Jiuxiang Dai

The multi-metallene with an ultrahigh surface area has great potential in precise tuning of surface heterogeneous d-electronic correlation by surface strain effect for the distinctive surface electronic structure, which is a brand new class of promising 2D electrocatalyst for sustainable energy device application. However, achieving such an atomically thin multi-metallene still presents a great challenge. Herein, we present a new synthetic method for an atomic-level palladium-iridium (PdIr) bimetallene with an average thickness of only ∼1.0 nm for achieving superior catalysis in the hydrogen evolution reaction (HER) and the formic acid oxidation reaction (FAOR). The curved PdIr bimetallene presents a top-ranked high electrochemical active area of 127.5 ± 10.8 m² g_Pd+Ir⁻¹ in the reported noble alloy materials, and exhibits a very low overpotential, ultrahigh activity and improved stability for HER and FAOR. DFT calculation reveals that the PdIr bimetallene herein has a unique lattice tangential strain, which can induce surface distortion while concurrently creating a variety of concave-convex featured micro-active regions formed by variously coordinated Pd sites agglomeration. Such a strong strain effect correlates the abnormal on-site active 4d¹⁰-t_2g-orbital Coulomb correlation potential and directly elevates orbital-electronegativity exposure within these active regions, resulting in a preeminent barrier-free energetic path for significant enhancement of FAOR and HER catalytic performance.

Publication date: December 2021

Source: Materials Today, Volume 51

Author(s): Junwei Liu, Mengyuan Gao, Juhee Kim, Zhihua Zhou, Dae Sung Chung, Hang Yin, Long Ye

An extremely uniform graphene oxide thin film (UGTF) is fabricated via a new method that is based on preheating treatment, controlling the properties of the suspension and low electrical energy plasma treatment. UTGF can also be uniformly patterned at the microscale. This technique is effective in one-step micropatterning of antibodies and cancer cells.

Abstract

Graphene oxide (GO) has proven to be a highly promising material across various biomedical research avenues, including cancer therapy and stem cell-based regenerative medicine. However, creating a uniform GO coating as a thin layer on desired substrates has been considered challenging owing to the intrinsic variability of the size and shape of GO. Herein, a new method is introduced that enables highly uniform GO thin film (UGTF) fabrication on various biocompatible substrates. By optimizing the composition of the GO suspension and preheating process to the substrates, the “coffee-ring effect” is significantly suppressed. After applying a special postsmoothing process referred to as the low-oxygen concentration and low electrical energy plasma (LOLP) treatment, GO is converted to small fragments with a film thickness of up to several nanometers (≈5.1 nm) and a height variation of only 0.6 nm, based on atomic force microscopy images. The uniform GO thin film can also be generated as periodic micropatterns on glass and polymer substrates, which are effective in one-step micropatterning of both antibodies and mouse melanoma cells (B16-F10). Therefore, it can be concluded that the developed UGTF is useful for various graphene-based biological applications.

Materials with a 2D kagome crystal structure yield potential for a wide range of tunable topological and correlated electron phases. The emergence of local magnetic moments resulting from strong electron-electron Coulomb interactions in a 2D kagome metal–organic framework is demonstrated. These findings pave the way for tunable electron correlations—and hence controllable electronic and magnetic quantum phases—in 2D organic materials.

Abstract

2D and layered electronic materials characterized by a kagome lattice, whose valence band structure includes two Dirac bands and one flat band, can host a wide range of tunable topological and strongly correlated electronic phases. While strong electron correlations have been observed in inorganic kagome crystals, they remain elusive in organic systems, which benefit from versatile synthesis protocols via molecular self-assembly and metal-ligand coordination. Here, direct experimental evidence of local magnetic moments resulting from strong electron–electron Coulomb interactions in a 2D metal–organic framework (MOF) is reported. The latter consists of di-cyano-anthracene (DCA) molecules arranged in a kagome structure via coordination with copper (Cu) atoms on a silver surface [Ag(111)]. Temperature-dependent scanning tunneling spectroscopy reveals magnetic moments spatially confined to DCA and Cu sites of the MOF, and Kondo screened by the Ag(111) conduction electrons. By density functional theory and mean-field Hubbard modeling, it is shown that these magnetic moments are the direct consequence of strong Coulomb interactions between electrons within the kagome MOF. The findings pave the way for nanoelectronics and spintronics technologies based on controllable correlated electron phases in 2D organic materials.

Porous single-layer graphene membranes for gas separation are synthesized by one-step chemical vapor deposition (CVD). Highly dense gas-sieving pores are created in graphene by tuning the CVD parameters. The resulting graphene membranes exhibit record-high H₂/CH₄ separation performance to date: H₂/CH₄ selectivity > 2000 while H₂ permeance > 4000 GPU.

