Ching-Ping Wong

Low-Cost High-Performance Solid-State Asymmetric Supercapacitors Based on MnO2 Nanowires and Fe2O3 Nanotubes

A low-cost high-performance solid-state flexible asymmetric supercapacitor (ASC) with α-MnO2 nanowires and amorphous Fe2O3 nanotubes grown on flexible carbon fabric is first designed and fabricated. The assembled novel flexible ASC device with an extended operating voltage window of 1.6 V exhibits excellent performance such as a high energy density of 0.55 mWh/cm(3) and good rate capability. The ASC devices can find numerous applications as effective power sources, such as powering color-switchable sun glasses and smart windows.

Hydrogenated ZnO Core–Shell Nanocables for Flexible Supercapacitors and Self-Powered Systems

Although MnO2 is a promising material for supercapacitors (SCs) due to its excellent electrochemical performance and natural abundance, its wide application is limited by poor electrical conductivity. Inspired by our results that the electrochemical activity and electrical conductivity of ZnO nanowires were greatly improved after hydrogenation, we designed and fabricated hydrogenated single-crystal ZnO@amorphous ZnO-doped MnO2 core-shell nanocables (HZM) on carbon cloth as SC electrodes, showing excellent performance such as areal capacitance of 138.7 mF/cm(2) and specific capacitance of 1260.9 F/g. Highly flexible all-solid-state SCs were subsequently assembled with these novel HZM electrodes using polyvinyl alcohol/LiCl electrolyte. The working devices achieved very high total areal capacitance of 26 mF/cm(2) and retained 87.5% of the original capacitance even after 10 000 charge/discharge cycles. An integrated power pack incorporating series-wound SCs and dye-sensitized solar cells was demonstrated for stand-alone self-powered systems.

Thermal conductivity, elastic modulus, and coefficient of thermal expansion of polymer composites filled with ceramic particles for electronic packaging

The effective thermal conductivity, elastic modulus, and coefficient of thermal expansion of epoxy resins filled with ceramic fillers like silica, alumina, and aluminum nitride were determined. The data obtained was compared with theoretical and semitheoretical equations in the literature that are used to predict the properties of two phase mixtures. It was found that Agaris model provided a good estimate of the composite thermal conductivity. The Hashin-Shtrikman lower bound for composite modulus fits the modulus data fairly well at low concentrations of the filler. Also, it was found that the coefficients of thermal expansion of the filled composites lie in between Schaperys upper and lower bounds.

Low-loss percolative dielectric composite

In this letter, we report a modified percolative polymer composite that has a low dielectric loss (tanδ∼0.02@10KHz, comparable to that of the polymer matrix), a high dielectric constant (k>100@10KHz, about 30 times higher than that of the polymer matrix), and a low frequency dependence. This high-k polymer hybrid is filled with self-passivated micro- and nano-aluminum particles. The self-passivation of an aluminum particle results in dense nanoscale insulating Al2O3 shells outside of the metallic spheres, which allows the electrons in the metallic core to tunnel through it, and thereby the aluminum/polymer composites exhibit a high dielectric constant as a percolation system; on the other hand, the insulating oxide layer restricts the electron transfer between aluminum particles, thus leading to a very low loss of the composites.

Silver Nanowires: From Scalable Synthesis to Recyclable Foldable Electronics

There is currently an urgent need for electronic devices with superior performance, robustness, smaller size, lower cost, user friendliness, and that do not increase the environmental burden. [ 1 , 2 ] Many materials scientists and engineers have been searching for novel fl exible semiconductive materials as integrated circuits (ICs) to achieve the properties of both fl exibility and stretchability. [ 3– 8 ] Meanwhile, other researchers focus on the substrate materials that cater to the “chip-on-fl ex technologies”, which are in a position of more imperative need in the current industry and consumer market. [ 1 , 9– 11 ] Recently, Siegel et al. demonstrated the feasibility of fabricating electrical circuits on paper for the purpose of foldable and disposable devices, which displays a promising future for the low-cost consumable electronic devices. [ 12 ] Compared to the conventional printed circuit board (PCB) technology, paper offers a few advantages. For example, paper is inexpensive and can decompose easily; it is much thinner than the ordinary PCBs and can be folded, unfolded, and creased easily; electronics based on paper can be stored in smaller spaces or made to form 3D self-standing structures. [ 12 , 13 ] Finally, with the porous and breathable nature, paper can potentially be applied in disposable components for adhesives and clinical diagnosis, such as being combined with portable analytical devices. [ 14 , 15 ] However, because ordinary

