Mono and digallium selenide clusters as potential superhalogens

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.

Fast gate-tunable photodetection in the graphene sandwiched WSe2/GaSe heterojunctions

We investigated electrical and photoelectrical properties of graphene sandwiched WSe₂/GaSe van der Waals heterojunctions. The device showed a high rectification ratio up to 300 at V_ds = 1.5/-1.5 V, which is attributed to the built-in electric field in the device. Due to the bipolar property of WSe₂, gate-tunable rectification inversion was observed. Meanwhile, the graphene sandwiched heterojunction showed excellent performances on photodetection, where the photoresponsivity of (6.2 ± 0.2) A W^-1 can be reached under V_ds = -1.5 V and P = 0.2 μW. The device also showed great external quantum efficiency of (1490 ± 50)% and fast response time of ∼30 μs. Our study identified the graphene sandwiched heterojunctions based on 2D materials have great potential for gate-tunable electronic and optoelectronic applications.

Thickness dependence on the optoelectronic properties of multilayered GaSe based photodetector

Two-dimensional (2D) layered materials exhibit unique optoelectronic properties at atomic thicknesses. In this paper, we fabricated metal-semiconductor-metal based photodetectors using layered gallium selenide (GaSe) with different thicknesses. The electrical and optoelectronic properties of the photodetectors were studied, and these devices showed good electrical characteristics down to GaSe flake thicknesses of 30 nm. A photograting effect was observed in the absence of a gate voltage, thereby implying a relatively high photoresponsivity. Higher values of the photoresponsivity occurred for thicker layers of GaSe with a maximum value 0.57 AW(-1) and external quantum efficiency of of 132.8%, and decreased with decreasing GaSe flake thickness. The detectivity was 4.05 × 10(10) cm Hz(1/2) W(-1) at 532 nm laser wavelength, underscoring that GaSe is a promising p-type 2D material for photodetection applications in the visible spectrum.

A comparative ab initio study to investigate the rich structural variety and electronic properties of GamTen (m = 1, 2 and n = 1–4) with analogous oxides, sulfides and selenides

A series of gallium telluride, Ga_mTe_n (m = 1, 2 and n = 1–4), clusters has been examined by using different computational methods.