Measurements of the population partitions and state-selected flight-time distributions of keV ion-beam-sputtered metastable atoms - art. no. 195417

摘要

A sensitive and generally applicable experimental procedure to determine the relative population on different quantum states of free metastable atoms is presented. The atoms are both element and state-selectively ionized using highly efficient double-resonant two-color two-step laser ionization. Population partitions can be quantitatively measured, by extending the procedure to include all metastable states. In combination with a pulsed atom source, state-selective flight-time distributions can be measured. Such experiments allow one to evaluate the kinetic energy of the released atoms. The methodology is demonstrated and fully commented with the measurement of the population partition of gas-phase atoms released from a hot Ni filament. A systematic study of the emission of neutral atoms during 15 keV Ar+ sputtering of clean polycrystalline Co and Ni foils is reported, illustrating that sets of population partitions and flight-time distributions can be obtained with the presented experimental procedure. The combined interpretation of the experimental evidence allows one to qualitatively model the emission of excited atoms during sputtering of metals as the result of a multichannel electron transfer process. In this model, a sputtered particle escapes from the surface as a positive ion and becomes neutralized into an atomic state by resonant transfer of an electron from the valence band of the metal. The velocity-dependent population of a particular state is governed by the correspondence of the electronic configuration of the atomic state with the bulk electronic configuration. [References: 61]