H. Eder

Electron emission from clean gold bombarded by slow Auq+ (q=1–3) ions

Total electron yields for impact of slow singly, doubly, and triply charged gold ions on a clean polycrystalline gold surface have been precisely determined via current measurements for incident ions and emitted electrons. Results of this study are of relevance for a proposed method to establish a new mass standard by determining atomic mass via accumulation of ions to amounts that can be weighed with high accuracy.

Search for projectile charge dependence of kinetic electron emission from clean polycrystalline gold

Abstract Total yields for ion-induced electron emission from atomically clean polycrystalline gold have been measured accurately (total errors ⩽±5%) for normal incidence of C q + ( q ⩽5)-, N q + ( q ⩽6)-, O q + ( q ⩽7)- and Ne q + ( q ⩽9) ions with impact velocities from below 10 5 m/s (exclusive potential emission/PE regime) up to 10 6 m/s (5 keV/amu). Contribution from kinetic emission (KE) to these total yields was studied by taking into account the respective PE yields and precise determination of the KE impact velocity threshold for corresponding singly charged ions. For given ion species Z 1 and impact velocity we have investigated whether KE yields depend on the ion charge state q . From q =1 toward 3 a slight decrease with q has been found, but there are no significant differences in KE yields at higher q values. Results are discussed in view of the q -dependence for relevant KE mechanisms.

Precise total electron yield measurements for impact of singly or multiply charged ions on clean solid surfaces

Total electron yields γ for impact of singly or multiply charged ions (H+, He+, He2+, N3+, N4+, O5+, O6+) on clean polycrystalline gold have been accurately measured at impact energies from almost zero [exclusive potential emission (PE) range] up to 40 keV times projectile charge state q (dominant kinetic emission range). Impact energies above 10 q keV have been approached by postacceleration of ions via target biasing with up to −30 kV. Total electron yields for γ⩾3 have been derived directly from the related electron number statistics (ES) with total experimental errors of ±3%. Smaller values of γ have been determined from the related ES in conjunction with measurements of the respective primary ion, and ejected-electron currents, which caused somewhat larger experimental errors of typically ±5%. At higher impact velocity discrepancies arise between results from ES-based and current-based measurements of the total electron yield, respectively, because of systematic errors of the latter method due to pro...

Excitation of plasmons by impact of slow ions on clean mono- and polycrystalline aluminum

Low-energy electron spectra have been measured for impact of slow (⩽10 keV) H+, H2+, He+, Ne+, Ne2+, Ar+ and Ar2+ ions on atomically clean poly and monocrystalline aluminum surfaces. In these spectra broad peaks at 11 and 6.6 eV result from one-electron decay of Al bulk and surface plasmons, respectively. Their relative intensity has been studied for different angles of ion incidence and electron emission. “Direct” or “potential” excitation of plasmons can take place if the available ion neutralization energy Epot exceeds the sum of plasmon energy (15.3 and 10.9 eV for bulk and surface plasmons, respectively) and Al work function (4.3 eV). At our experimental conditions excitation of bulk plasmons was considerably stronger than of surface plasmons. Potential excitation of bulk plasmons shows a quasi-resonant dependence on Epot and is not significantly more important for multiply than for singly charged ions. With too small potential energy plasmons can only “indirectly” be excited by fast electrons from concomitant kinetic emission. For proton impact on Al(1 1 1), structures in the electron spectra which have earlier been ascribed to plasmon excitation are here explained by diffraction of electrons from kinetic emission which undergo multiple scattering in the uppermost surface layers before escape.

Kinetic electron emission in the near-threshold region studied for different projectile charges

Abstract Total yields for ion-induced electron emission from atomically clean polycrystalline gold have been measured with an accuracy of ≤ ±5% for normal incidence of C q + ( q ≤ 5), N q + ( q ≤ 6), O q + ( q ≤ 7), and Ne q + ( q ≤ 9) at impact velocities from the exclusive potential emission (PE) regime up to 10 6 m/s (≈5 keV/amu). The contribution by kinetic emission (KE) to these total electron yields, which is commonly assumed as independent of projectile charge, can be estimated by subtracting the respective PE contribution after precise determination of KE impact velocity thresholds for the corresponding singly charged ions. At given projectile atomic number and impact velocity we have searched for a possible q dependence of the KE yield. For 1 ≤ q ≤ 3 the KE yields decrease slightly with increasing q , whereas no significant q dependence could be found for higher charged ions. These results are discussed by regarding the q dependencies of two different mechanisms which are believed to be relevant for KE.

Evaluation of skyline algorithms in PostgreSQL

In this paper, we present our work on evaluating the skyline algorithms BNL, SFS, and a variant of LESS in PostgreSQL. It is well known that the performance of skyline queries is sensitive to a number of parameters. From extensive experiments on skyline implementations we have discovered several rules, which are remarkably simple and useful, but hard to obtain from theoretical investigation. Our findings are beneficial for developing heuristics for the skyline query optimization, and in the meantime, provide some insight for a deeper understanding of the skyline query characteristics.

Projectile charge dependence of kinetic electron emission from clean gold

Total electron yields for impact of H+, He+, He2+, C5+, N+ ÷ N6+, O5+ and O6+ on clean polycrystalline gold up to impact energies of 40 keV times the projectile charge have been determined from both the related electron number statistics and the respective ion- and ejected electron currents. The results depend on the amount of projectile potential energy deposited until close surface contact as well as on potential- and kinetic projectile energies deposited below the surface. The first contribution can be satisfactorily explained by the classical over-barrier model for potential electron emission. The second contribution results mainly from kinetic electron emission which involves nonlinear screening of the projectile-configuration dependent interaction with the metal electron gas.