Electrical resistivity of carbon films Page: 5 of 16
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5- 3
with a nominal thickness of 500 A were investigated. The carbon
films used had a uniform brownish color with room temperature
resistivity of the films varying from .02 ohm-cm to 1 ohm-cm.
After high temperature heattreatment (7500C for 2 hours), all
films had about the same room temperature resistivity (ti 0.03Q-cm).
We attribute the differences in initial resistivity to differences
in the amounts of gases trapped in the films during growth. Heat-
treatment causes the gas molecules to diffuse out of the films
leaving them with acceptor type regions which are a source of
holes. Therefore, the resistivity decreases as the gas molecules
are removed. A similar phenomenon is observed in bulk carbon.0
Measurements were taken on the low resistivity samples (ti
.020-cm at room temperature) in a range 1.2 to 11000K.' Typical
room temperature resistivity values for other investigators range
from 0.ln-cm for 700 A thick films to about 2Q-cm for 500 A
thiek films. Due to the geometry of the samples we have measured
only planar resistivity.
A standard liquid helium cryostat was used for reaching tem-
peratures down to 1.20K while a Lindberg three zone furnace was
employed for achieving temperatures as high as 11000K. Tempera-
.tures below room temperature were measured with a calibrated car-
bon resistor and an a.c. bridge. Temperatures above room tempera-
ture were measured with a chromel-alumel thermocouple.
Low temperature measurements were made with the carbon film
on the original glass substrate. Copper or gold foil strips,
- with a layer of uncured Epotek silver epoxy, were used to make
electrical contact with the carbon films. To eliminate the effect'
of contact resistance, a four terminal method for measuring resis-
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Kupperman, D.S.; Chau, C.K. & Weinstock, H. Electrical resistivity of carbon films, report, June 26, 1972; (https://digital.library.unt.edu/ark:/67531/metadc1029930/m1/5/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.