Enhancing electrical conductivity and electrical thermal characteristics of a PEDOT:PSS thin layer by using solvent treatment and adding Ag nanoparticle solution

A method of enhancing the electrical conductivity of 3,4-ethylenedioxythiophene:poly styrene sulfonate (PEDOT:PSS) by combining solvent treatment (adding high polar solvent: 5 wt% ethylene glycol) and adding a small amount of silver (Ag) nanoparticles in a solution was investigated. The main purpose of this was to apply a PEDOT:PSS conductive layer to micro-thermal devices driven by electricity and, for this, to reduce the layer thickness (for low stiffness) while maintaining necessary high electrical conductivity. Layers with thicknesses of less than about 10 μm were examined for electrical conductivity and temperature when electricity was applied. The solvent treated PEDOT:PSS had suitable electrical resistance to generate appropriate temperature properties. The added Ag nanoparticles reduced the electrical resistance by 30–70% over the measured thickness range. The electric conductivity applied with this method was 200–260 Ω⁻¹ cm⁻¹ for thicknesses of 1–2 μm (conductive area: 12 mm × 10 mm) and the generated temperature increase was 20–50 °C at applied voltages of 3–5 V. These characteristics are considered to be suitable to use the conductive layer as a heating element. In addition, the method we used scarcely degraded the transparency of the layer. Measurements of the conductive area in a layer with conductive atomic force microscope (AFM) indicated that the added Ag nanoparticles contributed to increasing the conductive areas and distributing them more uniformly.     

纳米硬度计研究多晶硅微悬臂梁的弹性模量

利用纳米硬度计通过微悬臂梁的弯曲试验来测量其力学特性是一种简便而有效的方法,具有很高的载荷分辨率,可精确测量微悬臂梁纳米级弯曲形变。运用该方法在研究微悬臂梁的弯曲形变过程中,必须考虑压头在微悬臂梁上的压入以及微悬臂沿宽度方向的挠曲。微悬臂梁采用普通的集成电路工艺(IC)制造。试验研究表明,多晶硅微悬臂梁的纯挠曲与载荷成很好的线性关系,呈现弹性变形,通过该线性关系可计算得到梁的弹性模量。测得的多晶硅微悬臂梁的弹性模量为156±(2.9%-6.3%)GPa。     

Characterization of drop-on-demand microdroplet printing

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been used extensively in the fabrication of polymer light-emitting diode displays by drop-on-demand inkjet printing technique. In order to make a good thin film with high uniformity, it is crucial to control the drying behavior of inkjet-printed PEDOT:PSS droplets. In this work, the morphology of printed drops of ～10 pL after drying was examined and explained in a qualitative manner, which would extend the comparison with previous work described in published literature. Results show that drying behavior is sensitive to substrate temperature due to the high surface-to-volume ratio of a microfluid. There exists an appropriate range of temperatures to obtain a good drop with sharp edge and flat surface. On the other hand, when the temperature exceeds a limit, a ring-like structure was observed. Results from this experiment would be considered as a reference to achieve uniform film after drying and has potential to be applied in the modeling of drop impact.     

Comparison of two experimental methods for the mechanical characterization of thin or thick films from the study of micromachined circular diaphragms

The purpose of this study was to compare two experimental methods and evaluate the effectiveness of a set of analytical models in order to measure the initial stress and the Young's modulus value of thin and thick film materials. Two types of experiments were performed on micromachined circular diaphragms: bulge testing and vibrometry. The range of validity and accuracy of the analytical models with respect to the vibration of the diaphragms was discussed from the finite element simulations. It was shown that the a/t ratio should be considered carefully to determine the value of the Young's modulus by vibrometry with an acceptable error. A relative error of approximately ±10% on E was obtained for a/t ≤ 750. For 750 ≤ a/t ≤ 1000, the value of the dimensionless parameter k must also be considered. It has been shown that the residual stress value can be obtained with an accuracy of 10% or less, given that k > 12. As an illustration, experimental methods and models were applied to the characterization of a thick electroplated gold film and a sputter-deposited Inconel thin film. Circular structures were defined by vertical sidewalls etched on the back of a Si wafer using the deep reactive ion etching technique. In addition to analytical models, parametric finite element simulations and a design optimization technique were used to determine the material's mechanical properties. The static deflections of the diaphragms were measured as a function of the applied pressure. The resonant frequencies and mode shapes of the vibrating structures were observed under vacuum by white-light interferometric microscopy. For gold, it was found that E = (53 ± 20) GPa and σ(0) = (180 ± 10) MPa. For Inconel, it was found that E = (157 ± 14) GPa and σ(0) = (172 ± 5) MPa.     

