Si(100)-(2×1)表面上Si薄膜生长的模拟

本文在分析表面扩散各向异性、二聚体和二聚体列影响的基础上,建立了Si(100)-(2×1) 表面上Si薄膜生长的Kinetic Monte Carlo(KMC)模型,利用该模型对薄膜生长的初始阶段进行了研究.结果表明:吸附原子的扩散距离随温度的变化满足指数函数L=L0AeT/C.在一定的入射率下存在一最佳成岛温度,该温度随入射率的增大而升高.随入射率的减小,薄膜逐渐从离散生长向紧致生长转变,表面扩散的各向异性越显著.     

Lepidocrocite-like TiO2 and TiO2(110)–(1 × 2) supported on W(100)

Ultrathin films of TiO₂ were grown on a W(100)–O(2?×?1) substrate and characterised with a combination of scanning tunneling microscopy (STM) and low energy electron diffraction. In addition to islands of rutile TiO₂(110) with (1?×?1) termination that were reported previously, we also observed rutile TiO₂(110) islands with a (1?×?2) film termination. A lepidocrocite-like TiO₂ nanosheet was also observed on the W(100) surface. High resolution STM images show that the nanosheet grows in the principal orthogonal directions of the W(100) substrate and forms a commensurate (1?×?7) coincident cell.     

Novel Evolution Process of Zn-Induced Nanoclusters on Si(111)-(7×7) Surface

Nano-Micro Letters - A tiny number of Zn atoms were deposited on Si(111)-(7×7) surface to study the evolution process of Zn-induced nanoclusters. After the deposition, three types (type I, II,...     

溅射生长Ge/Si(100)2×1薄膜的分子动力学研究

以Si(100)2×1为基底,对不同入射角度、基底温度及入射能量时生长锗薄膜进行了分子动力学模拟.运用双体分布函数与原子直观构型及原子轨迹法对结果进行了分析讨论.模拟表明,以上3种因素对薄膜微结构都有一定影响,但基底温度的影响最重要;重构基底的二聚体键打开对实现锗外延生长很重要,而二聚体键断开过程主要发生在下一层锗入射阶段,因而下一层锗入射阶段是上一层锗外延晶化的关键阶段.     

O_2/Si(100)-2×1重构表面相互作用过程的动力学研究

对双原子分子O2与Si（100）－2×1重构表面的相互作用过程进行了动力学研究。建立了相互作用系统的LEPS势能超曲面，并在此基础上采用准经典轨迹方法计算了不同特征吸附位上的分子运动轨迹，得到了与理想表面模型相比更为合理的表面吸附特性。     

STM studies of island formation and surface ordering of Si on GaAs (001), (2×4) and c(4×4): Implications for δ-doping

Scanning tunnelling microscopy (STM) and reflection high energy electron diffraction (RHEED) have been used to study the deposition of Si below 400C onto GaAs (001) surfaces grown in situ by molecular beam epitaxy (MBE). The emphasis is on the island formation and growth, as well as surface ordering, for submonolayer quantities of Si (up to 0.2 ML) deposited on two different As-rich reconstructions of GaAs (0 0 1) (2 × 4) and c(4 × 4). For deposition on the c(4 × 4) surface, an asymmetric (3 × 1) RHEED pattern is formed, a consequence of anisotropic needle-like islands, which grow adjacent to each other along the [1 1 0] direction and produce a three-fold periodic superstructure. Individual islands grow by a site exchange process in which the additional As layer of the c(4 × 4) structure acts as a surfactant and enables the Si atoms to occupy Ga sites in the GaAs lattice. In contrast, Si deposition on the (2 × 4) surface does not lead to any new surface periodicities as monitored by RHEED. The Si atoms form poorly ordered clusters distributed randomly across the surface. The site exchange process cannot occur in this case as the (2 × 4) surface is terminated with only one layer of arsenic. Instead, the Si atoms occupy sites on top of the outer arsenic layer.     

Na、O在n-GaAs(100)-(4×1)表面吸附以及共吸附的光电子谱研究

利用紫外光电子谱,对Na、O在n型GaAs(100)-(4×1)表面吸附及共吸咐作了详细研究。结果表明:随着GaAs(100)表面Na覆盖度的变化,其表面呈现不同的能带弯曲。当Na的覆盖度很低时(通常认为θ≤0.02ML).n-GaAs(100)表面能带向下弯曲量达0.3eV。但随着覆盖度的增加,最后费米能级钉扎在价带顶以上0.8eV处。另外,O在n-GaAs(100)-(4×1)表面吸附。暴露量达10~5L时,导致了向上0.2eV的能带弯曲。如果在吸氧的表面继续蒸Na,则其费米能级钉扎在价带顶以上1.0eV处。同时还可看到,由于Na存在,O_2在n型GaAs(100)-(4×1)表面有粘附系数将大大地提高。     

