Polyaniline nanofiber/gold nanoparticle nonvolatile memory

A nonvolatile plastic digital memory device based on nanofibers of the conjugated polymer polyaniline decorated with gold nanoparticles is reported. The device has a simple structure consisting of the plastic composite film sandwiched between two electrodes. An external bias is used to program the ON and OFF states of the device that are separated by a 3-orders-of-magnitude difference in conductivity. ON-OFF switching times of less than 25 ns are observed by electrical pulse measurements. The devices possess prolonged retention times of several days after they have been programmed. Write-read-erase cycles are also demonstrated. The switching mechanism is attributed to an electric-field-induced charge transfer from the polyaniline nanofibers to the gold nanoparticles. The active polymer layer is created by growing nanometer size gold particles within 30-nm-diameter polyaniline nanofibers using a redox reaction with chloroauric acid. This device combines two exciting research areas--nanoparticles and conducting polymers--to form a novel materials system with unique functionality.     

LC-DAD-MS/SPE-NMR hyphenation. A tool for the analysis of pharmaceutically used plant extracts: identification of isobaric iridoid glycoside regioisomers from Harpagophytum procumbens

LC-DAD-MS monitored fractionation of a Harpagophytum procumbens DC. (Pedaliaceae) root extract was combined with a hyphenated LC-DAD-MS/SPE-NMR technique, thus providing the spectral data needed for structure elucidation. This approach allowed the characterization of isobaric iridoid glycoside regioisomers present only as minor constituents. The analytes were identified as the (E/Z) pairs of 6'-O-(p-coumaroyl)harpagide (6'-PCHG) and 8-O-(p-coumaroyl)-harpagide (8-PCHG). The fact that 8-(Z)-PCHG constitutes a new natural product underlines the analytical power of this combined approach. Furthermore, derivatives 6'-(Z)- and 6'-(E)-PCHG are new constituents for H. procumbens.     

Double-step annealing and ambient effects on phosphorus implanted emitters in silicon

Emitters of npn silicon bipolar transistors have been made by a phosphorus implantation at 50 keV P⁺ to a dose of 1×10¹⁶ cm^?2. This was followed by high temperature processes to reduce lattice disorder, to drive-in the phosphorus atoms, and to form oxide layers. The first process step was carried out by using single- and double-step anneals in various ambients (dry N₂, dry O₂ and steam) while the drive-in and oxidation steps were common for all structures. Electrical measurements on emitter/base leakage current, low frequency (popcorn) noise and current gain showed that the annealing ambient had a major influence. The transistors with implanted emitters annealed in a dry N₂ ambient are comparable to commercial ones with thermally-diffused emitters. TEM observations on samples annealed in steam ambients revealed dislocatons extending into the sidewall of the emitter/base junction. This sidewall penetration of dislocations is the main origin of the degradation of the emitter/base junction characteristics.     

The mixed finite element method applied to two-dimensional elastic contact problems

The application of the mixed finite element method to two-dimensional elastic contact problems is investigated. Since in the mixed method, both displacements and stresses are retained as variables, it is found that all the contact conditions—displacement as well as stress—can be approximated directly. A significant novelty is that some of the displacement variables are treated as natural boundary conditions in the contact region. In cases where the contact region is independent of the applied loading, an iterative procedure is used to establish the sliding and adhering portions of the contact region. In cases where the contact region is a function of the applied loading, for example progressive contact, an incremental formulation is employed to describe the discretized contact stages before invoking the former iterations. Several numerical examples are presented and the results are compared with those from the conventional potential energy or displacement finite element method.     

Wrinkled 2D Materials: A Versatile Platform for Low‐Threshold Stretchable Random Lasers

A stretchable, flexible, and bendable random laser system capable of lasing in a wide range of spectrum will have many potential applications in next‐ generation technologies, such as visible‐spectrum communication, superbright solid‐state lighting, biomedical studies, fluorescence, etc. However, producing an appropriate cavity for such a wide spectral range remains a challenge owing to the rigidity of the resonator for the generation of coherent loops. 2D materials with wrinkled structures exhibit superior advantages of high stretchability and a suitable matrix for photon trapping in between the hill and valley geometries compared to their flat counterparts. Here, the intriguing functionalities of wrinkled reduced graphene oxide, single‐layer graphene, and few‐layer hexagonal boron nitride, respectively, are utilized to design highly stretchable and wearable random laser devices with ultralow threshold. Using methyl‐ammonium lead bromide perovskite nanocrystals (PNC) to illustrate the working principle, the lasing threshold is found to be ≈10 µJ cm^?2, about two times less than the lowest value ever reported. In addition to PNC, it is demonstrated that the output lasing wavelength can be tuned using different active materials such as semiconductor quantum dots. Thus, this study is very useful for the future development of high‐performance wearable optoelectronic devices.     

