zemin zheng

The graphene-like 2D III-nitride semiconductor materials have unique physical properties such as high stability, wide and tunable bandgap, and magnetism, etc. Those advantages prove them to be useful in optoelectronic, electronic, and spin-based devices and so on. The pro perties, growth methods, and applications of graphene-like 2D III-nitride materials are introduced and reviewed.

Abstract

2D III-nitride materials have been receiving considerable attention recently due to their excellent physicochemical properties, such as high stability, wide and tunable bandgap, and magnetism. Therefore, 2D III-nitride materials can be applied in various fields, such as electronic and photoelectric devices, spin-based devices, and gas detectors. Although the developments of 2D h-BN materials have been successful, the fabrication of other 2D III-nitride materials, such as 2D h-AlN, h-GaN, and h-InN, are still far from satisfactory, which limits the practical applications of these materials. In this review, recent advances in the properties, growth methods, and potential applications of 2D III-nitride materials are summarized. The properties of the 2D III-nitride materials are mainly obtained by first-principles calculations because of the difficulties in the growth and characterizations of these materials. The discussion on the growth of 2D III-nitride materials is focused on 2D h-BN and h-AlN, as the developments of 2D h-GaN and h-InN are yet to be realized. Therefore, applications have been realized mostly based on the 2D h-BN materials; however, many potential applications are cited for the entire range of 2D III-nitride materials. Finally, future research directions and prospects in this field are also discussed.

Hexagonal boron nitride (h-BN) is an exciting two dimensional dielectric due to its atomic flatness, free of dangling bonds, exceptional thermal and chemical stabilities. Here we report a method of silicon-assisted synthesis of monolayer h-BN on germanium (Ge) by chemical vapor deposition. The silicon atoms dissolve into Ge (110) and promote the growth of h-BN domains by formation of Si–N bonds. The oxidation dynamic shows that monolayer h-BN film is a high-performance passivation layer, preserving Ge from oxidation in air at high temperature. This work sheds lights on the outstanding oxidation resistance of h-BN for further Ge-based electronic devices.

The tape exfoliation method is still the easiest and most convenient way to obtain large-area two-dimensional (2D) monolayers in experimental research. Recently, there are some important advances in tape exfoliation method for large 2D monolayer materials. This review mainly introduced three kinds of new tape exfoliation methods including modified Scotch tape exfoliation method, metal-assisted tape exfoliation method and gel-assisted tape exfoliation method. We highlight the operation process and exfoliated mechanism of each method. We point out several problems to be solved and give an outlook on the development direction of the new tape exfoliation method. We hope this review will help researchers, especially for beginners, quickly and easily obtain a variety of 2D monolayers for their own experiments.

Nature Communications, Published online: 26 May 2021; doi:10.1038/s41467-021-23310-w

Superconductivity often appears due to suppression of competing electronic orders. Here, the authors present a contrary example showing a superconducting dome inside the parent phase with a stripe charge order in IrTe2 nanoflakes and identify their unusual superconducting properties.

Nature Communications, Published online: 27 May 2021; doi:10.1038/s41467-021-23435-y

A 3D quantum Hall effect has been reported in Dirac semimetal ZrTe5 due to a magnetic-field-driven Fermi surface instability. Here, the authors show evidence of quasi-quantized Hall response without Fermi surface instability, but they argue that it is due to the interplay of the intrinsic properties of ZrTe5 electronic structure and Dirac semi-metallic character.

Nature Communications, Published online: 14 May 2021; doi:10.1038/s41467-021-23476-3

Author Correction: Direct observation of excitonic instability in Ta₂NiSe₅

Nature Communications, Published online: 11 May 2021; doi:10.1038/s41467-021-22906-6

Chiral superconductors are predicted to realize Majorana normal fluid at its boundary, but remain elusive experimentally. Here, Bae et al. report anomalous surface normal fluid response in UTe2 single crystal which is further attributed to a chiral spin-triplet pairing state.

Nature Communications, Published online: 10 May 2021; doi:10.1038/s41467-021-23418-z

Author Correction: Direct identification of Mott Hubbard band pattern beyond charge density wave superlattice in monolayer 1T-NbSe₂

Magnetic anisotropy is an important characteristic of magnetic materials. Particularly, perpendicular magnetic anisotropy (PMA) is superior for the design of spintronic devices, with the advantages of scalability, endurance, thermal stability, and low switching current density. Although a series of two-dimensional (2D) or quasi-2D layered ferromagnets have been demonstrated, the room temperature intrinsic ferromagnets with PMA is rarely found. Here, we report PMA in a room-temperature layered ferromagnet of Cr-intercalated CrTe 2 . By self-intercalation of the native Cr atoms, the in-plane anisotropy of CrTe 2 can be switched to PMA. Meanwhile, the Cr-intercalated CrTe 2 crystal can be easily exfoliated into thin flakes with thickness ∼10 nm. Besides the robust PMA at room temperature, Cr-intercalated CrTe 2 also exhibits high saturation magnetization (208 emu cm −3 at 300 K), large anomalous Hall angle (2.23% at 300 K) and giant ...

We report about the investigation of twisted MoSe 2 homo- and MoSe 2 –WSe 2 heterobilayers by means of low-frequency Raman spectroscopy (LFRS) and low-temperature micro photoluminescence ( µ PL). In room-temperature LFRS experiments on both, twisted MoSe 2 homobilayers and twisted MoSe 2 –WSe 2 heterobilayers, we observe moiré phonons, i.e. folded acoustic phonon modes due to the moiré superlattice. In the heterobilayers, we can identify moiré phonons of both materials, MoSe 2 and WSe 2 . While the twist angles for the homobilayers are relatively precisely known from the applied tear-and-stack preparation method, the twist angles of the heterobilayers have to be determined via second-harmonic-generation microscopy on monolayer regions of the samples, which has significant uncertainties. We show that by the moiré phonons of the heterobilayers, the relative twist angles can be determined on a local s...

