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| Hypersonic acoustic devices in nanostructured silicon | ||||||||||||
The project will create structures in porous silicon that use the porosity dependence of the acoustic properties of the material to demonstrate novel devices for GHz elastic waves propagating in multilayer samples. After careful initial calibration experiments, we have recently demonstrated 1D phononic crystals (acoustic mirrors) in nanoporous silicon for elastic waves with a frequency of 1GHz. This has opened up a new field of research for porosified silicon, which has great potential for device applications. This project will build on the recent research to design and demonstrate a range of novel devices. The successful applicant will be fully involved in designing samples, etching them from crystalline silicon and then characterising them by optical spectroscopy before performing full GHz acoustic experiments on the devices. There are various opportunities to be explored in the project that will adapt and grow according to results obtained. Possible avenues for exploration are: (a) Acousto-optic devices in microcavities. We can now trap light and sound in microscale cavities, which can enhance the interaction described by the elasto-optic tensor. The strain associated with the elastic wave should modulate the refractive index of the cavity layer modifying the optical properties of the device. (b) Advanced hypersonic filter design for communication systems. Only porous silicon offers the ability for apodisation and impedance matching of spatial impedance profiles to give detailed control of filter functions in the frequency domain. (c) Planar devices Propagation of trapped hypersonic waves in waveguides fabricated from pSi can be explored with possible opportunities for developing 2D phononic crystals at hypersonic frequencies. (d) Higher frequency band gaps. It is known from work with optical Bragg mirrors, that the techniques used to produce layered devices with band gaps at frequencies of ~1GHz can be scaled to produce layers that should exhibit stop bands at frequencies up to ~40GHz. Collaboration with an ultrafast laser group will measure acoustic band gaps at these frequencies via time-resolved modulated reflectivity experiments. Funding Notes Applications: Applicants should have a background in the physical sciences and have or expect to gain a First or Upper Second Class UK Honours degree, or the equivalent from an overseas University. Possible funding sources include the Doctoral Training Account (for UK applicants) or, for EU or exceptional overseas candidates, a University studentship. Contact Dr Paul Snow (pyspas@bath.ac.uk) for further information on the project, or see http://www.bath.ac.uk/grad-office/apply/ for details on how to apply. |
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