Research ArticleMATERIALS SCIENCE

Terapascal static pressure generation with ultrahigh yield strength nanodiamond

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Science Advances  20 Jul 2016:
Vol. 2, no. 7, e1600341
DOI: 10.1126/sciadv.1600341
  • Fig. 1 Images of NCD balls and their Raman characteristics.

    (A) NCD balls as seen under an optical microscope: a transparent ball (left) and translucent one in the same field of view. (B) Raman spectra obtained from microballs of different crystallinity. Top curve corresponds to transparent NCD [synthesis conditions: P (pressure), 18 GPa; T (temperature), 2000°C; MgO pressure medium], whereas middle curve corresponds to translucent nanodiamond containing a small amount of polycrystalline component (18 GPa, 1850°C; MgO). For comparison, bottom curve presents a typical Raman spectrum of polycrystalline or single-crystal diamond. Only those microballs that showed a Raman spectrum characteristic for nanodiamond (without the diamond Raman peak A1g at ~1331 cm−1) were selected for the present study. a.u., arbitrary units.

  • Fig. 2 The scheme of the experiment on the measurement of the yield strength of an NCD microball.

    (A) Schematic showing a pressure chamber with an NCD ball squeezed between two diamond anvils. The pressure exactly above the microball (Pmb) and the pressure inside of the pressure chamber (Pch) were measured as described in the text [see also two separate studies by Dubrovinsky et al. (5, 13) for details]. The pressure chamber was filled with paraffin used as a pressure-transmitting medium. (B) Image of a real pressure chamber of a DAC taken under an optical microscope through the diamond window. (C) High-magnification image of the NCD ball in this DAC. (D) Pressure profile across the pressure chamber (see text for details).

  • Fig. 3 The unit cell volume of NCD as a function of pressure.

    At pressures above ~33 GPa, the NCD microball seems to become more compressible, but the observed effect is a consequence of bridging of the microball between the DAC’s anvils and the development of deviatoric stresses (13). Error bars are within the size of the dots.

  • Fig. 4 The results of HRTEM and high-angle annular dark-field scanning TEM investigations.

    (A and B) Aberration-corrected HRTEM images of the diamond nanoparticles. Scale bars, 5 nm. (A) The boundaries between the individual diamond grains (marked with black arrows) are not coherent and often appear to be disordered. White arrows indicate the {111} twin planes. (B) Surface layer around the diamond nanoparticles forming fullerene-like reconstructions (marked with arrows). (C) High-angle annular dark-field scanning TEM (HAADF-STEM) image of a typical region of the diamond nanocrystals. Scale bar, 5 nm. This region was scanned using spatially resolved EELS, collecting the carbon-K edge. (D) Color map of the EELS signal depicting the sp3-bonded carbon in green and the sp2-bonded carbon in red. The color map was generated by fitting each pixel in the acquired EELS data set with a diamond and amorphous carbon spectral reference in a linear combination and plotting the diamond component strength in green and the amorphous carbon component strength in red. (E) EELS spectra measured from the areas indicated in (D), showing the fine structure of the C-K edge along with the standard spectra from diamond, graphite, and amorphous carbon. The spectrum from region 1 corresponds to diamond-like sp3-bonded carbon, that from region 2 is a combination of the diamond and graphitic-like contributions, and that from region 3 is reminiscent of graphitic-like sp2-bonded carbon.

  • Fig. 5 Microstructure of NCD and NPD materials.

    (A) NCD. (B) NPD. Grain-size statistics (1), electron diffraction pattern (2), and grain imaging (3) give evidence to different microstructures of NCD and NPD. Most of the diamond nanograins in NCD have sizes in the range of 3 to 10 nm, whereas the diamond grains in NPD include submicrometer particles. The electron diffraction pattern of NCD shows continuous diffraction rings characteristic of nanocrystalline materials, whereas the pattern of NPD is spotty, as expected for materials containing quite coarse grains. The particle size was measured manually from dark-field TEM images on 218 and 219 particles for the NCD and NPD materials, respectively.

