Compared to van der Waals two-dimensional (2D) layers with lateral covalent bonds, metallic bonding systems favor close-packed structures, and thus, free-standing 2D metals have remained, for the most part, elusive. However, a number of theoretical studies suggest a number of metals can exist as 2D materials and a few early experiments support this notion. Here we demonstrate free-standing single-atom-thick crystalline chromium (Cr) suspended membranes using aberration-corrected transmission electron microscopy and image simulations. Density functional theory studies confirm the 2D Cr membranes have an antiferromagnetic ground state making them highly attractive for spintronic applications. Moreover, the work also helps consolidate the existence of a new family of 2D metal layers.

Centre of Polymer and Carbon Materials Polish Academy of Sciences M Curie Sklodowskiej 34 Zabrze 41 819 Poland

Institute of Environmental Technology VSB Technical University of Ostrava 17 Listopadu 15 Ostrava 708 33 Czech Republic

Leibniz Institute for Solid State and Materials Research Dresden P O Box 270116 Dresden D 01171 Germany

NJ Explosives Research Branch Picatinny Arsenal Picatinny Arsenal New Jersey 07806 United States

Polish Center for Technology Development Ul Stabłowicka 147 Wrocław 54 066 Poland

School of Energy and Power Engineering Xi'an Jiaotong University No 28 Xianning West Road Xi'an Shaanxi 710049 China

Soochow Institute for Energy and Materials Innovations College of Physics Optoelectronics and Energy Collaborative Innovation Center of Suzhou Nano Science and Technology and Key Laboratory of Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province Soochow University Suzhou 215006 China

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Two-Dimensional Metals Over, Inside, or Beneath Templates

In Situ Fabrication of Freestanding Single-Atom-Thick 2D Metal/Metallene and 2D Metal/ Metallene Oxide Membranes: Recent Developments