The cBN and hBN samples used in this study were randomly oriented powders that were attached to a Ta substrate with conductive silver epoxy. The 1000 iBN/Si film was prepared using ion-assisted, pulsed-laser deposition under conditions similar to those described previously.[3] X-ray diffraction studies of similarly prepared films have shown no evidence for long-range structural ordering, indicating an incoherent or fine-grained structure with a characteristic size less than about 200 nm.[5] Other BN thin film growth conditions, such as ion-assisted electron-beam evaporation with high deposition rates, have been shown to give an incoherent structure as well.[6]
NEXAFS spectra were measured both at the IBM/U8 beam line at the National Synchrotron Light Source and at the 8-1 beamline at the Stanford Synchrotron Radiation Laboratory. At NSLS, soft x-ray absorption was measured in the secondary-electron, partial-yield mode that monitors the 0-10 eV electron intensity as a function of monochromatic photon energy. At SSRL, the total electron yield was measured by monitoring the current flowing from ground into the sample with a picoammeter. Agreement between these two methods of data collection is excellent, as will be shown below.