Checkerboard Self-Patterning of an Ionic Liquid Film on Mercury

A-resolution studies of room temperature ionic liquid (RTIL) interfaces are scarce, in spite of their long-recognized importance for the science and many applications of RTILs. We present an A-resolution x-ray study of a Langmuir film of an RTIL on mercury. At low (high) coverage [90 (50) angstrom A(2)/molecule] a mono-(bi) layer of surface-parallel molecules is found. The molecules self-assemble in a lateral ionic checkerboard pattern, unlike the uniform-charge, alternate-ion layers of this RTIL at its bulk-solid interface. A 2D-smectic order is found, with molecules packed in parallel stripes, forming long-range order normal to, but none along, the stripes.