DLC-coated Substrate for Infrared Absorption Spectroscopy in Supercritical Water
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DLC-coated Substrate for Infrared Absorption Spectroscopy in Supercritical Water Takuji Ube and Takashi Ishiguro Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan ABSTRACT The stability of several kinds of substrates, such as Corning #1737 glass, fused silica, synthetic silica, water free synthetic silica, zinc selenide, silicon, and diamond like carbon (DLC) coated Si in supercritical water (663K and 25MPa ) were examined. Their reaction with the water was evaluated by using Fourier transform infrared (FT-IR) spectroscopy. As a result of the present experiment, it was found that DLC-coated Si is one of the most stable and useful substrates for IR spectroscopy in supercritical water. INTRODUCTION Water is one of the most accessible, safe and inexpensive materials. In particular, the use of water at high temperature and pressure (HTP), including the supercritical state, has been expected to be an environmentally friendly technology as it emits no pollutants in the fields of food, medicines, semiconductor manufacturing, etc. In addition, extreme environments, such as those surrounding abyssopelagic hydrothermal vents have attracted much attention from the areas of geological science and biological evolution. In our previous study, it was confirmed that, by boiling glass in ultrapure water, the metallic aluminum thin film on the glass substrate was transformed into transparent boehmite (aluminum hydroxide) film, which showed larger optical transmittance than that of the glass substrate itself [1]. Thicker film reforming of the functional material could be accelerated by using the water at HTP. With increasing temperature and pressure, the reactivity of water increases. Depending on the conditions, a severe reaction can take place in the water and the substrate itself can be degraded. In addition, the detection of water molecules and/or hydroxyl is important in hydrothermal reactions. One of the useful methods to detect them is infrared absorption spectroscopy. Therefore, in order to investigate the hydrothermal reforming of functional films at the HTP condition, it is necessary that the substrate be a transparent material in the infrared range and be stable in water at HTP. In this study we first examined the stability of several kinds of substrate materials in supercritical water. As the substrate candidates, Corning #1737 glass, fused silica, synthetic silica, water free synthetic silica, zinc selenide (ZnSe), and silicon (Si) were examined. In addition to them, Si coated with DLC deposited by the plasma CVD method was finally examined. EXPERIMENT As the typical optical glass substrate, commercially available glass plates were chosen: 0.70mm-thick Corning #1737 glass, 1.51mm-thick fused silica, 1.0mm-thick synthetic silica, and 4.16mm-thick water free synthetic silica. As the transparent substrate in the infrared region,
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commercially available 5.0mm-thick ZnSe, and 525ȝm-thick Si crystal plates were chosen. A DLC-coated 200ȝm-thick double-sid
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