Essay about Optical Absorption Of Gold Nps

1967 Words Sep 3rd, 2016 8 Pages
Because of the strong optical absorption of gold NPs at 520 nm by the localized surface plasmon enhancement, upon excitation the laser pulse heats up the NP in hundreds of picoseconds (14), and this results in its nonequilibrium temperature of ~900 K at the fluence J =10 mJ/cm2, that is below the melting point of gold (25). Notably, if the pump fluence is above the threshold for the melting of gold NPs, the NP-dimer will fuse into a bigger NP in dozens of nanoseconds (see Fig. S5), which has also been demonstrated by El-Sayed, Link and others (25). The thermal energy in the pair subsequently dissipates to the surroundings including the liquid and the low-frequency van der Waals modes between the particle and substrate. The high nonequilibrium temperature of the NP, which is far above the boiling point of water (~400 K), is sufficient to overcome the latent heat of water and to convert the adjacent water molecules into steam NBs (26). Due to the imperfect symmetry of the NP-dimer and thus the nonuniform heating on it, the rapid nucleation, expansion and collapse of NBs near the surface could induce an impulsive force and torque on the dimer to trigger the dynamics, as schematically shown in Fig. 3B. This mechanism is experimentally confirmed by the continuous e-beam imaging of the gold NP-dimer heated by fs-laser pulses with 3 mJ/cm2 fluence (Fig. 3C and D, see also Movie S1). The high image contrast of the continuous e-beam imaging mode allows the NB to be visible near the…

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