A Silicon Monoxide Lithium-Ion Battery Anode with Ultrahigh Areal Capacity

Silicon monoxide(SiO)is an attractive anode material for next-generation lithium-ion batteries for its ultra-high theoretical capacity of 2680 mAh g−1.The studies to date have been limited to electrodes with a rela-tively low mass loading(<3.5 mg cm^(−2)),which has seriously restricted the areal capacity and its potential in practical devices.Maximizing areal capacity with such high-capacity materials is critical for capitalizing their potential in practi-cal technologies.Herein,we report a monolithic three-dimensional(3D)large-sheet holey gra-phene framework/SiO(LHGF/SiO)composite for high-mass-loading electrode.By specifically using large-sheet holey graphene building blocks,we construct LHGF with super-elasticity and exceptional mechanical robustness,which is essential for accommodating the large volume change of SiO and ensuring the structure integrity even at ultrahigh mass loading.Additionally,the 3D porous graphene network structure in LHGF ensures excellent electron and ion transport.By systematically tailoring microstructure design,we show the LHGF/SiO anode with a mass loading of 44 mg cm^(−2)delivers a high areal capacity of 35.4 mAh cm^(−2)at a current of 8.8 mA cm^(−2)and retains a capacity of 10.6 mAh cm^(−2)at 17.6 mA cm^(−2),greatly exceeding those of the state-of-the-art commercial or research devices.Furthermore,we show an LHGF/SiO anode with an ultra-high mass loading of 94 mg cm^(−2)delivers an unprecedented areal capacity up to 140.8 mAh cm^(−2).The achievement of such high areal capacities marks a critical step toward realizing the full potential of high-capacity alloy-type electrode materials in practical lithium-ion batteries.

Chemical vapor deposition growth of single-crystalline cesium lead halide microplatelets and heterostructures for optoelectronic applications

Organic-inorganic hybrid halide perovskites, such as CH3NHgPbI3, have emerged as an exciting class of materials for solar photovoltaic applications; however, they are currently plagued by insufficient environmental stability. To solve this issue, all-inorganic halide perovskites have been developed and shown to exhibit significantly improved stability. Here, we report a single-step chemical vapor deposition growth of cesium lead halide （CsPbX3） microcrystals. Optical microscopy studies show that the resulting perovskite crystals predominantly adopt a square-platelet morphology. Powder X-ray diffraction （PXRD） studies of the resulting crystals demonstrate a highly crystalline nature, with CsPbC13, CsPbBr3, and CsPbI3 showing tetragonal, monoclinic, and orthorhombic phases, respectively. Scanning electron microscopy （SEM） and atomic force microscopy （AFM） studies show that the resulting platelets exhibit well-faceted structures with lateral dimensions of the order of 10-50 μm, thickness around 1 μm, and ultra-smooth surface, suggesting the absence of obvious grain boundaries and the single-crystalline nature of the individual microplatelets. Photoluminescence （PL） images and spectroscopic studies show a uniform and intense emission consistent with the expected band edge transition. Additionally, PL images show brighter emission around the edge of the platelets, demonstrating a wave-guiding effect in high-quality crystals. With a well-defined geometry and ultra-smooth surface, the square platelet structure can function as a whispering gallery mode cavity with a quality factor up to 2,863 to support laser emission at room temperature. Finally, we demonstrate that such microplatelets can be readily grown on a variety of substrates, including silicon, graphene, and other two-dimensional materials such as molybdenum disulfide, which can readily allow the construction of heterostructure optoelectronic devices, including a graphene/perovskite/ graphene vertically-stacked photodetector with photoresponsivity 〉 10^5 A/W. The extraordinary optical properties of CsPbX3 platelets, combined with their ability to be grown on diverse materials to form functional heterostructures, can lead to exciting opportunities for broad optoelectronic applications.

