Surface-Passivant Dependence of Dynamic Charging Effect in Alkanethiolate-Passivated Au Nanoparticles on Graphite Substr
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0899-N07-07.1
Surface-Passivant Dependence of Dynamic Charging Effect in Alkanethiolate-Passivated Au Nanoparticles on HOPG Substrates Studied by Photoelectron Spectroscopy Akinori Tanaka, Masaki Imamura, and Hidehiro Yasuda Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501, Japan ABSTRACT We have performed a photoemission study of various alkanethiolate- (AT-) passivated Au nanoparticles with diameter of 4 nm on the highly oriented pyrolytic graphite (HOPG) substrates. It is found that the photoemission spectra in the vicinity of Fermi level of all the present AT-passivated Au nanoparticles on the HOPG substrates do not exhibit the metallic Fermi edge, with the steep slope being away from the Fermi level. Moreover, it is found that these spectral features depend on the surface-passivant molecules. We attribute the unusual spectral features in the vicinity of Fermi level to the dynamic charging effect in photoemission final-state, indicative of the interaction between the nanoparticle and substrate through the surface-passivants on a femtosecond time scale.
INTRODUCTION Metallic nanoparticles ranging from a few nanometers to several tens of nanometers are of interest from the viewpoints of both fundamental and device physics, since they show the distinctive physical and chemical properties found in neither corresponding bulk nor molecular/atomic systems, such as high catalytic activity [1] and Coulomb blockade [2]. Recently, the surface-passivated metallic nanoparticles have been chemically synthesized in the solution including surfactants [3, 4]. These surface-passivated nanoparticles are monodisperse and very stable even at room temperature, and therefore, these are suitable to characterize their fundamental size-dependent properties. Furthermore, these surface-passivated nanoparticles exhibit closed-packed nanoparticle self-assemblies on the single-crystalline substrates [5, 6], and therefore, it is considered that they could be important constituents of future nanostructured devices, such as single electron device, catalyst, and ultrahigh-density memory. In order to elucidate their detailed intriguing properties and to develop the future devices, it is indispensable to understand the interactions with the substrates supporting the nanoparticles as well as their electronic structures. In the present study, we have performed a photoemission study of various alkanethiolate- (AT-) passivated Au nanoparticles supported on the highly oriented pyrolytic graphite (HOPG) substrates. From the discussions regarding the dynamic charging effect in photoemission final-state, we will discuss the nanoparticle-substrate interactions through the surface-passivants of AT-passivated Au nanoparticles on the HOPG substrates.
EXPERIMENTAL DETAILS The AT-passivated Au nanoparticles used in this work were synthesized by a method developed by Lin et al [7]. Firstly, 156 mg of didodecyldimethyl-ammonium (98 %) was added
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to 15 ml of toluene (99 %) and 24 ml of deionized water in
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