Nanoscale convection assisted self-assembly of nanoparticle monolayer

Micron and sub-micron particles tend to be self-organized into well-defined arrays during conventional convective assembly, however this technique hardly works for the assembly of tiny nanoparticles smaller than 10 nm into monolayered arrays. The intrinsic difficulty is mainly related to the evaporation and convections occurring at a much larger volume than nanoparticle size. As a result, multilayered nanoparticle arrays are usually created. In this paper, we report that solvent evaporation and nanoparticle convection are artificially confined in nanoscale grooves near a pipette's periphery and the grooves can help assemble parallel strips because of the uni-directional translation of the pipette. The stacking layer of each strip is correlated with the grooves' diameter, thus the nanoparticle monolayer is fabricated in the tiny grooves. The narrowest strip width observed experimentally is geometrically limited by the effective diameter of the charged nanoparticles in gold colloid because nanoparticle convections from the inner chamber to the pipette's periphery will not occur within the grooves finer than the effective diameters.