Xuming Sun

Morphological effects on the field emission of ZnO nanorod arrays

The field-emission properties of ordered ZnO nanorod arrays with different morphologies were investigated in detail. After comparison of three different morphologies, it was found that the morphology of the ZnO nanorods has considerable effect on their field emission properties, especially the turn-on field and the emission current density. Among them, the ZnO nanoneedle arrays have the lowest turn-on field, highest current density, and the largest emission efficiency, which is ascribed to the small emitter radius on the nanoscale. On the other hand, high nanorod density remarkably reduces the local field at the emitters owing to the screening effect, which is related to the density of the emitters. The analysis results could be valuable for the application of field-emission-based devices using ZnO nanorod arrays as cathode materials.

r-Shaped Hybrid Nanogenerator with Enhanced Piezoelectricity

Piezoelectric and triboelectric nanogenerators (NGs) have been proposed in the past few years to effectively harvest mechanical energy from the environment. Here, a polydimethylsiloxane (PDMS) layer is placed under the aluminum electrode of polyvinylidene fluoride (PVDF), thus forming an r-shaped hybrid NG. Micro/nanostructures have been fabricated on the PDMS surface and the aluminum electrodes of PVDF to enhance the output performance. Power densities of the piezoelectric part and the triboelectric part are 10.95 and 2.04 mW/cm(3), respectively. Moreover, influence of the triboelectric charges on the piezoelectric output voltage is investigated. Both finite element method simulations and experimental measurements are conducted to verify this phenomenon. The novel hybrid NG is also demonstrated as a power source for consumer electronics. Through one cycle of electric generation, 10 light-emitting diodes are lighted up instantaneously, and a 4-bit liquid crystal display can display continuously for more than 15 s. Besides, the device is integrated into a keyboard to harvest energy in the typing process.

Magnetic-assisted triboelectric nanogenerators as self-powered visualized omnidirectional tilt sensing system

The triboelectric nanogenerator (TENG) is a promising device in energy harvesting and self-powered sensing. In this work, we demonstrate a magnetic-assisted TENG, utilizing the magnetic force for electric generation. Maximum power density of 541.1u2005mW/m2 is obtained at 16.67u2005MΩ for the triboelectric part, while the electromagnetic part can provide power density of 649.4u2005mW/m2 at 16u2005Ω. Through theoretical calculation and experimental measurement, linear relationship between the tilt angle and output voltage at large angles is observed. On this basis, a self-powered omnidirectional tilt sensor is realized by two magnetic-assisted TENGs, which can measure the magnitude and direction of the tilt angle at the same time. For visualized sensing of the tilt angle, a sensing system is established, which is portable, intuitive, and self-powered. This visualized system greatly simplifies the measure process, and promotes the development of self-powered systems.

Self-Cleaning Poly(dimethylsiloxane) Film with Functional Micro/Nano Hierarchical Structures

This paper reports a novel single-step wafer-level fabrication of superhydrophobic micro/nano dual-scale (MNDS) poly(dimethylsiloxane) (PDMS) films. The MNDS PDMS films were replicated directly from an ultralow-surface-energy silicon substrate at high temperature without any surfactant coating, achieving high precision. An improved deep reactive ion etching (DRIE) process with enhanced passivation steps was proposed to easily realize the ultralow-surface-energy MNDS silicon substrate and also utilized as a post-treatment process to strengthen the hydrophobicity of the MNDS PDMS film. The chemical modification of this enhanced passivation step to the surface energy has been studied by density functional theory, which is also the first investigation of C4F8 plasma treatment at molecular level by using first-principle calculations. From the results of a systematic study on the effect of key process parameters (i.e., baking temperature and time) on PDMS replication, insight into the interaction of hierarchical multiscale structures of polymeric materials during the micro/nano integrated fabrication process is experimentally obtained for the first time. Finite element simulation has been employed to illustrate this new phenomenon. Additionally, hierarchical PDMS pyramid arrays and V-shaped grooves have been developed and are intended for applications as functional structures for a light-absorption coating layer and directional transport of liquid droplets, respectively. This stable, self-cleaning PDMS film with functional micro/nano hierarchical structures, which is fabricated through a wafer-level single-step fabrication process using a reusable silicon mold, shows attractive potential for future applications in micro/nanodevices, especially in micro/nanofluidics.

Design and microfabrication of integrated magnetic MEMS energy harvester for low frequency application

An integrated vibration-to-electrical micro energy harvester based on electromagnetic methods was studied, targeting at low frequency application. The harvester was microfabricated without manual assembly of magnets and integrated into small size. The device developed special beams and magnet array for low frequency performance. Two types of harvester were fabricated with different magnet arrays and the magnetic field was investigated. The device volume is 5mm×5mm×1mm with a tested low resonant frequency as 64Hz. This magnetic harvester is suitable for bench fabricated by MEMS process and integrated with IC used in low frequency applications, such as micro implantable devices and portal devices.

