Effect of Argon Addition on Morphology and Structure of Diamond Films(from Microcrystalline to Nanocrystalline)

Micro-/nanocrystalline diamond films deposited in Ar/H2/CE4 microwave plasmas have been studied,with argon flow rates in the range of 70-100 seem.The effects of argon addition on morphology,surface roughness,quality and structure were investigated by scanning electron microscopy,surface profiler,Raman spectrometer and X-ray diffraction（XRD）.It is demonstrated that when the argon flow rate is 70 sccm or 75 sccm,well-faceted polycrystalline diamond films can be grown at a low substrate temperature less than 610 ℃.With the increase in the argon flow rate,the smooth crystallographic planes disappear gradually.Instead,rough crystallographic planes made up of small aggregates begin to take shape,resulting from the increase in the secondary nucleation rate.Nanocrystalline diamond films were obtained at a flow rate of 100 sccm,and all of the prepared diamond films were smooth,with a surface roughness（Ra） less than 20 nm.Raman analyses reveal that the amount of amorphous carbon increases significantly with the increase in argon flow.The results of XRD show that crystalline size and preferential orientation of diamond films depend on the argon content in the plasmas.