Lead Microclusters in the Vapor Phase as Studied by Molecular Beam-Electron Diffraction. Vestige of Amorphous Structure.

摘要

The metal microclusters are formed in the gas phase by an isobaric cooling due to argon carrier gas, followed by adiabatic expansions through nozzle apertures. Electron diffraction patterns of these condensates show the typical Debye-Scherrer rings for the f.c.c. Pb metal. The average size of clusters obtained, depending on the experimental conditions, ranges from 30 to 100 angstrom in diameter, and the cubic lattice parameters for these clusters are essentially the same, within an experimental error of 0.3%, as that for the bulk crystal. The analysis of the Bragg-peak intensities is carried out based on the usual kinematical theory and the dynamical (two-beam approximation) theory by Blackman. The former theory fails completely in accounting for small angle reflections (s less than 5 1/angstrom), whereas the latter explains successfully the whole observed intensities, except for the 2nd and 3rd order reflections (400), (440), (333), and (600). From the damping of peak intensities the temperatures of these clusters are estimated to be of the order of 150 K.