Using extraordinarily low pressure ͑0.1-1 Torr͒ we obtained high-density nucleation of diamond on mirrorpolished silicon in a hot-filament chemical vapor deposition ͑HF-CVD͒ system. A diamond nuclei density as high as 10 10 -10 11 cm Ϫ2 was achieved, which was comparable to the largest nuclei density obtained in a microwave-plasma chemical vapor deposition system. The low-pressure nucleation technique and the pressure effect on diamond nucleation were discussed in detail based on molecular

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... ics. The enhanced nucleation at low pressure was attributed to an increased mean free path, which gave rise to an increased concentration of nucleating species at the substrate and other beneficial nucleating factors. The present work suggests that very low pressure may be an effective approach to nucleate and grow diamond films on untreated substrates via HF-CVD. ͓S0163-1829͑97͒04524-4͔