Laser Desorption Ionization of As2Ch3 (Ch = S, Se, and Te) Chalcogenides Using Quadrupole Ion Trap Time-of-Flight Mass Spectrometry: A Comparative Study

Arsenic-Doped SnSe Thin Films Prepared by Pulsed Laser Deposition

Pulsed UV laser deposition was exploited for the preparation of thin Sn50-x As x Se50 (x = 0, 0.05, 0.5, and 2.5) films with the aim of investigating the influence of low arsenic concentration on the properties of the deposited layers. It was found that the selected deposition method results in growth of a highly (h00) oriented orthorhombic SnSe phase. The thin films were characterized by different techniques such as X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, atomic force microscopy, Raman scattering spectroscopy, and spectroscopic ellipsometry. From the results, it can be concluded that thin films containing 0.5 atom % of As exhibited extreme values regarding crystallite size, unit cell volume, or refractive index that significantly differ from those of other samples. Laser ablation with quadrupole ion trap time-of-flight mass spectrometry was used to identify and compare species present in the plasma originating from the interaction of a laser pulse with solid-state Sn50-x As x Se50 materials in both forms, i.e. parent powders as well as deposited thin films. The mass spectra of both materials were similar; particularly, signals of Sn m Se n + clusters with low m and n values were observed.

Laser Ablation Generation of Bismuth Selenide Clusters from Mixtures of Elements, Crystalline Bi2Se3, or Thin Films: Laser Desorption Ionization (LDI) and Surface Assisted LDI Time-of-Flight Mass Spectrometry using Graphene and Nanodiamonds

A bismuth-selenium system from mixtures of the powdered elements in various molar ratios and from Bi₂Se₃ crystals and/or thin films was studied using laser desorption ionization and surface assisted laser desorption ionization. The Bi_mSe_n clusters were observed in both positive and negative ion modes, but the mass spectra were more intense, and also a higher number of clusters was formed in the positive ion mode than in the negative mode. The BiSe_n⁺ (n = 1-8), Bi₂Se_n⁺ (n = 1-5), and Bi₃Se_n⁺ (n = 1-6) clusters were detected. Similarly, in the negative ion mode, BiSe_n^- (n = 2-9) and Bi₂Se_n^- (n = 1-2) clusters were observed. In addition, the formation of Bi_m⁺ (m = 1-5), Se_n⁺ (n = 1-8), and Se_n^- (n = 1-7) clusters was also observed. In total, 33 clusters were generated, and 4 new bismuth selenide clusters that have not been reported before (namely, BiSe₇^+/-, BiSe₈^+/-, BiSe₉^-, and Bi₂Se₅⁺) were detected. The formation of similar clusters was also observed from bismuth-selenium mixtures and from crystalline Bi₂Se₃. Furthermore, the Bi₂Se₃ thin films prepared from a magnetron sputtering technique were also examined via laser desorption ionization. The generation of clusters from the surface of graphene and nanodiamonds was also studied, but no remarkable difference with comparison to the metal surface was observed.

Amorphous Ge-Bi-Se Thin Films: A Mass Spectrometric Study

The Ge-Bi-Se thin films of varied compositions (Ge content 0-32.1 at. %, Bi content 0-45.7 at. %, Se content 54.3-67.9 at. %) have been prepared by rf magnetron (co)-sputtering technique. The present study was undertaken in order to investigate the clusters generated during the interaction of laser pulses with Ge-Bi-Se thin films using laser ablation time-of-flight mass spectrometry. The stoichiometry of the clusters was determined in order to understand the individual species present in the plasma plume. Laser ablation of Ge-Bi-Se thin films accompanied by ionization produces about 20 positively and/or negatively charged unary, binary and ternary (Gex+, Biy+, Sez+/-, GexSez+/-, BiySez+/- and GexBiySez-) clusters. Furthermore, we performed the laser ablation experiments of Ge:Bi:Se elemental mixtures and the results were compared with laser ablation time-of-flight mass spectrometry analysis of thin films. Moreover, to understand the geometry of the generated clusters, we calculated structures of some selected binary and ternary clusters using density functional theory. The generated clusters and their calculated possible geometries can give important structural information, as well as help to understand the processes present in the plasma processes exploited for thin films deposition.

