A metastable pentagonal 2D material synthesized by symmetry-driven epitaxy

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Abstract
Most two-dimensional (2D) materials experimentally studied so far have hexagons as their building blocks. Only a few exceptions, such as PdSe2, are lower in energy in pentagonal phases and exhibit pentagons as building blocks. Although theory has predicted a large number of pentagonal 2D materials, many of these are metastable and their experimental realization is difficult. Here we report the successful synthesis of a metastable pentagonal 2D material, monolayer pentagonal PdTe2, by symmetry-driven epitaxy. Scanning tunnelling microscopy and complementary spectroscopy measurements are used to characterize this material, which demonstrates well-ordered low-symmetry atomic arrangements and is stabilized by lattice matching with the underlying Pd(100) substrate. Theoretical calculations, along with angle-resolved photoemission spectroscopy, reveal monolayer pentagonal PdTe2 to be a semiconductor with an indirect bandgap of 1.05 eV. Our work opens an avenue for the synthesis of pentagon-based 2D materials and gives opportunities to explore their applications such as multifunctional nanoelectronics.
Funding Information
  • U.S. Department of Energy (No. DE-SC0019215, No. DE-SC0019215)
  • United States Department of Defense | United States Air Force | AFMC | Air Force Research Laboratory (No. FA9550-20-1-0322, No. FA9550-20-1-0322, No. FA9550-20-1-0322)
  • Villum Fonden (No. 25931, No. 25931, No. 11744, No. 25931, No. 11744, No. 11744)
  • Natural Science Foundation of Jiangsu Province (BK20200873, BZ2020011, BK20200873, BZ2020011)
  • National Natural Science Foundation of China (22173067, No. 22173067)

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