Abstract

Single-layer graphene containing molecular-sized in-plane pores is regarded as a promising membrane material for high-performance gas separations due to its atomic thickness and low gas transport resistance. However, typical etching-based pore generation methods cannot decouple pore nucleation and pore growth, resulting in a trade-off between high areal pore density and high selectivity. In contrast, intrinsic pores in graphene formed during chemical vapor deposition are not created by etching. Therefore, intrinsically porous graphene can exhibit high pore density while maintaining its gas selectivity. In this work, the density of intrinsic graphene pores is systematically controlled for the first time, while appropriate pore sizes for gas sieving are precisely maintained. As a result, single-layer graphene membranes with the highest H₂/CH₄ separation performances recorded to date (H₂ permeance > 4000 GPU and H₂/CH₄ selectivity > 2000) are fabricated by manipulating growth temperature, precursor concentration, and non-covalent decoration of the graphene surface. Moreover, it is identified that nanoscale molecular fouling of the graphene surface during gas separation where graphene pores are partially blocked by hydrocarbon contaminants under experimental conditions, controls both selectivity and temperature dependent permeance. Overall, the direct synthesis of porous single-layer graphene exploits its tremendous potential as high-performance gas-sieving membranes.

A 2D hafnium diselenide (HfSe₂) memristor crossbar array (CBA) is demonstrated via wafer-scale molecular beam epitaxy growth and metal-assisted van der Waals transfer techniques. The CBA enables artificial neural network with high recognition accuracy of 93.34%, and achieves hardware convolution image processing using energy-efficient multiply-and accumulate operations.

Abstract

Memristor crossbar with programmable conductance could overcome the energy consumption and speed limitations of neural networks when executing core computing tasks in image processing. However, the implementation of crossbar array (CBA) based on ultrathin 2D materials is hindered by challenges associated with large-scale material synthesis and device integration. Here, a memristor CBA is demonstrated using wafer-scale (2-inch) polycrystalline hafnium diselenide (HfSe₂) grown by molecular beam epitaxy, and a metal-assisted van der Waals transfer technique. The memristor exhibits small switching voltage (0.6 V), low switching energy (0.82 pJ), and simultaneously achieves emulation of synaptic weight plasticity. Furthermore, the CBA enables artificial neural network with a high recognition accuracy of 93.34%. Hardware multiply-and-accumulate (MAC) operation with a narrow error distribution of 0.29% is also demonstrated, and a high power efficiency of greater than 8-trillion operations per second per Watt is achieved. Based on the MAC results, hardware convolution image processing can be performed using programmable kernels (i.e., soft, horizontal, and vertical edge enhancement), which constitutes a vital function for neural network hardware.

The interface of liquid metals is used as natural filtering for doping and harvesting 2D doped metal oxide semiconductors. 2D Bi₂O₃-doped SnO semiconducting sheets are produced based on the different migration tendencies of Sn and Bi metals within the bulk competing for the selective enrichment of the liquid metal interface.

Abstract

The introduction of trace impurities within the doping processes of semiconductors is still a technological challenge for the electronics industries. By taking advantage of the selective enrichment of liquid metal interfaces, and harvesting the doped metal oxide semiconductor layers, the complexity of the process can be mitigated and a high degree of control over the outcomes can be achieved. Here, a mechanism of natural filtering for the preparation of doped 2D semiconducting sheets based on the different migration tendencies of metallic elements in the bulk competing for enriching the interfaces is proposed. As a model, liquid metal alloys with different weight ratios of Sn and Bi in the bulk are employed for harvesting Bi₂O₃-doped SnO nanosheets. In this model, Sn shows a much stronger tendency than Bi to occupy surface sites of the Bi–Sn alloys, even at the very high concentrations of Bi in the bulk. This provides the opportunity for creating SnO 2D sheets with tightly controlled Bi₂O₃ dopants. By way of example, it is demonstrated how such nanosheets could be made selective to both reducing and oxidizing environmental gases. The process demonstrated here offers significant opportunities for future synthesis and fabrication processes in the electronics industries.

Interpreting 2D Materials Bio-Nano Interactions

In article number 2100251, Khuloud T. Al-Jamal and co-workers demonstrate that the interpretation of bio-nano interactions for 2D nanomaterials requires extra care. Minor surface chemistry changes on 2D nanomaterials result in various serum protein binding levels, colloidal stabilities, and aggregation status in biological media. Thus, using label-free approaches such as Synchrotron radiation-based Fourier-transform infrared spectromicroscopy (SR-FTIR) provides an alternative gateway to study the bio-nano interfaces in the naïve form.

