Boron ions B interaction with Si(100) and Ge(100) surfaces

The goal of this work is simulation of possible structures, formed by boron ions (B⁺) during adsorption on Si(100) and Ge(100) surfaces. Calculations were carried out using a semi-empirical method, known as the Modified Neglect of Differential Overlap method (MNDO). The surface was simulated using of Si₄₉(Ge₄₉) and Si₆₃(Ge₆₃) clusters. Results of quantum-chemical calculations the boron ion (B⁺) interaction with Si(100) − 2 × 1 and Ge(100) − 2 × 1 surfaces are presented and show adsorption barriers for boron ions and migration barriers of adsorbed boron ion (during migration along surface dimer row and along surface dimer).     

Confinement of one-dimensional electrons in dimer row segments at Ge/Si(001) surfaces

During the initial growth, Si(001) surfaces were covered by thin Ge wetting layers. At the wetting layer surfaces, Ge atoms were reconstructed into dimers, which were aligned along the [110] direction to form one-dimensional (1D) ‘dimer rows’. In addition, the dimer rows were partitioned by dimer vacancy lines at the Ge/Si(001) surfaces. As a result, the surfaces were covered spontaneously by an array of 1D dimer row segments. Scanning tunneling microscope images demonstrated that the 1D free-electrons in the dimer rows are confined in each segment and form an ultra-high density array of 1D quantum wells at the surfaces.     

Electronic structure of bulk and (0 0 1) surface layers of pyrite FeS2

The electronic structure of bulk and (0 0 1) surface layers of iron pyrite FeS₂ have been calculated using a modern ab initio pseudo-potential method. For the bulk pyrite the calculated lattice constant, position parameter of sulfur, and band gap are in agreement with experimental values. For the (0 0 1) surface it is found that surface states form a conducting band. The conducting band and the conducting band tail of the bulk conduction manifold overlap and the width of the band gap is not influenced by the surface state. The surface states arise mainly from the iron 3d orbitals in the topmost layer with a smaller contribution from the sulfur 3p states. The relaxation of iron and sulfur atoms is found to be greatest in the top most layer. The surface energy is calculated to be equal to 1.063 J/m².     

Ge组分渐变的Si1-x-yGexCy薄膜的制备

用化学气相淀积方法在Si（100）衬底上外延生长了Ge组分最高约0．40的组分渐变的Si1-x-yGexCy合金薄膜,研究了生长温度等工艺参数的影响．结果表明,生长温度和C2H4分压的提高均导致薄膜中碳组分的增加和合金薄膜晶格常数的减小,这表明外延薄膜中的C主要以替位式存在．C掺入量的变化可有效地调节薄膜的禁带宽度,而提高生长温度有助于改善Si1-x-yGexCy薄膜的的晶体质量．组分渐变的Si1-x-yGexCy合金薄膜包括由因衬底中Si原子扩散至表面与GeH4．C2H4反应而生成的Ni1-x-yGexCy外延层和由Ni1-x-yGexCy外延层中Ge原子向衬底方向扩散而形成的Ni1-xGex层．     

硅、锗材料在Si(100)表面的生长研究

利用扫描隧道显微镜和超高真空实验装置系统进行了Si(10 0 )表面生长Si,Ge的实验研究。分析了所生成表面的形貌、结构等物理性质。研究表明 :Si在Si(10 0 )表面的同质生长可以形成纳米结构薄膜。Ge在Si(10 0 )表面生长形成规则的三维小岛。而在Si/Ge/Si(10 0 )多层膜上生长则形成大小二种三维岛。研究表明大岛具有Ge/Si/Ge的壳层结构     

