Epitaxial growth mechanism and electronic properties of ultra-thin uranium films on W(110)

Epitaxial growth of uranium films is essential for exploring the exotic properties of U 5f electrons. However, the growth mechanism during the initial stages of U film formation remains unclear. In this study, the adsorption behavior of uranium (U) atoms on a tungsten (W)(110) substrate was investigated using scanning tunneling microscopy (STM) and first-principles calculations. It was found that an isolated U atom is more stable on the hollow site of the W(110) surface compared to the top and bridge sites. Additionally, two U atoms tend to adsorb on neighboring edge-sharing rhomboid hollow sites of W(110). As the concentration of U atoms increases, a directional two-dimensional (2D) growth trend along two high-symmetry directions of 0° and approximately 105° is observed. When the film thickness reaches 4 monolayers (ML), the close-packed U atoms exhibit a pseudo-hexagonal arrangement, accompanied by an enhanced tunneling signal near the Fermi level. Furthermore, thickness-dependent dI/dV spectra were obtained, showing strong consistency with the calculated results. These findings provide a clearer understanding of the initial growth mechanism of ultra-thin U films on the W(110) surface and open new scientific avenues for exploring the remarkable properties of uranium.