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Bimetallic transition metal phosphides (TMPs) as potential candidates for superior electrochemical performance are still facing great challenges in the controllable preparation of two-dimensional (2D) structures with high aspect ratio. Herein, a novel structure of quasi-monolayered NiCo-bimetal-phosphide (NiCoP) has been designed and successfully synthesized by the newly developed process combined with ultrasonic-cavitation and phase-transition. This is the first time to break through the controllable preparation of 2D bimetal-phosphides with a thickness of 0.98 nm in sub-nanoscale. Based on the advantages of 2D quasi-monolayer structure with dense crystalline-amorphous interface and the reconfigured electronic structure between Niδ+/Coδ+ and Pδ−, the optimized Ni5%CoP exhibits an outstanding bifunctional performance for electrocatalyzing both hydrogen evolution reaction and oxygen evolution reaction in an alkaline medium. Ni5%CoP presents lower overpotentials and voltage of 84 mV & 259 mV and 1.48 V at the current density of 10 mA·cm−2 for HER & OER and overall water splitting, respectively, which are superior to most other reported 2D bimetal-phosphides. This work provides a new strategy to optimize the performance of electrolytic water for bimetal-phosphates and it may be of significant value in extending the design of other ultrathin 2D structured catalysts.

MnCo2O4 is regarded as a good electrode material for supercapacitor due to its high specific capacity and good structural stability. However, its poor electrical conductivity limits its wide-range applications. To solve this issue, we integrated the MnCo2O4 with Ni3S4, which has a good electrical conductivity, and synthesized a MnCo2O4/Ni3S4 nanocomposite using a two-step hydrothermal process. Comparing with individual MnCo2O4 and Ni3S4, the MnCo2O4/Ni3S4 nanocomposite showed a higher specific capacity and a better cycling stability as the electrode for the supercapacitor. The specific capacity value of the MnCo2O4/Ni3S4 electrode was 904.7 C g−1 at 1 A g−1 with a potential window of 0–0.55 V. A hybrid supercapacitor (HSC), assembled using MnCo2O4/Ni3S4 and active carbon as the cathode and anode, respectively, showed a capacitance of 116.4 F g−1 at 1 A g−1, and a high energy density of 50.7 Wh kg−1 at 405.8 W kg−1. Long-term electrochemical stability tests showed an obvious increase of the HSC’s capacitance after 5500 charge/discharge cycles, reached a maximum value of ∼162.7% of its initial value after 25,000 cycles, and then remained a stable value up to 64,000 cycles. Simultaneously, its energy density was increased to 54.2 Wh kg−1 at 380.3 W kg−1 after 64,000 cycles.

MEMS microphone has a wide range of application prospects in electronic devices such as mobile phones, headphones, and hearing aids due to its small size, low cost, and reliable performance. Research and development of MEMS microphones involves multiple thermo-electro-mechanical couplings among various physical and electrical fields. Unfortunately, there is not an accurate three-dimensional (3D) MEMS microphone simulation platform, which can be applied for the design of chip parameters and packaging characteristics. Herein, based on commercial COMSOL software, we have established a 3D simulation platform for MEMS microphones, which is used to systematically study the influences of geometric structure and physics parameters on the sensitivity and frequency responses of the microphone and consider the influences of packaging characteristics on the performance of the microphone. The simulation results are consistent with those obtained using a lumped element method, which proves the accuracy of the simulation platform. The platform can be used to design and explore new principles or mechanisms of MEMS microphone devices.

In this paper, we report acoustofluidic behaviors of zinc oxide (ZnO) thin film surface acoustic wave (SAW) devices fabricated on aluminum (Al) plate/sheet (600m/200m) substrates using hybrid modes. Finite element analysis (FEA) ulation and experimental results indicate that the wave vibration modes are changed from Rayleigh mode to hybrid modes and subsequently to Lamb wave modes with the increased device's wavelength or decreased substrate thickness. For the Rayleigh, hybrid and zero-order Lamb wave modes, the droplet movement is a combination of rolling and sliding, whereas for Sezawa mode and one-order Lamb wave modes, the droplet movement is a combination of jumping and sliding. Moreover, for Lamb wave modes, the asymmetrical modes present a better pumping performance than those of symmetrical modes.

