Low-resistance ohmic contacts have been fabricated on a naturally occurring B-doped diamond crystal and on polycrystalline diamond films by B ion implantation and subsequent Ti/Au bilayer metallization. A high B concentration was obtained at the surface by ion implantation, a post-implant anneal, and a subsequent chemical removal of the graphite layer. A bilayer metallization of Ti followed by Au, annealed at 850 °C, yielded specific contact resistance (ρc) values of the order of 10−5 Ω cm2 for chemical vapor deposition grown polycrystalline films and the natural IIb crystal. The ρc values from transmission line model measurements on three different contact configurations, namely, standard rectangular pads, rectangular pads on diamond mesas, and three-ring circular structures have been compared. These contacts were stable to a measurement temperature of ∼400 °C and no degradation due to temperature cycling was observed. Chemical analysis by x-ray photoelectron spectroscopy (XPS) in conjunction with Ar+ sputter depth profiling of the annealed samples indicated that the Au overlayer was not effective in preventing oxidation of the underlying Ti. The XPS study also indicated the formation of TiC at the Ti/diamond interface.

No abstract

No abstract

Equivalent conductivity, viscosity, contraction in volume and refractive index of mixtures of pyridine and acetic acid at different percentage compositions have been determined. In all cases the above properties exhibit a maximum at a composition of 83 mole % of acetic acid. Previous workers who investigated some of these properties ascribe the maxima to the formation of a complex. We have explained on a different basis that no such compound is formed, and that instead at that composition acetic acid attains maximum ionization. At least 17 mole % of pyridine has been shown to be necessary for complete ionization of acetic acid in pyridine.

Management of solid oxide fuel cell (SOFC) thermal gradients is vital to limit thermal expansion mismatch and thermal stress. However, owing to harsh operation conditions of SOFCs and limited available space in stack configuration, the number of techniques available to obtain temperature distribution from the cell surface is limited. The authors previously developed and studied a thermocouple array pattern to detect surface temperature distribution on an SOFC in open circuit conditions. In this study, the performance in terms of mechanical durability and oxidation state of the thin film thermoelements of the thermocouple array on the porous SOFC cathode is investigated. A thin-film multi-junction thermocouple array was sputter deposited using a magnetron sputter coater. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) characterisation techniques were carried out to understand characteristics of the thin film before and after temperature (20 °C–800 °C) measurement. Temperature readings from the sensor agreed well with the closely placed commercial thermocouple during heating segments. However, a sensor failure occurred at around 350 °C during the cooling segment. The SEM and XPS tests revealed cracks on the thin film thermoelements and oxidation to the film thickness direction.