Commensurate-uniaxial-incommensurate transition of monolayer nitrogen on graphite

Abstract

Heat-capacity measurements were made to study the orientational-ordering transition of ${\mathrm{N}}_{2}$ on graphite in commensurate and incommensurate phases. Whereas a sharp heat-capacity peak was observed in the commensurate (C) and striped or uniaxial-incommensurate (UI) phases, only a broad and weak anomaly was found in the triangular-incommensurate phase. These heat-capacity traces show regions of coexistence indicating the C-UI transition to be first order.