Preparation Of Single Crystal Diamond Thick Film By MPCVD

Diamond is a high-performance material with excellent physical properties such as high hardness,high thermal conductivity,high wear resistance,and low thermal expansion coefficient.It is commonly used in cutting,drilling,and grinding tools such as saw blades,drill bits,grinding wheels,and abrasives,and is widely used in scientific,medical,and industrial fields,such as windows and detectors in X-ray,laser,and high-pressure experiments.Natural diamonds are formed from carbon elements of deep underground under high-temperature and high-pressure conditions,which result in the extremely slow,difficult mining,rare output and high cost.However,synthesized single-crystal diamonds can greatly reduce costs and can be customized in shape,size and doping as needed.Given the excellent performance and wildly application prospects of diamonds,researchers in various countries have begun to focus on the synthesis technology of single-crystal diamonds.Currently,there are mainly two methods for the synthesis of single-crystal diamonds:high-temperature high-pressure(HTHP)method and chemical vapor deposition(CVD)method.And the MPCVD method is the most widely used method for synthesizing high-quality single-crystal diamonds.The main development trends for using the MPCVD method to synthesize single-crystal diamonds are high growth rate,large area,high quality,doping,and thick film preparation.The thick-film preparation is of high current interest for single-crystal diamond materials.The technical problem of thick-film preparation is to find suitable process conditions with long-time growth process.Therefore,first part is to compare the disk-shaped chamber and the cylindrical chamber and optimize the growth conditions in the cylindrical chamber,such as methane concentration and growth temperature.The growth rate,surface morphology,and crystal quality were compared by using the microscope,Raman spectrometer,and high-resolution Xray diffractometer to determine that 6%methane concentration and 975℃ growth temperature in the cylindrical chamber are the optimal growth conditions.Further research was conducted on the effect of nitrogen on the growth of single-crystal diamond,and it was found that nitrogen doping is one of the effective methods to increase the growth rate.As the nitrogen concentration increased,both the lateral and vertical growth rates increased,and the step-growth morphology on surface was observed.After excluding the influence of temperature unevenness on the behavior of crystal surface bending,it was found that under the influence of nitrogen,the crystal surface evolved toward the concave plane,and the higher the nitrogen concentration,the more severe the concave became.Finally,the changes in crystalline quality during 8h and 16h of MPCVD homoepitaxial growth under nitrogen doping conditions were compared,and it was found that as the growth time increased,the crystalline quality decreased.The third part was to further investigate the anharmonic phonon effects of different types of single crystal diamonds.With increasing temperature,the Raman peak positions of both HTHP and CVD samples with different doping types exhibited a redshift and the Raman halfwidths showed a certain degree of broadening.A one-to-one correspondence was established between the Raman shift of the optical phonon modes and temperature,providing a nondestructive,non-contact,and high spatial resolution method for temperature detection of diamond in heat dissipation applications.The contribution of thermal expansion,three-phonon,and four-phonon to the Raman peak positions and full width at half maximum(FWHM)were discussed by theoretical models.The thick film preparation of single crystal diamonds was carried out in fourth part.With the increase of the thickness,the growth rate of diamond decreased and polycrystalline rim issue intensified.Therefore,the growth was continued using a pocket substrate holder,and a 3mm thick single crystal diamond film was prepared.The thick film preparation of multiple single crystal diamonds was completed in two stages,and the thickness reached 2.8mm.