Metal Monochalcogenide Research Articles

Electrons, holes, and spin in the IV-VI monolayer four-six-enes

Bandedge states in the indirect-gap group-IV metal monochalcogenide monolayers ('four-six-enes' such as SnS, GeTe, etc.) inherit the properties of nearby reciprocal space points of high symmetry at the Brillouin zone edge. We employ group theory and the method of invariants to capture these essential symmetries in effective Hamiltonians including spin-orbit coupling, and use perturbation theory to shed light on the nature of the bandedge states. In particular, we show how the structure of derived wavefunctions leads to specific dominant momentum and spin scattering mechanisms for both valence holes and conduction electrons, we analyze the direct optical transitions across the bandgap, and expose the interactions responsible for subtle features of the local dispersion relations.

In situ capping for size control of monochalcogenide (ZnS, CdS and SnS) nanocrystals produced by anaerobic metal-reducing bacteria

Metal monochalcogenide quantum dot nanocrystals of ZnS, CdS and SnS were prepared by anaerobic, metal-reducing bacteria using in situ capping by oleic acid or oleylamine. The capping agent preferentially adsorbs on the surface of the nanocrystal, suppressing the growth process in the early stages, thus leading to production of nanocrystals with a diameter of less than 5 nm.

Detection of nanoscale embedded layers using laboratory specular X-ray diffraction

Unusual specular X-ray diffraction patterns have been observed from certain thin film intergrowths of metal monochalcogenide (MX) and transition metal dichalcogenide (TX2) structures. These patterns exhibit selective “splitting” or broadening of selected (00l) diffraction peaks, while other (00l) reflections remain relatively unaffected [Atkins et al., Chem. Mater. 24, 4594 (2012)]. Using a simplified optical model in the kinematic approximation, we illustrate that these peculiar and somewhat counterintuitive diffraction features can be understood in terms of additional layers of one of the intergrowth components, MX or TX2, interleaved between otherwise “ideal” regions of MX-TX2 intergrowth. The interpretation is in agreement with scanning transmission electron microscope imaging, which reveals the presence of such stacking “defects” in films prepared from non-ideal precursors. In principle, the effect can be employed as a simple, non-destructive laboratory probe to detect and characterize ultrathin layers of one material, e.g., 2-dimensional crystals, embedded between two slabs of a second material, effectively using the two slabs as a highly sensitive interferometer of their separation distance.

Optoelectronic properties of single-layer, double-layer, and bulk tin sulfide: A theoretical study

SnS is a metal monochalcogenide suitable for use as absorber material in thin film photovoltaic cells. Its structure is an orthorhombic crystal of weakly coupled layers, each layer consisting of strongly bonded Sn-S units. We use first-principles calculations to study model single-layer, double-layer, and bulk structures of SnS in order to elucidate its electronic structure. We find that the optoelectronic properties of the material can vary significantly with respect to the number of layers and the separation between them: the calculated band gap is wider for fewer layers (2.72 eV, 1.57 eV, and 1.07 eV for single-layer, double-layer, and bulk SnS, respectively) and increases with tensile strain along the layer stacking direction (by ∼55 meV/1% strain).

Hydrothermal synthesis of metal polychalcogenides. Structural characterization of [Mo12Se56]12-. A cluster of clusters

Recently, the authors have been exploring the chemistry of metal polychalcogenides with various synthetic methods such as traditional room temperature solution and unusual molten salt techniques with considerable success. In order to expand the synthetic repertoire in this area, they have been experimenting with hydrothermal conditions to assess their potential as variable synthetic routes to novel metal polychalcogenides. Hydrothermal synthesis of chalcogenides is very little studied, despite its demonstrated usefulness in the synthesis of a variety of other important, and often inaccessible by other techniques, materials such as quartz and zeolites. Hydro(methano)thermal conditions have been used to prepare some very interesting metal monochalcogenide compounds by using alkali carbonates as mineralizers. Using Se{sub x}{sup 2{minus}} as mineralizers, the authors have uncovered a new route to novel polychalcogenides. They report here the first hydrothermal synthesis of a metal polychalcogenide complex, the remarkable (Mo{sub 12}Se{sub 56}){sup 12{minus}} (I), possessing an extraordinary structure.