Standing-wave scanning tunneling spectroscopy

Interference between incident and elastically reflected surface-state waves gives density oscillations proportional to $\cos (2kx+\varphi )$. Their real-space period is $\pi /k$, half the travelling-wave wavelength.

Low-temperature scanning tunneling spectroscopy resolves energy-dependent interference in the surface electronic density of states near scattering features. Its coexistence with a structural map distinguishes electronic corrugation from atomic positions. The 1993 Cu(111) observation provides an early example.