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Synthesis of an open-framework allotrope of silicon

Nature Materials volume 14, pages 169–173 (2015)Cite this article

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Abstract

Silicon is ubiquitous in contemporary technology. The most stable form of silicon at ambient conditions takes on the structure of diamond (cF8, d-Si) and is an indirect bandgap semiconductor, which prevents it from being considered as a next-generation platform for semiconductor technologies1,2,3,4. Here, we report the formation of a new orthorhombic allotrope of silicon, Si24, using a novel two-step synthesis methodology. First, a Na4Si24 precursor was synthesized at high pressure5; second, sodium was removed from the precursor by a thermal ‘degassing’ process. The Cmcm structure of Si24, which has 24 Si atoms per unit cell (oC24), contains open channels along the crystallographic a-axis that are formed from six- and eight-membered sp3 silicon rings. This new allotrope possesses a quasidirect bandgap near 1.3 eV. Our combined experimental/theoretical study expands the known allotropy for element fourteen and the unique high-pressure precursor synthesis methodology demonstrates the potential for new materials with desirable properties.

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Figure 1: Crystal structures of Na4Si24 and Si24.
Figure 2: Structure determination and composition information for Si24.
Figure 3: Electronic and optical properties of Si24.
Figure 4: Absorption spectra.

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Acknowledgements

The experimental work was supported by DARPA under contract numbers W31P4Q-13-1-0005 and W911NF-11-1-0300. The theoretical work was supported by Energy Frontier Research in Extreme Environments (EFree) Center, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science under award number DE-SC0001057. We thank T. Muramatsu and V. Struzhkin for assistance with electrical measurements, J. Holaday and Y. Kono for helping with experimental synthesis, J. Armstrong for support with SEM measurements, and J. Smith, B. Baptiste and H. Gou for help with XRD. Facilities and infrastructure support were provided by the following. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA under Award No. DE-NA0001974 and DOE-BES under Award No. DE-FG02-99ER45775, with partial instrumentation funding by NSF. The Advanced Photon Source is a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. X-ray diffraction facilities at the Geophysical Laboratory were supported, in part, by the WDC Research Fund. Na4Si24 precursor synthesis experiments with in situ XRD were performed at the ID06 beamline at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. We are grateful to W. Crichton, J. Guignard and Y. Le Godec for providing assistance in using this beamline.

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Author notes

  1. Duck Young Kim, Stevce Stefanoski, Oleksandr O. Kurakevych and Timothy A. Strobel: These authors contributed equally to this work.

Authors and Affiliations

  1. Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015, USA

    Duck Young Kim, Stevce Stefanoski, Oleksandr O. Kurakevych & Timothy A. Strobel

  2. IMPMC, UPMC Sorbonne Universités, UMR CNRS 7590, Muséum National d’Histoire Naturelle, IRD UMR 206, 75005 Paris, France

    Oleksandr O. Kurakevych

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  1. Duck Young Kim
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Contributions

D.Y.K. performed all theoretical calculations. S.S., O.O.K. and T.A.S. performed all experimental synthesis and characterization. All authors discussed the results and contributed to the manuscript.

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Correspondence to Timothy A. Strobel.

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Kim, D., Stefanoski, S., Kurakevych, O. et al. Synthesis of an open-framework allotrope of silicon. Nature Mater 14, 169–173 (2015). https://doi.org/10.1038/nmat4140

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