Re: Flat conductors (was I need help).

[Larry Woolf <larry.woolf@GAT.COM>]

Graphite is a semi-metal. There is a small band overlap, and at T=0K, the
carrier density is about 10^18/cm3. The carrier density is temperature
dependent as is the scattering.  The material is formed by heat treating
graphitizable carbons at temperatures of 2500-3500C. The electrical
resistivity increases with increasing temperature for high heat treatment
temperatures (~3500C), but decreases with increasing temperature for lower
heat treatment temperatures (~2500C). This change in temperature dependent
resistivity is due to changes in the crystallite size, which changes the
amount of temperature independent boundary scattering.
See "Electrical Transport Properties of Benzene Derived Graphite Fibers," L.
D. Woolf, J. Chin, Y. R. Lin-Liu, and H. Ikezi, Physical Review B, volume
30, p. 861 (1984) for details.

The room temperature electrical resistivity of carbons and graphites can
vary between 10^-6 ohm-m and 10^-2 ohm-m depending on heat treatment
temperature.
See: Ch2. "he Electronic Transport Properties of Graphite, Diamond, Carbon,
and Related Materials" by Ian Spain, ib Chemistry and Physics of Carbon, Vol
16, ed. by P. L. Walker and P. A. Thrower.


Larry Woolf; General Atomics; 3550 General Atomics Court, San Diego, CA
92121; Phone:858-455-4475; FAX:858-455-4268; http://www.sci-ed-ga.org

-----Original Message-----
From:  Bernard Cleyet
Sent: Monday, February 25, 2002 10:35 PM
A semiconductor implies a band gap.  Since carbon (graphite) hasz a
negative exponential thermal coeffic ient of resistance, it is a
semiconductor;  besides the web told me so.

bc

Ludwik Kowalski wrote:

> After looking at the table of conductivities I see 0.45 ohm*m
> for Ge, at room temperature. For Pasco paper it is 0.32 ohm*m.
> Perhaps we should refer to this material as a semiconductor.
> Ludwik Kowalski.