Observation of a uniaxial incommensurate phase for orientationally ordered nitrogen molecules physisorbed on graphite and proposal of a phase diagram

Abstract

A previously unobserved uniaxial incommensurate phase of nitrogen molecules physisorbed on graphite occurs at 15 K for monolayer densities less than 1.05 times that of the commensurate phase. The orientational ordering superlattice is similar to that of the commensurate phase: a two-sublattice in-plane herringbone structure with two overlayer glide lines. The previously observed triangular incommensurate structure occurs only at higher densities at 15 K. A phase diagram is proposed for $10<T<\mathrm{}40\mathrm{}$ K.