Hafnium pentatelluride (Hf Te 5 ) is a layered two-dimensional material with various exotic properties. It is thought to be a topological insulator. Whereas bulk Hf Te 5 has a small band gap, single layers are predicted to be a quantum spin hall insulator with a large band gap. Here we measured band gap energies for samples with varying thicknesses and found a clear increase of gap energies for the thinner samples. With decreasing thickness an increase of the measured band gap energies from 40 to 304 meV is observed.

Semiconducting two-dimensional (2D) materials-based devices usually exhibit inferior electrical performance compared to their theoretical predictions, which is mainly attributed to the presence of high density of interfacial defect induced trap states within the bandgap of 2D materials. It is pertinent to control the density of interface traps ( D it ) and identify their respective energy levels inside the band gap of the 2D materials to understand the tailored device performance. Here, we report the large modulation of D it by electrical gating and varying the channel thickness of tungsten diselenide (WSe 2 ) placed on ultra-clean hexagonal boron nitride (hBN) gate insulator in a metal–insulator–semiconductor structure, which is revealed by performing multi-frequency capacitance and conductance measurements. Analysis of the 2D hBN/WSe 2 interface reveals that with the increase of WSe 2 thickness, D it

We study the origin of in-plane ferromagnetism in monolayer VSe 2 focusing on the effect of charge doping and mechanical strain. We start from an anisotropic spin Hamiltonian, estimate its parameters from density functional calculations, and determine the spectrum of spin-wave excitations. We show that 1T-VSe 2 is characterized by relatively strong on-site Coulomb repulsion ( U  ≃ 5 eV), favoring an antiferromagnetic ground state, which contradicts experimental observations. We calculate the magnetic phase diagram as a function of charge doping and strain, and find a transition to the ferromagnetic state with in-plane easy axis under moderate hole doping (∼10 14 cm −2 ). Analysis of spin-wave excitations in doped monolayer VSe 2 reveals a gap due to the in-plane anisotropy, giving rise to long-range magnetic order well above 300 K, in agreement with recent experiments. Our findings suggest that experimentally available 1T-VSe...

Nature Communications, Published online: 04 May 2021; doi:10.1038/s41467-021-22711-1

Twisted double bilayer graphene is a novel van der Waals system that hosts an electric-field-tunable correlated state at half-filling. Here the authors reveal the delocalized nature of this state by scanning tunnelling microscopy and spectroscopy, suggesting an underlying mechanism of symmetry breaking driven by non-local exchange.

Two-dimensional (2D) materials offer opportunities to explore both fundamental science and applications in the limit of atomic thickness. Beyond the prototypical case of graphene, other 2D materials have recently come to the fore. Of particular technological interest are 2D semiconductors, of which the family of materials known as the group-VI transition metal dichalcogenides (TMDs) has attracted much attention. The presence of a bandgap allows for the fabrication of high on–off ratio transistors and optoelectronic devices, as well as valley/spin polarized transport. The technique of chemical vapor deposition (CVD) has produced high-quality and contiguous wafer-scale 2D films, however, they often need to be transferred to arbitrary substrates for further investigation. In this review, the various transfer techniques developed for transferring 2D films will be outlined and compared, with particular emphasis given to CVD-grown TMDs. Each technique suffers undesirable process-relat...

Single-crystal copper substrates have gained importance for the preparation of high-quality graphene and hexagonal boron nitride monolayer films by chemical vapor deposition (CVD). Especially, large-scale single-crystal copper foils with high-index planes are synthesized recently and attract great interests. However, the current synthesis methods of single-crystal copper foils and films are energy and time-consuming. Here, we show a rapid and efficient approach for the preparation of centimeter-scale single-crystal copper foils by making small incisions at the edges of polycrystalline copper foils before high-temperature annealing. 1.5 cm × 4 cm pieces of grain-boundary-free copper foils can be prepared by annealing at 1080 °C for 60 min. The annealed copper foil manifests a single high-index plane and is grain-boundary-free over the whole area. We also show that CVD of graphene on the high-index single-crystal copper affords a higher growth rate than on low-index copper substra...

We combine synchrotron-based near-field infrared spectroscopy and first principles lattice dynamics calculations to explore the vibrational response of CrPS 4 in bulk, few-, and single-layer form. Analysis of the mode pattern reveals a C 2 polar + chiral space group, no symmetry crossover as a function of layer number, and a series of non-monotonic frequency shifts in which modes with significant intralayer character harden on approach to the ultra-thin limit whereas those containing interlayer motion or more complicated displacement patterns soften and show inflection points or steps. This is different from MnPS 3 where phonons shift as 1/size 2 and are sensitive to the three-fold rotation about the metal center that drives the symmetry crossover. We discuss these differences as well as implications for properties such as electric polarization in terms of presence or absence of the P–P dimer and other aspects of local structure, sheet density,...

Nature Communications, Published online: 21 April 2021; doi:10.1038/s41467-021-22681-4

Precisely regulating Pt catalytic sites is important and challenging. Herein the authors engineer the clustering of single atomic Te vacancies in atomically thin PtTe2 to optimize the electronic structure, adsorption energy, and catalytic performance of atomically defined Pt sites.