World Applied Sciences Journal 16 (8): 1131-1136, 2012 ISSN 1818-4952 © IDOSI Publications, 2012 Corresponding Author: S.A.A. Oloomi, Department of Mechanical Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran. 1131 Appropriate Coating for Optimum of Radiative Properties of Nanoscale Multilayer Structures S.A.A. Oloomi Department of Mechanical Engineering, Yazd Branch, Islamic Azad University, Yazd, Iran Abstract: A great number of the optical components and semiconductors are being covered with thin films, so study of the surfaces which covered by thin films are very important. This work uses transfer-matrix method for calculating the radiative properties. Lightly doped silicon is used and the coherent formulation is applied. The empirical expressions for the optical constants of lightly doped silicon are employed. Silicon dioxide and silicon nitride are used as thin film coatings. It is possible to choose the suitable coating for maximum emittance, minimum transmittance and or minimum reflectance. It depends on industrial usages. This paper considered effects of thin films’ number with various compositions of coating materials (9 cases). High emittance is needed for suitable thermal balance of the thin-film solar cells for space applications. Optical coatings that provide high emittance must be formed on the solar cells to overcome that problem by increasing number of thin film layers. Radiative properties are complex function of wavelength. Increasing number of thin film layers lead to more complexity and dependency on wavelength regard to wavelength interferences. Results showed that increasing number of thin film coating is more effective on radiative properties than increasing thickness. For example in the constant total thickness, it is possible to reach greater emittance by increasing layers’ numbers. From results, the average emittance for bare silicon from 0.0444 reaches to 0.1117 with coatings in case number 8. Key words: Different Coatings Reflectance Emittance Transmittance Optimum properties INTRODUCTION silicon is used and the empirical expressions for the Optical and thermal radiative properties are Silicon dioxide, silicon nitride and gold are used as thin fundamental physical properties that describe the film coatings. This paper considered effects of thin films’ interaction between electromagnetic waves and matter number with various compositions of coating materials to from deep ultraviolet to far-infrared spectral regions [1]. gain optimum radiative properties of nanoscale multilayer Knowledge of the radiative properties of multilayer (9 cases). consisting of silicon and related materials, such as silicon dioxide (SiO ), silicon nitride (Si N ) and gold (Au) with Modeling 2 3 4 different thicknesses is required for many microsystem Incoherent Formulation: When the thickness of silicon applications [2]. In visible wavelengths the reflectance substrate is much greater than the coherent length and increases as the temperature increases, because of the considered wavelength falls in the semitransparent decreasing emittance. As the film thickness increases, the region of silicon, interferences in the substrate are free spectral range decreases, resulting in more generally not observable from the measurements. In this oscillations with thicker silicon dioxide film, but case, the incoherent formulation or geometric optics interferences in the substrate are generally not observable should be used to predict the radiative properties of the in incoherent formulation [3]. This work uses incoherent silicon substrate. Two ways to get around this problem formulation for calculating the radiative properties of are to use the fringe-averaged radiative properties and to semiconductor materials related to the recent treat thin-film coatings as coherent but the substrate as technological advancements that are playing a vital role incoherent [1]. Figure 1 shows the geometry of the silicon in the integrated-circuit manufacturing, optoelectronics wafer with multi thin-film coatings on both sides. Note and radiative energy conversion devices. Lightly doped that is the transmittance of the multilayer structure at optical constants of lightly doped silicon are employed. t