Materials Analysis

Structural analysis - X-ray and electron diffractometry:

X-Ray Diffraction

In X-Ray Diffraction (XRD), a collimated beam of X-rays is incident on a specimen and is diffracted by the crystalline phases in the specimen. The intensity of the diffracted X-rays is measured as a function of the diffraction angle, and the specimen's orientation. This diffraction pattern is used to identify the specimen's crystalline phases and other structural properties.

XRD can be used to perform the following analytical functions:

• Identification of unknown substances
• Trace element analysis
• Determination of crystal structure
• Phase analysis
• Determination of phase transformation
• Detection of crystal imperfections
• Layer thickness determination
• Measurement of mechanical stresses

The Advanced Materials Group is equipped with two Siemens Kristalloflex Diffractometer XRD units, using Cu Ka radiation (wavelength 1.5406 Å), combined with computers running Diffrac-AT analytical software for peak identification.

In addition, the Food Sciences Division houses a state-of the-art Siemens D5005 wide angle X-ray diffraction system, which is primarily used for the determination of amorphous/crystalline ratios in food materials.

The Semiconductor Physics Group (Physics) has a Philips X-Pert MRD facility which allows them to use a variety of scan modes to study the properties of thin films of semiconductor materials. Typical information gained using this technique includes the nature of the various phases present, their relative concentrations and their symmetry properties as well as grain size and grain size distribution.

Normal Incidence X-ray Standing Wave (NIXSW)

NISXW is a new derivation of X-ray diffraction techniques. It is applicable to any crystalline substrate, and gives the height of an adatom above the X-ray reflecting planes of the sample. By using two, or more, sets of planes, the full position of the adatom can be found by triangulation. We are still exploring the possibilities of this technique.

The Surface Science Group in Chemistry is using synchrotron facilities at Daresbury and at Grenoble to expand the capabilities of this technique. Recent studies have included the clean and Chlorine coated surfaces of the semiconductor InP; the structure of Cu(100)-Hg; iodine and CdI2 on Cu and PF3 and SO2 on Ni.

Low Energy Electron Diffraction (LEED)

Reflection High Energy Electron Diffraction (RHEED)

RHEED is an electron diffraction technique used in UHV systems primarily to study the surface structure and hence growth morphology and mechanisms of epitaxially grown crystals. The Semiconductor Physics Group (Physics) is using the technique in its two Molecular Beam Epitaxy (MBE) systems dedicated to the growth of advanced compound semiconductor materials and devices.