Si_3N_4/Si表面Ge生长过程的STM研究

利用STM和LEED分析了Ge在Si3 N4 /Si(111)和Si3 N4 /Si(10 0 )表面生长过程的结构演变。在生长早期 ,Ge在两种衬底表面上都形成高密度的三维纳米团簇 ,这些团簇的大小均在几个纳米范围内 ,并在高温退火时体积增大。当生长继续时 ,Ge的晶体小面开始显现。在晶态的Si3 N4 (0 0 0 1) /Si(111)表面 ,Ge的 (111)晶向的小面生长比其他方向优先。最后在大范围内形成以 (111)方向为主的晶面。相反 ,在非晶的Si3 N4 表面 ,即Si3 N4 /Si(10 0 ) ,Ge晶体的高指数侧面生长较顶面快 ,最终形成金字塔形的岛结构。对这样的表面生长过程进行了探讨并给出了合理的物理解释     

Si基Si_(1-x-y)Ge_xC_y合金生长中C的影响

报道了Si基Si1 x yGexCy 合金生长中C对Ge组分和生长速率的抑制作用 ,提出一个Si、Ge、C原子的排列构型 ,从理论上给出了C对Ge组分的抑制度和Ge/C原子比的关系 ,并指出在富Ge情况下C对Ge的抑制作用会趋向于饱和。     

Comparative study of adatom induced relaxations and energetics for Si, Ge and carbon adsorption on a (2×1) Si(001) surface

Surface complexes involving silicon, germanium and carbon adatom on predefined adsorption sites of the 2×1 reconstructed Si(001) surface are investigated for their energetics and associated structural relaxations. Tersoff’s semi-empirical potential is used and the relaxations are obtained by employing the Monte Carlo simulated annealing technique. The results for the cases of Si, Ge and carbon adsorptions are compared. It is found that Si and Ge as adatoms on Si(001) 2×1 reconstructed surface behave in a similar fashion but the carbon adatom behaves in a markedly different way. Specifically, the carbon adatom induces a Si-C-Si chain configuration. It is also found that the adsorption sites between two dimer rows are the most favourable ones.     

Anharmonic effects on Be(0 0 0 1): A molecular dynamics study

Using molecular dynamics simulations and a modified analytic embedded atom method (MAEAM), the anharmonic effects of Be(0 0 0 1) surface have been studied in the temperature range from 0 K to 1400 K. The temperature dependence of the interlayer separation, mean square vibrational displacement, phonon frequencies and phonon line width, and layer structure factor are calculated. The obtained results for temperature dependence of interlayer separation and mean square displacement show that the anharmonic effects are small in the temperature range from 0 K to 1100 K. The calculated layer order parameters indicate that Be(0 0 0 1) surface loses its long-range translational order, but do not premelt up to 50 K below the bulk melting point. The surface disordering may result from strongly contracted c/a ratio of Be.     

Evolution of interface diffusion and structure of Ni films sputter-deposited on Si(0 0 1)

Ni films were deposited on Si(0 0 1) substrates at 190°C by dc plasma-sputtering in Ar gas in order to investigate the Ni diffusion phenomena into the substrate and its effect on the structure of Ni films. The deposition time was 10, 15 or 30 min. The Ni/Si samples were studied by cross-sectional transmission electron microscopy and Rutherford backscattering. Ni adatoms are confirmed to diffuse into the Si substrate forming a diffusion layer. The diffusion layer consists of two regions. The first one is of homogeneous thickness and locates adjacent to the interface of film and substrate. The second one consists of several isosceles triangles with vertex angle of about 70° standing on the front of first region. Both the thickness of the first region and the number of triangles in the second region increase with increasing deposition time. The compositional ratio of Ni to Si in the diffusion layer is 1.3±0.1. The Ni films have a lot of voids at the interface and a rough surface. The density of the film is estimated to be 25% lower than that of bulk Ni. The thickness of the Ni films does not increase linearly with deposition time.     

