During the fellowship, I along with my principal supervisor Sir John Pendry and collaborator Prof. Richard Craster, were successful in the objective of developing a model to quantify phonon transmission by using the theory of elastic wave propagation. Interestingly, we were able to show that low frequency phonons can transmit across vacuum gap with a transmission coefficient of near unity. Using this model we were also able to estimate the heat transfer across vacuum gap due to the transmission of phonons.
In order for this result to be relevant to the industry, we quantified the heat transfer values for different materials commonly used in the nano and micro-mechanical industry such as silicon, germanium, quartz and polyethylene. We showed that for nanometer spacings the heat transfer from this mode of phonon transmission can exceed the heat conduction in the presence of air gap at room temperature and atmospheric pressure.
This result is highly important to the nano and microelectromechanical industry especially for the design of miniature devices where distance between components is of the order of a few nanometers. These results were discussed with the research staff of Seagate Hard drives during a Heat Transfer conference in Bad Honneff, Germany.
While developing the model we discovered that a simple coupled harmonic oscillator description can be used for such an analysis. A collaboration with Professor Girish Agarwal from Texas A&M university was established to extend this model to optical phonons. We successfully showed that such a coupled harmonic oscillator model can be used in place of the complication fluctuational electrodynamics theory that is currently employed by researchers to analyse near-field heat transfer.
