Stark effect on quantum well states in Au/Fe(100)

The quantum well (QW) states in Au/Fe(100) and their energy dependence on tip-sample distance are observed using scanning tunneling spectroscopy. When the tip-sample distance is decreased by 0.2 nm, the QW states shift by as large as 40 meV, which is approximately 20 times larger than the Stark shift observed in the surface state in noble metals. The observed shifts may be caused by the phase shift of the QW wave functions in the Au film as well as at the vacuum/Au interface. (c) 2007 American Institute of Physics.