Numerical investigation on the loading-delamination-unloading behavior of adhesive joints

An elastic-plastic interface model at finite deformations is utilized to investigate the irreversible delamination behavior of adhesive joints subjected to loading-delamination-unloading. The interface model accounts for the irreversible delamination in the fracture process zone induced by the localized plastic deformation and damage. The interfacial parameters in the cohesive model are obtained by fitting the available experimental data. Results suggest that the cohesive model can capture the irreversible delamination failure behavior observed in adhesively bonded joints during a loading-unloading cycle. The overall nonlinear response is dominated by the cohesive strength and initial damage displacement jump. Further, we also investigate the effect of the ductile mechanisms for the bulk layer on the competition between the plastic deformation of the bulk layer and the delamination of the interface. It is observed that the degradation of unloading stiffness is attributed to the inelastic behavior of the interface.     

Dirty money in clean systems

It is said that the laundering of the proceeds of crime is the third biggest industry by value worldwide. In the USA a survey stated that 90% of notes in circulation are tainted with narcotics. Governments all over the world are falling into line and drawing up legislation to control the movement of proceeds of crime. The EC (as it was) in 1991 accepted that it was not possible to control crime by targeting the criminal and that the only way of reducing crime seemed to be try to prevent criminals profiting from their labours. And of course, to profit, the criminal needs to spend money and, wherever money is spent, it sooner or later finds its way into the financial services industry through banking or investments.     

Tough,transparent, biocompatible and stretchable thermoplastic copolymer with high stability and processability for soft electronics

Materials with a variety of required properties, including stretchability, toughness, optical transparency, biocompatibility, processability, and recyclability are in great demand for soft electronics. Creation of such materials, however, has been hampered due to the challenges of balancing these properties. Herein, we report intrinsically stretchable thermoplastic copolymers with a random sequence of hard and soft domains in the polyimide backbone in which their superior traits are harnessed to enable the properties of the copolymer tunable and balanced. We obtained a tough and stretchable copolymer with high optical transparency, biocompatibility, thermal and chemical stability, and low water vapor transmission rate. In addition, the polymer is recyclable and shows excellent processability, allowing for the fabrication of fibers, thin films, and molded parts for soft electronics. Furthermore, the utility of the copolymer was successfully demonstrated for a wearable temperature sensor on the stretchable copolymer and a copolymer-based fully stretchable sweat collection patch, suggesting that they have great potential in soft electronics.     

湿法刻蚀条件对TFT中Cu电极坡度角和均一性的影响及工艺参数优化

目的 在高世代薄膜晶体管(Thin Film Transistor, TFT)产线的栅极刻蚀制程,明确大气压等离子体(Atmosphere Pressure Plasma, APP)清洗功率、清洗时间及刻蚀时间对刻蚀性能(关键尺寸偏差、均一性、坡度角)的影响规律,并获得最佳工艺条件,进而提升良率。方法 以APP清洗功率、清洗时间和刻蚀时间为影响因素,以关键尺寸偏差(CD Bias)、均一性、坡度角作为因变量,开展正交试验,明确因素影响重要性顺序;然后,对Cu电极坡度角的形成和刻蚀均一性变化进行分析;最后,采用回归分析获得刻蚀性能与刻蚀时间的函数关系式。结果 结果表明:刻蚀时间对刻蚀性能的影响最大,对APP清洁时间和功率的影 响较小。刻蚀时间延长,关键尺寸偏差(CD Bias)增加、均一性变差、坡度角变大。为改善均一性和平缓坡度角,应缩短刻蚀时间。最佳工艺组合为:刻蚀时间85 s,APP电压9 kV,APP传输速度5 400 r/min。结论 刻蚀时间延长,未被光刻胶覆盖的Cu膜层被完全刻蚀,形成台阶,该台阶使刻蚀液形成回流路径。沿着回流路径,刻蚀液浓度、温度逐渐下降,刻蚀均一性由此恶化,坡度角因此增加。采用回归分析得到的刻蚀性能与刻蚀时间的函数关系式,为预测刻蚀效果和优选刻蚀时间提供了依据。     

Tuning paradigm of external stimuli driven electronic,optical and magnetic properties in hybrid perovskites and metal organic complexes

We have witnessed a wide range of theoretical as well as experimental investigations to envisage external stimuli induced changes in electronic, optical and magnetic properties in the metal organic complexes, while hybrid perovskites have recently joined this exciting league of explorations. The flexible organic linkers in such complexes are ideal for triggering not only spin transitions but also a plethora of various different responses under the influence of various external stimuli like pressure, temperature and light. A diverse range of applications particularly in the field of optoelectronics, spintronics and energy scavenging have been manifested. The hysteresis associated with the light induced transitions and spin-crossover governed by pressure and temperature, are promising phenomena for the design principles behind memory devices and optical switches. The pressure induced optical properties tuning or piezochromism has also emerged as one of the prominent areas in the field of hybrid perovskite materials family. It is thus imperative to have a clear understanding of how the tuning in electronic, optical and magnetic properties occur under various stimuli, and selectivity of the stimulus could be influential behind the maximum efficiency in the field of energy and optoelectronic research, and in what future directions this field could be driven from the perspective of futuristic material properties. This review though primarily focuses on the theoretical aspects of understanding the different mechanisms of the phenomena, does provide a unique overview of the experimental literature too, accompanied by the theoretical understanding such that relevant device applications can be considered through a future roadmap of tuning paradigm of external stimuli. It also provides an insight as to how energy and memory storage may be combined by using the principles of spin transition in metal organic complexes.     

