Local spin polarization at surfaces probed by hollow atoms

Toward Probing Surface Magnetism with Highly Charged Ions

X-rays produced during collisions between Highly Charged Ions (HCI) and sample surfaces can potentially be used to investigate the surface’s magnetic properties, taking advantage of the (partial) conservation of the spin of the electrons captured by the ion during the collision. We conducted studies to characterize the X-ray detection system and to determine, with a sub-degree accuracy, the incident angle between the incoming ions and the sample surfaces. A series of proof-of-principle experiments are presented involving an Ar17+ ion beam interacting with a nonmagnetic Si sample. The obtained X-ray spectra show a significant dependency in terms of X-ray yield and energy on the ion incidence angle. These findings will be used to guide future ion–magnetic surface studies.

A low energy ion source for electron capture spectroscopy

We report on the design of an ion source for the production of single and double charged Helium ions with kinetic energies in the range from 300 eV down to 5 eV. The construction is based on a commercial sputter ion gun equipped with a Wien-filter for mass/charge separation. Retardation of the ions from the ionizer potential (2 keV) takes place completely within the lens system of the sputter gun, without modification of original parts. For 15 eV He(+) ions, the design allows for beam currents up to 30 nA, limited by the space charge repulsion in the beam. For He(2 +) operation, we obtain a beam current of 320 pA at 30 eV, and 46 pA at 5 eV beam energy, respectively. In addition, operating parameters can be optimized for a significant contribution of metastable He*(+) (2s) ions.

Time-domain ab initio study of Auger and phonon-assisted auger processes in a semiconductor quantum dot

We developed time-domain ab initio simulation of Auger phenomena, including multiple exciton generation (MEG) and recombination (MER). It is the first approach describing phonon-assisted processes and early dynamics. MEG starts below the electronic threshold, strongly accelerating with energy. Ligands are particularly important to phonon-assisted MEG, which therefore can be probed with infrared spectroscopy. Short-time gaussian component gives 5-10% of MEG, justifying rate theories that assume exponential dynamics. MER is preceded by electron-phonon relaxation to low energies.