Shulan Jiang

Synthesis of a nanowire self-assembled hierarchical ZnCo2O4 shell/Ni current collector core as binder-free anodes for high-performance Li-ion batteries

In this paper, ZnCo2O4 nanowires have been grown and self-assembled as hierarchical structures on a 3D conductive Ni foam substrate. Both leaf-like ZnCo2O4 and dandelion-like ZnCo2O4 assemblies were synthesized through a hydrothermal process followed by a post-annealing treatment. It is shown that leaf-like assemblies are directly grown on the substrate while dandelion-like assemblies are adsorbed on the surface of the structures. A possible formation mechanism of ZnCo2O4 hierarchical structures was proposed. It is shown that these nanowires are porous structures which provide much increased specific surface area. Further work was conducted by taking these Ni foam supported ZnCo2O4 structures as binder-free electrodes for Li-ion batteries. Remarkably, the leaf-like ZnCo2O4/Ni foam electrode exhibits greatly improved electrochemical performance with high capacity and excellent cycling stability. A high reversible capacity of 1050 mA h g−1 at the rate of 100 mA g−1 was obtained after 60 cycles. Meanwhile, the electrode showed a high rate of 416 mA g−1 with a high capacity of 850 mA h g−1 even after 50 cycles. Our work demonstrates that this unique nanowire self-assembled ZnCo2O4 hierarchical structure is promising for high-performance electrochemical energy applications.

Growth of Hierarchal Mesoporous NiO Nanosheets on Carbon Cloth as Binder-free Anodes for High-performance Flexible Lithium-ion Batteries

Mesoporous NiO nanosheets were directly grown on three-dimensional (3D) carbon cloth substrate, which can be used as binder-free anode for lithium-ion batteries (LIBs). These mesoporous nanosheets were interconnected with each other and forming a network with interval voids, which give rise to large surface area and efficient buffering of the volume change. The integrated hierarchical electrode maintains all the advantageous features of directly building two-dimensional (2D) nanostructues on 3D conductive substrate, such as short diffusion length, strain relaxation and fast electron transport. As the LIB anode, it presents a high reversible capacity of 892.6 mAh g−1 after 120 cycles at a current density of 100 mA g−1 and 758.1 mAh g−1 at a high charging rate of 700 mA g−1 after 150 cycles. As demonstrated in this work, the hierarchical NiO nanosheets/carbon cloth also shows high flexibility, which can be directly used as the anode to build flexible LIBs. The introduced facile and low-cost method to prepare NiO nanosheets on flexible and conductive carbon cloth substrate is promising for the fabrication of high performance energy storage devices, especially for next-generation wearable electronic devices.

Enhanced cycling stability of NiCo 2 S 4 @NiO core-shell nanowire arrays for all-solid-state asymmetric supercapacitors

As a new class of pseudocapacitive material, metal sulfides possess high electrochemical performance. However, their cycling performance as conventional electrodes is rather poor for practical applications. In this article, we report an original composite electrode based on NiCo2S4@NiO core-shell nanowire arrays (NWAs) with enhanced cycling stability. This three-dimensional electrode also has a high specific capacitance of 12.2 F cm−2 at the current density of 1 mA cm−2 and excellent cycling stability (about 89% retention after 10,000 cycles). Moreover, an all-solid-state asymmetric supercapacitor (ASC) device has been assembled with NiCo2S4@NiO NWAs as the positive electrode and active carbon (AC) as the negative electrode, delivering a high energy density of 30.38 W h kg−1 at 0.288 KW kg−1 and good cycling stability (about 109% retention after 5000 cycles). The results show that NiCo2S4@NiO NWAs are promising for high-performance supercapacitors with stable cycling based on the unique core-shell structure and well-designed combinations.

Scalable fabrication of carbon-based MEMS/NEMS and their applications: a review

The carbon-based micro/nano electromechanical system (MEMS/NEMS) technique provides a powerful approach to large-scale manufacture of high-aspect-ratio carbon structures for wafer-level processing. The fabricated three-dimensional (3D) carbon structures have the advantages of excellent electrical and electrochemical properties, and superior biocompatibility. In order to improve their performance for applications in micro energy storage devices and microsensors, an increase in the footprint surface area is of great importance. Various approaches have been proposed for fabricating large surface area carbon-based structures, including the integration of nanostructures such as carbon nanotubes (CNTs), graphene, nanowires, nanofilms and nanowrinkles onto 3D structures, which has been proved to be effective and productive. Moreover, by etching the 3D photoresist microstructures through oxygen plasma or modifying the photoresist with specific materials which can be etched in the following pyrolysis process, micro/nano hierarchical carbon structures have been fabricated. These improved structures show excellent performance in various applications, especially in the fields of biological sensors, surface-enhanced Raman scattering, and energy storage devices such as micro-supercapacitors and fuel cells. With the rapid development of microelectronic devices, the carbon-based MEMS/NEMS technique could make more aggressive moves into microelectronics, sensors, miniaturized power systems, etc. In this review, the recent advances in the fabrication of micro/nano hierarchical carbon-based structures are introduced and the technical challenges and future outlook of the carbon-based MEMS/NEMS techniques are also analyzed.

