Evidence of quantum lateral confinement in side-gated resonant tunnelling diodes formed by patterned substrate regrowth

MBE regrowth on patterned np-GaAs wafers has been used to fabricate GaAs/AlGaAs double barrier resonant tunnel diodes with a side-gate in the plane of the quantum well. The physical diameters vary from 1 to 20 μm. For a nominally 1 μm diameter diode the peak current is reduced by more than 95% at a side-gate voltage of -2 V at 1.5 K, which we estimate corresponds to an active tunnel region diameter of 75 nm ± 10 nm. At high gate biases additional structure appears in the conductance data. Differential I-V measurements show a linear dependence of the spacing of subsidiary peaks on gate bias indicating lateral quantum confinement. © 1996 American Institute of Physics.

Influence of ion energy and substrate temperature on the optical and electronic properties of tetrahedral amorphous carbon (ta-C) films

The properties of amorphous carbon (a-C) deposited using a filtered cathodic vacuum arc as a function of the ion energy and substrate temperature are reported. The sp3 fraction was found to strongly depend on the ion energy, giving a highly sp3 bonded a-C denoted as tetrahedral amorphous carbon (ta-C) at ion energies around 100 eV. The optical band gap was found to follow similar trends to other diamondlike carbon films, varying almost linearly with sp2 fraction. The dependence of the electronic properties are discussed in terms of models of the electronic structure of a-C. The structure of ta-C was also strongly dependent on the deposition temperature, changing sharply to sp2 above a transition temperature, T1, of ≈200°C. Furthermore, T1 was found to decrease with increasing ion energy. Most film properties, such as compressive stress and plasmon energy, were correlated to the sp3 fraction. However, the optical and electrical properties were found to undergo a more gradual transition with the deposition temperature which we attribute to the medium range order of sp2 sites. We attribute the variation in film properties with the deposition temperature to diffusion of interstitials to the surface above T1 due to thermal activation, leading to the relaxation of density in context of a growth model. © 1997 American Institute of Physics.

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.