Surface_Science_Poster_2004

Advanced Diffractometry at UWM

Robert Morien and Paul LymanPhysics Department

University of Wisconsin-Milwaukee,Milwaukee, WI 53211

X-ray diffractometry is used for:

• A non-destructive technique in analyzing semi-conductor wafers and thin films for contamination and atomic spacings– Determination of substrate and film coherence– Information concerning the stresses and strains

between lattice and film mismatches• Primary method for determining molecular structure of

proteins, particularly DNA which was determined by use of x-ray diffraction

• Analysis of crystalline phases present in any sample

crystals variousofpatternsn diffractio Typical

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How are x-ray photons developed?

• X-rays are developed in an evacuated x-ray tube• The tube is made of two electrodes, the anode and the

cathode• The cathode is usually constructed of a tungsten filament

held at a high negative potential• The anode is held at ground potential• The cathode is heated producing thermionic emission• Electrons are accelerated towards the anode ejecting

electrons of the anode material• The hole of the ejected electron is filled by an outer shell

electron which creates x-ray radiation – the x-ray source• Energy and thus the wavelength of the x-ray beam is

dependent upon material selected for the anode

The characteristic lines represent the energy and thus wavelength which are characteristic of the emmited atom

Conventional Four-circle arrangement at UWM

Kappa diffractometer at UWM under construction

Using the Kappa Diffractometer with additional circle for detector yields:

• Additional degree of freedom to detect out-of-surface plane scattering vectors

• Can use additional constraint to use grazing incidence angles for surface diffraction

• Kappa geometry allows better access to sample (NO OBSTRUCTING CHI CIRCLE)

X-ray diffractometry techniques are continuing to advance. Each new step leading to the solution of the phase problem.

Acknowledgements

• X-ray diffraction, a practical approach, C. Suryanarayana and M. Grant Norton, Plenum Press, 1988

• Colorful discussions with Prof. Paul Lyman and H.T. Johnson-Steigelman, University of WI-Milwaukee

• Pringle,Daniel; Shen Qun “New five-Circle kappa diffractometer for reference beam diffraction studies” Journal of Applied Crystalography 27 September 2002 http://staff.chess.cornell.edu/~shen/articles_published/Jac_2003_v.36_p29.pdf

• http://physics learning.colorodo.edu/PIRA/