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Unformatted text preview: Superlattice Nanowire Pattern Transfer (SNAP) JAMES R. HEATH* Caltech Division of Chemistry & Chemical Engineering and the Kavli Nanoscience Institute, MC 127-72, 1200 East California Boulevard, Pasadena, California 91125 RECEIVED ON JANUARY 16, 2008 CON SPECTUS D uring the past 15 years or so, nanowires (NWs) have emerged as a new and distinct class of materials. Their novel structural and physical properties separate them from wires that can be prepared using the standard methods for manufacturing electronics. NW-based applica- tions that range from traditional electronic devices (logic and memory) to novel biomolecular and chemical sensors, thermoelectric materials, and optoelectronic devices, all have appeared during the past few years. From a fundamental perspective, NWs provide a route toward the investiga- tion of new physics in confined dimensions. Perhaps the most familiar fabrication method is the vapor- liquid- solid (VLS) growth technique, which produces semiconductor nanowires as bulk materials. However, other fabrication methods exist and have their own advantages. In this Account, I review a particular class of NWs produced by an alternative method called superlattice nanowire pat- tern transfer (SNAP). The SNAP method is distinct from other nanowire preparation methods in several ways. It can pro- duce large NW arrays from virtually any thin-film material, including metals, insulators, and semiconductors. The dimensions of the NWs can be controlled with near-atomic precision, and NW widths and spacings can be as small as a few nanom- eters. In addition, SNAP is almost fully compatible with more traditional methods for manufacturing electronics. The moti- vation behind the development of SNAP was to have a general nanofabrication method for preparing electronics-grade circuitry, but one that would operate at macromolecular dimensions and with access to a broad materials set. Thus, elec- tronics applications, including novel demultiplexing architectures; large-scale, ultrahigh-density memory circuits; and com- plementary symmetry nanowire logic circuits, have served as drivers for developing various aspects of the SNAP method. Some of that work is reviewed here. As the SNAP method has evolved into a robust nanofabrication method, it has become an enabling tool for the inves- tigation of new physics. In particular, the application of SNAP toward understanding heat transport in low-dimensional sys- tems is discussed. This work has led to the surprising discovery that Si NWs can serve as highly efficient thermoelectric materials. Finally, we turn toward the application of SNAP to the investigation of quasi-one-dimensional (quasi-1D) super- conducting physics in extremely high aspect ratio Nb NWs....
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