Electron fringes and standing wave states in a quantum wedge

A quantum wedge, a nanoscale wedge structure of a metal with its thickness varied monotonically by discrete atomic planes is, in effect, an assembly of quantum wells of incremental sizes and an ideal system for exploring wave properties of electrons under spatial confinement. A set of size-dependent electron standing wave states and their energy spectra formed inside a quantum wedge can be revealed with an atomic accuracy using the STM and STS. The tunnel junction provides an intrinsic mechanism for the energy filtering and contrast enhancement, which facilitates direct STM imaging of electron interference fringes formed spontaneously at the surface of the quantum wedge. Together STM and STS offer a new technique to nondestructively characterize a buried interface in all three dimensions. An atomic lattice buried under a metal film whose thickness is as much as ten times its Fermi wavelength can be clearly resolved with the STM. The fine lateral imaging resolution of a buried lattice is attributable to the anisotropic motion of the confined electrons in the metal and to the dispersion of their discrete transverse energy spectra as a result of the scattering from a boundary with natural atomic corrugations. (C) 2000 Elsevier Science B.V. All rights reserved.