Graphene’s many potential applications have prompted a search for other two-dimensional elements and compounds. In 2012, Boris Yakobson and colleagues at Rice University, Houston, TX, USA, published a theoretical study showing that elemental boron could exist in flat, free-standing metallic monolayers.

Now, these researchers report the results of a density functional theory study of electron-phonon coupling strength in boron monolayers. They compared theoretical polymorphs with no vacancies and vacancies in 1/6 and 1/5 of the lattice sites. The study showed that boron monolayers could have intrinsic conventional superconductivity at temperatures below 10–20 K. The critical temperatures would be higher in phases with fewer vacancies. A metal substrate or inert protecting layer (e.g., 2D hexagonal BN) could stabilize the monolayer, and strong adhesion to a metal substrate could reduce the superconducting critical temperature.

As this study was being prepared for publication, three other research groups published papers on the synthesis of 2D boron polymorphs on silver substrates [1–3], and other researchers reported possible superconductivity in thicker boron films [4].

• Can Two-Dimensional Boron Superconduct?,
  Evgeni S. Penev, Alex Kutana, Boris I. Yakobson,
  Nano Letters 2016.
  DOI: 10.1021/acs.nanolett.6b00070

• [1] B. Feng, J. Zhang, Q. Zhong, W. Li, S. Li, H. Li, P. Cheng, S. Meng, L. Chen, K. Wu, Experimental Realization of Two-Dimensional Boron Sheets, Nature Chem. 2015. DOI: 10.1038/nchem.2491
• [2] B. Feng, J. Zhang, R.-Y. Liu, I. Takushi, C. Lian, L. Chen, K. Wu, H. Li, S. Meng, F. Komori, I. Matsuda, Realization of Metallic Boron in Monolayer Structures, 2015. arXiv:1512.05270
• [3] A. J. Mannix, X.-F. Zhou, B. Kiraly, J. D. Wood, D. Alducin, B. D. Myers, X. Liu, B. L. Fisher, U. Santiago, J. R. Guest, M. J. Yacaman, A. Ponce, A. R. Oganov, M. C. Hersam, N. P. Guisinger, Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs, Science 2015, 350, 1513−1516. DOI:
• [4] Y. Zhao, S. Zeng, J. Ni, Superconductivity in two-dimensional boron allotropes, Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 014502. DOI: 10.1103/PhysRevB.93.014502