title: Bismuth telluride (Bi2Te3) nanowires: synthesis by cyclic electrodeposition/stripping, thinning by electrooxidation, and electrical power generation.
abstract: Nanowires composed of the thermoelectric material Bi2Te3 were synthesized on highly oriented pyrolytic graphite (HOPG) electrodes using the electrochemical step edge decoration (ESED) method. Nanowire synthesis was initiated by applying a voltage pulse of -0.75 V versus SCE for 5 ms to an HOPG electrode in an aqueous solution containing both Bi3+ and TeO22-, thereby producing nuclei at the step edges. Bi2Te3 was electrodeposited onto these nuclei using a cyclic electrodeposition-stripping scheme that involved the electrodeposition of bismuth-rich Bi2Te3 on a negative-going voltammetric scan (to -0.05 V) and the subsequent anodic stripping of excess bismuth from these nanowires during a positive-going scan (to +0.35 V). When this cycle was repeated 10-50 times, Bi2Te3 nanowires in the 100-300-nm-diameter range were obtained. These nanowires were narrowly dispersed in diameter (RSDdia = 10-20%), were more than 100 microm in length, and were organized into parallel arrays containing hundreds of wires. Smaller nanowires, with diameters down to 30 nm, were obtained by electrooxidizing 150-nm-diameter Bi2Te3 nanowires at +0.37 V under conditions of kinetic control. This oxidation process unexpectedly improved the uniformity of Bi2Te3 nanowires, and X-ray photoelectron spectroscopy (XPS) shows that these nanowires retain a Bi2Te3 core but also have a thin surface layer composed of Bi and Te oxides. The ability of Bi2Te3 nanowires to generate electrical power was assessed by transferring ensembles of these nanowires onto cyanoacrylate-coated glass surfaces and evaporating 4-point nickel contacts. A dimensionless figure of merit, ZT, ranging from 0 to 0.85 was measured for fresh samples that were less than 1 day old. XPS reveals that Bi2Te3 nanowires are oxidized within a week to Bi2O3 and TeO2. These oxides may interfere with the application by evaporation of electrical contacts to these nanowires.
authors.affiliation: Institute for Surface and Interface Science and Department of Chemistry, University of California, Irvine, California 92679-2025, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Menke
authors.forename: M A
authors.initials: MA
authors.lastname: Brown
authors.forename: Q
authors.initials: Q
authors.lastname: Li
authors.forename: J C
authors.initials: JC
authors.lastname: Hemminger
authors.forename: R M
authors.initials: RM
authors.lastname: Penner
mesh_terms: D000497:Alloys / Q000138:chemical synthesis* / Q000737:chemistry; D001729:Bismuth / Q000737:chemistry*; D011211:Electric Power Supplies; D004563:Electrochemistry; D004566:Electrodes; D004595:Electroplating; D006108:Graphite / Q000737:chemistry; D043942:Nanotubes / Q000737:chemistry*; D010084:Oxidation-Reduction; D010316:Particle Size; D012680:Sensitivity and Specificity; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D013053:Spectrophotometry / Q000379:methods; D013691:Tellurium / Q000737:chemistry*; D013997:Time Factors; D014961:X-Ray Diffraction; D014965:X-Rays
chemical_list: D000497:Alloys; D006108:Graphite; D013691:Tellurium; D001729:Bismuth