Overview

Electron spectroscopy encompasses two main techniques, X-ray photoelectron spectroscopy (XPS; also known as electron spectroscopy for chemical analysis; ESC) and Auger electron spectroscopy (AES). Both techniques identify and quantify elements present and can indicate the chemical state or functionality of elements at the surface. For best results, AES relies upon the sample being electrically conducting and consequently it is very rarely used in polymer analysis [1]. Hence it is not discussed further here.

XPS uses an X-ray beam to cause the emission of electrons from the surface of the sample. The electrons analysed do not have enough energy to escape from a depth of more than ~3-5 nm, so the XPS technique is inherently surface sensitive. The binding energy of the emitted electrons is measured and used to identify the elements present.

XPS is best performed using a monochromatic X-ray source. Monochromatic XPS inflicts the least damage to delicate materials and optimises chemical state sensitivity. A monochromatic X-ray source is an essential requirement to extract the maximum information content from most polymer systems.

The thickness of surface layers and the depth distributions in the extreme surface region can be measured using angle-dependent XPS. By simply changing the angle of the sample to the detector, the effective depth of analysis can be varied in the range 1 10 nm.

XPS is a good technique for elemental analysis of solids and low vapour pressure liquids, with a detection limit to most elements of ~1000 ppm. It can be directly quantified; showing not...