Haiyong He

Rational design of MoS2@graphene nanocables: towards high performance electrode materials for lithium ion batteries

Here, we have successfully developed a novel contact mode between MoS2 and graphene, where graphene rolls up into a hollow nanotube and thin MoS2 nanosheets are uniformly standing on the inner surface of graphitic nanotubes, thus forming mechanically robust, free-standing, interwoven MoS2@graphene nanocable webs (MoS2@G). Such a hybrid structure can maximize the MoS2 loading in the electrode in which over 90% of MoS2 nanosheets with stacked layer number of less than 5 can be installed. Remarkably, when calculated on the basis of the whole electrode, this binder free electrode not only shows high specific capacity (ca. 1150 mA h g−1) and excellent cycling performance (almost 100% capacity retention even after 160 cycles at a current density of 0.5 A g−1) but exhibits a surprisingly high-rate capability of 700 mA h g−1 at the rate of 10 A g−1 despite such a high MoS2 loading content, which is one of the best results of MoS2-based electrode materials ever reported thus far.

Synthesis of 3D nitrogen-doped graphene/Fe3O4 by a metal ion induced self-assembly process for high-performance Li-ion batteries

We demonstrate the fabrication of three-dimensional nitrogen-doped graphene (3D N–G)/nanoparticle anode architectures consisting of 3D N–G networks and Fe3O4 nanoparticles. In such a hybrid structure, the N–G networks act as a buffer matrix to accommodate the volume change of Fe3O4, and the interconnected N–G sheets effectively prevent the aggregation of nanoparticles during cycling, both of which enable the structural integrity and electrochemical stabilization of such composite electrodes. Furthermore, the as-obtained porous nitrogen-doped hybrid materials promote efficient transport of both lithium ions and electrons upon charging/discharging, and also provide defect sites as Li+ active sites on the surface of N–G sheets. As a result, the hybrids exhibit much-improved lithium storage performance.

Controlled Synthesis of Organic/Inorganic van der Waals Solid for Tunable Light–Matter Interactions

High-quality organic and inorganic van der Waals (vdW) solids are realized using methylammonium lead halide (CH3 NH3 PbI3 ) as the organic part (organic perovskite) and 2D inorganic monolayers as counterparts. By stacking on various 2D monolayers, the vdW solids exhibit dramatically different light emissions. Futhermore, organic/h-BN vdW solid arrays are patterned for red-light emission.

Room-temperature ferroelectricity in CuInP2S6 ultrathin flakes

Two-dimensional (2D) materials have emerged as promising candidates for various optoelectronic applications based on their diverse electronic properties, ranging from insulating to superconducting. However, cooperative phenomena such as ferroelectricity in the 2D limit have not been well explored. Here, we report room-temperature ferroelectricity in 2D CuInP2S6 (CIPS) with a transition temperature of ∼320 K. Switchable polarization is observed in thin CIPS of ∼4 nm. To demonstrate the potential of this 2D ferroelectric material, we prepare a van der Waals (vdW) ferroelectric diode formed by CIPS/Si heterostructure, which shows good memory behaviour with on/off ratio of ∼100. The addition of ferroelectricity to the 2D family opens up possibilities for numerous novel applications, including sensors, actuators, non-volatile memory devices, and various vdW heterostructures based on 2D ferroelectricity.

A novel SnS2@graphene nanocable network for high-performance lithium storage

A unique SnS2@graphene nanocable structure with a novel contact model between SnS2 nanosheets and graphene has been successfully fabricated, in which the graphene layers are rolled up to encapsulate the SnS2 nanosheets, forming a mechanically robust, free-standing SnS2@graphene nanocable network. This distinctive structure provides an effective architecture as an electrode in lithium ion batteries to effectively accommodate the volume change of SnS2 during the charge–discharge cycling, facilitates the easy access of electrolyte to the active electrode materials, and also offers a continuous conductive network for the whole electrode. Interestingly, this binder-free electrode not only shows high specific capacity and excellent cycling performance with a specific capacity of 720 mA h g−1 even after 350 cycles at a current density of 0.2 A g−1 and over 93.5% capacity retention, but exhibits a high-rate capability of 580 mA h g−1 at a current rate of 1 A g−1

