Optical Properties of Zn₂Mo₃O₈: Combination of Theoretical and Experimental Study

We have investigated the electronic structure and optical properties of zinc molybdenum oxide (Zn₂Mo₃O₈) by using both first-principle calculations and experiments. Optical properties of this material is very similar to other ternary oxides of tetravalent molybdenum (A₂Mo₃O₈: A = Mg, Fe, Cd); therefore, this study provides meaningful insight into optical properties and possible phtotovoltaic applicability of these class of metal oxide cluster compounds. We use state-of-the-art methods, based on density functional theory and the GW approximation to the self-energy, to obtain the quasiparticle band structure and absorption spectra of the material. Our calculations shows that Zn₂Mo₃O₈ is a near indirect gap semiconductor with an indirect gap of 3.14 eV. The direct gap of the material is 3.16 eV. We also calculate the optical absorption in the material. Calculated results compare well with UV–visible spectroscopy and spectroscopic ellipsometry measurements done on polycrystalline thin films of Zn₂Mo₃O₈. We show the material has a large excitonic binding energy of 0.78 eV

Magnitude and Origin of Electrical Noise at Individual Grain Boundaries in Graphene

Grain boundaries (GBs) are undesired in large area layered 2D materials as they degrade the device quality and their electronic performance. Here we show that the grain boundaries in graphene which induce additional scattering of carriers in the conduction channel also act as an additional and strong source of electrical noise especially at the room temperature. From graphene field effect transistors consisting of single GB, we find that the electrical noise across the graphene GBs can be nearly 10 000 times larger than the noise from equivalent dimensions in single crystalline graphene. At high carrier densities (<i>n</i>), the noise magnitude across the GBs decreases as ∝1/<i>n</i>, suggesting Hooge-type mobility fluctuations, whereas at low <i>n</i> close to the Dirac point, the noise magnitude could be quantitatively described by the fluctuations in the number of propagating modes across the GB