Photoelectron spectroscopy of organic thin films deposited by gas cluster ion sputtering

Deposition of organic molecules via sputtering by argon gas cluster ion beams (GCIBs) in situ in X-ray photoelectron spectroscopy (XPS) instruments is demonstrated. GCIB deposition provides precise thickness control of coatings with in situ monitoring using XPS metrology methods. Soft-landing of amino acids, proteins and polymers allows the use of photoelectron spectroscopy to study both the material properties of the depositing molecules and their interactions at interfaces. Furthermore, the low-cost target mounting method described here enables existing GCIB-equipped XPS instruments to probe interfacial chemical reactions without modification. Small molecules can be transported to substrates in vacuo with no detectable ion beam damage or fragmentation. Ejecta from protein and highly cross-linked polymer targets produce films that retain the target chemistry while consisting of lower molecular weight species. These results show GCIB deposition to be a versatile and accessible approach for the in situ investigation of organic thin films and interfacial chemistry by XPS.