Photoemission Study of Thiol-Capped Gold Nanoparticles
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Photoemission Study of Thiol-Capped Gold Nanoparticles Tazumi Nagasawa, Akinori Tanaka, Hiroyuki Sasaki, Yosuke Kuriyama, Shoji Suzuki, Shigeru Sato, and Tsutomu Sekine1 Department of Physics, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan 1 Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan ABSTRACT A photoemission study of dodecanethiol (DT)-capped Au nanoparticles on the highly oriented pyrolytic graphite (HOPG) substrates has been carried out in order to investigate in detail the electronic structures of metallic nanoparticles supported on the substrates. The present DT-capped Au nanoparticles show that the leading edge in the photoemission spectra near the Fermi level is not the Fermi edge, with the midpoint of the steep slope being away from the Fermi level. From these results, we discuss the electronic structures of DT-capped Au nanoparticles, especially nanoparticle-HOPG substrate interaction.
INTRODUCTION Metallic nanoparticles are recently attracting much interest, since metallic nanoparticles exhibit the quantum size effect and novel physical properties. Recently, surface-passivated metallic nanoparticles have been chemically synthesized by precipitation in the solution including surfactant [1, 2]. These nanoparticles are suitable for studies of quantum size effects and other physical properties, because their size and shape are homogeneous and they are very stable at room temperature. Furthermore, it has been reported that the metallic nanoparticle show the Coulomb blockade at room temperature [3] and high catalytic activity [4]. Therefore, these surface-passivated nanoparticles have potentialities as a candidate for the nanostructured devices, such as single electron device, catalyst device, and ultra highly density memory media. In order to elucidate the intriguing physical properties of metallic nanoparticles and develop the future devices, it is indispensable to understand the detailed electronic structure and electronic interactions with substrate. Photoemission spectroscopy has been used to study the electronic structure, but to our knowledge few studies have reported the detailed electronic structures of surface-passivated metallic nanoparticles by means of photoemission spectroscopy. In this work, we have carried out a photoemission study of DT-capped Au nanoparticles with various sizes deposited on the HOPG substrates. From these results, we discuss the electronic structures of DT-capped Au nanoparticles, especially the interaction with the HOPG substrates.
EXPERIMENT DT-capped Au nanoparticles were prepared in the procedure developed by Brust et al. [1] An aqueous solution of hydrogen tetrachloroaurate (15 mL of a 30 mM) was mixed with a solution of tetraoctylammonium bromide in toluene (10.2 mL of a 200 mM) and vigorously stirred for an W9.40.1
hour. After transfer of the tetrachloroaurate to the organic phase, the organic phase was separated. DT (325 µL) was mixed with the organic phase and then stirred v
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