Beamline & Optics R&D: Enhancing Tools at NSLS, NSLS-II

"Synchrotron sources have quickly become an essential tool for a wide spectrum of research. All the action takes place at beamlines, each one consisting of a suite of sophisticated scientific instruments. The robust beamlines at NSLS produce remarkable science, and we made excellent progress on developing NSLS-II beamlines and associated science programs." — Qun Shen Director, Photon Division

While keeping the existing ring and beamline mechanical systems running, Photon Sciences staff completed a number of R&D projects this year that will improve the tools of researchers at NSLS and, in the near future, NSLS-II.

One of the major accomplishments was the installation and commissioning of NSLS beamline X17A, which is optimized for x-ray total scattering and atomic pair distribution function (PDF) experiments. The new beamline will alleviate the large demand for beam time on high-energy beamlines X17B1, X17B2, and X17B3. The scientific focus of X17A will be the structural characterization of disordered, nanocrystalline and complex nanostructured bulk materials at ambient and extreme conditions. The beamline features a novel Laue diffraction monochromator design that uses two-axis bending of the silicon crystal to simultaneously focus the beam in two orthogonal planes. Due to the bending, lattice strain increases integrated reflectivity of the Laue diffraction crystal by an order of magnitude compared to a perfect crystal. Anticlastic bending, a natural phenomenon for a crystal under strain, is typically considered a nuisance that must be “controlled.” In this case, it allows meridional focusing. A bender design, one that holds a rectangular crystal at the corners and bends it at the edges, makes slight adjustments to the "natural" anticlastic curvature to give the two-dimensional focusing.

The X17A monochromator in the X17 front end, shown when rolled out of the chamber

Also this year, researchers developed a new method for measuring x-ray optics aberrations. Creating the very small x-ray spots used for synchrotron nanoscale research requires a specialized and nearly perfectly formed optic to modify the phase profile of the beam. To look for aberrations — errors in the phase profile due to the optics (which can broaden and distort the spots) — scientists usually scan a slab of metal called a knife edge across the beam face. But to measure the beam size accurately with this method, the knife edge must be smaller than the beam. This is a problem for the types of nanoscience experiments planned at NSLS-II, where the beam is so small that the knife edge would have to be just one atomic plane thick — much too thin to fabricate. Photon Sciences researchers, along with colleagues at Argonne National Laboratory, the University of Rochester, and Cornell University, have figured out how to use an alternative called phase retrieval. The technique allows researchers to scan the beam with much larger feature sizes and then mathematically reconstruct the data to characterize the beam and its aberrations at any point along its path.

Top: Experimental setup of the phase retrieval technique. Bottom: Measured and simulated lens aberrations (left) and their corresponding through focus amplitude of reconstructions (right) for different lens angular misalignments. (From Manuel Guizar-Sicairos et al., Appl. Phys. Lett. 98, 111108 [2011])

Other achievements made in 2010 were the installation of a transmission x-ray microscope at beamline X8C and the use of a wedged multilayer Laue lens to reach a record level of x-ray nanofocusing (see sidebars), and the creation of a large scanning stage that allows researchers to take x-ray fluorescence images of hefty items like paintings in a very short time frame. Art historians have been particularly interested in the latter development as a way to test the authenticity and genesis of artwork.

Lens Development for X-ray Nanofocusing at NSLS-II

Multilayer Laue lens (MLL) deposition system, built in collaboration with CVD Equipment Corporation in Ronkonkoma, NY.

NSLS-II will use a wedged multilayer Laue lens (MLL) to achieve an unprecedented level of x-ray nanofocusing. MLLs are fabricated by magnetron sputter deposition onto small silicon blanks. They consist of many thousands of layers, with a total growth thickness goal of about 100 microns.

In 2009, the optics R&D lab designed and built a new magnetron sputtering system in collaboration with CVD Equipment Corporation in Ronkonkoma, NY. The system consists of a 23-foot, ultra-high vacuum chamber containing nine magnetron-sputtering guns, four cryogenic pumps, and a high-precision, linear-motion platform to enable the guns to deposit a stack of multi-film layers. The latest growths have been 43 microns thick with 6,510 layers and grew continuously for five days. All three metrics are records.

New NSLS Transmission X-ray Microscope Enhances Nanoscale Studies

Brookhaven scientist Jun Wang at the transmission x-ray microscope on beamline X8C

A new microscope installed this year will give NSLS users a powerful way to image energy storage materials, microelectronics, and biofuels. The transmission x-ray microscope (TXM), mounted at beamline X8C for use with hard x-rays, has an application energy range of 5,000-11,000 electron volts, and a target imaging resolution of 30 nanometers.

NSLS was awarded $2 million in American Recovery and Reinvestment Act (ARRA) funding to purchase the microscope — called the nanoXCT-S200. It was ordered from Xradia, Inc., headquartered in California, and will play an important role in the future of photon science research at Brookhaven Lab. With future funding anticipated, the microscope will be moved to a superconducting wiggler source at NSLS-II.