Highly crystallized graphite films prepared by high-temperature heat treatment from carbonized aromatic polyimide films Original Research Article

Highly crystallized graphite films were prepared by successive heat treatments at 3100 °C for 40 minutes and then 3200 °C for 23 minutes under atmospheric pressure of pure argon gas from thin carbonized polyimide films. The starting polyimide films were a commercially available Kapton and a laboratory prepared high-modulus-polyimide film formed via polyamic acid gel. The crystallinity of the graphite films obtained was examined by the measurements of interlayer spacing d002, mosaic spread MS, electrical conductivity σ at 300 and 77 K, residual resistivity ratio RRR, and maximum transverse magnetoresistance (AΔϱϱ)max, mean magnetoresistance anisotropy ratio r, and Hall coefficient RH at 77 K. The present graphite films exhibit the highest crystallinity as graphite films obtained from polyimide films (i.e., the values of d002, MS, σ at 300 K, RRR, and (AΔϱϱ)max and r in the field of 1 T at 77 K were 0.3354 nm, 1.7–2.3 °, 1.80–2.14 × 106 S/m, 13.49–17.26 and 0.0040–0.0086, respectively, and small positive values of RH in fields around 0.2 T at 77 K were observed).