Chengxue Huo

Two-dimensional antimonene single crystals grown by van der Waals epitaxy

Unlike the unstable black phosphorous, another two-dimensional group-VA material, antimonene, was recently predicted to exhibit good stability and remarkable physical properties. However, the synthesis of high-quality monolayer or few-layer antimonenes, sparsely reported, has greatly hindered the development of this new field. Here, we report the van der Waals epitaxy growth of few-layer antimonene monocrystalline polygons, their atomical microstructure and stability in ambient condition. The high-quality, few-layer antimonene monocrystalline polygons can be synthesized on various substrates, including flexible ones, via van der Waals epitaxy growth. Raman spectroscopy and transmission electron microscopy reveal that the obtained antimonene polygons have buckled rhombohedral atomic structure, consistent with the theoretically predicted most stable β-phase allotrope. The very high stability of antimonenes was observed after aging in air for 30 days. First-principle and molecular dynamics simulation results confirmed that compared with phosphorene, antimonene is less likely to be oxidized and possesses higher thermodynamic stability in oxygen atmosphere at room temperature. Moreover, antimonene polygons show high electrical conductivity up to 104 S m−1 and good optical transparency in the visible light range, promising in transparent conductive electrode applications.

All-inorganic quantum-dot light-emitting diodes based on perovskite emitters with low turn-on voltage and high humidity stability

Recently, both light-to-electricity and electricity-to-light conversion efficiencies of perovskite achieved a breakthrough, e.g. 22.1% for solar cells and 11.7% for light-emitting diodes (LEDs), so the next fatal problem towards practical application, the device stability, became the key issue in this field. Here, we report all-inorganic LEDs including inorganic perovskite emitters (CsPbBr3) and inorganic charge transport layers (CTLs), with an emphasis on the significantly improved device stability. The quantum dot LEDs (QLEDs) were fabricated according to ITO/NiO/CsPbBr3 QDs/ZnO/Al device configuration. On the one hand, the all-inorganic LED lifetime under 65% humidity corresponding to a 70% electroluminescence (EL) conservation rate can be improved up to 3.5 times when compared with LEDs adopting conventional organic CTLs due to the intrinsic chemical stability of these inorganic CTLs and their less hydrophilic surfaces. Furthermore, as a surprise, the bare all-inorganic LED without encapsulation can work in water for about 20 seconds, which is over 10 times more sustainable than the organic–inorganic LED, which proves the excellent water-isolation ability. On the other hand, the all-inorganic QLEDs show the lowest turn-on voltage of 2.4 V among all the reported CsPbBr3 QLEDs because the inorganic CTLs possess well-matched energy band alignments with CsPbBr3, and hence result in efficient carrier injection. This work paves the way to constructing all-inorganic devices for stable perovskite photovoltaic and light-emitting devices.

Boosting Two-Dimensional MoS2/CsPbBr3 Photodetectors via Enhanced Light Absorbance and Interfacial Carrier Separation

Transition metal dichalcogenides (TMDs) are promising candidates for flexible optoelectronic devices because of their special structures and excellent properties, but the low optical absorption of the ultrathin layers greatly limits the generation of photocarriers and restricts the performance. Here, we integrate all-inorganic perovskite CsPbBr3 nanosheets with MoS2 atomic layers and take the advantage of the large absorption coefficient and high quantum efficiency of the perovskites, to achieve excellent performance of the TMD-based photodetectors. Significantly, the interfacial charge transfer from the CsPbBr3 to the MoS2 layer has been evidenced by the observed photoluminescence quenching and shortened decay time of the hybrid MoS2/CsPbBr3. Resultantly, such a hybrid MoS2/CsPbBr3 photodetector exhibits a high photoresponsivity of 4.4 A/W, an external quantum efficiency of 302%, and a detectivity of 2.5 × 1010 Jones because of the high efficient photoexcited carrier separation at the interface of MoS2 and CsPbBr3. The photoresponsivity of this hybrid device presents an improvement of 3 orders of magnitude compared with that of a MoS2 device without CsPbBr3. The response time of the device is also shortened from 65.2 to 0.72 ms after coupling with MoS2 layers. The combination of the all-inorganic perovskite layer with high photon absorption and the carrier transport TMD layer may pave the way for novel high-performance optoelectronic devices.

Retraction of “Few-Layer Antimonene: Large Yield Synthesis, Exact Atomical Structure, and Outstanding Optical Limiting”

The predictions of arsenene and antimonene open a gate to new two-dimensional (2D) materials. In contrast to the severe unstability of black phosphorus in ambient atmosphere, arsenene and antimonene were recently predicted to be of high stability, as well as outstanding physical and chemical properties, such as extremely high mobility, superior thermal conductivity, high refractive index, and directionally optically transparent. Significantly, monolayer and few-layer antimonenes were recently experimentally fabricated by mechanical exfoliation, however the yield was very low and there’s lack of clear characterizations on the atomical structure and potential applications, which are critical and necessary to promote the developments of this field. Here, we report on a high-yield experimental preparation of high quality, few-layer antimonenes via liquid exfoliation, their atomic level structural elucidation, and unexpected but outstanding nonlinear optical limiting properties even better than graphene in the visible and near infrared region (532 nm-2000 nm) and high transmission (more than 80%) when dispersed in solutions or high concentration doped in Ormosil gel glasses, which might lead to many promising applications in nonlinear optical fields such as laser protection. This work demonstrates that Group 15 2D materials beyond BP could be not only a new 2D crystal family with stability in ambient condition, but also of unique properties

