Observation of assembly of fluorescent Si nanoparticles under the influence of electric current

A silicon substrate patterned by an oxide is immersed in an alcohol solution of low-doped 1-nm Si nanoparticles. Reverse biasing draws particles to the substrate, mostly along the conducting current paths. Scanning electron and fluorescence microscopy show a tree-like network on the substrate. Avoidance of closed loops and preference for an angle of branching of 90 degrees-120 degrees are observed. The building block of the tree network is not individual particles but spherical particle aggregates approximately 150 nm in diameter.