Large electronic sputtering yield of nanodimensional Au thin films: Dominant role of thermal conductivity and electron phonon coupling factor

Abstract

Detailed experiments and theoretical calculations on electronic sputtering of Au thin films (5-200 nm) on a quartz substrate are performed, revealing unusually large electronic sputtering, dependent on the thickness of the films. The dependence of electronic thermal conductivity (κe), electron-phonon coupling factor (g), and lattice thermal conductivity (κa) on the effective electron mean free path is taken into account in the thermal spike calculation for nanodimensional systems to elucidate the combined effect of the thickness and grain size on the electronic sputtering yield. The thermal spike simulation with refined parameters for nanodimensional systems gives a better explanation of the electronic sputtering process with a very good correlation between the experimental and theoretical yields than that of the thermal spike model with bulk parameters.

Sputtering of bismuth thin films under MeV Cu heavy ion irradiation: Experimental data and inelastic thermal spike model interpretation.

“…It was interpreted to be caused by a rapid degradation of the Au films due to the same ionization mechanism as that occurring when fission fragments form tracks in discontinuous metallic films, followed by a stabilization of the target erosion due to ionization‐induced cracking of hydrocarbons. Also, similar sputtering yield trends were recently reported for the same target material with different thicknesses (up to 200 nm) and grain sizes under the impact of 120‐MeV Au and Ag ions . They were explained in terms of the i‐TS model by considering an enhanced electronic scattering from the grain boundaries on the film surface that induce drastic changes in their electrical and thermal transport proprieties …”

“…These correlated behaviors were explained by inelastic electronic collision mechanisms mainly taking place within the Bi material electronic stopping power regime below the threshold (S e ~24 keV/nm for Bi) for latent track formation . These interaction mechanisms are linked to the material specific intrinsic proprieties, such as the film thickness and the grown grain size or those connected to its thermal transport proprieties that suffer drastic changes under ion irradiation caused by deposited large electronic energy density confined in a nanometer‐sized volume close to the Bi film surface …”

MeV irradiation of tungsten nanowires: structural modifications

“…Since electrons are confined due to finite size, an increase in surface scattering processes is expected. Hence, a larger e-ph coupling is expected as seen in recent experiments in metallic nanofoams [13] and thin films [14], but it is not clear how much compared to bulk. Also, studies [15,16] show a dependence of the electron thermal conductivity with the diameter of the NW.…”

Electronic heat transport versus atomic heating in irradiated short metallic nanowires

“…Although these values are relatively well known, those for nanostructures could be very different. Values up to 20g, with g the bulk value for the e-ph coupling, have been used to explain experiments in Au thin films [60]. Laser irradiation of metallic foams is still poorly understood, since the behavior of the electronic system after irradiation may deviate from that of a bulk metal.…”

“…For example, since electrons are confined to the nanostructure, an increase in surface scattering is expected; thus e-ph coupling should change but it is not clear how much or how compared to bulk. Recent experiments show an increase in e-ph coupling in metallic nanofoams [59] and thin films [60]. In addition, studies [61,62] show that the electron thermal conductivity depends on NW diameter due to the geometrically restricted electron motion.…”