Direct observation of strain-induced change in surface electronic structure

We have observed a novel modification of a surface state due to a local strain field induced by a nanopattern formation. N adsorption on the Cu(100) surface induces a nanoscale grid pattern, where the clean Cu regions remain periodically. The lattice is contracted on the clean region by adjacent c(2 x 2)N domains, which have a larger lattice constant. On this patterned surface, we have investigated the Tamm-type surface state at M by means of angle-resolved ultraviolet photoelectron spectroscopy. The binding energy of the Tamm state shifts toward the Fermi level continuously with increasing N coverage, i.e., the intensity of the strain field. This behavior due to the strain field is completely different from that caused by electron confinement observed on vicinal surfaces. The Brillouin zone extension corresponding to the lattice contraction was also detected.