Electron spin-labeling techniques, specifically the use of electron-spin-polarized He+ ions coupled with energy-resolved measurements of the ejected electron polarization, are used to probe the dynamics of low-energy (≲60 eV) He+ ion neutralization at a magnesium surface. Analysis of the polarization data indicates that incident ions undergo Auger neutralization. However, inelastic scattering and secondary electron production in the bulk also provide important contributions to the ejected electron signal at low electron energies. The measurements provide no evidence that excitation of multipole surface plasmons leads to significant electron emission.

Spin labelling techniques, specifically the use of electron-spin-polarized He+ ions coupled with measurements of the ejected electron polarization, are used to examine the dynamics of transient He−* (1s 2s2) ion formation at an Al(100) surface with a submonolayer coverage (Θ=0.15) of potassium. The data show that, contrary to some earlier suggestions, the He−* ions are created by a two-step process in which the incident He+ ions are first neutralized by resonant tunneling of an electron from the surface into the 2s orbital. A second electron is then captured into the 2s orbital to form the He−* ion.

Measurements of the energy distributions and energy-resolved polarizations of electrons ejected by incident polarized He+ ions are used to probe the dynamics of He+ ion neutralization at clean Al(100), Au(100), and Cu(100) surfaces for incident ion energies in the range 10-500 eV. The results are interpreted using recent theory and suggest that neutralization occurs at typical atom/surface separations of similar to2-3 a.u., significantly smaller than those inferred from earlier experimental studies of ion scattering and ion neutralization at surfaces. Close to the surface strong short-range repulsive interactions become important and lead to increases in the maximum energy of the ejected electrons and to a spin-dependent increase in the local density of electronic states near the Fermi energy.

The neutralization of He+ ions at a solid CO2 surface is investigated by analyzing the energy distribution of electrons ejected from the surface and by use of spin-labeling techniques, specifically the use of electron-spin-polarized He+ ions coupled with energy-resolved measurements of the ejected-electron polarization. The data indicate that ion impact leads to efficient electron ejection through formation of an autoionizing collision complex comprised of the incident ion and two neighboring CO2 molecules in which a significant portion of the initial kinetic energy of the ion is converted to potential energy.

Recent experiments have revealed a marked correlation in the spins of the electrons involved in Auger neutralization of (polarized) He+ ions incident on a clean Au(100) surface. A theoretical model is discussed which suggests that the experimental data can be explained by considering the perturbation in surface electronic structure induced by the presence of the ion. The factors that influence the induced density of states and its spin dependence are considered including the surface work function, the widths of the atomic levels, and the ion velocity parallel to the surface. The results indicate that comparisons between theory and experiment can provide new insights into the dynamics of ion neutralization at surfaces.

We describe the patterning of silicon by exposing a hydrogen-passivated Si(100) surface to Ar(3P0,2) metastable atoms through a fine Ni grid in the presence of a small background pressure of oxygen. Metastable atom impact leads to the formation of a uniform oxide layer that is sufficiently resistant to chemical etching to allow feature depths ≳20 nm to be realized. With optical manipulation of the incident metastable atoms, this technique could provide the basis for massively parallel nanoscale fabrication on silicon without the use of organic resists.

Recent improvements to a source of electron-spin-polarized He+4 ions based on an optically pumped, rf-excited helium discharge are described that have resulted in ion polarizations P+ of ∼0.18 at currents of ∼1 nA and in an increase of over an order of magnitude in the quality factor P+2I.

We report the use of metastable Ar(3P0,2) atoms and a physical mask to pattern octadecylsiloxane self-assembled monolayers grown directly on silicon surfaces. The damage to the monolayer is confirmed using lateral force microscopy, changes in hydrophilicity, and x-ray photoelectron spectroscopy analysis. Metastable atom exposures sufficient to uniformly damage the monolayer should allow pattern transfer to the underlying Si(100) substrate following chemical and plasma etching. With optical manipulation of the incident metastable atoms, this technique could provide the basis for massively parallel nanoscale fabrication on silicon.

Spin-labelling techniques, specifically the use of electron-spin-polarized He+ ions coupled with energy-resolved measurements of the ejected electron polarization, are used to probe the dynamics of He+ ion neutralization at Al(100), Au(100) and Cu(100) surfaces. A marked correlation in the spins of the electrons involved in ion neutralization is observed and is discussed using a theoretical model that considers the perturbation in the surface electronic structure induced by the presence of the ion. Factors that influence the ejected electron polarization such as the (unperturbed) surface electronic structure and matrix element effects are considered. The results demonstrate that comparisons between theory and experiment can provide new insights into the dynamics of ion neutralization at surfaces.

Studies using a compact retarding-potential Mott polarimeter have revealed an unanticipated source of potential systematic error that can introduce significant error in the measured polarizations. The origin of this is discussed together with a simple procedure that can be used to test for its presence.

A source of low-energy, electron-spin-polarized He+4 ions based on an optically pumped, rf-excited helium discharge is described. Ion polarizations P+ of ∼0.13 are achieved at beam currents of ∼0.1 nA, decreasing to ∼0.09 at currents of ∼0.5 nA. Ion beam energies as low as 10 eV have been realized, with an energy spread of ≲3 eV full width half maximum. The ion polarization can be reversed (P+→−P+) simply by changing the sense of circular polarization of the optical pumping radiation. The source is suitable for use in a wide variety of applications including surface physics studies.