Delivered by Ingenta to: Boston College IP : 136.167.55.151 Fri, 19 May 2006 17:35:30 Copyright © 2006 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 6, 1050–1053, 2006 ShapeEvolutionofLeadTellurideand Selenide Nanostructures Under Different Hydrothermal Synthesis Conditions B. Poudel, ∗ W. Z. Wang, D. Z. Wang, J. Y. Huang, and Z. F. Ren ∗ Department of Physics, Boston College, Chestnut Hill, MA 02467, USA Face-open nanoboxes of lead telluride and selenide have been synthesized by a simple hydrother- mal method. Nano- and microcrystals of various morphologies, including microflowers, semi- microflowers, cubic nanoparticles, etc., have also been observed at different synthesis conditions. Temperature, time, and concentrations of various reactants play a major role in controlling the mor- phology and shape evolution of the product. This simple synthesis technique for the growth of various nano- and microstructures opens a new route to prepare hierarchical structures of a variety of binary semiconducting materials in a large quantity. A possible growth mechanism of such nano- and microstructures has been proposed. Keywords: Lead Telluride and Lead Selenide, Nanoboxes, Hydrothermal Method. 1. INTRODUCTION Binary IV–VI semiconducting compounds form a very interesting class of materials because of their potential applications in thermoelectric, electronic, and opto- electronic devices due to their unique thermal and electri- cal properties. 1 2 Among the IV–VI class of materials, lead telluride (PbTe) and selenide (PbSe) have attracted great attention for their applications in thermoelectric power generations. Both of these materials have small band gap and large exciton Bohr radius, which allows size- quantization effect to be observed easily even for relatively large crystal size. After the earlier reports on hierarchi- cal nanostructures of ZnO 3 and MgO, 4 many reports have been published on hierarchical structures of various mate- rials such as SiGe, BiSe, and metal oxides, with mor- phologies including nanobelts, multipods, nanotrees, and microflowers 5–18 during the last a couple of years. Also, there are some reports on flower-like structures obtained with lead sulphide (PbS). 19–25 Here, we report a few inter- esting nano- and micro-structures of PbTe and PbSe that were synthesized by a simple hydrothermal method, which may find their application in thermoelectric and other inno- vative technologies. This technique could be applied to prepare various similar nanostructures of other semicon- ducting materials. ∗ Authors to whom correspondence should be addressed. 2. EXPERIMENTALDETAILS Both PbTe and PbSe with various morphologies were pre- pared by a simple hydrothermal method. Starting materials including Polyethylene Glycol (PEG, molecular weight: 20,000), Sodium Hydroxide (NaOH), Sodium Tellurite (NaTeO 3 ), Sodium Selenite (NaSeO 3 ), Lead Acetate Tri- hydrate (PbAc), and Hydrazine Hydrate were purchased from Aldrich and/or Alfa-Aesar. In a typical synthesis of PbTe face-open nanoboxes, 50 mg of PEG and 2.4 g of NaOH were added to 50 mL of de-ionized water. After a few minutes of stirring, 1 mMol each of NaTeO 3 and PbAc were added to the solution and stirred until the reactants were dissolved completely. 10 mL of Hydrazine Hydrate was finally added to the solution and transferred into a Teflon-lined autoclave. The sealed vessel was kept in a furnace at a temperature of 100  C for 10 hours and then cooled down to room temperature. The product was washed several times with water. The morphology of the samples was examined using a Scanning Electron Micro- scope (SEM, JEOL-6340F) and a Transmission Electron Microscope (TEM, JEOL-2010F), while the atomic com- position was determined using an Energy Dispersive X-ray Analysis (EDX) spectrometer attached to the TEM. The phase of an individual nano- or micro-crystals was studied using Selected Area Electron Diffraction (SAED) while the phase of the bulk powder was analyzed by X-ray diffraction (XRD, Bruker-AXS, G8 GAADS) using Cu- K radiation. 1050 J. Nanosci. Nanotechnol. 2006, Vol. 6, No. 4 1533-4880/2006/6/1050/004 doi:10.1166/jnn.2006.163