Porous-Graphene Single Layers on SI/SIO₂

Porous graphene is synthesized from oxo-functionalized graphene (oxoG), as reported in article number 2100783 by Siegfried Eigler and co-workers. The 3D atomic force microscopy image of oxoG with pores on the 100 nm scale looks like a mountain with ridges. The red pits represent the pores. The higher peaks around the pits represent the active sites, which are easily hit by lightning. The lightning has a two-fold meaning, the etching of pores and the enhancement of photoluminescence of MoS₂ by the porous graphene.

Nature Communications, Published online: 10 September 2021; doi:10.1038/s41467-021-25656-7

Room-temperature exciton polaritons in a monolayer WS2 are shown to display strong motional narrowing of the linewidth and enhanced first-order coherence. They can propagate for tens of micrometers while maintaining partial coherence, and display signatures of ballistic (dissipationless) transport.

This review summarizes the latest research related to the strategies to fabricate the metal halide perovskites@metal oxide (MHPs@MO _x ) composites, techniques to systematically evaluate the performances, and structures of the composites. Recent achievements in various applications are also presented based on different MO _x . Finally, conclusions and future research prospects are also outlined to ensure a bright future of MHPs@MO _x .

Abstract

Metal halide perovskites (MHPs) have become a promising candidate in a myriad of applications, such as light-emitting diodes, solar cells, lasing, photodetectors, photocatalysis, transistors, etc. This is related to the synergy of their excellent features, including high photoluminescence quantum yields, narrow and tunable emission, long charge carrier lifetimes, broad absorption spectrum along with high extinction absorptions coefficients, among others. However, the main bottleneck is the poor stability of the MHPs under ambient conditions. This is imposing severe restrictions with respect to their industrialized applications and commercialization. In this context, metal oxide (MO _x ) coatings have recently emerged as an efficient strategy toward overcoming the stabilities issues as well as retaining the excellent properties of the MHPs, and therefore facilitate the development of the related devices’ stabilities and performances. This review provides a summary of the recent progress on synthetic methods, enhanced features, the techniques to assess the MHPs@MO _x composites, and applications of the MHPs@MO _x . Specially, novel approaches to fabricate the composites and new applications of the composites are also reported in this review for the first time. This is rounded by a critical outlook about the current MHPs’ stability issues and the further direction to ensure a bright future of MHPs@MO _x .

A graphdiyne (GDY)/MoS₂ bilayer memory without any blocking layer is constructed. Through controllable oxygen plasma treatment, relatively large-area and smooth 2D GDY with additionally introduced CO and C═O is obtained, which enables excellent van der Waals coupling with MoS₂ and allows for constructing the bilayer memory. With more introduced states, multilevel and dual operating mode is achieved.

Abstract

Direct charge trapping memory, a new concept memory without any dielectric, has begun to attract attention. However, such memory is still at the incipient stage, of which the charge-trapping capability depends on localized electronic states that originated from the limited surface functional groups. To further advance such memory, a material with rich hybrid states is highly desired. Here, a van der Waals heterostructure design is proposed utilizing the 2D graphdiyne (GDY) which possesses abundant hybrid states with different chemical groups. In order to form the desirable van der Waals coupling, the plasma etching method is used to rapidly achieve the ultrathin 2D GDY with smooth surface for the first time. With the plasma-treated 2D GDY as charge-trapping layer, a direct charge-trapping memory based on GDY/MoS₂ is constructed. This bilayer memory is featured with large memory window (90 V) and high degree of modulation (on/off ratio around 8 × 10⁷). Two operating mode can be achieved and data storage capability of 9 and 10 current levels can be obtained, respectively, in electronic and opto-electronic mode. This GDY/MoS₂ memory introduces a novel application of GDY as rich states charge-trapping center and offers a new strategy of realizing high performance dielectric-free electronics, such as optical memories and artificial synaptic.

Author(s): Yuelin Zhang, Jie Liu, Yongqi Dong, Shizhe Wu, Jianyu Zhang, Jie Wang, Jingdi Lu, Andreas Rückriegel, Hanchen Wang, Rembert Duine, Haiming Yu, Zhenlin Luo, Ka Shen, and Jinxing Zhang

Dzyaloshinskii-Moriya interaction in magnets, which is usually derived from inversion symmetry breaking at interfaces or in noncentrosymmetric crystals, plays a vital role in chiral spintronics. Here we report that an emergent Dzyaloshinskii-Moriya interaction can be achieved in a centrosymmetric ma...

