Scanned probe microscope images of electron flow away from a quantum point contact formed in a two dimensional electron gas inside a GaAs/AlGaAs heterostructure. Small angle scattering causes branches of electron flow to form at distances less than the mean free path.

Robert Westervelt, Harvard University, Arthur C. Gossard, UC, Santa Barbara, Physics Today 56(12) (2003).

Image courtesy: Dr. Robert Westervelt, Harvard University.