Elevated serum and synovial fluid TNF-like ligand 1A (TL1A) is associated with autoantibody production in patients with rheumatoid arthritis.

Objectives: Tumour necrosis factor (TNF)-like ligand 1A (TL1A) is involved in rheumatoid arthritis (RA) but its clinical relevance in RA has not been fully elucidated. We analysed TL1A levels in the serum and synovial fluid (SF) of RA patients and investigated its clinical significance. Methods: TL1A levels were measured by enzyme-linked immunosorbent assay (ELISA) in 109 RA patients, 29 patients with osteoarthritis (OA), and 126 healthy controls. Anti-cyclic citrullinated peptide (anti-CCP) antibodies and rheumatoid factor immunoglobulin G (RF-IgG) were tested by ELISA. RF-IgM, anti-keratin antibody (AKA), and anti-perinuclear factor (APF) antibodies, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and immunoglobulins were measured by standard laboratory techniques. The associations between TL1A and the clinical and serological features of RA were analysed. Results: TL1A concentrations were significantly elevated in both serum and SF of RA patients compared with OA patients and healthy controls. TL1A levels in RA SF were significantly higher than those in matched serum. A positive correlation was found between SF and serum TL1A levels. Serum TL1A concentrations were associated with RA-specific autoantibodies including RFs (RF-IgG, RF-IgM) and anti-citrullinated protein antibodies. Antibody production by peripheral blood mononuclear cells (PBMCs) from RA patients was elevated upon TL1A stimulation. However, there was no correlation between serum or SF TL1A levels and RA disease activity. Conclusions: TL1A levels are significantly elevated in RA serum and SF and positively correlated with autoantibody production in RA, but failed as a disease activity marker. TL1A promotes antibody production by PBMCs from RA patients. The role of TL1A in the humoral autoimmune response may be important in the development of RA.

Stacked flexible parylene-based 3D inductors with Ni 80 Fe 20 core for wireless power transmission system

This paper presents a new high quality factor parylene-based stacked 3D spiral inductor with Ni80Fe20 core for wireless power transmission system. To achieve multilayers, planarization of parylene by oxygen plasma etching was realized. Ni80Fe20 was added as the magnetic core to enhance the performance. The maximum quality factor of the designed circular double-layer inductor reached 99.3 at 60MHz, which is much higher than the square coils with the same area. The double-layer inductor shows a 408% increment of maximum quality factor compared with single-layer coil. Furthermore, inductors with magnet arrays exhibited better performance than those with one magnet. Forming the power transmission system with these 3D inductors, the minimum attenuation was -26dB at 118MHz.

Microstructure and magnetic properties of micro NiFe alloy arrays for MEMS application

NiFe alloy arrays with various geometry sizes and shapes were designed, fabricated and investigated. Electrodeposition was introduced as a highly effective integrated method to fabricate the alloy film. The influence of dimensional size and geometry shape of the array unit was discussed. With decreasing size, the soft magnetic properties of the samples are improved with a 78.6% decrease of coercivity and an 65.0% decrease of squareness ratio. Compared with square and rectangular arrays, circular arrays exhibit smaller coercivity, higher permeability and smaller squareness ratio. Additionally, different compositional arrays were also tested for their crystal structures. It is found that the alloy with a content of Ni80Fe20xa0can achieve a face-centered cubic structure and realize the best soft magnetic properties. A coercivity of 0.383 Oe, a squareness ratio of 4.21 × 10−4xa0and a saturation magnetization of 4.2 T have been successfully achieved in circular arrays within an area of 2000 × 2000xa0µm2.

Springless cubic harvester for converting three dimensional vibration energy

This paper reports the design, fabrication and measurement of a springless cubic energy harvester. Based on the flexible printed circuits, coils are fabricated onto both sides of the polyimide substrate and then folded to a cubic box, meanwhile sealed a free magnet inside the box. As the coils are folded on three different directions, vibration in all dimensions can cause the change of magnetic flux and the energy is effectively harvested. Output performance of the device is both theoretically and experimentally investigated. Benefit from the springless structure, maximum output is achieved at low frequencies with a wide bandwidth. Moreover, the device can be placed on a backpack or wrist to harvest vibration energy from daily life.

Electrodeposition and characterization of CoNiMnP-based permanent magnetic film for MEMS applications

Electroplated CoNiMnP-based permanent magnetic films with thickness of 4µm, 25µm and 43.5µm were fabricated and tested. Composed of 76.38 wt% Co, 16.66 wt% Ni, 3.64 wt% P and 2.32 wt% Mn, the films exhibited good surface morphology. In the case of 4µm thick film, we successfully achieved a high lateral coercivity of 711Oe, a retentivity up to 8933Gs and an energy density of 16.9kJ/m3. The film thickness dependence of magnetic property was also investigated, showing a decrease of the retentivity and coercivity with the increase in thickness. In addition, it was observed that Zn as an additive could improve the surface morphology by eliminating micro cracks.