Angle-resolved photoemission utilizing synchrotron radiation as a source was used to measure the occupied and unoccupied band structure of aluminum. The occupied portion of the bands displays a dispersion in qualitative agreement with the nearly-free-electron model and self-consistent band calculations. The measured occupied bandwidth is 10.6 eV, which is 0.5 eV smaller than calculated, due to electron-electron interactions (self-energy). The measured gap at $X$ is 1.68±0.08 eV wide and centered 1.99±0.08 eV below the Fermi energy. The magnitude and position of this gap do not simultaneously agree with any calculation or fit to the Fermi surface. The band structures which are derived by fitting to the Fermi surface or to optical properties reproduce the gap magnitude correctly, but not its position. Band-structure calculations do not reproduce either the gap magnitude or position due to ∼0.5-eV discrepancy in the $X_1$ point. The experimental band structure above the vacuum level is in qualitative agreement with calculations, once inelastic scattering (short mean free path) and evanescent waves from the vacuum solid interface are included. The lifetime broadening of both initial and final states was measured. Finally, a new surface state was observed on the A1(100) surface.

• Received 28 June 1982

DOI:https://doi.org/10.1103/PhysRevB.27.727