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Dielectric particles in a non-uniform electric field are subject to a force caused by a phenomenon called dielectrophoresis (DEP). DEP is a commonly used technique in microfluidics for particle or cell separation. In comparison with other separation methods, DEP has the unique advantage of being label-free, fast, and accurate. It has been widely applied in microfluidics for bio-molecular diagnostics and medical and polymer research. This review introduces the basic theory of DEP, its advantages compared with other separation methods, and its applications in recent years, in particular, focusing on the different electrode types integrated into microfluidic chips, fabrication techniques, and operation principles.

The morphology modulation of target crystals is important for understanding their growth mechanisms and potential applications. Herein, we report a convenient method for modulating the morphology of MoO2 by controlling different growth temperatures. With an increase in growth temperature, the morphology of MoO2 changes from a nanoribbon to a nanoflake. Various characterization methods, including optical microscopy, atomic force microscopy, (vertical and tilted) scanning electron microscopy, Raman spectroscopy, high-resolution transmission electron microscopy, and selected area electron diffraction, were performed to unveil the morphology modulation and lattice structure of MoO2. Both MoO2 nanoribbons and nanoflakes display a standing-up growth mode on c-sapphire substrates, and their basal planes are MoO2(100). Further investigations into devices based on MoS2 with Au/Ti/MoO2 electrodes show the potential applications of MoO2 in two-dimensional electrodes. These findings are helpful for the synthesis of MoO2 with different morphologies and applications in the field of optoelectronic nanodevices.

A ferroelectric is a material with a polar structure whose polarity can be reversed (switched) by applying an electric field 1 , 2 . In metals, itinerant electrons screen electrostatic forces between ions, which explains in part why polar metals are very rare 3 – 7 . Screening also excludes external electric fields, apparently ruling out the possibility of ferroelectric switching. However, in principle, a thin enough polar metal could be sufficiently penetrated by an electric field to have its polarity switched. Here we show that the topological semimetal WTe 2 provides an embodiment of this principle. Although monolayer WTe 2 is centro-symmetric and thus non-polar, the stacked bulk structure is polar. We find that two- or three-layer WTe 2 exhibits spontaneous out-of-plane electric polarization that can be switched using gate electrodes. We directly detect and quantify the polarization using graphene as an electric-field sensor 8 . Moreover, the polarization states can be differentiated by conductivity and the carrier density can be varied to modify the properties. The temperature at which polarization vanishes is above 350 kelvin, and even when WTe 2 is sandwiched between graphene layers it retains its switching capability at room temperature, demonstrating a robustness suitable for applications in combination with other two-dimensional materials 9 – 12 . Two- and three-layer WTe 2 exhibits spontaneous out-of-plane electric polarization that can be switched electrically at room temperature and is sufficiently robust for use in applications with other two-dimensional materials.

The advanced electrochemical properties, such as high energy density, fast charge–discharge rates, excellent cyclic stability, and specific capacitance, make supercapacitor a fascinating electronic device. During recent decades, a significant amount of research has been dedicated to enhancing the electrochemical performance of the supercapacitors through the development of novel electrode materials. In addition to highlighting the charge storage mechanism of the three main categories of supercapacitors, including the electric double-layer capacitors (EDLCs), pseudocapacitors, and the hybrid supercapacitors, this review describes the insights of the recent electrode materials (including, carbon-based materials, metal oxide/hydroxide-based materials, and conducting polymer-based materials, 2D materials). The nanocomposites offer larger SSA, shorter ion/electron diffusion paths, thus improving the specific capacitance of supercapacitors (SCs). Besides, the incorporation of the redox-active small molecules and bio-derived functional groups displayed a significant effect on the electrochemical properties of electrode materials. These advanced properties provide a vast range of potential for the electrode materials to be utilized in different applications such as in wearable/portable/electronic devices such as all-solid-state supercapacitors, transparent/flexible supercapacitors, and asymmetric hybrid supercapacitors.

Exploiting the excellent electronic properties of two-dimensional (2D) materials to fabricate advanced electronic circuits is a major goal for the semiconductor industry 1 , 2 . However, most studies in this field have been limited to the fabrication and characterization of isolated large (more than 1 µm 2 ) devices on unfunctional SiO 2 –Si substrates. Some studies have integrated monolayer graphene on silicon microchips as a large-area (more than 500 µm 2 ) interconnection 3 and as a channel of large transistors (roughly 16.5 µm 2 ) (refs.  4 , 5 ), but in all cases the integration density was low, no computation was demonstrated and manipulating monolayer 2D materials was challenging because native pinholes and cracks during transfer increase variability and reduce yield. Here, we present the fabrication of high-integration-density 2D–CMOS hybrid microchips for memristive applications—CMOS stands for complementary metal–oxide–semiconductor. We transfer a sheet of multilayer hexagonal boron nitride onto the back-end-of-line interconnections of silicon microchips containing CMOS transistors of the 180 nm node, and finalize the circuits by patterning the top electrodes and interconnections. The CMOS transistors provide outstanding control over the currents across the hexagonal boron nitride memristors, which allows us to achieve endurances of roughly 5 million cycles in memristors as small as 0.053 µm 2 . We demonstrate in-memory computation by constructing logic gates, and measure spike-timing dependent plasticity signals that are suitable for the implementation of spiking neural networks. The high performance and the relatively-high technology readiness level achieved represent a notable advance towards the integration of 2D materials in microelectronic products and memristive applications. High-integration-density 2D–CMOS hybrid microchips for memristive applications are made demonstrating in-memory computation and electrical response suitable for the implementation of spiking neural networks representing an advance towards integration of 2D materials in microelectronic products and memristive applications.

