High Resolution X-ray Optics and Microscopy at the Advanced Photon Source

Ian McNulty
Advanced Photon Source
Argonne National Laboratory

October 16, 1998

The Advanced Photon Source at Argonne National Laboratory is the world's premier multiuser facility for research with x-ray synchrotron radiation. The APS is based on a 7 GEV synchrotron storage ring that supports numerous high brilliance x-ray sources, beam transport lines, and associated experimental stations. These x-ray sources, known as undulators, provide highly collimated, tunable, partially coherent x-ray beams to the experimental stations in upm to 38 sectors around the ring. At Sector 2 of the APS we are developing high resolution x-ray optics for focusing and shaping of these intense x-ray beams for use in x-ray microscopy, diffraction, and scattering experiments. The current state-of-the-art enables us to achieve focal spot sizes of less than 100 nm and numerical apertures approaching 0.01 at x-ray wavelengths. This presentation focuses on the recent progress in x-ray optics and microscopy at Sector 2 of the APS.

Minutes from the SMSI Meeting of 10/16/98
Bill Mikuska called the meeting to order at 7 P.M. and tabled the issue of where to hold the After Christmas, Christmas party. Dave Roy provided further information and an update regarding his attempts to explore the particulars of a website for SMSI.

The featured speaker. Dr. Ian McNulty, brought a wide ranging overview and a wealth of insight into the nature and potential of a relatively new and still upcoming experimental facility in his presentation of "High Resolution X-ray Optics and Microscopy at the Advanced Photon Source." This addition to Argonne National Laboratory is providing scientists with an extremely versatile tool, capable of supporting several thousand experiments simultaneously. These experimenters will utilize the highest resolution imaging energy source available to date. This energy comes in the form of a 7 GeV X-ray beam, generated when positrons are accelerated to high energies in a synchrotron and then tangentially diverted to anyone of the 30 odd sectors where they are "wiggled" in a magnetic undulator. At Sector 2 the X-rays are directed through a scanning X-ray microscope to a detector where data is electronically sent to a computer and subjected to digital analysis. Fresnel Zone Plate Lenses, utilized for the diffractive focusing of the X-rays, call for special attention to details such as zone thickness, refractive index and diffraction order to enhance their focusing efficiency and resolution performance.

The X-ray microscope is also suitable for 3D imaging because it can produce holographic images having 100-300 Angstrom resolution.

A promising application which is currently being developed is tomography, possibly down to nano scale. Real time tomographic imaging, as pursued by Dr. McNulty and his team at sector 2. could well develop into a new level of video camera. The computer support for this endeavor is formidable. requiring teraflop processing. A real advantage of X -ray microscopy is its relatively nondestructive nature (less damage to samples than SEM) which makes it desirable for everything from biological samples to microelectronic devices. In the latter case, where for example the goal might be the study of defects in computer chips, X-rays provide some obvious advantages. i.e. low charging, low damage and no sample sectioning. While studies to less than 100 J.UD can be achieved there is always a race to bring resolution up to speed with the ever evolving (i.e. smaller) microchip features. Specific elemental sensitivity (in this case applied to a blown microelectronic fuse) demonstrated the ability of scanning microtomography to see what other methods cannot. On a macroscopic scale. the nondestructive tomographic reconstruction of a dinosaur tooth illustrates desirable versatility. An electron microprobe, by contrast, is 100.000 times less sensitive than its X-ray counterpart. X-ray fluorescence microscopy can "look" at parts per billion. X-ray diffraction microscopy provides high spacial resolution and can observe a target of I-few !-LID on a sample. . The Advanced Photon Source is a work in progress with truly amazing potential. The $7M invested in sector 2 over several years promises to be a bargain relative to services provided. As a m dollar supported institution. The APS emphasizes non-proprietary research and employs scientific guidelines for screening customers. Microscopical imaging, composite material analysis and structural biology come together at the ring, where the future looks bright.

In the discussion period following the presentation. Garth Ziemba caught Dr. McNulty's attention with questions regarding the observation of crystals in oil and the application of cryo technology to the problem.

Submitted by: John Macdonald, Recording Secretary