X-ray microscope becomes three times sharper express
An X-ray beam can peer inside an opaque piece of metal and show where cracks or stresses are hiding. But to see such defects, the beam must be focused into a very narrow pencil, just as sunlight is focused by a magnifying glass into a hot spot. In an X-ray microscope, the lens plays the role of the magnifying glass. Only glass won't work for X-rays: the rays pass straight through it, barely bending. So scientists make lenses from many alternating layers of two materials — molybdenum and silicon. Each layer deflects the beam by a tiny angle, and together they focus it to a point.
The authors of the new study placed not one such layered lens but two, crossed at right angles, in the X-ray microscope at the ESRF synchrotron in Grenoble, France. Each lens focuses the beam in one direction, and together they focus it into a small spot. The resulting spot was 56 nanometers across — three times smaller than what the previous plastic lens achieved. For comparison: the flu virus is about 100 nanometers in diameter, so the new microscope can resolve details half the size of a virus.
The new lens transmits 26.7% of the X-ray light — enough to produce bright, high-contrast images. The scientists tested the microscope on a silicon pillar that connects layers of a microchip (such pillars are called TSVs). They could see how the silicon atoms are arranged inside the pillar and spot places where the crystal lattice is slightly tilted. These tilts often herald cracks that could cause the chip to fail.
Original abstract
as written by the authors arXiv:2604.20309
We introduce the use of a crossed pair of Multilayer Laue Lenses (MLLs) as an objective in Dark-Field X-ray Microscopy (DFXM). In a demonstration experiment at the ID03 beamline at ESRF, two flat Mo-Si MLLs were used, with a physical aperture of 50 x 50 $$\mathrm{\mu m^2}$$ and a focal length of 14.25 mm at 19 keV. Applying a 10 % criterion to the Modulation Transfer Functions (MTFs) acquired, a spatial resolution of 56 nm is obtained in bright-field mode -- more than three times better than with a compound refractive lens (CRL) objective. The dark-field resolution is similar. With an efficiency of 26.7 % the MLL objective expands the science domain of DFXM significantly, both for bulk and near-surface studies. Similar to the CRL case, the reciprocal space resolution is dominated by the numerical aperture (NA) of the objective, with the NA being three times larger in the MLL case. This enables faster orientation mapping and implies improved options for the use of tomographic reconstruction algorithms. Although the MLL objective pupil varies with energy and position, secondary peaks are suppressed, simplifying both interpretation and forward simulations. We present an example DFXM application using the MLL as an objective, imaging a through-silicon via Kelvin device.
The new lens is made of alternating layers of molybdenum and silicon, each only a few nanometers thick, like a stack of thousands of sheets of paper, but each sheet is a thousand times thinner than a human hair.