(A) study on co-nanoparticle arrays on solid surfaces

Abstract

The two-dimensional arrays of 8.0 nm Co-nanoparticles capped with sodium bis(2-ethylhexyl)sulfosuccinate (NaAOT) formed on solid surfaces have been studied using ultra-high vacuum scanning tunneling microscopy (UHV-STM) and atomic force microscopy (AFM). The Co-nanoparticle arrays formed on H-passivated Si(111) by both dropping and spin-coating methods are studied using UHV-STM. By the dropping method, the Co-nanoparticles form small aggregates consisting of 4-6 nanoparticles on H-passivated Si(111), whereas by the spin-coating method, this surface is covered with mono-dispersed Co-nanoparticle arrays. Also, the Co-nanoparticle arrays formed on highly oriented pyrolytic graphite (HOPG) by both dropping and spin-coating methods are studied using AFM in a tapping mode. By the dropping method, the close-packed two-dimensional arrays of Co-nanoparticles with 1-2 ML height are observed on HOPG. However, by the spin-coating method, the Co-nanoparticles form wire-like ordered arrays oriented into one-direction on HOPG. The formation of Co-nanoparticle arrays on both surfaces observed in this work can be explained in terms of van der Waals interaction between the nanoparticle and the substrate.