Towards the Fabrication and Characterization of a Nanomechanical Electron Shuttle
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First proposed in the late 1990's, a nanomechanical electron shuttle is a device where an electrically isolated island moves a definite number of electrons between two leads, producing a current that is directly related to the number of electrons moved in a cycle and to the vibration frequency of the island. Since nanomechanical structures can have very well defined vibration frequencies, a device of this type is useful as, among other things, a current standard for metrology. The experimental shuttle implementations to date have had large island-lead spacings, which has limited their performance. The work presented here takes the first steps towards the fabrication of a nanomechanical electron shuttle using the process of electromigration to define very small lead-island gaps with conductivity on the order of the conductance quantum G_0=2e^2/h. These small gaps, coupled with the high vibration frequencies achievable with nanostructures, will allow investigation deeper into the realm of quantum effects. In this work, the fabrication steps for the creation of these devices were developed. Electromigration of a single junction was successfully achieved to the 10--100\,k\ohm range. The simultaneous and symmetric electromigration of two junctions, as required for the shuttle, has not yet been achieved. The development of a fast electromigration cut-off circuit, however, gives hope that double-breaking success will be achieved soon.