Novel Lenses Enable X-ray Microscopy with Record Resolution

Modern particle accelerators provide ultrabright and high-quality X-ray beams that are ideal for the microscopic investigation of complex materials, but taking full advantage of these properties requires highly efficient and almost perfect optics in the X-ray regime. Developing these optics has proven difficult, but researchers at DESY have reported the creation of novel lenses that enable X-ray microscopy with record resolution.

The new lenses consist of over 10,000 alternating layers of a new material combination—tungsten carbide and silicon carbide—that allowed the team to achieve a focus spot size with a diameter of less than ten nanometers, smaller than most virus particles. “The selection of the right material pair was critical for the success,” says Sasa Bajt, the DESY scientist who led the team. “It does not exclude other material combinations but it is definitely the best we know now.”

The new material combination is a type of multilayer Laue lenses (MLLs), a group of specialized X-ray optics that researchers use since X-rays cannot be focused as easily as visible light. MLLs consist of alternating layers of two different materials with nanometer thickness prepared with a coating process called sputter deposition. 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 researchers have to precisely control the layer thickness of the materials. The layers must gradually change in thickness and orientation throughout the lens, with a focus size proportional to the smallest layer thickness in the MLL structure.

The new lenses have a spot size of 8.4 nanometers by 6.8 nanometers, measured at the Hard X-ray Nanoprobe experimental station at the National Synchrotron Light Source NSLS II at Brookhaven National Laboratory, and an efficiency of more than 80 percent.

The new lenses can be used in a wide range of applications including nano-resolution imaging and spectroscopy. To show this, Bajt’s team tested the lenses with an experiment on marine plankton conducted on DESY’s X-ray source PETRA III. “These MLLs open up new and exciting opportunities in X-ray science. They can be designed for different energies and used with coherent sources, such as X-ray free-electron lasers. This great achievement would not have been possible without a wonderful team with expertise in X-ray optics and theory, nanofabrication, material science, data processing and instrumentation. Since we now know how to optimize the lens design, our work paves the way to ultimately reach the goal of one nanometer resolution in X-ray microscopy.”