Formation of excited states of atoms and ions in laser plasma from CuInS2

Abstract

Emission spectra and the energy distribution of the excited-state population density of atoms and ions in erosion laser plasma from CuInS 2 with various crystal-structure orderings are analyzed. It is shown that increased ordering of the target crystal structure causes the excited-state energies of indium atoms generated in the laser erosion plume to increase and that sulfur atoms always emit only in transitions from highly excited states. The ratio of relative ion concentrations in the laser plasma plume is Cu + /In + /S + = 0.3/0.08/2, which corresponds neither to the atomic ratio of Cu/In/S (1/1/2) in the target nor to the ratio of ionization energies. The results are explained by recombination processes for ions and by the atomization specifics of the CuInS 2 target exposed to long-wavelength radiation. The atomization consists essentially of dissociative processes expressed by CuInS 2 → CuInS + S and CuInS 2 → Cu + InS + S. The electron temperature of polycrystal (single-crystal) plasma at a distance of 1 mm from the target is 0.3 eV (0.4 eV) for atoms and 1.3 eV (2.7 eV) for ions and varies negligibly for plasma up to a distance of 7 mm from the target.Key words: erosion laser plasma, emission spectroscopy, excited-state population densities of atoms and ions, electron temperature, atomization of CuInS2 target. Introduction.Laser spectral analysis is one of the most common and reliable methods for finding the qualitative and quantitative compositions of matter [1]. The principal difficulties and therefore potential for increasing the information value of emission analysis of plasma produced by laser ablation of multi-component targets are explaining the atomization specifics of the target [1], forming excited states of atoms and ions [2], and knowing the space-time evolution of the laser plasma plume [3].The amount of various atoms vaporized from a target of a multi-component alloy can be found by knowing the fundamental thermal physical characteristics of the separate elements in the alloy. Thus, a coefficient normalizing the intensity ratio of diagnostic spectral lines for atoms of the various elements can be calculated in order to determine the stoichiometric ratio of these elements in the target [4]. Spectroscopic analysis for a multi-component chemical compound is complicated because of, first, specifics of the destruction of chemical bonds where, as shown previously [2], selective removal of ions from the surface of ionic crystals is possible through the action of laser radiation; second, the presence of many methods for destroying molecules, which the laser parameters facilitate [5]; and third, possibilities for chemical reactions on the surface of a multi-component target and in its vapor, especially with incoherent melting where the compound is separated into several phases of different compositions [6]. It was concluded [5] that Rydberg molecular states are formed through breakdown of molecular vapor by laser radiation. The decomposition of such molecules and their ionization and recombination det...