Computer Simulation of Early Stage in Thin-Film Growth

Nucleation and growth process has been studied on atomic scale for the early stage of thin-film growth by means of computer simulation.The island number and its shape vary with a set of control conditions,such as deposition flux R,surface diffusion rate W and coverage.The kinetic parameters p and q obtained from simulation are positive and dependent on the growth process.The transition from the initial steps of nucleation to growth is also explored.The simulation results are consistent with the experiments and the rate equations from nucleation theory.

Nonlinear Behavior of Multiple Cluster Growth Simulated by Monte Carlo Method

Monte Carlo simulations have been carried out to investigate the kinetic growth process of ultrathinfilm.It is found that the area of cluster S(t)grows with time t as tk,where growth exponent k is less than 1 when averaged from all clusters.The further results indicate that the cluster growth is nonlinear,i.e.,the bigger the cluster area S is,the faster it grows(the larger the k).Similar results also show the fractal dimension D increases with the increasing S.Both the slope a of lgk-lgS and the slopeδof 1gD-lgS are positive and related to the nucleation and growth kinetics.

Simulation of Nucleation of Anisotropic Si Islands on Reconstructed Si(100)(2x1)Surface

The nucleation of anisotropic Si islands on reconstructed Si(100)(2x1)surface has been studied by computer simulation,in which the anisotropic diffusion rate along different direction of the substrate is included.Some results such as anisotropic islands formed at various substrate temperatures,the number of islands(including single Si dimers)with different anisotropic diffusion are obtained.It is shown that the shape and number of anisotropic Si islands are dependent obviously on the substrate temperature and the anisotropic diffusion.The simulation results are consistent with the experimental observations.

Theoretical Study of Extraction of a Single Al Atom from Al(111) Surface by Scanning Tunneling Microscopy W Tip

Based on the discrete variational method with the local-density-functional approximation,the cluster models were chosen to simulate the extraction of a single Al atom from Al(111)sample surface by a scanning tunneling microscopy W tip with and without external bias voltages.The calculated results show that the tip-sample effects of W tip on the extraction of an Al atom are very important.The Al atom can be extracted from the Al(111)surface by the pure W tip without external bias,as the tip approaches the sample within 10 a.u.(5.3Å).When the separation between the tip and the sample is larger than 10 a.u.,a positive bias must be applied to the sample.The extracted Al atom is expected to have net positive charge when it escapes from the Al(111)sample surface.The corresponding critical field is about 0.6V/Å.This value is in good agreement with experimental results.

Ionic Conduction of Nanophase Solid Ca_((1-x))La_xF_(2+x)

People are very interested in the research into fluorine ionic conductor, because F^- is the smallest negative ion, and it has only one charge which is in favour of migration; fluoride has quite a large change of free energy when forming, so it can be used as spacer material to get a battery with high voltage and high energy density; in addition, structure of fluoride is simple, its electron-conductivity is very low, so its theoretical model for ion-moving becomes simplified. Usually people apply the method of mingling with fluoride having higher valence in order to enhance ionic conductivity. For example, Insti-

Resistivity of Two Kinds of Amorphous Alloys Under High Hydrostatic Pressure

Amorphous ferromagnetic alloy has excellent magnetism, and its resistivity is oneor two orders of magnitude higher than that of crystal alloy of the same composition.It is extensively applied in America, Japan, Germany, France etc., since it can beused as the material to make the core in a transformer to reduce the energy loss andenhance the working frequency.