On-chip aberration correction for planar nanofocusing x-ray lenses by focused ion-beam milling

Aberration-free x-ray optics are a prerequisite for nondestructive scanning x-ray microscopy with highest spatial resolution in order to understand complex material systems and processes. Nevertheless, due to highly challenging manufacturing requirements, even state-of-the-art x-ray optics often still suffer from residual lens aberrations, and diffraction-limited performance can often only be achieved by inserting additional corrective optical elements. Here, the concept of tailor-made refractive x-ray phase plates is expanded by integrating these corrective optical elements into the focusing device directly. In this case, planar nanofocusing x-ray lenses out of silicon are corrected for aberrations by structuring the phase plate into the lens chip via focused ion-beam milling. The concept is demonstrated by focusing x-rays with an energy of 18 keV into a diffraction-limited focal spot with a size of 50 x 65 nm 2 full-width at half-maximum and a reduction in residual intensity outside the focus by a factor of well over three.