Phonon Conduction in Periodically Porous Silicon Nanobridges

Marconnet, A.M., Kodama, T., Asheghi, M., and Goodson, K.E., 2012, "Phonon Conduction in Periodically Porous Silicon Nanobridges," Nanoscale and Microscale Thermophysical Engineering, Vol. 16, No. 4, pp. 199-219.

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Thermal conduction in periodically porous nanostructures is strongly influenced by phonon boundary scattering, although the precise magnitude of this effect remains open to investigation. This work attempts to clarify the impact of phonon-boundary scattering at room temperature using electrothermal measurements and modeling. Silicon nanobeams, prepared using electron beam lithography, are coated with a thin palladium overlayer, which serves as both a heater and thermometer for the measurement. The thermal conductivity along the length of the silicon nanobeams is measured using a steady-state Joule heating technique. The thermal conductivities of the porous nanobeams are reduced to as low as 3% of the value for bulk silicon. A Callaway-Holland model for the thermal conductivity is adapted to investigate the relative impact of boundary scattering, pore scattering, and phonon bandgap effects. Both the experimental data and the modeling show a reduction in thermal conductivity with increasing pore diameter, although the experimentally measured value is up to an order of magnitude lower than predicted by the model. The model further indicates that scattering at boundaries dominates the reduction in thermal conductivity, while phonon bandgap effects are minimal.

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