Spectroscopic Investigations of Dendrimer-Au Hybrid Nanoclusters
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Spectroscopic Investigations of Dendrimer-Au Hybrid Nanoclusters Akinori Tanaka1,2, Yoshiaki Murase1, Takanobu Kitagawa1, Masaki Imamura2, and Hidehiro Yasuda1,2 1 Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 6578501, Japan 2 Department of Mechanical and Systems Engineering, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501, Japan ABSTRACT We have synthesized the dendrimer-Au hybrid nanoclusters by solution routes, and have carried out the various spectroscopic studies in order to investigate their electronic structures. From the line-shape analyses for Au 4f core-level photoemission spectra measured with hard Xray synchrotron-radiation of Au nanoclusters with mean diameter of 2-3 nm stabilized outside the dendrimer, it is found that Au 4f core-level photoemission spectrum consists of two components. We attribute these components to interior Au atoms and surface Au atoms bonded to dendrimers. In the valence-band photoemission spectrum of these Au nanoclusters, we have observed the bandwidth narrowing of Au 5d-derived band compared to that of bulk Au crystallite. Moreover, we have observed the characteristic spectral feature in the vicinity of Fermi level due to the dynamic final-state effect in photoemission. We have also carried out the optical spectroscopic measurements of these Au nanoclusters. From these results, we discuss the electronic structures and interfacial properties of the dendrimer-Au hybrid nanoclusters.
INTRODUCTION Metallic nanoclusters are attracting much interest from the viewpoints of both device and fundamental physics, because they show the distinctive physical and chemical properties found in neither bulk nor molecular/atomic systems, such as high catalytic activity [1] and Coulomb blockades [2]. Recently, dendrimers have been attracted interest as a new template for preparing metallic nanoclusters with a size in the range of angstrom to a few nanometers [3, 4]. The nanoclusters formed inside dendrimers are highly monodisperse, stable even at room temperature, and free from aggregation. Therefore, these dendrimer-encapsulated nanoclusters are suitable to study their fundamental size-dependent properties and functions. In order to elucidate their intriguing properties and to develop future devices, it is indispensable to characterize the electronic structures of these dendrimer-Au hybid nanoclusters. In this work, we have synthesized the dendrimer-Au hybrid nanoclusters by solution routes, and have carried out the various spectroscopic studies. We found out the formation of relatively smaller Au nanoclusters encapsulated inside dendrimers and relatively larger ones stabilized outside dendrimers by the present synthesis method. Especially, we report here the results of hard X-ray photoemission studies using synchrotron radiation of relatively larger dendrimer-Au hybrid nanoclusters. From these results, we discuss the electronic properties of dendrimer-Au hybrid nanoclusters.
EXPERIMENT Dendrimer-Au hybrid nanoclusters used in this wor
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