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Preservation of high-pressure volatiles in nanostructured diamond capsules


High pressure induces dramatic changes and novel phenomena in condensed volatiles1,2 that are usually not preserved after recovery from pressure vessels. Here we report a process that pressurizes volatiles into nanopores of type 1 glassy carbon precursors, converts glassy carbon into nanocrystalline diamond by heating and synthesizes free-standing nanostructured diamond capsules (NDCs) capable of permanently preserving volatiles at high pressures, even after release back to ambient conditions for various vacuum-based diagnostic probes including electron microscopy. As a demonstration, we perform a comprehensive study of a high-pressure argon sample preserved in NDCs. Synchrotron X-ray diffraction and high-resolution transmission electron microscopy show nanometre-sized argon crystals at around 22.0 gigapascals embedded in nanocrystalline diamond, energy-dispersive X‑ray spectroscopy provides quantitative compositional analysis and electron energy-loss spectroscopy details the chemical bonding nature of high-pressure argon. The preserved pressure of the argon sample inside NDCs can be tuned by controlling NDC synthesis pressure. To test the general applicability of the NDC process, we show that high-pressure neon can also be trapped in NDCs and that type 2 glassy carbon can be used as the precursor container material. Further experiments on other volatiles and carbon allotropes open the possibility of bringing high-pressure explorations on a par with mainstream condensed-matter investigations and applications.

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Fig. 1: Schematic of the NDC synthesis process.
Fig. 2: Diffusion of argon into GC under pressure.
Fig. 3: Synchrotron XRD and pressure-tuning of NDC samples.
Fig. 4: Characterization of high-pressure crystalline argon grains in NDCs using TEM-based techniques.

Data availability

The data supporting the findings of this study are available from the corresponding authors upon reasonable request.


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We thank the National Key Research and Development Programme of China for financial support (nos. 2019YFA0708502, 2018YFA0703400 and 2021YFA0718900) and the National Natural Science Foundation of China (nos. 51871054 and U1930401). We thank V. B. Prakapenka, C. Prescher and E. Greenberg from the Center for Advanced Radiation Sources, University of Chicago, and J. Smith, Y. Meng and R. Hrubiak from HPCAT, APS and ANL for their kind help with synchrotron XRD experiments. We thank Y. Chen, D. Xu, Y. Yang, H. Shu and X. Du from HPSTAR for their help with experiments. The XRD work was performed at beamlines 13 ID-D of GSECARS, 16 ID-B of HPCAT, APS, ANL, and 15U1 of SSRF, China. GSECARS is supported by the NSF (no. EAR-1634415) and DOE (no. DE-FG02-94ER14466). HPCAT is supported by the Department of Energy (DOE)-National Nuclear Security Administration under award no. DE-NA0001974, with partial instrumentation funding by the NSF. The gas-loading system at GSECARS is supported by COMPRES under NSF Cooperative Agreement no. EAR-1606856, by GSECARS through NSF grant no. EAR-1634415 and by DOE grant no. DE-FG02-94ER14466. The TEM experiments were performed at the Center for Nanoscale Materials (CNM) at ANL. The SAXS work was performed at beamline 12 ID-B, APS, ANL. Work performed at CNM and APS, both US DOE Office of Science user facilities, was supported by the US DOE, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357.

Author information

Authors and Affiliations



Q.Z., Z.Z., W.L.M. and H.-k.M. initiated the research project. Q.Z. and Z.Z. designed experiments. Z.Z., L.T. and L.Y. synthesized NDCs. Z.Z., Q.Z., X. Zhang, L.T., H.L. and X. Zuo carried out synchrotron XRD and high-pressure SAXS experiments. Z.Z. and J.W. performed TEM experiments. Z.Z., Q.Z., J.W., B.C., W.Y. and X. Zuo analysed data. Z.Z., Q.Z., W.L.M. and H.-k.M. wrote the paper. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Wendy L. Mao, Ho-kwang Mao or Qiaoshi Zeng.

