Atomic Diffusion in Cu/Si （111） and Cu/SiO2/Si （111） Systems by Neutral Cluster Beam Deposition

The Cu films are deposited on two kinds of p-type Si （111） substrates by ionized duster beam （ICB） technique. The interface reaction and atomic diffusion of Cu/Si （111） and Cu/SiO2/Si （111） systems are studied at different annealing temperatures by x-ray diffraction （XRD） and Rutherford backscattering spectrometry （RBS）. Some significant results are obtained： For the Cu/Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃ and 500℃ are 8.5 ×10^-15 cm^2.s^-1 and 3.0 ×10^-14 cm^2.s^-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2//Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 ×10^-16 cm^2.s^-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.     

First-Principles Calculations of Atomic and Electronic Properties of T1 and In on Si（111）

The atomic and electronic structures of T1 and In on Si（111） surfaces are investigated using the firstprinciples total energy calculations. Total energy optimizations show that the energetically favored structure is 1/3 ML T1 adsorbed at the T4 sites on Si（111） surfaces. The adsorption energy difference of one T1 adatom between （√3 × √3） and （1 × 1） is less than that of each In adatom. The DOS indicates that TI 6p and Si 3p electrons play a very important role in the formation of the surface states. It is concluded that the bonding of TI adatoms on Si（111） surfaces is mainly polar covalent, which is weaker than that of In on Si（111）. So T1 atom is more easy to be migrated than In atom in the same external electric field and the structures of T1 on Si（111） is prone to switch between （√3 × √3） and （1 × 1）.     

Structural and electrical characterization of annealed Si1-xCx/SiC thin film prepared by magnetron sputtering

Si-rich Sil-xCx/SiC multilayer thin films are prepared using magnetron sputtering, subsequently followed by thermal annealing in the range of 800-1200 ℃. The influences of annealing temperature （Ta） on the formation of Si and/or SiC nanocrystals （NCs） and on the electrical characteristics of the multilayer film are investigated by using a variety of analytical techniques, including X-ray diffraction （XRD）, Raman spectroscopy and Fourier transform infrared spectrometry （FT-IR）, current-voltage （I-V） technique, and capacitance-voltage （C-V） technique. XRD and Raman analyses indicate that Si NCs begin to form in samples for Ta _ 800 ~C. At annealing temperatures of 1000 ℃ or higher, the formation of Si NCs is accompanied by the formation of SiC NCs. With the increase in the annealing temperature, the shift of FT-IR Si-C bond absorption spectra toward a higher wave number along with the change of band shape can be explained by a Si-C transitional phase between the loss of substitutional carbon and the formation of SiC precipitates and a precursor for the growth of SiC crystalline. The C-V and I-V results indicate that the interface quality of Si1-xCx/SiC multilayer film is improved significantly and the leakage current is reduced rapidly for Ta ≥ 1000 ℃, which can be ascribed to the formation of Si and SiC NCs.     

Wettability of Si and Al–12Si alloy on Pd-implanted 6H–SiC

Si C monocrystal substrates are implanted by Pd ions with different ion-beam energies and fluences,and the effects of Pd ion implantation on wettability of Si/Si C and Al–12 Si/Si C systems are investigated by the sessile drop technique.The decreases of contact angles of the two systems are disclosed after the ion implantation,which can be attributed to the increase of surface energy(σ_(SV)) of Si C substrate derived from high concentration of defects induced by the ionimplantation and to the decrease of solid–liquid surface energy(σ_(SL)) resulting from the increasing interfacial interactions.This study can provide guidance in improving the wettability of metals on Si C and the electronic packaging process of Si C substrate.     

Studies of diamond-like carbon （DLC） films deposited on stainless steel substrate with Si/SiC intermediate layers

In this work, diamond-like carbon （DLC） films were deposited on stainless steel substrates with Si/SiC intermediate layers by combining plasma enhanced sputtering physical vapour deposition （PEUMS-PVD） and microwave electron cyclotron resonance plasma enhanced chemical vapour deposition （MW-ECRPECVD） techniques. The influence of substrate negative self-bias voltage and Si target power on the structure and nano-mechanical behaviour of the DLC films were investigated by Raman spectroscopy, nano-indentation, and the film structural morphology by atomic force microscopy （AFM）. With the increase of deposition bias voltage, the G band shifted to higher wave-number and the integrated intensity ratio ID/IG increased. We considered these as evidences for the development of graphitization in the films. As the substrate negative self-bias voltage increased, particle bombardment function was enhanced and the sp^3-bond carbon density reducing, resulted in the peak values of hardness （H） and elastic modulus （E）. Silicon addition promoted the formation of sp^3 bonding and reduced the hardness. The incorporated Si atoms substituted sp^2- bond carbon atoms in ring structures, which promoted the formation of sp^3-bond. The structural transition from C-C to C-Si bonds resulted in relaxation of the residual stress which led to the decrease of internal stress and hardness. The results of AFM indicated that the films was dense and homogeneous, the roughness of the films was decreased due to the increase of substrate negative self-bias voltage and the Si target power.     

