Jiuxiang Dai

Sujiao Cao, Lang Ma, Chong Cheng, and co-workers (DOI:10.1002/inf2.12299) have comprehensively summarized the physicochemical structures of the most representative emerging 2D materials and the design of their nanostructures for engineering high-performance bioelectronic devices. In this cover, the recent developments of emerging 2D materials in bioelectronics have been introduced, such as neural interface simulation, biomolecular/biomarker detection, and microbial/skin sensors.

Sujiao Cao, Lang Ma, Chong Cheng, and co-workers (DOI:10.1002/inf2.12299) have comprehensively summarized the physicochemical structures of the most representative emerging 2D materials and the design of their nanostructures for engineering high-performance bioelectronic devices. In this cover, the recent developments of emerging 2D materials in bioelectronics have been introduced, such as neural interface simulation, biomolecular/biomarker detection, and microbial/skin sensors.

Patterned nanostructures with ultrasmall features endow functional devices with unique nanoconfinement and performance enhancements. Beyond conventional lithography—which is limited by unavoidable factors—advanced patterning techniques have been reported to produce nanoscale features down to molecular or even atomic scale. In this review, unconventional techniques for sub-100 nm nanopatterning are discussed according to their template dependency (as shown in the image), in particular the principles by which to achieve the desired patterns and other important ultrahigh-resolution issues (as shown in Figure 14).

Abstract

Patterned nanostructures with ultrasmall features endow functional devices with unique nanoconfinement and performance enhancements. The increasing demand for miniaturization has stimulated the development of sub-100 nm nanopatterning techniques. Beyond conventional lithography—which is limited by unavoidable factors—advanced patterning techniques have been reported to produce nanoscale features down to molecular or even atomic scale. In this review, unconventional techniques for sub-100 nm nanopatterning are discussed, in particular the principles by which to achieve the desired patterns (among other important issues). Such techniques can be classified into three categories: template-replica, template-induced, and template-free techniques. Moreover, multi-dimensional nanostructures consist of various building materials, the unique properties of which are summarized. Finally, the remaining challenges and opportunities for large-scale patterning, the improvement of device performance, the multi-dimensional nanostructures of biocompatible materials, molecular-scale patterning, and the carbon footprint requirements for future nanofabrication processes are discussed.

A selective area reconstruction method is proposed for in-situ growth of high-quality customized monolayer graphene structures on copper substrates. The feature size of the fabricated arbitrary graphene structure is comparable with that of the photolithographic technology. This method provides a new approach for direct growth of high-quality, scalable, and high-precision graphene structures, which is promising for optoelectronic applications.

Abstract

High-quality customized monolayer graphene structures are a prerequisite for various applications such as electronics, optoelectronics, and energy devices. Top-down photolithography is the main method for graphene patterning, but it is greatly affected by complex manufacturing processes and residual photoresist. Recently, bottom-up methods based on catalyst or precursor patterning have been developed. Although these methods can achieve high-resolution graphene patterns, it is difficult to control the number of graphene layers and has a high defect density. Here, the authors propose a selective area reconstruction method for in-situ growth of high-quality monolayer graphene structures on copper substrates. The method utilizes selective oxidation and high-temperature reduction technologies, which can effectively regulate the surface characteristics of the copper substrate, thereby precisely controlling the nucleation and growth behavior of the customized graphene structure. The feature size of the fabricated graphene structure is less than 1 µm and it has high monolayer coverage and extremely low defect density. The performance of the photoluminescence device and photodetector based on the customized monolayer graphene structure is characterized. The method provides a new approach for the direct growth of high-quality, scalable, and high-precision functional graphene structures, which is expected to have great potential in the optoelectronic applications.

Nature Reviews Materials, Published online: 27 May 2022; doi:10.1038/s41578-022-00448-7

2D materials hold promise as inks for printed technologies. This Review discusses ink formulation processes, from materials selection and deposition techniques to applications, and the perspectives for the commercialization of printed devices.

