Imaging coherent electron flow through semiconductor nanostructures

Scanning probe microscopy is used to probe coherent electron flow in semiconductor nanostructures. We have developed a technique for imaging coherent electron flow through a two-dimensional electron gas (2DEG). The images are acquired using a scanning probe microscope at low temperature. The conductance through the device as a function of tip position is measured to obtain an image of electron flow. The images of electron flow are decorated by interference fringes spaced by half the Fermi wavelength. We use the spacing of these fringes to measure the local electron density. The variation of the density with back gate voltage agrees with a parallel plate capacitor model.; We use our imaging technique to characterize the rate of energy loss for electrons traveling through the 2DEG. A source-drain voltage is applied to the electrons, which accelerates them and causes them to loss energy more quickly. By imaging the electron flow, the rate that the electrons lose their excess energy is determined. The results agree with the electron-electron scattering rate in a 2DEG for different distances and energies.; Images of electron flow through three electron-optic devices are presented. An electrostatic prism is used to control the direction of electron flow based on the density under its gate. Images are shown using a round gate as a defocusing lens for electron waves and as a circular scatterer. The potential profile from an electrostatic gate is investigated by creating a narrow channel for electrons. By imaging the trajectories of electrons, the profile of the potential from the gate is found.; The origin of the interference fringes, which decorate all of our images of electron flow is investigated. They are clue to interference between paths backscattered from the tip and ones backscattered from scattering objects at nearly the same distance. This is confirmed by the addition of a small reflecting gate, which enhances the interference fringes at the same distance from the quantum point contact. The interference fringes move as the position of the reflector is changed indicating that the fringes are due to backscattering from the reflector.