Wen Ting Yeh1, Sea-Fue Wang2,
James Sung1
1.
Kinik Company, and National Taipei University, Taipei, Taiwan, R.O.C.
2.
National Taipei University, Taipei, Taiwan, R.O.C.
Amorphous diamond can be conveniently
deposited by cathodic arc. The arc
contains vaporized carbon ions that are driven toward the substrate by a
negative bias. Amorphous diamond is
made of tightly packed carbon atoms jointed together by distorted graphitic (sp2)
bonds, or diamond-like (sp3) bonds. The sp3/sp2 bond ratio is dependent on the
kinetic energy of carbon ions. This
kinetic energy can be increased by the bias of substrate. However, with increasing of argon gas
pressure, the mean free path of carbon ions reduces, so is their kinetic
energy. Hence it is expected that sp3/sp2
bond ratio to increase with the
increasing bias, but it may decrease with increasing rate of argon flow.
Amorphous
diamond films were deposited onto cemented tungsten carbide (K10) substrates
for 1 hour at two bias levels (-15 and –20 V) with two rates of argon (16 and
125 SCCM). The thickness of these films
was estimated by examining SEM micrographs of cross sections. The measured values ranged from 0.65 to 1.25
microns. It was found that the
thickness of amorphous diamond tended to surge with the small increase of bias,
possibly due to the increase of the flux speed of carbon ions. However, when the rate of argon flow
increased, the deposition rate also gained slightly.
The
hardness of amorphous diamond was determined by Vickers scale to range from
2484 to 3457 Kg/mm2. It did
not vary much with the small change of bias.
However, with the increasing rate of argon flow, the carbon ions lost
some kinetics energy, hence the hardness reduced. The adherence of amorphous diamond was tested by observing
compressional spauling of films under the load (150 Kg) of a Rockwell
indenter. It would appear that the adherence
was greatly strengthened by increasing the rate of argon flow. This increase is likely due to the rise of sp3/sp2
bond ratio, and hence the reduction of compressional stress that is the driving
force for delaminating the amorphous diamond film from the substrate.