Thin film silicon tandem junction solar cells based on amorphous silicon (a-Si:H) and microcrystalline silicon (µc-Si:H) were developed with focus on high open-circuit voltages for the application as photocathodes in integrated photoelectrochemical cells for water electrolysis. By adjusting various parameters in the plasma enhanced chemical vapor deposition process of the individual µc-Si:H single junction solar cells, we showed that a-Si:H/µc-Si:H tandem junction solar cells exhibit open-circuit voltage over 1.5 V with solar energy conversion efficiency of 11% at a total silicon layer thickness below 1 µm. Our approach included thickness reduction, controlled SiH4 profiling, and incorporation of intrinsic interface buffer layers. The applicability of the tandem devices as photocathodes was evaluated in a photoelectrochemical cell. The a-Si:H/µc-Si:H based photocathodes exhibit a photocurrent onset potential of 1.3 V versus RHE and a short-circuit photocurrent of 10.0 mA/cm2. The presented approach may provide an efficient and low-cost pathway to solar hydrogen production.

Methods for the solution deposition of organic semiconductors (OSCs) show great potential for the production of large-area, inexpensive, and flexible organic electronics. A solution deposition method called solution shearing has consistently been shown to yield thin film transistors with improved performance over those created via other solution-based approaches. However, the need for discrete, electronically isolated devices requires the parallel development of a facile means of pattern definition compatible with the solution shearing process. In our work, we use a simple chemical prepatterning method to enable the solution shearing deposition of the small molecule OSC TIPS-pentacene on substrates with feature sizes as small as 100 µm. Grazing incidence x-ray diffraction (GIXD) was also used to confirm the existence of high performance TIPS-pentacene polymorphs in the patterned thin films. Mobilities as high as 1.13 cm2 V−1 s−1 were obtained on 400 µm wide patterns by depositing a high-performance, metastable polymorph of TIPS-pentacene.

The effects of surface modifications of multiwalled carbon nanotubes (MWCNTs) on their dispersibility in different solvents and poly(ether ether ketone) (PEEK) have been studied. MWCNTs were treated by mixed acids to obtain acid-functionalized MWCNTs. The acid-functionalized MWCNTs were modified with five different chemical agents separately, 1,6-diaminohexane, hexadecyltrimethyl ammonium bromide, silane coupling agent 3-aminopropyltriethoxysilane, anhydrous sulfanilic acid, and ethanolamine. Multiwalled carbon nanotube and PEEK (MWCNT/PEEK) composite films were fabricated to explore systematically the dispersibility of differently modified MWCNTs in PEEK as well as in different solvents. The morphology and structures of MWCNTs and the compatibility between MWCNTs and PEEK have been investigated. It was observed that the MWCNTs modified with anhydrous sulfanilic acid have an excellent dispersion in the PEEK grafted by sulfonic acid groups and that the MWCNTs modified with ethanolamine are also dispersed well in pure PEEK. The results herein provide useful insights into the development of MWCNT/PEEK composites for a wide variety of applications.

The conjugated polymer poly(2,5-dihexyl-1,4-phenylene-alt-2-amino-4,6-pyrimidine) was synthesized and used in the supramolecular functionalization of single-walled carbon nanotubes (SWNTs). It was found that this polymer can form strong supramolecular polymer–nanotube assembly and produce a stable composite in solution. The resulting polymerized nanotubes were analyzed by UV–Vis absorption and emission spectroscopy, thermogravimetry, transmission electron microscopy and scanning electron microscopy. It was found that the noncovalent functionalization did not damage the nanotube structure. The polymer content in the polymer–nanotube composite could be calculated to be 41% by thermogravimetry analysis. The composite exhibited certain solubility in dimethylacetamide (DMAc), where the solubility in the absence of excess free polymer solution is 78.7 mg L−1. The composite exhibited a conductivity of 0.005 S cm−1 and the anodic and cathodic peaks were observed at 0.47 and 0.37 V. Galvanostatical charge/discharge tests give good cycling behavior of maintaining a stable capacitance value of 66.7 F g−1 over 1000 cycles at a current load of 1 mA cm−2 without distinct drop.

Carbon nanotube (CNT)-reinforced aluminum composite powders were synthesized by cryogenic milling. The effects of different milling parameters and CNT contents on the structural characteristics and mechanical properties of the resulting composite powders were studied. Detailed information on powder morphology and the dispersion and structural integrity of the CNTs is crucial for many powder consolidation methods, particularly cold spray, which is increasingly utilized to fabricate metal-based nanocomposites. While all of the produced composite powders exhibited particle sizes suitable for spray applications, it was found that with increasing CNT content, the average particle size decreased and the size distribution became narrower. The dispersion of CNTs improved with milling time and helped to maintain a small Al grain size during cryogenic milling. Although extensive milling allowed for substantial grain size reduction, the process caused notable CNT degradation, leading to a deterioration of the mechanical properties of the resulting composite.

