Preparation Of Nanodiamond Vacuum Windows

In order to meet the demand for high-quality nanocrystalline diamond vacuum window applying in Scientific application fields.High-quality nanocrystalline diamond films were prepared by microwave plasma chemical vapor deposition using C₂H₆O/H₂/Ar as feed gas and the process of diamond deposition has been studied.Then,the methods of making free-standing nanocrystalline diamond window and the welding crafts with metal flange were explored.the mainly works contain as below:（1）The influence of ethanol and Ar on deposition of nanodiamond films.The results show that,intensities of C₂,H_β,H_αincrease with the ethanol concentration increasing,while intensities of CH,OH groups increasing first and then decrease.This is the result of drop in electron temperature.Argon can promote the dissociation of ethanol,so intensities of all main groups in plasma increase with the increasing of Ar concentration.The ratio of C₂/H_α,C₂/CH increase when concentration of both argon and ethanol increase.C₂ can improve the secondary nucleation rate of the nanocrystalline diamond,causing the grain size begins to appear nanocrystalline with the concentration of argon and ethanol increase but the quality is becoming poor.It is found that the effect of ethanol on improving the growth of diamond films is mainly by increasing concentration of CH and C₂ groups near diamond surface.（2）The influence of Substrate temperature on deposition of nanodiamond films.The results indicate that,diamond grains expand when the substrate temperature becoming higher,and thus The surface of diamond films become more rough.The content of diamond phase in diamond films increase with substrate temperature turning higher.Further more,thermal stress of films increase while initial stress turning from pressure stress to tensile stress with the rise of temperature.（3）The preparation of diamond ring frame for vacuum window.We explored a method to prepare diamond ring frame for by using mask technique,making vacuum windows with pure diamond structure.On this basis,we invented another method with higher efficiency by using graphical technique.Furthermore we wiped off macromolecular residue on the surface of the windows reverse side by using hydrogen plasma treatment.（4）Research of infrared transmittance and gas leak rate of diamond vacuum window.The results indicate that the thickness of window film can not below 11μm or it can not bear one bar pressure.To meet the application requirements,the window film must achieve the thickness of 19μm.The gas tightness of diamond film increases with the increase of membrane,and the limits of gas leak rate is 9.3×10^-10Pa·m³/s.The transmittance of diamond vacuum window decreases with the increase of argon concentration,it is influenced by the scattering of film surface and the internal absorption of diamond.Smooth surface can greatly reduce the scattering effect and the absorption is mainly related to internal non-diamond carbon and defects,so the balance between surface roughness and diamond quality is the key to improve the transmittance of diamond windows.（5）The welding test of diamond windows and metal flange was carried out by high frequency induction welding technique.The results indicate that diamond window and invar flange can be welded well with the new technique.The welding strength increases with the increase of heat preservation time and heating rate.