Speaker
Description
Ultrashort ion pulses enable time-resolved investigations of ion-surface interactions on picosecond timescales. Laser-stimulated desorption (LSD) from metallic nanotips has emerged as a promising approach for generating such pulses, combining nanometric spatial confinement with strong electrostatic field enhancement. We present recent progress in the characterization and optimization of a sub-100 picosecond ion source and outline its application in a novel time-of-flight-resolved low-energy ion scattering (TOF-LEIS) experiment.
The source consists of an electrochemically etched tungsten nanotip with a tip radius between 15-100 nm, biased to +6.5 kV. Femtosecond ultraviolet laser pulses induce the desorption and ionization of arbitrarily selectable adsorbed species, producing ions with sub-10 keV kinetic energies. TOF measurements reveal pulse durations of 84 ps for hydrogen ions with intrinsic synchronization to the driving laser [1].
Utilizing charged-particle trajectory simulations with the SIMION software package [2], the experimentally observed TOF spectra were quantitatively reproduced. The simulations demonstrate that the ion pulse widths are dominated by transport-induced temporal dispersion rather than intrinsic desorption dynamics. Geometric acceptance and trajectory filtering are identified as the primary factors for determining the temporal resolution, providing clear guidelines for source optimization towards the single digit picosecond regime.
Building on these insights, we are developing a TOF-resolved LEIS pump–probe experiment that exploits the inherent synchronization between the ultrashort ion pulses and the femtosecond laser. In this scheme, laser-induced and reversible surface modifications are probed by delayed ion pulses, extracting information on transient changes in surface stoichiometry and atomistic structure.
[1] A. Redl, et al., Physical Review Research 7, 043317 (2025)
[2] D. J. Manura and D. A. Dahl, Simion software package v8.1.2 (2014)