Sequential glass and melting transitions in semi-crystalline shape memory polymers (SMPs) provide great opportunities to design and generate multiple shape-memory effects (SMEs) for practical applications. However, the complexly dynamic confinements of coexisting amorphous and crystalline phases within the semi-crystalline SMPs are yet fully understood. In this study, an interfacial confinement model is formulated to describe dynamic relaxation and shape memory behavior in the semi-crystalline SMPs undergoing sequential phase/state transitions. A confinement entropy model is first established to describe the glass transition behavior of amorphous phase within the SMPs based on the free volume theory, where the free volume is critically confined by the crystalline phase. An extended Avrami model is then formulated using the frozen volume theory to characterize the melting and crystallization transitions of the crystalline phase in the SMPs, whose interfacial confinement with the amorphous phase has been identified as the driving force for the supercooled regime. Furthermore, an extended Maxwell model is formulated to describe the effect of dynamic confinement of two phases on the multiple SMEs and shape recovery behaviors in the semi-crystalline SMPs. Finally, the effectiveness of the newly proposed model is verified using the experimental data reported in the literature. This study aims to provide a new methodology for the dynamic confinements and cooperative principles in the semi-crystalline SMP towards multiple SMEs.

Effects of grain boundaries (GBs) in graphene on adsorption and diffusion of sodium were investigated using first principle calculations. Results showed that the presence of GBs in graphene enhanced the adsorption of sodium, with their adsorption energies in the range of -1.32~-0.79 eV, which were lower than the value of -0.67 eV for sodium adsorbed on pristine graphene. The diffusion energy barriers were in the range of 0.09 to 0.35 eV when sodium was diffused along GBs of graphene, whereas they were decreased when sodium was gradually diffused into the GBs. Results showed that graphene with GBs had a larger energy storage capacity for sodium than the pristine one, indicating that it can be used as a good anode material for sodium ion batteries.

A new antisolvent method was developed to prepare CH₃NH₃PbI₃ and electron transport layers for making efficient hybrid perovskite solar cells. By directly using [6,6]-phenyl-C61-butyric acid methyl ester in chlorobenzene solution as antisolvent, CH₃NH₃PbI₃ and electron transport layers were simultaneously formed in the films. This method not only simplifies the fabrication process of devices, but also produces uniform perovskite films and improves the interfacial structures between CH₃NH₃PbI₃ and electron transport layers. Large perovskite grains were observed in these films, with the average grain size of >1 μm. The so-formed CH₃NH₃PbI₃/electron transport layers demonstrated good optical and charge transport properties. And perovskite solar cells fabricated using these simultaneously-formed layers achieved a higher power conversion efficiency of 16.58% compared to conventional antisolvent method (14.92%). This method reduces nearly 80% usage of chlorobenzene during the fabrication, offering a more facile and environment-friendly approach to fabricate efficient perovskite solar cells than the conventional antisolvent method.

Progress in ZnO thin films and nanostructures for the acoustic wave microfluidic and sensing applications are reviewed in this chapter. ZnO thin films with good piezoelectric properties possess large electromechanical coupling coefficients and can be fabricated for the surface acoustic wave (SAW) and film-bulk acoustic resonator (FBAR) devices with a good acoustic performance. The SAWs can be excited to mix, stream, pump, eject, and atomize the liquid, and precision sensing can be performed using SAWs and FBARs. Therefore, the ZnO SAW devices are attractive to be integrated into a lab-on-chip system where the SAWs can transport bio-fluids to the desired area, mix the extracted DNA or proteins, and detect the changes of the signals using SAWs or FBARs. The ZnO SAW and FBAR devices in combination with different sensing layers could also be used to successfully detect gas, UV light, and biochemicals with remarkable sensitivities.

