Quantum Mechanics
Tunneling: slit + barrier

A wave passing through a narrow slit is scattered in many directions. Both the momentum parallel and perpendicular to the slit are no longer conserved.

Wave passing through narrow slit

Placing a tunnel barrier to the right of the slit can strongly modify the properties of the transmitted wave. The next animation shows the effect of a triangular potential barrier on the transmitted wave.

Wave passing through narrow slit + tunnel barrier

The properties of the transmitted wave packet strongly depends on the properties of the tunnel barrier and, to less extent, on the width of the slit whereas the length of the slit has little effect. A slit followed by a potential barrier provides a simple model to describe the electron emission from nanoscale sources.