This dissertation describes a project that brought together the physics of low-dimensional devices with the technology of low-temperature scanning probes. The low-dimensional devices were single or double quantum wires where electron motion is effectively restricted to a single dimension. Initially, the scanning probe functioned as an atomic force microscope (AFM) to locate a quantum wire. Without moving the AFM tip, the circuitry was changed to convert the scanning probe into a scanning charged tip. As the charged tip scanned over the device surface, the resistance of the device was recorded to build up an image. When the charged tip scanned over the quantum wire, the device resistance deviated. The images revealed broad structure which measured the electric potential of the tip itself, with additional small scale structure when the tip was positioned over the centre of the quantum wire. The small scale structure is a representation of quantum-mechanical electron modes resulting from modulations to the 1D eigenenergies. This experiment show electron density through low-dimensional devices. Both ends of the quantum wire were connected to a two-dimensional electron system (2DES) from which the resistance measurements were taken. When the tip scanned the 2DES region just outside the quantum wire, the tip's electric field scattered electrons. A small proportion of the electrons injected out of the quantum wire into the 2DES were scattered back through the quantum wire. This process is known as backscattering, which reduces the net electron flow through the quantum wire and increases the device resistance. The images revealed cones emanating from the quantum wires, to provide information on the angular distribution of injected electrons.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598172 |
| Date | January 2000 |
| Creators | Crook, R. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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