Beyond-lithium-ion batteries are promising candidates for high-energy-density, low-cost and large-scale energy storage applications. However, the main challenge lies in the development of suitable electrode materials. Here, we demonstrate a new type of zero-strain cathode for reversible intercalation of beyond-Li + ions (Na + , K + , Zn 2+ , Al 3+ ) through interface strain engineering of a 2D multilayered VOPO 4 -graphene heterostructure. In-situ characterization and theoretical calculations reveal a reversible intercalation mechanism of cations in the 2D multilayered heterostructure with a negligible volume change. When applied as cathodes in K + -ion batteries, we achieve a high specific capacity of 160 mA h g −1 and a large energy density of ~570 W h kg −1 , presenting the best reported performance to date. Moreover, the as-prepared 2D multilayered heterostructure can also be extended as cathodes for high-performance Na + , Zn 2+ , and Al 3+ -ion batteries. This work heralds a promising strategy to utilize strain engineering of 2D materials for advanced energy storage applications. Beyond-Li + -ion batteries are promising energy storage systems but suffer from lack of suitable electrode materials. Here the authors report a new type of zero-strain cathodes for Na + , K + , Zn 2+ , and Al 3+ ion batteries through strain engineering of a 2D multilayered VOPO 4 -graphene heterostructure.

The doping or the alteration of crystals with guest species to obtain desired properties has long been a research frontier in materials science. However, the closely packed lattice structure in many crystals has limited the applicability of this strategy. The advent of 2D layered materials has led to revitalized interest in utilizing this approach through two important strategies, gating and intercalation, offering reversible modulation of the properties of the host material without breaking chemical bonds. In addition, these dynamically tunable techniques have enabled the synthesis of new hybrid materials. Here, we review how interactions between guest species and host 2D materials can tune the physics and chemistry of materials and discuss their remarkable potential for creating artificial materials and architectures beyond the reach of conventional methods. Introduction of guest species into archetype materials lays out a foundational pathway for creating new materials classes with desired functionalities. This Review discusses two main strategies of such applied to 2D layered materials: gating, where the guest species rest on the surface, and intercalation, where the guest species are incorporated into the host lattice.

Two‐dimensional (2D) materials with free of dangling bonds have the potential to serve as ideal channel materials for the next generation of field‐effect transistors (FETs) due to their atomic‐thin and excellent electronic properties. However, the performance of 2D materials‐based FETs is still dictated by the interface between electrodes/dielectrics and 2D materials. Several technical challenges such as improving device stability, reducing contact resistance, and advancing mobility need to be overcome. Herein, we focus on the effects of atomic‐scale interface engineering on the contact resistance and dielectric layer for 2D FETs. Universal strategies we consider to achieve ohmic contact and develop high‐quality, defect‐free dielectric layers are provided. Furthermore, advancing the performance of 2D materials‐based FETs and binding to silicon substrates are briefly analyzed. Atomic‐scale interface engineering in 2D materials‐based field‐effect transistors (FETs) for ohmic contacts and high‐κ dielectric layer are reviewed. Treatments and electrode fabrication methods are introduced for ohmic contact. Methods including inserting buffer layer, utilizing native oxides, and van der Walls transfer are introduced to form high quality and defect‐free dielectric layer.

Aqueous graphite-based dual ion batteries have unique superiorities in stationary energy storage systems due to their non-transition metal configuration and safety properties. However, there is an absence of thorough study of the interactions between anions and water molecules and between anions and electrode materials, which is essential to achieve high output voltage. Here we reveal the four-stage intercalation process and energy conversion in a graphite cathode of anions with different configurations. The difference between the intercalation energy and hydration energy of bis(trifluoromethane)sulfonimide makes the best use of the electrochemical stability window of its electrolyte and delivers a high intercalation potential, while BF 4 − and CF 3 SO 3 − do not exhibit a satisfactory potential because the graphite intercalation potential of BF 4 − is inferior and the graphite intercalation potential of CF 3 SO 3 − exceeds the voltage window of its electrolyte. An aqueous dual ion battery based on the intercalation behaviors of bis(trifluoromethane)sulfonimide anions into a graphite cathode exhibits a high voltage of 2.2 V together with a specific energy of 242.74 Wh kg −1 . This work provides clear guidance for the voltage plateau manipulation of anion intercalation into two-dimensional materials. The interactions between water molecules, electrode materials and anions are essential yet challenging for aqueous dual ion batteries. Here, the authors demonstrate the voltage manipulation of dual ion batteries through matching intercalation energy and solvation energy of different anions.

Spin-dependent phenomena and applications in graphene and other 2D materials are discussed in this Review. The isolation of graphene has triggered an avalanche of studies into the spin-dependent physical properties of this material and of graphene-based spintronic devices. Here, we review the experimental and theoretical state-of-art concerning spin injection and transport, defect-induced magnetic moments, spin–orbit coupling and spin relaxation in graphene. Future research in graphene spintronics will need to address the development of applications such as spin transistors and spin logic devices, as well as exotic physical properties including topological states and proximity-induced phenomena in graphene and other two-dimensional materials.