Atomic—Scale Kinetic Monte Carlo Simulation of {100}—Oriented Diamond Film Growth in C—H and C—H—CI Systems by Chemical Vapour Deposition

We simulate the {100}-oriented diamond film growth of chemical vapour deposition (CVD) under different models in C-H and C-H-Cl systems in an atomic scale by using the revised kinetic Monte Carlo method.The simulation results show that:(1) the CVD diamond film growth in the C-H system is suitable for high substrate temperature,and the film surface roughness is very coarse;(2) the CVD diamond film can grow in the C-H-Cl system either at high temperature or at low temperature,and the film quality is outstanding;(3) atomic Cl takes an active role for the growth of diamond film,especially at low temperatures.The concentration of atomic Cl should be controlled in a proper range.     

Effect of Reagent Vibrational and Rotational Excitation on the F＋H2 Reaction： Theoretical Study of the Stereodynamics Using Quasi-Classical Trajectory Method

The vector correlations in the reaction F＋H2 （v =0-3, j =0-3）→ HF（v＇, j＇）＋H are investigated using the quasi- classical trajectory method on the Stark-Werner potential energy surface at a collision energy of 1.0eV. The potential distribution P（θr） to angles between k and j＇, the distribution P（Фr） to dihedral angles, denoting k - k＇ - j＇ correlation and the polarization-dependent generalized differential cross sections, are calculated. The effect of reagent vibrational and rotational excitation on the F＋H2 reaction is discussed in detail The results suggest that the different vibrational and rotational quantum states of H2 have different influences on the product polarization.     

Molecular dynamical simulations on a-C:H film growth from atomic flux of C and H: Effect of H fraction

Molecular dynamical simulations are carried out to studying the hydrogenated amorphous carbon (a-C:H) film growth from C and H atoms. The effects of the H fraction in source atoms and incident energy on the film formation are investigated. Our simulations show that almost all the H atoms incorporating into the films bond to carbon and the amount of H₂ molecules is very slight. Increasing the H fraction in source atoms raises the sp³-C fraction, leads to a linear increase of H concentration in film, but decreases the film growth rate. The influence of H fraction on the film growth mechanism is also discussed.     

Atomic scale characterization of nanostructured a-C:H films

Hydrogen incorporation in nanostructured carbon films grown by supersonic cluster beam deposition has been theoretically investigated by classical molecular dynamics. Simulations are shown to enlight the role of the local nanostructure on the formation of hydrogen-related complexes in different carbon environments. Received 23 January 2002 Published online 6 June 2002     

X射线荧光全息术中入射能量对原子像的影响

X射线荧光全息术是一种新型的显微成像技术，它能在原子水平上直接观察到晶体内部的三维结构。然而它所得到的原子像存在明显的孪生像现象。因此，采用多重能量的全息记录来消除孪生像。分别以单个和多个铁原子为模型，数值模拟了它们在4π立体角范围内、不同范围的入射能量的情况下记录的全息图。比较由这些全息图重构得到的原子像，发现入射能量范围越宽，其消除孪生像的效果越好，而且随着入射能量的提高，其原子像的分辨力也越高。     

a-C:N:H纳米尖端荧光产生的机理

用CH4,H2和NH3为反应气体,利用等离子体增强热丝化学气相沉积在沉积有碳膜的Si衬底上制备了a-C:N:H纳米尖端,并用扫描电子显微镜和微区Raman光谱仪对碳膜和纳米尖端进行了表征。结果表明:Raman谱中含有与碳和氮相关的峰,且纳米尖端的Raman谱比碳膜的Raman谱有很强的荧光背景。Raman谱中的峰说明沉积的碳膜和纳米尖端是a-C:N:H薄膜和a-C:N:H尖端。a-C:N:H纳米尖端的Raman谱中强荧光背景的产生表明其在激发光源照射的过程中发射了强荧光,对a-C:N:H纳米尖端产生强荧光的机理进行了探讨。     

