Zirong Tang

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 photovoltaic performance and stability of carbon counter electrode based perovskite solar cells encapsulated by PDMS

We report the encapsulation of low temperature carbon counter electrode based hole-conductor-free mesoscopic methylammonium lead iodide perovskite/TiO2 heterojunction solar cells with polydimethylsiloxane. The solar cells demonstrate improved photovoltaic performance, where we obtain an optimal short-circuit photocurrent JSC = 23.5 mA cm−2, open-circuit photovoltage VOC = 0.97 V, and fill factor FF = 0.474, corresponding to a light to electric power conversion efficiency of 10.8% under a standard AM 1.5 solar light of 100 mW cm−2 intensity. The results exhibit a remarkable 54% enhancement over those without encapsulation. The cross-sectional SEM images indicate that the PDMS layer can condense the carbon electrode by filling the gaps in the mesoscopic carbon film during the solidification of PDMS, resulting in an improved MAPbI3/carbon interface condition. The photoluminescence and electrical impedance spectroscopy measurements prove that the improved efficiency is ascribed to a more efficient charge transfer process and slower charge recombination between interfaces. In addition, the robust polydimethylsiloxane isolates water in air, avoiding the degradation of the CH3NH3PbI3 perovskite and leading to an impressive stability during a testing period of 3000 h. Our work paves the way for realizing low cost, highly efficient and stable hybrid photovoltaic cells.

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.

Improved model-based infrared reflectrometry for measuring deep trench structures

Model-based infrared reflectrometry (MBIR) has been introduced recently for characterization of high-aspect-ratio deep trench structures in microelectronics. The success of this technique relies heavily on accurate modeling of trench structures and fast extraction of trench parameters. In this paper, we propose a modeling method named corrected effective medium approximation (CEMA) for accurate and fast reflectivity calculation of deep trench structures. We also develop a method combining an artificial neural network (ANN) and a Levenberg-Marquardt (LM) algorithm for robust and fast extraction of geometric parameters from the measured reflectance spectrum. The simulation and experimental work conducted on typical deep trench structures has verified the proposed methods and demonstrated that the improved MBIR metrology achieves highly accurate measurement results as well as fast computation speed.

Dynamic selective etching: a facile route to parabolic optical fiber nano-probe

A dynamic etching approach is proposed through the appropriate variation of etchant composition ratio during the etching process, resulting in the parabolic shape of optical fiber nano-probe with a favorable changing of cone angle. The probe formation mechanism is thoroughly analyzed to illustrate the controllability and simplicity of this method. Optical properties of as-made probes are simulated and experimentally characterized and compared with the linear shape probes of different cone angles. It shows that the parabolic shape probes are superior to the linear shape ones with respect to the transmission efficiency and light focusing capability.

Construction of porous CuCo 2 S 4 nanorod arrays via anion exchange for high-performance asymmetric supercapacitor

To push the energy density limit of supercapacitors, proper pseudocapacitive materials with favorable nanostructures are urgently pursued. Ternary transition metal sulfides are promising electrode materials due to the better conductivity and higher electrochemical activity in comparison to the single element sulfides and transition metal oxides. In this work, we have successfully synthesized porous CuCo2S4 nanorod array (NRAs) on carbon textile through a stepwise hydrothermal method, including the growth of the Cu-Co precursor nanowire arrays and subsequent conversion into CuCo2S4 NRAs via anion exchange reaction. The CuCo2S4 NRAs electrode exhibits a greatly enhanced specific capacitance and an outstanding cycling stability. Moreover, an asymmetric supercapacitor using the CuCo2S4 NRAs as positive electrode and activated carbon as negative electrode delivers a high energy density of 56.96 W h kg−1. Such superior performance demonstrate that the CuCo2S4 NRAs are promising materials for future energy storage applications.

High-throughput dielectrophoretic manipulation of bioparticles within fluids through biocompatible three-dimensional microelectrode array†

Dielectrophoresis (DEP) has been deemed as a potential and ideal solution for bioparticle manipulation. A 3‐D carbon micro‐electro‐mechanical system (MEMS) fabricated from the latest developed carbon‐MEMS approach has advantages of offering low‐cost, biocompatible and high‐throughput DEP manipulation for bioparticles. In this paper, a typical process for fabrication of various 3‐D microelectrode configurations was demonstrated; accurate numerical analysis was presented on electric field gradient distribution and DEP force based on various microelectrode array configurations. The effects of electrode edge angle, electrode edge‐to‐edge spacing and electrode height on the electric field distributions were investigated, and optimal design considerations and rules were concluded through analysis of results. The outcomes demonstrate that the sharp edge electrode is more effective in DEP manipulation and both electrode edge‐to‐edge spacing and electrode height are critical design parameters for seeking optimal DEP manipulation. The gradient magnitude increases exponentially as the electrode spacing is reduced and the electric field extends significantly as the electrode height increases, both of which contribute to a higher throughput for DEP manipulation. These findings are consistent with experimental observations in the literature and will provide critical guidelines for optimal design of DEP devices with 3‐D carbon‐MEMS.

Generalized formulations for aerial image based lens aberration metrology in lithographic tools with arbitrarily shaped illumination sources.

In the current optical lithography processes for semiconductor manufacturing, differently shaped illumination sources have been widely used for the need of stringent critical dimension control. This paper proposes a technique for in situ measurement of lens aberrations with generalized formulations of odd and even aberration sensitivities suitable for arbitrarily shaped illumination sources. With a set of Zernike orders, these aberration sensitivities can be treated as a set of analytical kernels which succeed in constructing a sensitivity function space. The analytical kernels reveal the physical essence of partially coherent imaging systems by taking into account the interaction between the wavefront aberration and the illumination source, and take the advantage of realizing a linear and analytical relationship between the Zernike coefficients to be measured and the measurable physical signals. A variety of mainstream illumination sources with spatially variable intensity distributions were input into the PROLITH for the simulation work, which demonstrates and confirms that the generalized formulations are suitable for measuring lens aberrations up to a high order Zernike coefficient under different types of source distributions. The technique is simple to implement and will have potential applications in the in-line monitoring of imaging quality of current lithographic tools.

Carbonization-assisted integration of silica nanowires to photoresist-derived three-dimensional carbon microelectrode arrays

We propose a novel technique of integrating silica nanowires to carbon microelectrode arrays on silicon substrates. The silica nanowires were grown on photoresist-derived three-dimensional carbon microelectrode arrays during carbonization of patterned photoresist in a tube furnace at 1000 °C under a gaseous environment of N(2) and H(2) in the presence of Cu catalyst, sputtered initially as a thin layer on the structure surface. Carbonization-assisted nucleation and growth are proposed to extend the Cu-catalyzed vapor-liquid-solid mechanism for the nanowire integration behaviour. The growth of silica nanowires exploits Si from the etched silicon substrate under the Cu particles. It is found that the thickness of the initial Cu coating layer plays an important role as catalyst on the morphology and on the amount of grown silica nanowires. These nanowires have lengths of up to 100 µm and diameters ranging from 50 to 200 nm, with 30 nm Cu film sputtered initially. The study also reveals that the nanowire-integrated microelectrodes significantly enhance the electrochemical performance compared to blank ones. A specific capacitance increase of over 13 times is demonstrated in the electrochemical experiment. The platform can be used to develop large-scale miniaturized devices and systems with increased efficiency for applications in electrochemical, biological and energy-related fields.