3.1 Introduction

A knowledge of the surface chemistry of substrates is important in our understanding of adhesion. There are many techniques which provide information on the surface chemistry of plastics. Of particular importance is XPS, also known as electron spectroscopy for chemical analysis (ESCA). This technique is outlined in Section 3.2. Static secondary ion mass spectrometry (SSIMS) and reflection infrared analysis are also widely used. Topography, which can have an important effect on adhesion, may be examined using electron microscopy or atomic force microscopy.

3.2 X-Ray Photoelectron Spectroscopy (XPS)

In this technique a solid, e.g., a plastic film, is bombarded with X-rays of known energy under high vacuum. Photoelectrons from different core levels are ejected. Photoelectrons from the first few atomic layers have a characteristic kinetic energy depending on the elements present in the surface regions. The binding energy of a photoelectron from a particular core level is given by the equation:

(2)

A schematic diagram of the equipment used is shown in Figure 1. By scanning different energies, a spectrum is obtained. The elements present in the first few atomic layers can be readily identified from their characteristic binding energies. The percentage concentration of each element can be calculated from the following equation:

(3)