Tuesday, January 7, 2014

Photothermal Heating of Nanowires

Paden B. Roder , Bennett E. Smith , E. James Davis , and Peter J. Pauzauskie

A theoretical model is developed here in tandem with single-beam laser trapping experiments to elucidate the effects of the numerous thermal, optical, and geometric parameters that affect internal temperature distributions within finite nanowires (NWs) during laser irradiation. Analytical solutions to the heat-transfer equation are presented to predict internal temperature distributions within individual nanowires based on numerical calculations of the internal electromagnetic heat source. Single-beam laser-trapping experiments are performed to measure photothermal heating of silicon NWs. Silicon has not been considered to date for photothermal heating applications due to its indirect bandgap and low absorption coefficient in the near-infrared tissue-transparency window. We also show here that ion-implantation may be used to increase the optical absorption of silicon nanowires (SiNWs) leading to significant heating to temperatures greater than 42°C in an aqueous environment at an irradiance of 3 MW/cm^2. Experimental observations of photothermal heating agree well with theoretical predictions. Calculations for comparison with amorphous-carbon NWs reveal significantly greater heating effects, as well as internal radial gradients not observed for SiNWs.

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