Conversion of chirality to twisting via sequential one-dimensional and two-dimensional growth of graphene spirals

Conversion of chirality to twisting via sequential one-dimensional and two-dimensional growth of graphene spirals

Nature Materials 23, 331–338 (2024).

Zhu-Jun Wang#,*, Xiao Kong#, Yuan Huang#, Jun Li#, Lihong Bao, Kecheng Cao, Yuxiong Hu, Jun Cai, Lifen Wang, Hui Chen, Yueshen Wu, Yiwen Zhang, Fei Pang, Zhihai Cheng, Petr Babor, Miroslav Kolibal, Zhongkai Liu, Yulin Chen, Qiang Zhang, Yi Cui, Kaihui Liu, Haitao Yang, Xinhe Bao, Hong-Jun Gao, Zhi Liu, Wei Ji*, Feng Ding* & Marc-Georg Willinger*

Abstract:

The properties of two-dimensional (2D) van der Waals materials can be tuned through nanostructuring or controlled layer stacking, where interlayer hybridization induces exotic electronic states and transport phenomena. Here we describe a viable approach and underlying mechanism for the assisted self-assembly of twisted layer graphene. The process, which can be implemented in standard chemical vapour deposition growth, is best described by analogy to origami and kirigami with paper. It involves the controlled induction of wrinkle formation in single-layer graphene with subsequent wrinkle folding, tearing and re-growth. Inherent to the process is the formation of intertwined graphene spirals and conversion of the chiral angle of 1D wrinkles into a 2D twist angle of a 3D superlattice. The approach can be extended to other foldable 2D materials and facilitates the production of miniaturized electronic components, including capacitors, resistors, inductors and superconductors.

DOI: 10.1038/s41563-023-01632-y

Also See: News & Views – A double-helix dislocation in graphene | Nature Materials
Also See: Focus – Constructing 2D moiré and chiral materials | Nature Materials

Room-temperature ferromagnetism in Fe-doped SnSe bulk single crystalline semiconductor

Room-temperature ferromagnetism in Fe-doped SnSe bulk single crystalline semiconductor

Materials Today Physics 38,101251 (2023)
Guangqiang Mei, Wei Tan, Xingxia Cui, Cong Wang, Qing Yuan, Yafei Li, Cancan Lou, Xuefeng Hou, Mengmeng Zhao, Yong Liu, Wei Ji, Xiaona Zhang, Min Feng*, Limin Cao*

The quest for pragmatic room-temperature (RT) magnetic semiconductors (MSs) with a suitable bandgap constitutes one of the contemporary opportunities to be exploited. This may provide a materials platform for to bring new-generation ideal information device technologies into real-world applications where the otherwise conventionally separately utilized charge and spin are simultaneously exploited. Here we present RT ferromagnetism in an Fe-doped SnSe (Fe:SnSe) van der Waals (vdW) single crystalline ferromagnetic semiconductor (FMS) with a semiconducting bandgap of ∼1.19 eV (comparable to those of Si and GaAs). The synthesized Fe:SnSe single crystals feature a dilute Fe content of <1.0 at%, a Curie temperature of ∼310 K, a layered vdW structure nearly identical to that of pristine SnSe, and the absence of in-gap defect states. The Fe:SnSe vdW diluted magnetic semiconductor (DMS) single crystals are grown using a simple temperature-gradient melt-growth process, in which the magnetic Fe atom doping is realized uniquely using FeI2 as the dopant precursor whose melting point is low with respect to crystal growth, and which in principle possesses industrially unlimited scalability. Our work adds a new member in the family of long-searching RT magnetic semiconductors, and may establish a generalized strategy for large-volume production of related DMSs.

Intralayer Negative Poisson’s Ratio in 2D Black Arsenic by Strain Engineering

Intralayer Negative Poisson’s Ratio in 2D Black Arsenic by Strain Engineering

Small Strucutures (2023), DOI: 10.1002/sstr.202300178

Jingjing Zhang#, Weihan Zhang#, Leining Zhang#, Guoshuai Du, Yunfei Yu, Qinglin Xia, Xu Wu, Yeliang Wang, Wei Ji, Jingsi Qiao*, Feng Ding*, Yabin Chen*

Abstract:

