Minrui Zheng

Zn2SnO4 nanowires versus nanoplates: electrochemical performance and morphological evolution during Li-cycling.

Zn2SnO4 nanowires have been synthesized directly on stainless steel substrate without any buffer layers by the vapor transport method. The structural and morphological properties are investigated by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical performance of Zn2SnO4 nanowires is examined by galvanostatic cycling and cyclic voltammetry (CV) measurements in two different voltage windows, 0.005-3 and 0.005-1.5 V vs Li and compared to that of Zn2SnO4 nanoplates prepared by hydrothermal method. Galvanostatic cycling studies of Zn2SnO4 nanowires in the voltage range 0.005-3 V, at a current of 120 mA g(-1), show a reversible capacity of 1000 (±5) mAh g(-1) with almost stable capacity for first 10 cycles, which thereafter fades to 695 mAh g(-1) by 60 cycles. Upon cycling in the voltage range 0.005-1.5 V vs Li, a stable, reversible capacity of 680 (±5) mAh g(-1) is observed for first 10 cycles with a capacity retention of 58% between 10-50 cycles. On the other hand, Zn2SnO4 nanoplates show drastic capacity fading up to 10 cycles and then showed a capacity retention of 80% and 70% between 10 and 50 cycles when cycled in the voltage range 0.005-1.5 and 0.005-3 V, respectively. The structural and morphological evolutions during cycling and their implications on the Li-cycling behavior of Zn2SnO4 nanowires are examined. The effect of the choice of voltage range and initial morphology of the active material on the Li-cycleabilty is also elucidated.

Thiol-Capped ZnO Nanowire/Nanotube Arrays with Tunable Magnetic Properties at Room Temperature

The present study reports room-temperature ferromagnetic behaviors in three-dimensional (3D)-aligned thiol-capped single-crystalline ZnO nanowire (NW) and nanotube (NT) arrays as well as polycrystalline ZnO NT arrays. Besides the observation of height-dependent saturation magnetization, a much higher M(s) of 166 microemu cm(-2) has been found in NTs compared to NWs (36 microemu cm(-2)) due to larger surface area in ZnO NTs, indicating morphology-dependent magnetic properties in ZnO NW/NT systems. Density functional calculations have revealed that the origin of ferromagnetism is mainly attributed to spin-polarized 3p electrons in S sites and, therefore, has a strong correlation with Zn-S bond anisotropy. The preferential magnetization direction of both single-crystalline NTs and NWs lies perpendicular to the tube/wire axis due to the aligned high anisotropy orientation of the Zn-S bonds on the lateral (100) face of ZnO NWs and NTs. Polycrystalline ZnO NTs, however, exhibit a preferential magnetization direction parallel to the tube axis which is ascribed to shape anisotropy dominating the magnetic response. Our results demonstrate the interplay of morphology, dimensions, and crystallinity on spin alignment and magnetic anisotropy in a 3D semiconductor nanosystem with interfacial magnetism.

Surface‐Charge‐Mediated Formation of H‐TiO2@Ni(OH)2 Heterostructures for High‐Performance Supercapacitors

An electrochemically favorable Ni(OH)2 with porously hierarchical structure and ultrathin nanosheets in a core-shell structure H-TiO2 @Ni(OH)2 is achieved through modulating the surface chemical activity of TiO2 by hydrogenation, which creates a defect-rich surface of TiO2 , thereby facilitating the subsequent nucleation and growth of Ni(OH)2 . These configuration-tailored H-TiO2 @Ni(OH)2 core-shell nanowires exhibit a superior electrochemical performance and good flexibility.

Diameter‐Dependent Thermal Transport in Individual ZnO Nanowires and its Correlation with Surface Coating and Defects

A systematic study of the thermal transport properties of individual single-crystal zinc oxide (ZnO) nanowires (NWs) with diameters in the range of ∼50-210 nm is presented. The thermal conductivity of the NWs is found to be dramatically reduced by at least an order of magnitude compared to bulk values, due to enhanced phonon-boundary scattering with a reduction in sample size. While the conventional phonon transport model can qualitatively explain the temperature dependence, it fails to account for the diameter dependence. An empirical relationship for assessing diameter-dependent thermal properties is observed, which shows an approximately linear dependence of the thermal conductivity on the cross-sectional area of the NWs in the measured diameter range. Furthermore, it is found that an amorphous-carbon layer coating on the NWs does not perturb the thermal properties of the NW cores, whereas 30 keV Ga(+) ion irradiation at low dose (∼4 × 10(14) cm(-2)) leads to a remarkable reduction of the thermal conductivity of the ZnO NWs.

3D TiO2@Ni(OH)2 Core-shell Arrays with Tunable Nanostructure for Hybrid Supercapacitor Application.

