Bombardment induced surface chemistry on Si under keV C60 impact

Molecular dynamics simulations of the sputtering of Si by C₆₀ keV bombardment are performed in order to understand the importance of chemical reactions between C atoms from the projectile and Si atoms in the target crystal. The simulations predict the formation of strong covalent bonds between the C and Si atoms, which result in nearly all of the C atoms remaining embedded in the surface after bombardment. At low incident kinetic energies, little sputtering of Si atoms is observed and there is a net deposition of solid material. As the incident kinetic energy is increased, the sputtering yield of Si atoms increases. At 15 keV, the yield of sputtered Si atoms is more than twice the number of C atoms deposited, and there is a net erosion of the solid material.     

XPS and RBS investigations of Si–Er–O interactions on a Si(1 0 0)-2x1 surface

The interactions among erbium, oxygen and silicon atoms on a Si(1 0 0)-2x1 reconstructed surface have been studied by means of X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. Erbium and oxygen were deposited at 600 °C on the Si surface and their behavior has been observed after different thermal processes. It was found that at 600 °C, the formation of a stable surface complex Er–O–Si is obtained together with Si oxidation; after an 800 °C annealing, the amount of oxygen bound to Si decreases and the remaining O atoms are mainly bonded to Er. An abrupt change was observed after 900 and 1000 °C annealings, which bury the Er atoms about 60 Å below the substrate surface. Our results give some hints to hypotise the O diffusion towards the Si bulk.     

Tailorable acceptor C(60-n)B(n) and donor C(60-m)N(m) pairs for molecular electronics

Our first-principles calculations demonstrate that C(60-n)B(n) and C(60-m)N(m) can be engineered as the acceptors and donors, respectively, needed for molecular electronics by properly controlling the dopant number n and m in C60. We show that acceptor C48B12 and donor C48N12 are promising components for molecular rectifiers, carbon nanotube-based n-p-n (p-n-p) transistors, and p-n junctions.     

Si2CmN团簇的结构及稳定性的密度泛函理论研究

用密度泛函理论(DFT)的B3LYP/6-311G*方法,对Si2CmN(m=2-10)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=2-10的团簇为线性结构,随着m的增大,团簇的自旋多重度均为2,Si原子在C与N原子形成的线性链端部成键,团簇的基态能量近似线性增大。m为偶数的Si2CmN团簇比m为奇数的更为稳定。     

Self-catalytic growth of horizontal and straight Si nanowires on Si substrates using a sputter deposition technique

We report on the growth of horizontal and straight Si nanowires (NWs) on Si substrate using sputter deposition of the Si layer followed by thermal annealing at 1000 °C and above. The growth of horizontal NWs was achieved without the use of any metal catalyst. Uniform cylindrical shaped Si NWs with a diameter in the range of 50–60 nm and a length of up to 8 μm were synthesized. The as-synthesized Si NWs have a Si core covered with a thin amorphous native oxide layer, as revealed by high resolution transmission electron microscopy. The aspect ratio of these Si NWs is in the range of 100–160. Micro-Raman studies on the NWs reveal a tensile strain on the Si NW core due to presence of a thin oxide layer. From the Raman shift, we calculate a strain of 1.0% for the catalyst free Si NW. FTIR analysis indicates the presence of interstitial oxygen atoms in the Si NWs, as expected from oxidation of Si NWs. For comparison, metal catalyst (Au) assisted Si NWs have also been grown on Si(100) substrate by a similar process. These NWs have a similar diameter and a marginally higher aspect ratio. A model for the growth mechanism of horizontal NWs is presented. This represents one of the first examples of direct horizontal growth of straight Si NWs on commonly used Si substrates suitable for nanoelectronic device fabrication.     

