Semitransparent CVD diamond detectors for in situ synchrotron radiation beam monitoring

Chemically vapour-deposited (CVD) diamond thin films have been used for X-ray beam monitoring. Advances in experiments using synchrotron light sources have generated a demand for permanent in-line radiation hard X-ray monitors in the energy range 1.5-25 keV. CVD diamond has two distinct advantages over all other detector materials: it has a low atomic number resulting in a low X-ray absorption cross-section and it exhibits a high radiation and temperature hardness allowing long term operation. This combination enables thin-film photodetectors to be inserted in the beam line causing only low level intensity perturbations downstream. Diamond membranes 20 μm thick were grown on silicon using the microwave plasma CVD technique. Four-quadrant position-sensitive devices were fabricated on CVD diamond using other low atomic number materials such as graphite and aluminium for contact formation. Positional analysis of 4 keV photons from a third generation synchrotron radiation facility (ESRF) under typical operating conditions (10¹²-10¹³ photons cm^-2 s^-1) has demonstrated a spatial resolution of 2 μm over a 200 μm×200 μm area with 80% transmission remaining. For demanding experiments such as XAFS, this feature allows real time monitoring of beam instabilities and therefore simultaneous position correction during data acquisition.