Synthesis and Characterization of Quantum Dots: A Case Study Using PbS

Abstract

A research project for senior undergraduates of chemistry has been developed to introduce syntheses of a series of monodispersed semiconductor PbS quantum dots (QDs) and their characterization methodologies. In this paper, we report the preparation of monodispersed semiconductor PbS QDs with sizes smaller than the exciton Bohr radius using a simple, one-step process, and the characterization of the QDs using a range of instruments, including Fourier-transform infrared spectroscopy, transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and energy-dispersive X-ray spectroscopy. Our synthesis approach involves dissolving powdered sulfur (as the S precursor) in 1-tetradecene and adding PbCl 2 as the Pb precursor to the suspension as well as oleylamine as a capping ligand. The PbS QD project represents, we believe, an almost ideal opportunity to provide exposure of undergraduate students to nanotechnology research via syntheses and characterization of semiconductor nanoparticles.A dvances in nanotechnology in the past 20 years have resulted in enormous interest in introducing nanomaterials and associated technologies into the undergraduate curriculum, especially in chemistry. 1−6 As examples, Pavel et al. 2 have reported experiments involving a scattering species, rhodamine 6G (R6G), adsorbed onto silver nanoparticles (AgNPs), with the purpose of quantitatively measuring the surface-enhanced Raman scattering (SERS) phenomenon for the system; this study also incorporated absorbance and emission measurements. Reid et al. 3 developed a laboratory experiment involving semiconductor ZnO quantum dots (QDs) focusing on band gap 3 and absorbance characterization. Also, Lisensky et al. 6 discussed a laboratory experiment involving absorbance and emission characterization of semiconductor CdSe QDs. However, most of the reported studies involve theoretical issues that are somewhat sophisticated for undergraduate chemical education purposes. In this article, we present our recently developed research project of semiconductor QD synthesis and characterization to help to promote and improve college-level education focusing on undergraduate research. We also demonstrate that an undergraduate research project can be conveniently utilized as a laboratory experiment for curriculum development purposes.The main reason we selected lead sulfide QDs to introduce nanoscience research to our undergraduates is that lead sulfide QDs can be conveniently synthesized under mild temperature in a simple, one-step noninjection process. Our approach significantly reduce burn risks to undergraduates that may occur when high-temperature syntheses are undertaken. In addition, undergraduates can gain some basic knowledge related to semiconductor QDs and their applications.Semiconductor lead chalcogenide (PbS, PbSe, PbTe) QD materials show strong quantum confinement effects due to their relative large exciton Bohr radii and dielectric constants. 7,8 The quantum confinement phenomenon 3 associated with lead chalcogenide QDs can be easily obs...

Electronic Processes within Quantum Dot-Molecule Complexes

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Design Strategy of Quantum Dot Thin‐Film Solar Cells

“…reported that the size of PbS QDs can be varied from 2 to 16 nm, resulting in bandgaps of 1.8 to 0.5 eV. [ 29 ] Following the development of methods to enhance the conductivity of QD films through short‐ligand exchange, PbS QDs have begun to be used for solar cell research in earnest. In the case of single active cells, PbS QDs with excitonic absorption peaks at wavelengths as long as 950 nm have been used to fabricate solar cells with the best performance since the first depleted heterojunction solar cell architecture was proposed.…”

Synthesis and Analysis of Zinc Copper Indium Sulfide Quantum Dot Nanoparticles

“…This fundamental nanochemistry concept has been frequently illustrated in this Journal . Laboratory experiments using QDs have made use of CdSe, − CdS, ,− ZnO, , C, , PbS, , Cu 2 O, and CsPbX 3 . QDs are an intriguing material for applications in solar cells, , in video displays, as hydrolysis photocatalysts, in white LED lighting, in photoluminescent labeling for bioimaging, and for cancer treatment .…”