To reinforce the reliability issue brought by excessive interfacial reaction with the dimensional scale-down of electronic device, an electroless Ni–P–ZrO2 (17.5 at.% of P) composite coating was developed as the under bump metallization (UBM) for lead-free solder interconnect. ZrO2 nanoparticles were proved to be homogeneously distributed and helped improve wetting ability of the layer. Both Sn–3.5Ag/Ni–P–ZrO2 and Sn–3.5Ag/Ni–P solder joints were prepared and aged at various conditions to study the interfacial reaction. Growth of intermetallic compounds (IMCs) without serious spalling in solder/Ni–P–ZrO2 joint was slowed down because of the barrier property of incorporation of ZrO2 nanoparticles, which blocked the diffusion of Ni and Cu atoms. Based on the IMC growth, the activation energy of solder/Ni–P–ZrO2 was estimated to be higher than that of plain solder joint. The top-view of IMCs demonstrated a much finer grain size compared with that of solder/Ni–P joint. A reactive diffusion-induced compound formation mechanism was proposed to address the microstructural evolution in detail. Moreover, solder/Ni–P–ZrO2 joint demonstrated higher shear strength than did solder/Ni–P joint for different aging durations. The fracture surface of solder/Ni–P joint after shear test showed ductile transition failure, with big dimples and plastic deformation.

Cobalt was doped into the Ce-doped SrMnO3 system to enhance the low ionic conductivity of Ce-doped SrMnO3 (SCM) for solid oxide fuel cell cathode application. Structural and conductivity changes as a function of the Co content were investigated. Sr0.9Ce0.1Mn1–xCoxO3−δ (SCMCo, x = 0.1, 0.2, 0.3) cathode materials were synthesized by an EDTA citrate complexing process, which yielded a single perovskite structure, and the lattice volume was expanded by substituting Ce and Co ions. The increased lattice volume was attributed to a decrease in the valence state of the manganese and cobalt and an increase in the oxygen vacancy concentration. An increase in the concentration of oxygen vacancies with increasing Co content was identified by thermogravimetric analysis. The electrical conductivity decreased with increasing Co content, which was attributed to an increase in the activation energy for polaron hopping. Although the electrical conductivity was decreased by cobalt-doping, the polarization resistance of SCMCo also decreased significantly (from 5.611 to 1.171 Ω cm2 at 800 °C). The decreased polarization resistance is attributed to enhanced oxygen-ion transfer kinetics with cobalt-doping. We conclude that cobalt substitution leads to enhancement in the electrochemical properties of the cathode due to an increase in oxygen vacancy concentration.

In this article, a comprehensive investigation on the thermal properties of Yb3Al5O12 is conducted, including Debye temperature, thermal expansion coefficient (TEC), thermal diffusivity, heat capacity, and thermal conductivity. The calculated Debye temperature of Yb3Al5O12 from the measured elastic properties is 625 K. The linear and volumetric thermal expansions of Yb3Al5O12 from 298 to 1273 K are (7.83 ± 0.14) × 10−6 and (23.74 ± 0.42) × 10−6 K−1, respectively. The linear TEC of the polycrystalline bulk Yb3Al5O12 determined by dilatometer is (8.22 ± 0.3) × 10−6 K−1. The measured thermal conductivities of Yb3Al5O12 are 4.67 and 2.05 W (m K)−1, respectively, at 300 and 1400 K. The estimated minimum thermal conductivity, κmin, is 1.22 W (m K)−1. The high temperature thermal conductivity is close to the evaluated κmin, which is lower than most commonly used thermal barrier coating (TBC) material such as Y2O3-stabilized-ZrO2 (YSZ). The unique combination of these properties renders Yb3Al5O12 being a very promising candidate material for TBC.

From the view of tissue engineering, the deficiency in porosity has impeded further application of bacterial cellulose (BC) as a super biomaterial. In this study, we used a combination method consisting of acetic acid treatment and freeze-drying operation to improve the porous profile of BC, as well as a simple and fast method to measure the thickness, density, and porosity of BC. Results have shown a significant improvement in the porosity of the inner structure of BC treated with acetic acid and freeze-drying. Microscopic observation by scanning electron microscopy exhibited explicit evidences that more orderly porous layer-by-layer structures and more pores were formed along the cross section of modified BC as compared with the control. The enhancement of mechanical properties and crystallinity of modified BC was also demonstrated due to the improvement of material porosity in the particular extent from 50.3 to 76.43%. Cell culture of human fibroblast cells exhibited good cell viability on modified BC, suggesting that a better porous profile of BC on the surface and cross section helps facilitate cells to attach, as well as potentially promotes cells to grow in. These significant results may open the possibility of producing BC nanomaterials for tissue engineering with desirable properties.

