Predicted properties of the uniaxially incommensurate phase of N2 monolayers on graphite.

Abstract

A Monte Carlo calculation and an analytic model calculation are used to determine the properties of ${\mathrm{N}}_{2}$ monolayers on graphite at surface densities \ensuremath{\rho} just above that of the 2 \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 commensurate ground state, with \ensuremath{\rho}=1. At densities 1.006 75\ensuremath{\le}\ensuremath{\rho}\ensuremath{\lesssim}1.0563 it is established that a nonuniform, striped, uniaxial incommensurate, in-plane herringbone phase is thermodynamically stable, and there is evidence that this state may continuously evolve toward the commensurate phase as \ensuremath{\rho} approaches unity, encumbered only by the physical size of the monolayer domains. The width of the uniaxial incommensurate stripes appears to be independent of density and the lattice parameters and molecular orientations in the stripes are consistent with broadly determined experimental values. At densities \ensuremath{\rho}g1.05 the stripes become poorly defined and a modulation around commensurate lattice points of an otherwise uniform uniaxial incommensurate structure occurs. It is speculated that mass-density waves may be supported by this system.