High Spatial Resolution Assessment of the Structure, Composition, and Electronic Properties of Nanowire Arrays
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High Spatial Resolution Assessment of the Structure, Composition, and Electronic Properties of Nanowire Arrays M.S. Sander1, A.L. Prieto1, Y.M. Lin2, R. Gronsky3, A.M. Stacy1, T.D. Sands3, M.S. Dresselhaus4 1 Department of Chemistry, University of California, Berkeley, CA 94720 2 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, 02139 3 Department of Materials Science & Engineering, University of California, Berkeley, CA 94720 4 On leave from Departments of Physics and Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, 02139
ABSTRACT We have employed transmission electron microscopy (TEM) and analytical electron microscopy to perform preliminary assessment of the structure, composition and electronic properties of nanowire arrays at high spatial resolution. The two systems studied were bismuth and bismuth telluride nanowire arrays in alumina (wire diameters ~40nm), both of which are promising for thermoelectric applications. Imaging coupled with diffraction in the TEM was employed to determine the grain size in electrodeposited Bi2Te3 nanowires. In addition, a composition gradient was identified along the wires in a short region near the electrode by energy-dispersive x-ray spectroscopy. Electron energy loss spectroscopy combined with energyfiltered imaging in the TEM revealed the excitation energy and spatial variation of plasmons in bismuth nanowire arrays. INTRODUCTION Nanowire arrays consisting of an ordered distribution of uniform diameter wires within a supporting matrix have attracted considerable recent interest.1 These arrays can potentially be used to harness the properties of nanowires for robust applications in areas such as thermoelectrics, information storage, and photonics. Because transport in nanowires is confined to one dimension and the arrays have a large interfacial area, the array properties are particularly sensitive to even slight variations in structure and composition in the wires and at the wirematrix interfaces. Therefore, to obtain an understanding of the relationship between the array characteristics and the array properties, it is necessary to assess the nanowires and wire-matrix interfaces at high spatial resolution. In this work, we have focused on assessing the local characteristics in nanowire arrays of bismuth and bismuth telluride in alumina. These nanocomposite materials have potentially good thermoelectric properties.2,3 Thermoelectric materials are currently not in widespread use for cooling and power generation applications due to their relatively low efficiency. A promising approach to increase thermoelectric efficiency is through confinement of the charge carriers in low-dimensional structures, as demonstrated recently in quantum well systems,4 and this approach may be possible in two-dimensionally confined nanowires. The bismuth-alumina nanowire array system is also a good model system for understanding the relationship between C4.36.1
wire and interface chara
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