Laser desorption ionization time-of-flight mass spectrometry of Ge-As-Te chalcogenides

RATIONALE: GexAsyTez glasses have a broad window of optical transparency and high refractive index which make them promising for applications in the infrared region. The aim of this work is to reveal structural motifs which could be present during the fabrication of Ge-As-Te thin films by plasma deposition techniques; such knowledge is important for the optimization of thin film growth. METHODS: Mass spectra were acquired using a laser desorption ionization time-of-flight (LDI-TOF) mass spectrometer equipped with a nitrogen laser (337 nm) coupled with a quadrupole ion trap, and recorded in positive and negative ion reflectron modes. XRD, SEM (EDX) and Raman spectroscopy were also used for the characterization of Ge-As-Te bulk or powdered samples. RESULTS: Bulk GexAsyTez samples (x = 10-20%, y = 20-60%, z = 30-70%) were synthesized. LDI-MS of Ge-As-Te powders provided evidence for the formation of both positively and negatively charged clusters, whose stoichiometry was determined as Ten(+/-) (n = 1-4), Te-5(+), binary AsTen+/- (n = 1-3), GeTen+/- (n = 1-3), As2Te+/-, As2Te3+, As3Te+, AsTe4+, Ge2H6+/-, ternary GeAsTe+, GeAsTe2+/-, GeAsH5+, GeAsH6+, GeAsH12+, and tertiary GeAsTeH5-, GeAsTeH8-, GeAsTe2H3+/-. CONCLUSIONS: The local structure of GexAsyTez materials is at least partly different from that of species identified in plasma by mass spectrometry, as deduced from Raman scattering spectroscopy analysis. However, LDI-TOFMS was found to be a suitable technique for the partial structure characterization of Ge-As-Te bulk samples and especially for the identification of the structural motifs present in the plasma during the preparation of the corresponding thin films. Copyright (C) 2015 John Wiley & Sons, Ltd.