An enduring research theme in our group concerns chemical reactions on surfaces, particularly those involved in CVD processes. Projects concerning partial oxidation in short-contact-time reactors; catalytic combustion; gas sensing using metal-insulator-semiconductor devices; and alkalai corrosion of ceramics have been conducted. Using fundamental understanding of the chemical mechanisms we develop robust models to facilitate process optimization and scale-up. Often, an industry partner (up to four in one case) is involved in the research.
Materials at the focus of our CVD research during the past two decades include hard or refractory materials (silicon carbide and boron nitride); materials used for microelectronics (titanium nitride); and transparent conducting oxides (indium oxide and tin oxide). In most cases incomplete knowledge of the chemical thermodynamics and kinetics of the process is a major barrier. Consequently, we employ ab initio quantum-chemistry techniques to develop the necessary thermochemistry, coupled with experimental measurements in highly controlled reaction environments (e.g. stagnation flow reactors; Fig. 1 ) in which it is possible to disentangle complex chemistry from the fluid flow. Reacting-flow codes such as the Chemkin suite are an essential tool.
An example of this work concerns the growth of tin oxide films on glass. This is a major industrial process used to make low-emissivity flat glass and front-side contacts for solar cells. We developed a database of thermodynamic properties for ~ 60 gas-phase tin species, including previously unsuspected reaction intermediates (e.g. Fig. 2 ). We then employed RRKM methods and kinetic analysis to predict the rates of organometallic precursor decomposition, measured tin oxide growth rates as a function of all key process parameters, and developed experimentally verified model to predict deposition rates. Our work enabled reactant utilization efficiency to double in the facility of our industrial partner.
Capabilities in this area include mechanism development, ab initio prediction of molecular thermochemistry, and modeling of chemically reacting flows.
Selected publications
Chae, Y.; Houf, W. G.; McDaniel, A. H.; Allendorf, M. D."Mechanisms for the Chemical Vapor Deposition of Tin Oxide from Monobutyltintrichloride," J. Electrochem. Soc. 2006, 153, C309.
Allendorf, M. D.; Mol, A. M. B. v."Gas-Phase Thermochemistry and Mechanism of Organometallic Tin Oxide Precursors," Topics in Organomet. Chem. 2005, 9, 1.
Chae, Y.; Houf, W. G.; McDaniel, A. H.; Allendorf, M. D."Stagnation Flow Reactor Investigation of Tin Oxide CVD from Monobutyl Tintrichloride," J. Electrochem. Soc. 2004, 151, C527.
Taylor, J. D.; Allendorf, M. D.; McDaniel, A. H.; Rice, S. F." In-Situ Diagnostics and Modeling of Methane Catalytic Partial Oxidation on Pt in a Stagnation-Flow Reactor," Indust. Eng. Chem. Res. 2003, 42, 6559.
Medlin, J. W.; Allendorf, M. D."A theoretical study of the adsorption of acetylene and hydrogen on the (111) surfaces of Pd, Pt, Ni, and Rh," J. Phys. Chem. B 2003, 107, 217.
Medlin, J. W.; McDaniel, A. H.; Allendorf, M. D.; Bastasz, R."Effects of Competitive carbon monoxide adsorption on the hydrogen response of Metal-Insulator-Semiconductor Hydrogen Sensors: the role of metal film morphology," J. Appl. Phys. 2003, 93, 2267.
Spear, K. E.; Allendorf, M. D."Thermodynamic Analysis of Alumina Refractory Corrosion by sodium or potassium hydroxide in glass melting furnaces," J. Electrochem. Soc. 2002, 149, B551.
McDaniel, A. H.; Lutz, A. E.; Allendorf, M. D.; Rice, S. F." Effects of Methane and Ethane on the Heterogeneous Production of Water from Hydrogen and Oxygen in Stagnation Flow," J. Catalysis 2002, 208, 21.
