🚀 go-pugleaf

In article <C1F58B.MF4@brunel.ac.uk>, mt90dac@brunel.ac.uk (Del Cotter) writes:
> 
> What colour is amorphous diamond film?  Just curious; we had a lecture on
> phase equilibria today and the question came up.
> 
> Any other gee-whiz facts on the manufacture/properties/applications of ADF?
> 
> -- 

OK, I'll bite as an expert in Diamond.  

First off there can not be such a thing as amorphous diamond.  You probably
realize this, but just in case: Diamond is a crystal therefor can not be 
amorphous.  Amorphous diamond comes about due to amorphous silicon, which
does exist.  The correct term would be amorphous sp3 carbon, to distinguish
it from amorphous sp2 carbon (ie: soot).  

I don't know if truely amorphous sp3 carbon can, or does exist.  If someone
claimed to have made it I'd be very heavy with the salt.  Amorphous or nano-
crystalline films have been made with large amounts of sp3 bonding.  These 
films are often called Diamond-Like Carbon (DLC) and have a wide range of 
properties.  DLC is generally produced under the same conditions as a diamond
thin film, but for some reason the experiment missed the sweet spot of diamond
deposition.  The closer to the sweet spot of diamond deposition the more
diamond like the material is.

As such these DLC films have their properties largely dominated by defects 
(carbon bonds left un-bonded, impurities, hydrogen contanination, etc).  
The term diamond-like comes from their mechanical properties, which approach
those of diamond, while the electrical and optical properties are much 
poorer.  In general a DLC film is black.  

If one could make a truely amorphous sp3 carbon film I'd expect it to be clear,
like diamond except that the band-gap would probably be compressed due to 
the disorder.  I'm sure someone could do a quick and dirty calculation of the 
band gap of amorphous sp3 based on the band gap of amorphous silicon.  Compress
the band gap enough and the film will absorb blue light.  However, this assumes
one could make a defect free amorphous sp3 carbon film.

As for amorphous carbon films (a-C) in general one of the easiest production 
techniques is sputtering of a graphite target.  If one adds hydrogen to the 
sputtering gas one gets amorphous carbon stabalized with hydrogen (a-C:H), add
nitrogen (a-C:N), etc.  This allows a whole recipe of different amorphous carbon
films with different mechanical optical and electrical properties.  Although
such films are used by the disk drive industry as a hard protective coatings
I suspect there are many other applications which have yet to be developed.  

I hope this satisfys your quiery.

Darin S. Olson
R & DD 
LMSC
Palo Alto CA