Electrodeposition of Group III Doped PbTe Nanowires
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1258-Q09-04
Electrodeposition of Group III Doped PbTe Nanowires 1
Peter Hillman1 and Angelica M. Stacy1 Department of Chemistry, University of California, Berkeley, California 94720
ABSTRACT Nanowire arrays of PbTe were electrodeposited into porous alumina templates with 40nm pores. Citric acid was used as a complexing agent for HTeO2+ shifting the reduction potential of HTeO2+/Te closer to that of Pb2+/Pb. Compositional analysis of the wires grown with the complexing agent show a 1:1 ratio of Pb:Te without any excess tellurium. Group III elements (In3+ and Tl+) can be added to the deposition solution and incorporated into the nanowires. It is proposed that indium incorporates into the PbTe lattice in a high energy interstitial site causing the lattice parameter to increase linearly with increasing indium incorporation. The addition of thallium to the deposition solution leads to a mixture of PbTe and TlTe nanowires. Upon annealing, the TlTe melts incongruently to Tl5Te3, which then alloys with PbTe, thereby increasing the lattice parameter. INTRODUCTION Increasing demands for new, clean, and renewable energy sources has led to resurgence in the field of thermoelectric materials. Thermoelectric devices have the ability to interconvert heat and electricity and for this reason have been proposed as a source for clean power generation and refrigeration.1 However, the figure of merit (zT), which is directly related to device efficiency, has remained too low for broad based applications, relegating thermoelectric devices to niche applications, such as the Voyager Missions.2,3 In order to compete effectively with commercial refrigeration and power generation units, a zT of 3-4 will be needed.4 Unfortunately, reaching these values for zT has proved especially difficult because the parameters that can be changed to optimize performance are not independent. One method to circumvent this constraint is to take advantage of the properties of nanomaterials. It is predicted that lower dimensional materials will have higher efficiencies than their bulk counterparts due to quantum confinement effects.5,6,7 This prediction has already been experimentally verified for thin multilayers of PbTe/Pb1-xEuxTe.8,9,10,11,12,13 In addition to quantum confinement effects, nanoscale materials have a reduced thermal conductivity due to increased phonon scattering. Using nanoscale morphology, researchers have already produced materials with some of the highest figures of merit to date.14 The electrodepostion of compounds into porous alumina templates with nanometer-sized pores is an attractive way to achieve the desired effects of quantum confinement and increased phonon scattering. Electrodeposition is both an inexpensive and easily scalable method that has already been used to produce a wide variety of interesting thermoelectric materials.15,16,17,18,19,20,21 Through fine-tuning of variables such as concentration and potential, a great deal of control is possible allowing for optimization of the deposited material. Lead telluride with its la
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