电磁驱动式微拉伸装置的研究

为了能精确地测试和评定微构件的力学特性,需研制微拉伸装置。本文对电磁－线圈力驱动器的结构和参数进行了优化设计,并将其应用于微拉伸装置。结果表明,由于磁场梯度与线圈的激励电流成线性关系,因而能进行精确的控制。在设计微拉伸装置时,样品的一端附在由叶片弹簧悬挂的可移动拉杆上,另一端固定。通过线圈激励产生的磁场对拉杆上的磁铁作用,施加拉力。利用光纤传感器测量位移。最后,采用内径α１＝０．００８ｍ,匝数ｎ＝     

Highly sensitive polymer-based cantilever-sensors for DNA detection

We present a technology for the fabrication of cantilever arrays aimed to develop an integrated biosensor microsystem. The fabrication process is based on spin coating of the photosensitive polymer and near-ultraviolet exposure. Arrays of up to 33 microcantilevers are fabricated in the novel polymer material SU-8. The low Young's modulus of the polymer, 40 times lower than that of silicon, enables to improve the sensitivity of the sensor device for target detection. The mechanical properties of SU-8 cantilevers, such as spring constant, resonant frequency and quality factor are characterized as a function of the dimensions and the medium. The devices have been tested for measurement of the adsorption of single stranded DNA and subsequent interstitial adsorption of lateral spacer molecules. We demonstrate that sensitivity is enhanced by a factor of six compared to that of commercial silicon nitride cantilevers.     

Friction and fracture properties of polysilicon coated with self-assembled monolayers

The increasing use of small micromechanical devices and advanced sensors has led to concern about the failure modes and reliability of these structures. The enormous promise will not materialize without substantial progress in overcoming the stiction, friction and wear associated with such devices and understanding the mechanical behavior of MEMS materials and structures. Self-assembled monolayers (SAMs) are release and anti-stiction coatings for MEMS. In this paper, the anti-stiction properties of octadecyltrichlorosilane (OTS) SAM were calculated. The microtribological properties of OTS SAM were investigated with a ball-on-flat microtribometer. The influence of OTS SAM on the mechanical properties of micromachined polysilicon films for MEMS was investigated with an accurate evaluation using the microtensile test device. It was concluded that the OTS SAM has good anti-stiction properties and low friction coefficients. The hydrophobic property of OTS is the main factor leading to an increase in the average fracture strength of micromachined polysilicon up to 32.46%. Thus, the operational stability and lifetime of MEMS can be raised when coated with self-assembled monolayers.     

纳米压痕技术表征Al2O3/3%TiO2爆炸喷涂涂层的各向异性

利用纳米压痕技术研究了爆炸喷涂涂层的微观结构特征和力学性能的关系。结果表明:相对于涂层表面,涂层横截面存在着尺度分布较宽的孔洞和微裂纹等缺陷;涂层微观结构的各向异性使得涂层的弹性、塑性、硬度和弹性模量等出现各向异性;与涂层横截面相比,涂层表面具有较好的抵抗外加载荷的能力和卸栽后良好的弹性恢复能力;涂层表面的硬度和弹性模量分别为10．3 GPa和170．7 GPa,而涂层横截面的分别为2．9 GPa和234．5 GPa。     

TiAlN/AlON纳米多层涂层的微观结构和力学性能研究

通过磁控溅射制取一系列不同AlON厚度的TiAlN/AlON纳米多层涂层,并用X射线衍射、扫描电镜、高分辨透射电镜和纳米压痕仪分别对微观结构和力学性能进行表征和测量。研究表明:非晶态的AlON在厚度约小于1 nm时,在TiAlN模板作用下转变为晶体结构,并与TiAlN呈共格外延生长,出现超硬效应,当AlON厚度为0.7 nm时,硬度和弹性模量分别最高可达38.1 GPa和385.6 GPa。当AlON厚度超过1 nm时,逐渐转变为非晶结构并且破坏了多层涂层的共格外延生长,硬度随之降低。因此利用这种机制可以制备出力学性能好、耐高温氧化性的刀具涂层,满足现代切削的需要。     

Note: Two-dimensional resistivity mapping method for characterization of thin films and nanomaterials

A two-dimensional resistivity mapping method is presented as an analysis tool for thin films. The spatial distribution of resistivity in the interior of the film is reconstructed with the data measured on its periphery. A square window with four electrodes on each side is fabricated as the test vehicle. While the current is applied to one electrode, the potentials on the other electrodes are monitored and an iterative method generates the resistivity map. The technique is demonstrated by measurements on a homogeneous organic PEDOT:PSS film and an inhomogeneous ZnO nanoparticle coating.     

