Correlated Membrane Fluctuations in Nanocrystal Superlattices

Superlattices of organic monolayer-stabilized silver nanocrystals exhibit structural integrity at temperatures well above the melting point of the hydrocarbon capping ligands (i.e., the C₈, C₁₂, and C₁₆ alkanethiols used in this study). Temperature-dependent small angle x-ray scattering reveals that topological disordering occurs with spatially correlated domains of characteristic length ξ that grow with increasing temperature until ξ diverges at a critical temperature Tc, as ξ~ξ₀(1-T/Tc)^-0.67. A power law analysis of the scattering intensity with wave vector indicates that interactions between membranes due to thermal undulations control the topology below Tc.