A platinum-coated singlemode-multimode structure is investigated in this paper as an optical fibre sensor (OFS) to monitor the phase transition of a phase change material (PCM). Paraffin wax has been used as an example to demonstrate the sensor’s performance and operation. Most materials have the same temperature but different thermal energy levels during the phase change process, therefore, sole dependency on temperature measurement may lead to an incorrect estimation of the stored energy in PCM. The output spectrum of the reflected light from the OFS is very sensitive to the bend introduced by the PCM where both liquid and solid states exist during the phase transition. The measurement of strain experienced by the OFS during the phase change of the PCM is utilized for identifying the phase transition of paraffin wax between the solid and liquid states. The experimental results presented in this paper show that the OFS can measure the phase change point of paraffin wax and the sensor with a multimode fibre length of 10 mm measured the phase transition temperature range from 37.8 ºC to 57.7 ºC.

Ni-Ti-Nb and Ni-Ti shape memory thin films were sputter-deposited onto silicon substrates and annealed at 600ºC for crystallization. X-ray diffraction (XRD) measurements indicated that all of the annealed Ni-Ti-Nb films were composed of crystalline Ni-Ti (Nb) and Nb-rich grains. X-ray photoelectron spectroscopy (XPS) tests showed that the surfaces of Ni-Ti-Nb films were covered with Ti oxides, NiO and Nb2O5. The corrosion resistance of the Ni-Ti-Nb films in 3.5 wt. % NaCl solution was investigated using electrochemical tests such as open-circuit potential (OCP) and potentio-dynamic polarization tests. Ni-Ti-Nb films showed higher OCPs, higher corrosion potentials (Ecorr) and lower corrosion current densities (icorr) than the binary Ni-Ti film, which indicated a better corrosion resistance. The reason may be that Nb additions modified the passive layer on the film surface. The OCPs of Ni-Ti-Nb films increased with further Nb additions, whereas no apparent difference of Ecorr and icorr was found among the Ni-Ti-Nb films.

Non-toxic copper containing chalcogenides are considered as promising alternate materials for the absorber layer in thin film solar cells and visible-light harvesting devices. In this paper, we reported synthesis of Cu3BiS3 thin films using a two-step thermal evaporation method for the first time. A Cu2S layer of 0.4 μm thickness was firstly evaporated onto glass substrate at room temperature, followed by evaporation of a Bi2S3 layer of 0.8 μm thickness. The Cu3BiS3 thin films were formed by thermally annealing and diffusing the two evaporated layers in a vacuum furnace. This method resulted in the improved crystallinity and phase purity of the grown Cu3BiS3 films. Effects of annealing temperature on different properties of the fabricated samples were investigated. The obtained low band-gap (1.45 eV) and good optical properties such as low transmittance (10–30%) and reflectance (~ 10%) of the Cu3BiS3 films demonstrated it as a suitable material for the absorber layer of solar cells.

This study presents successful growth of defective 2D terrace MoSe2/CoMoSe lateral heterostructures (LH), bilayer and multilayer MoSe2/CoMoSe LH, and vertical heterostructures (VH) nanolayers by doping metal Co (cobalt) element into MoSe2 atomic layers to form a CoMoSe alloy at the high temperature (~900 °C). After the successful introduction of metal Co heterogeneity in the MoSe2 thin layers, more active sites can be created to enhance hydrogen evolution reaction (HER) activities combining with metal Co catalysis, through the mechanisms including (1) atomic arrangement distortion in CoMoSe alloy nanolayers, (2) atomic level coarsening in LH interfaces and terrace edge layer architecture in VH, (3) formation of defective 2D terrace MoSe2 nanolayers heterogeneous catalyst via metal Co doping. The HER investigations indicated that the obtained products with LH and VH exhibited an improved HER activity in comparison with those from the pristine 2D MoSe2 electrocatalyst and LH type MoSe2/CoMoSe. The present work shows a facile yet reliable route to introduce metal ions into ultrathin 2D transition metal dichalcogenides (TMDCS) and produce defective 2D alloy atomic layers for exposing active sites, and thus eventually improve their electrocatalytic performance.

