We have investigated the mechanical properties of diamond-like carbon
(DLC) thin films that contain foreign atoms. The DLC films were prepared
by pulsed laser deposition. A novel target design was adopted to
incorporate foreign atoms into the DLC films during film deposition.
Copper, titanium and silicon are chosen as the dopants. The chemical
composition of the doped films was determined using Rutherford backscattering
spectrometry, X-ray photoelectron spectroscopy and calibrated extrapolation.
Experimental results of both visible and UV Raman are presented and
discussed in terms of peak shape and position. The effect of dopants
on the Raman spectrum is also analyzed, Optical microscopy of the
pure DLC of a certain thickness showed severe buckling. A brief review
of the theoretical background of adhesion is given and the possible
mechanisms of adhesion that may work in DLC coatings are discussed.
Qualitative scratch tests on the specimens show that pure DLC has
quite pool. adhesion due to the large compressive stress, while the
doped DLC films exhibit much improved adhesion. Wear tests show improved
wear resistance in the doped DLC coatings. Nanoindentation results
give an average hardness above 40 GPa and effective Young's modulus
above 200 GPa for pure DLC.:The copper doped DLC films showed slightly
decreased hardness and Young's modulus as compared to pure DLC films.
Ti and Si can reduce the hardness and Young's modulus more than Cu.
All these can be understood by analyzing the internal stress reduction
as derived from Raman G-peak shift to lower wavenumbers. A preliminary
model of the stress reduction mechanism is discussed. (C) 1999 Elsevier
Science Ltd, All rights reserved.
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