Multidimensional surface patterning based on wavelength-controlled disulfide-diselenide dynamic photochemistry

Controlling surface properties in a spatiotemporal and reversible manner is highly attractive for novel functional surfaces, as it allows them to act in a much smarter way. Surface modification strategies based on photochemical metathesis reactions are seemed as promising solutions for such demands, due to their high spatiotemporal controllability and the perfect reversibility. In this paper, we demonstrate a powerful strategy to precisely manipulate the surface functions by the combination of wavelength-controlled disulfide-diselenide dynamic photochemistry and a 405 nm digital light processing (DLP) projector. We show that, by this method, the arrangement of chemical moieties on a disulfide surface can be exactly controlled, leading to complex patterned surfaces with multinary and grayscale molecular distributions. Moreover, owing to the wavelength-dependent reactivity of the -S-S- and -S-Se- groups, the surface functions can be selectively and dynamically adjusted by light with different colors (wavelength). Based on these unique features, the chemical moieties on every point of the surface can be exactly controlled and dynamically manipulated by our strategy, making the generated surfaces quite versatile and smart. We demonstrate the successful application of this method in high-level information encryption and transformation.     

Structural characterization and thermal and mechanical properties of poly(propylene carbonate)/MgAl-LDH exfoliation nanocomposite via solution intercalation

Poly(propylene carbonate)/MgAl layered double hydroxide (PPC/MgAl-LDH) exfoliated nanocomposites were synthesized by solution intercalation of PPC into the galleries of organic modified MgAl-LDH (OMgAl-LDH) in cyclohexanone. The crystal morphological structures, thermal degradation behavior, and mechanical properties have been studied by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, and thermogravimetric analysis (TGA). The nanoscale dispersion of OMgAl-LDH layers in the PPC matrix has been verified by the disappearance of d_0 0 1 XRD diffraction peak of OMgAl-LDH and the observation of TEM image. The TGA data give evince that the thermal degradation temperature of the exfoliated PPC/MgAl-LDH nanocomposites with 1% OMgAl-LDH is 10 °C higher than that of pure PPC resin when 20% weight loss was selected as a point of comparison. The data from the mechanical test show that the tensile strength of the PPC/MgAl-LDH nanocomposites with 5% LDH is 36.9 MPa, which is 72% and 30% higher than those of pure PPC resin and simple mixed sample with the same content of LDH, and its Young’s modulus is 1303 MPa, which is 57% and 21% higher than those of the same two samples, respectively.     

A stable LaB6 nanoneedle field-emission electron source for atomic resolution imaging with a transmission electron microscope

Field-induced electron emission offers the best performance point electron source for electron microscopes. Herewith we report a new cold field-emission point electron source utilizing a nanoneedle made of lanthanum hexaboride (LaB₆) and its implementation in a spherical aberration-corrected transmission electron microscope (TEM). A sub-ångstrom resolution of 0.96 Å has been obtained with the TEM operated at an acceleration voltage of 60 kV and a smaller energy spread was also observed compared with the contemporary W(310) electron source. In particular, the LaB₆ nanoneedle cold field-emission electron source required no thermal flashing for continuous operation of extended hours (>100 hours) while exhibiting and sustaining a high stability in emission current (<1%). We attribute the excellent performance of the LaB₆ nanoneedle electron source to (i) a low work function of LaB₆; (ii) excellent alignment of the nanoneedle emitter by the electron and ion dual-beam processing with nanoscale precision and (iii) robustness of the nanometric structure that suppressed mechanical vibrations of the LaB₆ emitter even in a high electric field. This new LaB₆ nanoneedle cold field-emission electron source enables stable high-resolution imaging in TEM and it will also benefit cryogenic electron microscopy, scanning electron microscopy, electron beam lithography, and other electron beam technologies.     

Highly efficient liquid droplet manipulation via human-motion-induced direct charge injection

The current electrowetting mechanisms show a low efficiency, although manipulating liquid droplets is essential to biological and chemical fields. Herein, we propose a highly efficient droplet manipulating method using direct charge injection (DCI) via human motion induced triboelectricity. A triboelectric nanogenerator (TENG) is used to provide both the charges and strong electric fields to drive the movement of liquid droplets. Using this method, the charge quantity and average velocity of the droplet (10 μL) reach 0.25 nC and 255 mm s⁻¹, respectively, over 6 times higher than those of traditional methods (0.03 nC and 43.2 mm s⁻¹). Alternative charge injection was demonstrated to enable both reciprocating and jumping motions of the droplet. Finally, we also successfully devised and demonstrated a platform with versatile system-level functions including droplets transportation, positioning, merging, and cleaning. This work advances the current droplet manipulation field via introducing a compelling approach using human-motion-induced direct charge injection.