Ion beam induced surface modification of chemical vapor deposition diamond for x-ray beam position monitor applications

Abstract

The Advanced Photon Source at Argonne National Laboratory is a third-generation synchrotron facility that generates powerful x-ray beams on its undulator beamlines for a variety of scientific and industrial user research programs. It is very important to know the position and the angle of the x-ray beam during experiments. Due to very high heat flux levels, several patented x-ray beam position monitors (XBPMs) exploiting beneficial characteristics of chemical vapor deposition (CVD) diamond have been developed. These XBPMs have a thin layer of low-atomic-mass metallic coating so that photoemission from the x rays generates a minute but measurable current for position determination. Another concept has been the graphitization of the CVD diamond surface to create a very thin, intrinsic conducting layer that can stand much higher temperatures and have minimal x-ray transmission losses compared to coated metallic layers. In the present study, a laboratory sputter ion source was used to transform selected surfaces of a CVD diamond substrate into graphite. The effect of 1–5 keV argon ion bombardment on CVD diamond surfaces at various target temperatures from 200 to 500 °C was studied using Auger electron spectroscopy and in situ electrical resistivity measurements. Graphitization after the ion bombardment was confirmed, and optimum conditions for graphitization were studied. Raman spectroscopy was applied to identify the overall diamond structure in the bulk of CVD diamond substrate after the ion bombardments. It was found that the target temperature plays an important role in the stability and electrical conductivity of the irradiated CVD diamonds.