Group IVA elements (Si, Ge and Sn) are promising candidates for the anode materials of lithium ion batteries (LIBs) due to their large theoretical specific capacities. However, serious problems of pulverization and capacity degradation resulted from the huge volume changes during charge/discharge operations hindered their successful applications as the anode materials in the LIBs. In this work, diffusion behaviors of Li ions in Si(100) and Si(111) slabs with a piezoelectric field applied perpendicularly to the surfaces were investigated using density functional theory. Results showed that the diffusivity of the Li in Si can be significantly enhanced by applying the electric field generated from the piezoelectric material. This finding can explain well the recent experimental observations in which improved electrochemical performance was obtained using Si/carbon nanotube/BaTiO3 as the anode for the LIBs. New generation of anode composite materials can be designed based on this idea and the piezoelectric material is used not only to accommodate the volume variation of active materials of Si, but also to enhance the charging rate of the LIBs.

A multilayer structure of TeO2/interdigital transducers (IDTs)/ZnO(1120)/Si(100) was proposed and investigated to achieve both high sensitivity and temperature-stability for bio-sensing applications. Dispersions of phase velocities, electromechanical coupling coefficients K2, temperature coefficient of delay (TCD) and sensitivity in the multilayer structures were simulated as functions of normalized thicknesses of ZnO (hZnO/λ) and TeO2(hTeO2/λ) films. The fundamental mode of Love mode (LM) - surface acoustic wave (SAW) shows a larger value of K2 and higher sensitivity compared with those of the first mode. TeO2 film with a positive TCD not only compensates the temperature effect induced due to the negative TCD of ZnO(1120)/Si(100), but also enhances the sensitivity of the love mode device. The optimal normalized thickness ratios were identified to be hTeO2/λ=0.021 and hZnO/λ=0.304, and the devices with such structures can which generate a normalized sensitivity of -1.04×10-3 m3/kg, a TCD of 0.009 ppm/°C, and a K2 value of 2.76%.

Considering the normal contourlet transform only decomposed the low frequency coefficients of the signals, and ignored the high frequency coefficients, a novel complex contourlet packet transform is constructed by combining the analytic dual-tree complex wavelet packet transform and nonsubsampled directional filter banks. Then a complex contourlet packet image denoising algorithm based on neighbouring thresholding classification is proposed. The new transform has good characteristics of multiresolution, localization, directionality and anisotropy, as well as translation invariance. Furthermore, it has more abundant direction components. The experimental result shows that the complex contourlet packet transform can restrain Gibbs-like artificial around edges in the course of denoising, and preserve more details and textures of the images efficiently. The PSNR and the visual quality of this algorithm are also superior to the traditional methods.

Fretting occurs in mechanical joints of vibrating structures ranging from household appliances, automobiles, aircraft to electrical equipment or even human implants. Application of surface modification methods is expected to be an ideal solution to mitigate the fretting damage, however, the study on the application and the deterioration mechanisms of coatings under fretting conditions is rather limited. Doctor of Philosophy (MPE)

