Yixuan Yu1 Dian Yu2 Christine Orme1

1, Lawrence Livermore National Lab, Livermore, California, United States
2, University of California, Los Angeles, Los Angeles, California, United States

In this talk we describe the use of electric fields to drive nanocrystals assembly into superlattices. First we demonstrate that field driven assembly can deposit well-ordered superlattices with diffraction peaks out to (2,2,8) over large (cm2) areas. 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. Beyond simply depositing films, this flux control allows us to systematically change the nucleation density and growth rates. In this work we use in situ quartz crystal microbalance to measure growth rates and ex situ imaging to measure nucleation density. We use nickel and silver nanocrystals to show that films can grow either via a layer-by-layer or by an island formation mechanism. We show that the ligand plays a central role in determining whether nanocrystals assemble into thin films or colloidal crystals. This 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.