Figure 1 – Modeling the decomposition of trimethylindium on a gallium nitride substrate.

1. Modeling Indium Nitride Film Growth under High Pressure Beatriz H. Cardelino, Spelman College, DMR 0705219 Figure 1 – Modeling the decomposition of trimethylindium on a gallium nitride substrate. Films of gallium nitride (GaN), indium nitride (InN), and indium gallium nitride (InxGa1-xN) semiconductors are efficiently grown using a process called chemical vapor deposition. Film growth is achieved, under high nitrogen pressure (10 to 20 bar), to prevent film decomposition under the conditions required for decomposition of the source materials. In this investigation, computational models of GaN and InN substrates have been designed, in order to study deposition and decomposition reactions of the source materials (i.e., trimethyl-gallium, trimethylindium, and ammonia), under high pressure and high temperature. Color code: hydrogen is white; carbon is gray; indium is brown; nitrogen is blue; and gallium is lilac. Adsorbate-substrate distance shown with a red line. Figure 2 – Adsorbate-substrate distances between source species and gallium nitride (GaN) or indium nitride (InN) substrates. All species studied adsorb to the substrates by exergonic processes. The horizontal lines show the metal-nitrogen average distance in wurtzite crystals.

2. Modeling Indium Nitride Film Growth under High Pressure Project Outcome Beatriz H. Cardelino, Spelman College, DMR 0705219 Four model-substrates of gallium nitride (GaN) and indium nitride (InN) were designed, in order to represent the nitrogen surface and the metal surface of the substrates, where adsorption takes place. The model-substrates were validated by comparing the metal-nitrogen distances and heat capacity with experimental values. Quantum mechanical calculations were performed for adsorbed trimethylgallium and trimethylindium derivatives onto the nitrogen surface of the substrates, and ammonia (NH3) derivatives onto the metal surface of the substrates. The organometallic compounds included the metals (Ga and In) with three, two, one, or no methyl groups; the ammonia derivatives included products from bimolecular reactions occuring in the gas phase (NH3, NH2, NH, N, N2H4, N2H3, NNH2, NHNH, NNH and N2). Reaction rate constants were estimated for the adsorption reactions of the source materials onto the substrates and for the subsequent adsorbate dissociation reactions. These parameters were obtained for temperatures between 300 and 1400 K, and pressures between 1 and 100 bar. The quantum mechanical calculations were performed using a hybrid approach called ONIOM, that allowed representation of the molecules using two different levels of approximation. The substrate were simulated using semiempirical quantum mechanical methods, whereas the adsorbates were modeled using density functional theory. The reaction rate constants were estimated in a unique way, using the Debye’s approximation for solids, vibrational frequencies obtained from normal vibrational analyses, statistical thermodynamics and transition-state theory. This study was an extension of the following work: “Adsorption and Dissociation of Trimethylindium on an Indium Nitride Substrate. A Computational Study.”; by Beatriz H. Cardelino and Carlos A. Cardelino; J. Phys. Chem. C 2009, 113, 21765–21778. Potentially Transformative Research In this investigation, a unique semiclassical method was developed for calculating reaction rate constants for adsorption reactions and for dissociation reactions of adsorbed species. The approach incorporated the Debye’s approximation for solids into statistical thermodynamic and transition state equations.

3. Modeling Indium Nitride Film Growth under High Pressure Intellectual Merit of the Project Outcome Beatriz H. Cardelino, Spelman College, DMR 0705219 In this investigation, model indium nitride substrates have been designed and validated by comparing their estimated heat capacities with experimental values. A realistic method of calculation was employed to represent realistically the interaction between the substrate and the adsorbates. The model substrates were used to predict thermodynamic and chemical kinetic properties for the adsorption and dissociation processes of the source materials . A unique method for calculating thermodynamic and reaction rate constants of adsorbed species was developed, which incorporates the Debye’s approximation for solids. Broader Impacts of the Project Outcome Several students from Spelman College, a historically-black-college for women, performed research in computational chemistry, and presented their results during the National Conference for Undergraduate Research (NCUR). The outcomes of this investigation were presented and discussed with graduate students from the Physics Department of Georgia State University. Elements from this investigation were introduced into: (a) the Earth System Modeling class at the Georgia Institute of Technology, as a homework assignment; (b) the Physical Chemistry Laboratory at Spelman College, as a computational project to study the pyrolysis of methane; (c) the Physical Chemistry II course at Spelman College, as examples of applications of the Lindeman’s mechanism. • Publications Relevant to the Project Outcome • A. Jackson; “Equilibrium Concentrations of Ammonia Dissociation Products under High Temperatures and Pressures; a Theoretical Study”; Proceedings of 2010 NCUR. • J. Subramanian; “Hydrogen and Methyl Dissociation of Trimethylindium Derivatives and Trimethylindium Dimer”; Proceedings of 2010 NCUR; “Structure and binding energies of group III organometallic dimers”; Proceedings of 2009 NCUR. • B. H. Cardelino, C. A. Cardelino: “Adsorption and dissociation of trimethylindium on an indium nitride substrate”; J. Phys. Chem. C 2009, 113, 21765-21778. • A. Jordan; “A theoretical study of the chemical kinetics for the dissociation of indium nitride source materials”; Proceedings of 2009 NCUR. • K. Stubbs, A. Jackson; “Prediction of the equilibrium distribution of species in indium nitride chemical vapor deposition; Proceedings of 2009 NCUR. Website www.spelman.edu/~bcardeli/