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Professor of Physics durbin@purdue.edu Office: Physics 180 Telephone: (765) 494-6426 Fax: (765) 494-0706

B.A. Physics 1976 University of Chicago
M.S. Physics 1977 University of Illinois, Urbana
Ph.D. Physics 1983 University of Illinois, Urbana

NSF Presidential Young Investigator Award 1987

Research Interests

• X-ray studies of vibrational modes in biomolecules
• X-ray fluorescence imaging
• X-ray holographic imaging
• Sector Four at the Advanced Photon Source

Research Activities

X-ray studies of vibrational modes in biomolecules

While the static structures of simple proteins like myoglobin and hemoglobin are fairly well understood, their biological activity is likely to also depend on their dynamic vibrational properties. A new x-ray synchrotron technique is being exploited to measure the vibrational spectrum of iron atoms in the heme group, the major functional structure in myoglobin and several other important proteins. Utilizing the extremely high brightness of an undulator x-ray source at the Advanced Photon Source (APS) at Argonne National Laboratory, an x-ray beam whose energy is very close to the Mossbauer nuclear resonance (14.4 keV) and having meV energy resolution is incident on the Mb specimen. If a vibrational mode has an energy equal to the difference between the x-ray beam and the nuclear resonance, the resonance can be excited, with subsequent deexcitation which can be detected as Fe fluorescence. By monitoring this fluorescence as the x-ray energy is scanned through the resonance, an approximate map of the Fe vibrational density of states is obtained. This is especially important because the modes are specific to Fe, so there is no interference from the other parts of the protein; this provides an excellent complement to other Raman scattering and other vibrational probes.

This work is done in colaboration with Tim Sage and Paul Champion of Northeastern University, and Ercan Alp and Wolfgang Sturhahn at the Advanced Photon Source.

X-ray fluorescence imaging

One of the major new opportunities due to intense, high brightness synchrotron sources of x-rays is the ability to image x-rays using various x-ray optical elements. This project extends the well-known Kirkpatrick-Baez imaging method to fluorescence to obtain an image of element distribution from small samples. A prototype has been assembled by graduate student Alex Bakulin, and is now in the testing stages. This could have a significant impact on standing wave measurements, XAFS studies, and other x-ray probes. The mirrors are coated with multilayers fabricated by collaborators at the Advanced Photon Source - Al Macrander, Chian Liu, and Jenny Erdmann. Some of the characterization is being done with Terrence Jach at NIST (Gaithersburg).

X-ray holographic imaging

Holography was originally proposed by Gabor in 1948 as a technique which could allow one to "see" an atom inside its host structure. Recent developments by Thomas Gog and others have brought this somewhat closer to reality, in that holographic images can now be obtained by measuring the total yield of x-ray fluorescence from a specimen under suitable synchrotron irradiation. These initial results have been limited by relatively low count rates and long data collection times. We have been developing new methods for collecting the total x-ray fluorescence from a holographic specimen, so that data can be obtained from 100 to 1000 times faster than before. A long-range goal might be to holographically image the Fe atom centered in the heme group of myoglobin, for example.

Sector Four at the Advanced Photon Source

Working closely with Professor Roberto Colella and others, the goal of this project is the construction of a specialized beam line at the Advanced Photon Source This beam line is under construction, and will soon be the only beam line at the Advanced Photon Source which can have two insertion devices operating simultaneously - a standard undulator for hard x-rays, and an elliptically polarized undulator for soft x-rays. This is funded by the DOE, and will serve the research needs of the X-ray Physics Group, which also includes Roberto Colella (Purdue), Don Bilderback and Qun Shen (Cornell), Terrence Jach (NIST), John Arthur (Stanford), Al Thompson (Berkeley), and Simon Moss (Houston).

Teaching Interests

Professional Affiliations

• American Physical Society
• Advanced Photo Source Users Organization

Selected Publications

1. J.-C. Chung, S.M. Durbin, "Dynamical Diffraction in Quasicrystals," Phys. Rev. B 51, 14976-14979, 1995.
2. S.M. Durbin, G.C. Follis, "Darwin Theory of Heterostructure Diffraction," Phys. Rev. B 51, 10127-10133, 1995.
3. S.M. Durbin, "Darwin Spherical-wave Theory of Kinematic Surface Diffractio n," Acta Crysta. A 51, 258-268, 1995.
4. S.M. Durbin, "The Advanced Photon Source," Advanced Materials 3, 85-86, 1991.
5. S.A. Hoffmann, S.M. Durbin, et al., "Structural and Transport Measurements in ," Phys. Rev. B 43, 7852-7858, 1991.
6. S.M. Durbin, T. Gog, "Surfaced-induced Perturbation of LVV Auger Spectra,& quot; Phys. Rev. Lett. 63, 1304-1306, 1989.
7. T. Gog, S.M. Durbin, "UHV Rotary Manipulator with Arcesecond Resolution for X-ray Standing Wave Experiments," Rev. Sci. Inst. 60, 3030-3034, 1989.
8. S.M. Durbin, T. Gog, "Grazing-incidence Bragg-laue X-ray Diffraction," Acta Crysta. A 45, 132-141, 1989.

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