There are several advantages of growing carbon nanotubes (CNTs) directly on bulk metals, for example in the formation of robust CNT-metal contacts during growth. Usually, aligned CNTs are grown either by using thin catalyst layers predeposited on substrates or through vapour-phase catalyst delivery. The latter method, although flexible, is unsuitable for growing CNTs directly on metallic substrates. Here we report on the growth of aligned multiwalled CNTs on a metallic alloy, Inconel 600 (Inconel), using vapour-phase catalyst delivery. The CNTs are well anchored to the substrate and show excellent electrical contact with it. These CNT-metal structures were then used to fabricate double-layer capacitors and field-emitter devices, which demonstrated improved performance over previously designed CNT structures. Inconel coatings can also be used to grow CNTs on other metallic substrates. This finding overcomes the substrate limitation for nanotube growth which should assist the development of future CNT-related technologies.
Structural components subject to cyclic stress can succumb to fatigue, causing them to fail at stress levels much lower than if they were under static mechanical loading. However, despite extensive research into the mechanical properties of carbon nanotube structures for more than a decade, data on the fatigue behaviour of such devices have never been reported. We show that under repeated high compressive strains, long, vertically aligned multiwalled nanotubes exhibit viscoelastic behaviour similar to that observed in soft-tissue membranes. Under compressive cyclic loading, the mechanical response of the nanotube arrays shows preconditioning, characteristic viscoelasticity-induced hysteresis, nonlinear elasticity and stress relaxation, and large deformations. Furthermore, no fatigue failure is observed at high strain amplitudes up to half a million cycles. This combination of soft-tissue-like behaviour and outstanding fatigue resistance suggests that properly engineered nanotube structures could mimic artificial tissues, and that their good electrical conductivity could lead to their use as compliant electrical contacts in a variety of applications.
Arrays of Cr zigzag nanosprings and slanted nanorods, 15-55 nm and 40-80-nm-wide, respectively, were grown on SiO2/Si substrates by glancing angle deposition. The arrays exhibit a reversible change in resistivity upon loading and unloading, by 50% for nanosprings and 5% for nanorods, indicating their potential as pressure sensors. The resistivity drop is due to a compression of nanosprings (by a measured 19% for an applied external force of 10(-10) N per spring), which causes them to physically touch their neighbors, providing a path for electric current to flow between nanosprings. Repeated loading and unloading at large loads (> or =1 MPa) results in irreversible plastic deformation and a degradation of the pressure sensitivity.
Ba 1Ϫx Ca x TiO 3 thin films (xϭ0.05 to 0.17͒ were deposited on Pt-coated Si substrates using a pulsed excimer laser ablation technique. X-ray diffraction and scanning electron microscope studies of the Ba 1Ϫx Ca x TiO 3 targets exhibit a polycrystalline nature and thin films also show the same but with a significant orientation along the ͑111͒ direction. Secondary ion mass spectrometer analysis reveals the presence of a sharper interface existing at the thin film substrate. The dielectric phase transition temperature of (Ba 1Ϫx Ca x)TiO 3 targets were sharp and the transition temperature was found to decrease from 140°C to 110°C with an increase in the values of x (xϾ0.05 at. %). The laser ablated Ca-doped BaTiO 3 thin films deposited at 100 mTorr exhibited a higher dielectric constant, lower dielectric loss, and an anomalous decrease in phase transition was observed. The anomalous phase transition decrease was ascribed to the occupancy of the Ca 2ϩ in the Ti 4ϩ site. There was a cross over from the sharp to diffused phase transition for a higher composition of Ca ͑Ͼ9 at. %͒ in BaTiO 3 thin films. The diffuse transition behavior might be due to the larger number of the Ca 2ϩ ions occupying the Ti 4ϩ site, eventually introducing larger compositional and structural disorder and this occupancy leads to the generation of oxygen vacancies. The activation energy obtained from impedance spectroscopy was 1.05 eV, and was attributed to the oxygen vacancy motion.
Relaxation and conduction mechanisms under small ac fields of laser ablated ZrTiO 4 thin films were analyzed in the light of impedance and modulus spectroscopy. The overall dielectric properties were mainly dominated by a Maxwell-Wagner type of relaxation with grains and the grain boundary two distinct parts of the circuit. Each of these parts was found to follow the universal power law of frequency dispersion. The modulus plot confirmed that the capacitive parts were relatively independent of the frequency and temperature, whereas the impedance and ac conduction studies exhibited significant temperature and frequency dependence. The conduction inside the grains was suggestive of a hopping mechanism through various defect sites whereas the interface barrier potential dictated grain boundary conduction.
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