Generation, analysis, and deposition of silicon nanocrystals up to 10 nm in diameter

Abstract

Silicon clusters have been generated by CO2- laser-induced decomposition of SiH4 in a flow reactor. By introducing a conical nozzle into the reaction zone, the clusters are extracted into a molecular beam apparatus and analyzed with a time-of-flight mass spectrometer. Besides small clusters, the mass spectra show also very large aggregates containing a few thousand of silicon atoms. A velocity analysis of the neutral cluster beam reveals that the particle velocity decreases with increasing mass. Thus it is possible to perform a size selection of the neutrals by introducing a velocity selector into the cluster beam. The silicon clusters have been deposited at low energy, and TEM micrographs of size-selectively prepared films are presented. A quantitative analysis of two different deposits reveals mean particle diameters of 3.5 and 6.5 nm. The results demonstrate the possibility of fabricating thin films of nanostructured materials with a mean particle diameter controlled by combining the cluster beam deposition technique with a velocity selector.