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    Characterization of Palladium Nanoparticles by Using X-ray Reflectivity, EXAFS, and Electron Microscopy

    Year: 2006

    Journal: Langmuir 2006, 22, 807-816, 20111221

    Authors: Yuan Sun, Anatoly I. Frenkel, Rebecca Isseroff, Cheryl Shonbrun, Michelle Forman, Kwanwoo Shin, Tadanori Koga, Henry White, Lihua Zhang, Yimei Zhu, Miriam H. Rafailovich, and Jonathan C. Sokolov

    Organizations: Department of Materials Science and Engineering, State UniVersity of New York at Stony Brook, Stony, Brook, New York 11794-2275, Department of Physics, YeshiVa UniVersity, New York, New York 10016, Stella K. Abraham High School, Hewlett, New York 11557, Department of Materials Science and Engineering, K-JIST, Oryong-dong, Buk-gu, Kwang-ju, 500-712, Korea, and Brookhaven National Laboratory, Upton, New York 11973

    Wecompared the characteristics of dodecanethiolate palladium nanoparticles synthesized by two different techniques, a one-phase method and a two-phase method. From transmission electron microscopy (TEM), we determined that the particle sizes were 46 ( 10 Å and 20 ( 5 Å for the one- and two-phase particles, respectively. Electron diffraction confirmed that their structure was face-centered cubic (fcc). The lattice constant a0 was 3.98 ( 0.01 Å and 3.90 (0.01 Å for the one- and two-phase particles, respectively. High-resolution TEM (HRTEM) showed that the one-phase particles had an ordered core surrounded by a disordered shell structure, while the two-phase particles appeared to be crystalline throughout. The particles were also analyzed with extended X-ray absorption fine structure (EXAFS). A cuboctahedral fcc model was used to fit the data, which implied particle sizes of less than 10 Å for both the oneand two-phase particles. The discrepancy between the two techniques was attributed to the presence of a disordered phase, which we presumed was composed of Pd-S compounds. Compared with the bulk palladium, lattice expansion was observed in both one- and two-phase particles by electron diffraction, HRTEM, and EXAFS. At the air/water interface, a uniform film that produced surface pressure/area isotherms could only be obtained from the two-phase particles. The one-phase particles did not wet the water surface. X-ray reflectivity data indicated that the Langmuir monolayer of the two-phase particles was only 13 Å thick. TEM revealed the diameter of the particles in this layer to be 23 Å; hence the particles assumed an oblate structure after spreading. EXAFS examination of a stack of 750 Langmuir monolayers indicated far fewer Pd-S compounds, which may have dissolved in the water. The data were consistent with a model of a monolayer of truncated cuboctahedron Pd particles that were 7 Å thick and 19 Å in diameter.