Following and Controlling Formation and Function of Bottom-Up Assembled Nanomaterials

Design advances for the bottom-up assembly of highly ordered functional nanomaterials have generated a wide range of fundamental questions that must be answered to continue to advance material properties, recently including strong electronic and mechanical coupling. We focus on colloidal nanocrystal advances that incorporate electrostatics to promote the formation of ordered superlattice structures from nanocrystals with high dielectric constants. Through a multiscale suite of hard X-ray scattering experiments ranging from small- to wide-angle, incoherent to coherent, and storage ring to free electron laser over a wide dynamic range of time scales, we characterize the phases, their fluctuations, and the dynamic interconversion between phases of this enigmatic system, non-invasively and in real-time, identifying the helpful role of a liquid-like intermediate phase that admits an unusually high degree of control over product yield, size, and order. We find that controlled, ordered assembly requires a balance of nanocrystal screening and surface charge that is facilitated by moderate to high dielectric ratios between the nanocrystals and their surroundings. We also find that laser absorption reversibly alters the surface charge and growth of the ordered superlattice phase and intend to leverage these finding to infer strategies to self-assemble more common low-dielectric nanocrystals into ordered structures by driving them far from equilibrium with optical excitation.