Nanocrystals (NCs) are extensively used to create self-assembled
nanostructures; however, little has been achieved on the assembly
of NCs with an anisotropic shape. A key challenge with the anisotropic
NCs is assembling them into positional order with preferential atomic
crystallographic orientations. Here, we use the air–liquid
interface to prepare two-dimensional (2D) assemblies of crystalline
gold nanodisks (AuNDs) with preferentially oriented atomic lattices
and report on the in situ structural and optical
properties of the nanostructures. The structure of 2D assemblies driven
by in-plane surface pressure was monitored using grazing incidence
small-angle X-ray scattering (GISAXS) and grazing incidence X-ray
diffraction (GIXD), and optical properties were monitored using UV–vis
spectroscopy. We observe that the preferentially oriented atomic lattice
of the NDs leads to the formation of 2D hexagonal superlattices, exhibiting
a continuous blue shift of the plasmonic band with increasing surface
pressure. We quantify the packing by X-ray scattering to understand
the plasmonic properties induced by the surface pressure. This controlled
process to tune the plasmon resonance property paves a novel way to
establish the essential correlation between the structure and properties
of anisotropic NCs and opens door to the rational design of programmable
NC networks.