Probing the local interface properties at a graphene-MoSe2 in-plane lateral heterostructure: an ab initio study.

We report a theoretical study of the local interface properties at a graphene-MoSe2 (G-MoSe2) in-plane lateral heterostructure. Using a combination of first-principles density functional theory (DFT) calculations and simulations of X-ray Absorption Near-Edge Structure (XANES) spectroscopy at the C K-edge, we examined different local interface arrangements. The simulated XANES signal from interface carbon atoms showed new features compared to the pristine graphene region, which provides a way of identifying different chemical environments and/or geometries of the local interface in the G-MoSe2 lateral hybrid system. Our results also revealed that the local electronic and magnetic properties are dependent on the interface atomic structure, where metallic, semiconductor or half-metallic character was achieved at the G-MoSe2 interface. These findings indicate the great potential of 2D lateral heterojunctions for nanoelectronic and spintronic applications.

Nanodots of transition metal dichalcogenides embedded in MoS2 and MoSe2: first-principles calculations.

The energetic stability and the electronic properties of nanodots (NDs) composed of transition metal dichalcogenides, XS2 and XSe2 (with X = Mo, W and Nb) embedded in single layer MoS2 and MoSe2 hosts, were investigated based on first-principles calculations. We find that through a suitable combination of the ND and host materials it is possible to control the electron-hole localization. For instance, in NDs of WS2 in the MoS2 host we find the highest occupied (hole) states localized in the ND region, while the lowest unoccupied (electron) states spread out in the MoS2 host. On the other hand, by changing the ND and host materials, the electron states become localized in the MoS2 ND in the WS2 host. Further electronic structure calculations show that the NDs of NbS2 and NbSe2 give rise to a set of spin degenerate empty states within the energy gap of the MoS2 and MoSe2 hosts. The spin degeneracy can be removed by negatively charging the ND system. Such n-type doping was examined by considering a van der Waals (vdW) heterostructure composed of a graphene layer lying on the NbS2 and NbSe2 NDs. Indeed we found a net magnetic moment localized in the ND region.

H2O incorporation in the phosphorene/a-SiO2 interface: a first-principles study.

Based on first-principles calculations, we investigate (i) the energetic stability and electronic properties of single-layer phosphorene (SLP) adsorbed on an amorphous SiO2 surface (SLP/a-SiO2), and (ii) the further incorporation of water molecules at the phosphorene/a-SiO2 interface. In (i), we find that the phosphorene sheet binds to a-SiO2 through van der Waals interactions, even in the presence of oxygen vacancies on the surface. The SLP/a-SiO2 system presents a type-I band alignment, with the valence (conduction) band maximum (minimum) of the phosphorene lying within the energy gap of the a-SiO2 substrate. The structure and the surface-potential corrugations promote the formation of electron-rich and electron-poor regions on the phosphorene sheet and at the SLP/a-SiO2 interface. Such charge density puddles are strengthened by the presence of oxygen vacancies in a-SiO2. In (ii), because of the amorphous structure of the surface, we consider a number of plausible geometries for H2O embedded in the SLP/a-SiO2 interface. There is an energetic preference for the formation of hydroxyl (OH) groups on the a-SiO2 surface. Meanwhile, in the presence of oxygenated water or interstitial oxygen in the phosphorene sheet, we observe the formation of metastable OH bonded to the phosphorene, and the formation of energetically stable P-O-Si chemical bonds at the SLP/a-SiO2 interface. Further x-ray absorption spectra simulations are performed, which aim to provide additional structural/electronic information on the oxygen atoms forming hydroxyl groups or P-O-Si chemical bonds at the interface region.