Graphene and novel graphitic ZnO and ZnS nanofilms: the energy landscape, non-stoichiometry and water dissociation

Abstract

Ab initio energy landscapes of thin ZnO and ZnS films reveal new structures, non-stoichiometry and different behaviour of adsorbed water.

Energy landscapes of perfect and defective solids: from structure prediction to ion conduction

“…Other compounds with the wurtzite structure should also demonstrate this behaviour [56]. For ZnS, which is most stable in the zinc-blende structure, the low-energy polymorphism is rather less extensive than for ZnO, related to the relative preference of S compared to O for fourfold coordination over threefold planar coordination; polar ZnS nanofilms are predicted to lose Zn ions spontaneously and so become non-stoichiometric [57].…”

“…Ultra-thin films and nanoscale synthesis also offer important routes by which different structures can be stabilised. We have reported density functional theory (DFT) [55,56] and more recently hybrid B3LYP calculations [57] that demonstrate that a single layer of ZnO adopts a graphene-like structure, while for a small number of layers, an "eclipsed" graphite-like structure, isostructural with hexagonal boron nitride, is adopted in which Zn atoms in one layer lie above the O in that beneath and vice versa (Fig. 3).…”

“…Other lowenergy possibilities for a small number of layers, shown also in Fig. 3, include a body-centred tetragonal (BCT) form [60] comprised of Zn 3 O 3 rings which are not flat but have boat conformations and a "staggered" graphitic form [57] in which adjacent graphene sheets are displaced relative to each other. The latter is particularly interesting in showing a spontaneous symmetry breaking across the film and a band gap that decreases substantially with film thickness, associated with the transfer of electron density from one layer to another.…”

First principles study on thickness dependent structural and electronic properties unveiling the growth and stability of 2D layered II–VI semiconducting compounds

“…5 In recent years, the scientific fraternity has been mainly interested in the exfoliation of 2D layers, particularly from covalent or semi-covalently bonded bulk compounds such as SiC and ZnO. [6][7][8][9][10][11][12] This intuition was undoubtedly ignited after the exfoliation of a graphene sheet from graphite using the mechanical exfoliation method. 13 This isolated sheet has a tremendous impact on technological as well as scientific aspects, owing to its exotic electronic and mechanical properties.…”