Ultrafast Laser-Induced Formation of Hollow Gold Nanorods and Their Optical Properties

Laser irradiation has been shown to be an efficient means to modify structures and shapes of plasmonic nanoparticles for tuning their properties. Thermomechanical deformations of single-crystal and penta-twinned gold nanorods by femtosecond laser irradiations have been studied by classical molecular dynamics simulations. It is demonstrated that hollow gold nanorods could be formed by femtosecond laser irradiations under certain conditions of maximum temperatures in nanorods by laser heating and cooling rates due to the extrinsic solvent. For a given maximum temperature and cooling rate, a larger cavity is induced in the irradiated single-crystal nanorod. The results also indicate that at the same cooling rate a higher threshold of maximum temperature can be required for producing the cavity in the twinned nanorod. The optical spectra of the laser-irradiated gold nanorods are calculated, and the shifts in the surface plasmon resonance peak of the nanorods are illustrated due to the thermal reshaping and the plasmon hybridization mechanism. Moreover, we show the formation of the hollow gold nanorod possessing the surface plasmon resonance peak in the second near-infrared window and a relatively small aspect ratio (similar to 2.8), which is highly desirable and suitable for serving as agents in biomedical imaging and photothermal therapy applications.