Particulate mobility in vertical deposition of attractive monolayer colloidal crystals

In the colloidal self-assembly of charged particles on surfaces with opposite polarity, disorder often dominates. In this report, we show that ionic strength, volume fraction, and solvent evaporation temperature can be optimized in the vertical deposition method to yield hexagonal close-packed monolayer arrays with positively charged colloids on negatively charged bare glass. We further extend our study to form well-defined binary two-dimensional superlattices with oppositely charged monolayers grown layer-by-layer. Our results suggest that the lack of particulate mobility in oppositely charged systems is the main cause of disorder, and maximum mobility is attained when all three growth parameters are finely adjusted to increase the time scale for the particles to stabilize and order during crystal growth in these attractive systems. A clear understanding and control of the collective behavior of highly mobile colloids could lead to the creation of greater diversity of nanoarchitectures.