Abstract
The photothermal effect of the gold nanoparticles capped with different molecules, including citrate, cetyltrimethylammonium bromide (CTAB), and methoxyl-polyethylene glycol thiol (mPEG), has been investigated by collecting the time-resolved thermal infrared emission with a step-scan Fourier-transform interferometer. Upon the photoexcitation of the gold nanoparticles with nanosecond pulse laser (25 mJ cm–2 from a 5-ns pulsed laser) at 532 nm, the transient infrared emission lasts about 1μs, referring to the thermal relaxation from gold nanoparticle to the surroundings. By comparing the infrared emission contours in 90–120 ns with the blackbody radiation spectrum, the temperatures can reach up to 400 oC as the 24-nm mPEG-AuNP. Moreover, the photoexcitation of 35 nm CTAB-AuNP reveals higher transient temperature than that of 55 nm and 89 nm CTAB-AuNP, consisting with the prediction by Mie theory that the smaller nanoparticles possesses higher contribution of absorption in the extinction coefficient. In addition, gold nanoparticles upon photoexcitation bring about melting below melting temperature. Electron microscopy shows the morphology change before and after photoexcited gold nanoparticles. The time-resolved emission spectroscopy has the advantage of the duplexity on the temporal capability and broadband spectroscopic window and makes it a promising non-contact tool to quantify the transient photothermal event of miscellaneous metallic nanostructures.