放电等离子烧结Gd/Gd5Si2Ge2复合材料磁热效应研究

以高纯钆和Gd5Si2Ge2合金为原料,采用放电等离子烧结技术制备了两组元Gdx(Gd5Si2Ge2)1-x(x=0,0.33,0.5,0.7,1)层状复合磁制冷材料.通过自制的磁热效应测量仪器直接测量了复合材料在外加磁场1.5 T下的磁热效应(ΔTad).随着复合比例的变化,材料的最大绝热温变(ΔTad)从x=0.3时的1.6 K增加到x=0.7时的2.0 K,而最大绝热温变峰的位置从286K变到了293 K.同时,与单组元的Gd5Si2Ge2合金相比,随着钆的含量增加时,复合材料的最大绝热温变峰变宽.当x=0.7时,层状复合磁制冷材料在外加磁场1.5 T下的最大绝热温变(ΔT)在260-310K范围里从1.1 K变到2.0 K,这种材料非常适合作为室温磁制冷材料.     

Comparison between Double Crystals X-ray Diffraction and Micro-Raman Measurement on Composition Determination of High Ge Content Si1-xGex Layer Epitaxied on Si Substrate

It is important to acquire the composition of Si1-xGex layer, especially that with high Ge content, epitaxied on Si substrate. Two nondestructive examination methods, double crystals X-ray diffraction （DCXRD） and micro-Raman measurement, were introduced comparatively to determine x value in Si1-xGex layer, which show that while the two methods are consistent with each other when x is low, the results obtained from double crystals X-ray diffraction are not credible due to the large strain relaxation occurring in Si1-xGex layers when Ge content is higher than about 20%. Micro-Raman measurement is more appropriate for determining high Ge content than DCXRD.     

Preparation and characterization of Ge epitaxially grown on nano-structured periodic Si pillars and bars on Si(001) substrate

The selective epitaxial growth of germanium on nano-structured periodic silicon pillars and bars with 360 nm periodicity on Si(001) substrate is studied to evaluate the applicability of nano-heteroepitaxy on the Ge-Si system for different fields of application. It is found that SiO₂ used as masking material plays the key role to influence the strain situation in the Si nano-islands. To analyze this in detail, X-ray diffraction techniques in combination with theoretical simulations based on the kinematical X-ray scattering from laterally strained nano-structures and finite element method (FEM) calculations of the strain field are applied. The oxide related strain in the Si scales about linearly with the thickness of the SiO₂ mask, but FEM simulations supposing a homogeneous stress distribution in the oxide are not sufficient to describe the local strain distribution in the nano-structures. It is demonstrated that the Ge lattice relaxes completely during growth on the Si nano-islands by generation of misfit dislocations at the interface, but a high structural quality of Ge can be achieved by suited growth conditions.     

Observation of metal on Si(0 0 1) by STM/STS and its consideration based on the first principles calculations

Local density of states (LDOS) is obtained by the first principles calculation based on the density functional theory on the Si(0 0 1)2 × 1 surface and on the surface with an Al dimer. At an Al dimer, LDOS has a high intensity in the conduction band region, which cannot be seen on the Si(0 0 1)2 × 1 surface. This tendency is observed in STS measurements as well. The possibility for a microelementary analysis is presented by applying this method to other metal atoms on the Si surface. Furthermore, it is pointed out that STS measurements should be always performed at the same tip-sample separation to obtain reproducible STS spectrums.     

用乙硅烷及固态锗源外延生长应变GeSi／Si合金

采用气态源分子束外延（ＧＳＭＢＥ）法成功地生长出应变ＧｅｘＳｉ１－ｘ／Ｓｉ异质结合金，所使用的源分别是乙硅烷和固态锗。用固态锗取代气态锗烷，即保留了生长中由氢化物裂解产生的氢原子在生长表面上的活化作用（ｓｕｒｆａｃｔａｎｔ ｅｆｆｅｃｔ），又利用了固态源炉通过挡板能够迅速切断分子束流的优点。样品的Ｘ射线双晶衍射，透射电子显微镜及光荧光测量表明ＧｅｘＳｉ１－ｘ合金具有较好的晶格完整性及平坦的异质结界     

UHV/CVD生长锗硅材料的偏析现象

本文对利用超高真空CVD方法生长的Si1-xGex合金外延层中的锗表面分布情况和Ge在界面偏析现象进行了深入的研究.通过XPS和SIMS图谱的研究,指出表面由于锗的偏析,造成锗在体内和表面的含量不同,在低温时生长锗硅合金,表面氢原子的吸附可有效地抑制锗的偏析,但随着温度的升高,氢的脱附造成锗的偏析现象更加明显.     

