Glycine as a complexing agent in CdS thin films: Theoretical insights Aned de Leon * , M.C. Acosta-Enríquez, S.J. Castillo, D. Berman-Mendoza, Abraham F. Jalbout Departamento de Investigación en Física, Universidad de Sonora, Blvd. Luis Encinas y Rosales S/N, Col. Centro, Hermosillo, Sonora, Mexico article info Article history: Received 23 January 2010 Received in revised form 5 April 2010 Accepted 7 April 2010 Available online 11 April 2010 Keywords: Glycine Semiconductors CdS Thin films MP2 abstract Glycine has been reported to be a complexing agent for transition metals such as Fe, Ni and Cr. In this work we propose that it could also yield good results for Cd in the application of depositing CdS thin films. To understand the behavior of the systems we performed a theoretical analysis at the MP2/ LANL2DZ level of theory. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Cadmium sulfide (CdS) is an interesting semiconductor material that has been successfully applied as thin films in high perfor- mance solar energy conversion devices such as CdS–CdTe and CdS–Cu(In,Ga)Se 2 solar cells [1]. Several techniques are employed for the deposition of CdS thin films [2], namely, chemical bath deposition (CBD), close spaced sublimation (CSS), molecular beam epitaxy (MBE), metal organic vapor phase epitaxy (MOVPE), metal organic chemical vapor deposition (MOCVD), physical vapor depo- sition (PVD), successive ionic layer adsorption and reaction (SILAR) and screen printing (SP). The efficiency of the CBD technique along with the simplicity of the process and equipment required enables it to be widely used [3]. The optimum semiconductor films are produced by the means of CBD, modulating temperature [4], pH [5] and reagent concentra- tions [6] of the reaction solution. In this technique, thin films are deposited on substrates in contact with dilute baths containing metal ions. Thus, the morphology of the film depends strongly on the precipitation of the solid phase. Therefore, complexing agents are crucial in the structure of the thin film deposited. One of the most common complexing agents is ammonia. Nevertheless, its volatility and toxicity of this hazardous material have contributed to the search of other chemicals. Among them, ethylene-diamine (ED) and ethylene-diamine-tetra-acetic acid (EDTA) demonstrated to be good complexing agents of CdS films obtained by CBD [7]. On our search for a different complexing agent for CdS films we have proposed glycine (Gly). This aminoacid has been used as a complexing agent for the electrochemical deposition of Fe, Ni and Cr thin films on stainless steel and copper substrates [8] which leads us to believe that Gly could also form a complex with the transition element Cd and with the compound CdS. Therefore, the theoretical study presented herein is mainly focused on under- standing the interaction between Gly, Cd and CdS to depict its role in the deposition of the CdS thin films. We have considered the fact that Cd forms better coordination compounds with two instead of four Gly molecules. It is our belief that if we extend the number of Gly atoms bound to the central Cd atom the effects of the change will indeed be minimum with the physical characteristics remaining consistant. The calculations presented in this work were also corroborated by an analysis of using four Gly molecules instead of two. The cal- culations suggest that using two Gly molecules there is a repulsive nature and the energy of association decreases by 3 kcal/mol. Also, it can be observed from the calculations that the two additional Gly molecules tend to dimerize with the Gly molecules already attached to the Cd molecule so as to create repulsive effects. While, the physical meaning is consistant the coordination chemistry around the Cd atom prefers two instead of four Gly molecules. The minimum energy structures with four Gly molecules is Cd((Gly) 2 ) 2 with (Gly–Gly)-Cd-(Gly–Gly) whereby Gly–Gly denotes a van der Waals dimer complex. The subject of these configura- tions are also interesting and will be the subject of a future report. 2. Computational methods Ab initio quantum mechanical calculations were carried out with the GAUSSIAN [9] program codes. Geometry optimizations and frequency computations were obtained with the Møller–Ples- 0166-1280/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2010.04.003 * Corresponding author. E-mail address: d_aned@hotmail.com (A. de Leon). Journal of Molecular Structure: THEOCHEM 951 (2010) 34–36 Contents lists available at ScienceDirect Journal of Molecular Structure: THEOCHEM journal homepage: www.elsevier.com/locate/theochem