Role of delocalized nitrogen in determining the local atomic arrangement and mechanical properties of amorphous carbon nitride thin films

We report the results of a comprehensive study of the mechanical properties and chemical structure of carbon nitride thin films deposited by magnetron sputtering. Nanoindentation measurements show that the films an very elast ic. Using a modified Oliver-Pharr method, to account for the elasticity of the films, the reduced elastic modulus was calculated to fall in the range of 35-55 OPa for all films measured. No quantifiable plastic deformation wa s measured in the tested films, therefore the hardness calculated (6 GPa) c an only be assumed to be a lower bound. Fourier transform infrared spectros copy of the carbon nitride films indicates the presence of large amounts of single and double bonds, and very small amounts of triple bonding, between carbon and nitrogen. Near edge x-ray absorption fine structure data sugges ts that there are three predominant types of bonds between carbon and nitro gen. This is consistent with the x-ray photoelectron spectroscopy data whic h shows N(ls) and C(ls) core spectra with multiple, chemically shifted feat ures, The data suggest, but do not confirm, the presence of nitrogen atoms participating in four bonds (three sigma, one pi). A self-consistent argume nt is presented that links parametric changes in mechanical properties with changes in a proposed film structure based on nitrogen participating in fo ur bonds. This marks a new approach to the interpretation of nitrogen bondi ng with carbon in the solid state not only for amorphous carbon nitride, bu t also other systems such as diamond and boron nitride thin films. (C) 2000 American Vacuum Society. [S0734-2101(00)01306-3].