PNNL

Abstract

X-ray beam damage is often observed during surface analysis of beam sensitive materials as indicated in the introduction to this issue and in a wide variety of references. While damage occurs in a wide range of materials, those that are most susceptible to damage are materials that contain low energy covalent bonds such as polymers or other organic materials. Even amongst the relatively easily damaged polymers, there is a wide range of damage rates. The focus of this submission is on poly(2-chloroethyl methylacrylate) [PCEMA] films. In order to determine the extent to which localized sample heating could influence damage rates the temperature of the substrate holding the PECMA was controlled during irradiation. PCEMA presumably degrades primarily by photo-ionization, resulting in the production of HCl through H and Cl bond cleavage. PCEMA has been recommended as a polymer for use as a reference for evaluating x-ray damage. PCEMA has been shown to be more sensitive to degradation than PVC which has also been used as a damage sensitive material useful for comparison of damage rates. Measurements of several relatively common materials on one instrument can provide a data base that allows damage rates on one instrument to be linked or compared to other damage data in the literature.3,4,5, Therefore for purposes of comparison, damage rates for bulk PVC at the same three different temperatures used for the PCEMA data have been collected and are also presented in this volume. Other data collected at the same x-ray parameters include thin films of PVC (for which damage rates are essentially identical to the bulk material) and of poly(acrylonitrile) PAN which is more stable that either PCEMA or PVC.