Influence of atomic tip structure on the intensity of inelastic tunneling spectroscopy data analyzed by combined scanning tunneling spectroscopy, force microscopy and density functional theory

TL;DR

This study demonstrates that atomic tip structure significantly influences IETS signal intensity, with combined STM, AFM, and DFT analysis revealing how tip configuration and molecular positioning affect tunneling current pathways.

Contribution

It introduces a combined experimental and theoretical approach to identify atomic tip structures and their impact on IETS signal strength, advancing understanding of tunneling mechanisms.

Findings

Single atom tips yield higher IETS intensities.

Elevated CO molecules reduce tip dependence of IETS.

Tip structure and molecular positioning control tunneling pathways.

Abstract

Achieving a high intensity in inelastic scanning tunneling spectroscopy (IETS) is important for precise measurements. The intensity of the IETS signal can vary up to a factor three for various tips without an apparent reason accessible by scanning tunneling microscopy (STM) alone. Here, we show that combining STM and IETS with atomic force microscopy enables carbon monoxide front atom identification, revealing that high IETS intensities for CO/Cu(111) are obtained for single atom tips, while the intensity drops sharply for multi-atom tips. Adsorbing the CO molecule on a Cu adatom [CO/Cu/Cu(111)] such that it is elevated over the substrate strongly diminishes the tip dependence of IETS intensity, showing that an elevated position channels most of the tunneling current through the CO molecule even for multi-atom tips, while a large fraction of the tunneling current bypasses the CO molecule in the case of CO/Cu(111).