Trapping and patterning nanoparticles from spray

Gas-phase self-assembly of nanoparticles into microscale patterns by spray deposition and dielectrophoresis is demonstrated. Fluorescent nanospheres are sprayed using two different modes, pneumatic spray and electrospray. Nanospheres are trapped using microfabricated RF electrodes driven by both DC and AC voltages and the resulting particle distributions are visualised using confocal fluorescence microscopy. Pneumatic spray and dielectrophoresis leads to sharply defined patterns at electrode edges, at the expense of particle clustering. In contrast, nanospray dielectrophoresis leads to improved particle dispersion due to charge repulsion, but suffers from DC focusing effects due to surface charges. Controlled switching between the different modes is demonstrated, by manipulating the charge-state of the nanospheres and the trapping potential.