Influence of the adsorption geometry of PTCDA on Ag(111) on the tip–molecule forces in non-contact atomic force microscopy

Gernot Langewisch,Jens Falter,André Schirmeisen,Harald Fuchs

doi:10.3762/bjnano.5.9

Abstract

Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) adsorbed on a metal surface is a prototypical organic–anorganic interface. In the past, scanning tunneling microscopy and scanning tunneling spectroscopy studies of PTCDA adsorbed on Ag(111) have revealed differences in the electronic structure of the molecules depending on their adsorption geometry. In the work presented here, high-resolution 3D force spectroscopy measurements at cryogenic temperatures were performed on a surface area that contained a complete PTCDA unit cell with the two possible geometries. At small tip-molecule separations, deviations in the tip-sample forces were found between the two molecule orientations. These deviations can be explained by a different electron density in both cases. This result demonstrates the capability of 3D force spectroscopy to detect even small effects in the electronic properties of organic adsorbates.

Highlights

Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) adsorbed on the Ag(111) surface is a prototypical organic–anorganic interface that has been investigated by a large variety of different methods in the past [1]
In the past, scanning tunneling microscopy and scanning tunneling spectroscopy studies of PTCDA adsorbed on Ag(111) have revealed differences in the electronic structure of the molecules depending on their adsorption geometry
As already described by Moll et al for PTCDA on Cu(111) [16], the contrast in Atomic force microscopy (AFM) images recorded at tip–sample distances that correspond to the regime of repulsive forces reflects the electron density distribution of the molecules

Summary

Introduction

Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) adsorbed on the Ag(111) surface is a prototypical organic–anorganic interface that has been investigated by a large variety of different methods in the past [1]. A correlation between the electronic differences of the two PTCDA molecules of the unit cell and a force contrast in AFM experiments has not been reported yet.

Results

Conclusion