Surface Action Spectroscopy: A Review and a Perspective on a New Technique to Study Vibrations at Surfaces.

Y Liu,H Kuhlenbeck,Z Wu,H.‐J Freund

doi:10.1002/tcr.202000111

Abstract

A new vibrational spectroscopy method aimed at the investigation of solid surfaces in ultrahigh vacuum, called "Surface Action Spectroscopy (SAS)", is described and the first results are reviewed. This technique is based on ideas and experiments performed in the gas phase. A surface is exposed to a messenger species at low temperature. This messenger species is desorbed via absorption of tunable infrared light from a free-electron laser and the desorption rate of the messenger species is recorded via mass spectrometry. It is shown that the technique is extremely surface sensitive and we discuss the basic mechanisms of the technique. We show a feasibility study on a V2 O3 (0001) surface, where we know the surface structure. We then proceed to the example of iron oxide films to study the surface structure in parallel with calculations of the surface phonons, which allow us to confirm the surface structure of Fe3 O4 (111) to be Fetet terminated. It also provides evidence for the so-called biphase structure. To conclude, we discuss possibilities to apply the technique to interesting questions in model and real catalysis, since the technique may provide interesting information independent of long-range order of the sample.

Highlights

Vibrational spectroscopy is a very important source of information in almost all fields of natural sciences
Infrared absorption spectroscopy is a standard tool used for molecules in solution
Authors have studied the effect of vibrational excitation of adsorbed molecules by pulsed infrared laser light.[36]. They found only thermal desorption related to transient sample heating and alluded to the relevant role of energy dissipation into the metallic substrate. It has been shown in the literature that when DIET experiments are performed on dielectric substrates exhibiting a band gap, as opposed to a metal, the desorption cross sections increase considerably, due to different energy dissipation channels

Summary

Introduction

Infrared absorption in the gas phase, one has to deal with the given sample density. In fundamental gas phase studies involving molecular beams the density is often so low that simple absorption measurements, even when sophisticated laser-based techniques are involved, are bound to fail. Authors have studied the effect of vibrational excitation of adsorbed molecules by pulsed infrared laser light.[36] They found only thermal desorption related to transient sample heating and alluded to the relevant role of energy dissipation into the metallic substrate It has been shown in the literature that when DIET experiments are performed on dielectric substrates exhibiting a band gap, as opposed to a metal, the desorption cross sections increase considerably, due to different energy dissipation channels (see ref.[36] and references therein). Beyond this we will discuss possible future experiments and perspectives of the technique to study surfaces in general and catalyst surfaces in particular

The Experiment

Systems Studied

Conclusion and Perspective