Uniform distribution of bias-enhanced nucleation of diamond has been improved on Si substrate of an area of 1 × 1 cm2 by using a dome-shaped Mo counter electrode in a microwave plasma chemical vapor deposition reactor. A nucleation density of 109 cm2 can be reached within a few minutes when the bias voltage of - 100 V is applied on the substrates. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that a single-crystalline diamond in a few nanometered size can be deposited on a volcano-shaped cubic SiC which is epitaxially formed on a Si cone. Examination reveals a large fraction of diamond nuclei are oriented along with one side of SiC on each Si cone. The Si cone formed on the Si substrate is due to plasma etching. The diamond nuclei have a shape close to rhombus in TEM. With further growth, secondary nucleation of diamond occurs on top of diamond nuclei and SiC which grows with Si cones. As a result, polycrystalline diamonds are deposited on each Si cone.