Pingfan Gu, Yujia Sun, Cong Wang, Yuxuan Peng, Yaozheng Zhu, Xing Cheng, Kai Yuan, Chao Lyu, Xuelu Liu, Qinghai Tan, Qinghua Zhang, Lin Gu, Zhi Wang, Hanwen Wang, Zheng Han, Kenji Watanabe, Takashi Taniguchi, Jinbo Yang, Jun Zhang, Wei Ji, Ping-Heng Tan & Yu Ye
Abstract
Materials with a quasi-one-dimensional stripy magnetic order often exhibit low crystal and magnetic symmetries, thus allowing the presence of various energy coupling terms and giving rise to macroscopic interplay between spin, charge, and phonon. In this work, we performed optical, electrical and magnetic characterizations combined with first-principles calculations on a van der Waals antiferromagnetic insulator chromium oxychloride (CrOCl). We detected the subtle phase transition behaviors of exfoliated CrOCl under varying temperature and magnetic field and clarified its controversial spin structures. We found that the antiferromagnetism and its air stability persist down to few-layer samples, making it a promising candidate for future 2D spintronic devices. Additionally, we verified the magnetoelastic coupling effect in CrOCl, allowing for the potential manipulation of the magnetic states via electric field or strain. These virtues of CrOCl provide us with an ideal platform for fundamental research on spin-charge, spin-phonon coupling, and spin-interactions.
Jun Zhang, Linwei Zhou, Pengcheng Chen, Bingkai Yuan, Zhihai Cheng, Wei Ji & Xiaohui Qiu
Abstract
Catalytic bond cleavage and formation of transient intermediates on metal substrates play an essential role in surface synthesis and heterogeneous catalysis. Previous studies usually focus on the bond-breaking process, whereas the knowledge regarding the construction of dissociative moieties that lead to the final products is limited. Here, we investigate the facet-selective dissociation of dibenzotetrathiafulvalene (DBTTF) molecules on Cu(110) and Cu(100) surfaces using low-temperature scanning tunneling microscopy and first-principles calculations. Atomic resolution images enable the identification of various intermediates and reaction pathways on different facets. The dissociation of DBTTF molecules generated 1,2-BDT–Cu complex chains on Cu(110), while phenyl diradical superstructure islands were observed on Cu(100). The various chemical species found on different Cu facets were explained in the context of their formation energies related to the spatial inhomogeneity of surface electronic states. Our results address the effects of electronic and geometrical diversities on the surface mobility of intermediate products and subsequent on-surface reaction pathways.
Intrinsic antiferromagnetism in van der Waals (vdW) monolayer (ML) crystals enriches our understanding of two-dimensional (2D) magnetic orders and presents several advantages over ferromagnetism in spintronic applications. However, studies of 2D intrinsic antiferromagnetism are sparse, owing to the lack of net magnetisation. Here, by combining spin-polarised scanning tunnelling microscopy and first-principles calculations, we investigate the magnetism of vdW ML CrTe2, which has been successfully grown through molecular-beam epitaxy. We observe a stable antiferromagnetic (AFM) order at the atomic scale in the ML crystal, whose bulk is ferromagnetic, and correlate its imaged zigzag spin texture with the atomic lattice structure. The AFM order exhibits an intriguing noncollinear spin reorientation under magnetic fields, consistent with its calculated moderate magnetic anisotropy. The findings of this study demonstrate the intricacy of 2D vdW magnetic materials and pave the way for their in-depth analysis.
Ping Chen, Jinbo Pan, Wenchao Gao, Bensong Wan, Xianghua Kong, Yang Cheng, Kaihui Liu, Shixuan Du, Wei Ji, Caofeng Pan & Zhong Lin Wang
Abstract
Transition metal dichalcogenides (TMDCs) with 2H phase are expected to be building blocks in next-generation electronics; however, they suffer from electrical anisotropy, which is the basics for multi-terminal artificial synaptic devices, digital inverters, and anisotropic memtransistors, which are highly desired in neuromorphic computing. Herein, the anisotropic carrier mobility from 2H WSe2 is reported, where the anisotropic degree of carrier mobility spans from 0.16 to 0.95 for various WSe2 field-effect transistors under a gate voltage of −60 V. Phonon scattering, impurity ions scattering, and defect scattering are excluded for anisotropic mobility. An intrinsic screening layer is proposed and confirmed by Z-contrast scanning transmission electron microscopy (STEM) imaging to respond to the electrical anisotropy. Seven types of intrinsic screening layers are created and calculated by density functional theory to evaluate the modulated electronic structures, effective masses, and scattering intensities, resulting in anisotropic mobility. The discovery of anisotropic carrier mobility from 2H WSe2 provides a degree of freedom for adjusting the physical properties of 2H TMDCs and fertile ground for exploring and integrating TMDC electronic transistors with better performance along the direction of high mobility.
Yanping Guo, Linlu Wu, Jinghao Deng, Linwei Zhou, Wei Jiang, Shuangzan Lu, Da Huo, Jiamin Ji, Yusong Bai, Xiaoyu Lin, Shunping Zhang, Hongxing Xu, Wei Ji & Chendong Zhang
Abstract
Semiconducting heterojunctions (HJs), comprised of atomically thin transition metal dichalcogenides (TMDs), have shown great potentials in electronic and optoelectronic applications. Organic/TMD hybrid bilayers hold enhanced pumping efficiency of interfacial excitons, tunable electronic structures and optical properties, and other superior advantages to these inorganic HJs. Here, we report a direct probe of the interfacial electronic structures of a crystalline monolayer (ML) perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA)/ML-WSe2 HJ using scanning tunneling microscopy, photoluminescence, and first-principle calculations. Strong PTCDA/WSe2 interfacial interactions lead to appreciable hybridization of the WSe2 conduction band with PTCDA unoccupied states, accompanying with a significant amount of PTCDA-to-WSe2 charge transfer (by 0.06 e/PTCDA). A type-II band alignment was directly determined with a valence band offset of ∼ 1.69 eV, and an apparent conduction band offset of ∼ 1.57 eV. Moreover, we found that the local stacking geometry at the HJ interface differentiates the hybridized interfacial states.
