Guanglan Liao

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.

Quantum dot-sensitized hierarchical micro/nanowire architecture for photoelectrochemical water splitting.

We report the fabrication of quantum dot-sensitized hierarchical structure and the application of the structure as a photoanode for photoelectrochemical water splitting. The structure is synthesized by hydrothermally growing ZnO nanowires on silicon microwires grown with the vapor-liquid-solid method. Then the hierarchical structure is further sensitized with CdS and CdSe quantum dots and modified with IrOx quantum dots. As a result, the silicon microwires, ZnO nanowires, and the quantum dot/ZnO core/shell structure form a multiple-level hierarchical heterostructure, which is remarkably beneficial for light absorption and charge carrier separation. Our experimental results reveal that the photocurrent density of our multiple-level hierarchical structure achieves a surprising 171 times enhancement compared to that from simple ZnO nanowires on a planar substrate. In addition, the photoanode shows high stability during the water-splitting experiment. These results prove that the quantum dot-sensitized hierarchical structure is an ideal candidate for a photoanode in solar water splitting applications. Importantly, the modular design approach we take to produce the photoanode allows for the integration of future discoveries for further improvement of its performance.

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.

Gearbox condition monitoring using self-organizing feature maps

Abstract This paper proposes a novel technique for the condition monitoring of gearboxes based on a self-organizing feature maps (SOFM) network. In order to visualize the learned SOFM results more clearly, an improved method based on the unified distance matrix (U-matrix) method is presented, in which the overall topological information condensed into the map units is considered so as to project the high-dimensional input vectors into a two-dimensional space and give a better picture of their intrinsic structure than the original U-matrix method. The feature data extracted from industrial gearbox vibration signals measured under different operating conditions are analysed using the proposed technique. The results show that trained with the SOFM network and visualized with the improved method, the feature data are mapped into a two-dimensional space and formed clustering regions, each indicative of a specific gearbox condition. Therefore, the gearbox operating condition with a fatigue crack or broken tooth compared with the normal condition is identified clearly. Furthermore, with the trajectory of the image points for the feature data in two-dimensional space, the variation of gearbox conditions is observed visually, and the development of gearbox early-stage failures is monitored in time.

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.

Defect Inspection of Flip Chip Solder Bumps Using an Ultrasonic Transducer

Surface mount technology has spurred a rapid decrease in the size of electronic packages, where solder bump inspection of surface mount packages is crucial in the electronics manufacturing industry. In this study we demonstrate the feasibility of using a 230 MHz ultrasonic transducer for nondestructive flip chip testing. The reflected time domain signal was captured when the transducer scanning the flip chip, and the image of the flip chip was generated by scanning acoustic microscopy. Normalized cross-correlation was used to locate the center of solder bumps for segmenting the flip chip image. Then five features were extracted from the signals and images. The support vector machine was adopted to process the five features for classification and recognition. The results show the feasibility of this approach with high recognition rate, proving that defect inspection of flip chip solder bumps using the ultrasonic transducer has high potential in microelectronics packaging.

Sensitivity Analysis of a Bioinspired Refractive Index Based Gas Sensor

It was found out that the change of refractive index of ambient gas can lead to obvious change of the color of Morpho butterfly’s wing. Such phenomenon has been employed as a sensing principle for detecting gas. In the present study, Rigorous Coupled-Wave Analysis (RCWA) was described briefly, and the partial derivative of optical reflection efficiency with respect to the refractive index of ambient gas, i.e., sensitivity of the sensor, was derived based on RCWA. A bioinspired grating model was constructed by mimicking the nanostructure on the ground scale of Morpho didius butterfly’s wing. The analytical sensitivity was verified and the effect of the grating shape on the reflection spectra and its sensitivity were discussed. The results show that by tuning shape parameters of the grating, we can obtain desired reflection spectra and sensitivity, which can be applied to the design of the bioinspired refractive index based gas sensor.

Genetic algorithms for defect detection of flip chips

Abstract Flip chip packaging technology is widely used in high density assembly and superior performance devices. The solder joints are sandwiched between dies and substrates, leading to the defects optically opaque. Defect inspection of flip chips become more difficult. In this paper, a nondestructive detection method was presented. Ultrasonic excitations were forced on the surface of the flip chips and the raw vibration signals were measured by a laser scanning vibrometer. Eleven time domain features and twenty-four frequency domain features were extracted for analysis. After that, the genetic algorithm was introduced for feature selection and the back propagation network was adopted for classification and recognition. The flip chips were divided into three categories: good flip chips, flip chips with missing solder joints, and flip chips with open solder joints. They are recognized under the features selected by genetic algorithms rapidly and accurately, compared with those under other feature datasets, demonstrating that the approach using genetic algorithms is effective for defect inspection in flip chip packaging.