Chapter 2 . X - Ray Diffuse Scattering

In this research program, modern x-ray scattering techniques are used to study structures and phase transitions in thin films and on surfaces. We have two principal experimental facilities. At MIT, we have four high-resolution computer-controlled x-ray spectrometers with high intensity rotating anode x-ray generators. The angular resolution can be made as fine as 1.8 seconds of arc, enabling us to probe the development of order from distances of the order of the x-ray wavelength, ~ 1A, up to 30,000 A. The sample temperature may be varied between 2 K and 500 K with a relative accuracy of 2x10-3K. We also maintain, in collaboration with IBM, a two-spectrometer system at the National Synchrotron Light Source at Brookhaven National Laboratory. A third beam line designed to operate at short wavelengths is in the final stages of construction at the laboratory. These systems make possible high resolution scattering experiments with a flux more than three orders of magnitude larger than that from a rotating anode x-ray generator. These experiments, in turn, have opened up the possibility for a new generation of experiments in this area.