Reversible buckling in monolayer of gold nanoparticles on water surface

Formation of condensed films of nanoparticles having small ratio of metal-core-diameter to organic-shell-thickness is desired for several applications in nanotechnology. We report here results of a X-ray scattering study carried out to understand structure and morphology of monolayer of such nanoparticles having gold-core and thiol-shell directly on the water surface before the monolayer undergoes a continuous transition to a bilayer. Our results demonstrate buckling of the monolayer over a large surface pressure range (1 to 15 mN/m). The buckled state exhibits reversibility on decompression and can be annealed with temperature. We also show that condensed monolayer films of nanoparticles can be formed by annealing the buckled monolayer before transferring to solid substrates.