The growing demand for higher energy density batteries is increasing due to needs of electric vehicle (EV) [1]. Until now, it cannot exceed the one-time charging distance of an internal combustion engine vehicle, due to energy limit of batteries. Li metal anode (LMA) is one of the attractive anode candidates because of the lowest electrochemical redox electrode potential (-3.04 V vs. SHE) and the extremely high theoretical gravimetric capacity (3,860 mAh g-1) compared to graphite anode (372 mAh g-1) [2]. However, uneven Li deposition causes dendritic growth leading to low Coulombic efficiency (CE) and safety hazards which is impeding the practical use of LMAs [3]. Recently, to suppress such dendritic growth, various solutions such as introduction of solid-state electrolyte (SSE) [4], artificial solid electrolyte interphase (ASEI) [5], 3D current collector (CC) [6], and lithiophilic materials [7] have been proposed. Among the several approaches, introducing lithiophilic material on a CC is one of the facile and effective strategies to increase the lithiophilicity, and hence to induce the planar growth of Li. Also, assuming that electroplating is largely divided into two steps: nucleation and growth, lithiophilic material can change the intrinsic nucleation behavior by preferentially forming a different phases such as Li alloys [8]. Since the Li nucleation process significantly influences the final growth of Li, different cycling behaviors of LMAs would be expected depending on lithiophilic material [9]. As for the methods to adopt the lithiophilic materials, the electrodeposition is very attractive, since it can easily control the surface morphology, which might affect the Li deposition morphology and the related behavior. In this regard, we chose the tin (Sn) as a lithiophilic material, which can be deposited on Cu CC by electroplating, and moreover have a fast Li ion diffusion coefficient [10]. Specifically, in this work, we study the effect of surface morphology of lithiophilic Sn deposited on copper CC by testing Li deposition/stripping behavior for a LMAs. For different morphology, a direct current electrodeposition (DC) and pulsed electrodeposition (PED) were used. Fig.1 is FE-SEM images of Cu@Sn with DC growth and PED growth. Fig.1 (a) shows Sn particles are growing without filling the pores. However, Fig.1 (c) shows Sn particles are growing with filling the pores. At Fig.1 (b) and (d), the morphology difference is conspicuous between DC and PED growth. Fig.1 (b) presents island growth in which nuclei grow on existing nuclei because there is only Ton without relaxation time. While, Fig.1 (d) shows that after rearrangement of deposited atom at Toff, new nucleation sites are created by continuously applying pulses, thereby obtaining the coalescence growth. At Fig.2, Cu@Sn (PED) shows the longer cycle life than bare Cu and Cu@Sn (DC) because Cu@Sn (PED) has an uniformly distributed nano Sn morphology, which provides more sites for Li nucleation to prevent dendritic growth. References [1] PARAJULY, Keshav; TERNALD, Daniel; KUEHR, Ruediger. The Future of Electric Vehicles and Material Resources: A Foresight Brief. 2020. [2] XU, Wu, et al. Lithium metal anodes for rechargeable batteries. Energy & Environmental Science, 2014, 7.2: 513-537. [3] CHENG, Xin-Bing, et al. Toward safe lithium metal anode in rechargeable batteries: a review. Chemical reviews, 2017, 117.15: 10403-10473. [4] YU, Seungho, et al. Elastic properties of the solid electrolyte Li7La3Zr2O12 (LLZO). Chemistry of Materials, 2016, 28.1: 197-206. [5] LI, Nian‐Wu, et al. An artificial solid electrolyte interphase layer for stable lithium metal anodes. Advanced materials, 2016, 28.9: 1853-1858. [6] YUN, Qinbai, et al. Chemical dealloying derived 3D porous current collector for Li metal anodes. Advanced Materials, 2016, 28.32: 6932-6939. [7] YAN, Kai, et al. Selective deposition and stable encapsulation of lithium through heterogeneous seeded growth. Nature Energy, 2016, 1.3: 1-8. [8] PEI, Allen, et al. Nanoscale nucleation and growth of electrodeposited lithium metal. Nano letters, 2017, 17.2: 1132-1139. [9] CHEN, Xiao-Ru, et al. Role of Lithiophilic Metal Sites in Lithium Metal Anodes. Energy & Fuels, 2021, 35.15: 12746-12752. [10] SHI, Jianjian; WANG, Zhiguo; FU, Yong Qing. Density functional theory study of diffusion of lithium in Li–Sn alloys. Journal of materials science, 2016, 51.6: 3271-3276. [11] IBL, N.; SCHADEGG, K. Surface roughness effects in the electrodeposition of copper in the limiting current range. Journal of the Electrochemical Society, 1967, 114.1: 54. Figure 1