Evolution of interlayer stacking orders and rotations in bilayer PtSe₂ visualized by STEM

Abstract

Understanding the evolution mechanisms of interlayer stacking structures, particularly at the atomic scale, is of great significance for modulating the physical properties and realizing the full potential of 2D materials in electronics and quantum information applications. Herein, by performing in situ experiments using aberration corrected scanning transmission electron microscopy, the evolution of diverse interlayer stacking sequences (from 3R to N, N to 3R and N(3R) to AB′-stacked) in bilayer PtSe2 are directly observed. Furthermore, the interlayer rotational angles are tuned (e.g. 13.3° to 9.4°, 16.8° to 11° and 16.1° to 6°) in situ at real time in bilayer PtSe2. Density functional theory calculations reveal a small energy barrier (<0.2 eV per formula unit) for the kinetic evolution of interlayer structures. The illumination electron beam, while being as an atomic-scale probe for imaging, transfers enough energy initiating the transition. The bilayer PtSe2 has show the rich stacking and twisted structures which may create novel physical phenomena. These findings shed new light on the diversity of structural properties of bilayer PtSe2, which may be valuable for constituting a step further toward their potential uses for next generation of 2D transition metal dichalcogenides-based device applications.

Raman spectroscopy of monolayer to bulk PtSe2 exfoliated crystals

“…2L ′ samples are a noticeable exception, with a singular Raman signature differing from the one of 2L (detailed comparison in figure SM4). In fact, the comparison of absorption behavior with DFT predictions for 2L ′ suggests an AB stacking [12], which has been theoretically identified as a stable phase for 1T − PtSe 2 [5,12,30,34], and is a common defect in grown films [35,36].…”

Stacking Polymorphism in PtSe2 Drastically Affects Its Electromechanical Properties

“…[ 21 ] observed 1H/1T in‐plane PtSe 2 heterostructures at different annealing temperatures, while Xu et al. [ 28 ] obtained trigonal prismatic bilayer PtSe 2 .…”

“…[25] PtSe 2 has been observed in different coordination phases: For instance, Wang et al [26] showed the formation of MoS 2 -like 2H-PtSe 2 nanoflakes by chemical vapor deposition at 900 °C, while Tong et al [27] reported that single-layer of the same material was formed by liquid immersion of Pt(111) in Na 2 Se. Furthermore, Lin et al [21] observed 1H/1T in-plane PtSe 2 heterostructures at different annealing temperatures, while Xu et al [28] obtained trigonal prismatic bilayer PtSe 2 .…”

Twisted charge-density-wave patterns in bilayer 2D crystals and modulated electronic states

“…The recent exploration of the twisted bilayer (BL) two-dimensional (2D) system was initiated in graphene [1][2][3][4] and soon extend to TMDC [5][6][7] and other 2D materials [8][9][10]. The twisted 2D system leads to various intriguing properties, such as unconventional superconductivity [2,11], Mott insulator and flat bands [1,4], Hofstadter's butterfly spectra [12,13], moiré excitons [14][15][16], piezoelectric networks [17], quasicrystalline [18] and thus open a new research area known as twistronics [19][20][21].…”