Few-Layer Antimonene: Anisotropic Expansion and Reversible Crystalline-Phase Evolution Enable Large-Capacity and Long-Life Na-Ion Batteries

Two-dimensional (2D) antimonene is a promising anode material in sodium-ion batteries (SIBs) because of its high theoretical capacity of 660 mAh g-1 and enlarged surface active sites. However, its Na storage properties and sodiation/desodiation mechanism have not been fully explored. Herein, we propose the sodiation/desodiation reaction mechanism of 2D few-layer antimonene (FLA) based on results acquired by in situ synchrotron X-ray diffraction, ex situ selected-area electron diffraction, and theoretical simulations. Our study shows that the FLA undergoes anisotropic volume expansion along the a/b plane and exhibits reversible crystalline phase evolution (Sb ⇋ NaSb ⇋ Na3Sb) during cycling. Density-functional theory calculations demonstrate that the FLA has a small Na-ion diffusion barrier of 0.14 eV. The FLA delivers a larger capacity of 642 mAh g-1 at 0.1 C (1 C = 660 mA g-1) and a high rate capability of 429 mAh g-1 at 5 C and maintains a stable capacity of 620 mA g-1 at 0.5 C with 99.7% capacity retention from the 10th to the 150th cycle. Considering the 660 mAh g-1 theoretical capacity of Sb, the electrochemical utilization of Sb atoms of FLA is as high as 93.9% at a rate of 0.5 C for over 150 cycles, which is the highest capacity and Sb utilization ratio reported so far. Our study discloses the Na storage mechanism of 2D FLA, boosting promising applications of 2D materials for advanced SIBs.

Nickel concentration-dependent opto-electrical performances and stability of Cu@CuNi nanowire transparent conductors

Compared to monometallic counterparts, core–shell structured nanowires may possess additional performances or even new properties because of synergistic effects between two components. Particularly, the alloying shell may bring the advantage that we can adjust its components and sizes to achieve the desired performance. Here, we mainly study Ni-dependent electric stability and opto-electrical performances of Cu@CuNi NW electrodes. And we find that the increase of nickel content has little effect on optical performance, but effectively improves the stability of Cu@CuNi NW electrodes. We can also achieve ideal performance through regulating the nickel content and outstanding performance may come from the particular structure. Hence we studied Ni-dependent microstructure variations of Cu@CuNi NWs with the corresponding properties. The high stability NWs with a high nickel content have smooth CuNi alloying shells which effectively protect the NWs from oxidation. At the same time, the large length diameter ratio and high degree of crystallinity of Cu@CuNi NWs are the reasons for good transparent conductive properties. These demonstrations of controlling the composition of alloying shells for oxidation resistance of the NWs could bring forth great opportunities for transparent, flexible, stretchable, and wearable electronic and optoelectronic devices.

Field-Effect Transistors Based on van-der-Waals-Grown and Dry-Transferred All-Inorganic Perovskite Ultrathin Platelets

Nowadays, the research on perovskite transistors is still in its infancy, despite the fact that perovskite-based solar cells and light-emitting diodes have been widely investigated. Two major hurdles exist before obtaining reliable perovskite-based transistors: the processing difficulty for their sensitivity to polar solvents and unsatisfactory perovskite quality on the transistor platform. Here, for the first time, we report on high-performance all-inorganic perovskite FETs profiting from both van der Waals epitaxial boundary-free ultrathin single crystals and completely dry-processed transfer technique without chemical contaminant. These two crucial factors ensure the unprecedented high-quality perovskite channels. The achieved FET hole mobility and on-off ratio reach 0.32 cm2 V-1 s-1 and 6.7 × 103, respectively. Moreover, at the low temperature, the mobility and on-off ratio can be enhanced to be 1.04 cm2 V-1 s-1 and 1.3 × 104. This work could open the door for the FET applications based on perovskite single crystals.

A comprehensive investigation on CVD growth thermokinetics of h-BN white graphene

As an isomorph of graphene, monolayer hexagonal boron nitride (h-BN), so-called white graphene, has been in the spotlight of two-dimensional materials due to its outstanding properties. However, the growth of large and uniform white graphene monocrystalline with low density of defects is still a great challenge. Here, we present a comprehensive investigation on the growth thermokinetics of white graphene monocrystalline domains via atmospheric pressure chemical vapor deposition with the solid ammonia borane as precursors, which will be more suitable for future industrial production due to the handy process and precursor. The single domain size, coverage on substrate, and thickness of white graphene were taken as targeted parameters of products. And then, their dependences on the flow rate of carrier gas, heating temperature of ammonia borane, growth temperature and time were studied in details. Finally, after optimizing the above conditions, both white graphene monocrystalline domains as large as 80 μm2 and polycrystalline ultrathin film with coverage ratio of 95%–100% can be achieved facilely without using vacuum technique. Such white graphene products would be of great significance for the tunnel barrier for the tunneling transistor and the dielectric layers for nanocapacitor with the graphene based heterostructures.