Synthesis and Properties of Lead Selenide Nanocrystal Solids
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Synthesis and Properties of Lead Selenide Nanocrystal Solids Feng Chena , Kevin L. Stokesa , Weilie Zhoua , Jiye Fanga and Christopher B. Murrayb a Advanced Material Research Institute, University of New Orleans, New Orleans, LA 70148, USA b IBM T.J. Watson Research Center, Yorktown Heights, NY 10598, USA ABSTRACT We present results of our investigation of the synthesis, structural properties and electrical transport properties of lead selenide (PbSe) nanoparticle-derived solids. Stable colloidal solutions containing crystalline PbSe particles with sizes on the order of 5–10 nm were synthesized using an organometallic lyothermal growth method in high-temperature organic solvents (100∼200 ◦ C). The nanoparticle powders have been characterized by X-ray scattering (WAXS/SAXS), electron microscopy and optical absorption. Thin films were formed by controlled precipitation of the nanoparticles from solution onto insulating substrates. Electrical resistance (R) and Seebeck coefficient (S) for conductive PbSe films from different annealing conditions were studied and compared. We were able to obtain conductive PbSe films from colloids by low temperature annealing which did not disturb the nanoparticle self-assembly. INTRODUCTION Bulk PbSe is one of the promising materials for the thermoelectric cooling and power generating devices [1]. Nanoparticles can potentially improve the thermoelectric properties over bulk by increasing the Seebeck coefficient due to the altered electronic density of states or making use of a compositionally modulated material that would block phonons while transmitting electrons [2–5]. Nanoparticles prepared by colloidal method were used for fabricating self-assembled films [6]. However, the organic capping species between the nanoparticles need to be removed without destroying the nanoparticle arrangement. We report here the synthesis, structural properties and electrical transport properties of PbSe thin films. EXPERIMENTAL DETAILS The colloidal PbSe nanocrystallites were synthesized using a high temperature co-precipitation approach in organic solution [7, 8]. Typically, lead acetate was dissolved in diphenyl ether along with oleic acid (stabilizing agent). The mixture was heated up to 180 ◦ C under flowing argon with constant stirring, then trioctylphosphine (TOP) with pre-dissolved Se metal (1M) was injected in using a syringe, and the system was maintained at 180 ◦ C for 10 minutes under argon environment. The resulting PbSe colloid was then cooled down to room temperature and subsequently precipitated by adding a polar alcohol solvent and centrifugation. The particles were redispersed in a proper solvent such as hexane, octane or trichloro-triflouroethane. The particle size of PbSe ranged from ∼5 nm to 10 nm. To further narrow the size distribution, a size-selection treatment was performed using the solvent-nonsolvent pair of hexane and ethanol [8]. The resulting
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Figure 1: Left: self-assembled 6 nm PbSe nanoparticles. Right: 0.3 × 0.4 µm area of selfassembled nanoparticles. monodispersed PbSe s
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