| A novel type of single crystal like polycrystalline (SCLPC) nano-diamond compositethin film is proposed to improve the performance and quality of nano-diamond films. Theformation mechanisms of diamond/Si nano-composite films were studied with first-principlesmethod which is based on density functional theory (DFT).The films calculation models weredesigned by process characteristics of chemical vapor deposition and the growth mechanismof nanocrystalline diamond films. The nucleation, growth, and interface structure ofdiamond/Si nano composite films have been studied respectively. Firstly, nucleationmechanism has been explored by investigating the features of silicon surface and diamondsurface,adsorption behaviors of particles at these surfaces. Secondly,to investigate adsorptionevolution of H atoms and radicals (C, CH, CH2and CH3) on the diamond crystal nucleussurface, growth mechanism of the diamond grain has been clarified. Finally, the formationcondition of the C–Si interface and the function of Si particles in the formation were exploredby analyzing interface stability and the evolution of C and Si particles in diamond/Sinano-composite films. Above all, the conclusion indicated that:(1) On Si(001) surface, it is conducive to diamond nucleation when defect rate come to12.5%. Compared with diamond (001) surface, H atoms desorb from Si(001) surface moreconveniently, which means impurity H atoms in the films could be reduced/eliminated. Ondiamond(001)surface, the Si atoms diffuse easier than C atoms,tending to diffuse out of thediamond crystal and form interface.Ideal diamond(001) surface energy is about quadruple ofSi(001) surface energy so that carbon radicals prefer to grow at diamond(001) surface.(2) At the growth process in diamond films, hydrogen atoms can lead to stabilize of thediamond structure. In addition, activation H atoms can activate graphite and extract H atomsfrom C-H bonds to make a radical site. The activation of CH2, CH and CH3groups on thesurface reduced in a row. CH2is the most efficient group in the process of diamond filmgrowth. CH group hinder the growth of CVD diamond film, resulted to generatecopioushydrogen atoms, non-diamond carbon atoms and vacancies, and lower the quality of films. (3) The lower migration activation energy of Si particles will diffuse easily into diamondfilms and fill the vacancies on diamond grain boundary, thus reduce the quantity ofnon-diamond carbon atoms and stabilize diamond structure. Meanwhile, C-Si interface hasbeen formed as Si particle bonded with C particle on grain boundary. However,it isimpossible to form monolayer Si interface in diamond/Si composite films, but a monolayerSiC interface that proportion of C and Si atoms amount is1:1, and such interface is moreconducive to second nucleation.Through the research of this paper, it is verified to the adsorption site, diffusion pathwayand evolution rule of particles onto substrate surface, nucleation surface and interface.Observe the particles growth in situ at the atomic level. Si atoms in diamond/Sicompositefilms are able to stabilize the diamond structure of C atoms in crystalline efficiently, andreduce impurityhydrogen atoms, non-diamond carbon atoms and vacancies on grain boundary.C-Si interface of that Si atom bonded with C atom has ability of controlling the size andshape of grain in the films, and improving the performance and quality of films. |
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