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Gold is a promising material for movable components in MEMS devices by the high mass density, which allows reduction of the Brownian noise. Mechanical properties of metallic materials are known to be affected by the sample size effect. When bending test is utilized, the sample geometry effect is another factor. In this study, effects of the shape of the cross-section, or the cross-sectional geometry effect, are evaluated using micro-cantilevers with a trapezoidal cross-section. The yield stresses are ranged from 112 MPa to 185 MPa in micro-cantilevers composed of single crystalline gold, and the yield stresses varied from 372 MPa to 489 MPa in polycrystalline gold micro-cantilevers. The yield stress is found to be higher in the micro-cantilever having a smaller ratio of the top width over the bottom width, which demonstrates the cross-sectional geometry effect. Also, the cross-sectional geometry effect is more significant in the polycrystalline micro-cantilevers.

Wastewater containing synthetic dyes has caused a significant risk to the environment and human health. Among the various methods to treat wastewater, photocatalysis recommends itself as a particularly efficient tool for the removal of dyes from industrial effluents. In this work, Au@Cu2O core@shell nanocrystals with controllable shell thicknesses from 38.1 ± 2.8 (Au@Cu2O-2), 48.1 ± 3.7 (Au@Cu2O-3) to 59.1 ± 4.1 nm (Au@Cu2O-4) have been prepared and immobilized on polyethylene terephthalate (PET) fabrics for applications in photocatalytic degradation of methylene orange (MO). The influence of the shell thickness of Au@Cu2O on the photocatalytic performance of the functionalized PET fabrics has been examined. Among all the samples tested, immobilization of Au@Cu2O-3 rendered PET fabrics the largest photocatalytic activity for MO degradation, achieving an apparent rate constant of MO degradation of 7.43 × 10−3 min−1. A plausible mechanism accounting for the degradation process of MO over the functionalized PET has been proposed based on the results of scavenger experiments. This work has provided a delicate yet practical functional textile paradigm by combining the photocatalytic capability of Au@Cu2O and the adaptable feature of PET fabrics. The findings from this study can deliver a viable idea for the design of versatile textiles with competent photocatalytic capacity for environmental purifications and energy conversion.

High strength Ni matrix TiO2 composites are prepared by co-electrodeposition with an electrolyte composed of Ni Watts bath, surfactants, CO2 in the supercritical fluid state and various sizes of TiO2 particles. The surfactants and supercritical CO2 (SC-CO2) are used to emulsify the aqueous Ni Watts bath to promote the incorporation of TiO2 particles into the Ni matrix. TiO2 particles with three different average sizes are used in the co-electrodeposition to evaluate the effect on properties of the Ni-TiO2 composites. The grain sizes of the Ni matrix in the composites are compared from the X-ray diffraction results and the Scherrer eq. A refined average grain size in the Ni matrix is observed when using TiO2 particles with a larger size. The TiO2 is evaluated by energy-dispersive X-ray spectroscopy (EDX), and the TiO2 distribution is quantified by the coefficient of variation (cov) of the local density of Ti from the EDX result. The TiO2 content attained 4.5 wt% with the lowest cov value (which suggests the most uniform distribution) in the composite when the smallest (21 nm) TiO2 particles are used. The TiO2 content achieves 22.3 wt% with the highest cov value (which suggests the least uniform distribution) when the largest (5 μm) TiO2 particles are used. Microhardness of the Ni-TiO2 composites is found to be highly depended on the cov value. Hence, the Ni-TiO2 composite prepared with the smallest TiO2 particles shows the highest microhardness at 1274 HV.

This study reports the micro-mechanical property and sample size effect in Ni-TiO2 composites (NTO) fabricated by supercritical CO2 emulsified co-electroplating (SCNTO). NTO by conventional co-electroplating (CVNTO) is also prepared as a comparison. The micro-mechanical property is evaluated by micro-compression test of micro-pillars prepared from the NTO by focus ion beam system. Cross-sections of the micro-pillars are 5 μm × 5 μm, 7.5 μm × 7.5 μm and 10 μm × 10 μm, and the height is kept twice of one side of the cross-section. The yield strength of a SCNTO micro-pillar with the dimensions of 7.5 μm × 7.5 μm × 15 μm is 3.37 GPa, which is three times higher than that of the CVNTO. The sample size effect is not observed in the SCNTO micro-pillars, while a smaller-is-weaker effect is observed in the CVNTO micro-pillars. The ultrafine (

Platinum metallization of polyethylene terephthalate (PET) textile is realized by a supercritical carbon dioxide catalyzation process using palladium (II) hexafluoroacetylacetonate as the source of Pd catalyst, and ε-caprolactam as an additive. A commercially available Pt electroless plating solution is used to deposit Pt on the catalyzed PET textile. Surface morphology of the Pt metallized PET textile changes from granular particle to plate-like morphology when the Pt deposition time increases from 1 to 40 min. The Pt layer thickness reaches 270 nm, 580 nm, and 780 nm after 20 min, 60 min and 240 min, respectively, of the Pt deposition time. The Pt metallized PET textile prepared with 240 min of the Pt deposition time shows the lowest electrical resistance at 0.4 Ω, and the electrical resistance merely increases to 0.7 Ω and 1.0 Ω after one and two times, respectively, of a tape adhesion test.

