Etching of diamonds for x-ray monochromators

Abstract

Results of a study of etching of synthetic diamond single crystals are reported. The studies were done to examine the efficacy for improvements in the performance of synchrotron based x-ray monochromators. The three diamonds that we studied were all type Ib and were all (111) oriented. Synthetic diamonds are commonly type Ib and are yellow in color due to nitrogen impurities. Such diamonds are good candidate crystals for use as synchrotron-based x-ray monochromators because reasonably low dislocation densities can result. X-ray topography and x-ray double-crystal diffractometry with the diamond (111) reflection in a slightly dispersive geometry and Cu Kα (8 keV) radiation were used to assess the diffraction properties. Two separate etching procedures were studied. In the first, 1 keV oxygen+argon ion bombardment was used to sputter clean the surface and to introduce oxygen, followed by chemical oxidation at 720–730 °C. The oxidation was performed with KOH and Na2O2. Rocking curve full width at half maximum (FWHM) was improved from 7.3 to 6.4 arc sec and from 8.1 to 6.7 arc sec for two sides of the same slab that were treated separately. The theoretical ideal value is 5.8 arc sec. For the second technique, a patented and commercially available procedure that involves plasma deposition of SiOk compounds on a platter followed by abrasion of the diamond against this platter was studied. Two separate diamonds were treated with this second process, and, for one, the FWHM was slightly improved from 7.2 to 6.6 arc sec, but, for the other, the FWHM values were found to be increased from 8.0 to 8.5 arc sec.