Molecular nanostructures with strong dipole moments on the Si(111) 5 × 2-Au surface

Switchable organic molecules adsorbed on a silicon surface combine the flexibility and the low cost of molecular electronic devices with the sophistication of modern silicon technology. The first step towards creating such hybrid devices is the formation of regular, ordered patterns of molecules on a silicon surface. A stepped Si surface passivated by a sub-monolayer of gold is found to provide a useful substrate for forming ordered molecular patterns. Molecules with strong dipole moments, such as fluorophenols, form a one-dimensional molecular array on such a substrate by adsorbing on top of the step edges. Local barrier height measurement by scanning tunneling spectroscopy demonstrates the possibilities to detect the direction of the dipole moment of an individual molecule. Polarization-dependent x-ray absorption spectroscopy reveals an oriented adsorption in both the azimuthal and polar directions.     

Effect of Si(100)-<Emphasis Type="Italic">c</Emphasis>(4 × 12)-Al and Si(111)-(5.55 × 5.55)-Cu reconstructions on the deposition of cobalt onto silicon surface

The use of surface reconstructions for modifying properties of single crystal silicon substrates with a view to the creation of new nanostructures is a promising direction in the development of nanotechnologies. Systems Si(100)-c(4 × 12)-Al and Si(111)-(5.55 × 5.55)-Cu occupy special positions among stable reconstructions of the silicon surface, which have been recently demonstrated to be promising templates. The adsorption of cobalt on these surfaces at various temperatures has been studied using scanning tunneling microscopy. The room-temperature deposition leads to the formation of a weakly ordered layer of metallic Co with retained initial reconstructions at the Co/Si interface. An increase in the temperature leads to the formation of faceted cobalt silicide islands on both reconstructed surfaces.     

Nanofabrication of PTCDA molecular chains on rutile TiO(2)(011)-(2 × 1) surfaces

The adsorption of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on a rutile TiO(2)(011)-(2 × 1) surface is studied using ultra-high vacuum scanning tunneling microscopy. The self-assembly process is dominated by the fine interplay between the lateral intermolecular interactions and the binding to the substrate. By means of temperature-induced change in the adsorption configuration and the activation of diffusion, the molecules are assembled into one-dimensional chains oriented along the [Formula: see text] crystallographic direction.     

Thermal Stability of ALD Lanthanum Aluminate Thin Films on Si(100)

The thermal stability of high-K dielectrics on Si is critical in avoiding the malfunction of metal oxide field effect transistors(MOSFET) in devices.Series of annealing experiments have been performed to investigate the thermal stability of atomic layer deposited(ALD) lanthanum aluminate(LAO) thin films,a promising amorphous high-K candidate.The abrupt interface between LAO and Si remains intact at temperatures below 600 C.Above this temperature,a SiO_2-rich interfacial layer begins to appear and thickens at higher temperatures.At900 ℃,the interface is roughened due to the formation of nano sized crystal nuclei above the interfacial layer,which indicates the interfacial reactions with the Si substrate.The thermal stability of ALD Al_2O_3 thin films on Si have also been studied under similar conditions.The Al_2O_3/Si interface retains its smoothness even after full crystallization.This comparison suggests that the rare earth element may catalyze the interfacial reactions.Further annealing experiments on LAO films with different thickness and with a capping layer show that the oxygen source of the interfacial layer mainly comes from the ALD oxide films.     

Si(100)面的STM观察

使用超高真空扫描隧道显微镜(STM)观察了Si(100)面,得到了清洁Si(100)面的STM像。从Chadi模型的形成和表面原子的各向异性扩散分析了STM像的两种类型的台阶棱。Si(100)面的STM像存在许多缺陷,缺陷位置能从在同一区域样品上加正负偏压的STM像来确定。     

Initial Oxidation of γ-TiAl(111) Surface:Density-functional Theory Study

In this paper,we reported a first-principles investigation on the structural and electronic properties of O adsorption on the γ-TiAl(111) surface,to illustrate the oxidation process.It has been found that:(1) rather than stopping with one full monolayer of coverage,oxygen adsorption continues till two monolayer coverage,rendering an oxide-like structure;(2) full structural relaxation makes the surface oxide layer denser and more stable,which hinders the subsequent O adsorption(oxidation) process.In addition...     

