| Uranium and its alloys are important materials in nuclear weapon and nuclear energy industry, and their electronic structure and properties are always the focus of study. However, due to the radioactivity and chemical reactivity of uranium, very few researches have been done, especially for the study of5f electronic character. Valence band and band structure studies are hard to obtain due to the lack of high quality single crystal samples, and no work has been done in China. In this paper, growth conditions and parameters have been obtained by growing single crystal Ce films, and then ordered uranium films and their electronic structure have been studied. Based on this, UO2-x thin films were also studied. We also tried to grow single crystal films on Si (111)-7×7. Four main parts are included in this paper.1) Ce film was deposited onto W (110) substrate, and its morphology, crystal structure, chemical state, valence band and band structure have been studied by STM, LEED, XPS and ARPES. STM results show that for the as-deposited film, it contains both ordered and disordered regions, and some triangular and hexagonal pits can be seen on the surface. After being annealed at600K for10min, LEED patterns become very sharp, and the pits all disappeared, instead triangular and hexagonal terraces appear. After being oxidized, reconstruction surface can be seen and the reconstruction period is11.2A×12.67A. XPS result shows that the oxidized film is not the standard stoichiometric Ce2O3, but Ce2O3-x instead. The peak near EF always exists even after the surface has been oxidized, indicating that metal Ce still exists. The dispersion of both Ce4f and O2p bands have been more obvious after been oxidized.2) U film was deposited onto the W (110) substrate. During the deposition of U film, the growth mode was layer-by-layer. High-oriented single crystal film can be obtained by annealing the sample to900K in high vacuum conditions (better than5×10-10mbar), and LEED show very sharp diffraction patterns. The surface morphology was studied by STM, which show steps and terraces for typical single crystals. Valence band spectrum and band structure were obtained by ARPES, and UPS spectra of the film have very high electron state density near the Fermi level, and strong hybridization between5f and6d orbital can be observed within the binding energy1-3eV. In order to determine the exact crystal structure of the grown film, the density of states and band structure were calculated using DFT method, and the experimental result showed large difference with that of hcp-U, but very similar to alpha-U.3) After the fresh uranium film was left in5×10-8mbar O2conditions for2h, many nanostructures can be observed on the surface, and the average size is about2nm. After being annealed at1080K for10min, two typical morphologies appear on the surface, one show very flat terraces and another show many point structures on the terraces and the steps. By further annealing at1080K for1h, the whole surface show very flat terraces, which is typical for the surface of single crystals. Parallel streaks appear on the surface, and at this stage LEED show sharp patterns. New phase of UO2-X has been obtained, and dI/dV spectroscopy, valence band and band structure of the new phase have been obtained.4)3ML U film was deposited onto Si (111)-7×7surface, and the surface morphologies with different annealing temperature were studied by STM. The crystal structures of the new phases were studied with both RHEED and LEED, and the electronic structure with different annealing temperature was studied by ARPES. The result shows that for the as-deposited film the surface was disordered, after being annealed at870K, LEED showed very sharp hexagonal patterns, which indicated that two-dimensional film was formed. A new superstructure was found after being annealed at1000K, and Si (111)-7×7surface was observed after being annealed at1200K with high islands on it.
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