Wear stability of polymer nanocomposite coatings with trilayer architecture

A polymer trilayer (sandwiched) film with a thickness of 20–30 nm has been designed to serve as a wear resistant nanoscale coating for silicon surfaces. These surface structures are formed by a multiple grafting technique applied to self-assembled monolayers (SAM) and functionalized tri-block copolymer, followed by the photopolymerization of a topmost polymer layer. The unique design of this layer includes a hard-soft-hard nanoscale architecture with a compliant rubber interlayer mediating localized stresses transferred through the topmost hard layer. This architecture provides a non-linear mechanical response under a normal compression stress and allows additional dissipation of mechanical energy via the highly elastic rubber interlayer. At modest loads, this coating shows friction coefficient against hard steel below 0.06, which is lower than that for a classic molecular lubricant, alkylsilane SAM. At the highest pressure tested in this work, 1.2 GPa, the sandwiched coating possesses four times higher wear resistance than the SAM coating. The wear mechanism for this coating is stress and temperature induced oxidation in the contact area followed by severe plowing wear.     

Air-coupled acoustic method for testing and evaluation of microscale structures

A noncontact testing and characterization approach for microscale structures based on air-coupled acoustic excitation and optical sensing is proposed and demonstrated. Using an air-coupled transducer to externally excite and a laser Doppler vibrometer/interferometer to capture transient displacement wave forms, the experimental approach results in a technique to determine mechanical properties of microscale structural elements. The effectiveness of this method has been demonstrated on commercially available microcantilever beams and microscale rotational oscillators fabricated for this study. The resonance frequencies and mechanical properties (Young's modulus and stiffness) extracted from the transient displacement wave forms have been compared, with good agreement, to computational and simplified analytical models for each case. It is also shown that the technique could serve to diagnose stiction problems of microscale structures. Some potential advantages of the approach described include the simplicity of the test setup, functionality at room conditions, noncontact and nondestructive operations, and repeatability and rapid turn-around time for the evaluation of modal parameters and mechanical properties of microscale structures.     

Nanomechanical properties of alginate-recovered chondrocyte matrices for cartilage regeneration

Tissue-engineered cartilage constructs designed for in-vivo applications intuitively should mimic the mechanical properties of native cartilage. The objective of the present work was to characterize the nanomechanical properties of alginate-recovered chondrocyte matrices as a function of ex-vivo incubation time. Chondrocytes isolated from the articular cartilage of the mature bovine metacarpophalangeal joints were cultured with alginate hydrogel to allow for the formation of extracellular matrices. The recovered chondral constructs after 2, 4, 8, and 12 weeks of ex-vivo incubation were analysed using nanoindentation with atomic force microscopy to determine their mechanical properties. Chondral constructs had average Young's moduli of 123 +/- 22 kPa, 174 +/- 31 kPa, 373 +/- 40 kPa, and 564 +/- 79 kPa after incubation for 2, 4, 8, and 12 weeks respectively, indicating the gradual attainment of mechanical stiffness. This escalating trend of micromechanical properties as a function of increasing ex-vivo incubation time suggests that chondral constructs via a tissue-engineering approach are capable of elaborating extracellular matrices and increase mechanical stiffness. The relationship between Young's modulus and incubation time of the chondral constructs is useful in the design and fabrication of tissue-engineered cartilage constructs.     

Predictive optimized adaptive PSS in a single machine infinite bus

Power System Stabilizer (PSS) devices are responsible for providing a damping torque component to generators for reducing fluctuations in the system caused by small perturbations. A Predictive Optimized Adaptive PSS (POA-PSS) to improve the oscillations in a Single Machine Infinite Bus (SMIB) power system is discussed in this paper. POA-PSS provides the optimal design parameters for the classic PSS using an optimization predictive algorithm, which adapts to changes in the inputs of the system. This approach is part of small signal stability analysis, which uses equations in an incremental form around an operating point. Simulation studies on the SMIB power system illustrate that the proposed POA-PSS approach has better performance than the classical PSS. In addition, the effort in the control action of the POA-PSS is much less than that of other approaches considered for comparison.     