Electroluminescence of Si Nanocrystal-Doped SiO2

We perform a comparative st udy on the electroluminescence （EL） and photoluminescence （PL） of Si nanocrystaldoped SiO2 （nc-Si：SiO2） and SiO2, and clarify whether the contribution from Si nanocrystals in the EL of nc-Si：SiO2 truly exists. The results unambiguously indicate the presence of EL of Si nanocrystals. The difference of peak positions between the EL and PL spectra are discussed. It is found that the normal method of passivation to enhance the PL of Si nanocrystals is not equally effective for the EL, hence new methods need to be explored to promote the EL of Si nanocrystals.[第一段]     

Density functional investigations for geometric and electronic properties of In4M and In12M （M = C,Si, In） clusters

First-principle calculations are performed to study geometric and electronic properties of both neutral and anionic In4M and In12M （M = C, Si, In） clusters. In4C and In4Si are found to be tetrahedral molecules. The icosahedral structure is found to be unfavourable for In12M. The most stable structure for In12C is a distorted buckled biplanar structure while for In12Si it is of an In-cage with the Si located in the centre. Charge effect on the structure of In12M is discussed. In4C has a significantly large binding energy and an energy gap between the highest-occupied molecularorbital level and the lowest unoccupied molecular-orbital level, a low electron affinity, and a high ionization potential, which are the characters of a magic cluster, enriching the family of doped-group-IIIA metal clusters for cluster-assembled materials.     

Strain-Driven Formation of Nanostripes on In/Si（113） Surface

Periodic nanostripe arrays are observed on In/Si（113） surface using scanning tunneling microscopy. The stripe superstructures are identified as N × 1 reconstructions elongating in [211] or [121] direction and consisting of one vacancy line, one Si adatom row, and N - 2 In rows, in which N = 5 is predominant. The vacancy line formation relieves the strain induced by the Si adatom row and In rows, and plays an important role in stabilizing the stripe structures. The stability of nanostripe structures is demonstrated by analyzing the strain-mediated interaction of vacancy lines in the framework of the Frenkel-Kontorova model, which indicates that the predominant vacancy line period of N = 5 corresponds to the minimum Frenkel Kontorova energy.     

Adsorption and diffusion of Si adatom near single-layer steps on Si surface

By use of the empirical tight-binding （ETB） method, the adsorption and diffusion behaviours ot single sllmon adatom on the reconstructed Si（100） surface with single-layer steps are simulated. The adsorption energies around the SA step, nonrebonded SB step, rebonded SB step, and rough SB step with a kink structure are specially mapped out in this paper, from which the favourable binding sites and several possible diffusion paths are achieved. Because of the rebonded and kink structures, the SB step is more ~uitable for the attachment of Si adatom than the SA step or defective surface.     

Structure Stability of LaAlO3 Thin Films on Si Substrates

A series of amorphous and single-crystalline LaAlO3 （LAO） thin films are fabricated by laser molecular-beam epitaxy technique on Si substrates under various conditions of deposition. The structure stability of the LAO films annealed in high temperature and various ambients is studied by x-ray diffraction as well as high-resolution transmission electron microscopy. The results show that the epitaxial LAO films have very good stability, and the structures of amorphous LAO thin films depend strongly on the conditions of deposition and post-annealing. The results reveal that the formation of LAO composition during the deposition is very important for the structure stability of LAO thin films.     

Effect of different Ge predeposition amounts on SiC grown on Si (1 1 1)

The SiC films were grown by solid source molecular beam epitaxy (SSMBE) on Si (1 1 1) with different amounts of Ge predeposited on Si prior to the epitaxial growth of SiC. The samples were investigated with reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and X-ray diffraction (XRD). The results indicate that there is an optimized Ge predeposition amount of 0.2 nm. The optimized Ge predeposition suppress the Si outdiffusion and reduce the formation of voids. For the sample without Ge predeposition, the Si outdiffusion can be observed in RHEED and the results of XRD show the worse quality of SiC film. For the sample with excess amount of Ge predeposition, the excess Ge can increase the roughness of the surface which induces the poor quality of the SiC film.     

Fabrication and Characterization of Si Nanocrystals Synthesized by Electron Beam Evaporation of Si and SiO2 Mixture

Silicon nanocrystals synthesized by electron beam （e-beam） evaporation of Si and SiO2 mixture are studied. Rutherford backscattering spectrometry of the as-deposited Si-rich silicon dioxide or oxide （SRO） thin film shows that after evaporation, the Si and SiO2 concentration is well kept, indicating that the e-beam evaporation is suitable for evaporating mixtures of Si and SiO2. The SRO thin films are annealed at different temperatures for two hours to synthesize silicon nanoerystals. For the sample annealed at 1050℃, silicon nanoerystals with different sizes and the mean diameter of 4.5 nm are evidently observed by high resolution transmission electron microscopy （HRTEM）. Then the Raman scattering and photoluminescence spectra arising from silicon nanocrystals are further confirmed the above results.     

