Vibrational assignments and line shapes in inelastic tunnelling spectroscopy: H on Cu(100)

TL;DR

This computational study uses density functional theory and Lorente-Persson theory to analyze vibrational modes and line shapes in inelastic tunneling spectroscopy of a hydrogen atom on Cu(100), explaining observed spectral features.

Contribution

The paper provides a detailed theoretical explanation for the broad and asymmetric peaks in STM-IETS of H on Cu(100), highlighting the effects of instrumental broadening and mode overlap.

Findings

Single broad peak arises from overlapping vibrational modes.

Instrumental broadening affects vibrational energy measurements.

Asymmetry causes apparent shifts and reduced energy separation.

Abstract

We have carried out a computational study of the inelastic electron tunneling spectrum (IETS) of the two vibrational modes of a single hydrogen atom on a Cu(100) surface in a scanning tunneling microscopy (STM) junction. This study addresses key issues about vibrational assignment and line shape of observed peaks in IETS within the framework of density functional theory calculations and the Lorente-Persson theory for STM-IETS. We argue that the observation of only a single, broad peak in the STM-IETS [L.J. Lauhon and W. Ho, Phys. Rev. Lett. 85, 4566 (2000)] is not caused by any symmetry restrictions or any cancellation between inelastic and elastic vibrational contributions for one of the two modes but is due to strongly overlapping superposition of the contributions from the two modes caused by the rather large instrumental broadening and the narrow vibrational energy separation between the modes. In particular, we find that this broadening and the large asymmetry of the vibrational line shapes gives rise to substantial apparent vibrational energy shifts of the two modes and decrease their apparent energy separation.