Particle in a variable-size box: The influence of the tip in thin-film electron interferometry

The influence of the scanning-tunneling-microscopy tip on the conductance spectra measured in thin-film electron interferometry is considered, and is discussed in terms of coupled quantum wells. One of the wells is formed by the linear potential drop between the tip and sample, which gives rise to vacuum-field-emission resonances. The spectra of field-emission resonances are shown to be very sensitive to the properties of the tip, and can be understood in terms of confining the electron to triangular potential wells of different sizes. The other potential well is formed within the thin-film adlayer, and its spectrum should be largely independent of the properties of the tip. We consider the spectrum of the coupled system, and discuss it in terms of perturbation theory where we observe the tendency of the levels to repel each other when they are closely spaced in energy, and to cause level splitting when the levels are degenerate.