Vibrational Action Spectroscopy of Solids: New Surface-Sensitive Technique

Abstract

Vibrational action spectroscopy employing infrared radiation from a free-electron laser has been successfully used for many years to study the vibrational and structural properties of gas phase aggregates. Despite the high sensitivity of this method no relevant studies have yet been conducted for solid sample surfaces. We have set up an experiment for the application of this method to such targets, using infrared light from the free-electron laser of the Fritz Haber Institute. In this Letter, we present first results of this technique with adsorbed argon and neon atoms as messengers. We were able to detect surface-located vibrations of a thin V_{2}O_{3}(0001) film on Au(111) as well as adsorbate vibrations, demonstrating that this method is highly surface sensitive. We consider that the dominant channel for desorption of the messenger atoms is direct inharmonic vibrational coupling, which is essentially insensitive to subsurface or bulk vibrations. Another channel is thermal desorption due to sample heating by absorption of infrared light. The high surface sensitivity of the nonthermal channel and its insensitivity to subsurface modes makes this technique an ideal tool for the study of surface-located vibrations.

Chapter model systems in heterogeneous catalysis at the atomic level: a personal view

“…A novel technique, called surface action spectroscopy (SAS) has been developed [27,28], which is based on a wellknown approach used in gas phase spectroscopy [29,30]. The idea is to attach messengers to a sample, typically a molecule or metal cluster produced in a molecular beam.…”

Elucidating Surface Structure with Action Spectroscopy

“…In recent years a new vibrational method, Surface Action Spectroscopy (SAS) as a tool to measure surface vibrational spectra, has been developed at the Fritz Haber Institute. , This method is based on a concept that is now often applied in gas phase infrared spectroscopy if the sample’s density is extremely low and absorption measurements cannot be performed due to this: − molecules or clusters in a molecular beam are exposed to inert messenger species (for example rare gas atoms) which attach to them with a weak bond at low temperature. These messenger-decorated aggregates are then exposed to intense infrared radiation, often coming from a free electron laser (FEL).…”

“…If the photon energy is suitable for excitation of one of the aggregate’s vibrational modes, then the energy absorbed from the infrared beam may break the bonds between the messengers and the aggregates (this is the “action” in the term “action spectroscopy”), such that a flow of messenger atoms may be detected with a mass spectrometer. Recording the messenger desorption rate as a function of the photon energy produces a vibrational spectrum. − We have applied such a procedure to messengers adsorbed on surfaces and demonstrated its usefulness in surface vibrational spectroscopy. , …”

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

“…Based on these ideas we have developed a strategy to use "action spectroscopy" to interrogate solid surfaces. [31][32][33] A schematic illustration of the experimental setup is shown in Figure 2.…”