Computational Investigation of Electronic and Steric Effects in Surface Reactions of Metalorganic Precursors on Functionalized Silicon Surfaces Yichen Duan, Jia-Ming Lin, and Andrew V. Teplyakov* Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States * S Supporting Information ABSTRACT: Steric and electronic effects play a profound role in determining the mechanisms of surface reactions. In the case of reactions of metalorganic precursors on solid prefunctionalized surfaces, the contribution of these effects has to be considered both for the incoming metalorganic precursor molecule and for the functionalized surface itself. This study uses density functional theory calculations with simple cluster models to investigate the technologically important reactions of tetrakis(dimethylamido)titanium (TDMAT) and trimethylaluminum (TMA) with silicon surfaces functionalized with preadsorbed amines. This approach provides an opportunity to compare the contribution of electronic effects in the process of transamination for TDMAT and in the process of aluminum deposition followed by methane desorption for TMA. Bulky dimethylamido substituents of TDMAT are shown to suppress the electronic effects of the surface-bound amines unless the very open surface-bound structures of -NH 2 and -NHF are compared. At the same time, the relatively open structure of TMA allows for a comparison unobscured by the ligands of a precursor. A comparison within a number of substituted amines bound to the silicon surface is performed and electronic differences are explained by following the properties of the surface hydrogen needed for eliminating a substituent ligand during the deposition step. 1. INTRODUCTION Steric and electronic effects have long been used as the guiding principles for explaining the stability and geometry of molecules 1 or for manipulating the thermodynamics or kinetics of chemical reactions. 2-4 This combination has been studied in detail and reviewed for a wide variety of classical synthetic reactions, 5 catalytic processes, 6,7 biomedical applications, 8,9 and nanoelectronics. 10,11 While major efforts have been dedicated to optimizing the combination of steric and electronic factors for selected reactions, 5,6,8-10 substantial attention has also been directed at dif ferentiating the role of these effects in a number of processes. 7,12,13 More recently, substantial interest of science and engineering communities turned to the role of steric and electronic effects in surface processes , 14,15 since treating a surface as a (macro-)molecular reagent has been successful in a number of applications, including organic modification of semi- conductors 16-18 and heterogeneous catalysis. 19-21 However, in this case treating these two types of factors as independent is complicated by the role of the surface. Surface effects may be involved in both steric and electronic aspects of surface reactions. Not only does the surface restrict the geometry of a process but also it affects the electronics of chemical transformations. In addition, the presence of neighboring surface species, seemingly not directly involved in the reaction, may influence both steric and electronic factors. In other words, differentiation of steric and electronic effects can be challenging in homogeneous processes; 22,23 on surfaces this task can be even more complex. 24,25 A practical approach to evaluate steric and electronic factors is often related to a concept of acidity versus basicity of functional groups on solid surfaces. 26-28 One of the recent studies applied this concept to evaluate reactivity of amino- functionalized surfaces toward adsorption and following surface transamination reactions of metalorganic compounds with amino-based ligands, 29 utilizing the electron-withdrawing or electron-donating nature of the substituents. In the present work, technologically important reactions of tetrakis- (dimethylamido)titanium (TDMAT) and trimethylalane (TMA) with the cornerstone of microelectronics, function- alized silicon surfaces, are used as probes to estimate the initial ability of the lone pair on a nitrogen atom of surface amino functionality to nucleophilically attack the electrophilic site of the incoming metalorganic precursor molecule, and further surface processes following this initial attachment are evaluated. TMA is a common precursor used for deposition of Al 2 O 3 films onto the surface. 26 Al 2 O 3 film can serve as a protective layer that prevents the surface from further oxidation or can be utilized as an electrical insulator on silicon. 30 TDMAT is often used as a precursor to deposit titanium-containing thin films, Received: March 20, 2015 Revised: May 11, 2015 Published: May 22, 2015 Article pubs.acs.org/JPCC © 2015 American Chemical Society 13670 DOI: 10.1021/acs.jpcc.5b02722 J. Phys. Chem. C 2015, 119, 13670-13681