In this study, a non-enzymatic glucose composed of gold nanoparticle decorated polypyrrole (PPy) is reported. The PPy is prepared by electro-polymerization in 0.05 M phosphate-buffered saline (PBS) containing 0.1 M pyrrole monomer. The gold nanoparticles are decorated by directly dropping 0.1 mM KAuCl4 solution onto the PPy coated electrode. No enzymes are used in preparation of the catalytic electrode. The amount and size of the gold nanoparticles are both found to be dependent on amount of the KAuCl4 solution dropped onto the PPy electrode. The glucose sensing performance is evaluated by cyclic voltammetry in 0.05 M PBS containing 5 mM of glucose with pH at 7.4. The catalytic activity in the oxidation of glucose is confirmed when using the gold nanoparticle decorated PPy as the catalytic electrode, and the performance is found to be affected by the amount of KAuCl4 solution used in preparation of the electrode.

Polyetherimide (PEI) with 3-dimensional (3D) structures is a promising material for applications in electronic devices because of its numerous attractive properties. In the applications of PEI, the low electrical conductivity is often a shortcoming. The electrical conductivity can be improved by a metallization process. Electroless plating is a common metallization process for polymeric materials; however, conventional electroless plating process scarcely provides the metallized PEI. In this work, we overcome this limitation by a supercritical carbon dioxide (scCO2)-assisted electroless NiP plating process. This scCO2-assisted electroless NiP plating allows metallization of PEI with 3D structures and realizes a low electrical resistance suitable for practical use in the electronic devices.

A gold micro-electro-mechanical-systems (Au-MEMS) capacitive accelerometer having Ti/Au multi-layered structures is a promising device to detect very weak accelerations, such as muscle sounds, because of the high mass density of Au. However, Au is a soft metal, which raises concerns about the structural stability of the Au-MEMS capacitive accelerometers for practical use. In this work, we clarify the key geometric parameters to enhance their long-term structural stability by conducting a long-term vibration test for a total of 240 Ti/Au multi-layered micro-cantilevers with different geometric parameters, such as the length, width, and thickness of the micro-cantilevers, and the number of Ti/Au multi-layered structures. The long-term structural stability is evaluated from the change in the tip height of the micro-cantilevers before and after the vibration tests. These tests demonstrate that the micro-cantilevers with a shorter length, larger thickness, and more Ti/Au multi-layered structures are found to show better long-term structural stability.

Gold-based micro-electro-mechanical-systems (Au-MEMS) capacitive accelerometers can simultaneously realize high sensitivity and miniaturization because of the high mass density of Au. In order to further improve the sensitivity of the Au-MEMS capacitive accelerometers, Young's modulus of the cantilever-like spring part connected to the movable component is a key parameter. Considering the size effect in the mechanical property of metallic materials on micro-scale, the design of the spring part is expected to reflect their Young's modulus; that is, effective Young's modulus (Eeff). In this study, we clarify effects of the structural designs of the Au-based micro-cantilevers on their Eeff by experiments and finite element analyses (FEA) simulations. The Eeff of the Au micro-cantilevers having Ti/Au multi-layered structures is evaluated by resonance frequency method, which demonstrates the key structural parameters affecting their Eeff. The FEA calculations show a consistent trend with that observed in the experimental results.

In this study, the strain rate dependence in yield strengths of electrodeposited gold micro-pillars is evaluated for the design of movable components in MEMS devices. The micro-pillars are fabricated from electrodeposited gold by focused ion beam system. The strain rate dependence is quantified by the strain rate sensitivity, and the strain rate sensitivity is calculated from the yield strength obtained from compression tests of the gold micro-pillars having different sizes at different strain rates. An increase in the yield strength following a reduction in the pillar size is observed, which is the sample size effect. Also, weakening of the yield strength is observed following a decrease in the strain rate, which is the strain rate dependence, and the strain rate sensitivity of the gold micro-pillars is found be at roughly 0.03.

Au-based micro-electro-mechanical-system (Au-MEMS) capacitance accelerometers show high sensitivity by suppressing the mechanical noise because of the high mass density of gold (ρ = 19.3 g/cm3). On the other hand, their long-term reliability suffers from drift phenomena induced by the impurities incorporated in the key component during their fabrication process, such as the gold electroplating step. Herein, impurities in electroplated Au-based components for MEMS capacitive accelerometers are evaluated by thermal desorption spectrometry (TDS) measurements. The TDS measurement reveals that dominant desorption gases from the Au-based component are molecular hydrogen (H2) and water (H2O). These desorption gases are derived from impurities in the electroplated Au-based component, and the amount of these gases is significantly suppressed by a thermal treatment step. In conclusion, this study demonstrates that the electroplated Au-based component contains impurities originated from the fabrication process, and these impurities could be removed by a thermal treatment step.