Periodic Organic–Inorganic Halide Perovskite Microplatelet Arrays on Silicon Substrates for Room‐Temperature Lasing

Organic–inorganic metal halide perovskites have recently demonstrated outstanding efficiencies in photovoltaics as well as highly promising performances for a wide range of optoelectronic applications such as lasing, light emission, optical detectors, and even for radiation detection. Key to the realization of functional perovskite micro/nanosystems on the ubiquitous silicon optoelectronics platform is through sophisticated lithography. Despite the rapid progress made in halide perovskite lasing, direct lithographic patterning of perovskite films to form optical cavities on conventional substrates remains extremely challenging. This study realizes room‐temperature high‐quality factor whispering‐gallery‐mode lasing (Q ≈ 1210) from patterned lead halide perovskite microplatelets fabricated in periodic arrays on silicon substrate with micropatterned BN film as the buffer layer. By varying the size of the platelets, modal selectivity for single mode lasing can be achieved with different cavity sizes or by simply breaking the structural symmetry of the cavity through designing the pattern. Importantly, this work demonstrates a straightforward, versatile bottom‐up scalable strategy to realize high‐quality periodic perovskite arrays with variable cavity sizes for large‐area light‐emitting and optical gain applications.

High-quality monolayer superconductor NbSe 2 grown by chemical vapour deposition

The discovery of monolayer superconductors bears consequences for both fundamental physics and device applications. Currently, the growth of superconducting monolayers can only occur under ultrahigh vacuum and on specific lattice-matched or dangling bond-free substrates, to minimize environment- and substrate-induced disorders/defects. Such severe growth requirements limit the exploration of novel two-dimensional superconductivity and related nanodevices. Here we demonstrate the experimental realization of superconductivity in a chemical vapour deposition grown monolayer material—NbSe2. Atomic-resolution scanning transmission electron microscope imaging reveals the atomic structure of the intrinsic point defects and grain boundaries in monolayer NbSe2, and confirms the low defect concentration in our high-quality film, which is the key to two-dimensional superconductivity. By using monolayer chemical vapour deposited graphene as a protective capping layer, thickness-dependent superconducting properties are observed in as-grown NbSe2 with a transition temperature increasing from 1.0 K in monolayer to 4.56 K in 10-layer.Two-dimensional superconductors will likely have applications not only in devices, but also in the study of fundamental physics. Here, Wang et al. demonstrate the CVD growth of superconducting NbSe2 on a variety of substrates, making these novel materials increasingly accessible.

Ultrathin MoSe2@N-doped carbon composite nanospheres for stable Na-ion storage

Two-dimensional transition metal dichalcogenides are widely studied as anode materials for metal ion batteries. This application requires high electric conductivity which can be achieved by forming composites with conductive carbon. In this work, we demonstrate the creation of nanospheres composed of Mo-based thin nanosheets (MoS2, MoSe2 and Mo2C) uniform embedded within a N-doped carbon matrix. Using MoSe2/N-doped carbon nanospheres as an example, we investigate in detail the electrochemical property in Na ion storage and reveal the advantage over previously reported MoSe2 electrodes (higher capacity and improved capacity retention up to 500 cycles). Furthermore, we provide evidence by ex situ x-ray diffraction to the nominal irreversible conversion reaction during the first discharge.

A topologically substituted boron nitride hybrid aerogel for highly selective CO2 uptake

A topologically mediated synthesis of porous boron nitride aerogel has been experimentally and theoretically investigated for carbon dioxide (CO2) uptake. Replacement of the carbon atoms in a precursor aerogel of graphene oxide and carbon nanotubes was achieved using an elemental substitution reaction, to obtain a boron and nitrogen framework. The newly prepared BN aerogel possessed a specific surface area of 716.56 m2/g and exhibited an unprecedented twentyfold increase in CO2 uptake over N2, adsorbing 100 cc/g at 273 K and 80 cc/g in ambient conditions, as verified by adsorption isotherms via the multipoint Brunauer-Emmett-Teller (BET) method. Density functional theory calculations were performed to give hints on the mechanism of such high selectivity of CO2 over N2 adsorption in BN aerogel, which may be due to the interaction between the intrinsic polar nature of B–N bonds and the high quadrupole moment of CO2 over N2.