An Insight into Grain Refinement Mechanism of Ultrananocrystalline Diamond Films Obtained by Direct Current Plasma-Assisted Chemical Vapor Deposition

Abstract

The grain-refinement mechanisms involved during the deposition of diamond films by directcurrent plasma assisted chemical vapor deposition (DC-PACVD) were investigated as a function of the inter-electrode electric field (IEEF). As IEEF was increased from 260 to 940 V cm À1 , the local electron temperatures near the growth front increased strongly; as a result, a strong grain refinement occurred ultimately yielding ultrananocrystalline diamond films (UNCD). Such observations were attributed to novel features of the DC-PACVD, including the electron-stimulated desorption (ESD) of the hydrogen-terminated moieties located at the surface, and the consequently enhanced generation of bi-radical sites at the growing diamond surface.