Prismatic goldnanoparticles in the periodic monolayer arrays prepared with nanosphere lithography technique can be reshaped with femtosecond laser pulses at different powers and wavelengths. As the power density of 400 nm femtosecond laser increases, the prismatic particle tips begin to round and the overall particle shape changes from a prism to a sphere with a tripodal intermediate. The formation of the tip-rounded nanoprisms is probably due to the dewetting properties of gold on quartz surface and the low melting temperature at the tips. The formation of the tripodal nanoparticles is attributed to the inhomogeneous heating and lattice rearrangement of the as-deposited nanoparticles to a metastable state, which is more stable than the prismatic shape but less stable than the spherical shape. With 800 nm femtosecond laserirradiation, only tip-rounded nanoprisms are observed and no spherical nanoparticles are formed at the laser powers used. This is most likely due to the blueshift of the plasmonabsorption band for the transformed particles, so that they cannot absorb the required energy to overcome the barrier to make the spherical shape. With 700 nm femtosecond laserirradiation, the tip-rounded and the tripodal nanoparticles are formed and few spherical particles are observed at the higher laser power density. From the results of this work, it is shown that by changing the wavelength and power density of the femtosecond laser, one can control the final shape of the particles formed from the original prismatic nanoparticles.
- laser beam effect,
- absorption spectra,
- mode locking
Available at: http://works.bepress.com/wenyu_huang/30/