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The Mesh Analysis



  The Mesh Analysis      
  The performance of pnCCDs as X-ray detectors is characterized by electronic noise, energy resolution and a usable energy range with the lowest and highest detectable X-ray energy in particular. Usually these performance parameters determine the suitability of a specific CCD for a given application. However, these parameters do not define in which way the pnCCD pixel array reacts to incident X-ray photons when hitting the pixel structure at their boundaries.   Schematic of an X-ray tube setup with CCD and a mesh
  To view an individual description of the X-ray response, the signal amplitude of neighbouring pixels surrounding the pixel with the highest electron density can be parameterized with the so called mesh analyis: It shows how the signal charge generated by an X-ray photon is distributed over the pixel array of a CCD. By using the mesh analysis the position resolution of X-ray pnCCDs is improved to the order of one micrometers. Furthermore it is also employed to correct, verify and optimize device simulations and the realization of pnCCD designs.  
  The Japanese group around H. Tsunemi employed mesh analysis to enhance the position resolution of X-rays in MOS-CCDs. The method was later adapted and extended for the development of pnCCDs by MPI HLL. Scanning the CCD surface with a narrow X-ray beam (of about three to five μm) in an energy range of 0.2 to 10 keV with several 100,000 individual X-rays per pixel is very time consuming and inefficient. These difficulties can be overcome by placing an opaque metal foil – called mesh – with a regular hole grid in front of the pnCCD (figure on the right). A slight rotation of the mesh with respect to the pixel structure ensures that every hole has a different position relative to the pixel below (figure on the left).
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Schematic of the mesh on top of  a pixel arrsy