We noted that the tunneling-percolation framework is quite well understood at the extreme cases of percolationlike and hoppinglike behaviors but that the intermediate regime has not been previously discussed, in spite of its relevance to the intensively studied electrical properties of nanocomposites. Following that we study here the conductivity of dispersions of particle fillers inside an insulating matrix by taking into account explicitly the filler particle shapes and the interparticle electron-tunneling process. We show that the main features of the filler dependencies of the nanocomposite conductivity can be reproduced without introducing any a priori imposed cutoff in the interparticle conductances, as usually done in the percolationlike interpretation of these systems. Furthermore, we demonstrate that our numerical results are fully reproduced by the critical path method, which is generalized here in order to include the particle filler shapes. By exploiting this method, we provide simple analytical formulas for the composite conductivity valid for many regimes of interest. The validity of our formulation is assessed by reinterpreting existing experimental results on nanotube, nanofiber, nanosheet, and nanosphere composites and by extracting the characteristic tunneling decay length, which is found to be within the expected range of its values. These results are concluded then to be not only useful for the understanding of the intermediate regime but also for tailoring the electrical properties of nanocomposites.

The nature and the role of 1 to 5 nm thick TiO 2 seed layers for the growth of textured PbTiO 3 and Pb(Zr,Ti)O 3 thin films on textured Pt(111) thin film substrates have been studied. Under otherwise identical in situ sputter deposition process conditions, the PbTiO 3 texture could be turned from (100) to (111) orientation by adding the seed layer. This is demonstrated by patterning the TiO 2 film. Auger electron spectroscopy and x-ray photoemission spectroscopy showed that the seed layer was a continuous TiO 2 film. X-ray photoelectron diffraction measurements revealed epitaxial ordering in the seed layer. As there is no azimuthal order among the Pt grains, the reduced information of azimuthally averaged polar cuts is obtained. These give strong evidence for a strained rutile (110) structure. Various deposition experiments indicated that the TiO 2 is effective only when it is ordered before the PbTiO 3 nucleation starts. The epitaxial relationship between PbTiO 3 (111) and Pt(111) is thus mediated by the intermediate, epitaxial TiO 2 film, which is dissolved or transformed to PbTiO 3 afterwards. The observed growth behavior is discussed in terms of surface and interface energies.

A vast class of disordered conducting-insulating compounds close to the percolation threshold is characterized by nonuniversal values of transport critical exponent t, in disagreement with the standard theory of percolation which predicts t Ӎ 2.0 for all three-dimensional systems. Various models have been proposed in order to explain the origin of such universality breakdown. Among them, the tunneling-percolation model calls into play tunneling processes between conducting particles which, under some general circumstances, could lead to transport exponents dependent of the mean tunneling distance a. The validity of such theory could be tested by changing the parameter a by means of an applied mechanical strain. We have applied this idea to universal and nonuniversal RuO 2 -glass composites. We show that when t Ͼ 2 the measured piezoresistive response ⌫, i.e., the relative change of resistivity under applied strain, diverges logarithmically at the percolation threshold, while for t Ӎ 2, ⌫ does not show an appreciable dependence upon the RuO 2 volume fraction. These results are consistent with a mean tunneling dependence of the nonuniversal transport exponent as predicted by the tunneling-percolation model. The experimental results are compared with analytical and numerical calculations on a random-resistor network model of tunneling percolation.

The stabilities of Pt/Ti bilayer metallizations in an oxidizing atmosphere have been investigated with several thicknesses of interfacial Ti-bonding layers. Reactions in the Pt/Ti/SiO 2 /Si interface were examined as a function of various annealing conditions in the temperature range 200-800°C by using Rutherford backscattering spectrometry, Auger electron spectroscopy, x-ray diffraction, and transmission electron microscopy. Thermal treatment in oxygen was found to cause rapid oxidation of the Ti layer, accompanied by the migration of Ti into the Pt film. Diffusion of oxygen through the Pt grain boundaries was mainly responsible for the adverse reactions at the interface and loss of mechanical integrity. Thin Ti (10 nm) layers resulted in the depletion of the interfacial bonding layer causing serious adhesion problems, whereas thicker Ti films (100 nm) caused the formation of TiO 2-x in the Pt-grain boundaries, ultimately encapsulating the Pt surface with an insulating TiO 2 layer. Improved stability and adhesion in the Pt/Ti bilayer metallization compatible with ferroelectric thin film processing, were achieved by incorporating well reacted thin TiO 2 , layers in situ, and depositing Pt films at a high temperature.