Self-diffusion of (31)Si and (71)Ge in relaxed Si(0.20)Ge(0.80) layers

Self-diffusion of implanted (31)Si and (71)Ge in relaxed Si(0.20)Ge(0.80) layers has been studied in the temperature range 730-950 degrees C by means of a modified radiotracer technique. The temperature dependences of the diffusion coefficients were found to be Arrhenius-type with activation enthalpies of 3.6 eV and 3.5 eV and preexponential factors of 7.5 x 10(-3) m(2) s(-1) and 8.1 x 10(-3) m(2) s(-1) for (31)Si and (71)Ge , respectively. These results suggest that, as in Ge, in Si(0.20)Ge(0.80) both (31)Si and (71)Ge diffuse via a vacancy mechanism. Since in Si(0.20)Ge(0.80) (71)Ge diffuses only slightly faster than (31)Si , in self-diffusion studies on Si-Ge (71)Ge radioisotopes may be used as substitutes for the "uncomfortably" short-lived (31)Si radiotracer atoms.     

Near-surface compositional oscillations of Co diffused into Si(100) at -60 °C: a study by high-resolution Rutherford backscattering

Highly resolved Co depth profiles have been obtained during the initial stages of Co growth on Si(100) at low temperature (-60 °C) by in situ high-resolution Rutherford backscattering spectrometry. We found extensive Co in-diffusion in the submonolayer growth regime even at this low temperature, besides Co on top of the Si surface. The amount of diffused-in Co is larger than the amount of Co at the Si surface. Every second Si layer is depleted of Co, starting at the Si surface, thus giving rise to compositional oscillations of Co in the Si(100) lattice. At this low temperature the growth of metallic Co on the Si surface is observed at 0.1 ML of deposited Co, which continues for higher coverages. At much higher coverage (5.93 ML of Co) almost exclusively low Co content silicides are formed at the Co/Si interface. The data presented here are compared with previous room temperature deposition data and are different in several aspects. PACS 68.35.-p; 68.55.ag; 75.47.-m; 82.80.Yc     

扶手椅型碳化硅纳米管电子结构和光学性质的研究

本文基于密度泛函理论研究了扶手椅型碳化硅纳米管(SiCNT)的电子结构、成键机制以及其光学性质。研究结果表明:当碳和硅的原子比为1∶1时,SiCNT的结构最为稳定,并且表现出诸多的优良性质。通过分析计算结果我们发现,SiCNT是间接带隙材料,并且管子的带隙随着直径的增加而增加。从SiCNT的轨道图谱中我们看到碳和硅原子之间属于sp2杂化,同时硅原子周围的电子密度明显要低于碳原子周围的电子密度。对能态密度的计算我们得知碳原子和硅原子分别主导价带和导带。与其它纳米管(BN)有所不同,SiCNT的光学性质更接近于各向同性材料。     

C/O能谱测井非弹谱的解析方法软件及应用

报道了快中子非弹性散射γ能谱测井, 非弹γ谱的新解析方法软件及应用. 新的解析方法包括:以标准非弹γ谱为基础, 对用NaI(Tl)探测器记录的256道地层非弹γ谱, 作定量解析, 求出各主要元素产额的方法; 以及求新的C/O和Ca/Si比的方法. 可同时求出三种C/O和Ca/Si比值, 即碳氧产额比、 重量百分含量比和原子比;钙硅比也如此. 所设计的软件功能强, 对于孔隙度为35％、 100％油饱和砂岩地层与100％水饱和砂岩地层（刻度井模型地层）, 碳氧原子比之差值>0.33, C/O测井油水差值提高了60％以上, 并求得了地层的含油饱和度. 取得了国内首创和领先的成果. In this paper, the new analyzing method & software and applications of enelactic spectra from Carbon/oxygen spectrometry log is reported. It were included that enelastic Gamma ray spectra(256 channels)of the formations by NaI(Tl) detector were analyzed quantitatively based on standard enelastic spectra, the methods which the ratio of elements yields and new ratio of C to O & of Ca to Si, the ratio of yield of C to O and the ratio of weight percent of C to O and the ratio of atoms C to O were found, and the corresponding ratio of Ca to Si were found simultaneously in new analyzing method. The difference value of the ratio of atoms C to O is greater than 0. 33 between 100% oil saturation and 100% water saturation in sandstone formation for porosity is thirty fife percent. The difference value between oil and water increase by a factor of 60%. In addition oil saturations curves changed with the depth were computed.     

