Mikhail Pashchanka

Origin of self-organisation in porous anodic alumina films derived from analogy with Rayleigh–Bénard convection cells

Porous anodic aluminium oxide (PAOX) has different practical applications (e.g. filters with uniform pore sizes, adsorbers, porous templates for functional nanomaterials), but the formation mechanism is still poorly understood. Equal-sized hexagonally ordered pores are formed during anodic oxidation of aluminium in water solutions of some acids at certain concentrations and temperatures, and comparatively high electrode potentials. Today, a limited range of pore diameters and the degree of hexagonal ordering are reached with empirically found conditions. Here, a theoretical model explaining the appearance of honeycomb structure in porous anodic alumina is presented. The proposed mechanism is based on a dissipative self-organization process, but not on the earlier accepted field-assisted dissolution of pre-formed dense alumina. Our analysis rests on the concept that electrolyte currents near aluminium anode are organized in the same way as well-known Rayleigh–Benard convection currents. A simple yet effective way to predict pore formation in unexplored electrolytes is suggested. The validity of theoretical considerations is experimentally confirmed by the growth of hexagonally arranged porous alumina in a new electrolyte–aqueous formic acid solution.

Molecular based, chimie douce approach to 0D and 1D indium oxide nanostructures. Evaluation of their sensing properties towards CO and H2

The synthesis of a new molecular In(III) precursor complex, the generation of nanoscaled In2O3 (bixybyte structure) in 0D and 1D morphology, and the sensoric behavior of the 0D and 1D In2O3 nanostructures towards reducing gas atmospheres is studied. The indium precursor complex can be converted to a ceramic green body under mild reaction temperatures (160 °C), followed by conversion into crystalline indiumoxide at higher temperatures (350 °C). Geometric confinement by endotemplating of the molecular In precursor in track-etched polycarbonate templates yields polycrystalline indium oxide nanotubes in high yields. Controlled conversion of the molecular precursor without geometric confinement gives nanoparticulate crystalline In2O3. Both morphologically different In2O3 nanomaterials are sensitive to reducing gas conditions, however they show distinct differences towards reducing H2 and CO gas atmospheres.

A molecular approach to Cu doped ZnO nanorods with tunable dopant content

A novel molecular approach to the synthesis of polycrystalline Cu-doped ZnO rod-like nanostructures with variable concentrations of introduced copper ions in ZnO host matrix is presented. Spectroscopic (PLS, variable temperature XRD, XPS, ELNES, HERFD) and microscopic (HRTEM) analysis methods reveal the +II oxidation state of the lattice incorporated Cu ions. Photoluminescence spectra show a systematic narrowing (tuning) of the band gap depending on the amount of Cu(II) doping. The advantage of the template assembly of doped ZnO nanorods is that it offers general access to doped oxide structures under moderate thermal conditions. The doping content of the host structure can be individually tuned by the stoichiometric ratio of the molecular precursor complex of the host metal oxide and the molecular precursor complex of the dopant, Di-aquo-bis[2-(methoxyimino)-propanoato]zinc(II) 1 and -copper(II) 2. Moreover, these keto-dioximato complexes are accessible for a number of transition metal and lanthanide elements, thus allowing this synthetic approach to be expanded into a variety of doped 1D metal oxide structures.

Controlled synthesis and characterisation of MgO nanoparticles, thin films and polycrystalline nanorods derived from a Mg(II) single source precursor

The new magnesium (II) based oximato complex tris(aquo)-bis[2-(methoxyimino)-propanoato]magnesium(II) (1) has been prepared and fully characterised. This oximato complex serves as an ideal molecular single source precursor for chemical solution deposition and formation of cubic nanoscaled MgO from which thin films (2D morphology) and 1D materials (MgO rods) are accessible. A first ceramisation process starts with formation of an amorphous phase and occurs already at 190 °C and is completed after full conversion of the pre-ceramic into crystalline cubic MgO at 450 °C. Highly uniform and smooth films of MgO which show a preferential (111) orientation of the crystallites could be obtained at 450 °C. The low decomposition temperature of the precursor also allows the use of polymer based track-etched polycarbonate membranes as templates for 1D MgO structures with predictable geometric parameters (length and diameter). In this way, so far rarely observed polycrystalline MgO nanorods could be synthesised and fully characterised.

Template based precursor route for the synthesis of CuInSe2 nanorod arrays for potential solar cell applications

Summary Polycrystalline CuInSe2 (CISe) nanorods are promising for the fabrication of highly efficient active layers in solar cells. In this work we report on a nanocasting approach, which uses track-etched polycarbonate films as hard templates for obtaining three-dimensionally (3D) arranged CISe nanorod arrays. Copper and indium ketoacidoximato complexes and selenourea were employed as molecular precursors. Arrays of parallel isolated cylindrical pores of 100 nm nominal diameter and 5 μm length were used for the infiltration of the precursor solution under inert atmosphere, followed by drying, thermal conversion into a preceramic ‘green body’, a subsequent dissolution of the template, and a final thermal treatment at 450 °C. The nanorods that where synthesised in this way have dimensions equal to the pore sizes of the template. Investigation of the CuInSe2 nanorod samples by spectroscopic and diffraction methods confirmed a high purity and crystallinity, and a stoichiometric composition of the CISe ternary semiconductor compound.

P1.0.14 Inkjet printed In2O3 and In2O3/CNT hybrid microstructures for future gas sensing application

We report on the fabrication of In2O3/multiwalled carbon nanotubes (CNTs) composite microstructures via inkjet printing. The active sensor materials were derived from an inkjet printed suspension of carbon nanotubes and molecular In2O3 metalorganic single source precursor onto Si, SiO2 or alumina substrates followed by thermal conversion and gas sensing measurements. We found a good correlation of printed microstructures (e.g. tracks 100-150 μm wide) with pre-defined programmed patterns and a homogeneous distribution of CNTs in the composites. The ink-jet printed morphology is scalloped and continuous without breaks. Critical printing parameters like printing resolution or ‘coffee stain effect’ can be successfully controlled by changing precursor solution viscosity, substrate temperature and number of layers repeatedly printed on top of each other.