January 10, 2003

Workshop on Frontiers in Synchrotron X-Ray Microbeam Diffraction

The Workshop on Frontiers in Synchrotron X-Ray Microbeam Diffraction was held on January 10, 2003 in the Hamilton seminar room in the Chemistry Department at BNL, with a large gathering of over 40 persons. The purpose of this workshop was to inform the scientific, university and industrial community of the plans to design and install a state-of-the-art microdiffraction instrument at NSLS mini-gap undulator beamline X13B. This proposal is to be submitted to the DOE Office of Science towards the end of January and will be operated as a general user facility with an emphasis on nanoscale research. Opportunities in the cutting-edge science that could be accomplished with this instrument were explored, and user input was solicited.

The workshop was introduced and chaired by Dr. Elaine DiMasi (BNL Physics Dept.), who also outlined the motivation for the proposed instrument. The value of cutting-edge user facilities was described from the perspective of BNL management by Dr. Doon Gibbs, Associate Laboratory Director for Basics Energy Sciences (BES). He emphasized the importance to DOE and BNL of interacting with users at an early stage so that they can influence the evolutionary process by which new facilities are developed and built. He described the organizational structure of BNL BES as well as a number of exciting planned projects. Two such projects that will have a great impact on microbeam diffraction science at BNL are the proposed upgrade to the NSLS and the Center for Functional Nanomaterials (CFN). Dr. Gibbs concluded his presentation with a challenge to the audience to come up with ideas about scientific impacts that can be made by the future NSLS.

The CFN was further elaborated upon by NSLS scientist Dr. Ron Pindak. The CFN is one of five new DOE Nanoscale Science Research Centers (NSRCs). The user programs of the five centers will be launched at a workshop in Washington DC on February 26-28, 2003. The CFN has six scientific themes that involve interdisciplinary research on diverse systems that are listed and described on the CFN website http://www.cfn.bnl.gov/. The instrumentation and capabilities of the CFN are organized into “lab clusters,” such as materials synthesis, proximal probes, nanopatterning, etc. The CFN will be a user facility similar to the NSLS and both user programs will be coordinated through a common user office. Thus, one proposal can allow access to NSLS beamlines as well as CFN lab tools. Two of the NSLS beamlines, a SAXS beamline on X21 and the X13B microdiffraction beamline, will be optimized to service the needs of CFN General Users. The center, in addition to having the infrastructure to support state-of-the-art fabrication facilities, will provide offices and interaction areas for students and postdocs as well as regular staff.

Dr. Patricia Mooney of IBM presented a talk on materials research for silicon CMOS technology using microbeam x-ray sources. Strain-relaxed SiGe “virtual substrates” for strained silicon CMOS transistors were described and results of studies characterizing the defect microstructure of these films were presented. Dr. Mooney remarked on how the divergent beam available at X20A of the NSLS limited the resolution at which “micrograins” could be observed, and that a sub-micron, more parallel beam would be of great advantage in her work.

A survey of synchrotron microdiffraction capabilities around the world was given by Prof. Cev Noyan of IBM. He pointed out that several synchrotrons, in particular the ESRF and ALS, have put great emphasis and resources into microbeam diffraction. The great variety in hard x-ray microfocusing optics and a number of designs for accessing reciprocal space (pink beam Laue, scanning monochromator Laue, small sphere-of-confusion six-circle, single-axis, etc.) were explained. The following two talks described in detail the microdiffraction capabilities currently available at the NSLS. Dr. Ken Evans-Lutterodt of Agere described the X16C microdiffraction beamline. He used the example of selective growth of semiconductor materials on a patterned substrate to illustrate that microdiffraction combined with spectroscopy can be used to obtain strain as well as chemical composition information with micron-scale spatial resolution. Dr. Jean Jordan-Sweet of IBM next described the capabilities of beamline X20A. This capillary- and diffractometer- based instrument is primarily used to measure strain fields and mosaic structure by scanning diffraction topography. Results were presented on interfacial stress/strain in metal features on silicon and on electromigration-induced stress in narrow metal lines.

