Crystallization by post-treatment of reactive r.f.-magnetron-sputtered carbon nitride films

Carbon nitride (CN_x) films have been deposited on single crystal ZrO₂(100) substrates by reactive r.f. magnetron sputtering. The effect of thermal annealing at 900°C on the structural properties of the films has been studied by atomic force microscopy (AFM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). AFM results show a fine spread of well-defined grains with an average size of 500nm exhibited by the post-annealed films. TEM images confirmed that thermal annealing has transformed the predominantly amorphous as-deposited films into crystalline phases. The surface morphology observed is composed of carbon nitride nanofibres and p-C₃N₄ crystals in a less nitrogenated amorphous matrix. The size of the crystals ranges from about 0.05 to 1.5μm. The smallest of the nanofibres appear to be approximately 20nm in external diameter. Selected area electron diffraction indicates the fibre walls to be crystalline in nature. N1s peaks in XPS spectra of the annealed films indicate the presence of two different bonding states, one attributed to nitrogen inserted into the graphitic ring structure, and the other attributed to nitrogen surrounded by three carbons in the N-C network.