An amorphous carbon (a-C) semiconductor was prepared by the pyrolysis of naphthalene in the presence of AlCl3 under a nitrogen gas flow. Electrical properties, such as the Seebeck coefficient (S) and electrical conductivity, of the a-C materials were studied as a function of the heat treatment temperature (7731273 K) and time (530 h). The electrical conductivity of a-C increased with the heating temperature. At a heating temperature of 873 K, a-C exhibits p-type semiconducting behavior (S = 0.41mVK-1, α = 2.0 × 10 -5Scm-1) and consists of a mixture of sp2-bonded carbon sheets (average sheet size: ca. 1.0 nm) and polycyclic aromatic hydrocarbons (PAH). After prolonged heat treatment (30 h) at 873 K, the electrical conductivity of a-C was increased by a factor of approximately 50 without loss of the semiconductivity (S = 0.20mVK-1, α = 9.6 × 10 -4Scm-1). The increase in the electrical conductivity of a-C is attributed to the decomposition of insulating PAH compounds by the prolonged heat treatment. Thus, precise control of the heating temperature and time has a significant effect on the p-type semiconductivity and electrical conductivity of a-C materials.
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