Clivia M. Sotomayor Torres
Prof. Clivia M. Sotomayor Torres is full-time ICREA Research Professor at the Catalan Institute of Nanotechnology (ICN - http://www.nanocat.org/) where she set up the Phononic and Photonic Nanostructures group. Prior to joining ICN, she was research professor at the University College Cork, Tyndall National Institute, Ireland. Her research interests are in the field of science and engineering of optical nanostructures, especially novel lithography methods for their realisation, such as nanoimprint lithography. More recently she has been working on inorganic nanotubes and confined phonons in silicon-on-insulator thin films.
To get as close as possible to zero power electronics, the understanding of phonons and fluctuations in IT device-relevant materials is essential. Lattice vibrations or phonons are at the heart of heat generation, transport and storage starting at the atomic scale. In nanoscience we have learnt that the characteristics of excitations in solids are strongly modified as dimensions are reduced and become commensurate with their de Broglie wavelength. The dispersion relations determining their interactions are strongly modified and this impacts the way that, for example, phonons interact with electrons, spins, photons and plasmons. Therein exists a major opportunity to understand and modify the heat transport by phonons in nanoelectronics. The theoretical descriptions are in general classical, however, once quantised electrons come into play, quantum mechanics needs to be considered.
Viewing fluctuations as low frequency phonons helps us in our understanding of noise and energy harvesting. The descriptions in these cases are firmly based in statistical mechanics highlighting the need for a stronger interaction with that area of research. Quantum processes in photosynthesis, noise generation and transmission of information below KT are some of the examples demonstrating the need to bring together currently separate bodies of knowledge.
Our research is focused on confined acoustic phonons, which have been invoked in the explanation of thermal conductance in condensed matter in attempts to explain experimental results in, eg., Si and metals both bulk and microstructures. The predictions of Hicks and Dresselhaus of the dominant role of dimensionality in the thermoelectric figure of merit ZT spun renewed interest in the study of confined acoustic phonons. The theoretical background on the origin of these modes triggered inelastic light scattering studies. Perhaps the most unambiguous observations of confined acoustic phonons in Si nanostructures were those in sub 40 nm thick SOI membranes which showed acoustic phonons in low frequency Raman scattering, the frequencies of which increased with decreasing membrane thickness.
We will discuss progress in our understanding of confined phonons since, its impact on thermal transport and outstanding scientific questions.