Scientific publications

A direct gravure printing process for UV-curable indium tin oxide (ITO) nanoparticle patterns on polyethylene terephthalate and polyethylene naphthalate foils is presented for use as transparent electrodes. Both large-area coatings and patterns of ITO with thicknesses from 0.2 to > 1 μm and feature sizes on the order of 100 μm were realized with a sheet resistance down to 400 Ω□ and a transmission > 85% in the visible. In order to reach the lowest sheet resistance, a post-treatment under inert or reducing conditions at temperatures of 130 to 180 °C was used. Special requirements regarding the gravure printing of electronic material from nanoparticles and potential applications are discussed.

Fabrication of multilayer thin films through layer-by-layer (lbl) deposition of charged nanoparticles on tin-doped indium oxide (ITO) coated and uncoated glass substrates are reported. The thin films were constructed by alternately dipping a substrate into a colloidal suspension of chitosan capped zinc sulphide (ZnS) nanoparticles (30 nm) and citrate stabilized colloidal gold (Au) nanoparticles (20 nm) leading to electrostatic interactions between the oppositely charged nanoparticle layers. Thin films consisting of up to 200 deposition cycles by multiple dipping have been studied and surface morphology, changes in the optical absorption characteristics, thickness, uniformity, roughness and electrical characteristics are reported. The multilayered assemblies, attached to the surface by strong ionic bonds, were highly stable and could not be removed by moderate scratching. The current–voltage characteristics in the forward and reverse bias conditions demonstrated rectifying behaviors in the onset of conduction voltage which makes these films attractive for future electronic devices.

We present a set of criteria to optimize photodetectors based on n-type metal oxide nanowires and a comparison methodology capable of overcoming the present lack of systematic studies dealing with such devices. The response of photoconductors is enhanced following different fabrication strategies, such as diminishing the distance between the electrical contacts, increasing the width of the photoactive area, or improving the electrical mobility of the nanomaterials. The validity of the theoretical background is verified by experimental results obtained with devices based on ZnO nanowires. The performances of our devices show that the normalized gain of single ZnO nanowire-based photodetectors exceeds those of thin films.

Dissipated power in metal oxide nanowires (rNW<45 nm) often causes important self-heating effects and as a result, undesired aging and failure of the devices. Nevertheless, this effect can be used to optimize the sensing conditions for the detection of various gaseous species, avoiding the requirement of external heaters. In this letter, the sensing capabilities of self-heated individual SnO2 nanowires toward NO2 are presented. These proof-of-concept systems exhibited responses nearly identical to those obtained with integrated microheaters, demonstrating the feasibility of taking advantage of self-heating in nanowires to develop ultralow power consumption integrated devices.

Deposition of thin films through vaccum processes plays an important role in industrial processing of decorative and functional coatings. Many metal oxides have been prepared as thin films using different techniques, however obtaining compositionally uniform phases with a control over grain size and distribution remains an enduring challenge. The difficulties are largely related to complex compositions of functional oxide materials, which makes a control over kinetics of nucleation and growth processes rather difficult to control thus resulting in non-uniform material and inhomogeneous grain size distribution. Application of tailor-made molecular precursors in low pressure or plasma-enhanced chemical vapor deposition (CVD) techniques offers a viable solution for overcoming thermodynamic impediments involved in thin film growth. In this paper molecule-based CVD of functional coatings is demonstrated for iron oxide (Fe2O3, Fe3O4), vanadium oxide (V2O5, VO2) and hafnium oxide (HfO2) phases followed by the characterization of their microstructural, compositional and functional properties which support the advantages of chemical design in simplifying deposition processes and optimizing functional behavior.

One-dimensional nanoscopic Fe3O4 architectures are grown by molecule-based chemical vapor deposition CVD using [Fe(OBut)3]2 precursor and Au particles as growth templates. Growth of magnetite shell on tin oxide nanowires is also achieved, obtaining magnetic-semiconductor heterostructures. Structural characterization of the different nanostructures and the first electrical measurements on an individual magnetite nanowire are reported.

One dimensional (1D) inorganic materials are gaining increasing attention because of their unique structural features and interesting functional properties. Given the structural stability, they show promising application potential in vacuum as well as in oxidizing atmospheres, which provides them a competitive edge over their carbon-based counterparts. A number of synthetic procedures have been developed and demonstrated for 1D nanostructures that have led to intriguing morphological variations (wires, tubes, belts, rods, etc.), however the control over radial and axial dimensions remains a continuing challenge. In addition, the choice of material is rather limited. We have developed a generic approach for the size-selective and site-specific growth of nanowires by combining vapor-liquid-solid (VLS) approach with molecule-based chemical vapor deposition. The synthesis of nanowires (NWs) is based on the decomposition of discrete molecular species, which allows growing nanowires at low temperatures with a precise control over their diameter and length. The precursor chemistry can be tuned to facilitate the stripping of organic ligands and to achieve complete decomposition that is critical for maintaining the gas phase super-saturation necessary for 1D growth. High-yield synthesis of elemental (Ge) and compound semiconductors (SnO2, Fe3O4, V2O5, In2O3) was performed by the chemical vapor deposition of appropriate metal-organic precursors. Axial and radial dimensions of the NWs were varied by adjusting the precursor feedstock, deposition temperature, and catalyst size. Finally, the device potential of these building blocks as photo- and gas sensors was investigated by integrating individual nanowires in electrical circuits using focussed ion beam (FIB) assisted nano-lithography.