Silicon carbide has attracted considerable attention in recent years as a potential material for sensor devices. This paper reviews the current status of SiC technology for a wide range of sensor applications. It is shown that SiC MEMs devices are well-established with operational devices demonstrated at high temperatures (up to 500 °C) for the sensing of motion, acceleration and gas flow. SiC sensors devices using electrical properties as the sensing mechanism have also been demonstrated principally for gas composition and radiation detection and have wide potential use in scientific, medical and combustion monitoring applications.

No abstract

The chemical termination of diamond has a dramatic impact on its electrical and chemical properties, where hydrogen and oxygen termination produce negative and positive electron affinities, respectively. However, the impact of halogen termination is not fully understood. We show that for low-index surfaces, 100% fluorinated surfaces exhibit chemically stable positive electron affinities in the 1.17 to 2.63 eV range, whereas 100% chlorination is energetically unfavorable. At lower coverage the positive electron affinity is smaller, being a combination of halogen-terminated and unterminated sites. For mixed halogen and hydrogen termination, a wide range of negative and positive electron affinities can be achieved by varying the relative concentrations of adsorbed species. © 2011 American Physical Society

Nickel-based contacts, deposited on 4H-SiC C-face substrates, were annealed at temperatures ranging from 800to1040°C and the phase composition of the contact layers analyzed by x-ray diffraction techniques. Ni2Si was identified as the dominant phase for annealing temperatures exceeding 925°C, with further increases in concentration with increasing temperature. At the highest annealing temperature of 1040°C, a 40nm thick nanocrystalline graphite film at the Ni2Si–SiC interface was discovered and its presence confirmed by Raman spectroscopy. The roles of the Ni2Si and graphite films in the formation of ohmic contacts were determined by their subsequent exclusion from the contact composition. Following deposition and annealing, the Ni2Si and graphite layers were etched away selectively and replaced with new metal films deposited at room temperature and without any annealing. Measurement of the current-voltage characteristics revealed that the ohmic nature of the contacts was preserved after removal of the Ni2Si and the graphite layers. It is concluded that the main reason for the conversion of Schottky to ohmic contacts during high-temperature annealing is a change of the electrical properties of the underlying SiC rather than being attributable to the presence of nickel silicides or graphite. It is proposed that a solid-state reaction between nickel and silicon carbide, similar to catalytic graphitization of carbon, may take place during Ni–SiC contact annealing at the temperature of 1040°C. This process may result in the creation of sufficient carbon vacancies in the near-interface region of the SiC to allow increased electron transport through the Schottky barrier.

Electroless templating on DNA is established as a means to prepare high aspect ratio nanowires via aqueous reactions at room temperature. In this report we show how Pd nanowires with extremely small grain sizes (< 2 nm) can be prepared by reduction of PdCl4(2-) in the presence of lambda-DNA. In AFM images the wires are smooth and uniform in appearance, but the grain size estimated by the Scherrer treatment of line broadening in X-ray diffraction is less than the diameter of the wires from AFM (of order 10 nm). Electrical characterisation of single nanowires by conductive AFM shows ohmic behaviour, but with high contact resistances and a resistivity (-10(-2) omega cm) much higher than the bulk value for Pd metal (-10(-5) cm @ 20 degrees C). These observations can be accounted for by a model of the nanowire growth mechanism which naturally leads to the formation of a granular metal. Using a simple combing technique with control of the surface hydrophilicity, DNA-templated Pd nanowires have also been prepared as networks on an Si/SiO2 substrate. These networks are highly convenient for the preparation of two-terminal electronic sensors for the detection of hydrogen gas. The response of these hydrogen sensors is presented and a model of the sensor response in terms of the diffusion of hydrogen into the nanowires is described. The granular structure of the nanowires makes them relatively poor conductors, but they retain a useful sensitivity to hydrogen gas.