Simple Cubic Super Crystals Containing PbTe Nanocubes and Their Core-Shell Building Blocks Jun Zhang, † Amar Kumbhar, ‡ Jibao He, § Narayan Chandra Das, | Kaikun Yang, | Jian-Qing Wang, ⊥ Howard Wang, | Kevin L. Stokes, # and Jiye Fang* ,† Department of Chemistry, State UniVersity of New York at Binghamton, Binghamton, New York 13902, Electron Microscope Facility, Clemson UniVersity, Anderson, South Carolina 29625, Coordinated Instrumentation Facility, Tulane UniVersity, New Orleans, Louisiana 70118, Department of Mechanical Engineering, State UniVersity of New York at Binghamton, Binghamton, New York 13902, Department of Physics, State UniVersity of New York at Binghamton, Binghamton, New York 13902, and Department of Physics, UniVersity of New Orleans, New Orleans, Louisiana 70148 Received August 4, 2008; E-mail: jfang@binghamton.edu Abstract: We report a preparation of high-quality cubic PbTe nanocrystals and their assembly into both square-array, two-dimensional patterns and three-dimensional simple cubic super crystals. The influence of oleylamine in the nanocrystal synthesis and core-shell formation through an anion-exchange mechanism was also studied. The simple cubic super crystals together with two-dimensional assembly patterns containing PbTe nanocubes and their core-shell building blocks were examined using TEM, SEM, AFM, XRD, SAXS, and FTIR. Such super crystals consisting of cubic structural building blocks may allow engineering of more complex materials from which novel properties may emerge. Introduction The super crystal (SC), 1-3 that is, three-dimensional (3D) self-assembly of a nanocrystal (NC) superlattice, has attracted increasing attention. However, the fabrication of an SC has remained a challenge and requires high-quality NC uniform in both size and shape. For identical spheres, both the hexagonal close-packing and the cubic close-packing give the highest packing efficiency, 74.04%. NCs used as building blocks could be present in various nonspherical shapes such as octahedrons 4 and cubes; in fact, an SC containing cubic NCs can achieve a packing density as high as 100% if the interparticle spacing is neglected. Although previous studies on two-dimensional (2D) ordered structures of cubic NCs indicate that formation of a square array is energetically more favorable than other close- packed arrangements such as a quasi-hexagonal array, 5 there have been very few reports that describe the manipulation and analysis of 3D SCs containing the building blocks of cubic NCs. 6,7 In general, a combination of structure-defined NC and long-range order assembly could offer unique electronic and optical properties. Here, we demonstrate our recent observation and analysis of simple cubic SCs containing PbTe nanocubes and their core-shell building blocks, PbTe@Pb(OH) 2 and PbTe@PbO, in size of ∼15 nm. Experimental Section Preparation of Monodisperse Cubic PbTe NCs. The fabrica- tion of cubic PbTe NCs is based on our previous wet-chemical approach 8 with improved processing control. Such NCs can be further assembled into monolayer or multilayers on a copper grid or on a silicon wafer (or other film) with different packing densities by tuning a number of processing factors such as the NC concentration and the rate of solvent evaporation (detailed below). In a typical experiment, 0.5 mmol of lead acetate trihydrate (99.99+%), 1.0 mL of oleic acid (90%), and 10 mL of oleylamine (70%) were loaded into a three-neck round-bottom flask equipped with a condenser and attached to a Schlenk line under an argon stream. The mixture was heated to 200 °C with vigorous stirring. Once a clear light-yellow solution was formed, 0.5 mL of pre- prepared triocylphosphine (90%) telluride 8 (99.999%) (1.0 M for Te) was rapidly injected into the system. The reaction was then ceased 1 min after the injection by promptly replacing the heating source with a cold water bath. 9 The resultant NCs were isolated † Department of Chemistry, State University of New York at Binghamton. ‡ Clemson University. Present address: CHANL Instrumentation Facility, Institute for Advanced Materials, NanoScience and Technology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3216. § Tulane University. | Department of Mechanical Engineering, State University of New York at Binghamton. ⊥ Department of Physics, State University of New York at Binghamton. # University of New Orleans. (1) Shevchenko, E. V.; Talapin, D. V.; Kotov, N. A.; O’Brien, S.; Murray, C. B. Nature 2006, 439, 55–59. (2) Desvaux, C.; Amiens, C.; Fejes, P.; Renaud, P.; Respaud, M.; Lecante, P.; Snoeck, E.; Chaudret, B. Nat. Mater. 2005, 4, 750–753. (3) Redi, F. X.; Cho, K.-S.; Murray, C. B.; O’Brien, S. Nature 2003, 423, 968–971. (4) Lu, W.; Liu, Q.; Sun, Z.; He, J.; Ezeolu, C.; Fang, J. J. Am. Chem. Soc. 2008, 130, 6983–6991. (5) Yamamuro, S.; Sumiyama, K. Chem. Phys. Lett. 2006, 418, 166– 169. (6) Li, F.; Delo, S. A.; Stein, A. Angew. Chem., Int. Ed. 2007, 46, 6666– 6669. (7) Dumestre, F.; Chaudret, B.; Amiens, C.; Renaud, P.; Fejes, P. Science 2004, 303, 821–823. (8) Lu, W.; Fang, J.; Stokes, K. L.; Lin, J. J. Am. Chem. Soc. 2004, 126, 11798–11799. (9) Caution: To deal with this hot solution, proper gloves should be worn and special care should be taken. Published on Web 10/21/2008 10.1021/ja806120w CCC: $40.75  2008 American Chemical Society J. AM. CHEM. SOC. 2008, 130, 15203–15209 9 15203