Ion Impacts in Real-Time (time4ions)

Exploring the ultrafast dynamics of electronic and atomic motion in a violently disturbed surface after heavy ion impact is the goal of this project. With an ultrafast ion source - the first of its kind - we will produce ion pulses with an unprecedented timing precision of sub-picoseconds. Using the powerful pump-probe technique, where a laser pulse and the ion pulse hit a solid surface with a very short and adjustable time delay allows us to follow the electronic and atomic dynamics in the surface directly after the ion impact by taking snapshots one at a time. Under the conditions of an ion impact many surface atoms are kicked out of their original positions and subsequent scattering leads to a local melting of a small surface volume. How this melting proceeds, how large the molten surface volume is and how quickly it cools down, is currently unclear. For ever smaller structures in semi-conductor devices tailored with ion beams, knowledge about the transiently affected volume and related processes such as enhanced atom diffusion, is crucial. In fact, for the ultimately thin 2D materials, direct ion beam implantation turns out to be very challenging and the deliberate introduction of defects will be very useful in technology. However, 2D materials behave completely different under ion impact when used as freestanding sheets or when placed on a substrate. This is due to dense cascade of moving atoms in the substrate after ion impact and additional damage produced by the cascade atoms. Getting direct experimental access to the atomic dynamics in the surface and layer substrates will help us in tailoring material properties with ion beams. Before we get there, fundamental research with the first experimental approach for true timing-resolution with ion beams will be done in this project. The flexibility of the pump-probe techniques also allows to turn the tables and use the ion pulse as a probe for a highly non-equilibrium surface. Now the laser plays the role of a pump, pushing electrons in the surface out of their equilibrium state. The interaction of ions with an optically excited solid is very important for astrophysical processes, where ions travel even through highly ionized plasmas in our sun. Since the laser pumped state of the surface decays quickly, the ions must arrive shortly after the laser pulse, again only possible with an ultrafast ion source.