Structural characterisation plays an important role in our research. Spintronics devices require a high degree of precision in material thickness and crystal structure. We determine these properties using a range of equipment including:
X-Ray Diffraction and Reflectivity (XRD and XRR)
The group posses a state-of-the-art x-ray system capable of a variety of measurement types. The two most common are XRR and XRD. The former relies upon interference between x-rays reflected from the sample-surface and sample-substrate interfaces. By monitoring the period of the resulting interference pattern, one can determine the thickness of the film with high precision. This is important for calibration of thin film deposition rates. XRD is used to determine the crystallographic structure and orientation of samples.
Raman spectroscopy experiments measure the shift in wavelength of light scattered from a sample due to molecular vibrations. II can be used to identify material structures by their characteristic phonon modes. The Raman system in the Condensed Matter Group has a lateral mapping facility for imaging and can reach temperatures from room down to 4.2K.
Reflection High-Energy Electron Diffraction (RHEED)
RHEED is used to characterise the surface of crystalline samples. A beam of electrons is incident on the sample surface at a small angle and reflected on to a detector screen. The electrons are diffracted from atoms on the surface, and interfere constructively. The interference pattern on the detector screen is characteristic of the crystal structure. Our RHEED system is inside the MBE, and used to monitor the crystal structure during growth.
Low-Energy Electron Diffraction (LEED)
LEED uses electrons with an energy comparable to interatomic distances in order to investigate the surface structure of a sample. A beam of electrons is incident on the sample and the diffraction pattern structure and sharpness reveals information about the crystal structure of the sample. The LEED system at Leeds is situated in the MBE prep chamber.
X-Ray Photoemission Spectroscopy (XPS)
In an XPS experiment the sample is irradiated with a beam of x-rays. The number and energy of electrons emitted from the surface are monitored and analysed to determine the composition and electronic configuration (amongst others) of the sample. The CM group uses the XPS system situated in the Molecular and Nanoscale Physics Group.