Seminars Archive

Soft-X-ray SpectroNanoscopes at the Pohang Light Source

Abstract
Soft x-ray spectroscopy, such as x-ray photoelectron spectroscopy (XPS) or x-ray absorption spectroscopy (XAS), has been developed and widely used to investigate the oxygen valency state, chemical states and electronic structure of a specimen. The need to obtain local spectral information has been the natural momentum for developing spectro-nanoscopy. Scanning photoelectron microscopy (SPEM) based on XPS and scanning transmission x-ray microscopy (STXM) based on XAS are the examples, and over the past several decades there has been much progress on the spectronanoscopy in space resolution wise and in practical application wise. In general, the space resolution of spectro-nanoscopes is still worse than those of electron microscopes. However, since the soft x-ray spectronanoscopes have their unique advantages in application, such as capability of topmost surface or single-layer specimen investigation by using SPEM without any special treatment and ability of in solution and in-situ investigations on soft and damageable samples by using STXM, there will be many promising application fields for the future of soft x-ray spectronanoscopes. In this presentation I will introduce a SPEM and a STXM and their recent activity examples at the Pohang Light Source in Korea. The SPEM has been operational more than 10 years. The space resolution is larger than 250 nm and mostly running at 400 – 1200 eV photon energy. Even though the space resolution is not quite attractive, SPEM has been succefully applied for the investigation of graphene and MoS2 layers, mostly in terms of materials scientists’ point of view that SPEM can be utilized for the identification of their samples, functionalized samples, and for supporting their sample fabrication mechanisms. The STXM opened last year. Currently, the space resolution is around 30 nm (with a 25 nm outermost zone plate, but 17 nm structures can be visualized). In future we will try to make the resolution better by utilizing a better zone plate or by using Ptychography technique. I will describe in detail on the STXM setup and its current functionality, and then, briefly, introduce what kind of sample systems are under investigation. The beamline for the STXM is based on an EPU undulator and provides photons ranging 100 – 2000 eV with spectral resolving power of ~5000.