Deposition of diamond/β-SiC composite gradient films by HFCVD: A competitive growth process

• Novel diamond/β-SiC composite gradient films have been synthesized by HFCVD.
• The composition of the surface changed gradually from pure diamond to pure β-SiC.
• The growth mechanism of diamond/β-SiC has been systematically investigated.
• The growth rates of diamond and β-SiC depend on local gas compositions and substrate temperatures.
• There is a competition between diamond and β-SiC to occupy the available space.

Surfaces featuring gradients of chemical composition and/or morphology allow high-throughput investigations and systematic studies in disciplines such as physics, chemistry, materials science, and biology. In this work, novel diamond/β-SiC composite films exhibiting a gradient composition were synthesized by a hot filament chemical vapor deposition (HFCVD) technique utilizing H2, CH4, and tetramethylsilane (TMS) as reaction gases. A specific filament-sample arrangement in the HFCVD chamber induced a gradation in chemical composition of the gas phase above the substrate surface, which, in turn, leads to a gradual change in the composition of the deposited films potentially ranging from pure diamond to pure β-SiC. It was possible to control the actual details of the diamond/β-SiC ratio in the gradient films by adjusting deposition pressure and TMS concentration. Aside from film characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy were employed to determine the presence and quality of both diamond and β-SiC phases, respectively. The wealth of information provided by such diamond/β-SiC composite films allowed for a systematic investigation of the mechanism governing their growth. It turned out, that the growth process features nonequilibrium characteristics. It is dominated by a competition between a kinetic product (diamond) and kind of a thermodynamic product (β-SiC) to occupy any available positions on the substrate and the growing surface, respectively. With higher hydrogen radical concentration [H] and substrate temperature, the deposition is kinetically controlled, leading to diamond dominated films. On the other hand, a lower [H] and substrate temperature, consequently resulted in a predominantly thermodynamically controlled deposition, featuring a higher β-SiC content in the film.