Abstract
The fundamental process underlies the synthesis of ultra-nanocrystalline diamond (UNCD) films, using a modified low-pressure, heat-assisted bias-enhanced nucleation and growth (BEN-BEG) technique, involving H2/CH4 chemistries. This growth process yields UNCD films similar to those produced by the Ar-rich/CH4 chemistries, with pure diamond nanograins (3-5 nm), but smoother surface (~6 nm root-mean-square) and higher growth rate (~1 µm/hr). X-Ray synchrotron analysis, atomic force microscopy, and transmission electron microscopy studies on the BEN-BEG UNCD films provided information critical to understand the nucleation and growth mechanism and growth conditions-nanostructure-properties relationships. For the purpose of improving the electron field emission properties (EFE) of the UNCD films, we developed three different approaches: Firstly, nitrogen species were doped into UNCD films by microwave plasma chemical vapor deposition (MPCVD) process at high substrate temperature. Secondly, nitrogen-doped UNCD was conformal coated on silicon nanowires by a modified ultra-sonication process. The EFE properties of silicon nanowires were pronouncedly improved due to UNCD coating. Lastly, nitrogen ions with varied energies were implanted into UNCD films grown by microwave plasma chemical vapor deposition process at high substrate temperature 800°C. The EFE properties of the films were significantly improved. The feasible mechanisms will be discussed. The interaction of UNCD with neural stem cells (NSCs) has been studied and its surface modification in order to improve its function as a biomaterial has been investigated. Hydrogen- and oxygen-terminated UNCD films were compared with standard grade polystyrene in terms of their impact on the growth, expansion, and differentiation of NSCs.