Jiuxiang Dai

Pursuing killer applications of graphenes is the core topic that determines the future of graphene industry. This review systematically discusses how graphenes can be uniquely and practically used for electrochemical energy storage compared to traditional carbon materials, and illustrates their promising killer uses for advanced batteries with three typical examples such as conductive additives, heat dissipation and compact energy storage.

Abstract

Killer applications of graphenes are always being pursued and critical for realizing industrialization. Since the first attempt for using graphene in lithium-ion batteries, graphene has been demonstrated as a key component in electrochemical energy storage technologies. However, the unique roles of graphene beyond traditional carbon in energy storage are still unclear and need to be clarified. Here, this review starts with a glance over the history of graphene in electrochemical energy storage applications, and then briefly discusses the different dimensional graphenes and representative synthesis methods that are believed to be essential for energy-related applications. Importantly, three typical graphene technologies showing their practical potentials in electrochemical energy storage are illustrated in details, including the uses as conductive additives, in heat dissipation, and compact energy storage. The methodologies of science and technology for the above applications are systematically elaborated. This review also gives perspectives on the opportunities and challenges of practical graphene technologies in electrochemical energy storage. The authors expect this review to provide a comprehensive view of how graphene can be uniquely and practically used for electrochemical energy storage, paving the way for promoting the development of the graphene industry.

Nature, Published online: 08 June 2022; doi:10.1038/s41586-022-04678-1

Precise control over the quantum state of a two-dimensional Fermi gas together with single-particle-resolved fluorescence imaging enables the direct observation of the formation of Cooper pairs at the Fermi surface.

Nature Photonics, Published online: 02 June 2022; doi:10.1038/s41566-022-01012-z

The strongly temperature-dependent band-edge absorption from gallium arsenide enables an optical thermometer with nanokelvin temperature resolution and microscale spatial resolution.

Nature Photonics, Published online: 26 May 2022; doi:10.1038/s41566-022-01008-9

It is shown that rhombohedral stacked MoS2 can enable scalable photovoltaic effects induced by spontaneous polarization throughout few-micrometre-sized exfoliated flakes. This is exploited in a graphene–MoS2-based photovoltaic device.

2D magnetic semiconductor α-MnSe flakes are synthesized by space-confined CVD. Impressively, the spin-ordering-related magnons and defects confirmed by low-temperature photoluminescence spectra confer themselves with a broadband luminescence from 550 to 880 nm, an ultraviolet–near-infrared photoresponse from 365 to 808 nm, and enhanced photon-to-electron conversion performance at 80 K.

Abstract

Two-dimensional (2D) magnetic semiconductors are considered to have great application prospects in spintronic logic devices, memory devices, and photodetectors, due to their unique structures and outstanding physical properties in 2D confinement. Understanding the influence of magnetism on optical/optoelectronic properties of 2D magnetic semiconductors is a significant issue for constructing multifunctional electronic devices and implementing sophisticated functions. Herein, the influence of spin ordering and magnons on the optical/optoelectronic properties of 2D magnetic semiconductor α-MnSe synthesized by space-confined chemical vapor deposition (CVD) is explored systematically. The spin-ordering-induced magnetic phase transition triggers temperature-dependent photoluminescence spectra to produce a huge transition at Néel temperature (T _N  ≈ 160 K). The magnons- and defects-induced emissions are the primary luminescence path below T _N and direct internal ⁴ _aT_1g→⁶A_1g transition-induced emissions are the main luminescence path above T _N . Additionally, the magnons and defect structures endow 2D α-MnSe with a broadband luminescence from 550 to 880 nm, and an ultraviolet–near-infrared photoresponse from 365 to 808 nm. Moreover, the device also demonstrates improved photodetection performance at 80 K, possibly influenced by spin ordering and trap states associated with defects. These above findings indicate that 2D magnetic semiconductor α-MnSe provides an excellent platform for magneto-optical and magneto-optoelectronic research.

Nature Electronics, Published online: 06 June 2022; doi:10.1038/s41928-022-00769-z

Transistors based on two-dimensional semiconductors suffer from electrical instabilities because charges readily get trapped in the gate oxides. As charge trapping is sensitive to the energetic alignment of the channel Fermi level to the defect bands in the oxide, the number of electrically active traps can be reduced by tuning the channel Fermi level.

Light: Science & Applications, Published online: 06 June 2022; doi:10.1038/s41377-022-00814-8

Pristine PN junction toward atomic layer devices

Nature Communications, Published online: 02 June 2022; doi:10.1038/s41467-022-30742-5

The major challenge for the development of spin based information processing is to obtain efficient ways of controlling spin. Here, Michiardi et al show that the Rashba spin-splitting at the surface of Bi2Se3 topological insulator can be controlled via optical pulses on picosecond timescales.

