Mark is an internationally recognized expert in X-ray photoelectron spectroscopy (XPS). He has several highly-cited publications in the field which focus on improvements in both sample analysis and data interpretation techniques, particularly in the analysis of transition metals. Mark also authors and maintains the X-ray Photoelectron Spectroscopy (XPS) Reference Pages, a repository of techniques, tips and reference materials designed to help XPS users worldwide. He is author or co-author of over 70 peer-reviewed publications and has issued over 3000 proprietary technical reports to industry.