Yong Xiang

High ductility of a metal film adherent on a polymer substrate

In recent development of deformable electronics, it has been noticed that thin metal films often rupture at small tensile strains. Here we report experiments with Cu films deposited on polymeric substrates and show that the rupture strains of the metal films are sensitive to their adhesion to the substrates. Well-bonded Cu films can sustain strains up to 10% without appreciable cracks and up to 30% with discontinuous microcracks. By contrast, poorly bonded Cu films form channel cracks at strains about 2%. The cracks form by a mixture of strain localization and intergranular fracture. The films rupture at large strains when the localization is retarded by the adherent substrates.

Robust microcapsules with polyurea/silica hybrid shell for one-part self-healing anticorrosion coatings

Silica/polyurea hybrid microcapsules loaded with hexamethylene diisocyanate (HDI) as core materials were prepared via a combined strategy of interfacial polymerization and an in situ sol–gel process in an oil-in-water emulsion. They were clearly characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The resultant microcapsules have diameters of 57–328 μm, shell thicknesses of 1–8 μm, and core fractions of 51.2–65.6%. The diameter and shell thickness were linearly related to the agitation rate in the double logarithm coordinates, and the core fraction were linearly related to the agitation rate, indicating that the structure and component of the microcapsules can be controlled effectively. The resistant properties against thermal and solvent attacks were assessed by using thermogravimetric analysis and titration. The results show that the microcapsules had outstanding thermal stability with initial evaporation temperature (defined at 5% of weight loss), increased by around 58 °C compared with that of pure core material, and good resistance to xylene with less than 25.9 ± 0.7 wt% reduction of core content after immersion for 100 h. Self-healing anticorrosion coatings based on microcapsules were fabricated on a steel substrate. Preliminary results indicated significant corrosion retardancy occurred in the coatings under an accelerated corrosion process, showing the great potential of our microcapsules in the development of catalyst-free, one-part, self-healing coatings for corrosion control.

The Mechanical Properties of Electroplated Cu Thin Films Measured by means of the Bulge Test Technique

The mechanical properties of freestanding electroplated Cu films were determined by measuring the deflection of Si-framed, pressurized membranes. The films were deformed under plane-strain conditions. The pressure-deflection data are converted into stress-strain curves by means of simple analytical formulae. The microstructure of the Cu films was characterized using scanning electron microscopy and x-ray diffraction. The yield stress, Youngs modulus, and residual stress were determined as a function of film thickness and microstructure. Both yield stress and Youngs modulus increase with decreasing film thickness and correlate well with changes in the microstructure and texture of the films.

Measuring the elastic modulus and ultimate strength of low-k dielectric materials by means of the bulge test

The mechanical properties of organosilicate glass (OSG) thin films were measured for the first time using bulge testing of OSG / silicon nitride (SiN/sub x/) freestanding membranes. Evaluation of two different OSG films revealed significant differences in Youngs modulus and residual stress between the two dielectric films. Youngs modulus of both types of OSGs was independently measured using nanoindentation and found to be at least 8.5-17% greater than that measured using the bulge test. It is well known, and demonstrated herein, that modulus data obtained from nanoindentation is influenced by mechanical properties of the substrate. Operating without this constraint, it is believed that data obtained using the bulge test more accurately represents the intrinsic mechanical properties of OSG thin films.

Sb‐Triggered β‐to‐α Transition: Solvothermal Synthesis of Metastable α‐Cu2Se

Control over phase stabilities during synthesis processes is of great importance for both fundamental studies and practical applications. We describe herein a facile strategy for the synthesis of Cu2Se with phase selectivity through a simple solvothermal method. In the presence and absence of SbCl3, monoclinic α-Cu2Se and cubic β-Cu2Se can be synthesized, respectively. The formation of α-Cu2Se requires optimization of the Cu/Se molar ratio in the starting reagents, the reaction temperature, as well as the timing for the addition of SbCl3. Differential scanning calorimetry of the synthesized α-Cu2Se has shown that a part of it undergoes a phase transition to β-Cu2Se at 135u2009°C, and that this phase transition is irreversible on cooling to ambient temperature. Kinetic studies have revealed that in the presence of Sb species the kinetically favored β-Cu2Se transforms to the thermodynamically favored α-Cu2Se. In this β-to-α phase transition process, the distribution of Cu ions in β-Cu2Se, as determined by the Cu/Se ratio and temperature, is likely to play a crucial role.

Controllable fabrication of ternary ZnIn2S4 nanosheet array film for bulk heterojunction solar cells

Large-scale uniform ternary ZnIn2S4 nanosheet array films have been grown on indium-tin oxide (ITO) glass substrates effectively by a simple direct elemental reaction route. Inorganic–organic bulk heterojunction photovoltaic devices were fabricated with ZnIn2S4 film as an electron acceptor and poly (2-methoxy-5-(2/-ethylhexoxy)-1,4-phenylene vinylene (MEH-PPV) polymer as electron donor. The formation of the ZnIn2S4 nanosheet film was characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and UV-VIS-NIR spectroscopy. The as-prepared ZnIn2S4 nanosheet film was demonstrated as an n-type semiconductor exhibiting an apparent photocurrent response and good photostability. The photovoltaic performance of the constructed solar cell device with the active structure of ITO/ZnIn2S4:MEH-PPV/Au was evaluated at room temperature under AM1.5G (100 mW cm−2) simulated globe sun illumination from a filtered Xenon lamp.

