Condensed-Matter Physics & Materials Science Seminar
"The X-ray Standing Wave Technique: Principles and Applications"
Presented by Sambhunath Bera, Northern Illinois University
Wednesday, June 12, 2013, 11 am
Bldg. 480 conference room
Hosted by: Ivan Bozovic
When two plane wave X-ray beams of nearly equal amplitudes interfere coherently, an X-ray standing wave (XSW) field is generated. There are many ways of generation of coherently related plane waves for the generation of XSW, such as: (i) total external reflection from smooth surfaces of materials, (ii) Bragg diffraction in single crystals, (iii) Bragg diffraction from a periodic multilayer system etc. In all these cases the incident beam and the reflected beam are coherently coupled. The X-ray standing wave (XSW) technique is a powerful tool for accurate determination of the microscopic structure of surfaces and interfaces. It employs X-ray interference and X-ray scattering. The fringes of an X-ray interference field (XIF) can be spatially modulated in a controlled way. From the characteristic scattering response of the atoms within the range of interference field, spatial distribution of specific kinds of atoms can be determined. Atomic distributions are determined independently for each individual element present in the system. Sensitivity of the XSW technique is ∼ 1013 atoms/cm2 or better and positional resolution is 0.01 ˚A for single crystals and ∼ 1 ˚A for thin films and periodic multilayers under grazing incidence. As an element-sensitive high-resolution structural probe, the XSW technique has been used to investigate a wide range of surface, interface, and thin film structures. These include semiconductor, metal, and oxide surfaces; electrochemical interfaces; organic membranes; and multilayers. In this talk, I will present basic principles of the major types of XSW techniques and several important case studies.