A Fresnel zone plate is used to focus monochromatic X-rays to a small spot size (~30 nm). The sample is raster scanner through the focal point while detecting transmitted photons. While the technique is mainly bulk-sensitive, since samples tend to be very thin to allow adequate transmission in the soft X-ray region (e.g. ~100 nm for C 1s), surface adsorbed species can often be detected.
Photoejected electrons are magnified and imaged with a spatial resolution of ~50 nm. The environment is ultrahigh vacuum, and samples must be conducting and extremely flat. This surface sensitive full field technique features two contrast modes:
X-ray absorption spectroscopy(NEXAFS) - images are generated using the main low kinetic energy peak. Photon energy is scanned. Typically 5-10 nm sampling depth.
Photoelectron spectroscopy (XPS) - images are generated using energy selected electrons. Three possible scan modes:
- scan kinetic energy of electrons with fixed photon energy (XPS)
- scan photon energy with fixed electron kinetic energy (CFS)
- scan photon and electron kinetic energy simultaneously (CIS)