Indications for Enhanced Auger-Electron Absorption in a Hot-Electron Gas

Abstract

Solid-state Auger-electron angular distributions are known to be largely independent of the type of excitation, following roughly a cosine law for low ejection energies. In this Letter it is shown that the iontrack dynamics and the corresponding high electron temperatures lead to significant variations of these Auger distributions. Ratios for different degrees of inner-shell ionization versus angle are sensitive to the high-energy-deposition density. The ratios show a minimum for emission angles close to the ion-track direction, consistent with enhanced inelastic electron-energy losses or electron absorption, respectively. Thus Auger-electron yields are influenced by the spatial electronic excitation distribution. DOI: 10.1103/PhysRevLett.99.197602 PACS numbers: 79.20.Rf, 34.50.Bw, 72.15.Lh, 79.20.Fv Hot electrons play an important role for the heat transport inside highly excited materials by laser or ion bombardment as well as in other areas such as in degenerate cores of white dwarfs and giant stars [1]. In fact, the nonequilibrium electron temperatures determine the charge-state dynamics of ions in the solar wind [2] as well as the dynamics in tokamak plasmas [3]. Furthermore, the influence of the electron temperature on the behavior of clusters, plasmas, solids, and solid-state surfaces excited by high-power short-pulse lasers is the subject of intense research worldwide. There is rapidly growing knowledge not only on the corresponding materials modification [4] but also on the primary electron temperature [5] and on ejected electrons [6] and ions [7]. The trend towards short-pulse x-ray lasers [8] shows that high-power laser beams and laser-solid interaction processes [9] are approaching the time resolution, spatial resolution, and mean energy transfer of individual swift heavy ions interacting with solids. Ions (lasers) transfer 50% (nearly 100%) of their energy via dipole transitions during an interaction time of 10 ÿ18 to 10 ÿ17 s (10 ÿ15 to 10 ÿ13 s) within a nm spot for a single ion (a m spot for a laser beam of similar power density). Both types of radiation, fast heavy ions and high-power lasers, are complementary laboratory sources and probes of nonequilibrium processes driven by strong electronic excitations.So far, electron temperatures in ion-solid interactions have been measured using only high-resolution spectroscopy of Auger electrons, resulting from the decay of target inner-shell vacancies in the central ion-track region. Most quantitative determinations are based on the high-energy slopes of Auger structures induced by incident ions in comparison with those resulting from incident electrons as a (virtually asymptotic) low-temperature reference. Using different Auger lines, these data yield snapshots of the time evolution of the solid a few 10 ÿ15 s after the rapid electronic excitation. Contrary to most lattice-modification studies, such investigations allow for a clear distinction of track-formation mechanisms [10].The pathways of the relaxation of high ionization densities inside sol...

Laser-pump/X-ray-probe experiments with electrons ejected from a Cu(111) target: space-charge acceleration

“…At high electron temperatures (high laser-excitation power density) additional excitation channels open up (Arista & Brandt, 1984), but enhanced electron screening leads to an all-over reduction of inelastic transition rates and a corresponding enhancement of self-consistent inelastic lifetimes in a free electron gas (Echenique, 2007). For fast electrons in materials with an electronic gap or also at high electron temperature, this may be different (Schiwietz et al, 2007).…”

Search for short-time phase effects in the electronic damage evolution – A case study with silicon

“…The electron temperature influences the populated electronic density-of-states and hence, the initial Auger-electron source-spectra [12][13][14]16]. The electron temperature leads also to an enhanced absorption of Auger electrons during their transport to the surface and modifies the corresponding Auger angular distribution [17]. The nucleartrack potential resulting from ionization and charge separation in the ion track, leads to decelerated convoy electrons [11,12] and Auger electrons [9,10,12].…”

Swift heavy ion induced structural evolution in InP

“…(9), simulation requires the values of t 0 (deposition time) and r 0 (the radius of the cylinder in which the nuclear energy is deposited). It is generally accepted that the atomic motion of the target atoms on SHI irradiation occurs on a time scale of 10 À13 e10 À12 s [43]. Also, the lifetime of a collision cascade in an SHI irradiation is about~1e5 Â 10 À13 s [44].…”

“…attained [43]. The electronic energy loss ε e is proportional to the square of the charge state [28].…”