A 13C isotopic tracing study of a-C:H thin-film growth

The growth mechanisms of amorphous carbon (a-C:H) thin films obtained by the decomposition of methane gas in a multipolar plasma set up were studied using ¹³C as a tracer. Hydrogenated carbon films first grown in a methane plasma with natural isotopic composition (¹²C) were further grown in highly enriched ¹³C methane discharge (experiments were also carried out with the reverse order). ¹³C profiles were obtained by resonant nuclear reaction depth profiling using the narrow (FWHM<100 eV) resonance at 1747.6 keV, in the ¹³C(p, )¹⁴N nuclear reaction. Plasma conditions were varied so as to vary the energy of particles arriving at the sample surface from 30 eV to 500 eV. In all cases, a system of two layers was observed: a pure ¹³C film overlaying a pure ¹²C film (or the reverse order) with a rather sharp interface between the two layers. These results suggest layer by layer amorphous hydrogenated carbon film growth with minimal mixing or interdiffusion of the isotopic layers induced by the ionic bombardment during the growth.     

Electrochemical corrosion behaviors of a-C:H and a-C:NX:H films

The a-C:H and a-C:N_X:H films were deposited onto silicon wafers using radio frequency (rf) plasma enhanced chemical vapor deposition (PECVD) and pulsed-dc glow discharge plasma CVD, respectively. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize chemical nature and bond types of the films. The results demonstrated that the a-C:H film prepared by rf-CVD (rf C:H) has lower I_D/I_G ratio, indicating smaller sp² cluster size in an amorphous carbon matrix. The nitrogen concentrations of 2.9 at.% and 7.9 at.% correspond to carbon nitride films prepared with rf and pulse power, respectively.Electrochemical corrosion performances of the carbon films were investigated by potentiodynamic polarization test. The electrolyte used in this work was a 0.89% NaCl solution. The corrosion test showed that the rf C:H film exhibited excellent anti-corrosion performance with a corrosion rate of 2 nA cm⁻², while the carbon nitride films prepared by rf technique and pulse technique showed a corrosion rate of 6 nA cm⁻² and 235 nA cm⁻², respectively. It is reasonable to conclude that the smaller sp² cluster size of rf C:H film restrained the electron transfer velocity and then avoids detriment from the exchange of electrons.     

Field emission properties of a-C and a-C:H films deposited on silicon surfaces modified with nickel nanoparticles

The a-C and a-C:H films are deposited on silicon surfaces modified with and without nickel nanoparticles by using mid-frequency magnetron sputtering. The microstructures and morphologies of the films are analyzed by Raman spectroscopy and atomic force microscopy. Field emission behaviors of the deposited films with and without nickel nanoparticles modification are comparatively investigated. It is found that the hydrogen-free carbon film exhibits a high field emission current density and low turn-on electric field compared with the hydrogenated carbon film. Nickel modifying could increase the current density, whereas it has no significant effect on the turn-on electric field. The mechanism of field electron emission of a sample is discussed from the surface morphologies of the films and nickel nanoparticle roles in the interface between film and substrate.     

Deposition of a-C:H films on UHMWPE substrate and its wear-resistance

In prosthetic hip replacements, ultrahigh molecular weight polyethylene (UHMWPE) wear debris is identified as the main factor limiting the lifetime of the artificial joints. Especially UHMWPE debris from the joint can induce tissue reactions and bone resorption that may lead to the joint loosening. The diamond like carbon (DLC) film has attracted a great deal of interest in recent years mainly because of its excellent tribological property, biocompatibility and chemically inert property. In order to improve the wear-resistance of UHMWPE, a-C:H films were deposited on UHMWPE substrate by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-PECVD) technology. During deposition, the working gases were argon and acetylene, the microwave power was set to 800 W, the biased pulsed voltage was set to −200 V (frequency 15 kHz, duty ratio 20%), the pressure in vacuum chamber was set to 0.5 Pa, and the process time was 60 min. The films were analysed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, nano-indentation, anti-scratch and wear test. The results showed that a typical amorphous hydrogenated carbon (a-C:H) film was successfully deposited on UHMWPE with thickness up to 2 μm. The nano-hardness of the UHMWPE coated with a-C:H films, measured at an applied load of 200 μN, was increased from 10 MPa (untreated UHMWPE) to 139 MPa. The wear test was carried out using a ball (Ø 6 mm, SiC) on disk tribometer with an applied load of 1 N for 10000 cycles, and the results showed a reduction of worn cross-sectional area from 193 μm² of untreated UHMWPE to 26 μm² of DLC coated sample. In addition the influence of argon/acetylene gas flow ratio on the growth of a-C:H films was studied.