Adsorption site determination of a molecular monolayer via inelastic tunneling

TL;DR

This study combines microscopy, spectroscopy, and theoretical calculations to accurately identify adsorption sites of a molecular monolayer on a metal surface, revealing vibrational mode shifts as key indicators.

Contribution

The paper introduces a method integrating IETS and DFT to determine molecular adsorption sites, overcoming limitations of traditional STM spectroscopy.

Findings

Vibrational modes vary significantly with adsorption sites.

IETS detects distinct frequency shifts for different sites.

DFT calculations confirm vibrational mode assignments.

Abstract

We have combined scanning tunneling microscopy with inelastic electron tunneling spectroscopy (IETS) and density functional theory (DFT) to study a tetracyanoethylene monolayer on Ag(100). Images show that the molecules arrange in locally ordered patterns with three non-equivalent, but undeterminable, adsorption sites. While scanning tunneling spectroscopy only shows subtle variations of the local electronic structure at the three different positions, we find that vibrational modes are very sensitive to the local atomic environment. IETS detects sizeable mode frequency shifts of the molecules located at the three topographically detected sites, which permits us to determine the molecular adsorption sites through identification with DFT calculations.