Microwave Plasma Technology For The Preparation Of Diamond Films

Diamond film has excellent physical and chemical properties,such as the low thermal expansion coefficient,the coefficient of friction,the high wear resistance,the forbidden band width,the infrared transmittance and the biological compatibility,etc.It has broad application prospects in the fields of optics,electrics,biology and mechanics.Thus,its preparation process and functional application have become the hot spot in the field of material science.However,diamond film with high quality and large size is also a strategic product,under the background of the preparation technology and the products being monopolized by foreign countries,in this paper,diamond films were synthesized by microwave plasma chemical vapor deposition based on a home-made MPCVD system.By means of optimizing the process conditions,the parameters of the diamond film,such as purity,crystal structure,growth rate,crystal size,surface quality,and so on,were regulated by MPCVD,and the growth mechanism of diamond film and the synergistic mechanism of auxiliary gas were discussed as well.In our work,the diamond film samoles were synthesized in a 3 kW/2450MHz home-made MPCVD system based on single crystal silicon(100)and the association regularity of substrate temperature,reaction chamber pressure and methane concentration on the purity and the growth rate of diamond films were studied respectively.The optimal process parameters combination was obtained by response surface optimization design experiments.The growth rate of diamond film is 0.378?m/h,and the content of diamond phase was enhaned from 84.7%to about 89.5%under the condition of its substrate temperature is 837?,the relative concentration of methane/hydrogen is about 2%,and the pressure of the reaction chamber is about 6.95 kPa.On the basis of obtaining the best preparation technology of CH4/H2 system,the growth behavior of diamond film was studied by oxygen and argon assisting gas regulation.The synergistic regulation of the composition of different oxygen argon mixture components on the surface quality of micron scale diamond films was studied.It was found that the surface roughness of the diamond film was the lowest(about 81.5 nm)when the O2:Ar flow was 1 sccm:14 sccm,and the purity of the diamond phase was about 86.1%.In the meanwhile,the relationship between O2 flow and the growth of nano diamond film was studied.The results show that when the O2 flow is lower than 0.5 sccm,the effect of 02 on the grain growth is dominant.In the contrary,when the O2 flow is higher than 0.5 sccm,the effect of O2 on the secondary nucleation is dominant.The flammable and explosive risk was found after the obtaining of the CH4/H2 system which prepared diamond film process.In order to solve the problem above,the process of preparing diamond film by the raw material system without hydrogen was studied,which creatively adopted methanol-argon system to prepare diamond films.The results show that the diamond film has a good crystalline quality with preferential(111)lattice plane and the content of diamond phase was up to 75.71%without any pieces of graphite.Based on the investigation of the preparation process of pure diamond film,the preparation of boron doped with diamond film was studied.Boron doped with diamond films was successfully prepared by using boron oxide ethanol solution as boron source,and the boron doped with diamond film presents(111)as a preferential crystal plane,good crystallinity and film quality.Adding a small amount of boron element can improve the uniformity of diamond film particles and when the hydrogen bubble flow is 3 sccm,the consistency of boron doped with diamond film grain is the best,the potential window is 3.1V,and the electrochemical reversibility is well.