Materials Research Laboratory

Background

In X-ray Diffraction...

Instrumentation.
A complex of instruments for x-ray diffraction analysis has been established for both materials research and specimen characterization. These include facilities for studying single-crystal defects, and a variety of other materials problems.

Location
148 Materials Research Laboratory

Philips X'pert
Two state-of-the-art modular "Xpert" XRD systems from Philips have been installed at the CMM at the Materials Research Laboratory (lab room 148). This system has multi modular primary and secondary optics in order to account for the various requirements of primary x-ray beam divergence and detector angular acceptance. A Cu source with possibilities of line or point focus is used. In the high-resolution mode, a 12 arc-sec angular divergence of the primary beam can be achieved by using a four-crystal Ge monochromator, allowing for the investigation of thin films and multilayered systems with high crystalline quality. A Guttman mirror is also available in the primary optics increasing the efficiency of primary beam, making it ideal for the investigation of diffuse scattering arising from defects in thin films. In addition, a three-bounce analyzer crystal can be placed between the sample and the detector in order to limit the detector acceptance to ~ 12 arc-sec. This configuration is ideal for a full mapping of the reciprocal lattice of the material allowing for a complete separation between strain variation effects and defect-related contribution to the diffracted intensities. Composition and lattice parameter variations within 10-5 can be determined, and effects as mosaicity, strain relaxation, curvature, layer tilt, etc., are easily separated. Finally, the system is also well suited for reflectivity measurements by probing diffraction intensities at glancing angles of incidence in order to quantify thin film thickness and interface abruptness. Primary and secondary optics of the instrument can also be interchanged to accommodate conventional texture, stress and phase identification analysis. In this case, a crossed-slit collimator primary beam optics and a secondary optics with flat-graphite and parallel plates can be used. A sample cradle, with Eullerian rotation and flexibility to accommodate different sample thickness and shapes, also allow for pole figure analysis and low-resolution reciprocal lattice mapping. Demonstration and training in this new XRD system can be scheduled by contacting Dr. Mauro Sardela at the CMM, phones 4-0547 (office number #370) or 3-1612 (lab), or by-email at sardela@illinois.edu

Two rotating anode sources that provide high intensities have been equipped with:

• a four-circle diffractometer, with a cold (He) stage, an incident beam graphite monochromator, and automated data collection,
• a high-resolution (triple-axis) diffractometer,
• a high-resolution diffractometer system with channel cut monochromation for mapping reciprocal space and reflectivity measurements.

There are, in addition, a number of lower power general purpose units:

• an automated Rigaku Geigerflex with the D-MAX system for the aquisition of powder diffraction patterns. Hot and cold stages allow one to change the sample temperature from 1500 C to room temperature and from there to 77 K,
• an automated Scintag powder diffractometer, which has a horizontal sample holder especially suitable for powders that are difficult to mount or might melt. There is a hot stage usable to about 1200 C,
• a third diffractometer with a four-circle goniometer and software suitable for obtaining pole-figure diagrams,
• a back-reflection Laue system,
• a Buerger precession camera for single-crystal work.

Applications
X-ray crystallography is one of the most useful methods for exploring the nature of matter and is used by researchers in many disciplines. It is used for phase identification, structure determination, as an adjunct to chemical analysis in the identification of the constituents of mixtures of crystalline phases, for measurements of the lattice parameters, and determination of the crystal perfection.