Self-assembly of gold nanorods (NRs) with aspect ratio of ∼4.6 (12 nm in diameter and 50-60 nm in length) has been studied using transmission electron microscopy (TEM). Under appropriate conditions such as nanoparticle concentration, solvent evaporation, narrow size distribution, ionic strength, and surfactant concentration of the parent solution, gold nanorods assemble into one-, two-, and three-dimensional structures. Some of the three-dimensional assemblies extend to superlattices of NRs. The translation and orientation symmetries of the self-assembled structures are determined. The factors affecting the formation of the ordered self-assembly are discussed.
We studied the shape transformation (by use of TEM and optical absorption spectroscopy) of gold nanorods
in micellar solution by exposure to laser pulses of different pulse width (100 fs and 7 ns) and different
energies (μJ to mJ) at 800 nm, where the longitudinal surface plasmon oscillation of the nanorods absorb. At
moderate energies, the femtosecond irradiation melts the nanorods to near spherical particles of comparable
volumes while the nanosecond pulses fragment them to smaller near-spherical particles. At high energies,
fragmentation is also observed for the femtosecond irradiation. A mechanism involving the rate of energy
deposition as compared to the rate of electron−phonon and phonon−phonon relaxation processes is proposed
to determine the final fate of the laser-exposed nanorods, i.e., melting or fragmentation.
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