Electrical and Optical Properties of γ-SnSe: A New Ultra-narrow Band Gap Material

We describe the unusual properties of γ-SnSe, a new orthorhombic binary phase in the tin monoselenide system. This phase exhibits an ultranarrow band gap under standard pressure and temperature conditions, leading to high conductivity under ambient conditions. Density functional calculations identified the similarity and difference between the new γ-SnSe phase and the conventional α-SnSe based on the electron localization function. Very good agreement was obtained for the band gap width between the band structure calculations and the experiment, and insight provided for the mechanism of reduction in the band gap. The unique properties of this material may render it useful for applications such as thermal imaging devices and solar cells.

Sample preparation induced phase transitions in solution deposited copper selenide thin films

Thin films of CuSe were deposited onto GaAs substrate. XRD showed that the as-deposited films were of the Klockmannite (CuSe – P6₃/mmc 194) phase with lattice parameters a₀ = b₀ = 0.3939 nm, c₀ = 1.7250 nm; however, electron diffraction in the TEM surprisingly indicated the β-Cu_2−xSe phase (Cu_1.95Se – R3̄m 166) with lattice parameters a₀ = b₀ = 0.412 nm, c₀ = 2.045 nm. The discrepancy originated from the specimen preparation method, where the energy of the focused ion beam resulted in loss of selenium which drives a phase transition to β-Cu_2−xSe in this system. The same phase transition was observed also upon thermal treatment in vacuum, as well as when the 200 keV electron beam was focused on a powder sample in the TEM. The initial phase can be controlled to some extent by changing the composition of the reactants in solution, resulting in thin films of the cubic α-Cu_2−xSe (Cu_1.95Se – Fm3̄m) phase co-existing together with the β-Cu_2−xSe phase.

Ion beam irradiation causes Klockmannite CuSe to lose Se and transform into β-Cu₂Se. Caution must be taken when using the dual beam FIB for preparing TEM specimen.

Fundamental Aspects and Comprehensive Review on Physical Properties of Chemically Grown Tin-Based Binary Sulfides

The rapid research progress in tin-based binary sulfides (Sn_xS_y = o-SnS, c-SnS, SnS₂, and Sn₂S₃) by the solution process has opened a new path not only for photovoltaics to generate clean energy at ultra-low costs but also for photocatalytic and thermoelectric applications. Fascinated by their prosperous developments, a fundamental understanding of the Sn_xS_y thin film growth with respect to the deposition parameters is necessary to enhance the film quality and device performance. Therefore, the present review article initially delivers all-inclusive information such as structural characteristics, optical characteristics, and electrical characteristics of Sn_xS_y. Next, an overview of the chemical bath deposition of Sn_xS_y thin films and the influence of each deposition parameter on the growth and physical properties of Sn_xS_y are interestingly outlined.