Measurements of the population partitions and state-selected flight-time distributions of keV ion-beam-sputtered metastable atoms

Abstract

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 ϩ 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.

Odd‐Even Effects in Ion‐Beam‐Induced Desorption of Biphenyl‐Substituted Alkanethiol Self‐Assembled Monolayers

“…[15] Detailed information about the setup is available elsewhere. [33] In brief, the desorption was induced by a pulsed (500 ns) Ar + ion beam (15 keV) directed onto the sample surface at an incidence angle of 458. The experiments were performed in the static regime with a total ion fluence of about 8 10 10 ions cm…”

Influence of the atomic structure on the quantum state of sputtered Ir atoms

“…The experimental apparatus is described in detail elsewhere [6]. An ion gun directs 13-keV Ar + ions at 45°incidence onto an polycrystalline Ir foil (Goodfellow, purity 99%) located centrally in an UHV vessel with a base pressure below 3 ϫ 10 −10 mbar.…”

“…To probe the Ir atoms sputtered in the ground state and the lowest-lying metastable states, an experimental procedure based on two-color twostep resonance laser ionization was used. Details of this experimental procedure can be found elsewhere [6]. Here, we only sketch the main aspects of the ionization procedure.…”

“…Later, it was recognized that also the electron configuration of the quantum state influences to a large extent the velocity-dependent population of the different atomic states [3,4]. Recent investigations on the sputtering of atoms in metastable states from several pure transition metals showed that it in fact is the interplay between the atomic electron configuration and the bulk electron configuration of the bombarded solid that determines the final state of the ejected particles [5][6][7]. These latter investigations had in common that the ground and metastable states of the employed transition metals (Co, Ni, and Cu) have a rather simple electronic structure, i.e., the configuration interaction between atomic states is weak and the degree of level mixing is not significant.…”

Deexcitation of sputtered metastable aluminum atoms

“…A resonant electron transfer (RET) model has also been used by the Leuven group [23,26,31] to explain population partitions and velocity distributions of sputtered species. In this model, the sputtered particle crosses the metal surface as a positive ion (i.e.…”