Optimization of Bismuth Nanowire Arrays by Electrochemical Deposition
- PDF / 900,067 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 229 Views
Optimization of Bismuth Nanowire Arrays by Electrochemical Deposition J. H. Barkyoumb*, J. L. Price*, N. A. Guardala*, N. Lindsey*, D. L. Demske*, J. Sharma*, H. H. Kang† and L. Salamanca-Riba†, *Carderock Division, Naval Surface Warfare Center, West Bethesda, MD, Dept. of Materials and Nuclear Engineering U. of Maryland, College Park, MD 20742
†
ABSTRACT Bismuth nanowires for thermoelectric applications have been made by electrochemical deposition from an aqueous Bi solution into nanoporous mica substrates, and Anopore (Al2O3) filters. The nanoporous substrates are created by acid etching damage tracks that are produced in the mica using heavy-ion irradiation. In this work, further improvements in the fabrication process are made by investigating the electrochemical growth at the 1-d to 2-d transition region at the nanochannel-substrate surface interface as a function of deposition time and electrochemistry. Issues related to doping of the Bi wires with Te along with the problem of electrochemical growth of contacts to the nanowires as compared to vacuum deposition of contacts will be discussed. INTRODUCTION Nanometer size wires of bismuth have been predicted to have a much higher thermoelectric figure of merit (ZT) than that of bulk bismuth.[1,2] This is due to bismuth’s unique properties such as a long electron mean free path at low temperatures and a small carrier effective mass which allows quantum confinement effects to be observed for relatively large wire diameters. The low electron density and low thermal conductivity of bismuth also make it attractive as a high ZT material. Magnetoresistance results indicating quantum confinement and a semimetalto-semiconductor transition for wire diameters less than 790 nm confirm these effects.[3] Recently, Bi nanowires have been prepared by pressure injection[4] and by a vapor-phase technique into porous alumina hosts.[5] Also, stoichiometric Bi2Te3 alloys for thermoelectric applications have been grown successfully using electrochemical methods.[6] Electrochemical growth of Bi nanowires from an aqueous solution through the nanochannels is an alternative that may have advantages over these methods. A number of issues needs to be resolved to better quantify this technique in order to evaluate the utility of electrochemical growth. In this paper we examine the electrochemical growth process with the goal of ascertaining the quality of the nanowires during the growth process and to improve the quality control for the process. In anticipation of the need to eventually dope these Bi wires with tellurium for n-type operation, we also have investigated the conditions needed for tellurium incorporation into the electrochemically grown wires at the same time. EXPERIMENT The process by which nanochannels are created in a mica substrate has been described previously.[7] In brief, sheets of 10 µm thick muskovite mica are irradiated with high-energy (15 MeV) C4+ ions to fluences of between 1011 and 1013 ions/cm2. At this ion-beam energy, the carbon ions traverse the thickness of t
Data Loading...
