The Structure And Formation Mechanism Of Nanodiamond Composite Films: Ab Initio Study

In order to improve the quality and performance of the composite film, a new type ofsingle crystal like poly crystalline composite (SCLPC) Diamond/Si nano-composite filmwas proposed. In the paper, the formation mechanism of the Diamond/Si nano-compositefilm was calculated with the first principle method based on the density functional theory(DFT). First of all, the interface structure of the Diamond/Si composite film wasinvestigated with the first principle method. Then the evolution behavior of the4C1Siisland configuration was researched for observing the doping silicon particles. In theprocess of researching the4C1Si evolution, we found that the carbon particle was difficultto migrate from the bridge site of the ring-closing to that of the ring-opening. The situationwould make the diamond films in homogeneous. In order to solve this problem, thevariation of the film structure and the change of the migration difficulty about the carbonparticles in the diamond crystal doped with other particles(B、P、N、C、Si、Cu、Ag) wereresearched based on the research above. At last, the diamond film was deposited with theMPCVD method and the surface morphology and the size of the diamond particle weretested by the AFM、SEM testing equipment. The following conclusions were got:(1)The monolayer Si interface can adsorb stably on diamond (001) surface. However,the monolayer Si interface is broken when the hydrogen atom or the CH2radical adsorbson it. The monolayer Si interface can’t exist stably in Diamond/Si nano-composite films.Meanwhile, the four kinds of monolayer SiC interface configurations with carbon andsilicon atomic ratio of1:1are calculated. Through the results we know that the SiCinterface structure in which the carbon atoms are located in the bridge site of thering-closing and silicon atoms are located in the bridge site of the ring-opening and the SiCinterface structure in which the silicon atoms are located in the bridge site of thering-closing and carbon atoms are located in the bridge site of the ring-opening representthe same interface. In addition, the SiC interface structure is more stable than the others.The monolayer SiC interface isn’t broken when the hydrogen atom or the CH2radical adsorbs on it. It means that the SiC inter-face is in favor of the nucleation of thenano-diamond films and can exist stably in the process of Diamond/Si nano-compositefilms deposition.(2)Through investigating the evolution behavior of the4C1Si island configuration, wecan conclude that the silicon particles tend to stay at the boundary areas of the diamondislands or grains rather than the inside of diamond islands or grains in the process of thediamond/Si deposition. Besides, the silicon atom is more active than the carbon atom ondiamond (001) surface.(3)Through calculating the migration activation energy of the carbon atom and thedoping atom in the1C1M island configuration, we can conclude that: the carbon atom ofthe2C island needs5.915eV energy to migrate from the bridge site of the ring-closing tothat of the ring-opening. The carbon atom of the1C1Cu island needs3.112eV energy tomigrate from the bridge site of the ring-closing to that of the ring-opening. The migrationactivation energy of the carbon atom decreases when doping copper particles. Besides, thecopper atom needs1.5775eV energy to migrate. Compared with the carbon atom of the1C1Cu island, the copper atom is easier to migrate. The situation will cause that the copperparticle migrates but the carbon particle migrates hardly. So the copper particle can notpromote the migration of the carbon particle very well. For the other doping particles, thecarbon atom needs more energy to migrate. It is not in conformity with the experiment. So,the selected doping particles in the paper can’t promote the migration of the carbonparticles very well. It needs to observe many other elements later.(4)The diamond films were prepared under the500℃、650℃、800℃、850℃fourkinds of different temperatures when the other process parameters are the same. Throughobserving the film by Raman spectrometer, we can get that the major component of thefilm is the diamond phase. Through comparing the surface morphology of the diamondfilms, we can conclude that: the gather ability of the diamond grains in the films increasesas the temperature increases. Also the roughness of the film surface decreases. In addition,the (100) crystalline phase tends to be the dominant position when the temperature is 850℃. Besides, the grains show the sheet structure in the850℃temperature. Besides, thebest temperature for deposition among the four selected ones is800℃.