Photoemission microspectroscopy of occupied and unoccupied surface states of crystalline facets formed on polycrystalline copper

Microbeam photoemission spectroscopy of 30-meV energy resolution and 0.3-μm lateral resolution has been applied to observe (111) surface domains formed on a polycrystalline copper plate. The light source was fs-coherent radiation at a wavelength of 140 nm (8.9 eV). The images based on the intensity of the Shockley-surface-state feature clearly show many crystalline domains, exposing the (111) surface. The energy of the surface-state feature was distributed in the range from -−0.3 to −0.1 eV with respect to the Fermi level (E_F). In addition to the μm-scale information, the high-energy-resolution spectroscopy provides detailed insight on the nm-scale surface morphology. Surface images based on the unoccupied image-potential state were also measured by employing two-photon photoemission with uv light at a wavelength of 280 nm (4.43 eV). The image state was always at 4.10 eV, which is very close to the state of single-crystalline Cu(111). The Shockley state was observed even on poorly crystallized areas, while the image-potential state was observed only on areas where mean (111) terrace lengths are sufficiently long.