Surface Geometry and Chemistry of Hydrothermally Synthesized Single Crystal Thorium Dioxide

Author

Scott W. Key

Date of Award

3-26-2015

Document Type

Thesis

Degree Name

Master of Science in Nuclear Engineering

Department

Department of Engineering Physics

First Advisor

Tony D. Kelly , PhD.

Abstract

The surface chemistry and geometry of hydrothermally grown, single crystal ThO2 was studied using X-ray Photoemission Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The crystal was studied before and after sputter etching with Ar⁺, heating up to 675 K, and dehydration with dry nitrogen. The hydrothermal growth technique incorporated Cs and F into the near surface bulk. Heating to 675 K drove off the F, but did not the Cs. Sputtering with Ar⁺ at 75° cleaned the crystal and created a more uniform surface geometry. The Th 4f peak resolution, as measured by XPS improved by a factor of 3, the surface roughness, as measured by AFM, reduced by a factor of 2, and the error in adhesion force measurements at different location on the crystal reduced by a factor of 2. The surface of ThO₂ becomes more metallic with heating. X-rays, used in XPS, created 7.3 eV of charging on the ThO₂ crystal surface at room temperature. Metallic Th 4f peaks appeared in the XPS spectrum at 675 K, while the charging was reduced. The as-grown crystal, the adhesion force strength by metal was AuInNiTi. Post cleaning the adhesion force change to InAuNiTi. Interface energy computations confirm that the Au metal adhesion decreased by half for the cleaned crystal. Based on these results, indium is the best choice of metal for application of contacts to the ThO₂ single crystal used in this research.

AFIT Designator

AFIT-ENP-MS-15-M-87

DTIC Accession Number

ADA614955

Recommended Citation

Key, Scott W., "Surface Geometry and Chemistry of Hydrothermally Synthesized Single Crystal Thorium Dioxide" (2015). Theses and Dissertations. 83.
https://scholar.afit.edu/etd/83