Investigation of silicon wear against non-porous and micro-porous SiO2 spheres in water and in humid air

Tribochemical wear, a method to achieve controlled material removal without residual damage on substrates, plays a very important role in super-smooth silicon surface manufacturing. By using non-porous SiO2 spheres and micro-porous SiO2 spheres, the wear of silicon substrates was comparatively investigated in DI water, humid air (50% RH) and dry air. The wear behaviors presented entirely different cases at the same load in DI water and humid air: (a) less material removal of silicon against non-porous SiO2 spheres than micro-porous SiO2 spheres in water and (b) more serious wear of silicon substrate against non-porous SiO2 spheres in humid air. When the wear tests were operated in dry air, no obvious damage was incurred on the silicon surface against the non-porous SiO2 spheres but slight wear was observed against micro-porous SiO2 spheres under the given conditions. Raman results revealed that a hydrolysis reaction was involved in the tribochemical wear of the silicon substrate and the micro pores in SiO2 spheres could accelerate this process. The corresponding analysis suggests an exponential dependence of wear rate on contact stress, which is consistent with the stress-assisted chemical kinetics model. Although with much lower elastic modulus, micro-porous SiO2 spheres caused a larger wear rate of silicon substrate than non-porous SiO2 spheres at the same contact pressure both in water and humid air. The results indicate that the micro-porous SiO2 spheres can promote the tribochemical reaction due to the storage of water molecules in micro pores.

Inline Measurement of Particle Concentrations in Multicomponent Suspensions using Ultrasonic Sensor and Least Squares Support Vector Machines.

This paper proposes an ultrasonic measurement system based on least squares support vector machines (LS-SVM) for inline measurement of particle concentrations in multicomponent suspensions. Firstly, the ultrasonic signals are analyzed and processed, and the optimal feature subset that contributes to the best model performance is selected based on the importance of features. Secondly, the LS-SVM model is tuned, trained and tested with different feature subsets to obtain the optimal model. In addition, a comparison is made between the partial least square (PLS) model and the LS-SVM model. Finally, the optimal LS-SVM model with the optimal feature subset is applied to inline measurement of particle concentrations in the mixing process. The results show that the proposed method is reliable and accurate for inline measuring the particle concentrations in multicomponent suspensions and the measurement accuracy is sufficiently high for industrial application. Furthermore, the proposed method is applicable to the modeling of the nonlinear system dynamically and provides a feasible way to monitor industrial processes.

UV/ozone-assisted tribochemistry-induced nanofabrication on Si(100) surfaces

A UV/ozone-assisted tribochemistry-induced nanofabrication method is proposed to improve the efficiency of nanofabrication on monocrystalline silicon (Si). Experimental results indicated that the UV/ozone oxidation process provides a simple and efficient method to prepare SiOx films on Si substrates. After UV/ozone oxidation for 10 min, a SiOx film with 3 nm thickness and 42% oxygen content was prepared on a Si substrate. In addition, the SiOx film prepared via UV/ozone oxidation shows super-hydrophilicity, which is beneficial to the following tribochemistry-induced nanofabrication. Through the control of the UV/ozone oxidation period, nanostructures with various depths can be easily fabricated on Si substrates. With the increase of the UV/ozone oxidation period from 0 min to 30 min, the stable depth of the nanogrooves on the Si substrate increased from 2.5 nm to 230 nm. The proposed method provides a new approach for the fabrication of a wide variety of nanoscale structures and devices, including nanogratings, micro/nanofluidic devices, Si molds, and surface textures.

Ultrasonic spectrum for particle concentration measurement in multicomponent suspensions

This paper studies the feasibility of applying the ultrasonic spectrum technique to the measurement of particle concentrations in multicomponent suspensions. A combination of the kernel partial least squares (KPLS) model and the interval selection methods is implemented to build the relationship between the ultrasonic spectra of the first reflected pulses and the particle concentrations. First of all, the interval selection methods are used to select optimal spectral interval(s) from full spectra. Then, the KPLS models with optimal spectral interval(s) are tuned, built and evaluated to obtain the optimal model. Finally, the optimal KPLS model is employed to measure the particle concentrations in the mixing process and its online prediction ability is evaluated. In comparison with the linear partial least squares (PLS) models, the optimal KPLS model shows the best performance. The results demonstrate that particle concentrations in multicomponent suspensions can be measured online by the ultrasonic spectrum technique, and the KPLS model with optimal spectral interval(s) shows the superiority in model calibration.

Humidity effects on tribochemical removal of GaAs surfaces

Defect-free tribochemical removal of gallium arsenide (GaAs) was demonstrated in vacuum, dry air, and various humidity environments by scratching with a SiO2 tip. The removal depth increases with increasing relative humidity (1–90%), and reaches its maximum value in water. A perfect crystal matrix without defects was observed in the cross section of the scratched groove using a transmission electron microscope. A model based on reactive tip scratching-induced oxidation, water solubility of debris, and adhesion effect was proposed to interpret tribochemical removal of GaAs surface. This study provides new insights into defect-free and site-controlled nanofabrication of GaAs.

Friction-induced fabrication of flexible supercapacitive microelectrodes

With miniaturized electronic devices becoming increasingly pervasive, micro energy storage devices have attracted great attentions. Micro-supercapacitors have great potentials due to its long lifetime and high power densities. Here we demonstrate low-cost and lithography-free fabrication of flexible micro-supercapacitive electrodes over large areas by friction-induced nanofabrication of silicon nanostructures array and electrodeposition of MnO2 nanostructures. The silicon nanostructures are fabricated by sliding a diamond tip on Si(100) surface under a given normal load combined with wet etching in potassium hydroxide (KOH) solution. Since the scratched pattern shows lower etching rate than that of non-scratched surface in KOH solution, such pattern can served as an etching mask to protect the silicon below from etching to some degree. Hence, the hillock silicon nanostructures can be realized on Si(100) surface. After reverse moulding, metal film sputtering and MnO2 nanostructures integration, the flexible microelectrodes are fabricated and show good electrochemical performances. The proposed friction-induced fabrication method has potential in bio-implantable and wearable miniaturized devices.