Direct observation of cation diffusion driven surface reconstruction at van der Waals gaps

Abstract

Weak interlayer van der Waals (vdW) bonding has significant impact on the surface/interface structure, electronic properties, and transport properties of vdW layered materials. Unraveling the complex atomistic dynamics and structural evolution at vdW surfaces is therefore critical for the design and synthesis of the next-generation vdW layered materials. Here, we show that Ge/Bi cation diffusion along the vdW gap in layered GeBi2Te4 (GBT) can be directly observed using in situ heating scanning transmission electron microscopy (STEM). The cation concentration variation during diffusion was correlated with the local Te6 octahedron distortion based on a quantitative analysis of the atomic column intensity and position in time-elapsed STEM images. The in-plane cation diffusion leads to out-of-plane surface etching through complex structural evolutions involving the formation and propagation of a non-centrosymmetric GeTe2 triple layer surface reconstruction on fresh vdW surfaces, and GBT subsurface reconstruction from a septuple layer to a quintuple layer. Our results provide atomistic insight into the cation diffusion and surface reconstruction in vdW layered materials.

Titanium Self-Intercalation Induced Formation of Orthogonal (1 × 1) Edge/Surface Reconstruction in 1T-TiSe2: Atomic Scale Dynamics and Mechanistic Study

“…As seen, it can be regarded as a monolayer 1T-TiSe 2 (i.e., a Ti−Se−Ti sandwich layer) seamlessly and orthogonally attached onto the Seterminated zigzag edge of the host 1T-TiSe 2 . While this reconstruction model bears similarities to previously reported structures, such as the 90-degree basal-plane-faced tilt grain boundary 27 and triple-layer surface reconstruction structure, 28,29 it introduces two prominent features: (i) this novel edge shares the same periodicity (1 × 1) and lattice arrangement with the subject matrix layer, and (ii) the newly formed Se−Ti−Se layer is oriented orthogonally to the subject matrix layer. Therefore, it is designated as the orthogonal (1 × 1) reconstruction model.…”

Visible-Light-Driven Highly Selective 5-Hydroxymethylfurfural Upgrading and H2 Generation via Atomically Dispersed Ni Sites on ZnIn2S4 Nanosheets

“…Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) was further performed to reveal detailed surface information at the atomic scale. In HAADF-STEM image mode, the contrast of the atomic columns is approximately proportional to the square of the atomic number ( Z ). − Here, since the atomic number of Ni is lower than that of Zn and In, it is difficult to clearly separate the isolated Ni atoms from the ZIS support; however, no Ni-based clusters or nanoparticles (NPs) are found in Ni 1 /ZIS. Additionally, energy-dispersive X-ray spectroscopy (EDS) elemental mapping (Figure d) displays the uniform distribution of Ni, Zn, In, and S elements on the 2D nanosheets, verifying the atomically dispersed Ni in the Ni 1 /ZIS sample.…”

Defect Chemistry Engineering Promotes the Dopability of Cu for an Extraordinary Thermoelectric Performance of Hole-Doped PbSe with Resonant States

“…However, for regions (red arrow in Figure c) with interstitial atoms, the line profile (red line in Figure d) clearly shows additional contrast between the Pb/Se peaks. As the intensity of the STEM image is proportional to the average atomic number projected along the zone axis, , the low intensity of the additional atomic columns indicates the interstitial atoms should be Cu, which are lighter than Pb or Se.…”