NPGS : Electron Pump
This scanning force microscope image shows a 7-junction electron pump fabricated at NIST in Boulder, CO. (The thin horizontal streaks are artifacts from the scanning force microscope.) The pattern was written in a bilayer of PMMA to create a mask with large undercut. A double-angle evaporation technique, with oxidation after the first layer, was then used to create small tunnel junctions where the two layers overlap. The seven small bright dots down the center are the tunnel junctions (~40 nm x 40 nm) and the larger structures along the sides are gate capacitors which allow control of tunneling of individual electrons. The distance between junctions is 0.6 µm. This device can pump individual electrons with an error of only 1 part in 108, and is the basis for a new type of capacitance standard. See M.W. Keller et. al., Appl. Phys. Lett. 69, 1804 (1996).