Scanning soft X-ray imaging at 10 nm resolution

The potential imaging and selected-area near-edge X-ray absorption fine structure spectroscopic (NEXAFS) performance of a new scanning probe X-ray microscope (SPXM) for soft X-rays from synchrotron radiation is examined by computer modelling; an optical design for the microscope is also given. Acceptable dwell times per pixel in image collection are predicted. The microscope is expected to have a spatial resolution for “water-window” X-ray wavelengths (2.3–4.4 nm) of about 10 nm for specimens up to 200 nm thick. The central component of the optical system is a tube collimator forming a probe a few wavelengths in diameter above a scanned specimen. The collimator is illuminated at near-normal incidence by a Fresnel zoneplate condenser, and its exit aperture is positioned a few wavelengths above the specimen. Physical understanding is gained by a two-dimensional (2D) waveguide approach, and by calculations using the full-vector theory of Maxwellʹs equations. The calculations, because of computational limitations, are carried out mainly in 2D. The vector results agree well with a multislice scalar calculation in 2D which is then applied to 3D to describe the 3D probe imaging and to estimate the energy throughput.