Electron beam lithography was used to fabricate platinum At-contacts over tungsten oxide nanorods formed on a mica substrate. This made possible the measurement of sensorial response of these self-assembled tungsten oxide nanorods to hydrogen gas for the first time. The nanorods were prepared by thermal evaporation from an oxide source. Consequently, two types of conductometric sensors were assembled: a) percolating network of nanorods and b) set of individually contacted WO3 nanorods. The preparation procedures are described in detail and the comparison of response of both types of assemblies is given. The first sensorial measurements revealed a good response of the b) type of sensor and the minimum repeatedly detected concentration of H-2 was 50 ppm. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The morphology, the structure and the orientation of tungsten oxide nanorods grown on mica are investigated as a function of the deposition time. The previous results are recalled to point out the changes with the nanorod thickness. The investigations were conducted by Atomic Force Microscopy (AFM) and Reflection High Energy Electron Diffraction (RHEED). The results evidence two successive growth modes. In the first stage thin and long nanorods were formed. They grew layer by layer with a hexagonal tungsten bronze structure and two different (1−10) and (2–10) planes parallel to the mica surface. In the second stage, as the deposition time increased thin nanorods with the (1−10) orientation grew in thickness when the others preserve their morphology and structure.

This work describes the processing of Au nanowire arrays on insulating substrate developed to contact tungsten-oxide nanorods self-organised on the mica surface. The combination of electron beam lithography in scanning electron microscope and lift-off process is shown to be effective in fabricating nanocontact finger patterns with a line width of about 270 nm and 400 nm on bare and WO3 nanorod covered mica surfaces, respectively, separated by a few micrometre distance. It is shown that at right selection of the distance between Au nanowires, the applied procedure makes possible to contact WO3 nanorods of different length and density even if the nanostructures do not form an interconnected net. It opens the way for fabrication of single-wire nanosensors grown on insulating substrates.

The growth of thin metallic coatings on oxide substrates prepared by vapour deposition of gold or copper on alumina or magnesia was investigated by transmission electron microscopy. The stresses developed during the growth were followed by the bending method. The evolution of stresses is related to the growth mechanisms. The stresses are compressive for discontinuous deposits and change to tensile as the deposit becomes continuous. The compressive stresses are interpreted as due to the increase of the free energy of the metal-oxide system during the growth of metal particles. The tensile stresses result from the deposit lattice mismatch with the substrate. During the growth partial recrystallization and annealing of defects occur which modify the tensile behaviour of continuous coatings. The adhesion of deposits (Au and Cu) on oxide substrates (Al2O3 and MgO) was evaluated by the pull-off method as a function of deposition temperature. Au/Al2O3, Cu/Al2O3 and Au/MgO systems exhibit identical behaviour, while Cu/MgO shows a large dependence on deposition temperature compared to the others. This behaviour is interpreted as due to the formation of chemical bonds between the metal (Cu) and the oxide (MgO), leading to an interfacial oxide.

The morphology of α Al 2 O 3 surfaces annealed in vacuum has been investigated by reflection high energy electron diffraction (RHEED). We have studied two kinds of faces: (0001) and [Formula: see text]. The two faces behave differently. At high temperature the (0001) surface is unstable with only small facets and give evidence for variations of stoichiometry and structure with formation of an Al layer. The [Formula: see text] surfaces give large facets and the diffraction patterns are consistent with (2 × 1) surface structure.

Deposition of three dimensional particles on flat single crystalline surface results in appearance of transmission diffraction features. Analysis of diffraction patterns gives a possibility to characterize in situ the particle structure and orientation as well as to determine the variation of lattice parameter during particle growth. We have used the RHEED-system equipped with a data acquisition tool permitting both image processing and real time analysis. Different mode of epitaxy and lattice parameter variations were observed. The RHEED results were correlated with ex situ observations of particle size by means of Transmission Electron Microscopy (TEM).

We have studied the morphology and the structure of Al2O3 alpha annealed under vacuum. Two types of faces (0001) and ((1) over bar 012) have been investigated by means of Atomic Force Microscopy (AFM) and Reflexion High Energy Electron Diffraction (RHEED). The two faces behave differently at high temperature (1500-1700 degrees C) : the (0001) surfaces are unstable and the RHEED patterns give evidence for an Al top layer; the ((1) over bar 012) planes give large facets and the RHEED patterns are consistent with a (2 x 1) surface structure.

Physicochemical interactions at, Cu-MgO buried interfaces are studied by electron X-ray emission spectroscopy and compared to results obtained for native interfaces. The atomic arrangement is also determined. The role of the characteristics of the substrate is evidenced. Results suggest that weak or strong interactions can je present at the interfaces.

We have studied the adhesion of small gold particles prepared by vacuum evaporation onto a substrate of alumina ⋎. Thin films of ⋎Al2O3 are obtained by oxidation of polycrystalline aluminium strip in air at 600°C during 24 h. The gold films are observed by transmission electron microscopy in order to study the density and size of particles, as function of average deposition thickness (from 0.1 to 5 nm). Two methods are proposed to determine the small particles adhesion. The first one uses the particle density at saturation which is related to the adsorption and diffusion energies. In the second method, we determine the adhesion energy from the particle shape. This study establishes the correlation between the adhesion and the growth mechanism.