Improvement of impact-resistant property of glass fiber-reinforced composites by carbon nanotube-modified epoxy and pre-stretched fiber fabrics

Glass fiber-reinforced plastic composites (GFRPs) are often suffered to impact loadings; it is essential to improve its damage-resistant properties and understand the energy absorption mechanisms. In this work, the low-velocity impact behaviors of GFRPs were investigated in consideration of epoxy resins modified with 0, 0.4, and 0.75xa0% multi-walled carbon nanotubes (MWCNTs) by weight content and pre-stretched fabric at 0, 1.27, and 2.47xa0kg weight. In comparison with pure GFRPs sample, MWCNT-modified specimens are effective in improving the impact resistance under impact energies at 9, 16, and 22xa0J in terms of reduced damage factor and enhanced perforation threshold. Microscopic fractographic analysis indicated that the incorporation of MWCNTs in epoxy matrix offered additional mechanisms through breakage, bridging, and pull-out of carbon nanotubes to favor load transfer effect, prevent crack propagation, and thus dissipate more energy. The dynamic thermo-mechanical analysis proved that MWCNTs improved the storage modulus and glass transition temperature of the composites. In addition, the pre-stretched GFRP composites showed more impact resistant than the non-stretched ones through instant load transfer effect.

A super energy mitigation nanostructure at high impact speed based on buckyball system.

The energy mitigation properties of buckyballs are investigated using molecular dynamics (MD) simulations. A one dimensional buckyball long chain is employed as a unit cell of granular fullerene particles. Two types of buckyballs i.e. C60 and C720 with recoverable and non-recoverable behaviors are chosen respectively. For C60 whose deformation is relatively small, a dissipative contact model is proposed. Over 90% of the total impact energy is proven to be mitigated through interfacial reflection of wave propagation, the van der Waals interaction, covalent potential energy and atomistic kinetic energy evidenced by the decent force attenuation and elongation of transmitted impact. Further, the C720 system is found to outperform its C60 counterpart and is able to mitigate over 99% of the total kinetic energy by using a much shorter chain thanks to its non-recoverable deformation which enhances the four energy dissipation terms. Systematic studies are carried out to elucidate the effects of impactor speed and mass, as well as buckyball size and number on the system energy mitigation performance. This one dimensional buckyball system is especially helpful to deal with the impactor of high impact speed but small mass. The results may shed some lights on the research of high-efficiency energy mitigation material selections and structure designs.

The effects of passivation layer and film thickness on the mechanical behavior of freestanding electroplated Cu thin films with constant microstructure

The goal of this paper is to investigate the effects of film thickness and the presence of a passivation layer on the mechanical behavior of electroplated Cu thin films. In order to study the effect of passivating layers, freestanding Cu membranes were prepared using standard silicon micromachining techniques. Some of these Cu membranes were passivated by sputter depositing thin Ti films with thicknesses ranging from 20 nm to 50 nm on both sides of the membrane. The effect of film thickness was evaluated by preparing freestanding films with varying thickness but constant microstructure. To that effect, coatings of a given thickness were first vacuum annealed at elevated temperature to stabilize the microstructure. The annealed films were subsequently thinned to various thicknesses by means of chemical mechanical planarization (CMP) and freestanding membranes were prepared both with and without Ti passivation. The stress-strain curves of the freestanding Cu films were evaluated using the bulge test technique. The residual stress and elastic modulus of the film are not affected significantly by the passivation layer. The elastic modulus does not change with film thickness if the microstructure keeps constant. The yield stress increases if the film is passivated. For passivated films, yield stress is proportional to the inverse of the film thickness, which is consistent with the formation of a boundary layer of high dislocation density near the interfaces.

Electrodeposition-based electrochromic devices with reversible three-state optical transformation by using titanium dioxide nanoparticle modified FTO electrode

Reversible electrodeposition-based electrochromic devices are highly promising for extensive applications owing to their facile and low-cost fabrication. Herein, a novel electrodeposition-based electrochromic device with reversible three-state optical transformation, i.e. transparent, mirror, and black, was fabricated by introducing a fluorine-doped tin oxide (FTO) electrode modified with commonly available and inexpensive titanium dioxide (TiO2) nanoparticles. Typically, the fabricating strategy mainly involved three procedures, namely obtaining a stable dispersion of TiO2 nanoparticles by milling, achieving a surface modification of the FTO electrode with TiO2 nanoparticles by spin-coating and sintering, and assembling the device by sandwiching gel electrolyte between the modified FTO electrode and a flat FTO electrode. By applying different voltages for a short while, this transparent smart device can be immediately switched to black (+2.5 V/20 s) or mirror (−2.5 V/20 s) state by depositing Ag on the surface of the modified or unmodified FTO electrode respectively. There is below 1% transmittance in the black state and over 80% reflectance in the mirror state for the device. By changing the surface structure of the TiO2 modified FTO electrode, the optical properties of the device in different states can be controlled effectively. Moreover, the optical transformation exhibited good stability over 1500 cycles of testing.