(698c) An Initial Experimental Design Methodology Incorporating Expert Conjecture, Prior Data, and Engineering Models for Deposition of Iridium Nanoparticles in Supercritical Carbon Dioxide
AIChE Annual Meeting
Thursday, November 7, 2013 - 1:14pm to 1:36pm
The study and optimization of nanofabrication techniques in nanotechnology research is often challenging because experiments are costly to conduct in terms of time and money. In particular, for a new system that has not been previously studied at length, it is a challenge to efficiently plan the first round of experiments in the region of interest near the process optimum, and there may be multiple process inputs that must be optimized simultaneously. A purely statistical approach to this challenge would apply a space-filling experimental design, or, alternatively, domain knowledge could be applied to guide the experimental design. However, both of these approaches may waste precious resources by failing to sample efficiently near the desired process output. In this work, a novel technique termed Initial Experimental Design (IED) is applied to combine the statistical and experimental approaches for planning the initial round of experiments for a new system that is related to a similar but non-identical existing system. The new system is directed toward the deposition of iridium nanoparticles on a silicon wafer surface from an iridium hexafluoroacetylacetonate cyclooctadiene (Ir(hfac)(COD)) precursor in supercritical carbon dioxide (sc-CO2), while the older, related system studied the deposition of silver nanoparticles on Si from Ag(hfac)(COD) in sc-CO2. The goal was to deposit 40 nm mean size Ir nanoparticles within a tolerance of 5 nm. The previous data of mean particle size vs. temperature from the Ag(hfac)(COD) system were used in concert with expert opinions about the behavior of the new system, elicited via survey instrument, to efficiently plan the experiments in the new Ir(hfac)(COD) system. Four experts were surveyed for their conjectures on the design space and Arrhenius model structure for the new system. A unified model incorporating the experts' conflicting opinions was then built to use in the experimental design, which balanced a space-filling design with an objective-oriented design. The IED approach succeeded in directing experiments toward the desired process optimum at a temperature of 175 °C, although the variance of the prediction of the local mean Arrhenius model did not fall within the 5 nm tolerance for the local model chosen to fit the data. Moreover, an altogether unforseen growth mode was also observed for the Ir(hfac)(COD) system that had not been previously observed in the Ag(hfac)(COD) system.