Wavevector-dependent quantum-size effect in electron decay length at Pb thin film surfaces

The physical origin of quantum-size effects (QSEs) and its impact on the decay length of electrons in Pb thin films are studied by first-principles calculations. We show that QSE is not only size but also wavevector dependent: being maximum at (Gamma) over bar due to strong interlayer coupling between p(z) orbitals, but could be vanishingly small at other symmetry points due to weak interlayer coupling between p(x,y) orbitals. The electron decay length also exhibits systematic oscillations with film thickness and the (Gamma) over bar valley has the slowest decay. (C) 2008 American Institute of Physics.