(Invited) Fabrication and Characterization of Carbon-Based Nanoscale Devices: Insights and Applications

Nanoscale devices made from carbon-based materials are investigated for a variety of unique properties and features, including their promise to improve performance, decrease production costs, or provide totally new functionality relative to extant electronic devices. Because these devices have active areas composed of materials that are much thinner than those used in conventional devices, the details of the interfaces can often act to control the physics that lead to the operational device characteristics in unexpected ways. This is particularly true in molecular electronics, where design rules based on chemical intuition often fail to account for key physical aspects that dominate device behaviour. Thus, the ability to modify interfaces in a way that leads to control of device properties is a key to enabling next-generation devices based on nanoscale phenomenon. In addition, it is important to achieve an understanding of the processes that occur during carrier transport in nanoscale devices in order to obtain desirable functionality. This presentation will describe several aspects of carbon-based nanoscale devices, including fabrication and operation of molecular electronics and graphene field effect transistors (GFETs). After a discussion of some general physical principles that operate within the interfacial energy level alignment regime in molecular electoronics, a discussion of how light emission from nanoscale devices can be used to characterize them will be provided. In particular, we have used light emission from both large area molecular junctions and GFETs to understand important distance scales (elastic limits) and processes (transport and emission mechanisms). The data indicate that processes that involve hot carrier interactions with plasmonic structures in the devices lead to light emission, and that this phenomenon can be used to measure energy losses of carriers as they traverse a molecular layer. Results indicate that carriers can travel approximately 7 nm through a molecular junction before energy losses become significant, indicating that elastic transport is achieved for thin layers, but a transition in mechanism occurs for thicker films. The characteristics of the energy losses are reported for several different structures, providing insights into the nature of the transport in molecular electronics. Light emission from GFETs, on the other hand, appears to follow a novel mechanism that involves the excitation of plasmons in the graphene by hot carriers followed by decay through photon emission. By controlling the location of defects in the graphene lattice and the nanostructures around these scattering sites, emission could be localized to regions where this coupling is more optimized. In this second case, the devices may be able to be engineered through nanostructuring in order to gain control over the character of light emission. Finally, a few novel and emerging applications of nanoscale devices will be discussed, including using molecular devices in audio circuits, as well as for high frequency harmonic generation.

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