Diffusional growth of quantum dots in thin SiO-Cu films irradiated by laser pulses

High density diffraction gratings have been fabricated by irradiating thin films of SiO-Cu with two pulsed laser beams of 7 ns pulse duration, and pulse intensities of 2-6 MW/cm². Gratings were formed due to fast growth of Cu particles at the regions of high light intensity. The diffusional growth of quantum dot Cu particles in thin films of SiO-Cu was studied by transmission electron microscopy. It was measured that the average radius growth rate, dR/dt, is about 10^-4-10^-3 m/s depending on the light intensity. The heat distribution around the small absorbing particles inside the transparent matrix during the laser pulse has been analyzed, and a method for the determination of the diffusion activation energy using a periodically varying light intensity has been developed. Diffusion coefficients which limit the growth kinetics are of order of 10^-9-10^-11 m ²/s and correspond to diffusion in the liquid surrounding the hot metal particle. The activation energy was found to be 20 kJ/mol which also corresponds to diffusion in a liquid SiO matrix.