Photoemission Spectroscopy on Single Crystal Uranium (001)

We have conducted XPS and UPS measurements (173\underline { $<$} T\underline { $<$} 873 K) on high quality single-crystal U(001) and compared them with WIEN2K code electronic band structure calculations. We report significant correspondence between theory and experiment for binding energy (BE) $<$ 4 eV and report anomalous splitting of the 6p$_{1/2}$, 6p$_{3/2 }$bands at BE = 13-30 eV. Spectrometer resolution allows observation of a shift in spectral weight in the U6d-U5f electrons upon comparison of He I (21.21 eV) and He II (40.80 eV) spectra at T = 173 K. ARPES experiments confirm that our electron structure result is a representative bulk effect. LEED patterns indicate a well-ordered orthorhombic crystallographic surface structure. Additionally, our experiments show a temperature correlation between the U work function and the brittle to ductile transition at $\sim $ 450 K. Recent resistivity and specific-heat data will be discussed.