NARROWING SPUTTERED NANOPARTICLE SIZE DISTRIBUTIONS

By adjusting the sputtering rate and gas pressure, it is possible to f orm nanoparticles of different sizes, phases, and materials. We have i nvestigated the spatial distribution of sputtered particle formation u sing a vertical, linear arrangement of substrates. Collecting the part icles soon after they are formed, before they have time to grow and ag glomerate, allows one to obtain a narrow size distribution. In the cas e of molybdenum, a narrow distribution of cubic particles is formed at relatively large distances (8 cm) from the source. These cubic partic les collide and self-assemble in the vapor into arrays of larger cubic particles. The particle size histograms are fitted to lognormal distr ibution functions. How supersaturation occurs is discussed qualitative ly as a function of the distance from the substrate, sputtering rate, and the mean free path in the vapor. This method of nanocrystalline pa rticle formation has potential use in magnetic and opto-electronic (qu antum dot) applications, where a narrow size distribution is required.