Ultrathin wavy Rh nanowires as highly effective electrocatalysts for methanol oxidation reaction with ultrahigh ECSA

Direct methanol fuel cells (DMFCs) have received tremendous research interests because of the facile storage of liquid methanol vs.hydrogen.However,the DMFC today is severely plagued by the poor kinetics and rather high overpotential in methanol oxidation reaction (MOR).Here we report the investigation of the ultrathin Rh wavy nanowires as a highly effective MOR electrocatalyst.We show that ultrathin wavy Rh nanowires can be robustly synthesized with 2-3 nm diameters.Electrochemical studies show a current peak at the potential of 0.61 V vs.reversible hydrogen electrode (RHE),considerably lower than that of Pt based catalysts (~ 0.8-0.9 V vs.RHE).Importantly,with ultrathin diameters and favorable charge transport,the Rh nanowires catalysts exhibit an ultrahigh electrochemically active surface area determined from CO-stripping (ECSAco) of 144.2 m2/g,far exceeding that of the commercial Rh black samples (20 m2/g).Together,the Rh nanowire catalysts deliver a mass activity of 722 mA/mg at 0.61 V,considerably higher than many previously reported electrocatalysts at the same potential.The chronoamperometry studies also demonstrate good stability and CO-tolerance compared with the Rh black control sample,making ultrathin Rh wavy nanowires an attractive electrocatalyst for MOR.

Highly-anisotropic optical and electrical properties in layered SnSe

Anisotropic materials are of considerable interest because of their unique combination of polarization- or direction-dependent electrical, optical, and thermoelectric properties. Low-symmetry two-dimensional （2D） materials formed by van der Waals stacking of covalently bonded atomic layers are inherently anisotropic. Layered SnSe exhibits a low degree of lattice symmetry, with a distorted NaC1 structure and an in-plane anisotropy. Here we report a systematic study of the in-plane anisotropic properties in layered SnSe, using angle-resolved Raman scattering, optical absorption, and electrical transport studies. The optical and electrical characterization was direction-dependent, and successfully identified the crystalline orientation in the layered SnSe. Furthermore, the dependence of Raman-intensity anisotropy on the SnSe flake thickness and the excitation wavelength were investigated by both experiments and theoretical calculations. Finally, the electrical transport studies demonstrated that few-layer SnSe field- effect transistors （FETs） have a large anisotropic ratio of carrier mobility （N 5.8） bet- ween the armchair and zigzag directions, which is a record high value reported for 2D anisotropic materials. The highly-anisotropic properties of layered SnSe indicate considerable promise for anisotropic optics, electronics, and optoelectronics.

Suppressed threshold voltage roll-off and ambipolar transport in multilayer transition metal dichalcogenide feed-back gate transistors

The layered semiconducting transition metal dichaloogenides(S-TMDs)have attracted considerable interest as the channel material for field-effect transistors(FETs).However,the multilayer S-TMD transistors usually exhibit considerable threshold voltage(Vn)shit and ambipolar behavior at high source-drain bias,which is undesirable for modern digital electronics.Here we report the design and fabrication of double feedback gate(FBG)transistors,i.e.,source FBG(S-FBG)and drain FBG(D-FBG),to combat these challenges.The FBG transistors differ from normal transistors by including an extra feedback gate,which is directly connected t0 the source/drain electrodes by extending and overlapping the source/drain electrodes over the yttrium oxide dielectrics on s-TMDs.We show that the S-FBG transistors based on mutilayer MoSg exhibit nearly negligible VIn rlloff at large source drain bias,and the D-FBG mutilayer WSe2 transistors could be tailored into either n-type or p-type transport,depending on the polarity of the drain bias.The double FBG structure offers an effective strategy to tailor multilayer s-TMD transistors with suppressed Vn roll-off and ambipolar transport for high-performance and low-power logic applications.

Quantitative Surface Plasmon Interferometry via Upconversion Photoluminescence Mapping

Direct far-field visualization and characterization of surface plasmon polaritons(SPPs)are of great importance for fundamental studies and technological applications.To probe the evanescently confined plasmon fields,one usually requires advanced near-field techniques,which is typically not applicable for real-time,high-throughput detecting or mapping of SPPs in complicated environments.Here,we report the utilization of rare-earth-doped nanoparticles to quantitatively upconvert invisible,evanescently confined SPPs into visible photoluminescence emissions for direct far-field visualization of SPPs in a complicated environment.The observed interference fringes between the SPPs and the coherent incident light at the metal surface provide a quantitative measurement of the SPP wavelength and the SPP propagating length and the local dielectric environments.It thus creates a new signaling pathway to sensitively transduce the local dielectric environment change into interference periodicity variation,enabling a new design of directly measurable,spectrometer-free optical rulers for rapid,ultrasensitive label-free detection of various biomolecules,including streptavidin and prostate-specific antigen,down to the femtomolar level.