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Two-dimensional molybdenum-disulfide (MoS₂) catalysts can achieve high catalytic activity for the hydrogen evolution reaction upon appropriate modification of their surface. The intrinsic inertness of the compound's basal planes can be overcome by either increasing the number of catalytically active edge sites or by enhancing the activity of the basal planes via a controlled creation of sulfur vacancies. Here, we report a novel method of activating the MoS₂ surface using swift heavy ion irradiation. The creation of nanometer-scale structures by an ion beam, in combination with the partial sulfur depletion of the basal planes, leads to a large increase of the number of low-coordinated Mo atoms, which can form bonds with adsorbing species. This results in a decreased onset potential for hydrogen evolution, as well as in a significant enhancement of the electrochemical current density by over 160% as compared to an identical but non-irradiated MoS₂ surface.

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.).