Pulsed-Laser-Induced Phase Transition of Aqueous Colloidal Gold Nanoparticles at High Pressure : Picosecond Pump-Probe Study

Content Provider	Semantic Scholar
Copyright Year	2015
Abstract	[Introduction] Studies on the interaction of gold nanoparticles (AuNPs) with short pulsedlasers have been a subject of intensive research. 1 Revealing the time evolution of particle temperature initiated by the laser excitation of AuNPs is important because this information is crucial to fully understand the heating-induced phase transformations of the particle and the surrounding medium. 2 For this purpose, transient extinction spectroscopy is appropriate because temperature-induced bleaching has been known to occur for the localized surface plasmon resonance (LSPR), and the bleaching intensity is correlated with the particle temperature. Here we describe the transient spectroscopic study of a laser-induced supercritical layer around AuNPs and related phenomena by excitation with a 15 ps pulse, when the external pressure of 60 MPa is applied. The transient signals are used to figure out the particle temperature evolution and refractive index changes of the surrounding medium. [Experimental] We used 60-nm diameter AuNPs (BBI EMGC60) that are reshaped into spheres by laser annealing (59  4 nm by TEM). A picosecond pump-probe system with a custom-built mode-locked Nd 3+ :YAG laser was used to measure the transient spectra at various time delays in the ps-to-ns time regime: third-harmonic light (355 nm) with an FWHM of 15 ps was used as a pump pulse, and the picosecond white light continuum generated by focusing a fundamental pulse into a 10-cm quartz cell containing a 3:1 D2O and H2O mixture was used as a probe light. For measurements performed under a pressure of 60 MPa, the cuvette was placed in a hydrostatically pressurized container that enabled solution agitation. Post mortem particle characterization was performed by using transmission electron microscopy (TEM). [Results and Discussion] Transient extinction spectra evolved instantaneously within the excitation laser pulse and decayed in 20 ns. Given that the picosecond laser excitation contributes solely to the particle heating, the time evolution of spectra was ascribed to heatingFigure 1. Time evolution of extinction observed at 630 nm. 0.10 0.05 0.00 -0.05 -0.10  E x ti n c ti o n
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Alternate Webpage(s)	https://photochemistry.jp/2015/abstract/oral/2ABCD.pdf
Language	English
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Resource Type	Article