DEPOSITION AND ANALYSIS OF SILICON CLUSTERS GENERATED BY LASER-INDUCED GAS-PHASE REACTION

Silicon clusters have been generated by CO2-laser-induced decompositio n of SiH4 in a flow reactor. By introducing a conical nozzle into the reaction zone, they are extracted into a molecular beam apparatus and analyzed with a time-of-flight mass spectrometer. The mass spectra sho w that the cluster source emits, besides small clusters, also nanosize d species containing around 10(3) atoms. These clusters were deposited on silicon and sapphire targets at room temperature. The deposited fi lms have been analyzed with a Raman spectrometer and with a field emis sion scanning electron microscope (FE-SEM). The Raman spectra reveal a broad amorphouslike band and a relatively sharp peak at 518.1 cm(-1). Interpretation of the sharp Raman feature, based on the phonon confin ement model, suggests the presence of silicon nanocrystallites in the deposited films with a particle size of about 3-3.6 nm in diameter. Th e FE-SEM micrographs show an agglomerate of spherical particles of 3-1 2 nm in diameter, with a pronounced maximum in the size distribution a t around 3.5 nm. The various methods of characterization allow us to c onclude that the size of the nanoclusters is largely preserved if they are deposited on the substrate. Therefore, the technique presented he re might be an efficient means to produce silicon quantum dots of abou t 3 nm in diameter. (C) 1995 American Institute of Physics.