Nature Communications, Published online: 02 June 2022; doi:10.1038/s41467-022-30801-x

Organic polymer nanomechanics has been explored through precise nanometre-scale stiffness measurements in a high-mobility semiconducting polymer. Higher eigen-mode atomic force microscopy is used to measure nanomechnical variations in the film texture, as well as the nanoscale order in the material.

PdMoY alloy nanosheets deposited on ordinary paper enable high-performance, ultra-low-cost, room-temperature, and quantitative hydrogen detection with much greater sensitivity than devices fabricated on conventional interdigitated electrodes and can be patterned by inkjet printing. The combination of a new Pd alloy nanosheet composition, promising performance, flexibility, and low-cost demonstrates great potential for application in a future hydrogen energy economy.

Abstract

2D palladium nanostructures enable sensitive room-temperature detection of H₂. However, they can be limited by stability and fabrication costs. Stability may be improved by alloying Pd with other metals, while cost could be reduced by using paper as a substrate. An ultra-low-cost sensor using Pd alloy (PdMoY) nanosheets (NS) on paper is reported. The 2D Pd alloy nanosheets are prepared by a solution-phase route, drop cast onto paper (≈1 × 1 cm) with silver contacts drawn on it, and dried. The same material is deposited on an interdigitated electrode (IDE). Both sensors are tested for response to hydrogen in air. The resistance of the paper-based sensor decreased by ≈18.7% in 1% H₂, which is about 40 times the response of the IDE-based sensor. Its H₂ limit of detection (1 ppm) is also lower than that of the IDE-based sensor (5 ppm). Compared to pristine Pd NS, PdMoY NS are more stable to repeated H₂ pulses without any signs of buckling or cracks. The nanosheets are also deposited by inkjet printing to produce functional sensors, providing a simple route to manufacturing of ultra-low-cost gas sensors for use in fuel-cell vehicles and related infrastructure.

Nature Electronics, Published online: 02 June 2022; doi:10.1038/s41928-022-00768-0

The stability of graphene-based field-effect transistors with amorphous aluminium oxide serving as the top-gate oxide can be improved by tuning the Fermilevel of the two-dimensional channel material such that it maximizes the energy distance between the charge carriers in the channel and the defect bands in the gate oxide.

npj 2D Materials and Applications, Published online: 03 June 2022; doi:10.1038/s41699-022-00314-8

Interlayer shear coupling in bilayer graphene

Biotene, a 2D material with a minimum thickness of 2 nm, is introduced. Flexoelectricity allows the thin sheets to convert mechanical energy (through tapping, bending, and magnetic force application) into electrical energy. This unique 2D material harvests 17V when force and heat are applied simultaneously, making it a promising resource for next-generation energy collecting devices.

Abstract

In this work, the synthesis and characterization of ultrathin metal oxide, called biotene, using liquid-phase exfoliation from naturally abundant biotite are demonstrated. The atomically thin biotene is used for energy harvesting using its flexoelectric response under multiple bending. The effective flexoelectric response increases due to the presence of surface charges, and the voltage increases up to ≈8 V, with a high mechano-sensitivity of 0.79 V N⁻¹ for normal force. This flexoelectric response is further validated by density functional theory (DFT) simulations. The atomically thin biotene shows an increased response in the magnetic field and thermal heating. The synthesis of two-dimensional (2D) metal-oxide biotene suggests a wealth of future 2D-oxide material for energy generation and energy harvesting applications.

This paper opens opportunities for research laboratory to grow tall-carbon nanotubes in the cold wall chemical vapor deposition (CVD) system. This study is based on the low-pressure work which is more difficult than atmospheric to grow taller carbon nanotubes. These results allow 1 mm tall carpet of carbon nanotube without any support accessories used currently for hot-wall chemical vapor deposition system.

Abstract

This paper reports a multi-phase deposition for the growth of carbon nanotubes, intercalating phases of effective growth with purges of the reactor, based on the method recently proposed by the author to grow tall vertically aligned carbon nanotubes (VA-CNT) in a cold-wall system at low pressure. The test performed consists on running several growths varying the number of cycles during the deposition step and their duration, avoiding a massive study of number of cycles in function of the time and vice versa. The goal here is to verify if the chamber reconditioning and the purge cycles contribute to increase the height and the uniformity of the VA-CNT forests. The maximum height achieved is 1.1 mm for 11 cycles, in a total time of 110.5 min, with a non-uniformity of 6.0% under 6.8 Torr. The analysis of the saturation of the deposition is registered around 127 min.