Study of thermally-induced effects on Si–Ge amorphous layers using optical measurements

Thin films of elemental Si and Ge were grown one after another onto glass substrate using electron beam evaporation method. Optical measurements were used to probe the thermally-induced effects on Si–Ge layers upon annealing at 100 °C. Thermal treatment of the films was carried out under vacuum, to avoid oxidation of the films, at a temperature of 100 °C. X-ray diffraction, XRD, showed that the as-deposited layers are amorphous. The change of some optical parameters such as transmission and optical energy gap, as a result of the heat treatment, was explored. The optical energy gap as well as the optical transmission of the dual layer sample was found to increase with annealing time. The obtained results show the possibility of tailoring the layer structure to meet certain technological applications in terms of optical transmission and optical energy gap. Scanning Electron Microscope, SEM, was used to study the morphology of the as-deposited and annealed films. As-deposited films showed no crystalline features. However, the annealed films show some partial crystallization that increases with annealing time. The observed structural changes result in an increase of the optical energy gap with annealing.     

TOF-SARS study of hydrogen adsorption and desorption kinetics on Si(1 0 0)

The kinetics of atomic hydrogen isothermal adsorption and desorption on a Si(1 0 0) surface was studied using the time-of-flight scattering and recoiling spectrometry technique at temperatures below and above the thermal desorption threshold. A continuous decrease in saturation coverage with temperature under constant atomic hydrogen exposure has been observed in both regions for temperatures in the range 325-820 K. For T_S=500-650 K, the decrease is described by a kinetic model where Eley-Rideal (ER) abstraction is responsible for hydrogen removal from the surface and hydrogen coverage depends on the temperature due to the changing rate of migration from precursor to primary monohydride sites. For T_S=650 K and higher, in addition to the ER abstraction, the thermal desorption from primary monohydride sites leads to a further decrease of the saturation coverage. The first-order desorption rates after source shut-off have been measured and an activation barrier of 1.89 eV has been obtained.     

Confinement of one-dimensional electrons in dimer row segments at Ge/Si(001) surfaces

During the initial growth, Si(001) surfaces were covered by thin Ge wetting layers. At the wetting layer surfaces, Ge atoms were reconstructed into dimers, which were aligned along the [110] direction to form one-dimensional (1D) ‘dimer rows’. In addition, the dimer rows were partitioned by dimer vacancy lines at the Ge/Si(001) surfaces. As a result, the surfaces were covered spontaneously by an array of 1D dimer row segments. Scanning tunneling microscope images demonstrated that the 1D free-electrons in the dimer rows are confined in each segment and form an ultra-high density array of 1D quantum wells at the surfaces.     

First principles total energy studies of the adsorption of germane on Ge(001)-c(2 × 4)

We perform first principles total energy calculations to study the energetics, and the atomic structure of the adsorption of germane (GeH₄) molecules on the Ge(001)-c(2 × 4) surface. The adsorption of a GeH₄ unit occurs after its dissociation into a germanium trihydride (GeH₃) and a hydrogen atom and a subsequent decomposition into a germanium dihydride (GeH₂) subunit and H atoms. Consequently, we first consider the adsorption of GeH₂ in two different configurations; the on-dimer and the intra-row geometries. Similar to the adsorption of SiH₂ and GeH₂ on Si(001), it is found that the on-dimer site is more stable than the intra-row geometry by 0.13 eV. However, in the adsorption of a GeH₂ fragment together with two H atoms we find that the intra-row geometry is energetically more favorable, again, similar to the adsorption of SiH₂ and GeH₂ (plus two H atoms) on the Si(001) surface.