Grain boundaries in two-dimensional (2D) semiconductors generally induce distorted band alignment and interfacial charge, which impair their electronic properties for device applications. Here, we report the improvement of band alignment at the grain boundaries of PtSe2, a 2D semiconductor, with selective adsorption of a presentative organic acceptor, tetracyanoquinodimethane (TCNQ). TCNQ molecules show selective adsorption at the PtSe2 grain boundary with strong interfacial charge. The adsorption of TCNQ distinctly improves the band alignment at the PtSe2 grain boundaries. With the charge transfer between the grain boundary and TCNQ, the local charge is inhibited, and the band bending at the grain boundary is suppressed, as revealed by the scanning tunneling microscopy and spectroscopy (STM/S) results. Our finding provides an effective method for the advancement of the band alignment at the grain boundary by functional molecules, improving the electronic properties of 2D semiconductors for their future applications.
Emerging functionalities in two-dimensional materials, such as ferromagnetism,superconductivity and ferroelectricity, open new avenues for promising nanoelectronic applications.Here, we report the discovery of intrinsic in-plane room-temperature ferroelectricity in two-dimensional Bi2TeO5 grown by chemical vapor deposition, where spontaneous polarization originates from Bi column displacements. We found an intercalated buffer layer consist ofmixed
Bi/Te column as 180° domain wall which enables facile polarized domain engineering, including continuously tunable domain width by pinning different concentration of buffer layers, and even ferroelectric-antiferroelectric phase transition when the polarization unit is pinned down to single atomic column. More interestingly, the intercalated Bi/Te buffer layer can interconvert to polarized Bi columns which end up with series terraced domain walls and unusual fan-shaped ferroelectric domain. The buffer layer induced size and shape tunable ferroelectric domain in two-dimensional Bi2TeO5 offer insights into the manipulation of functionalities in van der Waals materials for future nanoelectronics.
主要工作成果 Selected Publications (代表性年度论文) Ferroelectricity in untwisted heterobilayers of transition metal dichalcogenides Lukas ROGÉE#, Lvjin WANG#,…, Manish CHHOWALLA*, Wei JI*, and Shu Ping LAU* Science 376(6596) pp.973-978 (2022)
Van der Waals epitaxial growth of air-stable CrSe2 nanosheets with thickness-tunable magnetic order Bo Li#, Zhong Wang#, Cong Wang#, Peng Chen#, Xidong Duan*, Wei Ji*, Xiangfeng Duan*, et al. Nature Materials 20, 818-825 (2021)
Universal mechanical exfoliation of large-area 2D crystals Yuan Huang, Yu-Hao Pan, Rong Yang … Peter Sutter*, Wei Ji*, Xing-Jiang Zhou* and Hong-Jun Gao* Nature Communications 11, 2453 (2020)
Stacking tunable interlayer magnetism in bilayer CrI3 Peiheng Jiang, Cong Wang … Zhicheng Zhong* and Wei Ji* Phys. Rev. B 99, 144401 (2019) arXiv:1806.09274 PRB Editors’ Suggestion
Few-layer Tellurium: one-dimensional-like layered elementary semiconductor with striking physical properties Jingsi Qiao, Yuhao Pan, Feng Yang, Cong Wang, Yang Chai and Wei Ji* Sci. Bull. 63(3), 159-168 (2018)
Advanced exfoliation techniques are crucial for exploring the intrinsic properties and applications of 2D materials. Though the recently discovered Au-enhanced exfoliation technique provides an effective strategy for the preparation of large-scale 2D crystals, the high cost of gold hinders this method from being widely adopted in industrial applications. In addition, direct Au contact could significantly quench photoluminescence (PL) emission in 2D semiconductors. It is therefore crucial to find alternative metals that can replace gold to achieve efficient exfoliation of 2D materials. Here, the authors present a one-step Ag-assisted method that can efficiently exfoliate many large-area 2D monolayers, where the yield ratio is comparable to Au-enhanced exfoliation method. Differing from Au film, however, the surface roughness of as-prepared Ag films on SiO2/Si substrate is much higher, which facilitates the generation of surface plasmons resulting from the nanostructures formed on the rough Ag surface. More interestingly, the strong coupling between 2D semiconductor crystals (e.g., MoS2, MoSe2) and Ag film leads to a unique PL enhancement that has not been observed in other mechanical exfoliation techniques, which can be mainly attributed to enhanced light-matter interaction as a result of extended propagation of surface plasmonic polariton (SPP). This work provides a lower-cost and universal Ag-assisted exfoliation method, while at the same time offering enhanced SPP-matter interactions. DOI:10.1002/advs.202204247
Abstract: Magnetic topological insulators (MTIs) have received considerable attention owing to the demonstration of various quantum phenomena, such as the quantum anomalous Hall effect and topological magnetoelectric effect. The intrinsic superlatticelike layered MTIs MnBi2Te4/(Bi2Te3)n have been extensively investigated mainly through transport measurements; however, a direct investigation of their superlattice-sensitive magnetic behaviors is relatively rare. In this paper, we report a microscopic real space investigation of the magnetic phase behaviors in MnBi4Te7 using cryogenic magnetic force microscopy. The intrinsic robust A type antiferromagnetic (AFM), surface spin-flip (SSF) + AFM, ferromagnetic (FM) + SSF + AFM, and forced FM phases are sequentially visualized via the increased external magnetic field, consistent with the magnetic behavior in the M-H curve. The temperature-dependent magnetic phase evolution behaviors are further investigated to obtain a complete H-T phase diagram of MnBi4Te7. Tentative local phase manipulation via the stray field of the magnetic tip is demonstrated by transforming the AFM into the FM phase in the surface layers of MnBi4Te7. Our study provides key real-space ingredients for understanding the complicated magnetic, electronic, and topological properties of such intrinsic MTIs and suggests new directions for manipulating spin textures and locally controlling their exotic properties.
