Single ion induced surface nanostructures – SIISU

After irradiation, either at low (ARRIBE) or at high energy (IRRSUD), the induced nano-structures will be characterised by different techniques, like Atomic Force Microscopy, Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy Low-Energy Electron Diffraction and Rutherford Backscattering Spectroscopy. The influence of the two main parameters, speed and charge state of the target ion, will be studied.

Goal of this project is to gain a better insight into the processes involved in the production of surface structures by the impact of slow as well as swift ions.

In the futur the study can be extended to other materials, e. g. semi-conductors, and to higher charge states of the projectile ions, by performing irradiations at other facilities with EBIT ion sources.

Publications as well as proceedings of international conferences are planned, like IISC, HCI, ALC, ICPEAC, ...

Ion impact on surfaces can induce surface modifications on the nano-scale. Different types of topological modifications are possible, like hillocks and craters, but in most cases, hillocks have been observed. These modifications can be produced by different types of ions. Ions deposit energy mainly by their potential energy (charge state) or kinetic energy (velocity). Slow highly charged ions (HCI), due to capture processes in front of the surface, as well as swift heavy ions (SHI), due to ionization processes inside the target, disturb the electronic system of the target heavily. A first indicator for this interpretation is the fact that the surface damage process usually has a threshold, either in the charge state (HCI) or the kinetic energy (SHI). Understanding, comparing and adapting the effects of different ion species for targeted surface modifications is the goal of the proposed project.
Besides their excitation of the electronic system, slow and fast ions induce their main damage in different locations: slow HCI produce predominantly surface damage, whereas SHI do their damage mainly in the bulk (ion track). In order to compare the two ion types more easily, we will concentrate on grazing incidence with SHI. This particular collision geometry forces the track to a region close to the surface, comparable with the shallow damage of slow HCI.
So far studies were done with individual combinations of irradiation parameters, like ion type, charge state and velocity, as well as target type and structure. We plan to concentrate on a relatively limited number of targets, but to study them in detail with a large number of ion types. We will start with three materials, whose reaction to ion beams is partially known, i.e. SrTiO3, TiO2 and CaF2. Depending on the obtained results, we will expand this initial choice to other types of materials.
Until now, the main tools for the study of surface modifications were near-field methods. In most cases, atomic force microscopy (AFM) was used, therefore studying the topology of the modifications. We propose to use other methods, like high-resolution transmission electron microscopy, to also study the structure of the damage, and especially its extent into the volume, and not only the surface shape. We will also perform chemical and structural investigations of the perturbed regions using surface characterization techniques such as XPS, Auger, LEED and RBS/channeling. These studies will be combined with tools with sufficiently high spatial resolutions, like AFM and MET, to examine the effect of individual ion impacts. This broad variety of techniques will allow us to explore the damaging processes, and can lead to a better understanding of the mechanisms involved, which may ultimately lead to the application of these specific ions in surface nano-engineering.
The choice of the partners is straightforward: the Vienna group is expert on surface characterization in particular with AFM, and has especially done ground-breaking work on interactions with slow, extremely highly charged ions with surfaces; whereas the Caen group has due to the GANIL facility, a large range of ions at their disposal, from eV to GeV kinetic energy. The French group is specialist on TEM measurements, and has done ground-breaking work on grazing angle incidence with swift heavy ions. The project will be the subject of a doctoral thesis on the Vienna side as well as a study by a post-doctoral fellow on the Caen side. Results will be disseminated on conferences and in international, peer reviewed publications.