The typical conditions for carbon nanomaterial synthesis include extreme temperatures and pressures that occur in plasmas or flames creating highly non-equilibrium initial distribution of reactive carbon species that during their relaxation map out a succession of metastable states corresponding to a broad range of products. The distribution of products in carbon nanomaterial synthesis is an intrinsic property of the carbon transformation reactions that occur by rearrangements of carbon-carbon bonding configurations during self-assembly from energetically unstable species. Consequently, these distributions are dominated by kinetics rather than by thermodynamic stability. This approach is highly effective in the discovery process because the desired structures can be isolated and purified for specific studies using chemical separation techniques. However, it is impractical for the mass production of carbon nanomaterials that is needed for applications. The complexity of these processes is well recognized and the obstacles to synthesis of carbon nanomaterials with desired structure are related to the poor understanding of the barriers and the reaction pathways connecting the initial molecular structures to final products. Controlling the assembly of carbon at the molecular level is the most promising avenue for gaining access to the remarkable properties of carbon nanomaterials. The focus of this talk is on chemical vapor deposition processes that occur at milder conditions promising greater control over the product distribution in the formation of carbon nanotubes and graphene. We use a molecular beam environment to suppress the secondary gas phase reactions and restrict the growth to heterogeneous surface reactions of specific molecular precursors on a single collision level such as acetylene. The carbon deposition kinetics is studied in real-time using time-resolved optical reflectivity methods. The kinetic behavior of these processes allows identification of a certain reaction type with a characteristic product distribution that is critical for obtaining carbon nanomaterials with desired properties.
Gyula Eres, Oak Ridge National Laboratory Division of Materials Science and Technology
Gyula holds a Ph.D. in chemical physics from the University of Illinois at Urbana-Champaign. His current research is focused on understanding the mechanisms and the kinetics of elementary surface processes that control the synthesis and properties of interfaces in epitaxial thin films, superlattices, and nanostructured materials relevant for advanced energy applications. The experimental approach combines energy enhanced and nonequilibrium growth techniques including pulsed laser deposition and supersonic molecular beam epitaxy with in situ time-resolved imaging, diffraction, and spectroscopic techniques such as surface x-ray diffraction, laser based optical diagnostics, mass spectrometry, and reflection high energy electron diffraction.
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University of Illinois at Urbana-Champaign