- 5.1: Surface Sensitivity & Surface Specificity
- In its simplest form, the question of sensitivity boils down to whether it is possible to detect the desired signal above the noise level. Assuming that a technique of sufficient sensitivity can be found, another major problem that needs to be addressed in surface spectroscopy is distinguishing between signals from the surface and the bulk of the sample.
- 5.2: Auger Electron Spectroscopy
- Auger Electron Spectroscopy (Auger spectroscopy or AES) was developed in the late 1960's, deriving its name from the effect first observed by Pierre Auger, a French Physicist, in the mid-1920's. It is a surface specific technique utilising the emission of low energy electrons in the Auger process and is one of the most commonly employed surface analytical techniques for determining the composition of the surface layers of a sample.
- 5.3: Photoelectron Spectroscopy
- Photoelectron spectroscopy utilizes photo-ionization and analysis of the kinetic energy distribution of the emitted photoelectrons to study the composition and electronic state of the surface region of a sample. Traditionally, when the technique has been used for surface studies it has been subdivided according to the source of exciting radiation into X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS).
- 5.4: Vibrational Spectroscopy
- Vibrational spectroscopy provides the most definitive means of identifying the surface species generated upon molecular adsorption and the species generated by surface reactions. In principle, any technique that can be used to obtain vibrational data from solid state or gas phase samples (IR, Raman etc.) can be applied to the study of surfaces - in addition there are a number of techniques which have been specifically developed to study the vibrations of molecules at interfaces.
- 5.5: Secondary Ion Mass Spectrometry
- The technique of Secondary Ion Mass Spectrometry (SIMS) is the most sensitive of all the commonly-employed surface analytical techniques - capable of detecting impurity elements present in a surface layer at < 1 ppm concentration, and bulk concentrations of impurities of around 1 ppb (part-per-billion) in favorable cases. This is because of the inherent high sensitivity associated with mass spectrometric-based techniques.
- 5.6: Temperature-Programmed Techniques
- There are a range of techniques for studying surface reactions and molecular adsorption on surfaces which utilise temperature-programming to discriminate between processes with different activation parameters. Of these, the most useful for single crystal studies is: Temperature Programmed Desorption (TPD)
Roger Nix (Queen Mary, University of London)