Structures and thermal properties of the N₂monolayer on Pb(1 1 1)

Abstract

The physisorption of N2 molecules has long been a model system of molecular adsorption. We present a low-energy electron diffraction (LEED) study of the adsorption structures and thermodynamics of monolayer N2 on Pb(1 1 1). The results indicate that the monolayer structure has a triangular incommensurate center-of-mass lattice, and that the N2-substrate interaction is weaker than that observed on other metal surfaces. The N2 monolayer undergoes a phase transition between an orientationally ordered phase (low-temperature) and an orientationally disordered phase at a temperature of 20 K. Potential energy and quasiharmonic calculations indicate that the weak N2-Pb(1 1 1) interaction is the main contributing factor for the difference in orientational order of incommensurate N2 monolayers on Pb(1 1 1) and other similar metal surfaces.

Approximating the 3D Character of a Van Der Waals Atom–Solid Potential

“…Having a framework such as presented here may also help recognize computational artifacts during the course of calculations. Extensions to diatomics on metals, such as N 2 /Ag(111) and N 2 /Pb(111), could test the basis of an assumed relation [4] between the perpendicular vibrational frequency and the librational frequency that sets the threshold for non-planar ordering of the monolayer solid. Another extension would be to adsorption on fcc(110) where there is evidence for top-row adsorption of Xe/Cu(110) [11,23,30] and Xe/Ni(110) [31,32].…”