EXPLORING MACROSCOPIC SURFACE-STRUCTURES ON X-RAY CCDS USING SILICON ABSORPTION-EDGE QUANTUM EFFICIENCY MEASUREMENTS

We have begun an experiment to systematically record the quantum effic iency variations of a silicon CCD across the K edges of it's constitue nt materials using the Synchrotron Radiation Source (SRS) at the Dares bury Laboratory. The ultimate goal of the program is to provide a deta iled calibration database of instrumental X-ray Absorption Fine struct ure (XAFS) in CCDs intended for X-ray astronomical space missions. Bec ause X-ray CCDs are single photon counting devices, the maximum flux t hat can be accommodated while still retaining full spectral resolution is typically a few hundred events cm(-2)s(-1), a requirement clearly incompatible with normal synchrotron usage. Thus, in order to carry ou t our experiments, the SRS had to be operated in a new low current mod e. We describe how the experiment was carried out and present a prelim inary analysis of data obtained on March 9, 1994. The data show consid erable structure in the quantum efficiency above the Si K edge at 1839 eV and, in fact, the response of a silicon CCD in this region is domi nated by the electrode and passivation structures.