Research ArticleMATERIALS SCIENCE

Facile diamond synthesis from lower diamondoids

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Science Advances  21 Feb 2020:
Vol. 6, no. 8, eaay9405
DOI: 10.1126/sciadv.aay9405
  • Fig. 1 Identification and characterization of as-synthesized diamond from lower diamondoids.

    (A) Top: Schematic illustration of laser-heated DAC and sample. Bottom: Transmitted light optical image of a sample (inside a DAC) after laser heating. (B) Representative Raman spectra of quenched–to–ambient pressure diamantane (C14H20) as a function of increasing synthesis temperature at pressures of 5, 15, and 20 GPa. Each Raman spectrum is collected from an individual laser spot with a specific P-T value. a.u., arbitrary units. (C) Scanning electron microscope (SEM) image of diamond formed from triamantane at 20 GPa and ~2000 K. Well-formed diamond grains are embedded in smaller crystalline diamond grains. (D) TEM image of diamond formed from triamantane oriented parallel to the laser-heating beam direction. Scale bars, 1 μm [(C) and (D)]. (E) HRTEM image showing the d-spacing of diamond (111) plane corresponding to 2.06 ± 0.03 Å. Scale bar, 5 nm. (F) Corresponding selected-area electron diffraction pattern with the scale bar of 2 1/nm. (G) EELS from a diamond grain representing nearly full sp3 hybridization of the diamond formed from triamantane (see fig. S3 for SEM and EELS of graphite flake and fig. S4 for energy-dispersive x-ray spectrum of diamond and XRD patterns and SEM images of gold nanoparticles).

  • Fig. 2 P-T synthesis diagrams of lower diamondoids.

    (A) P-T range in which diamond forms from lower diamondoids compared with conventional carbon materials using various synthesis techniques (6). HP-HT in the graph represents high-pressure, high-temperature diamond synthesis from laser heating at high pressure or multi-anvil apparatus. Catalyst HP-HT refers to diamond formed with the assistance of reagents/catalysts. The black dashed lines represent regions of diamond synthesis from diamondoids based on this work. (B to D) P-T synthesis diagrams of diamond versus graphite formation from adamantane, diamantane, and triamantane.

  • Fig. 3 Onset timing of diamond formation from lower diamondoids.

    (A) In situ XRD patterns of three diamondoids as a function of increasing laser-heating duration. Nonlabeled peaks belong to the sample. (B) Cake integration of two-dimensional diffraction images highlighting the texture of diamond growth as a function of increasing laser-heating time. Representative SEM images of nanodiamond and polycrystalline diamond. Scale bars, 2 μm.

  • Fig. 4 AIMD simulations for elucidating adamantane-to-diamond transformations.

    (A) Pristine adamantane unit cell. (B) Dehydrogenation of adamantane following 165 fs at 40 GPa and 2000 K. There is 28% H radical formation. The inset represents a pristine adamantane cage that has not yet been ruptured. (C) Dehydrogenation of adamantane following 215 fs at 40 GPa and 2000 K. Approximately 37% H radicals and 5% dihydrogen molecules are formed. The inset is a slightly distorted yet still a fully intact adamantane cage. The captured dehydrogenation processes are all metastable moments before full relaxation. The H–H bond distance cutoff was 0.851 Å. (D) Fully relaxed structure of adamantane at 5 GPa and 2000 K at t3. While the layers are not structurally in plane, graphene-like features are clearly observed as indicated by gray shaded areas. (E to G) C–C RDF, ADF, and CN of adamantane at 5 GPa and 2000 K. (H) Fully relaxed structure of adamantane at 40 GPa and 2000 K at t3. Colored in pink are the carbon atoms with fourfold coordination. (I to K) C–C RDF, ADF, and CN of adamantane at 40 GPa and 2000 K. The H-free systems were simulated for 9 ps. t1, t2, and t3 represent 0, 4, and 9 ps, respectively.

  • Fig. 5 Mechanisms of diamond formation from lower diamondoids.

    (A) Two unpassivated adamantane molecules can only fuse to form a hexagonal diamond cage. (B) Two unpassivated diamantane molecules can only fuse to form a hexagonal diamond cage. (C) Two unpassivated triamantane molecules fuse to form a cubic diamond cage enabled by the quaternary carbon atoms (blue spheres) and surrounding tertiary carbon atoms (circled in green).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/8/eaay9405/DC1

    Fig. S1. Representative Raman spectra of quenched products after laser-heating adamantane and triamantane at pressures of 5, 15, and 20 GPa.

    Fig. S2. Higher Raman frequency of adamantane compressed and heated to 10 GPa and ~2000 K.

    Fig. S3. Characterization of graphite formed from diamondoids.

    Fig. S4. XRD and SEM data of gold nanoparticles and energy-dispersive x-ray spectrum of diamond.

    Fig. S5. Structural evolution of dehydrogenated adamantane at 5 and 40 GPa and 2000 K.

    Fig. S6. False color plots indicating the calculated RDFs as a function of structural evolution time at 5 and 40 GPa.

    Fig. S7. Representative Raman spectra of quenched samples after laser-heating octadecane at the synthesis pressure of 12.5 GPa.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Representative Raman spectra of quenched products after laser-heating adamantane and triamantane at pressures of 5, 15, and 20 GPa.
    • Fig. S2. Higher Raman frequency of adamantane compressed and heated to 10 GPa and ~2000 K.
    • Fig. S3. Characterization of graphite formed from diamondoids.
    • Fig. S4. XRD and SEM data of gold nanoparticles and energy-dispersive x-ray spectrum of diamond.
    • Fig. S5. Structural evolution of dehydrogenated adamantane at 5 and 40 GPa and 2000 K.
    • Fig. S6. False color plots indicating the calculated RDFs as a function of structural evolution time at 5 and 40 GPa.
    • Fig. S7. Representative Raman spectra of quenched samples after laser-heating octadecane at the synthesis pressure of 12.5 GPa.

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