Imaging electrons at the nanoscale with a cooled scanning probe microscope

The ability to measure and manipulate electrons at the nanoscale gives insight into nanoscale physics and paves way for its applications in electronics and photonics. We present a design and implementation of a scanning probe microscope that is cooled to liquid nitrogen temperature, to image electrons at the nanoscale. The imaging technique relies on a conductive scanning tip that acts as a local, movable electrostatic gate. The tip creates a local change in density of electrons in the material directly underneath it deflecting the electrons away from their original path. This changes the conductance of the device. The conductance is measured as a function of tip position while the tip moves across the material. The conductance change vs. tip position gives the map of the electron flow in the material. To align the tip within a micron of the sample at liquid nitrogen temperature, we use a home-built coarse positioning system. By applying high voltages to a piezo tube, the tip is raster scanned over the sample. With this method, we plan to image the viscous flow of electrons in graphene at liquid nitrogen temperature. Our design also allows us to image electronic flow in other nanoscale materials such as 2D semiconductors and topological insulators.