Novel hybrid diblock copolymers consisting of bidentate ligand-functionalized chains have been synthesized via click reaction and RAFT radical polymerization. The chemical structure and molecular weight of the synthesized poly(methacrylate-POSS)-block-poly(4-vinylbenzyl-2-pyridine-1H-1,2,3-triazole) (PMAPOSS-b-PVBPT) were characterized by NMR and GPC. The copolymers had been utilized to construct metal-containing polymer micelle by the metal–ligand coordination and electrostatic interaction in this study. The self-assembly behaviors of PMAPOSS-b-PVBPT in chloroform, a common solvent, under the effect of Zn(OTf)2 and HAuCl4 were investigated by TEM, DLS, and variable temperature NMR. Besides, micellization of this diblock copolymer was achieved in ethylene glycol, a selective solvent for PMAPOSS-b-PVBPT. The experimental results revealed that the incorporation of heterocyclic rings bearing nitrogen atoms in polymer side chains played an important role in the construction of metal-containing copolymer micelles. The prepared metal-containing PMAPOSS-b-PVBPT micelles had good dynamic and thermal stability due to the strong metal–ligand coordination interaction and electrostatic interaction.

This study presented a novel fabrication process for TiNi thin films by vacuum diffusion technology using reactive Ni/Ti/Ni multilayer thin films. The sandwiched thin films were prepared by chemical nickel plating. Ni/Ti/Ni multilayer films were heat treated for various diffusion times and temperatures and the influences of the temperature and diffusion time on the interdiffusion behavior of the Ti–Ni system were researched in detail. The results showed that a homogeneous TiNi thin film was obtained at 1173 K with a diffusion time of 4 h. Moreover, the formation sequence of the intermetallics in the Ti–Ni diffusion system was investigated by thermodynamic analysis and experiment. It was found that three compounds – TiNi3, Ti2Ni, and TiNi – formed in the diffusion process at the Ti/Ni interfaces. More importantly, the nucleation of TiNi3 and Ti2Ni was prior to that of TiNi because of the lower reaction Gibbs free energy and increasing interface energy of TiNi3 and Ti2Ni.

Superelasticity of shape memory alloy (SMA) results from the reversible thermoelastic martensitic transformation. Although this property has been studied extensively at the macroscale, the study of this superelastic behavior at the micro/nanoscale is relatively new. In this work, we processed TiNi-based SMAs with different compositions and different phase transformation temperatures. Nanoindentations were performed with different peak loads and at various temperatures to systematically characterize the degree of localized stress-induced martensitic transformation at the nanoscale for each SMA. Micropillar compression tests were also performed to study the global superelastic behavior at the microscale. The physics of stress-induced martensitic transformation versus the phase transformation temperature, the testing temperature, and the peak load relations was explored and the difference between the localized and the global superelastic behaviors was discussed. Our results demonstrate the potential of integrating TiNi-based SMAs into functional micro- and nanodevices.

The effect of electric-current pulses on the evolution of microstructure and texture in cryogenically rolled copper was determined. The pulsed material was found to be completely recrystallized, and the recrystallization mechanism was deduced to be similar to that operating during conventional static annealing. The microstructural changes were explained simply in terms of Joule heating. A significant portion of the recrystallization process was concluded to have occurred after pulsing; i.e., during cooling to ambient temperature. The grain structure and microhardness were shown to vary noticeably in the heat-affected zone (HAZ); these observations mirrored variations of temper colors. Accordingly, the revealed microstructure heterogeneity was attributed to the inhomogeneous temperature distribution developed during pulsing. In the central part of the HAZ, the mean grain size increased with current density and this effect was associated with the temperature rise per se. This grain size was slightly smaller than that in statically recrystallized specimens.

Creep and electromigration (EM) have been two reliability concerns in microelectronic devices for a long time. The related failure mechanisms have been widely investigated and comprehended individually. However, there is a lack of attention with regard to the interaction(s) between current density and creep, the coupling effect of which is more analogous to the real service conditions of lead-free solder joint. In this study, a series of experiments were carried out on the simple shear lap joint to investigate the effects of current density magnitude on the creep behavior of solder joints. The results indicated that dislocation creep was the main failure mechanism for low current density sample. For high current density sample, the failure mechanism was mainly dominated by copper atom migrating process which led the joint experience a higher risk of brittle fracture failure.

The feasibility of an accelerated test method on revealing the high cycle fatigue (HCF) limit stresses of a near alpha titanium alloy was successfully verified firstly during the rotary bending tests. The stress-controlled low cycle fatigue (LCF) tests at room temperature were then carried out over a range of maximum stresses and stress ratios to reveal the basic LCF strength. Finally, the core emphasis was focused on the influences of the predamage from LCF loadings on the subsequent HCF limit stresses corresponding to the life of 106 cycles. A total of eight levels of predamage from LCF with different stress levels, stress ratios, and proportions of LCF life were introduced, which resulted in obvious deterioration of the HCF stress limits (even under only 2% of expected LCF life). The fracture analysis exhibited that there were typical LCF failure characteristics in crack initiation regions of specimens under prior LCF loadings.