Photoconductive Metal Nanowires with Embedded Semiconductor Nanonodes

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Technical Description: A new strategy is under investigation for the creation of nanometer-scale photoconductors that are both fast, in terms of the response and recovery of the photoconductive state to light (100 ns), and highly sensitive to light, possessing a high internal photoconductive gain (100). The gain, defined as the number of electrons produced for each absorbed photon, can be maximized by collapsing a semiconductor nanowire in length until it becomes a semiconductor nanoparticle, cradled between a pair of metal electrical contacts. This arrangement is achieved by preparing arrays of crossed nanowires in which an ultrathin (100 nm) optical absorbing layer of cadmium selenide, for example, is sandwiched between two gold nanowires. Light-emitting junctions or nanonodes are obtained using the same crossed-nanowire strategy except that one set of metal nanowires is replaced by p-type semiconductor nanowires, such as silver (I) oxide or PEDOT (poly (3,4-ethylene-dioxythiophene)). A photoemissive n-p junction is thereby formed. Processes for preparing dense arrays of crossed nanowire junctions that function as photoconductive optical sensors and photoemissive junctions are being developed. Fundamental aspects of these structures are being probed using single crossed nanowire junctions. The properties of photoconductive arrays for detecting spatially modulated light sources, and the collective properties of photoemissive arrays for generating spatially modulated light will be characterized. Non-technical Description: A new method is being studied for fabricating optical detectors and light sources that are smaller than the wavelength of light. In this project, linear arrays of nanowires composed of metal or semiconductors are superimposed on top of one another to create an array of nanowire crossings or junctions. This crossed nanowire strategy should be capable of producing arrays of millions of optical detectors or optical sources. This project provides a multidisciplinary training experience for graduate students that encompassing nanofabrication, surface chemistry, electrochemistry, condensed matter physics, and spectroscopy. A fellowship-based outreach program that targets economically disadvantaged high-school students is operating in parallel with these research activities.