Defects and X-ray Topography

  On the left is an optical image of (the Zn surface of a) ZnO substrate which gradually transforms into a x-ray reflection topograph. To the eye, other than a few scratches (in this case on the rear surface), the ZnO wafer looks clear and has a mirror finish. As the substrate is transparent, we see both surfaces in this (scanner) image. As the Cu K-alpha x-ray wavelength was used was in an asymmetric scattering geometry [(1 0 -1 4) reflection], the x-rays only penetrate a few microns into the surface. For this particular wafer, we can see that there is serious polishing damage and that the surface needs further pretreatment before it can be used as an epitaxial template for homoepitaxy.

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