The field of molecular electronics is aimed at the use of small ensembles or even individual molecules as functional building blocks in electronic circuitry. Single-molecule devices appear to be ideal candidates for future nano-electronics, as they possess the potential for creating high-density devices with low power consumption in combination with high speed. Moreover, because of their internal molecular structure, molecules may provide novel intrinsic functionality not found in today's silicon electronics.
Although molecular electronics can be regarded as a possible path to drive miniaturization beyond the limits being approached by conventional semiconductor technology, it also presents a significant challenge because of the need for reproducible fabrication at the molecular scale. If molecular devices can take advantage of self-assembly processes, however, molecular devices may also feature low manufacturing costs.
Understanding the underlying physics is the basis for building molecular electronic devices and circuits. Our efforts are therefore focused on investigating charge-carrier transport through single-molecule junctions in order to correlate chemical structure and device functionality. The mechanically controllable break-junction (MCBJ) technique (Figure 1, Figure 2) provides a reliable test geometry to probe the electrical properties of an individual or a small ensemble of molecules. Using this technique, the distance between two electrodes can be controlled in a very precise down to picometer resolution (Figure 3) to match the length of a single molecule (on the order of 0.5 to 5 nm), which can then be inserted between the two electrodes. This method allows a reliable and resilient electrical contact of the molecule to the two electrodes, thus forming the simplest two-terminal device (Figure 4). In that respect, understanding molecule-metal contacts is one of the most significant challenges. The MCBJ method enables us to measure the electrical properties of different molecular species, such as molecular insulators, wires, diodes, and molecular switches.
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