Photothermal structural modification of porous gold nanoshells via pulsed-laser irradiation: effects of laser wavelengths and surface conditions.

Pulsed lasers are promising candidates for fabricating plasmonic nanoparticles having unique structures, and there is a strong need for studies on the detailed effects of various experimental conditions on laser-induced fabrications. In this work, we demonstrate the effects of laser wavelengths and nanoparticle surface conditions, as well as laser fluences, in the structural modification of porous gold nanoshells induced by picosecond pulse irradiation. Laser wavelengths play a critical role in the modification because irradiating laser pulses excite not only porous gold nanoshells but also gold nanospheres, which have been produced via the melting of irradiated porous gold nanoshells. Significantly different localized surface plasmon resonances of gold nanospheres and porous gold nanoshells make the effect of laser wavelengths noticeable. The polyvinylpyrrolidone (PVP) concentration of colloid containing porous gold nanoshells also modifies the deformation of the structures. Gold nanostructures become positively charged by the irradiation, strengthening gold-PVP attraction. The stronger binding affinity of PVP is considered to reduce the deformation of irradiated porous gold nanoshells.