Condensation of vapor and nanoclusters formation within the vapor plume, produced by ns-laser ablation of Si, Ge and C

The condensation of vapor within the expanding plume produced by ns-laser ablation is discussed in the frame of Zeldovich and Raizer theory of condensation. The calculations have been performed for Si, Ge and C -vapors. Tt is shown that the size of clusters formed during the condensation is very small, typically of the order of few nanometers. The averaged cluster radius is calculated for different temperatures and densities of the initial plume. The generalisation of the theory is made for inhomogeneous plume where the rates of nucleation as well as condensation times are different sit different parts of the plume. The size distribution function is calculated for the plume expansion into vacuum. For the clusters moving together with vapor one can distinguish three different waves propagating through the plume: (1) The saturation wave, where the vapor becomes saturated, (2) The supercooling wave, where the highest supercooling is reached, and (3) The quenching wave, where the growth of cluster stops. The last stage of cluster formation is related to cooling of clusters and their crystallisation. This leads to delay in photoluminescence signal with typical delay time from 0.1 to 7 ms depending on the type of the background gas and its pressure.