Mapping X-ray absorption fine structure in the quantum efficiency of an X-ray charge-coupled device

Abstract

Recent measurements have shown that high-resolution silicon detectors are beginning to resolve x-ray absorption fine structure (XAFS) produced in the detectors themselves. Unless calibrated, such structure threatens to ‘pollute’ spectroscopic measurements. An experiment has begun map this structure to systematically in an x-ray charge-coupled device (CCD) over the energy range 300–2100 eV. The program is novel in that the synchrotron radiation source has to be operated with a ring current reduced by five orders of magnitude so that individual photons can be recorded by the CCD. Results of the detailed spectroscopic response around the nitrogen, oxygen and silicon K edges are presented. The measured quantum efficiency shows considerable near-edge structure which is modified by the presence of the various insulation layers used in MOS construction, reflecting the chemical rather than elemental nature of the interaction environment. It is pointed out that the measurement of XAFS in x-ray CCDs is potentially a powerful diagnostic tool with which to explore surface structures.