| Ultra-nanocrystalline diamond(grain size <10 nm)have extremely high hardness,extremely low friction coefficient,excellent wear resistance,good thermal conductivity,strong chemical inertia,good biocompatibility,and adjustable doping of electronic properties,so they have broad application prospects in many fields such as machinery,optics,biology,electronics and so on.Almost all the existing UNCD films are used in the form of thin coatings,but the thick self-supporting films urgently needed in many applications cannot meet the requirements,the important reason is the lack of fast and high-quality material growth technology.In view of this,in this paper,a 15-k W highpower MPCVD device was used for the first time to prepare UNCD films with a unique nitrogen-containing liquid organic small molecule source acetonitrile as the reaction source by adjusting microwave power under different growth temperature conditions,so as to optimize the growth conditions of the liquid source.On this basis,organic small molecule liquid sources with different carbon/nitrogen ratios were selected to investigate the effects of growth source components on the film quality and growth rate,and the growth effects were compared with traditional gaseous sources under different carbon and hydrogen concentrations,in order to obtain high-quality UNCD film rapid growth technology.The morphology,phase composition,growth characteristics,and mechanical properties of the films were analyzed by means of XRD,SEM,Raman,and nano-indentation with OES.The results show that:1.The UNCD films were prepared from Acetonitrile,a liquid organic small molecule with C/N ratio of 2,as the growth source.With the increase of microwave power,the substrate temperature increases from 450 ℃ to 650 ℃,the film growth rate increases from 0.82 μm/h to 5.29 μm/h,and the substrate temperature at 600 ℃ is the best.2.N-butylamine(C/N ratio 4)and Diisopropylamine(C/N ratio 6)were used as growth sources to prepare UNCD films.The results of acetonitrile growth combined with the results showed that the larger the C/N ratio of liquid organic small molecule growth sources,the better the compactness of the films and the smaller the grain size.With the increase of microwave power and substrate temperature,the three liquid organic small molecule sources showed similar growth characteristics,and the growth rate was higher than 5 μm/h.In terms of mechanical properties and growth rate,using Diisopropylamine as the growth source can meet the requirements of high quality and rapid preparation of UNCD film.At 600℃,the growth rate of Un CD film is 6.62 μm/h,and the hardness can reach 64.5 Gpa.3.With H2,Ar and CH4 mixture as the growth source,the surface morphology of the generated UNCD film has little difference under different carbon concentrations of hydrogen-poor argon-rich conditions,and the whole film is relatively uniform and compact.With the increase of carbon concentration,the membrane growth rate increased from 0.37 μm/h to 3.67 μm/h.With the increase of carbon concentration,the content of diamond phase in the film gradually increased,and the hardness and elastic modulus measured by nano-indentation increased,with the highest hardness of 57.4GPa.4.With H2,Ar and CH4 mixture as the growth source,the surface of the membrane becomes more compact and uniform under different hydrogen concentrations in the condition of hydrogen-poor and argon-rich.When hydrogen concentration increased from 9% to 45%,the film growth rate decreased from 1.93 μm/h to 0.79 μm/h.With the increase of hydrogen content,the impurity content in the membrane decreases and the quality improves gradually.The hardness and elastic modulus of the membrane are up to 57.4 GPa and 575.3 GPa.By using the new liquid source and the traditional gaseous source to prepare the UNCD membrane,the growth characteristics,material quality,and mechanical properties of the UNCD membrane were compared.The results showed that the nitrogen content of liquid organic small molecules as the growth source,under the condition that the membrane material quality and mechanical properties are equivalent,the presence of nitrogen is conducive to the growth rate of the membrane.In particular,when Diisopropyl amine with a C/N ratio of 6 was used as the growth source,the UNCD film with ideal speed,quality,and performance could be obtained at 600 ℃matrix temperature.In this case,the growth rate of UNCD film reached 5.82 μm/h,the grain size was only 8.86 nm,and the hardness and elastic modulus were up to 64.5 GPa and 716 GPa.It is a new technology that is expected to satisfy the high quality and rapid preparation of UNCD film. |
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