Angle-resolved UPS studies of organic thin films

This paper describes recent progress of angle-resolved photoelectron spectroscopy using synchrotron radiation (SR-ARUPS) on organic thin films. SR-ARUPS has been growing to a new surface analysis technique which can offer concrete information on the molecular orientation at the film surface as well as on the origin of the electronic structure, both of which are important in understanding functions of organic thin films. Some examples of the experimental determination of the molecular orientation by SR-ARUPS are shown for epitaxial ultrathin films of phthalocyanines and bis(1,2,5- thiadiazolo)-p-quinobis (1,3-dithiole) (BTQBT). The orientation of pendant naphthalene groups at the surface of thin film of paly(2-vinylnaphthalene) is also shown, where the comparison between the results obtained by SR-ARUPS and near edge X-ray absorption fine structure (NEXAFS) spectroscopy is made in order to understand an advantage of SR-ARUPS. Furthermore, it is pointed out by showing the result on C-60 thin film that the multicentered photoemission dominates the photoelectron intensity of thin films of large organic molecules.