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Competing interests

Q.Z., Z.Z., W.L.M. and H.-k.M. are in the process of applying for a patent related to the synthesis of nanostructured diamond capsules described in this work. The other authors declare no competing interests.

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Nature thanks Larissa Dobrzhinetskaya and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Fitting of the SAXS data.

a, Comparison of experimental SAXS data of an initial GC sample before compression (red circles) in a DAC and the fitting results (solid and dashed lines). A spheroid form factor was used for the SAXS fitting, which assumes the pores to be spheres. This is one of the simplest shape models, and also a good estimation to the actual shape since a previous study found the pores in high-temperature treated GC approach a spherical shape (Ref. 15). The black dashed line represents the scattering contribution from pores by fitting to the Guinier region with the spherical shape model and the log-normal size distribution function. The pink dashed line represents Porod background scattering contribution from large size structures (e.g., beamline optics, diamond anvil windows, and large domains in GC). The green dashed line presents a low constant background possibly from air and/or other sources. It should be noted that the black dashed curve contains both Guinier and Porod regions of pore scattering. b, The size distribution of the pores in GC derived from the fitting in a. The average size of pores obtained from the SAXS data fitting is 1.5 ± 0.5 nm in diameter, which is close to the average grain size of argon (~3 nm) estimated from the XRD peak width (Fig. 3a). It should be noted that the pore size could vary to some extent through the complex compression-heating-cooling-decompression process to synthesize NDCs samples. Details regarding how and how much the pore size changes call for future efforts.

Extended Data Fig. 2 Synchrotron XRD patterns collected at different locations of the argon NDCs sample.

a, Synchrotron XRD pattern (black circles) of the NDC containing high-pressure argon synthesized at ~49.0 GPa and ~2100 K (the same sample with Fig. 3a but collected at a different location with a different XRD intensity ratio between argon and diamond) and the Rietveld refinement (red curve). The x-ray wavelength was 0.3738 Å. The refined lattice parameters of diamond and argon are 3.57 Å and 4.21 Å, respectively. b, Two XRD patterns from the same NDC sample (blue curve from a and black curve from Fig. 3a) compared with that of pure nanocrystalline diamond (pink curve from Ref. 34). The XRD pattern in Fig. 3a is from an argon-rich region while the pattern here in a is from another relatively argon-poor region with a much weaker argon signal. A comparison of the three XRD patterns further supports the non-uniform argon-ND composite feature of the NDCs sample.

Extended Data Fig. 3 Synchrotron XRD of an NDCs sample synthesized at 34.5 GPa.

The XRD pattern (black circles) of a recovered NDCs sample synthesized at ~34.5 GPa and ~2200 K. The sample is also composed of cubic diamond and fcc high-pressure argon according to the Rietveld refinement (red curve). The x-ray wavelength was 0.4066 Å. This result demonstrates that with different synthesis conditions of a NDCs sample the peaks from diamond can be better separated from those of argon compared with the case in Fig. 3a.

Extended Data Fig. 4 EDS elemental mapping of the NDCs sample with two different magnifications in scanning transmission electron microscopy (STEM).

Relatively low magnification (ad): a, An HAADF-STEM image. b, EDS mapping of C, c, EDS mapping of Ar, d, An overlay of b and c showing the distribution of C (green) and Ar (red). The scale bars represent 100 nm. A relatively high magnification (eh): e, An HAADF-STEM image. f, EDS mapping of C, g, EDS mapping of Ar, h, An overlay of f and g showing the non-uniform distribution of argon (red) in the carbon (green) matrix. The scale bars represent 20 nm. It should be noted that the sample is the same with that studied in Fig. 4, which was obtained by mechanically crushing the NDCs sample in Fig. 3a.