TiN films with a thickness varying from 70 to 300 nm were deposited onto Cu substrates by reactive d.c. triode sputtering. The characteristic features of the deposition system are described in detail. In order to vary the structure of the as-deposited films, they were grown with and without substrate heating and with substrate bias. The as-deposited films (unheated substrate) were quasi-stoichiometric, as determined by Auger electron spectroscopy (AES). Transmission electron microscopy (TEM) showed that the latter films were randomly oriented crystal with a grain size between 8 and 12 nm, whereas the films deposited under substrate heating (250–400°C) or under substrate bias ( − 250 V) had larger grain size, between 50 and 600 nm, consisting of monocrystalline areas with (110) and (100) orientations parallel to the substrate plane. We determined a parameter value of 0.425 nm by electron diffraction as well as by X-ray diffraction for the as-deposited films (unheated substrate). A TEM cross-section of the latter showed a dense void-free columnar structure. It was shown also that this columnar structure is independent of the atomic fraction of the nitrogen. Finally, annealing of samples prepared without substrate bias at 700 C for 30 min showed from the AES depth profiles that there is no diffusion of Cu to the outer surface of the films and also that no reaction occurs at the interface. This behaviour is related to the low pressure and small deposition rate used.

A combination of the reflection high energy electron diffraction (RHEED) and electron stimulated desorption ion angular distribution (ESDIAD) methods has been used as a probe of supported particle morphology and crystallographic structure. It has been shown that these techniques can be used as a tool for in situ investigation of model catalysts prepared by molecular beam epitaxy. The Pd particles growing on (100) KCl were investigated. The (100)Pd//(100)KCl, [001]Pd//[001]KCl particle orientation with respect to the substrate is found. The particles exhibit the shape of a half octahedron with (111) faces.

This paper reports on the morphological characterization by transmission electron microscopy of the growth mechanism of thin gold films condensed onto polycrystalline γ-Al2O3 substrates at two different pressures, 10−6 and 10−8 Torr, and for the same deposition rate R = 1 × 1013atoms cm−2 s−1 and temperature 641 K. Granulometric parameters from electron micrographs such as number density, edge-to-edge distance, particle mean size and substrate coverage as a function of the deposit thickness were deduced from a statistical analysis. From the comparison between the results obtained in the two cases, we obtain evidence of the mobility or immobility of large particles on the substrate and the influence of the residual gas environment on the thin film growth.

We have performed experiments of sintering on Ni particles in various atmospheres : vacuum, CO, H-2, H2O and H2O + H-2 and for temperatures in a range of 200 - 900-degrees-C. The sintering is evaluated from S.E.M. observations and the surface contaminants are analysed by Auger spectroscopy. In this paper we give results obtained for a sintering temperature of 720-degrees-C during 2 minutes. The more efficient sintering is found for experiments in vacuum or in H2O + H-2 atmosphere.

The electronic structure, determined by EELS is an important parameter in the metal ceramic interaction. Using various substrates, we determine the influence of the reduction of an alumina surface on the growth mode which is determined by TEM and AES.

This paper reports the morphological characterization by transmission electron microscopy of the growth mechanism of thin gold films condensed onto polycrystalline γ-Al2O3 substrates for two deposition rates R1 = 1 × 1013 atoms cm−2 s−1 and R2 = 3 × 1013 atoms cm−2 s−1. From electron micrographs, size histograms were drawn and granulometric parameters such as number density, edge-to-edge particle distance and substrate coverage deduced from a statistic analysis depending on the deposit thickness determined. The interpretation of their variation in the deposit thickness range 0.9–4.5 nm on the basis of the log-normal distribution function model allows us to determine the contributions to the growth from dynamic and static coalescence.

We investigated the growth of small gold particles on thin alumina substrates obtained by oxidation of aluminum. The particles were vapor deposited in vacuum from a Knudsen cell source with a vapor rate of 1·1013 cm−2·s−1. In our experiments small Au particles on Al2O3 were examined by electron microscopy. From electron micrographs we draw a size histogram of Au particles depending on the mean deposit thickness and the deposition rate. For a mean thickness larger than 1.5 nm the particle size distributions show two peaks. The shapes and the positions of these two peaks allow us to determine the particle growth mechanism and to evidence the importance of the liquid-like coalescence resulting of diffusion and collision of the aggregates.

We study stresses induced in the deposit substrate interface during a metal deposit growth. The metal is deposited on a thin substrate in the form of a rectangular strip, one of its ends fixed. The stresses cause strains in the substrate and the displacement of the free end is measured by an optical method. This technique enables the observation of strain variations in situ during the deposit growth. We have investigated the stresses in the case of Au, deposited under vacuum on Al2O3, and the dependence of these stresses on the deposit mean thickness. For various temperatures, we show that the type of observed stresses depends on the growth process. The stresses are compressive and they increase during the first stages of growth. They decrease and become tensile when coalescence occurs.

The adhesion of small particles of palladium prepared by thermal evaporation onto a substrate of Al2O3 was studied. Al2O3 was obtained by oxidation of a pollycristalline aluminum strip. The deposit of palladium was observed by Transmission Electron Microscopy which allowed to determine the size and the density of particles according to the average deposition thickness. The adhesion of particles was determined by two methods: the study of particle number density, and the study of the particle shapes.

AbstractNiBr2 reduction in organic media gives an intermediate complex, whose decomposition leads to Ni particles of nm size.