  • Fig. 6 Images of an NCD ball before and after the FIB milling.

    (A) Secondary electron image of a ball before ion milling, as taken in the Scios DualBeam system (FEI Deutschland GmbH) at a voltage of 20 kV and a current of 0.8 nA. mag, magnification; Det, detector; ETD, Everhart Thornley detector; HV, high voltage; HFW, horizontal field width. (B) Gallium ion image of the same ball (taken at 30 kV and 30 pA) after milling at 30 kV and 5 nA.

  • Fig. 7 Schematic drawings of the setup for ultrahigh static pressure generation.

    (A) Testing of the performance of a single semiball forced against the diamond anvil in a LiF pressure medium in a conventional DAC. (B) ds-DAC assembly (not to scale) for experiments at ultrahigh pressures (above 1 TPa). Two transparent NCD semiballs were used as secondary anvils in a conventional DAC. Diameter of the NCD semiballs is ~20 μm, and the initial size of the sample is about 3 μm in diameter and about 1 μm in thickness.

  • Fig. 8 The synchrotron powder x-ray diffraction data of gold subjected to pressures above 1 TPa in a ds-DAC.

    (A) Sequence of the diffraction patterns obtained at ultrahigh pressures above 670 GPa. (B) GSAS plot for the diffraction data collected at a pressure of 1065(15) GPa for 120 s with an x-ray wavelength of λ = 0.31 Å. Red dots indicate the experimental points; blue curve, the simulated diffraction pattern; and dark line, the residual difference. A powder of Au was compressed in a ds-DAC using paraffin wax as a pressure-transmitting medium. The lattice parameter of gold is a = 3.1741(3) Å, and that of NCD is a = 3.347(1) Å. Pressure was determined according to the gold EOS (5, 33).

  • Fig. 9 Diffraction pattern of a mixture of gold [a = 3.400(1) Å] and platinum [a = 3.357(1) Å] compressed in a ds-DAC equipped with Bohler-Almax first-stage anvils.

    Experimental data are shown by red crosses; continuous green curve is due to simulation with the full-profile (GSAS) software. The pressures are 417(5) GPa, according to the platinum EOS, and 432(5) GPa, according to the EOS of gold [calculated using http://kantor.50webs.com/diffraction.htm; see also study by Fei et al. (35) and Dubrovinsky et al. (5)]. This small difference in pressures determined from the EOS of two metals with different mechanical and elastic properties suggests that possible effects of stresses are insignificant for Au (and Pt) at a multimegabar pressure range. Moreover, x-ray data were also collected in geometry, when the optical axis of a DAC is under the angle of 35° to the incident x-ray beam. This is possible due to a large (80°) opening of the DAC. In this geometry, we obtained the same (within uncertainties) positions of diffraction lines and the lattice parameters for both Pt and Au, compared to those in parallel geometry, thus confirming a negligible effect of stress. Obsd. and diff., observed and difference profiles.

  • Fig. 10 The Γ plot for Au at 1065(15) GPa.

    Θ is the diffraction angle, and am is the unit cell parameters calculated from the individual d spacings (dobserved) from table S1 for the hkl 200, 311, 220, 222, and 111 (dots from left to right). The line is a linear fit through experimental data points (dots); the dashed line shows the value of the lattice parameter obtained by the full-profile (GSAS) fitting. On the basis of these data and following the methodology described in the studies by Dorfman et al. (34) and Takemura and Dewaele (36), the maximal unixial stress component was evaluated to be less than 20 GPa, in good agreement with extrapolations of data of earlier measurements (34, 37).

  • Fig. 11 Scheme of the gasket preparation for ds-DACs.

