Core expertise:
Core expertise:
Core expertise:
Core expertise:
Core expertise:
Core expertise:
Core expertise:
Core expertise:
Theoretical Studies of Complex Polymeric Surfaces Including Laser Ablation and Materials Degradation via Chemical Reactions and Physical Sputtering
Description:
The Garrison group is expert at using molecular dynamics computer simulations to explore complex processes that occur in materials, e.g., they have examined keV particle bombardment of metals, semiconductors and now hydrocarbon systems. They have also made significant contributions in thin film growth when suitable and accurate potential energy surfaces are in hand, such as dimer insertion on diamond surfaces. Other examples are Garrison's recent work on polymer ablation, and efforts to include combining different methodologies to expand time or length scales, e.g., Monte Carlo studies of diamond film growth. Her efforts, supported by electronic surfaces developed by the Schatz group, will generate essential insights into the reactivity and degradation paths for complex surfaces subjected to reactive environments.
William L. Hase
Theoretical Studies of Energy Transfer and Reactive Chemistry in Gaseous, Interfacial, and Condensed Phase Environments
Description:
The Hase Group contributes to the theory of intramolecular and unimolecular dynamics, gas-surface collisional energy transfer, and to chemical dynamics simulations of complex many-atom reactive systems. The latter includes the development of algorithms and computer programs, incorporating powerful simulation methods such as quantum mechanical (QM), QM/MM direct dynamics and mixed classical/quantum dynamics, with applications to important problems in gas-phase, gas-surface, and interfacial dynamics.
Dennis C. Jacobs
Ion-Surface Scattering: Interfacial Reactions, Charge Transfer, and Etching
Description:
The Jacobs group explores the reactions of hyperthermal energy ions with surfaces; mass-selected ion source generates atomic and molecular ions native to LEO (e.g., H+, O+, O2+, NO+) and transports them to the surface target at collision energies ranging from 3 - 300 eV. His group's particular expertise with the scattering of O+ and H+ ions forms a superb complement to the neutral scattering efforts of Minton and Sibener. His effort will initially examine the degradation mechanisms of SiO2 which serves a protective coating for many space functions, including open wave guide antennas, solar panel arrays, and reusable surface insulation materials on reentry vehicles. Working with other MURI members, a much better understanding of this process is envisioned than could be accomplished by his group alone. He will also be a key participant in planned activities with organic coatings.
Timothy K. Minton
Gas-Surface Interactions Involving Hyperthermal Neutral Beams; Crossed-Beam Reactive Scattering; Degradation and Etching of Polymers in LEO
Description:
The Minton group brings to this MURI its unique capabilities with respect to examining the interaction of hyperthermal oxygen atoms with surfaces, providing a beautiful complement to the reactive scattering and energy transfer activities of the Jacobs and Sibener groups. His ability to examine medium-sized molecular oxidation processes in crossed-beams will also provide a valuable link between our current knowledge of gas-phase oxidation reactions and those occurring in the condensed phase. His activities will likely include synergistic effects involving UV radiation, gas-surface scattering dynamics, surface chemistry induced by fast O-atom/surface collisions, O-atom sticking on, and incorporation into, solid materials, and coordination of in-space experiments with relevant agencies.
George C. Schatz
Theoretical Studies of Reactive Potential Energy Surfaces and Dynamics; Electronic Structure; Quantum, Semiclassical, and Classical Theories of Chemical Reaction Dynamics; Reactivity of Species in Electonically Excited States; Collisional Energy Transfer
Description:
The Schatz group will be concerned with theoretical modeling of reactions of high energy atoms and ions with polymers. They will also study photochemistry and electron beam excitation of such materials. The primary tools will be electronic structure methods and dynamics methods based on classical dynamics and trajectory surface hopping. Relevant past work has been, in addition to methods development, mechanistic calculations involving O, N, H, and C, in both ground and excited electronic states, with representative medium-sized hydrocarbons. This program will set the stage for theoretical studies of polymer reactivity involving different functional groups, and will provide input to Garrison's polymer calculations. His program utilizes advances of particular relevance to this MURI such as new methods for representing complex potential energy surfaces, and dynamics methods for coupling multiple potential energy surfaces. Trajectory surface hopping calculations will provide realistic descriptions of polymer photodynamics & excited state effects in high energy collisions of atoms and ions with polymers.
Steven J. Sibener
Molecular Beam & Scanning Probe Microscopy Studies of Surface Chemistry, Energy Transfer, and Reaction Dynamics; Polymer Thin Films; Oxidation of Materials
Description:
Molecular beam scattering techniques have firmly established themselves among the major tools for studying the kinetics and dynamics of gas-surface interactions. Sibener's group (with prior AFOSR support) has constructed several novel gas-surface scattering and STM/AFM instruments with which one can incisively probe the dynamics and mechanistic chemical kinetics of complex heterogeneous reactions. Supersonic beams of O(3P), O(1D), and O2(1D) are generated in his laboratory. The Sibener group has elucidated many essential atomic-level details for metallic oxidation in aggressive oxidizing environments, including work on electron-stimulated oxidation, atomic oxygen, and high kinetic energy molecular oxygen. His group is also a leader in using AFM to examine, in real-time, the structural evolution of polymer surfaces. His focus will be on O-atom reactions, synergistic effects, & AFM imaging of reacting surfaces.
John C. Tully
Theory of Gas-Surface Interactions; Molecular Dynamics with Electronic Transitions; Simulation of Infrequent Events
Description:
Tully has contributed to the development of a number of the tools that are now standard in molecular simulations; trajectory surface-hopping methods for electronic transitions, diatomics-in-molecules interaction potentials, treatment of energy dissipation via phonon and electronic excitations, mixed quantum-classical dynamics, and treatment of slow reactions. He has applied these methods widely to elucidate the dynamics of adsorption, desorption and energy exchange at surfaces. He will work closely with Garrison and Schatz in constructing accurate and practical molecular simulation techniques designed specifically for this MURI, as well as in the development of kinetic Monte Carlo methods for extending the simulations to lab timescales. This will make possible direct comparison between the theory and experiments proposed herein.
Luping Yu
Synthesis of Multifunctional Polymers and Thin Films; Synthetic Methodology
Description:
The major theme of Luping Yu's research is focused upon the rational design, synthesis and characterization of novel functional and multifunctional polymers and molecules. They have developed new polymerization methodologies, including transition metal-mediated polycondensation and living chain polymerization (radical, anionic and cationic polymerizations). These new methodologies allowed them to synthesize new polymer structures more efficiently. They designed and synthesized numerous novel functional polymers, such as photorefractive polymers, 2nd-order nonlinear optical polymers, conjugated diblock polymers. Yu's group has a long-standing interest in interactions between polymers and radiation. He will synthesize custom polymers & SAMs, including fluorinated species, as part of his MURI effort.
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