Showing papers by "Simon Brown published in 2012"

Anisotropic oxidation of bismuth nanostructures: Evidence for a thin film allotrope of bismuth

Abstract: We present evidence that ultra-thin Bi(110) nanostructures oxidise from the edges, and that their top surfaces remain unoxidised. Even after prolonged oxidation, clean (unoxidised) bismuth is present in nanostructures that are less than 5 monolayers thick. Since the (110) surface of bulk bismuth is known to be readily oxidised, this is strong evidence for a thin film allotrope of bismuth. We present a comparison with calculated structures and the structures of polymeric nitrogen, which suggests that the allotrope is one of several complex or hybrid paired-layer structures.

Imaging shallow gas drilling hazards under three Forties oil field platforms using ocean-bottom nodes

Abstract: Reliable seismic images of gas accumulations in the shallow subsurface beneath production platforms are mitigating drilling risks in the Forties oil field. Ocean-bottom nodes (OBN) were selected to record the seismic data due to their ability to operate safely and efficiently in busy and obstructed oil fields. The resulting seismic images allow extra care to be taken during drilling where gas is likely to be encountered. The resulting operations can therefore be optimized in terms of both safety and costs.

Germanium nano-cluster films as humidity and hydrogen sensors

Abstract: Films of germanium nano-clusters of 30 nm diameter were fabricated in a high-vacuum deposition apparatus utilizing an inert-gas-aggregation source. The germanium films readily formed an oxide layer in high vacuum along with a corresponding resistance increase, a process that accelerated when films were exposed to dry air. A decrease in resistance was observed when films were exposed to ambient air, and this was attributed to water vapour adsorbing on the surface. The effects of film-thickness were investigated. A reversible change in resistance of 2 orders of magnitude was observed for 99% humidity, with a response time of tens of minutes. It is proposed that the resistance-decrease occurs because water vapour creates surface defects which act as donors causing the electron concentration in the n-type film to increase. The films were also sensitive to hydrogen concentrations above 1% in dry air, with up to a factor of 25 decrease in resistance observed for 5% hydrogen concentration at room temperature. Un...