Comparison of Clusters Produced from Sb2Se3 Homemade Polycrystalline Material, Thin Films, and Commercial Polycrystalline Bulk Using Laser Desorption Ionization with Time of Flight Quadrupole Ion Trap Mass Spectrometry

This study compared Sb₂Se₃ material in the form of commercial polycrystalline bulk, sputtered thin film, and homemade polycrystalline material using laser desorption ionization (LDI) time of flight mass spectrometry with quadrupole ion trap mass spectrometry. It also analyzed the stoichiometry of the Sb_mSe_n clusters formed. The results showed that homemade Sb₂Se₃ bulk was more stable compared to thin film; its mass spectra showed the expected cluster formation. The use of materials for surface-assisted LDI (SALDI), i.e., graphene, graphene oxide, and C₆₀, significantly increased the mass spectra intensity. In total, 19 Sb_mSe_n clusters were observed. Six novel, high-mass clusters-Sb₄Se₄⁺, Sb₅Se_3-6⁺, and Sb₇Se₄⁺-were observed for the first time when using paraffin as a protective agent.

Mass spectrometric investigation of amorphous Ga-Sb-Se thin films

Amorphous chalcogenide thin films are widely studied due to their enhanced properties and extensive applications. Here, we have studied amorphous Ga-Sb-Se chalcogenide thin films prepared by magnetron co-sputtering, via laser ablation quadrupole ion trap time-of-flight mass spectrometry. Furthermore, the stoichiometry of the generated clusters was determined which gives information about individual species present in the plasma plume originating from the interaction of amorphous chalcogenides with high energy laser pulses. Seven different compositions of thin films (Ga content 7.6–31.7 at. %, Sb content 5.2–31.2 at. %, Se content 61.2–63.3 at. %) were studied and in each case about ~50 different clusters were identified in positive and ~20–30 clusters in negative ion mode. Assuming that polymers can influence the laser desorption (laser ablation) process, we have used parafilm as a material to reduce the destruction of the amorphous network structure and/or promote the laser ablation synthesis of heavier species from those of lower mass. In this case, many new and higher mass clusters were identified. The maximum number of (40) new clusters was detected for the Ga-Sb-Se thin film containing the highest amount of antimony (31.2 at. %). This approach opens new possibilities for laser desorption ionization/laser ablation study of other materials. Finally, for selected binary and ternary clusters, their structure was calculated by using density functional theory optimization procedure.

Gallium selenide clusters generated via laser desorption ionisation quadrupole ion trap time-of-flight mass spectrometry

RATIONALE

Gallium selenide thin films important for electronics and phase-change materials are prepared via pulsed laser deposition (PLD); however, there are no studies concerning the analysis of gallium selenide clusters formed in the gas phase. Laser desorption ionisation (LDI) combined with time-of-flight mass spectrometry (TOF-MS) has great potential to generate charged Ga_m Se_n clusters, to analyse them and thus to develop new materials.

METHODS

LDI of Ga-Se mixtures using a pulsed laser (337 nm nitrogen) was used to generate gallium-selenide clusters. Mass spectra were recorded (in positive and negative ion mode) on a TOF mass spectrometer equipped with a quadrupole ion trap and reflectron mass analyser.

RESULTS

Ga-Se mixtures were found to be suitable for laser ablation synthesis (LAS) of gallium selenide clusters, although their composition was strongly dependent on the laser energy. The effect of laser energy on the stoichiometry of the generated clusters was established. In total, over 100 gallium selenide Ga_m Se_n clusters were generated and identified from Ga-Se mixtures. LDI of Ga₂ Se₃ crystals showed almost the same clusters up to m/z 1000 with lower intensities, whereas no clusters from Ga₂ Se₃ were observed above m/z 1000.

CONCLUSIONS

A family of over 100 gallium selenide clusters, generated and identified for the first time, shows rich and complex chemistry. Some of the clusters represent new compounds that have the potential to be used in the development of advanced materials.