An in situ CVD synthesis of high-quality single-crystal graphene/hBN/graphene trilayer van der Waals heterostructures is presented here. A single-crystal CuNi(111) film is produced on sapphire and then subjected to carbon dissolution. Single-crystal monolayer hBN and graphene are then synthesized. Carbon atoms diffuse to the hBN–CuNi(111) interface and form graphene. This study paves the way for future 2D-material-based large-area integrated circuits.

Abstract

van der Waals heterostructures based on graphene and hBN layers with different stacking modes are receiving considerable attention because of their potential application in fundamental physics. However, conventional exfoliation fabrication methods and layer-by-layer transfer techniques have various limitations. The CVD synthesis of high-quality large-area graphene and hBN multilayer heterostructures is essential for the advancement of new physics. Herein, the authors propose an in situ CVD growth strategy for synthesizing wafer-scale AAB-stacked single-crystal graphene/hBN/graphene trilayer van der Waals heterostructures. Single-crystal CuNi(111) alloys are prepared on sapphire, followed by the pre-dissolution of carbon atoms. Single-crystal monolayer hBN is synthesized on a plasma-cleaned CuNi(111) surface. Then, a single-crystal monolayer graphene is epitaxially grown onto the hBN surface to form graphene/hBN bilayer heterostructures. A controlled decrease in the growth temperature allows the carbon atoms to precipitate out of the CuNi(111) alloy to form single-crystal graphene at the interface between hBN and CuNi(111), thereby producing graphene/hBN/graphene trilayer van der Waals heterostructures. The stacking modes between as-grown 2D layers are investigated through Raman spectroscopy and transmission electron microscopy. This study provides an in situ CVD approach to directly synthesize large-scale single-crystal low-dimensional van der Waals heterostructures and facilitates their application in future 2D-material-based integrated circuits.

A quasi-shell-growth strategy for synthesizing highly luminescent green InP/ZnSe/ZnS quantum dots (QDs) with high photoluminescence quantum yields over 90% and narrow full-width at half-maximum of 36 nm is reported. The resulting QD light-emitting diodes based on these core/shell QDs with improved optoelectronic properties realize a high brightness of 15606 cd m⁻² and a long operational lifetime of over 5000 h.

Abstract

Indium phosphide (InP) based quantum dots (QDs) have been known as an ideal alternative to heavy metals including QDs light emitters, such as cadmium selenium (CdSe) QDs, and show great promise in the next-generation solid-state lighting and displays. However, the electroluminescence performance of green InP QDs is still inferior to their red counterparts, due to the higher density of surface defects and the wider particle size distribution. Here, a quasi-shell-growth strategy for the growth of highly luminescent green InP/ZnSe/ZnS QDs is reported, in which the zinc and selenium monomers are added at the initial nucleation of InP stage to adsorb on the surface of InP cores that create a quasi-ZnSe shell rather than a bulk ZnSe shell. The quasi-ZnSe shell reduces the surface defects of InP core by passivating In-terminated vacancies, and suppresses the Ostwald ripening of InP core at high temperatures, leading to a photoluminescence quantum yield of 91% with a narrow emission linewidth of 36 nm for the synthesized InP/ZnSe/ZnS QDs. Consequently, the light-emitting diodes based on the green QDs realize a maximum luminance of 15606 cd m⁻², a peak external quantum efficiency of 10.6%, and a long half lifetime of > 5000 h.

A monolayer MXene nanoelectromechanical piezo-resonator is reported for the first time, achieving high-resolution molecular sensing performance in high order mode. The effective measurements of signals have a low thermomechanical motion spectral density (9.66 ± 0.01 fmHz$\frac{{fm}}{{\sqrt {Hz} }}$) and an extensive dynamic range (118.49 ± 0.42 dB) with sub-zeptograms resolution (0.22 ± 0.01 zg).

