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Quantifying hexagonal stacking in diamond.

ABSTRACT: Diamond is a material of immense technological importance and an ancient signifier for wealth and societal status. In geology, diamond forms as part of the deep carbon cycle and typically displays a highly ordered cubic crystal structure. Impact diamonds, however, often exhibit structural disorder in the form of complex combinations of cubic and hexagonal stacking motifs. The structural characterization of such diamonds remains a challenge. Here, impact diamonds from the Popigai crater were characterized with a range of techniques. Using the MCDIFFaX approach for analysing X-ray diffraction data, hexagonality indices up to 40% were found. The effects of increasing amounts of hexagonal stacking on the Raman spectra of diamond were investigated computationally and found to be in excellent agreement with trends in the experimental spectra. Electron microscopy revealed nanoscale twinning within the cubic diamond structure. Our analyses lead us to propose a systematic protocol for assigning specific hexagonality attributes to the mineral designated as lonsdaleite among natural and synthetic samples.

SUBMITTER: Murri M

PROVIDER: S-EPMC6637244 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Quantifying hexagonal stacking in diamond.

Murri Mara M Smith Rachael L RL McColl Kit K Hart Martin M Alvaro Matteo M Jones Adrian P AP Németh Péter P Salzmann Christoph G CG Corà Furio F Domeneghetti Maria C MC Nestola Fabrizio F Sobolev Nikolay V NV Vishnevsky Sergey A SA Logvinova Alla M AM McMillan Paul F PF

Scientific reports 20190717 1

Diamond is a material of immense technological importance and an ancient signifier for wealth and societal status. In geology, diamond forms as part of the deep carbon cycle and typically displays a highly ordered cubic crystal structure. Impact diamonds, however, often exhibit structural disorder in the form of complex combinations of cubic and hexagonal stacking motifs. The structural characterization of such diamonds remains a challenge. Here, impact diamonds from the Popigai crater were char ...[more]

PMID: 31316094

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Project description:Lyotropic phases of amphiphiles are a prototypical example of self-assemblies. Their structure is generally determined by amphiphile shape and their phase transitions are primarily governed by composition. In this paper, we demonstrate a new paradigm for membrane shape control where the electrostatic coupling of charged membranes to short DNA (sDNA), with tunable temperature-dependent end-to-end stacking interactions, enables switching between the inverted gyroid cubic structure (QII(G)) and the inverted hexagonal phase (HII(C)). We investigated the structural shape transitions induced in the QII(G) phase upon complexation with a series of sDNAs (5, 11, 24, and 48 bp) with three types of end structure ("sticky" adenine (A)-thymine (T) (dAdT) overhangs, no overhang (blunt), and "nonsticky" dTdT overhangs) using synchrotron small-angle X-ray scattering. Very short 5 bp sDNA with dAdT overhangs and blunt ends induce coexistence of the QII(G) and the HII(C) phase, with the fraction of QII(G) increasing with temperature. Phase coexistence for blunt 5 bp sDNA is observed from 27 °C to about 65 °C, where the HII(C) phase disappears and the temperature dependence of the lattice spacing of the QII(G) phase indicates that the sDNA duplexes melt into single strands. The only other sDNA for which melting is observed is 5 bp sDNA with dTdT overhangs, which forms the QII(G) phase throughout the studied range of temperature (27 °C to 85.2 °C). The longer 11 bp sDNA forms coexisting QII(G) and HII(C) phases (with the fraction of QII(G) again increasing with temperature) only for "nonsticky" dTdT overhangs, while dAdT overhangs and blunt ends exclusively template the HII(C) phase. For 24 and 48 bp sDNAs the HII(C) phase replaces the QII(G) phase at all investigated temperatures, independent of sDNA end structure. Our work demonstrates how the combined effects of sDNA length and end structure (which determine the temperature-dependent stacking length) tune the phase behavior of the complexes. These findings are consistent with the hypothesis that sDNAs and sDNA stacks with lengths comparable to or larger than the cubic unit cell length disfavor the highly curved channels present in the QII(G) phase, thus driving the QII(G)-to-HII(C) phase transition. As the temperature is increased, the breaking of stacks due to thermal fluctuations restores increasing percentages of the QII(G) phase.

Dataset Information

Quantifying hexagonal stacking in diamond.

Publications

Quantifying hexagonal stacking in diamond.

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