Nanostripes and nanoripples: surface modifications by swift heavy ions

Swift heavy ion (SHI) irradiation is a powerful tool for materials modification on the nanoscale. When irradiated at grazing incidence angle, surface modifications in the form of long surface ion tracks can be observed [1, 2, 3]. Recently, it was demonstrated that grazing incidence SHI irradiation can also be applied for modification of graphene [4] and other 2D materials. In the present contribution, we present two new developments along this line of research, demonstrating the usability of SHI for nanoscale modifications of surfaces and custom made 2D materials. Grazing incidence SHI irradiation of GaN [5] yields the formation of two different kinds of surface ion tracks. While chains of nanohillocks were observed for higher values of electronic stopping power, chains of nanoholes were found by AFM for lower stopping power values. In addition, surface tracks were investigated using grazing incidence small angle X-ray scattering (GISAXS). This novel method yields good statistics and avoids typical difficulties in measurements due to the (unknown) AFM tip size. Preferential loss of nitrogen found by in situ TOFERDA measurements indicates a thermal decomposition of GaN as origin of the chains of nanoholes observed on its surface. Second experiment shown is grazing incidence SHI irradiation of thin ITO films. Here we also found two different surface ion track morphologies: for lower stopping powers, usual ion tracks were observed, but for high stopping power values nanostripes in the form of double tracks were found (Fig. 1a). After higher fluence SHI irradiation, yet another new feature was found: in a narrow range of stopping powers, straight uniform nanoscale ripples were observed for the first time (Fig. 1b.).