Atomistic Simulation and Virtual Diffraction Characterization of Alumina Interfaces: Evaluating Structure and Stability for Predictive Physical Vapor Deposition Models

The objectives of this work are to investigate the structure and energetic stability of different alumina (Al2O3) phases using atomistic simulation and virtual diffraction characterization. To meet these objectives, this research performs molecular statics and molecular dynamics simulations employing the reactive force-field (ReaxFF) potential to model bulk, interface, and surface structures in the θ-, γ-, κ-, and α-Al2O3 system. Simulations throughout this study are characterized using a new virtual diffraction algorithm, developed and implemented for this work, that creates both selected area electron diffraction (SAED) and x-ray diffraction (XRD) line profiles without assuming prior knowledge of the crystal system. First, the transferability of the ReaxFF potential is evaluated by modelling different alumina bulk systems. ReaxFF is shown to correctly predict the energetic stability of α-Al2O3 among the crystalline alumina phases, but incorrectly predicts an even lower energy amorphous phase. Virtual XRD patterns uniquely identify each phase and validate the minimum energy bulk structures through experimental comparison. Second, stable and metastable alumina surfaces are studied at 0, 300, 500, and 700 K. ReaxFF predicts minimum energy surface structures and energies in good agreement with prior studies at 0 K; however, select surface models at 500 and 700 K undergo significant reconstructions caused by the unnatural bias for a lower-energy amorphous phase. Virtual SAED analysis performed on alumina surfaces allow advanced characterization and direct experimental validation of select models. Third, ReaxFF is used to model homophase and heterophase alumina interfaces at 0 K. Predicted minimum energy structures of α-Al2O3 interfaces show good agreement with prior works, which provides the foundation for the first atomistic study of metastable alumina grain boundaries and heterophase alumina interfaces. Virtual SAED patterns characterize select alumina interfaces and help guide the construction of low-energy heterophase alumina interfaces by providing insight into crystallographic compatibilities. Combined, the energetic data extracted from bulk, surface, and interface simulations as well as insights gained through virtual diffraction will aid the development of mesoscale predictive models of polycrystalline alumina formation during physical vapor deposition

Space and Earth Sciences, Computer Systems, and Scientific Data Analysis Support, Volume 1

This Final Progress Report covers the specific technical activities of Hughes STX Corporation for the last contract triannual period of 1 June through 30 Sep. 1993, in support of assigned task activities at Goddard Space Flight Center (GSFC). It also provides a brief summary of work throughout the contract period of performance on each active task. Technical activity is presented in Volume 1, while financial and level-of-effort data is presented in Volume 2. Technical support was provided to all Division and Laboratories of Goddard's Space Sciences and Earth Sciences Directorates. Types of support include: scientific programming, systems programming, computer management, mission planning, scientific investigation, data analysis, data processing, data base creation and maintenance, instrumentation development, and management services. Mission and instruments supported include: ROSAT, Astro-D, BBXRT, XTE, AXAF, GRO, COBE, WIND, UIT, SMM, STIS, HEIDI, DE, URAP, CRRES, Voyagers, ISEE, San Marco, LAGEOS, TOPEX/Poseidon, Pioneer-Venus, Galileo, Cassini, Nimbus-7/TOMS, Meteor-3/TOMS, FIFE, BOREAS, TRMM, AVHRR, and Landsat. Accomplishments include: development of computing programs for mission science and data analysis, supercomputer applications support, computer network support, computational upgrades for data archival and analysis centers, end-to-end management for mission data flow, scientific modeling and results in the fields of space and Earth physics, planning and design of GSFC VO DAAC and VO IMS, fabrication, assembly, and testing of mission instrumentation, and design of mission operations center