Preparation of Intercalative Organic/MoO 3 Nanohybrid Thin Films and Their VOC Gas Sensing Properties
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Preparation of Intercalative Organic/MoO3 Nanohybrid Thin Films and Their VOC Gas Sensing Properties Ichiro Matsubara, Norimitsu Murayama, Woosuck Shin, and Noriya Izu National Institute of Advanced Industrial Science and Technology, Shimo-Shidami, Moriyama-ku, Nagoya 463-8560, Japan ABSTRACT Organic/MoO3 nanohybrid thin films have been successfully prepared by an ex-situ intercalation process. The host MoO3 films were first deposited on LaAlO3 (LAO) single crystal substrates by using a CVD method followed by the intercalation of butylammonium ions, (BuNH3)+, into the MoO3 films to give (BuNH3)xMoO3 thin films. The preparation of highly b-axis oriented MoO3 films is crucial to prepare the (BuNH3)xMoO3 films. The (BuNH3)xMoO3 thin films exhibit a resistance-increasing response to aldehyde gases as in the case of bulk samples, whereas no response was observed for methanol, ethanol, chloroform, acetone, toluene, and xylene. The thin film process developed for intercalative organic-inorganic hybrid makes it possible to apply this material in VOC sensor devices.
INTRODUCTION In recent years, the intercalated organic-inorganic materials have attracted much attention because of their unique microstructure and potentially useful properties involving chemical sensors, field-effect transistors, light emitters, and batteries [1-5]. The orthorhombic MoO3 with a semiconducting characteristic is a host inorganic compound to form intercalated organic-inorganic materials. The structure of MoO3 consists of vertex-sharing chains of distorted MoO6 octahedra, which share edges with two similar chains to form layers. The two dimensionally bonded double-octahedra oxide sheets are stacked in a layered arrangement and are held together by weak van der Waals forces (Figure 1). Many organic components can be intercalated into the interlayers [6-11]. We have synthesized Butylammonium ion, (BuNH3)+, intercalated molybdenum oxide (MoO3) hybrid materials, (BuNH3)xMoO3 (Figure 1), using a concomitant ion exchange reaction in a powder form [12]. The pressed pellets of the (BuNH3)xMoO3 powder show a distinct response to volatile organic compounds (VOCs) by increasing their electrical resistivity, which could be induced by the incorporation of VOC molecules into the interlayers of (BuNH3)xMoO3 [12]. The (BuNH3)xMoO3 pellets exhibit higher sensitivities to polar analytes such as formaldehyde and acetaldehyde, whereas they show almost no response to toluene and benzene [12]. The (BuNH3)xMoO3 hybrids are, therefore, potential sensing materials for the selective detection of VOCs. From the viewpoint of sensor applications of (BuNH3)xMoO3, it is necessary to fabricate thin film devices [13]. The most widely used thin film technique is the delamination/reassembling process, in which the organic and inorganic components are piled up from a colloidal state onto a substrate [14-16]. The thin films prepared by this method, however, have the problems of adhesion with the substrate and the films are easily peeled off. Solution-based or evaporative t
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