A Generalized Quasi-MMSE Controller for Run-to-Run Dynamic Models

This study proposes a generalized quasi-minimum mean square error (qMMSE) controller for implementing a run-to-run process control where the process input–output relationship follows a general-order dynamical model with added noise. The expression of the process output, the long-term stability conditions and the optimal discount factor of this controller are derived analytically. Furthermore, we use the proposed second-order dynamical model to illustrate the effects of mis-identification of the process I-O model on the process total mean square error (TMSE). Via a comprehensive simulation study, the model demonstrates that the TMSE may inflate by more than 150% if a second-order dynamical model with moderately large carryover effects is wrongly identified as that of a first-order model. This means that the effects of mis-identification of the process I-O model on the process total mean square error (TMSE) is not negligible for implementing a dynamic run-to-run (RTR) process control. Supplementary materials for this article are available online.     

Using big data to make better decisions in the digital economy

The question this special issue would like to address is how to harvest big data to help decision-makers to deliver better fact-based decisions aimed at improving performance or to create better strategy? This special issue focuses on the big data applications in supporting operations decisions, including advanced research on decision models and tools for the digital economy. Responds to this special issue was great and we have included many high-quality papers. We are pleased to present 13 of the best papers. The techniques presented include data mining, simulation and expert system with applications span across online reviews, food retail chain to e-health.     

Solid–liquid interdiffusion bonding of Cu/In/Ni microjoints

Low-temperature solder is needed for temperature-sensitive components, step soldering and wearable devices. Low-temperature bonding is effective for reducing temperature and manufacturing costs. Indium has a low melting point, low resistance and good anticorrosion properties. Indium plays important roles in transparent conductors, the aerospace industry and flexible displays. Solid–liquid interdiffusion (SLID) bonding is one of the most reliable 3D integration technologies. The microstructure of the Cu/In/Ni bonding interface was investigated in this study. A low temperature of 180 °C was used for SLID bonding. Cu-In compounds, Cu₁₁In₉ and CuIn₂, were formed after SLID bonding at 180 °C and storing at room temperature. The reaction between Cu and In is fast, even at room temperature. The low-temperature CuIn₂ phase is undoubtedly worth investigating for solder joints.

     

Minimization of Ion–Solvent Clusters in Gel Electrolytes Containing Graphene Oxide Quantum Dots for Lithium‐Ion Batteries

This study uses graphene oxide quantum dots (GOQDs) to enhance the Li⁺‐ion mobility of a gel polymer electrolyte (GPE) for lithium‐ion batteries (LIBs). The GPE comprises a framework of poly(acrylonitrile‐co‐vinylacetate) blended with poly(methyl methacrylate) and a salt LiPF₆ solvated in carbonate solvents. The GOQDs, which function as acceptors, are small (3?11 nm) and well dispersed in the polymer framework. The GOQDs suppress the formation of ion?solvent clusters and immobilize anions, affording the GPE a high ionic conductivity and a high Li⁺‐ion transference number (0.77). When assembled into Li|electrolyte|LiFePO₄ batteries, the GPEs containing GOQDs preserve the battery capacity at high rates (up to 20 C) and exhibit 100% capacity retention after 500 charge?discharge cycles. Smaller GOQDs are more effective in GPE performance enhancement because of the higher dispersion of QDs. The minimization of both the ion?solvent clusters and degree of Li⁺‐ion solvation in the GPEs with GOQDs results in even plating and stripping of the Li‐metal anode; therefore, Li dendrite formation is suppressed during battery operation. This study demonstrates a strategy of using small GOQDs with tunable properties to effectively modulate ion?solvent coordination in GPEs and thus improve the performance and lifespan of LIBs.