arXiv subjects

Eleni Ntemou

Publications and source records attributed to Eleni Ntemou.

3 recordsLinked to original sources

arXiv2026

Charge-State Dependence of Electronic Excitations in keV Ions Transmitted Through Solids Probed by Ion-Photon Coincidence Measurements

Investigating the electronic excitations caused by light keV ions in matter contributes to a better understanding of materials modification such as space weathering or plasma-wall interactions in fusion reactors as well as improved materials analysis methods such as low or medium energy ion scattering. This study investigates the dependence of specific excitations in keV He projectiles, the most common projectile employed in these analytical methods, on the kinetic energy of the ion. We report on photon emission at energies >10eV emitted by projectiles excited upon transmission through different sample systems. We separate exit charge states and report on measurements of ion-photon pairs in coincidence, i.e. we can link a photon to the specific ion emitting it. From these measurements we extracted charge state resolved photon yields and obtained a deep insight into the electronic excitation occurring. Our results show that the electronic excitation of the helium projectile is largely material independent and rising strongly with the kinetic energy of the projectile. The photon yields are in good agreement with a common excitation model initially developed for beam foil spectroscopy. We hence extend the validity of this model to higher photon energies and different sample materials. We further provide a detailed analysis of the employed coincidence approach and necessary corrections to the raw data, as the methodology has a broad applicability in fundamental research and materials analysis.

cond-mat.mtrl-sci↗

arXiv2024

Charge state dynamics of keV ions in solids

Fast dynamic processes between electrons in solids and a foreign atom represent a fundamental challenge for describing interactions in many-body systems and are a prerequisite for modelling materials modification. We experimentally determined the charge state distributions of slow He and Ne projectiles after transmission through thin single-crystalline silicon membranes. We found strong differences in velocity scaling and magnitude of the mean charge along different characteristic particle trajectories, providing direct insight on electron promotion and transfer processes inside the solid. Calculations of characteristic trajectories confirm the frequent spatial and ultrafast temporal accessibility of excitation channels commonly considered characteristic for large angle collisions. The commonly observed excess in energy deposition in amorphous targets compared to channelling trajectories and ab-initio calculations can thus be unambiguously linked to energy dissipation in frequent electron promotion as well as increased ionization density along the trajectory, driven by increased mean charge states. A quantitative comparison of energy loss and observed mean charge states further indicates complex deexcitation mechanisms at large interatomic distances masking the true equilibrium charge states along random trajectories.

cond-mat.str-el↗

arXiv2024

The influence of geometry and specific electronic and nuclear energy deposition on ion-stimulated desorption from thin self-supporting membranes

We investigate the dependence of the yield of positive secondary ions created upon impact of primary He, B and Ne ions on geometry and electronic and nuclear energy deposition by the projectiles. We employ pulsed beams in the medium energy regime and a large position-sensitive, time-of-flight detection system to ensure accurate quantification. As a target, we employ a single crystalline Si(100) self-supporting 50 nm thick membrane thus featuring two identical surfaces enabling simultaneous measurements in backscattering and transmission geometry. Electronic sputtering is identified as the governing mechanism for the desorption of hydrogen and molecular species found on the surfaces. Nevertheless, larger energy deposition to the nuclear subsystem by heavier projectiles as well as due to the directionality of the collision cascade appears to act in synergy with the electronic energy deposition leading to an overall increase in secondary ion yields. A higher yield of ions sputtered from the matrix is observed in transmission geometry only for B and Ne ions, consistent with the observed role of nuclear stopping.

physics.chem-ph↗