Jiuxiang Dai

We report a deterministic 2D material (2DM) transfer method to assemble any-stacking-order heterostructures incorporating suspended ultra-thin 2DMs, such as single-layer graphene (SLG) and bilayer graphene (BLG). The transfer procedure relies on a single-step preparation nitrocellulose micro-stamp, which combines both outstanding adhesion and softness. It permits the dry pick-up of naked 2D crystals (graphene, MoS 2 , and hBN) directly from a SiO 2 substrate, and to precisely transfer them on substrates or trenches. Optical and Raman data show that no significant defect is introduced upon transfer, even in suspended SLG and BLG. The areas transferred range up ∼1000 µ m 2 on substrate. High-yield transfer of suspended ultra-thin 2DMs does not require critical point drying for areas up to 15 µ m 2 or suspension heights down to 160 nm. To demonstrate the method’s capabilities, we assembled on-substrate and suspended optical cavities...

By first-principles molecular dynamics, this work proposes a phase change memory (PCM) process at the 2D limit that is achieved in a monolayer Sb₂Te₃ for the first time. This will be a potential strategy for improving the performance of PCM technology to realize high integrated density, fast speed, low power consumption, or even artificial intelligence applications.

Abstract

One central task of developing nonvolatile phase change memory (PCM) is to improve its scalability for high-density data integration. In this work, by first-principles molecular dynamics, to date the thinnest PCM material possible (0.8 nm), namely, a monolayer Sb₂Te₃, is proposed. Importantly, its SET (crystallization) process is a fast one-step transition from amorphous to hexagonal phase without the usual intermediate cubic phase. An increased spatial localization of electrons due to geometrical confinement is found to be beneficial for keeping the data nonvolatile in the amorphous phase at the 2D limit. The substrate and superstrate can be utilized to control the phase change behavior: e.g., with passivated SiO₂ (001) surfaces or hexagonal Boron Nitride, the monolayer Sb₂Te₃ can reach SET recrystallization in 0.54 ns or even as fast as 0.12 ns, but with unpassivated SiO₂ (001), this would not be possible. Besides, working with small volume PCM materials is also a natural way to lower power consumption. Therefore, the proposed PCM working process at the 2D limit will be an important potential strategy of scaling the current PCM materials for ultrahigh-density data storage.

In article number 2007768, a cathodic exfoliation method for scalable production of two-dimensional tellurium (Te) is described by Lawrence Yoon Suk Lee and co-workers. Te crystals are exfoliated to Te nanosheets at a low potential with simultaneous transition metal doping as single-atom electrocatalysts. The Pt-doped Te nanosheet exhibits high catalytic activity toward H₂ production via a collaborative mechanism between Te and Pt atoms.

Selective nitric oxide electroreduction to ammonia is an efficient pathway to solve the nitrogen oxide air pollution problem; it reveals that highly efficient NORR toward NH₃ can be achieved on Ru₂B₂, Mo₂B₂, and Cr₂B₂ MBenes with low limiting potentials. In terms of selectivity, the highly limiting potentials prevent the formation of N₂, H₂, and N₂O.

Abstract

Here, the authors performed density functional theory calculations to study the catalytic performance of the nitric oxide reduction reaction (NORR) via a series of transition metal borides (MBenes). This work screened the M₂B₂ type MBenes from the IVB to V transition metals from the periodic table and systematically probed the catalytic activity and selectivity for the NORR process. It has been reported that Fe₂B₂, Mn₂B₂, and Rh₂B₂ can be high-performance catalysts for converting NO to NH₃ with smaller limiting potentials than other MBenes, and Nb₂B₂ and Hf₂B₂ have low limiting potentials of −0.11 V and −0.17 V for the NO production of NH₃. The binding energy of ΔG*N can be a good descriptor of catalytic performance and is determined by the volcano plot of the rate-determining step. The reaction mechanisms for NO reduction to NH₃, N₂, and N₂O have been studied in detail, atomic *N can interact with another *N or one *NO molecule to form N₂ and N₂O via two successive hydrogenations. In this regard, *NO hydrogenation to *NOH has a lower formation energy than *HNO, and the MBenes have high selectivity for promoting the NORR and suppressing the hydrogen evolution reaction competition process.