A Novel Conformal RFID-Enabled Module Utilizing Inkjet-Printed Antennas and Carbon Nanotubes for Gas-Detection Applications

This letter introduces for the first time the integration of a conformal radio frequency identification (RFID) antenna with a single-walled carbon nanotube (SWCNT) composite in a chipless RFID node for toxic gas detection. The electrical performance characterization of the inkjet-printed SWCNT film is also reported for the first time up to 1 GHz. The whole module is realized by inkjet printing on a low-cost paper-based substrate, and the RFID tag is designed for the European UHF RFID band. The electrical conductivity of the SWCNT film changes in the presence of very small quantities of toxic gases like ammonia and nitrogen oxide, resulting in the variation of the backscattered power level, which can be easily detected by the RFID reader to realize reliable wireless toxic gas sensing.

A three-dimensional vertically aligned functionalized multilayer graphene architecture: an approach for graphene-based thermal interfacial materials.

Thermally conductive functionalized multilayer graphene sheets (fMGs) are efficiently aligned in large-scale by a vacuum filtration method at room temperature, as evidenced by SEM images and polarized Raman spectroscopy. A remarkably strong anisotropy in properties of aligned fMGs is observed. High electrical (∼386 S cm(-1)) and thermal conductivity (∼112 W m(-1) K(-1) at 25 °C) and ultralow coefficient of thermal expansion (∼-0.71 ppm K(-1)) in the in-plane direction of A-fMGs are obtained without any reduction process. Aligned fMGs are vertically assembled between contacted silicon/silicon surfaces with pure indium as a metallic medium. Thus-constructed three-dimensional vertically aligned fMG thermal interfacial material (VA-fMG TIM) architecture has significantly higher equivalent thermal conductivity (75.5 W m(-1) K(-1)) and lower contact thermal resistance (5.1 mm2 K W(-1)), compared with their counterpart from A-fMGs that are recumbent between silicon surfaces. This finding provides a throughout approach for a graphene-based TIM assembly as well as knowledge of vertically aligned graphene architectures, which may not only facilitate graphenes application in current demanding thermal management but also promote its widespread applications in electrodes of energy storage devices, conductive polymeric composites, etc.

Materials for Advanced Packaging

Significant progress has been made in advanced packaging in recent years. Several new packaging techniques have been developed and new packaging materials have been introduced. This book provides a comprehensive overview of the recent developments in this industry, particularly in the areas of microelectronics, optoelectronics, digital health, and bio-medical applications. This book discusses established techniques, as well as emerging technologies, in order to provide readers with the most up-to-date developments in advanced packaging.

Large-scale production of two-dimensional nanosheets

Two-dimensional (2D) nanomaterials such as graphene, boron nitride (BN), and molybdenum disulfide (MoS2) have been attracting increasing research interest in the past few years due to their unique material properties. However, the lack of a reliable large-scale production method is an inhibiting issue for their practical applications. Here we report a facile, efficient, and scalable method for the fabrication of monolayer and few-layer BN, MoS2, and graphene using combined low-energy ball milling and sonication. Ball milling generates two forces on layered materials, shear force and compression force, which can cleave layered materials into 2D nanosheets from the top/bottom surfaces, and the edge of layered materials. Subsequent sonication would further break larger crystallites into smaller crystallites. These fabricated 2D nanosheets can be well dispersed in aqueous solutions at high concentrations, 1.2 mg mL−1 for BN, 0.8 mg mL−1 for MoS2, and 0.9 mg mL−1 for graphene, which are highly advantageous over other methods. These advantages render great potential in the construction of high-performance 2D material-based devices at low cost. For example, a prototype gas sensor is demonstrated in our study using graphene and MoS2, respectively, which can detect several ppm of ammonia gas.

Mechanically robust superhydrophobicity on hierarchically structured Si surfaces

Improvement of the robustness of superhydrophobic surfaces is critical in order to achieve commercial applications of these surfaces in such diverse areas as self-cleaning, water repellency and corrosion resistance. In this study, the mechanical robustness of superhydrophobic surfaces was evaluated on hierarchically structured silicon surfaces. The effect of two-scale hierarchical structures on robustness was investigated using an abrasion test and the results compared to those of superhydrophobic surfaces fabricated from polymeric materials and from silicon that contains only nanostructures. Unlike the polymeric and nanostructure-only surfaces, the hierarchical structures retained superhydrophobic behavior after mechanical abrasion.