Erosion of metallic nano-islands with slow highly charged ions and investigation of swift heavy ion tracks

Abstract

Nowadays the use of ions is a common method to alter semiconductors or insulators on the nanometer scale. This can range from the creation of nano-hillocks and craters on the surface to melting of these materials. These effects can be triggered by either the kinetic energy or the potential energy of an ion in the case of insulating and semiconducting targets. For metallic targets, kinetic effects were measured, but potential energy effects were not observed until now, because free electrons in the conduction dissipate the energy fast enough to prevent permanent material damage. We performed irradiations of gold (Au) nano-islands on a molybdenum disulfide (MoS2) monolayer with highly charged ions (HCIs) and found that erosion of metallic targets is possible, if they are produced on the nanometer scale. This erosion manifests itself in height loss of these Au nano-islands and was therefore measured with an atomic force microscope (AFM). Furthermore, we found a charge-state dependent height loss, where the Au nano-islands decreased more in their height with increasing charge state. Additionally, a one-to-one measurement was performed, where the same Au nano-islands were compared before and after irradiation. In this way, a volume threshold was found, where these Au nano-islands seem to be more effected by the potential energy in terms of height loss.HCIs were also used to alter bismuth nano-clusters on calcium fluoride (CaF2) and sili- con dioxide (SiO2), but the measured height loss was too small to be attributed to the potential energy of the HCI, because the nano-clusters were produced too dense.The second part was the investigation of swift heavy ions (SHIs) in insulating materials, such as titanium dioxide (TiO2) and aluminium oxide (Al2O3). A SHI impinging an insu- lating or semiconducting target creates an energy density spike in the electronic system, which results in a trail of damage. This latent track consists of two parts, namely a con- ical damage profile and a discontinuous part, where amorphisation occurs. Transmission electron microscopy (TEM) was used to visualise these parts of the latent track. Although it was able to resolve the conical damage profile with different (TEM-) techniques, the discontinuous part could not be resolved. Furthermore, a TEM analysis showed, that these conical damage profiles are empty or voids.