Thermal analysis of gold nanorods heated with femtosecond laser pulses

• Published in: Journal of physics. D, Applied physics Vol. 41; no. 18; p. 185501
• Main Authors: Ekici, O, Harrison, R K, Durr, N J, Eversole, D S, Lee, M, Ben-Yakar, A
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 21.09.2008; Institute of Physics
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves; Physics; Transport properties of condensed matter (nonelectronic); Thermal diffusion; Gold; Polarization; Heat equation; Fluence; Laser-radiation heating; Heat treatments; Interfaces; Nanoparticles; Laser pulse; Electron lattice interaction; Thermal conductivity; Nanorod; Heat transfer
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/41/18/185501

We present an axisymmetric computational model to study the heating processes of gold nanoparticles, specifically nanorods, in aqueous medium by femtosecond laser pulses. We use a two-temperature model for the particle, a heat diffusion equation for the surrounding water to describe the heat transfer processes occurring in the system, and a thermal interface conductance to describe the coupling efficiency at the particle/water interface. We investigate the characteristic time scales of various fundamental processes, including lattice heating and thermal equilibration at the particle/surroundings interface, the effects of multiple laser pulses, and the influence of nanorod orientation relative to the beam polarization on energy absorption. Our results indicate that the thermal equilibration at the particle/water interface takes approximately 500 ps, while the electron-lattice coupling is achieved at approximately 50 ps when a 48×14 nm gold nanorod is heated to a maximum temperature of 1270 K with the application of a laser pulse having 4.70 J/m(2) average fluence. Irradiation by multiple pulses arriving at 12.5 ns time intervals (80 MHz repetition rate) causes a temperature increase of no more than 3 degrees during the first few pulses with no substantial changes during the subsequent pulses. We also analyze the degree of the nanorods' heating as a function of their orientation with respect to the polarization of the incident light. Lastly, it is shown that the temperature change of a nanorod can be modeled using its volume equivalent sphere for femtosecond laser heating within 5-15% accuracy.