Research at DND-CAT
DND-CAT Sector Description
To support this research program, DND intends to build six stations in total; three utilizing undulator A radiation and three utilizing each a part of the dipole radiation fan. A brief description of each station is given below:
The general purpose station will be equipped with a six circle diffractometer for single crystal work, small molecule crystallography and diffuse scattering. The station will be equipped with high and low temperature sample chambers, as well as sample environmental chambers of conventional design.
A large optical table located at the upstream side of the radiation enclosure will be used for specialized setups, novel optics (for example, microbeam mirror optics, microcapillaries, etc.) and commercially available, turn-key crystallography systems.
The microtomography apparatus is being designed for work on polymers, but other materials may be investigated. Of interest in our first experiments are macrocrazes formed by plane strain deformation of semicrystalline polymers such as polyethylene, polypropylene, nylon, etc. The first design will accommodate single edge notched (SEN) tensile samples, approximately 5x5x60 mm in size. The fully developed instrument will have variable temperature capabilities.
The proposed UHV surface chamber to be stationed at APS will be used for preparing and analyzing various types of surface, interface and thin film structures. The chamber will be designed to allow in-situ monitoring of various modes of surface growth and dynamics with synchrotron x-ray radiation. Surface preparation capabilities will include ion beam sputtering, electron-beam heating, cryogenic cooling, gas dosing, and Molecular Beam Epitaxy (MBE) with Knudsen effussion cells. Non-synchrotron x-ray surface techniques will include Low Energy Electron Diffraction (LEED), Auger / XPS, and Scanning Tunnelling Microscopy (STM). Synchrotron x-ray analysis capabilities will include the use of x-ray diffraction, x-ray reflectivity, x-ray standing waves (XSW), x-ray evanescent waves, x-ray fluorescence spectroscopy, x-ray absorption spectroscopy (XAS), x-ray photoelectron spectroscopy (XPS), and x-ray photo ion spectroscopy. A sample introduction system will make it possible to transfer samples from other preparation chambers with minimal contamination.
The primary chamber will be based on a design similar to that presently used at X22C (Gibbs) and X16A ( Fuoss and Robinson "Handbook on Synchrotron Radiation" Vol. 3, Eds. G. Brown and D.E. Moncton, Elsevier Science Publishers B.V., 1991]) at Brookhaven's National Synchrotron Light Source (NSLS) and at the Synchrotron Radiation Source (SRS) in Daresbury, England by Vlieg, et al. [Nucl. Instr. and Meth. A262 (1987). 522]. The chamber will be fixed to the base plate of a large heavy-duty 4-circle goniometer. The base plate will sit on an optical table with XZ translations and a Z-axis rotation. A differentially pumped rotary feedthrough with bellows and Teflon seals will connect the omega, chi, and phi angular motions of the diffractometer to the sample without moving the main body of the UHV chamber. The incident and scattered x-rays enter and exit through a Be cylindrical window which covers 200circ in 2 theta. Scattering takes place primarily in the vertical plane. The Z-axis (or alpha-axis), which is used as a 5th sample rotation axis, serves to make up for the limited (pm 20circ) range of the chi circle and is also used to do specular reflection in the horizontal plane when the surface normal of the sample lies in the horizontal plane.
A combination of features that will make this chamber unique include: (1) a manipulator that will allow the sample to flip from the surface diffraction geometry to the reflection geometry, (2) the ability to analyze the x-ray induced fluorescence, Auger, photo electrons, and photo ions while the sample is in the center of the diffractometer; (3) an STM subsystem, and (4) a sample introduction system. Features (1) and (2) will make it possible to do XSW measurements along with x-ray scattering experiments. This will be a unique experimental capability.
This station is for the simultaneous study of small angle x-ray scattering and wide angle x-ray scattering from polymers, composites etc. Five experimental sample chambers will eventually be constructed for the study of polymers and one for general purpose work. These are:
This station utilizes 1.95 mr of the bending magnet fan. The beam is offset up, 1 m above the orbit plane through a two crystal monochromator. The first crystal acts as a white beam mask for stations 5-BM-C and 5-BM-D; therefore it intercepts a part of the fan that would be wasted. The large offset moves the entire beamline out of the way of the 5-BM-C and 5-BM-D optical components and transport pipes. This station will house a compact general purpose four-circle diffractometer, suitable for all types of routine powder and single crystal diffraction experiments. We will explore possibilities for providing some tunability or at least a selection of energies by using multiple crystals.
The primary purpose for this station will be powder diffraction, amorphous scattering and conventional EXAFS work. Powder diffraction using synchrotron radiation holds great promise for structure refinement using Rietveld methods (see, for example, D.E. Cox, Handbook of Synchrotron Radiation, Vol 3, G. Brown and D.E. Moncton (eds), Elsevier Science publishers B.V. 1991). However, a number of problems need to be resolved first, most notably the need to better characterize reflection profiles and deal with preferred orientation more effectively. Nevertheless, even at the present stage of development, powder diffraction is a technique indispensable to many aspects of our scientific program (catalyst research, structure formation in polymers, phase analysis of inorganic materials etc.). We intend to use EXAFS as a complement to diffraction techniques, particularly in studies of catalysts under operating conditions.The station will use the inboard (i.e. toward the ring shield wall) .4 mr of the horizontal fan.
This station can be fed with a 2.8 mrad focused monochromatic beam tunable from 2.5-40 keV or 1.25 mrad of white dipole radiation and it will have ample in-hutch space for specialized optics. The main purpose for this station, as currently envisioned, will be for single crystal diffraction, some powder diffraction and amorphous scattering work. The station will be equipped with a six-circle diffractometer with high and low temperature and environmental chambers of standard design. The diffractometer and chambers will be identical with those of the 5-ID-B General Purpose station for compatibility. Space in the downstream half of 5-BM-D will be used by the UHV chamber/diffractometer described earlier. This instrument will be able to operate at 5-BM-D when undulator beam time is not available for the 5-ID-C station.