High resolution electron microscopy of graphite defect structures after keV hydrogen ion bombardment at elevated temperatures

Changes in the hexagonal layer structures were studied on the (002) lattice fringe images of the side edge regions, within the 40 nm just beneath the basal face of the graphite whiskers after the irradiations of keV H+ ions at 300-900 K. Projected ranges of 0.5 and 1.0 keV H+ ions were estimated from the depth profiles of the d002 spacings after the ion irradiation to fluences below 1x1017 H/cm2 at 300 K. Temperature dependences of the d002 depth profiles after the 1 keV H+ irradiations up to 1x1018-3x1018 H/cm2 were investigated at 300-900 K. As the irradiation temperatures were raised from 300 to 400-500, then 650 and finally to 900 K, the average d002 spacings within 10 nm deep subsurface layers were found to decrease from 0.52, to 0.44, then 0.39 and gradually to 0.34 nm, which were explained through the decreases in the equilibrium density of, first, the interlayer recombined H2, and then the H in triple bondC-H bonding at the higher temperatures. The (002) lattice fringes, being hardly distinguishable after the 300 K irradiations to the level of trapping site saturation, were more clearly observed after the higher temperature irradiations due to the recrystallization of the damaged layers near the surface. (orig.)