Electron standing-wave observation in the Pd overlayer on Au(111) and Cu(111) surfaces by scanning tunneling microscopy

Electron standing waves in monolayer-high Pd overlayers grown on the Au(111) and the Cu(111) surfaces were observed by low-temperature ultrahigh vacuum scanning tunneling microscopy. We found that the period of the oscillation in the Pd overlayers is longer than that of the clean surface of both Au(111) and Cu(111) substrates. The longer wavelength on the Pd overlayers is explained by an upward shift in energy level of the two-dimensional surface states.