SPECTROSCOPIC AND SELECTED MECHANICAL-PROPERTIES OF DIAMOND-LIKE CARBON-FILMS SYNTHESIZED BY BROAD-BEAM ION DEPOSITION FROM METHANE

Broad-beam ion deposition was employed to decompose methane for the synthesis of diamond-like-carbon (DLC or a-C: H) films, deposited to two thicknesses of approximately 1 and 5 mum onto AISI M50 substrates in the presence or absence of a submicrometer intermediate layer of either amorphous Si:C:H or elemental Si. During deposition from CH4 the current density supplied to the ion gun was maintained at a constant 2.5 mA cm-2, while the accelerating potential was varied over the range 250-700 eV. The resulting microstructures, characterized using scanning electron microscopy and stylus-type profilometry, revealed ultrasmooth and essentially featureless surfaces for all films. Raman spectroscopy produced spectra which could be deconvoluted most effectively by the superposition of peaks positioned at three wavenumbers, predominated by the peak ascribable to sp2-hybridized bonding; it was, however, unable to differentiate from among the films deposited at various ion-beam energies. Fourier-transform IR (FTIR) reflectivity revealed that the ratio of sp3 to sp2 carbon-bonded hydrogen in the films was approximately 3.5; FTIR results exhibited a modest trend toward decreasing sp-3 to sp2 ratio for films deposited with increasing ion-beam energy. Nanoindentation properties of hardness and elastic modulus were found to be essentially insensitive to ion accelerating energy; however, adherence between the film and mechanically polished M50 substrate as measured by the scratch technique displayed a modest dependence on accelerating energy, with a maximum critical force occurring for films deposited at the highest energy investigated, 677 eV. Conversely, an inverse relationship between friction coefficient and ion deposition energy emerged, with coefficients ranging between 0.105 and 0.153. The film grown to a thickness of approximately 5 mum exhibited decidedly inferior adherence to the M50 substrate than those grown to a thickness of approximately 1 mum. Deposition at an energy of 260 eV onto the elemental Si intermediate layer or deposition directly onto the M50 substrate in the absence of an intermediate layer failed to produce adherent films, spalling spontaneously either immediately or within days following deposition.