Abstract

2D materials-based nanoelectromechanical resonant systems with high sensitivity can precisely trace quantities of ultra-small mass molecules and therefore are broadly applied in biological analysis, chemical sensing, and physical detection. However, conventional optical and capacitive transconductance schemes struggle to measure high-order mode resonant effectively, which is the scientific key to further achieving higher accuracy and lower noise. In the present study, the different vibrations of monolayer Ti₃C₂Tx MXene piezo-resonators are investigated, and achieve a high-order f_2,3 resonant mode with a ≈234.59 ± 0.05 MHz characteristic peak due to the special piezoelectrical structure of the Ti₃C₂Tx MXene layer. The effective measurements of signals have a low thermomechanical motion spectral density (9.66 ± 0.01 fmHz$\frac{{fm}}{{\sqrt {Hz} }}$) and an extensive dynamic range (118.49 ± 0.42 dB) with sub-zeptograms resolution (0.22 ± 0.01 zg) at 300 K temperature and 1 atm. Furthermore, the functional groups of the Ti₃C₂Tx MXene with unique adsorption properties enable a high working range ratio of ≈3100 and excellent repeatability. This Ti₃C₂Tx MXene device demonstrates encouraging performance advancements over other nano-resonators and will lead the related engineering applications including high-sensitivity mass detectors.

Nature Reviews Materials, Published online: 27 May 2022; doi:10.1038/s41578-022-00455-8

An article in Nature Synthesis uses dynamic covalent chemistry to synthesize crystalline graphyne on a large scale.

Proceedings of the National Academy of Sciences, <a href="https://www.pnas.org/toc/pnas/119/22">Volume 119, Issue 22</a>, May 2022.

Multichannel selective, anisotropic, or consistent polarized-photon out-coupling has been realized in a set of 2D organic microcrystals, with the polarization direction and degree being either varied or retained with respect to the source luminescence. The molecular arrangement and spatial distribution of the transition dipole moments are found to play prominent roles in determining the polarization properties of the source and out-coupled emissions.

Abstract

Nano- and micromaterials with anisotropic photoluminescence and photon transport have widespread application prospects in quantum optics, optoelectronics, and displays. But the nature of the polarization information of the out-coupled light, with respect to that of the source luminescence, has never been explored in active optical-waveguiding organic crystals. Herein, three different modes (selective, anisotropic, and consistent) of polarized-photon out-coupling are proposed and successfully implemented in a set of 2D organic microcrystals with highly linearly-polarized luminescence. It is found that the polarization direction and degree of the luminescence out-coupled through different waveguiding channels can either be essentially retained or distinctly changed with respect to those of the original luminescence, depending on the molecular arrangement and the orientation of transition dipole moments of the crystal. This work demonstrates the promising potential of 2D emissive microcrystals in multi-channel polarized photon transport.

The developments of circuit-level memory technologies and in-memory computing applications realized experimentally using 2D materials are reviewed. Reports on large-scale material synthesis methods, circuits with different levels of integration, logic-in-memory, and neuromorphic computing applications are systematically summarized. Major challenges and perspectives of large-scale 2D-material-based integrated memory are provided.

Abstract

Memory technologies and applications implemented fully or partially using emerging 2D materials have attracted increasing interest in the research community in recent years. Their unique characteristics provide new possibilities for highly integrated circuits with superior performances and low power consumption, as well as special functionalities. Here, an overview of progress in 2D-material-based memory technologies and applications on the circuit level is presented. In the material growth and fabrication aspects, the advantages and disadvantages of various methods for producing large-scale 2D memory devices are discussed. Reports on 2D-material-based integrated memory circuits, from conventional dynamic random-access memory, static random-access memory, and flash memory arrays, to emerging memristive crossbar structures, all the way to 3D monolithic stacking architecture, are systematically reviewed. Comparisons between experimental implementations and theoretical estimations for different integration architectures are given in terms of the critical parameters in 2D memory devices. Attempts to use 2D memory arrays for in-memory computing applications, mostly on logic-in-memory and neuromorphic computing, are summarized here. Finally, challenges that impede the large-scale applications of 2D-material-based memory are reviewed, and perspectives on possible approaches toward a more reliable system-level fabrication are also given, hopefully shedding some light on future research.

A complementary chemical vapor deposition strategy is designed, enabling the large-area uniform fabrication of graphene glass fiber fabric in a wide range of sheet resistance. Notably, the obtained graphene glass fiber fabric presents impressive electrothermal performances in a wide temperature range at low-level working voltages, ultrafast electrothermal response, and uniform heating temperature, which realize the remarkable anti/deicing performances under low energy consumption.

