Deposition and analysis of carbon and silicon clusters generated by laser-induced gas phase reaction

Abstract

Laser driven gas-phase synthesis in a flow reactor was employed for the production of carbon and silicon cluster beams starting from gaseous compounds. It is based on a CO<SUB>2</SUB>-laser-induced decomposition of molecular gases containing carbon and silicon, such as C<SUB>2</SUB>H<SUB>2</SUB> and SiH4. By introducing a skimmer into the reaction zone, the generated clusters are transferred to the free molecular flow and analyzed with a time-of-flight mass spectrometer. The carbon clusters are characterized by a bimodal distribution. In the region of lower masses C(subscript n clusters were observed up to n equals 19 with the progression n equals 1. In the higher mass fullerenes were observed C<SUB>60</SUB> and C<SUB>70</SUB>. Also observed were two types of silicon: clusters with number of atoms up to 12 and also large ones with number of atoms 700 - 1000 which corresponds to nanometer-size. These clusters were deposited on a silicon or sapphire target at room temperature. Micro-Raman spectroscopy techniques were used for characterization of these deposits. In particular for silicon two features in the Raman spectrum were evident: one broad band and a sharp peak which correspondently were attributed to silicon amorphous and crystalline phase and that nanocrystallites deposited on the substrate consist of about 800 atoms (quantum dots with a size of about 3 nm). Thus, the present studies show that the laser-driven nucleation in a flow reactor is a powerful technique to produce fullerenes and silicon quantum dots and other nano- size semiconductors or high-temperature evaporated materials.