Yunli Da (笪蕴力)†, Ruichun Luo (罗瑞春)†, Bao Lei (雷宝), Wei Ji (季威) and Wu Zhou (周武)*
Abstract:
The design and preparation of novel quantum materials with atomic precision are crucial for exploring new physics and for device applications. Electron irradiation has been demonstrated as an effective method for preparing novel quantum materials and quantum structures that could be challenging to obtain otherwise. It features the advantages of precise control over the patterning of such new materials and their integration with other materials with different functionalities. Here, we present a new strategy for fabricating freestanding monolayer SiC within nanopores of a graphene membrane. By regulating the energy of the incident electron beam and the in-situ heating temperature in a scanning transmission electron microscope (STEM), we can effectively control the patterning of nanopores and subsequent growth of monolayer SiC within the graphene lattice. The resultant SiC monolayers seamlessly connect with the graphene lattice, forming a planar structure distinct by a wide direct bandgap. Our in-situ STEM observations further uncover that the growth of monolayer SiC within the graphene nanopore is driven by a combination of bond rotation and atom extrusion, providing new insights into the atom-by-atom self-assembly of freestanding two-dimensional (2D) monolayers.
Xiaocang Han, Mengmeng Niu, Yan Luo, Runlai Li, Jiadong Dan, Yanhui Hong, Xu Wu, Alex V. Trukhanov, Wei Ji, Yeliang Wang, Jiahuan Zhou, Jingsi Qiao*, Jin Zhang* & Xiaoxu Zhao*
Abstract:
Scanning probe microscopy and scanning transmission electron microscopy (STEM) are powerful tools to trigger atomic-scale motions, pattern atomic defects and lead to anomalous quantum phenomena in functional materials. However, these techniques have primarily manipulated surface atoms or atoms located at the beam exit plane, leaving buried atoms, which govern exotic quantum phenomena, largely unaffected. Here we propose an electron-beam-triggered chemical etching approach to engineer shielded metal atoms sandwiched between chalcogen layers in monolayer transition metal dichalcogenide (TMDC). Various metal vacancies (V_MX_n, n=0−6) have been fabricated via atomically focused electron beam in STEM. The parent TMDC surface was modified with surfactants, facilitating the ejection of sandwiched metal vacancies via charge transfer effect. In situ sequential STEM imaging corroborated that a combined chemical-induced knock-on effect and chalcogen vacancy-assisted metal diffusion process result in atom-by-atom vacancy formation. This approach is validated in 16 different TMDCs. The presence of metal vacancies strongly modified their magnetic and electronic properties, correlated with the unpaired chalcogen p and metal d electrons surrounding vacancies and adjacent distortions. These findings show a generic approach for engineering interior metal atoms with atomic precision, creating opportunities to exploit quantum phenomena at the atomic scale.
Zheng, Fangyuan; Guo, Deping; Huang, Lingli; Wong, Lok Wing; Chen, Xin; Wang, Cong; Cai, Yuan; Wang, Ning; Lee, Chun-Sing; Lau, Shu Ping; Ly, Thuc Hue; Ji, Wei and Zhao, Jiong
Abstract
Phase patterning in polymorphic two-dimensional (2D) materials offers diverse properties that extend beyond what their pristine structures can achieve. If precisely controllable, phase transitions can bring exciting new applications for nanometer-scale devices and ultra-large-scale integrations. Here, the focused electron beam is capable of triggering the phase transition from the semiconducting T” phase to metallic T’ and T phases in 2D rhenium disulfide (ReS2) and rhenium diselenide (ReSe2) monolayers, rendering ultra-precise phase patterning technique even in sub-nanometer scale is found. Based on knock-on effects and strain analysis, the phase transition mechanism on the created atomic vacancies and the introduced substantial in-plane compressive strain in 2D layers are clarified. This in situ high-resolution scanning transmission electron microscopy (STEM) and in situ electrical characterizations agree well with the density functional theory (DFT) calculation results for the atomic structures, electronic properties, and phase transition mechanisms. Grain boundary engineering and electrical contact engineering in 2D are thus developed based on this patterning technique. The patterning method exhibits great potential in ultra-precise electron beam lithography as a scalable top-down manufacturing method for future atomic-scale devices. DOI:10.1002/advs.202200702
Xiao-Wei Wang, Lin-Fang Hou, Wei Huang, Xi-Biao Ren, Wei Ji & Chuan-Hong Jin
Abstract
Defects play vital roles in tailoring structures and properties of materials including the atomically thin two-dimensional (2D) materials, and increasing demands are requested to find effective ways to realize the defect engineering, i.e., tuning the defects and thus the materials’ structure–property in a well-controlled way. Herein, we propose a novel method to tune the structures and configurations of one-dimensional (1D) line defects in monolayer MoS2 via mass transport induced structural transformation. By using atomic-resolved annular dark-field scanning transmission electron microscopy (ADF-STEM), we demonstrate in situ that sulfur vacancy line defect can be healed locally into defect-free MoS2 lattice via the desorption of Mo atoms from vacancy lines and adsorption into a moving Mo cluster. Furthermore, directional transport of Mo atoms (or Mo cluster) along the sulfur vacancy lines can induce the formation of Mo chains. Such a mass transport induced defect tuning provides more operational routes for the rational defect designing and property tuning in MoS2 as well as other related 2D materials.
