The present disclosure generally pertains to methods of preparing a well-ordered nanoparticle coating on a substrate. A nanoparticle solution having nanoparticles in a solvent is deposited on a sub-phase of a denser, immiscible liquid. A constrained area on the top surface of the sub-phase is provided, where nanoparticle solution spreading is physically limited and the nanoparticles spontaneously form a uniformly ordered monolayer on the sub-phase within the constrained area. Notably, no compression of the nanoparticle film occurs after the spreading phase in order to form the monolayer. After the monolayer is formed, a substrate is placed into contact with the monolayer and coated with a well-ordered nanoparticle coating.