Removal of surface states and recovery of band-edge emission in InAs nanowires through surface passivation.

Surface states in semiconductor nanowires (NWs) are detrimental to the NW optical and electronic properties and to their light emission-based applications, due to the large surface-to-volume ratio of NWs and the congregation of defects states near surfaces. In this paper, we demonstrated an effective approach to eliminate surface states in InAs NWs of zinc-blende (ZB) and wurtzite (WZ) structures and a dramatic recovery of band edge emission through surface passivation with organic sulfide octadecylthiol (ODT). Microphotoluminescence (PL) measurements were carried out before and after passivation to study the dominant recombination mechanisms and surface state densities of the NWs. For WZ-NWs, we show that the passivation removed the surface states and recovered the band-edge emission, leading to a factor of ∼19 reduction of PL linewidth. For ZB-NWs, the deep surface states were removed and the PL peaks width became as narrow as ∼250 nm with some remaining emission of near band-edge surface states. The passivated NWs showed excellent stability in atmosphere, water, and heat environments. In particular, no observable changes occurred in the PL features from the passivated NWs exposed in air for more than five months.

Characterisation of cell adhesion to substrate materials and the resistance to enzymatic and mechanical cell-removal

Cell-implant adhesive strength is important for prostheses. In this paper, an investigation is described into the adhesion of bovine chondrocytes to Ti6Al4V-based substrates with different surface roughnesses and compositions. Cells were cultured for 2 or 5 days, to promote adhesion. The ease of cell removal was characterised, using both biochemical (trypsin) and mechanical (accelerated buoyancy and liquid flow) methods. Computational fluid dynamics (CFD) modelling has been used to estimate the shear forces applied to the cells by the liquid flow. A comparison is presented between the ease of cell detachment indicated using these methods, for the three surfaces investigated. © 2008 Materials Research Society.

On the selective removal of steel by laser-assisted vortex machining

Of all laser-based processes, laser machining has received little attention compared with others such as cutting, welding, heat treatment and cleaning. The reasons for this are unclear, although much can be gained from the development of an effcient laser machining process capable of processing diffcult materials such as high-performance steels and aerospace alloys. Existing laser machining processes selectively remove material by melt shearing and evaporation. Removing material by melting and evaporation leads to very low wall plug effciencies, and the process has difficulty competing with conventional mechanical removal methods. Adopting a laser machining solution for some materials offers the best prospects of effcient manufacturing operations. This paper presents a new laser machining process that relies on melt shear removal provided by a vertical high-speed gas vortex. Experimental and theoretical studies of a simple machining geometry have identifed a stable vortex regime that can be used to remove laser-generated melt effectively. The resultant combination of laser and vortex is employed in machining trials on 43A carbon steel. Results have shown that laser slot machining can be performed in a stable regime at speeds up to 150mm/min with slot depths of 4mm at an incident CO2 laser power level of 600 W. Slot forming mechanisms and process variables are discussed for the case of steel. Methods of bulk machining through multislot machining strategies are also presented.