is diamond coating?
Diamond is the hardest known material
and consequently has been used as is an ideal abrasives for its
Also, diamond is the best thermal conductor while it
and is a good
electric insulator. This unique property
stems from its different thermal conduction
mechanism with that of metals. While heat
is transferred by free electron in metals,
heat is transferred by phonon in the diamond.
Because diamond is composed of light carbon
atoms and the bond strength is very high,
heat is quickly transferred by the lattice vibration. This highest
thermal conductivity makes diamond the most
promising material for heat-sink application.
The high phonon speed is closely related
with sound velocity and diamond is also
promising material for speaker diaphragm for high tone (tweeter) speaker diaphragms.
Also diamond is transparent to electromagnet
radiation ranging from X-rays to IR ,thus which
is making it suitable for applicable to X-ray
or IR windows. Besides, diamond
is also promising for high temperature-high
speed electronic devices because of its
low dielectric constant, high hole mobility, and wide band gap.
There were early attempts to synthesize
diamond from the 19th century. However, since the high pressure and temperature
required for diamond synthesis was not available
that time. it
was not until 1955 by that
Bundy et. al., the first successfully synthesized the first
man-made diamond was synthesized. Later, powder type diamond was
synthesized by the detonation method16
the synthetic diamond industry has grown
steadily and in some applications provides
to natural diamond. However, since products
of synthetic diamond by HT-HP methods are
limited to powder or particle type, its
applications were confined mainly to abrasives
or cutters only.
With the advent of the cutting edge technologies, the
trend is that the industrial needs for materials
are moving from bulk to thin film. Research on the low temperature
synthesis of diamond started from in the 1950s. However, at that
time, the gas activation process was not
employed and the instead
diamond was deposited on the seed
crystals by pyrolysis of hydrocarbon. This
utilized the low activation energy barrier of diamond nucleation
that of compared
to graphite nucleation on the seed crystal.
However, the substrate was confined to diamond
only and once graphite or amorphous carbon
is nucleated on the substrate, it quickly
covers the substrate. Accordingly, the synthesis
process required many cycles of growth followed
by hydrogen etching in order to remove graphite
or amorphous carbon, which made growth rate
very slow, only a few angstroms per hour.
However, after the gas
activation process such as hot filament
or plasma was introduced in the early 1980s,
the growth rate of diamond increased abruptly
and it became possible to deposit diamond
on various substrates. Diamond coated cutting
tools for non-ferrous metals, X-ray windows,
and heat-sinks are already commercially
available these days and intensive researches
are being performed on the thin film diamonds
for the electronic device applications.