Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics

Low temperature electrical transport studies on carbon nitride
films prepared by chemical vapour deposition
M. Prashantha, E.S.R. Gopal and K. Ramesh ∗
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
The search for new materials for advanced application leads to the discovery of new materials
with interesting electrical, physical, chemical and mechanical properties. The advancement of
society and quality of human life also depends on these advanced materials. In this aspect
carbon nitrides have been predicted to have high hardness, high wear resistance with low
friction coefficient. These properties make them as a promising material for various
applications such as organic semiconductors, fuel cells and photocatalysis, mechanical cutting
tools, protective coatings, biomedical applications, electroluminescence devices, optical
materials etc. The coating can reduce the wear, friction and corrosion, which can increase the
life time and efficiency of the high speed moving parts. Carbon nitride coating is also found to
be biocompatible. So, the successful synthesis of carbon nitride would have an enormous
impact not only on the basic science but also on the technological development.
In this work, we have attempted to prepare carbon nitride by chemical vapour deposition
(CVD). We have used Azabenzimidazole (C 6 H 5 N 3 ) as the precursor which has both carbon
and nitrogen bonding in its structure. In a two zone furnace, the vapours of the precursor
evaporated at 450 o C in Zone I are made to enter into Zone II which is kept at high
temperature. The vapours get pyrolysed and deposit on quartz and silicon substrates. The
samples were prepared at different pyrolysis temperatures of 725, 750, 775, 800 and 825 o C.
As the C-N bond is significantly strong, even at high temperatures a considerable amount of
C-N bonding is retained. This method is simple and enables one to have control over the
amount of nitrogen in the system by controlling the pyrolysis temperature, volume of the
liquid and the process time. The concentrations of N decreases gradually from 26 to 20 at %
for the films prepared at pyrolysis temperatures of 725 to 825 o C.
Electrical transport studies at low temperature (RT to 4.5K) show that the carbon nitride films
exhibit Metal-Insulator (MI) transition. The incorporation of nitrogen into carbon introduces
disorder in the structure. The disorder increases with the decrease of the nitrogen content,
greatly influences the electrical transport properties. Disorder induced metal-insulator
transitions are well known and can be studied by varying the temperature, pressure, doping
level etc. In present study, metal insulator transition exhibited by carbon nitrides prepared at
different pyrolysis temperatures has been studied. It is observed that the increase in pyrolysis
temperature shifts the MI transition temperature to lower values. The transition temperatures
for the samples prepared at 725 o C, 750 o C and 775 o C are 84.7 K, 67.7 K and 9.5 K
respectively. The reduced activation energy indicates that the metallic regime of the samples
prepared at pyrolysis temperatures > 800 o C lies at low temperatures. It is also observed that
the activation energy decreases with the increase in pyrolysis temperature.
∗ Corresponding author: kramesh@physics.iisc.ernet.in
1