INTERFACE FORMATION OF Ge/ZnSe(100) AND Ge/ZnS(111) HETEROJUNCTIONS STUDIED BY SYNCHROTRON RADIATION PHOTOEMISSION

The microscopic evolution of interface formation between Ge and Ⅱ-Ⅵ compounds such as ZnSe and ZnS single crystals has been studied by synchrotron radiation photoemission spectroscopy and low energy electron diffraction. Core level intensity measurements from the substrate as well as from the overlayer show a nearly ideal two-dimensional growth mode for the deposition of Ge on ZnSe(100) surface. How-ever, there is a certain deviation from the ideal two-dimensional mode in the case of Ge/ZnS(111) due to the diffusion of substrate atoms into Ge overlayer. Surface semi-tire core level spectra indicate that the reaction of Ge with S atoms at Ge/ZnS(111) interfaces is much stronger than that of Ge with Se atoms at Ge/ZnSe(100) interfaces.     

Molecular Dynamical Simulations on a-C：H Film Growth from C and H Atomic Flux： Effect of Incident Energy

Molecular dynamical simulation is carried out to investigate the effects of the incident energy on a-C：H film growth from C and tt atomic flux. Our simulations show that the film growth at low incident energy （1 eV） is dominated by the adsorption of H and C atoms. At moderate incident energy （10 and 20eV）, the abstraction reaction of incident H atoms with H atoms adsorbed at the surface becomes important. At high incident energy （30 and 40eV）, the a-C：H film growth is a two-step process： one is the adsorption and the shallow implantation of C atoms, and the other is the deep implantation of H atoms.     

Chemisorption of Fe on Au-passivated Si（001） surface

The chemisorption of one monolayer of Fe atoms on a Au-passivated Si(001) surface is studied by using the self-consistent tight-binding linear muffin-tin orbital method. The Fe adatom chemisorption on an ideal Si(001) surface is also considered for comparison. The chemisorption energy and layer projected density of states for a monolayer of Fe atoms on Au-passivated Si(001) surface are calculated and compared with that of the Fe atoms on an ideal Si(001) surface. The charge transfer is investigated. It is found that the most stable position is at the fourfold hollow site for the adsorbed Fe atoms, which might sit below the Au surface. Therefore there will be a Au－Fe mixed layer at the Fe/Au－Si(100) interface. It is found that the adsorbed Fe atoms cannot sit below the Si surface, indicating that a buffer layer of Au atoms may hinder the intermixing of Fe atoms and Si atoms at the Fe/Au－Si(001) interface effectively, which is in agreement with the experimental results.     

Adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co （200）： A first-principles density-functional study

First-principles calculations based on density functional theory are used to investigate the adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co(200). The preferred site for the carbon atom on the surface is the hollow site, and the preferred site in the subsurface is the octahedral site. There is charge transfer from the surface to the adsorbed carbon atom, and for the most favorable adsorbed structure the charge transfer is largest. Moreover, the energy barriers for the diffusions of carbon atoms on the surface and from the surface into the subsurface and then back to the surface are calculated in detail. The results indicate that the energy barrier for the diffusion of carbon atoms on the surface is comparable to that from the subsurface to the surface. The results imply that both the direct surface nucleation and the surface segregation from Co bulk can be observed in the chemical vapor deposition growth of graphene on Co(200)substrate, which can gain a new insight into the growth mechanism of graphene.     

Kinetics of Spherical Interface in Crystal Growth

The growth kinetics of spherical NiAl and CuZr crystals are studied by using molecular dynamics simulations.The growth rates of crystals are found to increase with the grain radius. The simulations show that the interface thickness and the Jackson α-factor increase as the growth proceeds, indicating that the interface becomes increasingly rough during growth. Due to the increasing interface roughening, the fraction of repeatable growth sites at interface f is proposed to actually increase in growth. An attachment rate, which is defined as the fraction of atoms that join the crystal interface without leaving, is used to approximate f, displaying a linear increase. With this approximation, we predict the growth rates as a function of the crystal radius, and the results qualitatively agree with those from the direct simulations.     

