Self Nucleation of Diamond on Zeolite by Chemical Vapor Deposition Method

The nucleation stage of diamond in Chemical Vapor Deposition (CVD) is still not properly understood. Several methods were found by trial and error studies to initiate the formation of diamond nuclei on nondiamond substrates, very frequently on single crystal Si wafers. We have obtained first time, diamond nucleation on zeolite substrate with out any pretreatment. Diamond nucleation on zeolite substrate gives some insight into the nucleation mechanism. Depositions were carried out in a hot-filament chemical vapor deposition (HFCVD) apparatus. The HFCVD system was fed with a mixture of methane (0.8%) and balance hydrogen. A series of depositions were done in the pressure range 20-120 torr and at substrate temperature 880 C. The morphologies of the as-deposited films analyzed by scanning electron microscopy (SEM) show isolated diamond grains in the initial nucleation stages, develop into a micro porous films in the next stage and form a continuous film after long time deposition. The grain sizes (20-25 microns) were uniform. Raman spectroscopy was used to investigate the crystal morphology, structure and non-diamond impurities in the films deposited at various growth conditions. The Raman spectra taken by focusing laser on single grain showed a single peak of diamond free from other non-diamond features. A single Lorentzian fit to the spectra revealed that the diamond peak is shifted towards higher wave numbers (1335 cm-1) when compared to natural diamond (1332 cm-1). This may be due to the compressive stress of diamond. The FWHM of the Raman peak is also quite high (approximately 10.5 cm-1) when compared to natural diamond (2 cm-1). A broad band corresponding to the graphite also appears approximately 1560 cm-1 in addition to the diamond band in the spectrum taken on large area of the sample. The nature of the hydrogen bonding with sp3 and sp2 network and the quantitative analysis were done by Fourier transform infrared (FTIR) spectroscopy. We hope a detailed Transmission Electron Microscopy (TEM) analysis will give more information on nucleation mechanism. A substrate onto which diamond nucleation is not required may enable us to develop the films with uniform grain sizes and it can be used as microfilters. We have used different types of zeolites (HZSM-5, H-beta, and NH4-Y) to study the effect of pore size on nucleation. Effect of pore size and Si/Al ratio on microstructure of diamond films will be reported.