Van der Waals interactions and the limits of isolated atom models at interfaces.

Shigeki Kawai,Adam S Foster,Torbjörn Björkman,Sylwia Nowakowska,Ernst Meyer,Lutz H Gade,Thomas A Jung,Jonas Björk,Filippo Federici Canova

doi:10.1038/ncomms11559

Abstract

Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter. Understanding the resulting structural motifs and patterns has become increasingly important in studies of the nanoscale regime. Here we measure the paradigmatic van der Waals interactions represented by the noble gas atom pairs Ar–Xe, Kr–Xe and Xe–Xe with a Xe-functionalized tip of an atomic force microscope at low temperature. Individual rare gas atoms were fixed at node sites of a surface-confined two-dimensional metal–organic framework. We found that the magnitude of the measured force increased with the atomic radius, yet detailed simulation by density functional theory revealed that the adsorption induced charge redistribution strengthened the van der Waals forces by a factor of up to two, thus demonstrating the limits of a purely atomic description of the interaction in these representative systems.

Highlights

Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter
Individual Ar, Kr and Xe atoms were adsorbed and stabilized at a nodal site of a molecular network on Cu(111), and their interaction with a Xe-functionalized tip of Atomic force microscopy (AFM) was measured at low temperature
Rare gas atoms stabilized by 2D MOF

Summary

Introduction

Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter. Atomic force microscopy (AFM) can directly measure the interaction between tip and sample down to the atomic scale via the frequency shift of an oscillating cantilever[17], and by integrating the measured frequency shift in the z-direction, the force and potential can be extracted quantitatively[18] This technique has been successfully used to discriminate embedded Si, Sn and Pb atoms in a Si(111) surface[19] as well as In, Sn and Si atoms in a heterogeneous III–IV chain on a Si(100) surface[20], and to study the complex interplay between deformations and electronic states in Pt–Pt and Cu–Cu metal contacts[21]. A detailed theoretical simulation generally corroborated the experimental findings, and provided insight into the role of tip-induced atomic relaxations and charge transfer processes that cause deviations from a pure van der Waals interaction between two individual atoms

Methods

Results

Conclusion