Ordered assemblies of nanocrystals called superlattices are promising materials for next generation devices. detectors and sensors. However, traditional methods to assemble nanocrystals lack the control needed for device integration. To fill this gap we show that electrophoretic deposition can be used to drive nanocrystal assembly. We will demonstrate that field-driven assembly can deposit well-ordered superlattices with diffraction peaks out to (2,2,8) over large (cm²) areas. Moreover, the process is amenable to wafer-level deposition, reversible and several orders of magnitude faster than conventional solvent evaporation or co-solvent techniques. The electric field controls the nanocrystal flux making the deposition process akin to vapor deposition. To demonstrate this new level of control, we use the field to systematically change the growth rates and nucleation density. These are confirmed using in situ quartz crystal microbalance to measure growth rates and ex situ imaging to measure nucleation density. We use nickel and silver nanocrystals to illustrate that films can grow either via a layer-by-layer or by an island formation mechanism and that ligands play a central role in determining whether nanocrystals assemble into thin films or colloidal crystals. This new level of control allows us to tune the correlation length, which we expect to have advantages for fundamental studies and to benefit device performance.

Work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.