Analysis of the fine structure ofSn11+–Sn14+ions by optical spectroscopy in an electron-beam ion trap

Abstract

We experimentally re-evaluate the fine structure of Sn 11+...14+ ions. These ions are essential in bright extreme-ultraviolet (EUV) plasma-light sources for next-generation nanolithography, but their complex electronic structure is an open challenge for both theory and experiment. We combine optical spectroscopy of magnetic dipole M 1 transitions, in a wavelength range covering 260 nm to 780 nm, with charge-state selective ionization in an electron beam ion trap. Our measurements confirm the predictive power of ab initio calculations based on Fock space coupled cluster theory. We validate our line identification using semi-empirical Cowan calculations with adjustable wavefunction parameters. Available Ritz combinations further strengthen our analysis. Comparison with previous work suggests that line identifications in the EUV need to be revisited. arXiv:1605.04236v1 [physics.atom-ph]

Extreme ultraviolet spectra of multiply charged tungsten ions

“…The similar inconsistency is also found in the previous Livermore EBIT spectra, where they observed W 6+ (65 eV required) lines at 43 eV and W 7+ (122 eV required) lines at 72 eV. Ionization from metastable excited states [18,19] may account for this inconsistency. Indeed, our CR model calculations on W 6+ and W 7+ indicate that the metastable states with an energy of ∼ 40 eV can have a population comparable with or even larger than that of the ground state.…”

Resonance Transitions in the Spectra of the Ag6+–Ag8+ Ions

“…It was found by extrapolation to Sn XIII that the identification of this spectrum should be revised. Similar conclusion was made after the identification of the M1 transitions between the levels of ground-state configurations in Sn XIII and other ions with open 4d-shell [23]. More data on the VUV spectra of the neighboring to Sn elements are needed.…”

Optical spectroscopy of complex open-4d-shell ionsSn7+–Sn10+

“…After each acquisition the electron beam acceleration potential was increased by 10 V, stepping from 137 V to 477 V at a constant beam current of 10 mA. This low current gives rise to a modest space-charge potential correction of approximately 25 V [16,36]. The chosen range of the acceleration potential enabled the production of charge states from Sn 7+ up to at least Sn 14+ [16].…”

“…This low current gives rise to a modest space-charge potential correction of approximately 25 V [16,36]. The chosen range of the acceleration potential enabled the production of charge states from Sn 7+ up to at least Sn 14+ [16]. After each energy scan the grating was rotated to measure an adjacent wavelength range while keeping a certain overlap.…”