Contamination of a beam of metastable helium atoms by fast neutral atoms: Characteristics of the secondary emission of these atoms at low energy (100 eV) in interaction with the surface of a solid

Abstract

The use of a time of flight technique reveals the contamination of a beam of metastable helium atoms with thermal kinetic energy by fast atoms in the ground state. The γ secondary emission coefficient of these fast atoms striking a solid target is demonstrated at energies as low as 30 eV. On a metal surface γ 0 varies in proportion to the coverage rate during adsorption of a gas such as O 2. An explanation of this dependence is suggested within the framework of the Fano- Lichten-Barat theory, which requires strong localization of the electrons which can be excited in the collision. The electron emission due strictly to metastable atoms is interpreted suitably within the two existing models: Auger neutralization and Auger de-excitation.