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

Abstract

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.

Low‐Symmetry PdSe2 for High Performance Thermoelectric Applications

“…As shown in Figure a, the transfer curves at 20 and 300 K of PdSe 2 flake were compared between before and after annealing at 480 K for 4 h. This thermal annealing temperature is safe to get rid of any phase change or material decompositions, which happens at a much higher temperature. [ 35,36 ] We also recorded the electrical resistance change of the PdSe 2 flake during annealing as shown in Figure S5, Supporting Information. The electrical resistance reduced gradually until a saturated value achieved without any sudden change, which confirms the PdSe 2 flake does not decompose under the current thermal annealing.…”

Two‐Dimensional Noble‐Metal Chalcogenides and Phosphochalcogenides

“…The NMDCs also showed an outstanding performance as sensors, for example, for pressure or for specific molecular species . Their chemistry, which includes highly anisotropic structural features, low‐energy differences between different polymorphs, controllable phase changes, and catalytic properties, differs from that of the transition‐metal dichalcogenides (TMDCs), such as MoS 2 and WSe 2 . This is caused by electron correlation and relativistic effects, which render their theoretical investigation challenging.…”

Applications of 2D-Layered Palladium Diselenide and Its van der Waals Heterostructures in Electronics and Optoelectronics

“…First, PdSe 2 can be transformed to PdSe 2- x with vacuum annealing. According to the traditional bulk Pd–Se phase diagram [ 49 ], the Se loss induces the change in the Pd/Se ratio. Hence, the phase transition occurs after 30-s pulse annealing at 400 °C and the PdSe 2- x ( x = 0–1) forms partially.…”

“…Another 30-s pulse annealing completed the phase transition into Pd 2 Se 3 . The long-time annealing at 400 °C or heating at high temperature (> 400 °C) leads to excess Se loss and thinning of 2D materials and finally form pure Pd materials [ 49 ]. Indeed, Se loss occurs in other metal selenide upon thermal annealing.…”