Seminars Archive

A Novel Form of Configurable CCD Detector System for use in X-Ray Microscpy

Abstract
The talk will describe a novel form of detector system developed for use in scanning transmission x-ray microscopy (STXM). It is based around an electron-multiplying CCD (iXon DV860 from Andor Technology) combining fast frame-transfer readout with very high sensitivity. The detector consists of a Peltier-cooled CCD array of 128 by 128 sensors, and makes use of visible light coupling to a phosphor screen, to make it easy to operate over a wide range of photon energies, from the oxygen K edge upwards. It has been successfully used for scanning transmission x-ray microscopy (STXM) on the Twinmic end-station at the Elettra synchrotron. In practice, a full CCD frame of data is collected from every pixel in the raster scan of the scanning microscope; the CCD thus provides a completely flexible range of configurable detector response functions that can be chosen after the image data has been recorded. By this means, a variety of different imaging modes can be produced simultaneously from a single scan of the sample, including brightfield and darkfield modes, and both absorption and phase contrast methods. This has advantages for the imaging of radiation-sensitive samples in x-ray microscopy, but the principles of the method are also directly applicable to other forms of microscopy. Measurements made at energies on either side of an x-ray absorption edge show there are considerable practical benefits to having both absorption and phase contrast information simultaneously available to the user, while through-focal series of images allow the relative importance of the real and imaginary parts of the complex refractive index to be investigated. As example, some measurements made using the Twinmic end-station at the Elettra synchrotron (BACH beamline) will be presented.