Anisotropic Growth and Scanning Tunneling Microscopy Identification of Ultrathin Even-Layered PdSe₂ Ribbons

Palladium diselenide (PdSe₂) is an emerging 2D layered material with anisotropic optical/electrical properties, extra-high carrier mobility, excellent air stability, etc. So far, ultrathin PdSe₂ is mainly achieved via mechanical exfoliation from its bulk counterpart, and the direct synthesis is still challenging. Herein, the synthesis of ultrathin 2D PdSe₂ on conductive Au foil substrates via a facile chemical vapor deposition route is reported. Intriguingly, an anisotropic growth behavior is detected from the evolution of ribboned flakes with large length/width ratios, which is well explained from the orthorhombic symmetry of PdSe₂. A unique even-layered growth mode from 2 to 20 layers is also confirmed by the perfect combination of onsite scanning tunneling microscopy characterizations, through deliberately scratching the flake edge to expose both even and odd layers. This even-layered, ribboned 2D material is expected to serve as a perfect platform for exploring unique physical properties, and for developing high-performance electronic and optoelectronic devices.