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 sy nthesis 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 eithe r amorphous Si:C:H or elemental Si. During deposition from CH4 the cur rent 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 25 0-700 eV. The resulting microstructures, characterized using scanning electron microscopy and stylus-type profilometry, revealed ultrasmooth and essentially featureless surfaces for all films. Raman spectroscop y 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, una ble to differentiate from among the films deposited at various ion-bea m energies. Fourier-transform IR (FTIR) reflectivity revealed that the ratio of sp3 to sp2 carbon-bonded hydrogen in the films was approxima tely 3.5; FTIR results exhibited a modest trend toward decreasing sp-3 to sp2 ratio for films deposited with increasing ion-beam energy. Nan oindentation properties of hardness and elastic modulus were found to be essentially insensitive to ion accelerating energy; however, adhere nce between the film and mechanically polished M50 substrate as measur ed by the scratch technique displayed a modest dependence on accelerat ing energy, with a maximum critical force occurring for films deposite d at the highest energy investigated, 677 eV. Conversely, an inverse r elationship between friction coefficient and ion deposition energy eme rged, with coefficients ranging between 0.105 and 0.153. The film grow n to a thickness of approximately 5 mum exhibited decidedly inferior a dherence to the M50 substrate than those grown to a thickness of appro ximately 1 mum. Deposition at an energy of 260 eV onto the elemental S i 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 de position.