Carbon Nitride Thin Films and Nanofibres Synthesised by Hot Filament CVD

Abstract

A hot filament chemical vapour deposition (HFCVD) process was used to grow carbon nitride materials from a gas phase reaction involving the decomposition of methane (CH₄) in a mixture of ammonia (NH₃) and nitrogen (N₂) containing a variable quantity of hydrogen. Structural and compositional analysis of the deposited films by high resolution scanning and transmission electron microscopy equipped with electron energy loss spectroscopy revealed the occurrence of amorphous, crystalline, and tubular structures. The spatial distribution of the planar, spherical, and tubular compounds on the substrate surface depends on the lateral distance from the hot filament. The higher temperatures around the filament and the short distance to the substrate result in higher deposition rates below the filament and favour the formation of cauliflower and wormlike structures. The fullerenelike products and C : N nanobeads appear at intermediate distances usually between 3–5 times the vertical distance. In regions at an even greater distance, the localised and random growth of tubular structures has been observed, where their diameter decreases with the lateral distance from the filament. In addition, the formation mechanisms of the tubules change from interconnection of nanobeads to wormlike fibres, and then to one-dimensional smooth growth along the same lateral distance. The presence of ammonia decreases the deposition rate and leads to finer structures. In contrast, addition of hydrogen to the inlet gas was not found to be beneficial for the formation of carbon nitride materials.