Three dimensional hierarchical nanostructures have attracted great attention for electrochemical energy storage applications. In this work, self-supported TiO2@Ni(OH)2 core-shell nanowire arrays are prepared on carbon fiber paper via the combination of hydrothermal synthesis and chemical bath deposition. In this core-shell hybrid, the morphology and wall size of the interconnected nanoflake shell of Ni(OH)2 can be tuned through adjusting the concentration of ammonia solution. Heterogeneous nucleation and subsequent oriented crystal growth are identified to be the synthesis mechanism affecting the nanostructure of the shell material, which consequently determines the electrochemical performance in both energy storage and charge transfer. Superior capabilities of 264 mAhg−1 at 1 A g−1 and 178 mAh g−1 at 10 A g−1 are achieved with the core-shell hybrids of the optimized structure. The asymmetric supercapacitor prototype, comprising of TiO2@Ni(OH)2 as the anode and mesoporous carbons (MCs) as the cathode, is shown to exhibit superior electrochemical performance with high energy and power densities. The present work provides a clear illustration of the structure-property relationship in nanocrystal synthesis and offers a potential strategy to enhance the battery type Ni(OH)2 electrode in a hybrid supercapacitor device.

Optical and electrical applications of ZnSxSe1−x nanowires-network with uniform and controllable stoichiometry

Single crystalline ternary ZnS(x)Se(1-x) nanowires with uniform chemical stoichiometry and accurately controllable compositions (0≤x≤ 1) were synthesized through a simple and yet effective one-step approach with a specially designed modification. Energy-gap-tuning via compositional change was achieved for a direct band gap from 2.6 to 3.6 eV. Raman spectroscopy studies revealed typical two-mode behavior indicative of high miscibility in the alloyed compound. Moreover, the enhanced electrical-conductivity and gating effect behavior after the formation of ternary alloy enable their application in nano/micro-field effect transistor devices. In addition, the slow recombination rate in the photo-response process indicates their potential for photoelectric applications.

3D hierarchical SnO2@Ni(OH)2 core–shell nanowire arrays on carbon cloth for energy storage application

A judicious combination of conducting materials with selected transition metal hydroxides to form core–shell nanostructures has attracted great attention owing to the underlying synergistic effect for energy storage. In this work, we fabricate a novel 3D nanostructure consisting of Ni(OH)2 ultrathin nanoflakes directly anchored on SnO2 nanowire arrays by a facile solution-based method, which utilizes the higher conductance of SnO2 nanowires as the supporting scaffold to deposit Ni(OH)2 for supercapacitor electrodes. Cyclic voltammetry and galvanostatic charge–discharge methods have been conducted to understand the capacitive performance of the SnO2/Ni(OH)2 core–shell nanocomposites. A specific capacitance of as high as 1553 F g−1 is achieved at 0.5 A g−1 in 6 M KOH aqueous solution. At a large current density of 10 A g−1, the electrode retains a high capacitance value of 934 F g−1. The superior capacitive behavior suggests that the hierarchical SnO2@Ni(OH)2 hybrid nanostructure is a very promising electrode material for fabricating high-performance supercapacitors.

Laser-induced Greenish-Blue Photoluminescence of Mesoporous Silicon Nanowires

Solid silicon nanowires and their luminescent properties have been widely studied, but lesser is known about the optical properties of mesoporous silicon nanowires (mp-SiNWs). In this work, we present a facile method to generate greenish-blue photoluminescence (GB-PL) by fast scanning a focused green laser beam (wavelength of 532 nm) on a close-packed array of mp-SiNWs to carry out photo-induced chemical modification. The threshold of laser power is 5 mW to excite the GB-PL, whose intensity increases with laser power in the range of 5–105 mW. The quenching of GB-PL comes to occur beyond 105 mW. The in-vacuum annealing effectively excites the GB-PL in the pristine mp-SiNWs and enhances the GB-PL of the laser-modified mp-SiNWs. A complex model of the laser-induced surface modification is proposed to account for the laser-power and post-annealing effect. Moreover, the fast scanning of focused laser beam enables us to locally tailor mp-SiNWs en route to a wide variety of micropatterns with different optical functionality, and we demonstrate the feasibility in the application of creating hidden images.

Stepped-surfaced GeSe2 nanobelts with high-gain photoconductivity

Single crystalline stepped-surfaced GeSe2 nanobelts (NBs) were synthesized by vapor transport and deposition method with the presence of Au catalyst. The NBs were grown via VLS mechanism with catalytic Au–Ge–Se alloy droplet formed at the tip of the NBs. The dynamic reshaping of the catalyst particle leads to formation of steps along the NB. Photodetectors comprising individually isolated NBs were fabricated to study their photodetection properties. The photoresponsivity of the devices was investigated at four different excitation wavelengths of 405 nm, 532 nm, 808 nm and 1064 nm. High photoresponsivity of ∼1040 A W−1 and a photoconductive gain of ∼121 800% was achieved at a wavelength of 1064 nm, suggesting that the excitation to defect-related energy states near or below the mid band-gap energy plays a major role in the generation of photocurrent in these highly stepped NB devices.

Room temperature ferromagnetism at self-assembled monolayer modified Ag nanocluster-ZnO nanowire interface

Magnetic characterization of ZnO nanowires (NW) decorated with thiol-capped Ag nanoclusters (NCs) reveals spontaneous field-dependent magnetization and hysteresis at room temperature. The saturation magnetization is temperature independent for the 13nm thiol-capped Ag NCs but unexpectedly increases with temperature for the 4nm thiol-capped Ag NCs. The high magnetic moment results from the efficient dispersal of Ag NCs on the ZnO NW scaffold and charge transfer interaction between Ag and ZnO. The anomalous magnetic behavior in 4nm NCs may be due to the spin reorientation of Ag–S dipoles mediated by Zn–S dipoles.