Si3Xn (X=C,O,N;n=1,2)团簇的密度泛函研究

使用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对Si3Xn(X=C,O,N;n=1,2)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的电子结构、振动特性、成键特性和电荷特性等进行了理论研究.结果表明团簇的几何结构都是平面结构,通常Si3X2出现是Si-X键,较少出现X-X键;而Si3X中出现Si-X键和Si-Si键共存,Si3Xn(X=C,O,N;n=1,2)团簇的电荷布局分布表明这种电荷转移的作用使得团簇中所有X原子呈负电性,Si原子显正电性.处于不同位置的Si原子呈不同大小布局数,而且由于Si3X2的对称性,2个X负电性相同.     

在超声分子束下气相四甲基硅分子的多光子解离与电离

采用超声分子束技术，以飞行时间质谱仪，在４１０～３７１ｎｍ内着重检测了不同波长、不同能量的激光对气相Ｓｉ（ＣＨ３）４分子多光子电离（ＭＰＩ）飞行时间（ＴＯＦ）质谱产物分布的影响。根据实验结果，对Ｓｉ（ＣＨ３）４分子多光子解离电离可能经历的通道和反应机理进行了讨论。     

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采用分子动力学模拟方法研究了样品温度对Ar+与SiC样品表面相互作用的影响。由模拟结果可知,SiC样品中Si原子的溅射产额随着温度的升高而增加,而温度对C原子的溅射产额影响不大。在相同温度下,Si原子的溅射产额要高于C原子的溅射产额。溅射出来的Si原子和C原子主要来源于样品的表层区域,样品中的Si和C原子密度、键密度及它们的成键方式也发生了较大的变化。初始样品中Si和C原子的密度是均匀的,而被轰击过后的样品表面Si原子的密度要高于C原子,而样品中部C原子的密度要高于Si原子。初始样品都是Si-C键,成键方式为Si-Csp3;被轰击过后又有Si-Si和C-C键,成键方式也发生了变化,还有Si-Csp1和Si-Csp2。     

Silicon carbide nanocones: Computational analysis of chemical shieldings for pristine and boron/nitrogen decorated models

Density functional theory (DFT) calculations were performed to investigate the electronic and structural properties of pristine and boron/nitrogen (B/N) decorated models of a representative silicon carbide nanocone (SiCNC). The atoms of apexes and tips were differently decorated by B/N atoms to make all possible decorations of the investigated SiCNC. The evaluated parameters by the optimization processes and nuclear magnetic resonance (NMR) calculations indicated that the overall and atomic scale properties of the investigated SiCNCs are significantly dependent on the ways of decorations of Si/C atoms by B/N atoms. The Si/C atoms close to the decorated regions also exhibited notable changes in comparison to the pristine model.     

Sb/Si(001)表面的半经验研究

用基于Chadi模型和格林函数方法的一种计算表面应力的半经验方法研究了Sb吸附在Si(001) 衬底上的性质.结果显示,Sb原子在Si(001)表面形成对称的dimer,其键长为0.293nm,表 面以下层的弛豫很小.Sb/Si(001)2×1表面沿着dimer方向的张应力为1.0eV/(1×1cell),而 沿垂直于dimer方向的压应力为-1.1eV/(1×1cell).Sb/Si(001)表面应力的主要贡献来自于 最上面三层表面. 关键词： 表面应力 异质生长 格林函数方法     

Transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si1−xCx nanocomposites mixed with Si nanoparticles and C atoms

Bright-field transmission electron microscopy (TEM) images, high-resolution TEM (HRTEM) images, and fast-Fourier transformed electron-diffraction patterns showed that n-butyl terminated Si nanoparticles were aggregated. The formation of Si_1−xC_x nanocomposites was mixed with Si nanoparticles and C atoms embedded in a SiO₂ layer due to the diffusion of C atoms from n-butyl termination shells into aggregated Si nanoparticles. Atomic force microscopy (AFM) images showed that the Si_1−xC_x nanocomposites mixed with Si nanoparticles and C atoms existed in almost all regions of the SiO₂ layer. The formation mechanism of Si nanoparticles and the transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si_1−xC_x nanocomposites mixed with Si nanoparticles and C atoms are described on the basis of the TEM, HRTEM, and AFM results. These results can help to improve the understanding of the formation mechanism of Si nanoparticles.     