Anisotropic sublimation behavior of wurtzite GaN is directly demonstrated using in situ heating transmission electron microscopy (TEM) technique. Sublimation preferentially occurs along [0001] and [0001¯$000\bar{1}$] directions. A hexagonal pyramid with the apex pointing to [0001] direction is generated as the sublimation-induced equilibrium crystal structure of wurtzite GaN. The observed phenomena is attributed to the asymmetric surface energies in wurtzite GaN.

Abstract

Thermal sublimation, a specific method to fabricate semiconductor nanowires, is an effective way to understand growth behavior as well. Utilizing a high-resolution transmission electron microscope (TEM) with in situ heating capability, the lattice-asymmetry-driven anisotropic sublimation behavior is demonstrated of wurtzite GaN: sublimation preferentially occurs along the [0001¯$000\bar{1}$] and [0001] directions in both GaN thin films and nanowires. Hexagonal pyramidal nanostructures consisting of six semipolar {11¯01}$\{ {1\bar{1}01} \}$ planes and one (0001¯$\bar{1}$) plane with the apex pointing to the [0001] direction are generated as a sublimation-induced equilibrium crystal structure, which is consistent with the lattice-asymmetry-driven growth behaviors in wurtzite GaN. These findings offer a new insight into the thermal stability of wurtzite GaN and provide essential background for tailoring the structure of III-nitrides for atomic-scale manufacturing.

The fusion of 2D transition-metal-dichalcogenide materials with micro/nanomachines can substantially accelerate scientific discovery and engineering implementations for micro/nanorobotics. Here, functional molybdenum disulfide is integrated into Janus micromotors that demonstrate unprecedented performance in response to ion addition and application for water disinfection. The unveiled working mechanism points toward a new scheme for making micro/nanomachines with designed performance.

Abstract

2D transition-metal-dichalcogenide materials, such as molybdenum disulfide (MoS₂) have received immense interest owing to their remarkable structure-endowed electronic, catalytic, and mechanical properties for applications in optoelectronics, energy storage, and wearable devices. However, 2D materials have been rarely explored in the field of micro/nanomachines, motors, and robots. Here, MoS₂ with anatase TiO₂ is successfully integrated into an original one-side-open hollow micromachine, which demonstrates increased light absorption of TiO₂-based micromachines to the visible region and the first observed motion acceleration in response to ionic media. Both experimentation and theoretical analysis suggest the unique type-II bandgap alignment of MoS₂/TiO₂ heterojunction that accounts for the observed unique locomotion owing to a competing propulsion mechanism. Furthermore, by leveraging the chemical properties of MoS₂/TiO₂, the micromachines achieve sunlight-powered water disinfection with 99.999% Escherichia coli lysed in an hour. This research suggests abundant opportunities offered by 2D materials in the creation of a new class of micro/nanomachines and robots.

Advanced Functional Materials, Volume 32, Issue 23, June 3, 2022.

Abstract

Two-dimensional (2D) indium arsenide (InAs) is promising for future electronic and optoelectronic applications such as high-performance nanoscale transistors, flexible and wearable devices, and high-sensitivity broadband photodetectors, and is advantageous for its heterogeneous integration with Si-based electronics. However, the synthesis of 2D InAs single crystals is challenging because of the nonlayered structure. Here we report the van der Waals epitaxy of 2D InAs single crystals, with their thickness down to 4.8 nm, and their lateral sizes up to ∼ 37 µm. The as-grown InAs flakes have high crystalline quality and are homogenous. The thickness can be tuned by growth time and temperature. Moreover, we explore the thickness-dependent optical properties of InAs flakes. Transports measurement reveals that 2D InAs possesses high conductivity and high carrier mobility. Our work introduces InAs to 2D materials family and paves the way for applying 2D InAs in high-performance electronics and optoelectronics.

Abstract

The emerging Au-assisted exfoliation technique enables the production of a wealth of large-area and high-quality ultrathin two dimensional (2D) crystals. Fast, damage-free, and reliable determination of the layer number of such 2D films can greatly promote layer-dependent physical studies and device applications. Here, an optical method has been developed for simple, high throughput, and accurate determination of the layer number for Au-assisted exfoliated MoS₂ and WS₂ films in a broad thickness range. The method is based on quantitative analysis of layer-dependent white light reflection spectra (WLRS), revealing that the intensity of exciton-induced reflection peaks can be used as a clear indicator for identifying the layer number. The simple yet robust method will facilitate fundamental studies on layer-dependent optical, electrical, and thermal properties and device applications of 2D materials. The technique can also be readily combined with photoluminescence (PL) and Raman spectroscopies to study other layer-dependent physical properties of 2D materials.

Light: Science & Applications, Published online: 06 June 2022; doi:10.1038/s41377-022-00842-4

“Clean” doping to advance 2D material phototransistors