The basic principle of the nanotechnology is that we try to change the behaviour of a material at the nanometric scale, in our case with the ions. This can even be to change few atoms. In this study, the ions are a very useful tool as we can put an enormous amount of energy in the material. In the past, a lot of studies have concerned what was happening inside the material, if the tracks caused by the irradiations could be revealed by chemical attacks. For example, if we irradiate polymers with heavy ions, we have tracks of the break-ups of the links of the polymers. We can perform chemical attacks on these tracks and produce porous membranes with holes of few nm of diameter. These pores can be functionalized or filled to create nanowires.

        CIRIL is an interdisciplinary laboratory that exists since the beginning of the 80’s. These last years, new collaborations appeared around the study of what is happening at the surface of the material. It means to look at the topology of the surface. When we look at the surface of the material, we sometimes see effects that are very deep in the material. For example, we have chosen to perform interactions at very grazing angles, very close to the surface. Between the surface and the incident angle, we went down to 0.3°. We see effects that are usually hidden in the material and that are visible at the surface.

        We can now produce strings of bumps on the surface. We want to better understand how they are created and on which materials. We have begun with the strontium titanate that is used as a substrate for the supraconductors. For pure silicon, all the previous studies showed that it is difficult to damage it by energy loss in the material. We would like to try it as our next experiment, purely in situ. Until now, because of the complexity of the accelerator, we studied our samples weeks after the irradiation. Of course, as soon as we break the vacuum, all sorts of reactions are possible with the atmosphere. To have our observation tools, like the microscope, near the sample, under vacuum, will make a much more complicated experiment but it is essential to work in extremely clean situations. It will also give a lot of new and interesting results.

        For the moment, we do not use at all radioactive beams in our research. The thermal spike model that is currently used because it gives quantitative results, predicts that around a track, the material is liquefied or even vaporized. If it is so, there is a material transportation from the inside to the outside of the material. If we deeply implant radioactive markers with SPIRAL or SPIRAL2, we may see this effect. We still have problems preparing clean surfaces and it will take a few years to reach this level. Therefore we did not contribute to the famous “white-blue” book of SPIRAL2.

More info:
    Henning Lebius's e-mail
    Interdisciplinary sciences session


Words collected by K. Turzó at the XV^e Colloque GANIL, Giens, France, from May 29^th to June 2^nd, 2006.