Project Objectives

The goal of the project is to find new knowledge based on experimental study of the time evolutions of radiation damages induced by energetic (MeV) ion beams. The focus is on studying:

1. influence of electronic stopping and related nanostructuring of materials by ion track methodology using swift heavy ions;
2. influence of nuclear stopping to radiation damage and amorphization in crystals, including materials of interest for future fusion reactors;
3. charge transport properties in crystalline materials, focusing on novel semiconductor materials for radiation detection

(i)influence of electronic stopping and related nanostructuring of materials by ion track methodology using swift heavy ions

Wide variety of ion beams in terms of both ion species and ion energy which can be delivered from 6 MV Tandem Van de Graaff accelerator at RBI will be used for materials modifications. 2 MeV protons, He (when available) and Lithium from 1 MV Tandetron accelerator will be used for monitoring ion track formation kinetics using RBS/c. In-situ analysis of ion track formation using RBS/c on the existing dual-beam chamber and ex-situ experiments elsewhere will be performed.

The investigation of ion tracks in SrTiO₃ will be extended to other wide band gap semiconductors like TiO₂ and GaN, since observed inconsistencies in description of ion tracks in SrTiO₃ with commonly used thermal spike models could provide clues to more accurate description of their formation. Potential material of interest could be CaF₂ whose investigation should provide answers to hotly debated topic on velocity effect in this material. SiO₂ quartz could be used for testing purposes, in order to demonstrate effectiveness of our proposed set-up and to quantify damage due to probing RBS/c beam. Finally, heavy ion particle induced X-ray emission (PIXE), especially in high-resolution mode, can provide additional information on ionization of the matter during passage of SHI. That information could be useful for understanding ion track formation processes. SiO₂ is natural choice for such study because its low value of threshold for ion track formation would enable to study different combinations of ion species and energies in order to produce ion tracks in this material.

All the above could be extended with use of facilities from our collaborators. In particular, selected samples can be irradiated using swift heavy ion beams at GANIL and highly charged ion beams at University of Duisburg-Essen. Complementary measurements, in particular ex-situ AFM are planned using existing AFM set-up at RBI. Also, in case of difficulties, or in case of interesting findings, high resolution AFM on selected samples can also be done at University of Duisburg-Essen. Additionally, structural data on ion tracks on surfaces and in the bulk can be obtained using GISAXS and TEM techniques, respectively. Swelling of the samples can also be investigated using profilometry. Optical properties of the ion irradiated materials can be probed using spectroscopic ellipsometry technique.Obtained experimental data will be treated using existing thermal spike models.

(ii) influence of nuclear stopping to radiation damage and amorphization in crystals, including crystalline and functional materials of interest for future fusion reactors;

We will study channeling implantation by MeV ions in selected materials using ion axial channeling effect. Channelling implantation profiles will be studied by means of ion channelling spectra in the backscattering geometry, and PIGE, NRA, PIXE and SEM as needed. This will be an effort in continuation to our first channelling experiments performed recently on silicon.

These experiments will also help us to establish the capability to conduct dual-ion irradiations that capture the key elements of the fusion neutron spectrum, estimate micro-structural changes in selected irradiated material of interest for fusion energy by channelling/random RBS/PIXE/PIGE, IBIC and SEM/TEM analyses and describe (experimental and/or computational) development and evolution of micro-structural changes in irradiated material in dependence on ion species, energies and doses. Combined effects of nuclear and electronic stopping will be identified by comparing dual-beam irradiation results with single-beam irradiation ones keeping all the parameters (temperature, energies, and fluxes) identical in the different experiments for the same irradiated material.

(iii)Charge transport properties in crystalline materials, focusing on novel semiconductor materials for radiation detection

Within this objective it has been planned to use dual beam scattering chamber in such a way that one ion beam will be used as a damaging beam, while the other one with the ion beam current reduced to approximately 1000 ions/sec will be used to probe the changes in electronic transport by IBIC measurement to extend knowledge about the radiation defect kinematics that could be important to other uses of materials like for example diamond and SiC. The nature of electric field polarisation is another effect that will be possible to explore with this approach. In order to be able to extract basic parameters of charge carrier transport in relationship to all parameters that will be varied (including materials) modelling of charge transport response will have to be used.

Funding Agency

Hrvatska zaklada za znanost (HRZZ) – Croatian Science Foundation