Microbeam X-ray Standing Wave and high resolution diffraction techniques at CHESS

A. Kazimirov

CHESS

High resolution X-ray diffraction and scattering techniques requires X-ray optics producing nearly perfect X-ray plane wave with small angular divergence. Any focusing optics, by its nature, creates a converging X-ray beam. As one of the possible solution to this problem we propose to use post-focusing collimating optics. In our experiments at CHESS we used a one-bounce X-ray capillary with the working distance of 30 mm to produce a round beam with a size of about 10 microns at the focused position 30 mm beyond the capillary tip. A miniature Si(400) channel cut crystal was inserted between the capillary tip and the focus to produce an X-ray microbeam with an instrumental angular resolution of 2.5 arc seconds.

This beam was used to perform high-resolution X-ray diffraction and X-ray Standing Wave (XSW) characterization of semiconductor structures with lateral dimensions of 15 to 80 microns grown by the selective area growth (SAG) technique. By using Bragg diffraction, the XSW field was generated inside both the InP(001) substrate and the 1000 angstrom thick semiconductor film and monitored by measuring the angular dependences of the fluorescence yield coming from the atoms composing the substrate (In-L lines) and the film (Ga-K and As-K lines) atomic lattices. The diffraction and XSW scans were performed by scanning the Bragg angle of the miniature channel-cut crystal.

This approach can be applied to other focusing optics such as Fresnel zone plates, refractive lenses and others. The future applications are not limited to the XSW method. We believe that this approach can also be applied to other microbeam techniques that require high angular resolution such as diffractometry, reflectometry, and reciprocal space mapping, using Fresnel zone plates, refractive lenses, KB mirrors, or capillaries, to create the microbeams.