Probing adsorption on a nanoscale: field desorption microspectroscopy

Yuri Suchorski

doi:10.1007/s10450-016-9824-7

Abstract

Combining an energy analyzer with a field ion microscope equipped with a probe-hole which corresponds to just few atomic surface sites, spatially resolved energy analysis of ions field desorbed from the adsorbent surface is possible on a nm-scale. The experimentally measured values of the kinetic energy of field ions can be related (by means of a thermionic cycle) to the physically meaningful binding energy of corresponding adsorbed species. The development of the technique into a full serviceable micro-spectroscopy on a nanoscale allowed recent detection of the weakly adsorbed CO species on Pt(111) which are largely analogous to those adsorbed at high pressures and provided first results for the binding energy of Li adatoms in a coadsorption system, namely Li–O–W(112) for various lithium and oxygen coverages. In the present contribution, an overview of the experimental possibilities of the technique is given and recent results are discussed.

Highlights

The term ‘‘microspectroscopy’’ is usually associated with a technique, where an X-ray or UV photon beam is focused into a fine spot and the energy of the locally emitted photoelectrons provides chemical information
This concept was first realized experimentally for adsorbed alkali atoms using a lithium field desorption microscope (Li-FDM), where the Li-ions field desorbed from the surface image the latter with a nearly atomic resolution (Medvedev et al 1994), combined with a retarding potential analyzer
The development of the technique into a full serviceable micro-spectroscopy on a nanoscale allowed recent detection of the weakly adsorbed CO species on Pt(111), which are largely analogous to those adsorbed at high pressures, and provided first measurements of the binding energy of particular adatoms in a coadsorption system, namely Li–O–W(112) for various lithium and oxygen coverages

Summary

Introduction

The term ‘‘microspectroscopy’’ is usually associated with a technique, where an X-ray or UV photon beam is focused into a fine spot and the energy of the locally emitted photoelectrons provides chemical information. Since in the case of the magnetic sector field selection, a constant electric field can be used for field desorption, a ‘‘gentle’’ collecting of adsorbed species without damaging the specimen surface is possible This concept was first realized experimentally for adsorbed alkali atoms using a lithium field desorption microscope (Li-FDM), where the Li-ions field desorbed from the surface image the latter with a nearly atomic resolution (Medvedev et al 1994), combined with a retarding potential analyzer. In this way, the binding energy of Li-adatoms field-desorbed from individual surface sites on W(111) was determined (Suchorski et al 1995; 1996). In the present contribution a short overview of our recent studies, namely the results for the weakly bound mobile CO adsorption layers, similar to those that exist during the high pressure adsorption and an example of the coadsorption (lithium and oxygen), are discussed

Principles and instrumentation

Extracting Li-adatoms from the Li–O coadsorption layers

Summary and outlook