Nature Nanotechnology, Published online: 06 May 2021; doi:10.1038/s41565-021-00887-3

Graphene promises long-distance transfer of spin information with concomitant high charge carrier mobility. Proximity coupling of bilayer graphene with the 2D interlayer antiferromagnetic CrSBr now enables active generation of spin currents in graphene both electrically and thermally.

npj 2D Materials and Applications, Published online: 14 May 2021; doi:10.1038/s41699-021-00230-3

Resolving few-layer antimonene/graphene heterostructures

npj 2D Materials and Applications, Published online: 14 May 2021; doi:10.1038/s41699-021-00235-y

Highly stable two-dimensional metal-carbon monolayer with interpenetrating honeycomb structures

The intercalation of layered materials produces a rich class of materials with tunable structural and electronic properties for both fundamental studies and practical technologies. The key intercalation methods for preparing layered intercalation materials are summarized, the associated modulation of multiple properties is reviewed, and further prospects regarding the future challenges and opportunities in layered intercalation materials are considered.

Abstract

2D layered materials typically feature strong in-plane covalent chemical bonding within each atomic layer and weak out-of-plane van der Waals (vdW) interactions between adjacent layers. The non-bonding nature between neighboring layers naturally results in a vdW gap, in which various foreign species may be inserted without breaking the in-plane covalent bonds. By tailoring the composition, size, structure, and electronic properties of the intercalated guest species and the hosting layered materials, an expansive family of layered intercalation materials may be produced with highly variable compositional and structural features as well as widely tunable physical/chemical properties, invoking unprecedented opportunities in fundamental studies of property modulation and potential applications in diverse technologies, including electronics, optics, superconductors, thermoelectrics, catalysis, and energy storage. Here, the principles and protocols for various intercalation methods, including wet chemical intercalation, gas-phase intercalation, electrochemical intercalation, and ion-exchange intercalation, are comprehensively reviewed and how the intercalated species alter the crystal structure and the interlayer coupling of the host 2D layered materials, introducing unusual physical and chemical properties and enabling devices with superior performance or unique functions, is discussed. To conclude, a brief summary on future research opportunities and emerging challenges in the layered intercalation materials is given.

Nature, Published online: 12 May 2021; doi:10.1038/s41586-021-03472-9

Electric contacts of semimetallic bismuth on monolayer semiconductors are shown to suppress metal-induced gap states and thus have very low contact resistance and a zero Schottky barrier height.

Nature Materials, Published online: 10 May 2021; doi:10.1038/s41563-021-01001-7

Centimetre-scale growth of few-layer black phosphorous with high crystalline quality and homogeneity is realized by pulsed laser deposition.

Flexible, transparent, and thermally stable gas barrier films are required to seal organic-based ultra-thin, flexible, and transparent electronic devices against moisture. Thermally stable, two-dimensional hexagonal boron nitride (hBN) is an ideal non-gas-permeable material with high transparency and flexibility. Nevertheless, the polycrystalline multilayer hBN (m-hBN) grown on a rough Fe foil by chemical vapor deposition is not sufficient for use as a gas barrier due to the non-uniformity and discontinuity of the film. Here, we report a novel method for synthesizing highly uniform and continuous m-hBN films on smooth Fe foil on a wafer scale via deposition of an amorphous Fe layer on a rough Fe foil. The amorphous Fe layer on a unary Fe foil is effectively recrystallized to become a smooth surface via post-thermal annealing treatment at 1100 °C. The smoothed surface allows for the uniform precipitation of B and N atoms to form a highly continuous m-hBN film, as confirmed by cro...

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 ...