The proposed microdiffraction instrument to be built at X13B was described in the next two talks. Dr. James Ablett of the NSLS presented specifications and recently measured spectral plots of the new X13 Mini-Gap Undulator (MGU) source. He then described the plan to use a 4-bounce silicon monochromator and a variety of x-ray microfocusing optics for the proposed instrument. The monochromator can be removed for pink-beam studies, and the optics will be interchangeable between KB mirrors, capillary, pinholes, zone plates and planar refractive lenses. The modular design will allow for great flexibility in beamsize and divergence selection. Dr. Ken Evans-Lutterodt further described the diffractometer and detector configurations. In order to minimize vibration and torque on the sample and optics, the detector arm will be a completely separate system. The entire microdiffraction instrument is being designed to be robust, easy to align and use, and modular, in order to serve a variety of users from students to busy experts.

After a break for lunch, the workshop resumed with presentations on scientific opportunities by researchers from a range of disciplines. Dr. Mehmet Sarikaya of the University of Washington began with an overview of the fascinating world of structural biomimetics. Biomaterials such as spiders’ silk, mother-of-pearl, protein coats on certain bacteria, sea urchin spines, and sponge spicules exhibit nanoorganization. Understanding the structural, functional, and process design characteristics of these self-assembled structures will lead to the invention of engineered “bio-inspired” materials of the future. Next, Dr. DiMasi presented a talk prepared by Dr. Joanna Aizenberg of Lucent Technologies, which described how self-assembled nano structures of calcite crystals and other materials can be formed using organic alkane chain templates which have a variety of attached functional groups. These assemblies of crystals can be patterned and oriented in many ways by changing the functional group, chain tilt, and lithographic pattern. Following this talk, Prof. Valery Kiryukhin of Rutgers University described several correlated electronic systems that form functional materials, which exhibit large changes in electrical or magnetic properties (such as colossal magnetoresistance) under relatively weak external perturbations. He showed an example of strain mapping in the vicinity of a grain boundary taken at beamline 2ID-D at the APS. In order to study these systems, a microdiffraction instrument with temperature control, precise sample positioning, optical access, and tunable energy is needed. The scientific opportunity session was concluded with a talk by Dr. Jeffrey Kysar of Columbia University who discussed the difficulty in determining the relationship between stress and strain in materials. He has simplified the problem by reducing it from 3-D to 2-D by performing experiments using a line of applied force rather than the conventional point indenter on a metal surface. A microbeam diffraction beamline would allow for the measurement of residual stresses and dislocation density on the surface of laser shock processed samples as a function of position from the “peened” line.

During the afternoon discussion session Dr. DiMasi read letters from members of the Clay Minerals Society email listserver. These researchers would like to see an instrument having high brilliance, a sensitive area detector, variable spot size, and control over temperature and humidity. Audience members also supported the desire for environmental control, citing the need to study self-assembly experiments in liquid solution rather than in just the dried post-assembly state. There is a need to get all information-- tilt, chemical, lattice spacing, transformation temperature, etc. from single grains on the order of a micron in size. Many times the need for a parallel beam was mentioned. A discussion about the measurement of organic and bio materials brought up the legitimate concern over the possibility of beam damage. Another desired capability mentioned several times is computed tomography. Questions were asked about the time structure of the existing NSLS x-ray ring vs. the proposed upgrade. Pump-probe experiments are possible now with a ~0.5 nanosecond period, and in the future with ~20 femtosecond resolution. The APS currently has a 50 picosecond timing structure. It was pointed out that single-shot microdiffraction would not yield enough intensity, but a locked-in, repeated pump-probe setup would be able to accumulate enough signal.

The workshop concluded with committee members encouraging researchers to try microbeam experiments now on existing instruments, in order to see what is needed and what works. It is expected that the new microdiffraction beamline will constantly evolve over time, and experience now will lead to a better instrument in the future. Many components are available now or will be soon for experimental trials. Interested parties are encouraged to apply for beamtime through the NSLS proposal system. More information is available on the web at http://www.nsls.bnl.gov/. Click on "User Information> Requesting Beamtime" on the menu in the blue field on the left-hand side of the page.

RELATED LINKS: Workshop Website