Nanowires
Nanowires are especially attractive for nanoscience studies as well as for nanotechnology applications. Nanowires, compared to other low dimensional systems, have two quantum quantum confinement confined directions while still leaving one unconfined direc
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4. Nanowires
4.1
4.2
4.3
Synthesis ............................................. 4.1.1 Template-Assisted Synthesis.......... 4.1.2 VLS Method for Nanowire Synthesis ................. 4.1.3 Other Synthesis Methods ............... 4.1.4 Hierarchical Arrangement and Superstructures of Nanowires ...............................
108
Characterization and Physical Properties of Nanowires ....................................... 4.2.1 Structural Characterization ............ 4.2.2 Transport Properties ..................... 4.2.3 Optical Properties .........................
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Applications ......................................... 4.3.1 Electrical Applications ................... 4.3.2 Thermoelectric Applications ........... 4.3.3 Optical Applications ...................... 4.3.4 Chemical and Biochemical Sensing Devices ........................... 4.3.5 Magnetic Applications...................
100 100 105 107
131 131 133 134 137 137
4.4 Concluding Remarks ............................. 138 References .................................................. 138
nanotechnology applications. Driven by: (1) these new research and development opportunities, (2) the smaller and smaller length scales now being used in the semiconductor, opto-electronics, and magnetics industries, and (3) the dramatic development of the biotechnology industry where the action is also at the nanoscale, the nanowire research field has developed with exceptional speed in the last few years. A review of the current status of nanowire research is therefore of significant broad interest at the present time. This review aims to focus on nanowire properties that differ from those of their parent crystalline bulk materials, with an eye toward possible applications that might emerge from the unique properties of nanowires and from future discoveries in this field.
Part A 4
Nanowires are especially attractive for nanoscience studies as well as for nanotechnology applications. Nanowires, compared to other low dimensional systems, have two quantum confined directions while still leaving one unconfined direction for electrical conduction. This allows them to be used in applications which require electrical conduction, rather than tunneling transport. Because of their unique density of electronic states, nanowires in the limit of small diameters are expected to exhibit significantly different optical, electrical, and magnetic properties from their bulk 3-D crystalline counterparts. Increased surface area, very high density of electronic states and joint density of states near the energies of their van Hove singularities, enhanced exciton binding energy, diameter-dependent bandgap, and increased surface scattering for electrons and phonons are just some of the ways in which nanowires differ from their corresponding bulk materials. Yet the sizes of nanowires are typically large enough (> 1 nm in the quantum confined direction) to have local crystal structures closely related to their parent materials, thereby allowing theoretical predictions about
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