    (1) A rhenium foil with an initial thickness of ~200 μm is indented to ~25 μm using a conventional DAC with diamond anvils having culets of 250 μm. (2) In the middle part of the initial indentation, an additional indentation with a final thickness of ~3 μm is made using 100-μm culet diamonds. (3) Using a pulsed laser, a hole with a diameter of ~3 to 4 μm is drilled at the center of the secondary indentation. (4) A sample (Au or Pt in our experiments) is loaded using the micromanipulator into the center of the secondary pressure chamber. NCD semiballs (secondary anvils) are attached to the gasket using traces of wax, and the whole assembly is mounted on the primary anvils (with either flat 250-μm or beveled 120-μm culets in our experiments). Empty space in the secondary chamber in our experiments was filled by wax or by Ar (loaded at 1.3 kbar).

  • Fig. 12 Examples of the diffraction patterns collected in gasketed ds-DACs.

    (A) Mixture of Au and paraffin wax at 688(10) GPa [pressure is given on the basis of the lattice parameter of gold and the EOS from Yokoo et al. (33)]. (B) Platinum compressed in argon. Pressure is given on the basis of the Pt EOS from Yokoo et al. (33). Rhenium reflections are due to gasket material compressed between primary anvils to about 60 GPa (A) and 120 and 135 GPa (B); although the full width at half-maximum (FWHM) of the x-ray beam is about 2 μm, the tails of the beam are intense enough to result in strong scattering by a large amount of rhenium surrounding the samples. Diffraction patterns were collected using x-ray with wavelength of ~0.41 Å and processed with the GSAS Software (red dots indicate experimental points, whereas blue lines indicate calculated values).

  • Fig. 13 X-ray images of the nanodiamond balls.

    (A) A single ball (left) and nine balls aligned in the direction of the x-rays (right), along the direction of view. The single ball is practically transparent, whereas the nine aligned balls look black because their set negatively focuses the light (it is seen that the nine balls are well aligned along the optical axis). (B) X-ray image of the same balls taken in the direction perpendicular to that of the alignment of the nine balls; the single ball (biggest one) is seen at about the center of the image. Primary slits were closed down to 50 μm; therefore, a nice interference pattern is seen around the balls. (C) X-ray image showing the divergent beam passing the negative lens. This negative diamond lens of nine aligned balls was tested on ID06 beamline at ESRF where a 10 μrad divergent 12-keV x-ray undulator beam was expanded to 100 μrad, giving an angular divergence value of 2 × 10−4.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/7/e1600341/DC1

    fig. S1. Images demonstrating comparative hardness of NCD, single-crystal diamond, and NPD.

    fig. S2. Raman spectra collected from the diamond anvil over the tip of a semiball and at its edge.

    fig. S3. Reflectance IR spectra collected through and beside an NCD semiball compressed in a LiF medium at the IR2 beamline at ANKA Synchrotron.

    fig. S4. Variations of the lattice parameters of gold (red circles) and NCD of secondary anvils (blue squares) as functions of the pressure in the chamber.

    fig. S5. Optical photograph of the sample (Au and paraffin wax) compressed in a gasketed ds-DAC at 688(10) GPa, as seen through the diamonds and NCD secondary anvils.

    table S1. Observed and calculated d spacing of Au at 1065(15) GPa.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Images demonstrating comparative hardness of NCD, single-crystal diamond, and NPD.
    • fig. S2. Raman spectra collected from the diamond anvil over the tip of a semiball and at its edge.
    • fig. S3. Reflectance IR spectra collected through and beside an NCD semiball compressed in a LiF medium at the IR2 beamline at ANKA Synchrotron.
    • fig. S4. Variations of the lattice parameters of gold (red circles) and NCD of secondary anvils (blue squares) as functions of the pressure in the chamber.
    • fig. S5. Optical photograph of the sample (Au and paraffin wax) compressed in a gasketed ds-DAC at 688(10) GPa, as seen through the diamonds and NCD secondary anvils.
    • table S1. Observed and calculated d spacing of Au at 1065(15) GPa.

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