底对纳米结构生长的影响，以及纳米结构的演化过程．搞清楚这些内在的生长机理，有助于人们今后实现可严格控制稀土金属硅化物纳米结构的形貌尺寸和分布的自组装生长．此外，文章还介绍了目前人们对稀土金属硅化物纳米线电学性质的研究进展．     

Preferential regrowth of indium–tin oxide (ITO) films deposited on GaN (0001) by rf-magnetron sputter

Effects of thermal treatments on the electrical properties and microstructures of indium–tin oxide (ITO)/GaN contacts have been investigated using a rf-magnetron sputter deposition followed by rapid thermal annealing. ITO films annealed at 800 °C revealed Schottky contact characteristics with a barrier height corresponding to ITO’s work function of 4.62 eV. The evolution of electrical properties of ITO/GaN contacts was attributed to the preferential regrowth of In₂O₃ (222)//GaN (0001) with an ideal metal–semiconductor Schottky contact. The feasible use of ITO/GaN as a transparent Schottky contact would be realized by the enhanced regrowth of In₂O₃ at high temperature. Received: 1 September 2000 / Accepted: 15 November 2000 / Published online: 28 February 2001     

低能CU6团簇在CU(001)表面和AU(001)表面沉积的分子动力学模拟研究

关键词：     

MoSi_2(001)表面的氧吸附行为

运用第一原理密度泛函理论方法,首先计算了MoSi_2各清洁表面的表面能,(001)Si-|-Si断面具有较低的表面能,是MoSi_2最可能的解理面;通过生成能及键布居分析研究了单氧原子、双氧原子及氧分子在(001)Si-|-Si断面的吸附行为,发现单氧原子在空位处吸附最稳定,此时O极易与Si结合,得到的Si-O-Si键长及键角与SiO_2的非常接近,表明低浓度下O极易与表面的Si结合生成SiO_2;双氧原子发生空位+顶位吸附时O原子除与Si有强作用外,可与Mo有一定相互作用;氧分子以平行的方式接近空位最有利于吸附,此时氧分子最易分解为氧原子,发生氧原子在空位的吸附.     

单晶Cu(001)薄膜塑性变形的分子动力学模拟

使用分子动力学方法,模拟研究了单晶Cu(001)薄膜在双向等轴拉伸应变下的塑性变形行为.当应变超过一定值时,样品通过产生位错、层错及孪晶而发生塑性变形.当应变相对较低时,不全位错首先在薄膜表面形核并在密排面上滑移,留下堆积层错;当应变增加时,位错在表面与内部同时成核生长,层错数量也随之增加.分析了相邻滑移面上的位错之间相互作用形成孪晶的微观过程.材料内部形成大量堆积层错及孪晶后,较大孪晶的密排面上的原子也会发生滑移,形成孪晶内部的层错结构以释放残余应力.     

In在Al(001)表面偏析的模拟

通过一种空位模型详细的描述了In在Al(001)表面的扩散偏析过程,利用周期性密度泛函理论方法计算了这个偏析过程中每步构型的能量和In原子扩散的能量壁垒,并对可能的偏析机理进行分析.结果表明:In原子从Al(001)表面第二层扩散偏析至表面层时,系统的能量降低了0.64 eV,最大的扩散迁移壁垒为0.34 eV;而从表面更内层向表面第二层扩散时系统能量基本保持不变,扩散需要克服的能量壁垒为0.65 eV,说明In原子在Al(001)表面只能由体内向表面扩散偏析.In在Al(001)的清洁表面具有强烈的偏析趋势,在热力学上是容易进行的. 关键词： 密度泛函理论 表面偏析 扩散 Al合金     

甘氨酸在Cu(001)表面的吸附结构

结合低能电子衍射(LEED)及其消失斑点规律和扫描隧道显微镜(STM)手段确定了室温下甘氨酸在Cu(001)表面能形成c(2×4)和两种(2×4)吸附结构((2×4)₁和(2×4)₂),并推断出在两种(2×4)结构单胞中两甘氨酸分子的羧基相对于衬底的吸附取向一致,而它们的氨基则不同.实验中还观察到c(2×4)与(2×4)₂结构能相互转变成窄条相互穿插共存,这说明几种吸附结构能量相近. 关键词：     

