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Th. Meinschad, C. Streli, P. Wobrauschek, C. Eisenmenger-Sittner:
" A windowless high power diffraction tube with Si anode for the efficient excitation of low Z elements for TXRF";
Poster: European Conference on Energy Dispersive X-Ray Spectrometry, Berlin, Deutschland; 2002-06-16 - 2002-06-21.

A WINDOWLESS HIGH POWER DIFFRACTION TUBE WITH SI ANODE
FOR THE EFFICIENT EXCITATION OF
LOW Z ELEMENTS FOR TXRF

Th.Meinschad1, Christina Streli1, P.Wobrauschek1, Ch. Eisenmenger-Sittner2,
1Atominstitut, Univ. of Technology, Vienna, Austria
2 Inst. of condensed matter, Vienna Univ.of Technology, Austria


To excite low Z elements efficiently low energy photons are required, specially to detect Al and Na on Si wafer surfaces photon with an energy below the Si ?K edge but above the Al-K edge. Using synchrotron radiation is the most effective way but also for lab scale instrumentation there are some approaches. Besides W-M lines also the use of Si K line is possible. An additional problem is the fact that total reflection geometry requires a collimated beam, so a fine focus X-ray tube configuration should be used. But this requires a low take off angle ( generally 6°) which leads to strong self absorption of the low energy X-ray photons.
A high power diffraction tube was modified by integrating the tube in the vacuum circuit of the measuring chamber. The anode block was constructed to be changeable, Si was used as anode material. The anode geometry was optimized for high brilliance and low absorption.
The results show an improvement of detection limits in comparison to a standard Cr anode fine focus tube. A detection limit of 90 pg for Na has been achieved with 600 W.