Scratch and indentation tests on seashells

In this work, the scratch and indentation properties of the outer and inner (nacre) layers of green mussel shells under dry and water-soaked conditions were investigated. In micro-scratch tests with increasing normal load, it was found that the scratch hardness of the inner and outer shell surfaces tended to decrease rapidly at lower loads as compared to the changes in hardness at higher loads. The readings varied in the ranges of 1.5-2.4 and 0.8-2.0 GPa for inner and outer surfaces, respectively. In nano-indentation tests, the responses of inner nacre were not affected by prior soaking as much as those of the outer shell surfaces. The outer shell surfaces showed a significant drop in nano-hardness from 4.5 to 2.8 GPa, while the Young's modulus increased from 62 to 84 GPa after soaking. However, the average nano-hardness and modulus of elasticity of nacreous inner layer only varied slightly in the range of 4.5-4.1 and 64-61 GPa, respectively. In addition, Vickers hardness readings showed that there was a detectable steady increase in micro-hardness of nacre as soaking time increased, although the differences were small. The reverse trend was observed for the outer layer. Analysis of the shells using Fourier transform infrared (FTIR) in reflectance mode gave strong evidence of the presence of sulphated saccharides, polyglycine and hydro-complex in the organic phase of the shell. Their interaction with calcium carbonate of the shell during scratch and indentation tests could be affected with the permeation of water due to soaking of shells.     

Multi-scale polymer properties with applications to solid lubricants in ironing

The use of polymer laminated steels have received significant interest from the can-making industry as a potential base material, mainly due to environmental benefits and excellent solid lubrication properties. Internal corrosion prevention is also very important with food cans. Previous research has experimentally and mathematically analyzed this material, but the mechanical properties, especially the shear strength, of the polymer coating is difficult to obtain given its very small thickness. This paper obtains predictions of polymer coating strength through two approaches: a millimeter-scale approach based on a mathematical model of ironing, and a sub-micrometer scale approach based on asperity plowing with an atomic force microscope. Once piezo-strengthening effects are accounted for, the polymer strength predictions from the two methods are very close.     

多晶硅微机械构件损伤的表面效应

利用电磁力驱动微拉伸装置，考察多晶硅微构件表面粗糙度和施加表面分子自组装膜(octadecyltrichlorosilane，简称OTS)对抗拉强度及断裂损伤的影响。结果表明，微构件的抗拉强度表现出依赖表面性质的表面效应。抗拉强度随表面粗糙度的增加而降低，并受环境气氛的影响。当构件表面施加表面分子自组装膜后，在以上两因素的作用下．多晶硅微构件的抗拉强度提高了32．46％。研究结果可用于微机械构件的材料表面改性设计。     

Contact fatigue and wear behaviour of bismaleimide polymer subjected to fretting loading under various temperature conditions

Cracking and wear induced by fretting is a critical problem for industrial composite structures. Thermosetting bismaleimide resin is a promising material due to its good mechanical and thermal properties. The effect of temperature regarding fretting cracking and fretting wear is presently investigated. The temperature effect on crack initiation and propagation is quantified combining experiments and modelling. The fretting wear is explained using a friction energy wear approach. A bilinear evolution of wear volume versus the dissipated energy is identified and related to a protective third body layer. These various damage evolutions are compared to the viscoelastic properties of the polymer.     

Scratch resistance of high performance polymers

Scratch tests were carried out on various high performance polymers, including (1) polybenzimidazole (PBI), (2) polyparaphenylene (PPP), (3) polyetheretherketone (PEEK), and (4) polyimide (PI). The scratch damage features were characterized using laser confocal and scanning electron microscope. Scratch resistance at room temperature decreased in the same order as the materials are listed above. It was attempted to correlate the scratch depth with basic mechanical properties, such as Young's modulus, tensile strength, and scratch hardness. Also, the scratch coefficient of friction was considered as a possible measure to differentiate between the various materials tested.     

硅微构件的弹性模量和残余内应力的测试

叙述了利用硅悬臂梁和两端固定梁微构件进行硅微薄膜材料的弹性模量和残余内应力的测试方法。本方法利用简单的光学装置,通过测量悬臂梁和两端固定梁的一阶谐振频率,分别求弹性模量和残余内应力。本方法测量系统简单,试样制作方便。本试验获得（100）面<110>方向单晶硅微薄膜的弹性模量为128GPa,残余内应力为74.7MPa.