RHEED studies of Si(100) surface structures induced by Ga evaporation

Si(100) surface structures induced by Ga molecular beam deposition in an ultra-high vacuum have been investigated using a reflection high-energy electron diffraction system (RHEED). It has been found that the Ga evaporation of submonolayer thickness on a clean Si(100) 2 × 1 surface produces surface structures of Si(100) 3 ×2, 5 × 2, 2 ×2 and 8 × 1 sequentially in the temperature range from 350 to 680° C. The RHEED patterns and a two-dimensional phase diagram including five superstructures are presented.     

Growth of oriented crystalline Ag nanoislands on air-exposed Si(0 0 1) surfaces

Growth of Ag islands under ultrahigh vacuum condition on air-exposed Si(0 0 1)-(2 × 1) surfaces has been investigated by in-situ reflection high energy electron diffraction (RHEED). A thin oxide is formed on Si via exposure of the clean Si(0 0 1)-(2 × 1) surface to air. Deposition of Ag on this oxidized surface was carried out at different substrate temperatures. Deposition at room temperature leads to the growth of randomly oriented Ag islands while well-oriented Ag islands, with (0 0 1)_Ag||(0 0 1)_Si, [1 1 0]_Ag||[1 1 0]_Si, have been found to grow at substrate temperatures of ≥350 °C in spite of the presence of the oxide layer between Ag islands and Si. The RHEED patterns show similarities with the case of Ag deposition on H-passivated Si(0 0 1) surfaces.     

Properties of ZnO thin films grown on Si substrates in vacuum and oxygen ambient by pulsed laser deposition

Epitaxial ZnO thin films have been synthesized directly on Si(1 1 1) substrates by pulsed laser deposition (PLD) in vacuum. The reflection high-energy electron diffraction (RHEED) indicates that streaky patterns can be clearly observed from the ZnO epilayers prepared at 600 and 650 °C, revealing a two-dimensional (2D) growth mode. While the ZnO thin film deposited in oxygen ambient shows ring RHEED pattern. There is a compressive in-plane stress existing in the ZnO epitaxial film, but a tensile one in the polycrystalline film. Compared with the ZnO epilayer, the ZnO polycrystalline film shows more intense ultraviolet emission (UVE) with a small full width at half maximum (FWHM) of 89 meV. It is suggested that the atomically flat epilayers may be powerfully used as transitive stratums to grow high-quality ZnO films suitable for the fabrication of optoelectronic devices.     

Si衬底上分子束外延Ge,Si时的反射式高能电子衍射强度振荡观察

本文观察了在Si(100)和Si(111)衬底上分子束外延Si,Ge时的反射式高能电子衍射(RHEED)强度振荡现象。其振荡特性表明,外延一定厚度的缓冲层可以改善表面的平整性,较慢的生长速率或中断生长一段时间有利于外延膜晶体质量的提高。Si(100)上外延Si或Ge时,沿[100]和[110]方位观测到的振荡特性均为单原子模式,起因于表面存在双畴(2×1)再构;而Si(111)上外延Ge时,[112]方位观测到的振荡为双原子层模式,但在[110]方位观察到不均匀周期的强度振荡行为。两种衬底上保持RHEED     

Molecular-beam epitaxy and properties of heterostructures with InAs nanoclusters in an Si matrix

The formation of heteroepitaxial structures with InAs nanoclusters in an Si matrix during molecular-beam epitaxy and variations in the parameters of these structures due to thermal annealing are investigated by reflection high-energy electron diffraction (RHEED), medium-energy ion scattering (MEIS), and scanning electron microscopy (SEM). It is demonstrated that the deposition of InAs onto the Si(100) surface at certain temperatures brings about the formation of tetrahedral nanopyramids with {111} orientation of the lateral faces. It is revealed that InAs nanoislands can be epitaxially overgrown with silicon, which leads to gradual smoothing of the three-dimensional relief. After annealing under vacuum, the Si/InAs/Si(100) structures are stable at tem-peratures up to 700°C.     

Self-organized in-plane incorporation of Si atoms in GaAs by molecular beam epitaxy

The preferential attachment of Si atoms at misorientation steps on vicinal GaAs(001) surfaces has been studied by RHEED. By analysing the time evolution of the specular beam intensity and the change in surface reconstruction during Si deposition we show that a self-organized Si incorporation along the step edges takes place. The observed (3×2) structure is due to an ordered array of dimerized Si atoms with missing dimer rows. Taking into account the structure of the (3×2) unit mesh and its orientation with respect to the As-terminated or Ga-terminated steps, a characteristic minimum in the RHEED intensity recording corresponds to the number of Ga step-edge sites. Since the preferential path for Ga as well as for Si adatom diffusion is along the [110] direction, the critical terrace width for wirelike Si attachment is much larger for a misorientation toward (111)As than for a misorientation toward (111)Ga. Despite the high local impurity concentration, the Si-modified surface can be overgrown with GaAs without adverse effects on the growth front. This is promising for the fabrication of doping wires.