Enhancement of the nucleation of smooth and dense nanocrystalline diamond films by using molybdenum seed layers

Abstract

A method for the nucleation enhancement of nanocrystalline diamond ͑NCD͒ films on silicon substrates at low temperature is discussed. A sputter deposition of a Mo seed layer with thickness 50 nm on Si substrates was applied followed by an ultrasonic seeding step with nanosized detonation diamond powders. Hot-filament chemical vapor deposition ͑HF-CVD͒ was used to nucleate and grow NCD films on substrates heated up at 550°C. The nucleation of diamond and the early stages of NCD film formation were investigated at different methane percentages in methane/ hydrogen gas mixtures by atomic force microscopy, micro-Raman spectroscopy, scanning electron microscopy, and grazing incidence x-ray analyses in order to gain specific insight in the nucleation process of NCD films. The nucleation kinetics of diamond on the Mo-coated Si substrates was found to be up to ten times higher than on blank Si substrates. The enhancement of the nucleation of diamond on thin Mo interlayers results from two effects, namely, ͑a͒ the nanometer rough Mo surface shows an improved embedding of ultrasonically introduced nanosized diamond seeds that act as starting points for the diamond nucleation during HF-CVD and ͑b͒ the rapid carbonization of the Mo surface causes the formation of Mo 2 C onto which diamond easily nucleates. The diamond nucleation density progressively increases at increasing methane percentages and is about 5 ϫ 10 10 cm −2 at 4.0% methane. The improved nucleation kinetics of diamond on Mo interlayers facilitates the rapid formation of NCD films possessing a very low surface roughness down to ϳ6 nm, and allows a submicron thickness control.

Metallic Seed Nanolayers for Enhanced Nucleation of Nanocrystalline Diamond Thin Films

“…The insets of Figure 2 show the presence of agglomerates consisting of a wide number range of ND particles. The formation of relatively large agglomerates (up to about 180 nm in lateral For the metallic nanolayers under investigation in this study, the ND seed particle densities are comparable or somewhat higher than that on the pristine Si surface (~1 × 10 10 cm -2 ), 38 except in the case of Cr. The self-assembly seeding of the ND colloids could be explained on the basis of interfacial forces.…”

“…38 Therefore, the topography of the coated samples is mainly determined by the sputtered metallic thin films. The layer thickness and RMS surface roughness of the six metallic films are given in Table 1.…”

Effects of copper interlayer on deposition and flexibility improvement of diamond microelectrode

“…In addition, the nano-structure, rich grain boundaries and defects generated during sputtering of the interlayer result in its high surface activity and higher roughness compared to the W surface [15,16,22]. It is the high surface activity and higher roughness of the sputtered copper layer that greatly enhance the adsorption of nano-diamond.…”

“…The other approach is to sputter an interlayer as a diffusion barrier on the surface of substrate before diamond film deposition. One advantage of sputtered layer is that it can significantly improve nucleation [15,16], which is primarily to obtain continuous and dense CVD diamond films. Forming void-free and continuous film is critical for BDD microelectrode for acquiring excellent electrochemical performance.…”

Microstructure evolution of thermal spray WC–Co interlayer during hot filament chemical vapor deposition of diamond thin films

“…But none of them was used in industrial scale production [12] because these interlayers can not achieve effective mechanical and thermal transition between diamond and steel [13] . Metal interlayers can increase the nucleation density after seeding process [14][15][16] and the thermal expansion coefficient is close to steel, but it is much larger than diamond. So they cannot release thermal stress.…”