Hollow multi-nanochannel carbon nanofiber/MoS2 nanoflower composites as binder-free lithium-ion battery anodes with high capacity and ultralong-cycle life at large current density

The electrode materials with high pseudocapacitance can enhance the rate capability and cycling stabil-ity of lithium-ion storage devices.Herein,we fabricated MoS2 nanoflowers with ultra-large interlayer spacing on N-doped hollow multi-nanochannel carbon nanofibers(F2-MoS2/NHMCFs)as freestanding binder-free anodes for lithium-ion batteries(LIBs).The ultra-large interlayer spacing(0.78～1.11 nm)of MoS2 nanoflowers can not only reduce the internal resistance,but also increase accessible active sur-face area,which ensures the fast Li+intercalation and deintercalation.The NHMCFs with hollow and multi-nanochannel structure can accommodate the large internal strain and volume change during lithi-ation/delithiation process,it is beneficial to improving the cycling stability of LIBs.Benefiting from the above combined structure merits,the F2-MoS2/NHMCFs electrodes deliver a high rate capability 832 mA h g-1 at 10 A g-1 and ultralong cycling stability with 99.29 and 91.60％capacity retention at 10 A g-1 after 1000 and 2000 cycles,respectively.It is one of the largest capacities and best cycling stability at 10 A g-1 ever reported to date,indicating the freestanding F2-MoS2/NHMCFs electrodes have potential applications in high power density LIBs.     

Flexible electronics: Prediction of substrate deformation during different steps of the lithography process

A numerical model was developed to simulate the micro-deformations of a polymeric substrate due to lithographic processing of different layers of a transistor-like structure. The results of the model were validated with the results from experiments. The model, a mechanical-thermal-hygroscopic model, takes into account the dimensional effects of temperature, moisture and stresses. It also includes the temperature dependent visco-elastic behaviour of the polymer substrate. The model can be used to predict overlay accuracies between different functional layers introduced by the lithographic process. It can also be used to understand the underlying processes such that it provides a tool to improve the overlay accuracy during actual processing.     

Innovative method to produce large-area freestanding functional ceramic foils

Using thick and thin films instead of bulk functional materials presents tremendous advantages in the field of flexible electronics and component miniaturization. Here, a low-cost method to grow and release large-area, microscale thickness, freestanding, functional, ceramic foils is reported. It uses evaporation of sodium chloride to silicon wafer substrates as sacrificial layers, upon which functional lead titanate zirconate ceramic films are grown at 710?°C maximum temperature to validate the method. The freestanding, functional foils are then released by dissolution of the sacrificial sodium chloride in water and have the potential to be integrated into low-thermal stability printed circuits and flexible substrates. The optimization of the sodium chloride layer surface quality and bonding strength with the underlying wafer is achieved thanks to pre-annealing treatment.     

Fabrication of paper based carbon/graphene/ZnO aerogel composite decorated by polyaniline nanostructure: Investigation of electrochemical properties

The cellulose derived carbon/graphene/ZnO aerogel composite was prepared as an electrode in order to investigate the electrochemical properties. Carbon aerogel was synthesized using paper as an available cellulose source, and the composite was obtained through a new and simple preparation method including the immersion of monolithic carbon aerogel in graphene oxide/Zn²⁺ suspension and subsequent chemical reduction and freeze drying. The morphology, functional groups and crystalline structure of the samples were studied with Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction Spectroscopy (XRD), respectively. Electrochemical performance of the prepared binder free electrodes was examined using Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The data revealed that flexible carbon/graphene/ZnO composite resulted in a low density (0.035 g cm⁻³) electrode with the capacitance of 900 mF cm⁻² at a high current density of 10 mA cm⁻², lower IR drop and high cyclic stability (capacitance retention of 96%) after 1000 cycles, at 10 mA cm⁻². These features were due to the presence of 3D porous conductive network, highly reduced graphene oxide, and the formation of ZnO nanoparticles on graphene sheets. Moreover, polyaniline (PANI) was introduced to carbon/graphene/ZnO composite electrode using electro-oxidation method at different reaction time and aniline concentration in order to achieve remarkably improved capacitance of 2500 mF cm⁻² (at 10 mA cm⁻²) and low charge transfer resistance. Also, after the supercapacitor device assembly, the capacitance was retained. Based on the results, the synthesized composite is a promising material for new generation of lightweight freestanding electrodes with the high electrochemical performance.     

