Emission Light from Prism/Silver/Molecular Ultrathin Films and Excitations of Multiple Surface Plasmons in ATR Kretschma
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Emission Light from Prism/Silver/Molecular Ultrathin Films and Excitations of Multiple Surface Plasmons in ATR Kretschmann Configuration Futao Kaneko1, Takayuki Nakano2, Toshiharu Sato2, Kazunari Shinbo1, Keizo Kato2, Takahiro Kawakami1 and Takashi Wakamatsu3 1 Dept. of Electrical and Electronics, Niigata University, Niigata 950-2181 Japan 2 Graduate School of Sci. and Tech., Niigata University, Niigata 950-2181 Japan 3 Dept. of Electrical Eng., Ibaraki National College of Tech., Hitachinaka Japan
ABSTRACT Emission light through the prism has been investigated from the Kretschmann configuration of the prism/ Ag thin film/ rhodamine-B (RB) LB film in the resonant excitation of the attenuated total reflection (ATR) measurement. The emission light and the spectra strongly depended upon the emission angles where the light was observed. The emission properties corresponded to the dispersion relation of the resonant excitations of surface plasmons (SPs) in the ATR configuration. It was concluded that the emission light was caused by multiple excitations of SPs in the ATR configuration. It is thought that the phenomenon will be used as a new sensing device.
INTRODUCTION The surface plasmon resonance (SPR) method, that is, the attenuated total reflection (ATR) method has attracted much attention for measurements and sensing, since surface plasmons (SPs) resonantly excited at ultrathin metal surfaces are strongly influenced by conditions of the surfaces [1]. The ATR measurements utilizing the SP excitations have been used to evaluate structure and optical properties of organic ultrathin films on metal ultrathin films, to estimate orientations of liquid crystal molecules and as a sensing method [1-4]. The ATR method has been also investigated for device applications, because of strong optical absorption and strong electric fields, that is, evanescent fields when SPs are resonantly excited [5]. Recently, emission light at a resonant angle region of SP excitations was observed through the prism in the Kretschmann configuration of the ATR measurements, when metal ultrathin films on the prism or organic ultrathin films on metal ultrathin films were directly irradiated from air by a laser beam, that is, by means of the reverse irradiation [6-9]. In this paper, emission light properties from the prism have been investigated for the ATR Kretschmann configuration of prism/ Ag thin film/ rhodamineB (RB) Langmuir-Blodgett (LB) film in the conventional ATR method.
EXPERIMENTAL DETAILS A well-known laser dye, that is, RB was used as an organic dye molecule for the LB dipping method. RB molecules, purchased from NIPPON KANKOH-SHIKISO KENKYUSHO CO. LTD., were mixed with arachidic acid (C20) to obtain better LB
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structure. The molecular structures are shown in Fig.1. The molar ratio of the mixture was [RB]: [C20] =1:5. The RB LB films with ten monolayers were deposited on cover glasses with evaporated Ag films of about 50 nm thick. The procedure of the LB deposition has been reported [8, 9]. Figure 2 shows the Kret
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