Honeycomb Carbon Networks: Preparation, Structure, and Transport

Summary

Honeycomb patterns with a single cell diameter of about 2 µm have been fabricated via spreading a drop of the initial polymer solution on the surface of cooled distilled water and following the subsequent influence of the water vapor on the resulting polymer thin film. We introduce an advanced structuring model capable to describe the underlying physical mechanism. The electrical conductivity of nitrocellulose extending from insulator to metal behavior distinctly changes by orders of magnitude via vacuum heat treatment at temperatures ranging from 600 to 1,000° C. For the case of carbon nets, the conductivity of which is far beyond the metal-insulator transition, the specific resistivity ρ depends on T as ρ(T) ∝ T ^-b exp ([T ₀/T]^1/p) in the range from 4.2 to 295 K. In the low-temperature regime, a Coulomb gap in the density of states located near the Fermi energy level occurs, i.e., p = 2. At high temperatures, the pre-exponential part ρ(T) ∝ T ^-b dominates. In the intermediate temperature range, we disclose Mott’s hopping law with p = 3. The electrical field dependence of variable range hopping is examined in its region of validity by ln ρ(T) ∝ T ^-1/2. We demonstrate the electrical conductivity σ caused by thermally nonactivated charge carriers at high fields to comply with ln σ(E) ∝ E ^-1/3.