Structural elucidation of AgAsS2 glass by the analysis of clusters formed during laser desorption ionisation applying quadrupole ion trap time-of-flight mass spectrometry.

Abstract

The structure of AgA(s)S2 glass, which has a broad range of applications, is still not well understood and a systematic mass spectrometric analysis of AgA(s)S2 glass is currently not available. Elucidation of the structure should help in the development of this material. The AgA(s)S2 glass was prepared by the melt-quenched technique. Laser desorption ionisation (LDI) using quadrupole ion trap time-of-flight mass spectrometry (QIT-TOFMS) was used to follow the generation of Ag(m)As(n)S(x) clusters. The stoichiometry of the clusters generated was determined via collision-induced dissociation (CID) and modelling of isotopic patterns. The AgA(s)S2 glass was characterised by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The LDI of AgA(s)S2 glass leads to the formation of unary (Ag+/− and As(3+)) species, 38 binary (As(n)S(x), Ag(m)S(x)), and 98 ternary (Ag(m)As(n)S(x)) singly charged clusters. The formation of silver-rich nano-grains during AgA(s)S2 glass synthesis has been identified using TEM analysis and also verified by QIT-TOFMS. TOFMS was shown to be a useful technique to study the generation of Ag(m)As(n)S(x )clusters. SEM, TEM and EDX analysis proved that the structure of AgA(s)S2 glass is ‘grain-like’ where grains are either: (1) Silver-rich ‘islands’ (Ag(m,) m up to 39) connected by arsenic and/or sulfur or arsenic sulfide chains or (2) silver sulfide (Ag2S)m (m = 9-20) clusters also similarly inter-connected. This obtained structural information may be useful for the development of ultra-high-density phase-change storage and memory devices using this kind of glass as a base.