S2D2 Diffractometer

s2d2 diffractometer

  While a member of Prof. Mike Bedzyk's group at Northwestern University, I designed a synchrotron x-ray endstation capable of combined scattering and spectroscopic measurements.  The diffractometer design is based upon the "S2D2" design of Ken Evans-Lutterodt.  [K. W. Evans-Lutterodt and M. T. Tang, J. Appl. Cryst. 28, 318 (1995).]  To simplify coupling the precision motions required for x-ray diffraction into ultrahigh vacuum (UHV), this design places two degrees of freedom on the sample, and two on the detector (instead of the more usual 3-sample/1-detector split). 

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In addition, two "non-precision" degrees of freedom are provided on the sample for alignment and for switching the sample normal between horizontal and vertical.  These degrees of freedom are provided using a modified Thermionics Corporation manipulator head GB-16 :


   Capabilities of the instrument are: x-ray diffraction (the sample flip allows optimal implementation of both grazing incidence x-ray diffraction and reflectivity), EXAFS, XSW, LEED, Auger, Al k-alpha XPS, ion sputtering, e-beam evaporation, sample heating and cooling.

   Unlike any surface diffraction machine that I know of constructed to date, an arbitrary point on the surface can be placed at the center of rotation using a precision XYZ stage from McAllister.  Previously, one used perfectly homogeneous surfaces, making this capability unimportant.  However, the extreme brightness of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL) has made it possible to do studies of small portions of the sample at a time ("microdiffraction"), providing the impetus for this capability. 

   The diffractometer and vacuum system are in the final stages of assembly and commissioning at DND-CAT of the APS.  For updates and pictures of the beast, see the web site of my former colleague at Northwestern, Osami Sakata

For a full writeup of the design, please see:
"UHV Surface-Analysis Endstation with X-ray Scattering and Spectroscopic Capabilities," P.F. Lyman, D.T. Keane, and M.J. Bedzyk, AIP Conference Proceedings 417, 10 (1997).

    S2D2 DiffractometerS2D2 in action
          Views of S2D2 along three directions.                 S2D2 Diffractometer "in action"