Cell engineering is concerned with the combination of engineered materials with biological cells to create useful devices. Cells in the body are organised spatially and this organisation is reflected in the shapes of the cells themselves and in how they are positioned relative to their neighbours. A necessary first step in re-growing cells to form a tissue-like implant is to re-create this original pattern in the re-grown cells.
A brief account is given of the effects of topographic and chemical patterning on the behaviour of cells.
The methods by which such patterning can be transferred into materials suitable for cell and tissue engineering are given. The advantages of using mechanical transfer in one of its many forms for this purpose are stressed.
Arrays of 40 - 50 nm quantum dots were fabricated from Si- Si1-xGex single quantum well and superlattice structures grown by molecular beam epitaxy. The dots showing strong luminescence were studied by synchrotron source x-ray diffraction. Some of the dots were coated with SiNx films containing different build-in stresses. It was found that the luminescence intensity depends strongly on the amount of stress in the SiNx coating, being strongest when the stress was close to zero. A strain symmetrization process occurred in the bright dots. Although an exact physical origin is not yet available, it is exciting that these quantum dot diodes work at room temperature and that the whole fabrication procedure is compatible with Si- technology.
We present experimental and theoretical results on the low temperature luminescence intensity of dry etched GaAs-AlxGa1-xAs quantum dots. The luminescence intensity was found to decrease by two orders of magnitude with the decrease of dot sizes from 1 micrometers to 60 nm. Our intrinsic model of the emission yield invokes slower momentum and energy relaxation mechanisms as the lateral dimensions decrease. The extrinsic effect, which we include in our interpretation of the luminescence intensity, involves carrier diffusion with a surface nonradiative recombination velocity. The combined effect (intrinsic and extrinsic) gives a very good fit to our data. The surface recombination velocity needed for the fit was approximately 105 cm/s. Raman studies on the quantum dots showed enhanced surface phonons with the decrease of the nanostructure sizes. `GaAs'-like and `AlAs'-like surface phonons were also observed for the first time in etched nanostructures, in good agreement with the theoretical predications.
A method for reactive ion etching (RIE) InP has been developed using CH4/H2 which allows the fabrication of dots of 6Onm diameter and 200nm height with good aspect ratio. The effect of the etch on the optical quality of the InP surface is investigated by phonon Raman scattering and 5K luminescence.
Conference Committee Involvement (1)
3 August 2003 | San Diego, California, United States