Negative Poisson’s ratio as the anomalous characteristic generally exists in artificial architectures, such as re-entrant and honeycomb structures. The structures with negative Poisson’s ratio have attracted intensive attention due to their unique auxetic effect and many promising applications in shear-resistant and energy absorption fields. However, experimental observation of negative Poisson’s ratio in natural materials barely happens, although various 2D layered materials are predicted in theory. Herein, the anisotropic Raman response and the intrinsic intralayer negative Poisson’s ratio of 2D natural black arsenic (b-As) via strain engineering strategy are reported. The results are evident by the detailed Raman spectrum of b-As under uniaxial strain together with density functional theory calculations. It is found that b-As is softer along the armchair than zigzag direction. The anisotropic mechanical features and van der Waals interactions play essential roles in strain-dependent Raman shifts and negative Poisson’s ratio in the natural b-As along zigzag direction. This work may shed a light on the mechanical properties and potential applications of 2D puckered materials.

DOI: 10.1002/sstr.202300178

Achieving a Large Energy Gap in Bi(110) Atomically Thin Films

Achieving a Large Energy Gap in Bi(110) Atomically Thin Films

Small Structures 4, 2300207 (2023).

Qing Yuan#, Yafei Li#, Deping Guo, Cancan Lou, Xingxia Cui, Guangqiang Mei, Chengxiang Jiao, Kai Huang, Xuefeng Hou, Wei Ji*, Limin Cao*, Min Feng*

Abstract:

Metal–insulator transition has long been one of the key subjects in condensed matter systems. Herein, the emergence of a large energy gap (Eg, 0.8–1.0 eV) in Bi(110) two-atomic-layer nanoribbons grown on a SnSe(001) substrate is reported, which normally has an intrinsic semimetal-like characteristic. The existence of this abnormally large Eg in Bi(110) is, however, determined by Bi coverage. When coverage is above ≈64 ± 2%, Eg vanishes, and instead, a Bi(110) semimetal-like phase appears through a singular insulator–metal transition. Measurements using qPlus atomic force microscopy demonstrate that either insulating or semimetal-like Bi(110) possesses a distorted black phosphorous structure with noticeable atomic buckling. Density function theory fully reproduces the semimetal-like Bi(110) on SnSe(001). However, none of the insulating phases with this large Eg could be traced. Although the underlying mechanism of the large Eg and the insulator-metal transition requires further exploration, experiments demonstrate that similar results can be achieved for Bi grown on SnS, the structural analog of SnSe, exhibiting an even larger Eg of ≈2.3 eV. The experimental strategy may be generalized to utilization of group-IV monochalcogenides to create Bi(110) nanostructures with properties unachievable on other surfaces, providing an intriguing platform for exploring the interesting quantum electronic phases.

DOI: 10.1002/sstr.202300207

Layer Sliding And Twisting Induced Electronic Transitions In Correlated Magnetic 1t-Nbse2 Bilayers

Layer Sliding And Twisting Induced Electronic Transitions In Correlated Magnetic 1t-Nbse2 Bilayers

Advanced Functional Materials 33, 2302989 (2023)

Jiaqi Dai#, Jingsi Qiao#, Cong Wang, Linwei Zhou, Xu Wu, Liwei Liu, Xuan Song, Fei Pang, Zhihai Cheng, Xianghua Kong, Yeliang Wang*, Wei Ji*

Abstract:

Correlated 2D layers, like 1T-phases of TaS2, TaSe2, and NbSe2, exhibit rich tunability through varying interlayer couplings, which promotes the understanding of electron correlation in the 2D limit. However, the coupling mechanism is, so far, poorly understood and is tentatively ascribed to interactions among the dz2 orbitals of Ta or Nb atoms. Here, it is theoretically shown that the interlayer hybridization and localization strength of interfacial Se pz orbitals, rather than Nb dz2 orbitals, govern the variation of electron-correlated properties upon interlayer sliding or twisting in correlated magnetic 1T-NbSe2 bilayers. Each of the layers is in a star-of-David (SOD) charge-density-wave phase. Geometric and electronic structures and magnetic properties of 28 different stacking configurations are examined and analyzed using density-functional-theory calculations. It is found that the SOD contains a localized region, in which interlayer Se pz hybridization plays a paramount role in varying the energy levels of the two Hubbard bands. These variations lead to three electronic transitions among four insulating states, which demonstrate the effectiveness of interlayer interactions to modulate correlated magnetic properties in a prototypical correlated magnetic insulator.

DOI: 10.1002/adfm.202302989