Abstract

The lightweight, flexible, high-performance electrothermal material is in high demand in object thermal management. Graphene glass fiber fabric (GGFF) is characterized by excellent electrical conductivity, light weight, and high flexibility, showing superiorities as an electrothermal material. However, the traditional single-carbon-precursor chemical vapor deposition (CVD) graphene growth strategy commonly suffers from the severe thickness nonuniformity of the large-sized graphene film along the gas-flowing direction. Herein, a complementary CVD graphene growth strategy based on the simultaneous introduction of high- and low-decomposition-energy-barrier mixed carbon precursors is developed. In this way, the large-area uniform GGFF with a dramatically decreased nonuniformity coefficient is fabricated (0.260 in 40 cm × 4 cm). GGFF-based heater presents a widely tunable temperature range (20–170 °C) at low working voltage (<10 V) and uniform large-area heating temperature (171.4 ± 3.6 °C in 20 cm × 15 cm), which realizes remarkable anti/deicing performances under the low energy consumption (fast ice melting rate of 79 s mm⁻¹ under a low energy consumption of 0.066 kWh mm⁻¹ m⁻²). The large-area uniform GGFF possesses substantial advantages for applications in thermal management, and the complementary CVD fabrication strategy shows reliable scalability and universality, which can be extended to the synthesis of various materials.

The vertical graphene/silicon dynamic diode generator (DDG) is proposed and the detailed hot carrier dynamics are explored. High voltage of 6.1 V and current of 235.6 nA are achieved in monolayer graphene/silicon DDG unit, attributing to ultrafast carrier transport and carrier multiplication in graphene. This work provides a novel and potential in situ source for harvesting mechanical energy from the environment.

Abstract

Dynamic semiconductor diode generators (DDGs) offer a potential portable and miniaturized energy source, with the advantages of high current density, low internal impedance, and independence of the rectification circuit. However, the output voltage of DDGs is generally as low as 0.1–1 V, owing to energy loss during carrier transport and inefficient carrier collection, which requires further optimization and a deeper understanding of semiconductor physical properties. Therefore, this study proposes a vertical graphene/silicon DDG to regulate the performance by realizing hot carrier transport and collection. With instant contact and separation of the graphene and silicon, hot carriers are generated by the rebounding process of built-in electric fields in dynamic graphene/silicon diodes, which can be collected within the ultralong hot electron lifetime of graphene. In particular, monolayer graphene/silicon DDG outputs a high voltage of 6.1 V as result of ultrafast carrier transport between the monolayer graphene and silicon. Furthermore, a high current of 235.6 nA is generated due to the carrier multiplication in graphene. A voltage of 17.5 V is achieved under series connection, indicating the potential to supply electronic systems through integration design. The graphene/silicon DDG has applications as an in situ energy source for harvesting mechanical energy from the environment.

Author(s): Xiang Chen, Yu-Tsun Shao, Rui Chen, Sandhya Susarla, Tom Hogan, Yu He, Hongrui Zhang, Siqi Wang, Jie Yao, Peter Ercius, David A. Muller, Ramamoorthy Ramesh, and Robert J. Birgeneau

The existence of long-range magnetic order in low-dimensional magnetic systems, such as the quasi-two-dimensional van der Waals (vdW) magnets, has attracted intensive studies of new physical phenomena. The vdW FeNGeTe2 (N=3, 4, 5; FGT) family is exceptional, owing to its vast tunability of magnetic …

[Phys. Rev. Lett. 128, 217203] Published Thu May 26, 2022

Nature Reviews Materials, Published online: 26 May 2022; doi:10.1038/s41578-022-00452-x

An article in Communications Engineering reports the upcycling of waste plastics from vehicles into graphene that can be then used as an additive in foams for cars.

Nature Materials, Published online: 26 May 2022; doi:10.1038/s41563-022-01267-5

Sub-100-mV switching at the nanosecond timescale is achieved in ferroelectric devices by approaching bulk-like perfection in prototypical BaTiO3 thin films.

npj 2D Materials and Applications, Published online: 26 May 2022; doi:10.1038/s41699-022-00309-5

Monolithic In₂Se₃–In₂O₃ heterojunction for multibit non-volatile memory and logic operations using optoelectronic inputs