Innovation Award

For a novel X-ray lens with unprecedented properties, a research team headed by CFEL group leader Saša Bajt has been awarded the 'Microscopy Today Innovation Award' by the current issue of Microscopy Today. The team's “High numerical aperture, high efficiency X-ray lenses” were judged as one of the ten best microscopy innovations in the 2018 competition, and the prize was awarded on Wednesday during the Microscopy & Microanalysis 2018 meeting in Baltimore (USA). Microscopy Today is the official magazine of the Microscopy Society of America (MSA). Team members are from CFEL Saša Bajt, Sabrina Bolmer, Henry Chapman (also University of Hamburg), Andrew Morgan, Mauro Prasciolu as well as Andrzej Andrejczuk of the University of Bialystok, Poland.

CFEL group leader Saša Bajt

The penetrating nature of hard X-rays and their short wavelengths below about 0.1 nanometers (millionths of a millimeter) make them attractive for imaging of objects such as biological cells at resolutions beyond that of visible light and without sectioning or thinning the sample as needed for transmission electron microscopy. However, these properties of X-rays also make them difficult to focus. One way is to use specialized X-ray optics called multilayer Laue lenses (MLLs). These lenses consist of alternating layers of two different materials with nanometer thickness. In contrast to conventional optics, MLLs do not refract light but work by diffracting the incident X-rays in a way that concentrates the beam on a small spot. To achieve this, the layer thickness of the materials has to be precisely controlled. The layers must gradually change in thickness and orientation throughout the lens.

The novel Multilayer Laue lenses (MLL) are typically 10 to 100 micrometers tall (aperture size), 100 micrometers wide and several micrometers thick (optical depth) with focal lengths of 1 to 10 millimeters. A micrometer is a thousandth of a millimeter. Credit: CFEL, Saša Bajt

The scientists made several innovations in the fabrication process to achieve high efficiency and to extend the numerical aperture (NA) far beyond what was previously possible, to enable imaging at spatial resolutions below 10 nanometers, with diffraction efficiencies exceeding 80 per cent. The new lenses consist of over 10 000 alternating layers of a new material combination, tungsten carbide and silicon carbide. To focus an X-ray beam in the vertical and horizontal directions it has to pass through two perpendicularly oriented lenses. By using this set-up, a spot size of 8.4 nanometers by 6.8 nanometers was demonstrated. The resolution of the new lenses is about five times better than achievable with typical state-of-the-art lenses.