A new photon source for ultraviolet photoelectron spectroscopy of organic and other damage-prone materials

Accurate measurements of the valence electronic structures of organic semiconductors are important for the development and understanding of organic electronic devices, materials, and interfaces. Ultraviolet photoelectron spectroscopy (UPS) is a well-established technique for probing valence electronic structures; however, many organic semiconductors undergo rapid sample degradation upon exposure to traditional laboratory-based vacuum ultraviolet (VUV) photon sources. Here, we report on a novel VUV photon source for UPS measurements that utilizes H Lyman-α emission with a narrow linewidth and a widely tunable intensity, and apply it to a number of organic materials of interest to show its ability to overcome this hurdle of sample degradation. Furthermore, the H Lyman-α source displays no measureable higher energy emission lines, which significantly reduces the background over typical He I discharge sources and allows for the onset of the density of states to be clearly observed over several orders of magnitude.