Mass spectrometry of chalcogenide glasses

                                             Fei Huang

Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 5/A14, 62500 Brno, Czech
                                             Republic

                        PhD Thesis supervisor: Prof. Dr. Josef Havel, DrSc


      Chalcogenide glasses are based mostly on sulfur, selenium, tellurium, etc., and elements from
the 14-15th group of the periodic system (germanium, arsenic, antimony, etc.). They are high–tech
materials with strategic importance for manufacturing phase change memory, optical fibers, etc.
However, the analysis of these glasses by mass spectrometry is not easy. We cannot use MALDI for
the ionization here, we have to apply laser desorption ionization or laser ablation of the
materials with Time Of Flight (TOF) MS. The possibilities of TOF MS for the characterization of
chalcogenide glasses and/or their structure elucidation are studied and evaluated here for four
selected cases.

(i)                  The formation of binary antimony selenides was studied via laser ablation
synthesis (LAS) from various mixtures of antimony and selenium was followed and 24 new Sb[m]Se[n]
clusters were identified [1].

(ii)                When Sb[2]Se[3] polycrystalline materials were analyzed, six high mass clusters
were detected  for the first time (Sb[4]Se[4]^+, Sb[5]Se[3]^+, Sb[5]Se[4]^+, Sb[5]Se[5]^+,
Sb[5]Se[6]^+, and Sb[7]Se[4]^+) [2].

(iii)              Chalcogenide's properties can be changed via doping with the other elements.
Silver doping of the ternary Ge-Sb-S glasses was studied and the results of MS were compared with
Raman spectroscopy. It was found that while Raman spectroscopy detects the basic structural units,
MS shows mostly just their fragments [3].

(iv)               Similarly, doping of ternary Ge-Sb-Se system with Te, while Se was partially
replaced by Te, was studied. A higher number of clusters is produced after the addition of Te to
the Ge-Sb-Se mixtures of elements [4] while many are quaternary.

      In contrast to Raman spectroscopy, which is not fragmenting the structures, LDI or LA
techniques with TOF MS can be used anyway to examine the formation of structural entities
(clusters). MS instrument can be considered as a kind of synthesizer. Often, new clusters are
synthesized in comparison to those formed via laser fragmentation of known structures.

      Concluding, LDI TOF MS is a powerful and useful tool to elucidate the composition of clusters
formed from chalcogenide glasses (determining their stoichiometry). Even if LDI TOF MS causes
chalcogenides structure to smaller clusters, this information is important. The fragmentation of
chalcogenides can be suppressed by mixing the samples with paraffin.

References:

[1] F. Huang et al., Laser Ablation Generation of Antimony Selenide Clusters: Laser Desorption
Ionization (LDI) Quadrupole Ion Trap Time of Flight Mass Spectrometry. J. Am. Soc. Mass Spectrom.
30, 634-638 (2019).

[2] F. Huang et al., Comparison of clusters produced from Sb[2]Se[3] homemade polycrystalline
material, thin films and commercial polycrystalline bulk using laser desorption ionization with
time of flight quadrupole ion trap mass spectrometry.  J. Am. Soc. Mass Spectrom. 30, 2756-2761
(2019).

[3] F. Huang, et al., Laser Desorption Ionization Time-of-Flight Mass Spectrometry of Silver-Doped
(GeS[2])[50](Sb[2]S[3])[50] Chalcogenide Glasses. ACS Omega 5, 28965–28971 (2020).

[4] F. Huang, et al., Doping of Ge-Sb-Se thin films with tellurium: clusters formation by Laser
Ablation of thin films and comparison with clusters formed from the mixtures of elements.
Quadrupole ion trap time of flight mass spectrometry study, to be published.