[Phys. Rev. Lett. 127, 117204] Published Fri Sep 10, 2021

Nature Nanotechnology, Published online: 09 September 2021; doi:10.1038/s41565-021-00966-5

Low-temperature ultraclean integration of large-area MoS2 thin-film transistors with nitride micro-LEDs through a back end of line process enables the demonstration of displays with high resolution and uniformity.

npj 2D Materials and Applications, Published online: 09 September 2021; doi:10.1038/s41699-021-00258-5

Optical versus electron diffraction imaging of Twist-angle in 2D transition metal dichalcogenide bilayers

Stacked 2D Materials

Stacked two-dimensional materials are achieved and analyzed in a surface science approach: Hexagonal boron nitride (h-BN) is formed on Pt(111) by the thermal decomposition of molecular precursor ammonia borane. A temporary Pt film deposited on h-BN serves as the platform for subsequent graphene growth using ethylene. The intercalation of the film through h-BN results in the desired van der Waals stacking. More details can be found in article 2102747 by Jörg Kröger and co-workers.

To further move “meta-photonics” toward real-world applications, a complementary metal–oxide–semiconductor (CMOS)-compatible nanofabrication method is developed for free-standing dielectric and plasmonic metasurfaces. The advantages of this method are revealed by demonstrating uniform and functional metasurfaces, including large-area metalenses for diffraction-limited focusing, spectrally selective high-quality-factor nanostructures, polarization-control birefringent metasurfaces, and aluminum plasmonic optofluidic biosensors.

Abstract

Metasurfaces have emerged as a breakthrough platform for manipulating light at the nanoscale and enabling on-demand optical functionalities for next-generation biosensing, imaging, and light-generating photonic devices. However, translating this technology to practical applications requires low-cost and high-throughput fabrication methods. Due to the limited choice of materials with suitable optical properties, it is particularly challenging to produce metasurfaces for the technologically relevant mid-infrared spectral range. These constraints are overcome by realizing functional metasurfaces on almost completely transparent free-standing metal-oxide membranes. A versatile nanofabrication process is developed and implemented for highly efficient dielectric and plasmonic mid-infrared metasurfaces with wafer-scale and complementary metal–oxide–semiconductor (CMOS)-compatible manufacturing techniques. The advantages of this method are revealed by demonstrating highly uniform and functional metasurfaces, including high-Q structures enabling fine spectral selectivity, large-area metalenses with diffraction-limited focusing capabilities, and birefringent metasurfaces providing polarization control at record-high conversion efficiencies.  Aluminum plasmonic devices and their integration into microfluidics for real-time and label-free mid-infrared biosensing of proteins and lipid vesicles are further demonstrated. The versatility of this approach and its compatibility with mass-production processes bring infrared metasurfaces markedly closer to commercial applications, such as thermal imaging, spectroscopy, and biosensing.

A novel self-growth strategy to precisely regulate the interlayer distance and lyophilicity of graphene layers simultaneously is demonstrated for the first time. The synergistic effect of expanded interlayer distance and enhanced lyophilicity can significantly improve the potassium ion storage performance, which has rarely been achieved before.

Abstract

Herein, a simple but effective self-growth strategy to simultaneously modulate the interlayer distance and lyophilicity of graphene layers, which results in ultrahigh potassium-storage performances for carbon materials, is reported. This strategy involves the uniform adsorption of individual metal ions on the oxygen-containing groups on graphene oxide via electrostatic/coordination interactions and in situ self-conversion reaction between the metal ions and the oxygen-containing groups to form lyophilic ultrasmall metal oxide nanoparticles modified/intercalated graphene skeleton (OM-G) with precisely regulated interlayer distance. The synergistic effect of expanded interlayer distance and enhanced lyophilicity is revealed for the first time to significantly reduce the ion diffusion barrier and enhance ion transport kinetics by experimental and theoretical analysis. As a result, such unique OM-G monolith as free-standing anode for potassium-ion battery (PIB) delivered an ultrahigh reversible capability of 496.4 mAh g⁻¹ at 0.1 A g⁻¹, excellent rate capability (306.6 mAh g⁻¹ at 10 A g⁻¹), and remarkable long-term cycling stability (96.3% capacity retention over 2000 cycles at 1 A g⁻¹), which are not only much better than those of previous graphene/carbon materials but also among the best performances for all PIB anodes ever reported. This study provides new fundamental insights for boosting the electrochemical properties of electrode materials.

The last decade has witnessed the significant progress of physical fundamental research and great success of practical application in two-dimensional (2D) van der Waals (vdW) materials since the discovery of graphene in 2004. Up to date, the vdW material is still a vibrant and fast expanding field, where tremendous reports have been published covering the topics from cutting-edge quantum technology to urgent green energy and so on. Here, we briefly reviewed the emerging hot physical topics and the intriguing materials, such as 2D topological materials, piezoelectric materials, ferroelectric materials, magnetic materials and twistronic heterostructures. Then various vdW material synthetic strategies were discussed in detail concerning the growth mechanisms, preparation conditions and the typical examples. Finally, prospects and further opportunities in the booming field of 2D materials were addressed.