Graphitization behavior of kapton-derived carbon film related to structure, microtexture and transport properties

Graphitization behavior of the carbonized film of commercially available aromatic polyimide film Kapton 25 mu m in thickness was studied by X-ray diffractometry, measurements of the transport properties such as the electrical resistivity, Hall coefficient and magnetoresistance, and scanning electron microscopy. The specimens were films carbonized at 900 degrees C and heat-treated at temperatures between 1000 and 3000 degrees C with a step of 100 degrees C. For the specimens carbonized and heat-treated below 2000 degrees C, the average lattice constant alpha(0) was measured to be lower than that of the single crystal of graphite. Changes related to the transformation from the turbostratic structure to the graphitic occurred at a heat treatment temperature around 2200 degrees C in the microtexture on the fracture surface and the resistivity at liquid nitrogen temperature. The changes also appeared in the ratio of the resistivity at room temperature to that at liquid nitrogen temperature, and the Hall coefficient and magnetoresistance at liquid nitrogen temperature. The dependences of the resistivity ratio and also the Hall coefficient on HTT for the specimens with turbostratic structure can be related to the average crystallite size L-alpha(110) along the alpha-axis. The results of the resistivity, Hall coefficient and magnetoresistance were analyzed by a simple model. (C) 1997 Elsevier Science Ltd.