Twin diamond Crystals Grown at High Temperature and High Pressure from the Fe-Ni-C System

Twin diamond crystals grown at high temperature and high pressure (HPHT) in the presence of FeNi catalyst have been examined by transmission electron microscopy(TEM).Direct observation by TEM shows that there are a large amount of twins which lie on the {111} planes in the HPHT-grown diamonds.The twins in the diamond may be formed and may extend into the inner crystal from the twin nucleus formed in the nucleation process.The twins can be formed due to the carbon atoms falling mistakenly into positions where a twin crystal can form during diamond growth,or condensation of supersaturated vacancies on the {111} plane.some hexagonal dislocation loops related to supersaturated vacancies are found on the twins.The Moire fringe image reveals that stacking faults terminate on the intersecting twin boundary.This suggests that,at the temperature that the HPHT diamond is grown,the bordering partial has propagated by gliding up to the twin interface,which can be described by the reaction of a Shockley partial dislocation with a twin on the {111} plane.     

Experimental investigation on underwater drag reduction using partial cavitation

For underwater drag reduction, one promising idea is to form a continuous gas or discrete bubbly layer at the submerged surface. Owing to the lower viscosity of gas than of water, this could considerably reduce underwater drag by achieving slippage at the liquid–gas interface. This paper presents an experimental investigation on underwater drag reduction using partial cavitation. Dense hydrophobic micro-grooved structures sustain gas in the valleys, which can be considered as defects that weaken the strength of the water body. Therefore, partial cavities are easily formed at lower flow speeds, and the dense cavities connect to form a lubricating gas layer at the solid–liquid interface. The results indicate that the proposed method achieves drag reduction without any additional energy or gas-providing devices, which should stimulate the development of underwater vehicles.     

Band alignment between NiO_x and nonpolar/semipolar GaN planes for selective-area-doped termination structure

Band alignment between NiO_x and nonpolar GaN plane and between NiO_x and semipolar GaN plane are measured by x-ray photoelectron spectroscopy. They demonstrate that the maximum value of the valence band in the unintentional-doped a-plane, m-plane, and r-plane GaN are comparable to each other, which means that all the substrates are of n-type with similar background carrier concentrations. However, the band offset at the NiO_x/GaN interface presents obvious crystalline plane dependency although they are coated with the same NiO_x films. By fitting the Ga 3 d spectrum obtained from the NiO_x/GaN interface, we find that relatively high Ga–O content at the interface corresponds to a small band offset. On the one hand, the high Ga–O content on the GaN surface will change the growth mode of NiO_x. On the other hand, the affinity difference between Ga and O forms a dipole which will introduce an extra energy band bending.     

Nanodots and microwires of ZrO_2 grown on LaAlO_3 by photo-assisted metal–organic chemical vapor deposition

ZrO_2 nanodots are successfully prepared on LaAlO_3(LAO)(100) substrates by photo-assisted metal-organic chemical vapor deposition(MOCVD). It is indicated that the sizes and densities of ZrO_2 nanodots are controllable by modulating the growth temperature, oxygen partial pressure, and growth time. Meanwhile, the microwires are observed on the surfaces of substrates. It is found that there is an obvious competitive relationship between the nanodots and the microwires. In a growth temperature range from 500℃ to 660℃, the microwires turn longest and widest at 600℃, but in contrast, the nanodots grow into the smallest diameter at 600℃. This phenomenon could be illustrated by the energy barrier, decomposition rate of Zr(tmhd)_4, and mobility of atoms. In addition, growth time or oxygen partial pressure also affects the competitive relationship between the nanodots and the microwires. With increasing oxygen partial pressure from 451 Pa to 75_2 Pa,the microwires gradually grow larger while the nanodots become smaller. To further achieve the controllable growth, the coarsening effect of ZrO_2 is modified by varying the growth time, and the experimental results show that the coarsening effect of microwires is higher than that of nanodots by increasing the growth time to quickly minimize ZrO_2 energy density.     

Velocity Transfer Spectroscopy of Rb 420 nm Transition

We propose and demonstrate the velocity transfer spectroscopy of a V-type energy structure with Rb atoms at 420nm transition. The weak oscillator strength of a lower excited state for V-type energy structure atoms limits the high signal-to-noise ratio of atomic laser spectroscopy, which can be usually realized by optical-optical double-resonance or double-resonance optical pumping for cascade-type energy structure atoms. For ^87Rb atoms, the weak 420 nm transition spectrum between the energy level of 5^2S1/2 and 6^2P3/2 is transferred to the spectrum on lower excited states at 780nm with strong oscillator strength, which is recorded by a 780 nm probe laser. This method, which ＆ similar to the electron-shelving detection method, at a certain degree can indirectly measure a higher excited state transition with weak oscillator strength for any V-type energy structure of atoms by transferring the transition spectrum information of the very weak oscillator strength to the strong oscillator strength in an optical-optical double-resonance configuration.