Synthesis of Highly Oriented Graphite Films with a Low Wrinkle Density and Near-Millimeter-Scale Lateral Grains

Principal defects found in graphite films include grain boundaries and wrinkles. These defects are well known to have detrimental effects on properties such as thermal and electrical conductivities as well as mechanical properties. With a two-fold objective of synthesizing graphite films with large single crystal grains and no wrinkles, we have developed a relatively low-temperature (<1150 degrees C) process that involves the precipitation of graphite films from nickel-carbon solid solutions followed by in-situ etching of the nickel foil substrates with anhydrous chlorine gas to obtain near wrinkle free continuous graphite films. The size (L-a) distribution of lateral grains (or single crystal regions) in these highly oriented graphite films has been found to be asymmetric with the largest grains about 0.9 mm in diameter, as determined by electron backscatter diffraction (EBSD). Thus, the growth of large-area graphite films with grains much larger than those reported for highly oriented pyrolytic graphite (HOPG, similar to 20 to 30 mu m), and with a low density of wrinkles, as in the case of HOPG, but prepared at much lower temperatures, is reported here.