L. Spiess

Sensing characteristics of NiO thin films as NO2 gas sensor

Abstract In this paper we present the results concerning the characterisation of nickel oxide thin films deposited by d.c. reactive magnetron sputtering. Different NiO thin films have been prepared by changing some deposition parameters, as the oxygen content in the reactive plasma and the sputtering mode (metal- or oxide-sputtering mode). The structure and surface morphology of the samples have been analysed by XRD and by atomic force microscopy and scanning electron microscope, respectively. The electrical responses of the NiO films towards NO 2 have been also considered. NiO thin films showed good responses to low NO 2 concentrations (1–10 ppm) with a maximum at 160 °C operating temperature.

Preparation of nickel oxide thin films for gas sensors applications

Abstract Nickel oxide (NiO) thin films were prepared by dc reactive magnetron sputtering from a nickel metal target in an Ar+O2 mixed atmosphere in two sputtering modes. The oxygen content in the gas mixture varied from 15% to 45%. The films prepared in the oxide-sputtering mode were amorphous while the films in metal-sputtering mode exhibited polycrystalline (fcc) NiO phase. In this case TEM observations showed a dense fine-grained structure with the grain size in the range 4–10 nm and AFM micrograph showed a rough surface with RMS=2.21 nm. We have found that good NiO stoichiometric films are obtainable with a polycrystalline (fcc) structure at 40% oxygen content in the metal-sputtering mode.

Interface behaviour in nickel composite coatings with nano-particles of oxidic ceramic

Advances in micro-technology demand that new functional materials be developed so that the technical properties of micro-devices can be improved at reasonable cost. The co-deposition of nanoscaled particles during an electroplating process has been shown to bring such an improvement. This work focuses on particles of oxidic ceramics, in this case those of Al2O3 and TiO2. The diameters of the primary particles ranges from 10 to 30 nm, electrodeposited by means of a conventional Watts nickel electrolyte. A series of nickel nano-ceramic composites were produced, with co-deposition of particles as a single primary particle in the nanometre range at one end of the scale and as agglomerates up to a size of a micrometer at the other. The influence of the presence of particles on crystallisation behaviour, residual stress and texture of the deposited nickel coatings was examined by X-ray diffraction (XRD). There is a report on the interfaces between the nickel grains and the oxidic ceramic particles, investigated using transmission electron microscopy (TEM). A decreasing corrosion stability indicates an attack along the interface nickel/particles.

Ohmic contacts to p-type 6H-silicon carbide

An AlTi-ohmic contact to p-type 6HSiC is described. Specific contact resistances were measured using the linear transmission line method [1] and varied between approximately 5 × 10−4 and 5 × 10−3 Ω·cm2 at room temperature. CV measurements of as-deposited contacts and those annealed at different temperatures will be presented.

Sputtered yttrium oxide thin films appropriate for electrochemical sensors

Abstract This work deals with Y 2 O 3 thin films prepared by r.f. diode sputtering for application in electrochemical sensors. The influence of annealing on selected electrical and mechanical properties of Y 2 O 3 thin films has been studied. With increasing annealing temperature the values of electrical strength and electrical resistivity increase, whereas, the values of relative permittivity and Youngs modulus decrease. Yttrium oxide films have a polycrystalline structure without cubic structural change caused by annealing. The change from compressive to tensile stresses takes place in Y 2 O 3 films with increasing temperature. The properties of Y 2 O 3 thin films are comparable with the published data. The Y 2 O 3 film was used as an insulation layer in vertically arranged electrodes in a microelectrochemical cell. The redox recycling phenomenon was demonstrated with the redox couple [Fe(CN) 6 ] 3−/4− .

Tribological characteristics of WC1-x, W2C and WC tungsten carbide films

Thin film coatings with dominant phases of WC1-x, W2C and WC, were prepared by magnetron sputtering. The microstructures and chemistry of the coatings were characterized by X-ray diffraction (XRD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The surface morphology and mechanical properties were examined by atomic force microscopy (AFM) and nanoindentation techniques. The tribological behaviour of the coatings was assessed by means of a microtribometer. Low hardness and indentation modulus of the W2C coatings were found to be from the high surface roughness. The W2C coatings were not wear resistant and were worn through in less than 15,000 cycles under a normal load of 40 mN. The WC1-X coatings were textured with the (200) plane parallel to the surface of substrate. The hardness and indentation modulus of the WC1-x coatings were ∼19 GPa and ∼600 GPa, respectively. A thick transfer layer was observed at the surface of the sphere employed in the sliding tests of the WC1-x coatings. The build-up and maintaining of this transfer layer was found to be important in determining the friction behaviour of the WC1-X coatings. A maximum hardness of ∼23 GPa and the lowest friction coefficient of 0.19 was obtained from the WC coating. In contrast to the large variation of the friction coefficients in the other coatings, the friction coefficient of WC was stable in the long-time running process.

Structural Evolution of Sputtered Indium Oxide Thin Films

Structural Evolution of Sputtered Indium Oxide Thin Films The indium oxide thin films were deposited at room temperature by reactive magnetron sputtering in the mixture of oxygen and argon on silicon and oxidized silicon substrates. The influence of the oxygen flow in the reactive mixture and post-deposition annealing on the structural properties were investigated. The as deposited In2O3 films showed a dominating randomly oriented nanocrystalline structure of cubic In2O3. The grain size decreased with increasing oxygen concentration in the plasma. Annealing in reducing atmospheres (vacuum, nitrogen and argon), besides improving the crystallinity, led to a partial cubic to rhombohedral phase transition in the indium oxide films.

Study of Annealed NiO Thin Films Sputtered on Unheated Substrate

Nickel oxide (NiO) thin films were deposited on unheated Si substrates by reactive dc magnetron sputtering. Post-deposition annealing was carried out for NiO films in dry air. The effect of annealing temperature (from 500 to 900°C) on the structural, compositional and surface morphological properties of thin NiO films was investigated. The films were characterized by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and atomic force microscopy (AFM). Only the as-deposited films in the metal-sputtering mode were crystalline. Annealing in dry air led to the formation of crystalline phases in all samples. During the annealing process, changes in the crystal structure occurred. All examined NiO films were semiconductors and their conductance increased by four orders of magnitude between 25 and 350°C.

Thin film voltammetric microsensor for heavy metal analysis

Thin film palladium (Pd) and indium tin oxide (ITO) microelectrodes modify by mercury (Hg) were developed for heavy metal analysis by anodic stripping voltammetry. In case of Pb/sup 2+/ determination the sensitivity of ITO-Hg array of disc electrodes was higher (130 nA//spl mu/M) in comparison with Pd-Hg interdigitated array of electrodes (60 nA//spl mu/M).

Pyrolyzed Photoresist Film Electrodes for Application in Electroanalysis

Pyrolyzed Photoresist Film Electrodes for Application in Electroanalysis Pyrolyzed photoresist film (PPF) electrodes for application in electroanalysis were prepared on alumina substrates. These electrodes were characterized for their electrical, microstructural (by Raman spectroscopy) and electrochemical properties. As a support, the PPF electrodes were tested for simultaneous determination of Pb(II), Cd(II) and Zn(II) in an aqueous solution on in-situ formed bismuth film by square wave voltammetry (SWV). The dependence of the stripping responses on the concentration of target metals was linear in the range from 1 × 10-8 to 9 × 10-8 mol/L. The effect of activation of the PPF surface by argon plasma on analytical performance of bismuth film electrode (BiFE) on PPF support was also investigated.