Abstract
Effects of CH 4 /H 2 ratio and bias voltage of the microwave plasma-enhanced chemical vapor deposition (MPE-CVD) process on the nucleation behavior and associated characteristics of nanodiamonds were investigated, While the scanning electron microscopy (SEM) microstructure and Raman crystal structure of the films insignificantly vary with CH 4 /H 2 ratio and bias voltage, electron field emission properties of the materials markedly change with these deposition parameters. The predominating factor modifying the electron field emission properties of the nanodiamond films is presumed to be the increase in the proportion of sp 2 -bonded grain boundaries when the grain size of the nanodiamond films decreases. Between these two major factors, the bias voltage shows more prominent effects on modifying the granular structure of the nanodiamonds than the CH 4 /H 2 ratio does. The best electron field emission properties attainable are J e =500 μA/cm 2 at 20 V/μm and E 0 =8.5 V/μm. © 2004 Elsevier B.V. All rights reserved.