Formation of self-assembled nanoscale graphene/graphene oxide photomemristive heterojunctions using photocatalytic oxidation.

Photocatalytic oxidation of graphene with ZnO nanoparticles was found to create self-assembled graphene oxide/graphene (G/GO) photosensitive heterostructures, which can be used as memristors. Oxygen groups released during photodecomposition of water molecules on the nanoparticles under ultraviolet light, oxidized graphene, locally forming the G/GO heterojunctions with ultra-high density. The G/GO nanostructures have non-linear current-voltage characteristics and switch the resistance in the dark and under white light, providing four resistive states at room temperature. Photocatalytic oxidation of graphene with ZnO nanoparticles is proposed as an effective method for creating two-dimensional memristors with a photoresistive switching for ultra-high capacity non-volatile memory.

Chemical Pressure Effect on the Stabilization of Rock-Salt ZnO-Lin-2MeOn-1 Solid Solutions Synthesized at High Pressure.

Metastable ZnO-Lin-2MeOn-1 (Me = Sc3+, Ti4+, Ta5+) solid solutions with a rock-salt structure were synthesized through the solid-state reaction of ZnO with Lin-2Men+On-1 (n = 3, 4, 5) complex oxides at 7.7 GPa and 1300-1500 K. In all investigated systems, single-phase rock-salt solid solutions can be quenched down to ambient conditions in a wide (up to 80 mol% ZnO) concentration range. The phase composition, thermal stability, and thermal expansion of the recovered rock-salt solid solutions were studied by synchrotron powder X-ray diffraction. At ambient pressure, these solid solutions exhibit high thermal stability (up to 1000 K), with the decomposition temperature and decomposition products depending on the nature of the multiple charge cations.

Kinetics of the wurtzite-to-rock-salt phase transformation in ZnO at high pressure.

Kinetics of the wurtzite-to-rock-salt transformation in ZnO has been studied in the 5-7 GPa pressure range at temperatures below the activation of diffusion processes. The detailed analysis of non-isothermal experimental data using the general evolution equation describing the kinetics of direct phase transformations in solids allowed us to study the kinetic particularities of both nucleation and growth of the rock-salt phase in parent wurtzite ZnO. The main rate-limiting processes are thermally activated nucleation (E(N) = 383 kJ mol(-1) at 6.9 GPa) and thermally nonactivated (most probably quasi-martensitic) growth (k(G) = 0.833 min(-1) at 6.9 GPa). The high impact of thermal deactivation of nucleation places has been evidenced in the case of slow heating, which indirectly indicates that the rs-ZnO nucleation places are mainly produced by pressure-induced stresses in the parent phase.

Luminescence properties of the structure built from 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate and caesium(I).

The structure of caesium(I) 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate (CsA), Cs(+).C(8)HN(4)O(2)(-), is related to its luminescence properties. The structure of CsA (triclinic, P-1) is not isomorphous with previously reported structures (monoclinic, P2(1)/c) of the KA and RbA salts. Nevertheless, the coordination numbers of the metals are equal for all salts (nine). Each anion in the CsA salt is connected by pairs of inversion-related N-H...O hydrogen bonds to another anion, forming a centrosymmetric dimer. The dimers are linked into infinite ribbons, stacked by means of pi-pi interactions, thus building up an anionic wall. Time-dependent density functional theory calculations show that the formation of the dimer shifts the wavelength of the luminescence maximum to the blue region. Shortening the distance between stacked anions in the row [from 3.431 (5) A for RbA to 3.388 (2) A for KA to 3.244 (10) A for CsA] correlates with a redshift of the luminescence maximum from 574 and 580 nm to 596 nm, respectively.

Luminescence properties of three structures built from 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate and alkaline metals (Na, K and Rb).

The structures of three salts of 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate with alkali metals (Na, K and Rb) are related to their luminescence properties. The Rb salt, rubidium(I) 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate, Rb(+).C(8)HN(4)O(2)(-), is isomorphous with the previously reported potassium salt. For the Na compound, sodium(I) 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate dihydrate, Na(+).C(8)HN(4)O(2)(-).2H(2)O, two independent sodium ions, located on inversion centers, are coordinated by four water molecules each and additionally by two cyano groups for one and two carbonyl groups for the other. The luminescence spectra in solution are unaffected by the nature of the cation but vary strongly with the dielectric constant of the solvent. In the solid state, the emission maxima vary with structural features; the redshift of the maximum luminescence varies inversely with the distance between the stacked anions.

Luminescent properties of three structures built from 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate and cadmium.

Yellow-orange tetraaquabis(3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olato-kappaN(3))cadmium(II) dihydrate, [Cd(C8HN4O2)2(H2O)4] x 2 H2O, (I), and yellow tetraaquabis(3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olato-kappaN(3))cadmium(II) 1,4-dioxane solvate, [Cd(C8HN4O2)2(H2O)4] x C4H8O2, (II), contain centrosymmetric mononuclear Cd2+ coordination complex molecules in different conformations. Dark-red poly[[decaaquabis(mu(2)-3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olato-kappa(2)N:N')bis(mu(2)-3-cyano-4-dicyanomethylene-1H-pyrrole-2,5-diolato-kappa(2)N:N')tricadmium] hemihydrate], [Cd3(C8HN4O2)2(C8N4O2)2(H2O)10] x 0.5 H2O, (III), has a polymeric two-dimensional structure, the building block of which includes two cadmium cations (one of them located on an inversion centre), and both singly and doubly charged anions. The cathodoluminescence spectra of the crystals are different and cover the wavelength range from UV to red, with emission peaks at 377 and 620 nm for (III), and at 583 and 580 nm for (I) and (II), respectively.