The piezoelectric response of silicon diaphragms covered with sputter-deposited PbZr 0.45 Ti 0.55 O 3 (PZT) films has been investigated in view of their application in ultrasonic micro-actuators. The behaviour of resonance frequencies and quasistatic deflections has been studied as a function of membrane thickness and d.c. bias. The total stress in the films and the piezoelectric constant, d 31 , have been derived by means of two different methods. The results are consistent with direct strain measurements by optical interferometry and with bulk ceramic values of identical composition.

For the first time we have characterized a micromotor driven by a piezoelectric PZT (PbZr x Ti 1-x O 3 ) thin film. Sputter and sol-gel techniques have been applied for the deposition of the PZT films onto a silicon stator membrane, which was 20 to 30 µm thick and had a diameter of 4 mm. The amplitudes of the membrane deflections have been measured by means of laser interferometry. They are as large as 800 nm/V at the first resonance (26 kHz), and 60 nm/V at 1 Hz. This is one order of magnitude larger than previously reported for a ZnO activated device of similar geometry. The operation of the motor was obtained at 1 to 3 V rms , with speeds of up to 200 rpm at 1.1 V rms and torques of 35 nN·m at 2.5 V rms and 1 mN force between rotor and stator. In comparison with the conceptually identical ZnO version published by Racine et al. this is an improvement by a factor of 3 in speed per volt. Taking into account the linear increase of the torque with the stator vibration frequency, the torque per voltage is a factor two higher. A long time test of 100 h showed no degradation of the motor performance.

The present work critically reviews the scientific and patent literature on low melting bismuth based oxide glass frits in materials for electronics, sensors and related applications such as sealing glasses, solar cells, architectural and automotive glass, the main motivation being to replace lead based materials by environmentally more benign ones. Due to similar glass forming properties of Bi and Pb, Bi based glasses are the closest 'drop-in' alternative for lead bearing formulations, and are therefore actually replacing them in many applications, helped also by previous experience with Bi containing materials in thick film technology and component metallisations. The outstanding issues are discussed, e.g. matching the lowest processing temperatures achieved by the classical lead based glasses without sacrificing durability and stability, as well as stability versus chemical reduction. Finally, consideration is also given to special 'heavy' glasses (often containing Bi and Pb together) that are useful in fields such as optics, superconductors and nuclear technology, as well as to specific Bi 2 O 3 containing crystalline compounds.Keywords: Glasses, Bismuth, Bi 2 O 3 , Electronics, Optics, Thick film technology, Sensors Introduction Low melting glasses in electronics and other applicationsAs for ceramics, inorganic glasses, glass-ceramic and glaze materials have long gone beyond their traditional uses to address a wide array of modern technological challenges, Owing to performance and cost criteria, most standard glasses have relatively high softening points. However, there are many technological applications where a low softening temperature is required, in order to lower energy expenditure, avoid damaging devices in contact with the glass during processing or ensure compatibility with other materials:(i) hermetic sealing of packages, lamps, electrical feedthroughs and semiconductor devices 13,14,16,17,19,44,45 (ii) hermetic sealing and mechanical attachment of sensors 23,27 ( Fig. 1) (iii) encapsulation of semiconductor devices 29,30 (iv) overglazing of automotive, packaging and architectural glass 33,34,[46][47][48] (v) photovoltaic (PV) solar cell technology -conductors and contacts 42,43,[49][50][51][52][53] (vi) enamelling of aluminium in architecture and home appliances 35,[54][55][56][57][58] (vii) thick film (TF) electronics and other devices 21,22,24,25,27,59 (Fig. 1, the section on 'PbO in low melting frits and TF technology'); especially, special low firing compositions for fabrication of circuits and sensors on glass or metals. 1,28,[66][67][68][69][70][71][72] For these applications, glasses are often formulated as frits (e.g. finely divided powder), which may be applied, dispersed in a suitable medium, onto a substrate by various methods such as slip casting, screen printing, roller/curtain coating, spraying, dispensing and electrophoresis, or as preforms for sealing. Classically, the aforementioned applications have to a great extent used lead based glasses, which have a rather unique combinat...

We have developed a robotic interface to train hand and finger function. HandCARE is a Cable-Actuated REhabilitation system, in which each finger is attached to an instrumented cable loop allowing force control and a predominantly linear displacement. The device, whose designed is based on biomechanical measurements, can assist the subject in opening and closing movements and can be adapted to accommodate various hand shapes and finger sizes. Main features of the interface include a differential sensing system, and a clutch system which allows independent movement of the five fingers with only one actuator. The device is safe, easily transportable, and offers multiple training possibilities. This paper presents the biomechanical measurements carried out to determine the requirements for a finger rehabilitation device, and the design and characterization of the complete system.