Depth-Resolved Cathodoluminescence of ThO\u3csub\u3e2\u3c/sub\u3e

Single crystal thorium dioxide (ThO2) samples were hydrothermally grown and studied using depth-resolved cathodoluminescence (CL) to characterize the surface and bulk electronic states. X-ray diffraction (XRD) measurements were collected to confirm that these crystals were ThO2 in the fluorite structure. Understanding the chemical and structural quality of ThO2 will aid in the fabrication of better neutron detectors as well as in the power production with thorium breeder reactors. Monte Carlo simulations predicted the expected energy-dependent electron interaction depths in the ThO2 crystals. CL was conducted with electron energy range of 1.5 - 12 keV, a current range of 30-62 µA, at pressures of 5 x 10-7 to 1.2 x 10-9 Torr, and temperatures of 24 K - 297 K. The initial CL measurements indicated that the as-grown sample exhibited more of an energy dependency than the cleaved sample. Time of flight secondary ion mass spectrometry (TOF SIMS) was conducted on the samples, which cleaned the surface. Additional CL measurements were conducted on both samples, which showed that the as-grown sample no longer had an energy dependency. With the CL results and peak deconvolutions, it is compelling to believe that the absorption edge is 5.1 eV, which is complemented with the absorption measurement of 5.4 eV