Kinetics of the X-ray induced gold nanoparticle synthesis.

Time resolved small angle scattering has been employed to follow the formation kinetics of gold nanoparticles from a solution of gold hydrochlorate and tris-sodium citrate at room temperature. While UV irradiation leads to a slow kinetics as observed by optical spectroscopy, the irradiation by the X-rays led to a reduction of the gold within a few minutes. The size and morphology evolution during the radiolytic formation of particles displays the initial nucleation phase and the growth kinetics, which exhibit very nonuniform behavior.

Small-angle pump-probe studies of photoexcited nanoparticles.

X-ray scattering experiments on femtosecond laser-excited gold nanoparticle suspensions are presented. It is shown that the time-resolved pump-probe technique using the X-ray pulse structure at synchrotron sources is capable of resolving structural dynamics on the nanometer scale to high precision. The estimation of X-ray flux density allows the projection of experiments on an X-ray free-electron laser probing single nanoparticles in a one-shot exposure.

A surface phase transition of supported gold nanoparticles.

A thermal phase transition has been resolved in gold nanoparticles supported on a surface. By use of asynchronous optical sampling with coupled femtosecond oscillators, the Lamb vibrational modes could be resolved as a function of annealing temperature. At a temperature of 104 degrees C the damping rate and phase changes abruptly, indicating a structural transition in the particle, which is explained as the onset of surface melting.

Turkevich method for gold nanoparticle synthesis revisited.

The growth of gold nanoparticles by reduction by citrate and ascorbic acid has been examined in detail to explore the parameter space of reaction conditions. It is found that gold particles can be produced in a wide range of sizes, from 9 to 120 nm, with defined size distribution, following the earlier work of Turkevich and Frens. The reaction is initiated thermally or in comparison by UV irradiation, which results in similar final products.

Excitation of nanoscale vapor bubbles at the surface of gold nanoparticles in water.

Intense nonequilibrium femtosecond laser excitation of gold nanoparticles in water leads to a transient heating of the nanoparticles, which decays via heat transfer to the water phase. It is shown that the water temperature rises to near the critical temperature and the water undergoes an explosive evaporation in the subnanosecond range. The formation of vapor bubbles shows a threshold dependence on laser fluence.