Competition between diamond nucleation and growth under bias voltage by microwave plasma chemical vapor deposition

Diamond nucleation on iridium (001) substrates was investigated under different bias conditions. High-density epitaxial nucleation can be obtained in a narrow bias window. This paper reports both the typical nucleation and growth behaviors of Ir substrates. The bias current change laws with the bias duration time were directly recorded; further, the surface modification of Ir substrates and nucleation behaviors at the interface were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In high-density epitaxial nucleation, the bias current decreases as the duration time increases when the iridium surface is dramatically modified with the furrows and arrows preferentially aligned along the [110] direction; however, no diamond grains can be observed from the TEM, except for the carbon layer at the interface. In bias-enhanced growth, the bias current initially decreased, then increased. The grains can be detected by SEM after the biasing stage. A competition mechanism between diamond nucleation and growth under a bias voltage is proposed for this phenomenon, in which the surface nucleation and bulk nucleation coexist and compete.