Drift Mechanism of Formation of Metal Nanowires in Liquid Helium

Abstract

The formation of nanowires or their system in liquid helium (in metal laser ablation products) and metal-enriched helium droplets is a particular case of the well-known diffusion-controlled anisotropic (in an electric field) aggregation of particles. Previously, we showed that the mechanism of rapid formation of metal nanowires in a single quantum vortex proposed by several authors is impossible because of the enormous heat release accompanying the fusion of nanoparticles, which leads to their separation from the vortex and destruction of quantum vortices in the vicinity of the fused particles. In the present work, it was shown theoretically that the formation of nanowires is described by the known drift mechanism under conditions when the drift of charged nanoparticles in an electric field substantially exceeds their diffusion. The charging of nanoparticles results from (a) ionization during laser ablation and (b) thermionic emission from nanoparticles extremely heated during coagulation (which is theoretically substantiated in the present work). The drift occurs due to the attraction of charged nanoparticles to any surfaces under the action of the electric field of the image (and occasionally also under the action of the external field) as well as due to the attraction of neutral particles to charged ones. We showed that in this case, the drift prevails over the diffusion. Under these conditions, nanoparticles aggregate into anisomeric structures acting as field concentrators, which, in turn, enhances the drift and provides positive feedback during the self-assembly of nanowires.