抛光对化学气相沉积金刚石自支撑膜断裂强度的影响

研究了抛光对化学气相沉积金刚石自支撑膜断裂强度的影响。结果表明,金刚石自支撑膜粗糙表面所带来的V形缺口会降低其断裂强度,而且随着膜厚的增加,降低的程度越明显,通过抛光粗糙表面,消除了V形缺口对断裂强度的影响,有利于提高金刚石膜的抗破坏能力。提出了一种金刚石膜断裂强度的经验计算方法,获得的断裂强度值更接近于金刚石膜的本征断裂强度。     

Development of etching processes for the micropatterning of silicalite films

Silicalite (SIL-1) polycrystalline films have been synthesized on Si wafers and then micropatterned using both dry (ion milling, reactive ion etching) and wet etching processes after deploying a resin mask on the film top surfaces. The advantages and characteristics of the different etching processes are discussed and related to the orientation of the zeolite crystals in the films. Finally, the etching processes developed can also be used to release freestanding zeolite structures. This is demonstrated for the fabrication of bulk zeolite microcantilevers with a high aspect ratio.     

Porous nitrogen-enriched hollow carbon nanofibers as freestanding electrode for enhanced lithium storage

One-dimensional porous carbons bearing high surface areas and sufficient heteroatom doped functional-ities are essential for advanced electrochemical energy storage devices, especially for developing free-standing film electrodes. Here we develop a porous, nitrogen-enriched, freestanding hollow carbon nanofiber (PN-FHCF) electrode material via filtration of polypyrrole (PPy) hollow nanofibers formed by in situ self-degraded template-assisted strategy, followed by NH3-assisted carbonization. The PN-FHCF retains the freestanding film morphology that is composed of three-dimensional networks from the entanglement of 1D nanofiber and delivers 3.7-fold increase in specific surface area (592 m2·g-1) com-pared to the carbon without NH3 treatment (FHCF). In spite of the enhanced specific surface area, PN-FHCF still exhibits comparable high content of surface N functionalities (8.8％, atom fraction) to FHCF. Such developed hierarchical porous structure without sacrificing N doping functionalities together enables the achievement of high capacity, high-rate property and good cycling stability when applied as self-supporting anode in lithium-ion batteries, superior to those of FHCF without NH3 treatment.     

Improving purity and size of single-crystal diamond plates produced by high-rate CVD growth and lift-off process using ion implantation

The lift-off process using ion implantation has recently been applied to produce large and thick single-crystal diamond plates by chemical vapor deposition (CVD). CVD growth conditions for undoped, as opposed to nitrogen-doped, diamond were investigated to improve the purity of plates produced by this technique. This utilized apparatus identical to that for high-rate growth with nitrogen addition under high-density plasma. By lowering the growth temperature to 900 °C, an undoped single-crystal CVD diamond plate with a maximum length of 9 mm and thickness of 0.47 mm was successfully produced without formation of non-epitaxial crystallites. The UV–Vis–NIR transmission spectrum of this plate was identical to high-pressure high-temperature (HPHT) synthetic IIa diamond, suggesting high purity of the plate. To increase the size of single-crystal CVD diamond plates, a process to enlarge the seed crystal by combining the lift-off process and a side-surface growth technique is proposed. By this process, a half-inch single-crystal CVD diamond seed crystal was successfully synthesized and half-inch freestanding single-crystal CVD diamond plates were produced from the seed.     

Mechanical characterisation of AlSi-hBN, NiCrAl-Bentonite, and NiCrAl-Bentonite-hBN freestanding abradable coatings

This paper reports recent research on abradable materials employed for aero-engine applications. Such thermal spray coatings are used extensively within the gas turbine, applied to the inner surface of compressor and turbine shroud sections, coating the periphery of the blade rotation path. The function of an abradable seal is to wear preferentially when rotating blades come into contact with it, while minimising over-tip clearance and improving the efficiency of the engine.Historically, our understanding of abradables has been limited, with their design and service operation often described as a “black art.” For instance, there is a distinct lack of materials property data for all abradable systems, mainly due to the difficulty of testing this unique class of material under bulk loading conditions (tension or compression).The present paper will describe the mechanical assessment of two families of abradables with either aluminium or nickel as the matrix phase. A novel method was developed to produce the free-standing abradable test specimens, employing thermal spraying and dissolvable moulds. These specimens were suitable for evaluation under static and cyclic tensile stress conditions. The absence of any substrate and associated mechanical interactions has meant that unique measurements of Young's modulus, tensile strength, and strain to failure were obtained for these complex composite materials in their own right.This work forms part of a wider programme to gain a greater understanding of abradable materials, how they perform, and ultimately how to improve their performance in-service.     

Developments of elemental technologies to produce inch-size single-crystal diamond wafers

Seen as the future of wide band gap semiconductor materials, single-crystal diamonds need to be fabricated in at least inch-size wafers if they are to be of use in industry. The key methods required to achieve this are 1) improving the growth of single crystals with sufficient quality over large areas at an acceptable growth rate, 2) enlarging the seed crystal, and 3) improving the fabrication of the freestanding wafers. This paper briefly reviews recent progresses and reports the most recent results of our research of solving these technical problems.