纳米Si/C/N复相粉体的微波介电特性

研究了纳米Si/C/N复相粉体在8.2—18GHz的微波介电特性,采用双反应室激光气相合成纳米粉体装置,以六甲基二硅胺烷((Me₃Si)₂NH)(Me∶CH₃)为原料,用激光诱导气相反应法合成纳米Si/C/N复相粉体,复相粉体的粒径为20—30nm.纳米Si/C/N复相粉体与石蜡复合体的介电常量的实部(ε′)和虚部(ε″)以及介电损耗角正切(tan δ=ε″/ε′)随纳米粉体含量的增加而增大,ε′和ε″与纳米粉体体积分数(v)之间符合二次函 关键词： 纳米Si/C/N复相粉体 微波介电常量 微观结构     

Stabilization of Si60 cage structure

A comprehensive search for the stable geometries of bare Si60 and Si60 supported on a C60 fullerene was carried out using first principles calculations based on density functional theory. In contrast to previous theoretical studies and in agreement with recent experiments, we show that Si60 and C(60)@Si(60) clusters are unstable in the fullerenelike cage structure. However, Si60 cage can be stabilized by including within it, as endohedral units, small magic clusters such as Al12X (X=Si, Ge, Sn, Pb) and Ba@Si(20).     

Behavior of N atoms in atomic-order nitrided Si0.5Ge0.5(1 0 0)

Behavior of N atoms in atomic-order nitrided Si_0.5Ge_0.5(1 0 0) by heat treatment in Ar at 600 °C was investigated by X-ray photoelectron spectroscopy (XPS). For thermal nitridation by NH₃ at 400 °C, nitridation of surface Si atoms tends to proceed preferentially over nitridation of surface Ge atoms. It is also clear that, with the heat treatment, nitridation of Si atoms proceeds by transfer of N atoms from Ge atoms. Angle-resolved XPS results show that Ge fraction beneath the surface nitrided layer increases significantly at 600 °C compared to the initial surface. These results indicate that preferential nitridation of Si atoms at surface over Ge atoms induces Ge segregation beneath the surface nitrided layer at higher temperatures above 400 °C.     

Epitaxial growth of μm-sized Cu pyramids on silicon

Triangular and quadratic Cu pyramids were epitaxially grown on Si(111) and Si(100) substrates, respectively, by pulsed laser deposition at elevated substrate temperatures above 200°C as well as by post-annealing of closed Cu layers prepared at room temperature. In both cases, three-dimensional pyramids with edge lengths of up to 9 μm were obtained, as observed by scanning electron microscopy and atomic force microscopy. Although the macroscopic shape is a pyramid, microscopically the islands consist of columnar grains (with lateral sizes of only about 50 nm at 260°C). The size and shape of the pyramids can be controlled by the substrate used, the amount of material deposited, and the temperature during deposition or annealing. Additionally, first hints were found that the pyramids can be aligned by structuring the substrate. The formation of such large pyramids is explained by a fast diffusion of Cu atoms on Si over distances of some μm and a high jump probability to higher pyramid layers.     

Formation of interfacial iron silicides on the oxidized silicon surface during solid-phase epitaxy

The early stages of iron silicide formation in the Fe/SiO _x /Si(100) ternary system during solid-phase epitaxy are studied by high-resolution (～100 meV) photoelectron spectroscopy using synchrotron radiation. The spectra of core and valence electrons taken after a number of isochronous heat treatments of the samples at 750°C are analyzed. It is found that the solid-phase reaction between Fe and Si atoms proceeds in the vicinity of the SiO _x /Si interface, which metal atoms reach when deposited on the sample surface at room temperature. Iron silicide starts forming at 60°C. Solid-phase synthesis is shown to proceed in two stages: the formation of the metastable FeSi interfacial phase with a CsCl-like structure and the formation of the stable β-FeSi₂ phase. During annealing, structural modification of the silicon oxide occurs, which shows up in the growth of the Si⁺⁴ peaks and attenuation of the Si⁺² peaks.