Striated 2D Lattice with Sub‐nm 1D Etch Channels by Controlled Thermally Induced Phase Transformations of PdSe2

• Published in: Advanced materials (Weinheim) 2019-11, Vol.31 (46), p.e1904251-n/a
• Main Authors: Ryu, Gyeong Hee, Zhu, Taishan, Chen, Jun, Sinha, Sapna, Shautsova, Viktoryia, Grossman, Jeffrey C., Warner, Jamie H.
• Format: Article
• Language: English
• Subjects: 1D channels; 2D crystals; Anisotropy; Bilayers; Binary systems; Channels; Crystals; Depletion; Lattices; Materials science; Nanoelectronics; Pd2Se3; PdSe2; Periodic variations; Phase transitions; Se vacancies; STEM
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201904251

2D crystals are typically uniform and periodic in‐plane with stacked sheet‐like structure in the out‐of‐plane direction. Breaking the in‐plane 2D symmetry by creating unique lattice structures offers anisotropic electronic and optical responses that have potential in nanoelectronics. However, creating nanoscale‐modulated anisotropic 2D lattices is challenging and is mostly done using top‐down lithographic methods with ≈10 nm resolution. A phase transformation mechanism for creating 2D striated lattice systems is revealed, where controlled thermal annealing induces Se loss in few‐layered PdSe2 and leads to 1D sub‐nm etched channels in Pd2Se3 bilayers. These striated 2D crystals cannot be described by a typical unit cells of 1–2 Å for crystals, but rather long range nanoscale periodicity in each three directions. The 1D channels give rise to localized conduction states, which have no bulk layered counterpart or monolayer form. These results show how the known family of 2D crystals can be extended beyond those that exist as bulk layered van der Waals crystals by exploiting phase transformations by elemental depletion in binary systems. A two‐dimensional striated lattice with sub‐nanometer one‐dimensional channels of Pd2Se3 is created in situ by annealing few‐layered PdSe2 two‐dimensional films at 400 °C. Annular dark‐field scanning transmission electron microscopy reveals the atomic structure and phase transformation of the striated lattice and density functional theory predicts the one‐dimensional channels act as localized conduction pathways within the system.