Influence of the surface structure on the initiation of nuclear-chemical processes under laser ablation of metals in aqueous media

Abstract

It is shown that the efficiency of nucleochemical transformations under conditions of laser ablation of metals in aqueous media under the influence of picosecond laser pulses with peak intensity IE ∼ 1010–1013 W/cm2 is largely determined by features of the metal’s surface relief in the region of high spatial frequencies (nanometer range) formed under these conditions. This is found through an atomic force microscopy study of the relief features of such surfaces formed with different laser ablation modes on specially prepared model samples. Analysis of the obtained images by means of flicker-noise spectroscopy with key 3D surface parameters in the nanometer range allow us to associate the rates of nuclear processes initiated upon laser ablation with sharpness factor as a measure of the chaotic constituent of the relief profile of a forming surface at the highest spatial frequencies. It is found that it is in the neighborhood of the greatest high-frequency irregularities of the surface that electric fields with the highest voltage that lowers the energy barrier to electron injection from the metal (the Frenkel effect) are located and the elevated values of mechanical tensile stresses that also contribute to reducing the work of an electron escaping from the metal (the Zhurkov effect) are found. It is concluded that the sharpness factor must play the key role in raising kinetic energy of electrons Ee to ∼5–10 eV in the subsurface regions of low-temperature plasma formed upon laser ablation in the metal subsurface region in which the above nucleochemical transformations can occur.