Growth behavior of nanocrystalline diamond films on ultrananocrystalline diamond nuclei: The transmission electron microscopy studies

Abstract

Micron-crystalline diamond (MCD) films with a unique microstructure were synthesized using a modified nucleation and growth process, in which a thin layer of ultrananocrystalline diamond (UNCD) was used as nucleation layer for growing diamond films in H2-plasma. Thus obtained (MCD)UNCD diamond films consist of nanosized diamond clusters (∼10 nm in size) surrounding the large diamond grains (∼300 nm in size), exhibiting better electron field emission (EFE) properties than the conventional diamond materials with faceted grains. The EFE of these (MCD)UNCD films can be turned on at E0=11.1 V/μm, achieving EFE current density as large as (Je)=0.7 mA/cm2 at 25 V/μm applied field, which can be attributed to the presence of large proportion of UNCD grains lying in between the MCD grains, forming an electron conduction path and thus facilitating the EFE process. Transmission electron microscopy examinations reveal that such a unique microstructure was formed by agglomeration and coalescence of the nanosized UNCD grains.