Structural Changes and Diffusion of Vacancy Clusters in Diamond and Paracyclophane Cycloaddition: Insights into Unusual Carbon Bonding
Slepetz, Brad M.
High energy irradiation of diamond produces point defects that are observable by spectroscopy. While many defects have been confirmed such as the monovacancy V1, the divacancy V2, and various interstitials, most remain unidentified. The prediction of the properties of these defects through computational modeling is an important ally in solving these mysteries. Computational work on smaller vacancy clusters Vn in diamond had previously been performed with n up to 14 but these were always done with assumptions about that structures of the low energy clusters. A novel generational algorithm has allowed for the identification of the low energy clusters without structural bias. By going beyond n=14 insights have been made into the structural optimizations of large voids in carbon materials, which is important in helping describe Carbide-derived carbons (CDCs) at the atomistic level. Studying the mechanism of V2 formation has uncovered multiple stable non-contiguous divacancy structures with high spin that may be found in the ESR. The unique environment of vacancy clusters, within the rigid framework of the diamond lattice, gives rise to unusual carbon-carbon bond lengths. Molecular analogous where this kind of bonding can be found are rare but paracylophanes--which undergo [4+4] cycloaddition, spanning the spectrum of sp2 to sp3-hybridized carbon--are one example. This process mimics the diamond-to-graphite transition, the modeling of which offers valuable insight.
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Unusual Carbon-Carbon Bonding in π-Conjugated Cyclic Hydrocarbons by High Pressure and in Quinonoid Diradicals by Mild Stimuli Qiu, Lili (Georgetown University, 2018)This work presents a series of [n]-Cycloparaphenylenes ([n]CPPs, n=5, 6, 7, 8, 9, 10 and 12) subjected to ambient and high pressures and their in situ Raman spectra. All Raman experiments were done by our collaborates. ...