Growth and Characterization of Organic Polymeric Thin Films From Isopropanol by PECVD.
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Growth and Characterization of Organic Polymeric Thin Films From Isopropanol by PECVD. J. O. Martínez-Gutiérrez, G. Romero-Paredes, R. Peña-Sierra, A. Ávila-García, G. Juárez-Díaz. CINVESTAV-IPN. Departamento de Ingeniera Eléctrica Sección de Electrónica del Estado Sólido. Av. IPN #2508, San Pedro Zacatenco, 07360 México D.F. Email: [email protected]. ABSTRACT Polymerized organic thin films were synthesized on a variety of substrates by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique using isopropanol as precursor. Hydrogen peroxide, ammonium hydroxide, and iodine dissolved in isopropanol were used as dopants and chlorobenzene as copolymerization precursor. The structural, optical and electrical properties of the films were studied as functions of the dopant type and concentration. The polymeric films were characterized by variable angle ellipsometry (VAE), atomic force microscopy (AFM), Fourier Transform Infrared spectroscopy (FTIR), ultraviolet-visible transmission spectroscopy and photoluminescence. The electrical film behavior was explored by the four points probe method. The growth rate, refractive index, optical bandgap, chemical structure and resistivity of the films strongly depend on the concentration and type of dopant added. The AFM microphotographs showed smooth surfaces with RMS roughness less than 10 nm. The optical bandgap values of the films were in the range of 2.6 to 3.26 eV, the resistivity was in the order of 103 – 104 ohm-cm. The photoluminescence response of the polymerized films was obtained in the visible region, by exciting with a UV laser. INTRODUCTION Plasma polymerization (formation of polymeric material under the influence of plasma [1]) has gained importance along the last decades as a tool for fabrication of polymer thin films. Plasma polymerization has been utilized for the preparation of polymer thin films for optoelectronic devices [2], coatings for corrosion protection [3, 4], surface treatment [5], low dielectric constant materials [6, 7], etc. Plasma enhanced chemical vapor deposition (PECVD) has become one of the most attractive polymer thin film deposition processes. PECVD uses a glow discharge to create activated species, such as radicals and ions, from the original monomer, and the polymer films are deposited through a gas phase and surface interaction of these active species [8]. Polymer films exhibit properties such as chemical inertness, transparency in the visible and infra-red regions, variable refractive index, low friction coefficient [9], highly crosslinked structures [10] and show chemically and physically stable characteristics [11]. These properties depend on several parameters for a given precursor, the type of the reactor and its geometrical configuration, frequency of the discharge voltage, power delivered to the discharge, flow of the monomer, working gas pressure, substrate temperature and substrate size and its position [12]. In this work isopropanol and doped isopropanol as the liquid precursors were used for plasma polymerization. Hydrogen
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