Spin labelling techniques, specifically the use of electron-spin-polarized He(23S) metastable atoms coupled with energy-resolved spin analysis of the ejected electrons, are used to investigate the dynamics of He(23S) deexcitation at solid surfaces. Data for a clean Au(100) surface are presented that show that deexcitation occurs exclusively through resonance ionization followed by Auger neutralization. The electrons involved in Auger neutralization are observed to be correlated in spin and possible reasons for this are discussed. Results obtained at Xe and NO films adsorbed on cooled Au(100) and Cu(100) substrates, respectively, show that He(23S) metastable atom deexcitation is analogous to gas-phase Penning ionization. Detailed differences are apparent that can be attributed to effects associated with the underlying substrate and interactions involving neighboring atoms in the film.

Spin labelling techniques, specifically the use of electron-spin-polarized He(2 S-3) metastable atoms coupled with energy-resolved spin analysis of the ejected electrons, are used to investigate the dynamics of He(2 3S) deexcitation at solid surfaces. Data for a clean Au(100) surface are presented that show that deexcitation occurs exclusively through resonance ionization followed by Auger neutralization. The electrons involved in Auger neutralization are observed to be correlated in spin and possible reasons for this are discussed. Results obtained at Xe and NO films adsorbed on cooled Au(100) and Cu(100) substrates, respectively, show that He(2 3S) metastable atom deexcitation is analogous to gas-phase Penning ionization. Detailed differences are apparent that can be attributed to effects associated with the underlying substrate and interactions involving neighboring atoms in the film.

Measurements of ejected electron energy distributions are used in conjunction with electron spin labeling techniques to probe the mechanisms by which He(2(3)S), He(2(1)S), and He(2(3)P) atoms are deexcited at Ar and Xe films adsorbed on a cooled Cu(100) substrate. The data for both surfaces contain features similar to those observed in gas-phase Penning ionization, indicating that ejection results, in part, from Auger deexcitation, i.e., surface Penning ionization. For Xe, however, additional features are observed that can be attributed to resonance ionization of an incident excited atom followed by neutralization of the resulting He' ion through an interaction that involves neighboring Xe atoms in the film. Indeed, the Xe data provide an exceptional example of a surface at which Auger deexcitation and resonance ionization occur in parallel with one another, with a branching ratio that changes significantly as the internal energy of the incident atoms increases. The ejected electron yield from both Ar and Xe films is substantially higher than for clean Cu(100), indicating that such films might form the basis of an efficient thermal-energy helium metastable-atom detector.

Spin labeling techniques are being used to investigate the dynamics of metastable atom deexcitation at surfaces. A beam of thermal-energy electron-spin-polarized He(2{sup 3}S) atoms is directed at the surface, and the energy and polarization distributions of the ejected electrons are measured. At clean, high work function metal surfaces He(2{sup 3}S) deexcitation proceeds via resonance ionization of the incident atom followed by Auger neutralization of the resulting He{sup +} ion. The data show that the electrons involved in the neutralization process tend to have antiparallel spins. This spin correlation may be explained in terms of modifications to the local surface electronic structure due to the presence of the He{sup +} ion, and efforts are underway tb model such effects theoretically. Measurements on surfaces comprising several monolayers of Xe frozen on a cooled substrate show features analogous to those observed in gas-phase Penning ionization, suggesting that electron ejection occurs, in part, through Penning ionization of adsorbed atoms. Other features, however, are apparent and can be attributed to interactions with neighboring atoms and to effects introduced by the substrate. These features are being explored further using He(2{sup 1}S) and He(2{sup 3}P) atoms and substrates with different work functions.

Spin labeling techniques, specifically the use of electron-spin-polarized He(2 3S) metastable atoms coupled with energy-resolved spin analysis of the ejected electrons, are used to investigate the dynamics of metastable atom deexcitation by molecules in a film several monolayers thick condensed on a cooled Cu(100) surface. Data for CO2, H2O, Cl2, and O2 films show that metastable deexcitation is analogous to gas-phase Penning ionization, i.e., the condensed molecules can be considered as a ‘‘solid gas.’’ Detailed differences are, however, evident that can be attributed to the presence of neighboring molecules. Data for C60 films are also presented which suggest the possibility of plasmon excitation as is observed in photoionization and electron energy loss data.

Spin-labelling techniques, specifically the use of electron-spin-polarized metastable atoms in conjunction with spin analysis of the ejected electrons, are used to probe the dynamics of metastable atom-surface interactions. Studies of clean and adsorbate covered metallic, semiconductor and insulating surfaces show that the electron ejection processes are more complex than suggested by conventional models of metastable atom deexcitation at surfaces and that effects such as secondary electron production, inelastic spin-flip scattering, and perturbation of the incident atom by the surface must also be considered.

A technique for absolute calibration of a Mott polarimeter is described that makes use of electrons of accurately known polarization obtained through surface Penning ionization. This approach provides higher count rates and lower uncertainties than obtained in earlier measurements based on gas-phase Penning ionization.

A novel technique for absolute calibration of a Mott polarimeter is described that make use of electrons of accurately known polarization obtained through chemiionization reactions involving spin polarized He(2 (3)S) metastable atoms. This technique has been used to calibrate a compact retarding-potential Mott polarimeter and values of the effective asymmetry (Sherman) function S(eff) are presented for both gold and thorium target foils under a variety of operating conditions.