STM study on surfaces of HOPG modified by implantation and heat treatment Original Research Article

High-energy ions, such as argon, copper and tungsten ions were implanted in pyrographite and the damages on surfaces, i.e. hillocks and craters, were studied mainly under scanning tunneling microscopy (STM). The number and area of the structural defects increase in function of atomic weight of implanted ions, while ion radius seems not to be a dominant parameter. A change of the inter-atomic distance between carbon atoms on hillocks was highlight by filtering STM images. The heat treatments of ion-implanted samples were performed, leading to an increase in volume of the pre-existing hillock in function of the temperature, i.e. no new hillock was created on the treated surfaces. Therefore, the diffusion of trapped-atoms (argon, copper and tungsten) is supposed to be weak and to occur towards the surfaces of pyrographite. In the proximity of the surfaces of irradiated sample, an easier diffusion of trapped-atoms is allowed by bond disrupted and interstitials, due to residual strain as shown on X-ray diffraction patterns and Raman spectra. A rearrangement of carbon atoms may also occur in pyrographite and on its surface, where the dot arrangement seems to be bend and focus only on some hillocks.