Si(111)7×7表面Na沉积过程的光学二次谐波法研究

用原位光学二次谐波方法监测了室温时Na在Si(111)7×7表面沉积过程中的信号变化。室温下Na沉积量小于饱和单层时信号变化比较复杂,随Na沉积量的变化依次出现三个特征峰。覆盖度约0.45 ML时出现较弱的峰A,其产生可能与碱金属诱导的占据态F和没有被占据的态A间的跃迁所引起的共振增强有关;随后在约0.9 ML的覆盖度下出现峰B并在沉积量大于饱和单层后信号快速增大,形成陡峭的峰C。相测量表明峰B与峰C信号之间存在明显的相位差,说明两者的起源有不同之处。峰C的出现与等离激元的激发密切相关。在峰B所处的覆盖度下,二维及二维-三维过渡结构的存在可能产生两种以上不同起源的二次谐波信号,其相干叠加促成了峰B的出现。     

Oxidation resistance of diffusion coatings formed by pack-codeposition of Al and Si on γ-TiAl

Oxidation resistance of the aluminide and silicide diffusion coatings pack-deposited on -TiAl were studied in air over the temperature range of 800 and 850°C for up to 4596 h. The oxidation kinetics of the coatings was monitored by intermittent weight gain measurement at room temperature. The XRD and SEM/EDS techniques were used to identify the oxide scales formed during the oxidation process and to assess the thermal stability of the coatings at the oxidising temperatures. It was revealed that the TiAl₃ coating underwent preferential Al oxidation to form the Al₂O₃ scale in the early oxidation stage, which resulted in Al depletion and formation of TiAl₂ in the subsurface of the coating. The Al depletion could not be sufficiently compensated by Al diffusion from the inner layer of the coating and eventually, in the late oxidation stage, led to the Ti oxidation and formation of the TiO₂ phase in the scale. The preferential Si oxidation was the main oxidation mechanism for the coatings with an outer silicide layer and an inner TiAl₃ layer with the formation of SiO₂ as the stable oxide scale. The thermal stability of the coatings over the temperature range up to 850°C was discussed in relation to the high-temperature stability of diffusion couples of different coating layers.     

Si(111)、Si(100)表面初期氧化的电子能谱研究

一、引言随着硅平面工艺的发展,硅表面氧化工艺、Si-SiO_2介面及硅初期氧化膜的结构和特性,由于在器件制造中的地位和作用,几十年来人们作了大量的研究。B-Lang等人利用离子刻蚀深度剖析研究了热氧化生长的厚SiO-2和真空室制备的SiO_2膜,结果发现,     

Photoabsorption properties of β-FeSi2 nanoislands grown on Si(111) and Si(001): Dependence on substrate orientation studied by nano-spectroscopic measurements

Photoabsorption properties of β-FeSi₂ nanoislands epitaxially grown on Si(111) and Si(001) have been discussed using photoabsorption nano-spectroscopy based on scanning tunneling microscope. The obtained spectra exhibit clear features around 0.86-0.91 eV and around 0.71-0.74 eV, which are explained as a direct and an indirect photoabsorption edge of β-FeSi₂, respectively. We also observed a blue shift of spectrum obtained from β-FeSi₂ nanoislands on Si(111) substrates, compared to those on Si(001) substrates. We attributed the dependence on Si-substrate orientation not to a quantum confinement effect but to an effect of elastic strain in the? β-FeSi₂ nanoislands epitaxially grown on the substrate.     

Morphology and properties of Mg2Si and Mg2(SixSn1−x) reinforcements in magnesium alloys

In this paper, the effects of Sr, Sb, Sr+Sb and Sn on Mg₂Si reinforcement phases in an Mg–Al–Zn–Si alloy are studied, and the structures and characteristics of Mg₂(Si_xSn_1?x) phases are analysed with first-principle calculations. The results show that the coarse eutectic Mg₂Si can be refined by modifying processes with Sr, Sb, and their combination. When alloying with Sn, a new reinforcement phase Mg₂(Si_xSn_1?x) forms by a substitution reaction, instead of Mg₂Si. Calculations indicate that Mg₂(Si_xSn_1?x) has a certain percentage of covalent bonds, which ensure it has sufficient hardness to act as a reinforcement phase. Calculated results for physical parameters, such as the bulk modulus and shear modulus, indicate that an Mg₂(Si_xSn_1?x) intermetallic exhibits greater ductility than Mg₂Si.

Highlights

• The coarse eutectic Mg₂Si can be refined by modifying processes.

• A new phase Mg₂(Si_xSn_1?x) forms by substitution reaction during solidification.

• Mg₂(Si_xSn_1?x) has certain covalent bound percentage.

• Mg₂(Si_xSn_1?x) has better plasticity than that of Mg₂Si.

     

Self-assembly of conductive Cu nanowires on Si(111)'5 × 5 '-Cu surface

Upon room-temperature deposition onto a Cu/Si(111)'5 × 5' surface in ultra-high vacuum, Cu?atoms migrate over extended distances to become trapped at the step edges, where they form Cu?nanowires (NWs). The formed NWs are 20-80?nm wide, 1-3?nm high and characterized by a resistivity of ～8?μΩ?cm. The surface conductance of the NW array is anisotropic, with the conductivity along the NWs being about three times greater than that in the perpendicular direction. Using a similar growth technique, not only the straight NWs but also other types of NW-based structures (e.g. nanorings) can be fabricated.