Density Functional Study of Benzoic Acid Derivatives Modified SnO 2 (110) Surface
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Density Functional Study of Benzoic Acid Derivatives Modified SnO2 (110) Surface Tegshjargal Khishigjargal and Kazuyoshi Ueda* Department of Chemistry, Graduate School of Engineering, Yokohama National University 79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501, Japan ABSTRACT Tin oxide is one of the popular metal oxide semiconductor used in solar cells, sensors, and catalysts. The surface modification by organic self assembled monolayer is one of the promising techniques to tune and to control the surface work function. In our study, we investigated the work function change of the SnO2 (110) surface which was modified with various benzoic acids derivatives using density functional theory (DFT). All calculations were carried out on Quantum Espresso program. Electron correlation and exchange parts were treated by local density (LDA), generalized gradient approximation (GGA) with Hubbard U term. To improve band structure calculation we used LDA+U method. The results of the calculation with LDA method indicated that the work functions of the pure and modified surface of SnO2 (110) with -C6H4-COOH molecule were calculated to be 7.40 eV and 6.18 eV, respectively. As the experimental value of work function of SnO2 (110) surface is about 7.74 eV, the results of the DFT calculation for pure SnO2 (110) surface modification by benzoic acid derivatives are in good agreement with the experimental. INTRODUCTION Density functional theory (DFT) studies on metal oxide surfaces have recently been used to investigate the surface electronic structures and the reaction processes [1-9]. One of the widely investigated metal oxides is tin oxide (SnOx). That is used for various fields, such as, gas sensors, solar cells, and catalysts and so on [10]. The surface of (110) rutile tin dioxide (SnO2) is the most stable [11] and was studied by various models and DFT methods [1-6,8-10,12-15]. In the application of electronic devices, tin dioxide can be modified by the treatment of the self assembled monolayer (SAM) [16,17] and the work function of the surface can be tuned by this modification. Many experiments were carried out [18-21] to understand the nature of the WF change. However, the detail mechanism of the effect of the modification of the surface by the organic molecules has not been fully understood yet. Recently, the progress of the quantum chemical calculation enables us to understand the phenomena from the electronic structure point of view. In our previous work [22], work function change was investigated by quantum mechanical calculation using a cluster model of SnO2. However, the estimated work function changes were higher than that of experimental measurements on benzoic acid SAM on indiumtin oxide (ITO) [17]. In this work, we investigated the WF change using the periodic DFT calculation with the model of benzoic acids (C6H4-COOH) on tin dioxide (110) surface. DFT calculation was performed with local density approximation (LDA) and generalized gradient exchange-correlation (GGA) functional. CALCULATION METHOD
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