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Optimization of the thermoelectric properties of low-dimensional structures via phonon engineering

We report the first direct observation of confined acoustic phonon modes in a single semiconductor thin film. High-resolution Raman spectroscopy of ultra-thin silicon-on-insulator (SOI) structures reveals multiple quasi-equidistant peaks in the spectral range from 50 cm/sup -1/ to 160 cm/sup -1/. Confined nature of phonon transport in low-dimensional structures with the finite acoustic mismatch indicates an additional tuning capability for optimizing of thermoelectric properties of these structures. Our experimental results are consistent with the recent theoretical predictions of the strong decrease of the lateral lattice thermal conductivity due to phonon confinement.