Extended Data Fig. 5 High-pressure argon grains in the NDCs sample investigated in Fig. 4.

a and b, HRTEM images of argon grains (marked by red squares) embedded in the nanocrystalline diamond matrix. The scale bars in the images represent 2 nm. Reduced FFT of images a and b are presented as insets c and d, respectively. The sharp diffraction spots from the argon grains are marked by red arrows.

Extended Data Fig. 6 Comparison of EELS spectra of various argon states.

EELS spectrum of high-pressure argon (~22 GPa) in NDCs (blue curve) is plotted together with that of gaseous argon (red dotted line, online standard data from Gatan Inc.) and that of solid argon precipitates in metals (black dotted curve) from Ref. 39 Compared with the data from Ref. 39, the Ar L2,3-edge of our high-pressure argon shift slightly to lower energy, which could be attributed to the different energy calibration in EELS measurements but needs further verification in the future. In our experiment, we calibrated the argon spectrum using the carbon K-edge of nanocrystalline diamond in the NDCs sample.

Extended Data Fig. 7 HRTEM and EELS results of Ar inclusions in NDCs.

a, An HRTEM image of NDCs containing high-pressure argon (the same NDCs sample as shown in Fig. 4). The scale bar represents 5 nm. b–e, Reduced FFT of the marked regions 1 (b), 2(c), 3(d), and 4(e) in a. The extra diffraction spots in addition to the diamond (111) ring or spots are marked by red arrows. f, EELS spectra collected at the regions 1–4. A zoom-in plot of all the EELS spectra of Ar L2,3-edge is shown as an inset. Both the Ar L2,3-edge and carbon K-edge features are present at an extended energy range for regions 1, 3, and 4. Only carbon K-edge features are present in region 2. The presence or absence of Ar L2,3-edges signals in EELS spectra coincide with the presence or absence of extra diffraction spots in be, indicating a strong one-to-one correspondence between them.

Extended Data Fig. 8 Stability of the NDC pressure.

a and b, HRTEM images of argon grains (marked by red squares) embedded in nanocrystalline diamond. The images were collected on the same sample investigated in Fig. 4 about one year later. The average argon (111) d-spacing is ~2.5 Å, almost the same as in Fig. 4d. The scale bars in the images represent 2 nm. Reduced FFT of images a and b are presented as insets c and d, respectively, showing clear diffraction spots from the argon grains (marked by red arrows) with consistently much larger d-spacings than the diamond (111) diffraction ring.

Extended Data Fig. 9 Characterization of the NDCs containing high-pressure neon.

a. An HRTEM image of the sample showing (111) d-spacing of diamond (2.06 Å) and a grain with smaller d-spacing (2.02 Å). The d-spacing of 2.02 Å matches the (111) d-spacing of neon at ~13.3 GPa. The scale bar represents 2 nm. Reduced FFT of the marked region 1 (blue square) (b) and region 2 (red square) (c). The green circles in b and c mark the position of the diamond (111) diffraction ring. Extra diffraction spots off the green circle in c are marked by red circles, which are consistent with the observation in the HRTEM image. d. An EDS spectrum with an energy range up to 10 keV collected on the entire area shown in a reveals an average neon content of ~5.2 at.%. Signals besides those from the NDCs sample (Ne and C) are very weak, which are mainly from the environment and discussed in details in Methods.

Extended Data Fig. 10 Synchrotron XRD of the NDCs containing high-pressure neon.

a, The XRD pattern of a recovered NDC sample containing high-pressure neon, which is the same sample as investigated by TEM in Extended Data Fig. 9. The raw XRD data (black circles) is fitted by Rietveld refinement (red curves) using a cubic diamond and fcc neon composite (b), or using a cubic diamond phase alone (c). The fit residuals are shown in blue curves. The x-ray wavelength was 0.3738 Å.

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Zeng, Z., Wen, J., Lou, H. et al. Preservation of high-pressure volatiles in nanostructured diamond capsules. Nature 608, 513–517 (2022).

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