Surface morphology of MgO (100) crystals implanted with MeV Al+ and Al2+ ions

MgO (100) single crystals are implanted with 1.50-MeV Al⁺ and 3.00-MeV Al₂ ⁺ ions at a fluence of 1×10¹⁵ Al  atoms  cm^-2 under high-vacuum conditions. The surface morphology of the substrate is measured in air using atomic force microscopy and X-ray reflectometry followed by computer-simulated spectrum analysis. The ion-irradiated areas are found to protrude to different heights on the nanometre scale. Small height differences are observed in the areas irradiated by Al⁺ and Al₂ ⁺ ions of comparable energy, dose rate and total fluence. The results indicate that protrusions are most likely caused by implantation-induced point defects (vacancies) generated in the crystal during implantation. Other possibilities for the cause of protrusions are discussed. Thermal treatment stimulates a partial recovery of the implantation damage and alters the topography of MgO surfaces. Received: 22 May 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Enhanced atomic-scale contrast on Fe3O4 (100) observed with an Fe STM tip

Clean (100) surfaces of a synthetic single crystal of magnetite (Fe₃O₄) have been prepared in situ using current pulses in a scanning tunneling microscope without subsequent annealing. We have observed atomically resolved terraces with rows of Fe²⁺ and Fe³⁺ ions of the B-sublattice (octahedrally coordinated lattice sites). Along these rows a long-distance corrugation (∼12 ?) has been observed at 300 K using in situ prepared Fe tunneling tips. This corrugation is interpreted as a Wigner localization associated with a Verwey transition above 300 K in the top surface layer. Received: 26 September 2000 / Accepted: 27 October 2000 / Published online: 3 May 2001     

Photoemission study of clean and c(4×2)-2CO-covered Pt (111) using high-harmonic radiation

An extreme ultraviolet (EUV) laser light source based on high-harmonic generation is presented. Coherent radiation in the photon energy range hν=20–120 eV is produced in the conversion media argon, neon and helium. High-harmonic radiation in the energy range 20–50 eV is applied to investigate photoemission spectra of Pt (111) and CO/Pt (111). In the photoemission spectra of the clean surface, new secondary electron emission structures are found which influence the cross section analysis of the CO states. When taking these Pt resonances into consideration, the 4σ and 5σ CO shape resonances are found at photon energies of 37 eV and 28 eV, respectively. Additionally, a resonance at hν=31 eV is also observed for the CO 1π state, in contrast to formerly published experimental data. Experimental and theoretical data suggest that this resonance is not connected to the well-known shape resonances in the σ-channel. Based on theoretical approaches, it is identified as an autoionization resonance. Received: 8 April 2002 / Accepted: 22 May 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +49-251/833-3604, E-mail: kutzner@uni-muenster.de     

WO_3(001)表面活性氧物种的理论研究

采用第一性原理结合周期性平板模型的方法,对O_2在完整和缺陷WO_3(001)表面的吸附行为进行了研究.结果表明:WO_3(001)完整表面上吸附态的O_2不易成为表面氧化反应的活性氧物种,当吸附质与表面作用时,将优先与表面晶格氧(O_t)成键,进而形成表面缺陷态,体系呈现金属性,电导率增大.比较O_2在缺陷表面上各吸附构型的吸附能发现,O_2的吸附倾向于发生在缺陷位置(W_v)上,且表现为氧气分子中的两个氧原子均与缺陷位W_v作用,形成新的活性氧物种(O_2~-);吸附后表面被氧化,电导率降低.     

Si(001)邻面上与台阶有关的电子态

我们用角分辨光电子谱(ARUPS)研究了Si(001)邻面上与台阶有关的电子态。在对称点Γ(K₁₁=0),发现此态的能级在E_F以下0.5—0.6eV处。同时还测得该态的色散(<0.3eV)比正常的Si(001)表面态的色散(0.6—0.7eV)来得小。 关键词：     

Cesium adsorption on the β2-GaAs(001) surface

The results of first-principles calculations of the cesium adsorption energy on the β2-GaAs(001) surface performed within approaches of the density functional theory are presented for two possible terminations of the surface. It is shown that, among the considered high-symmetry positions, the energy-preferred position for cesium is position T ₃ when the surface layer contains arsenic and position T ₄ for gallium terminated surface. Cesium introduces insignificant perturbations in the positions of surface-layer atoms, and surface dimers do not break even in the case of adsorption at the dimer bridge and top positions. It is shown that cesium bonding to the GaAs (001) substrate can be explained by sp hybridization of arsenic and gallium orbitals as well as by formation of cesium states mixed with delocalized states of a clean surface. At low coverage, more preferable adsorbate sites are those with nearest neighbor arsenic atoms for both surface terminations.