Aromatic‐Diimide‐Based n‐Type Conjugated Polymers for All‐Polymer Solar Cell Applications

All‐polymer solar cells (all‐PSCs) have attracted immense attention in recent years due to their advantages of tunable absorption spectra and electronic energy levels for both donor and acceptor polymers, as well as their superior thermal and mechanical stability. The exploration of the novel n‐type conjugated polymers (CPs), especially based on aromatic diimide (ADI), plays a vital role in the further improvement of power conversion efficiency (PCE) of all‐PSCs. Here, recent progress in structure modification of ADIs including naphthalene diimide (NDI), perylene diimide (PDI), and corresponding derivatives is reviewed, and the structure–property relationships of ADI‐based CPs are revealed.     

Four‐Bits‐Per‐Cell Operation in an HfO2‐Based Resistive Switching Device

The quadruple‐level cell technology is demonstrated in an Au/Al₂O₃/HfO₂/TiN resistance switching memory device using the industry‐standard incremental step pulse programming (ISPP) and error checking/correction (ECC) methods. With the highly optimistic properties of the tested device, such as self‐compliance and gradual set‐switching behaviors, the device shows 6σ reliability up to 16 states with a state current gap value of 400 nA for the total allowable programmed current range from 2 to 11 µA. It is demonstrated that the conventional ISPP/ECC can be applied to such resistance switching memory, which may greatly contribute to the commercialization of the device, especially competitively with NAND flash. A relatively minor improvement in the material and circuitry may enable even a five‐bits‐per‐cell technology, which can hardly be imagined in NAND flash, whose state‐of‐the‐art multiple‐cell technology is only at three‐level (eight states) to this day.     

The influence of low‐plasticity burnishing process on the fatigue life of friction‐stir‐processed Al 7075‐T6 samples

The effects of low‐plasticity burnishing (LPB) on the fatigue life of friction‐stir‐processed (FSP) Al 7075‐T6 plates were examined experimentally and numerically. Aluminum samples were taken from plates to test fatigue response in the presence of heat‐affected zone (HAZ) at different loading magnitudes. Finite element method was employed to numerically evaluate fatigue life of FSPed samples by means of the Smith–Watson–Topper (SWT) model. Through numerical analysis, the FSP and its cooling procedure were modelled on the basis of the arbitrary Lagrangian–Eulerian technique, and then, the effect of the LPB to assess fatigue response of samples was examined. Aluminum samples undergoing friction‐stir process presented lower‐fatigue life as stresses were highly concentrated within FSP regions. Involvement of LPB regained fatigue durability through compressive residual stress induced on the aluminum samples. The higher applied force over the LPB promoted compressive residual stress on the sample surface and improved fatigue life of samples. The predicted life results were found twice more in magnitude than those of experimentally obtained.     

Austrittsarbeitsanalyse von GaN basierten Lateral Polarity Strukturen durch Auger‐Elektronen‐Energie‐Messungen

Work Function Analysis of GaN‐based Lateral Polarity Structures by Auger Electron Energy Measurements Lateral polarity heterostructure (LPH) were grown with adjacent Ga‐ and N‐face domains in order to invert the polarity of the crystal within a periodicity of a few microns. In this study we focus on the analysis of these LPH by Auger electron spectroscopy (AES). Because of the relationship between the Auger electron energy and the Fermi level, AES is a suitable method to identify the domains of a lateral polarity heterostructure. In addition, we discuss the possibility of determining the work function difference of Ga‐ and N‐face GaN. This difference in the work function between Ga‐face and N‐face GaN is found to be 0.25 eV. This difference is caused by a surface band bending.     

Large‐Scale Plasmonic Hybrid Framework with Built‐In Nanohole Array as Multifunctional Optical Sensing Platforms

Light coupling with patterned subwavelength hole arrays induces enhanced transmission supported by the strong surface plasmon mode. In this work, a nanostructured plasmonic framework with vertically built‐in nanohole arrays at deep‐subwavelength scale (6 nm) is demonstrated using a two‐step fabrication method. The nanohole arrays are formed first by the growth of a high‐quality two‐phase (i.e., Au–TiN) vertically aligned nanocomposite template, followed by selective wet‐etching of the metal (Au). Such a plasmonic nanohole film owns high epitaxial quality with large surface coverage and the structure can be tailored as either fully etched or half‐way etched nanoholes via careful control of the etching process. The chemically inert and plasmonic TiN plays a role in maintaining sharp hole boundary and preventing lattice distortion. Optical properties such as enhanced transmittance and anisotropic dielectric function in the visible regime are demonstrated. Numerical simulation suggests an extended surface plasmon mode and strong field enhancement at the hole edges. Two demonstrations, including the enhanced and modulated photoluminescence by surface coupling with 2D perovskite nanoplates and the refractive index sensing by infiltrating immersion liquids, suggest the great potential of such plasmonic nanohole array for reusable surface plasmon‐enhanced sensing applications.     

A new monolithic Newton‐multigrid‐based FEM solution scheme for large strain dynamic poroelasticity problems

This paper presents a new efficient monolithic finite element solution scheme to treat the set of PDEs governing a 2D, biphasic, saturated theory of porous media model with intrinsically coupled and incompressible solid and fluid constituents for infinitesimal and large elastic deformation. Our approach, which inherits some of its techniques from CFD, is characterized by the following aspects: (1) it only performs operator evaluation with no additional Gateaux derivatives. In particular, the computations of the time‐consuming material tangent matrix are not involved here; (2) it solves the non‐linear dynamic problem with no restriction on the strength of coupling; (3) it is more efficient than the linear u v p solver discussed in previous works; (4) it requires weaker derivatives, and hence, lower‐order FE can be tested; and (5) the boundary conditions are reduced, solution independent and more convenient to apply than in the old u v p formulation. For the purpose of validation and comparison, prototypical simulations including analytical solutions are carried out, and at the end, an adaptive time stepping procedure is introduced to handle the rapid change in the numbers of nonlinear iterations that may occur. Copyright © 2016 John Wiley & Sons, Ltd.     

Reduced‐order modeling of parameterized PDEs using time–space‐parameter principal component analysis

This paper presents a methodology for constructing low‐order surrogate models of finite element/finite volume discrete solutions of parameterized steady‐state partial differential equations. The construction of proper orthogonal decomposition modes in both physical space and parameter space allows us to represent high‐dimensional discrete solutions using only a few coefficients. An incremental greedy approach is developed for efficiently tackling problems with high‐dimensional parameter spaces. For numerical experiments and validation, several non‐linear steady‐state convection–diffusion–reaction problems are considered: first in one spatial dimension with two parameters, and then in two spatial dimensions with two and five parameters. In the two‐dimensional spatial case with two parameters, it is shown that a 7 × 7 coefficient matrix is sufficient to accurately reproduce the expected solution, while in the five parameters problem, a 13 × 6 coefficient matrix is shown to reproduce the solution with sufficient accuracy. The proposed methodology is expected to find applications to parameter variation studies, uncertainty analysis, inverse problems and optimal design. Copyright © 2009 John Wiley & Sons, Ltd.     

Evaluation of power extraction circuits on piezo‐transducers operating under low‐frequency vibration‐induced strains in bridges

The concept of piezoelectric energy harvesting (PEH) provides a promising solution for perpetually running low‐power electronic devices such as wireless sensor networks by harvesting ambient vibrations generated from civil structures such as long span bridges, city flyovers, elevated metro corridors, which are constantly under dynamic loads. However, its successful industrial‐scale deployment on civil structures is still not realised because of the low‐frequency of vibrations (typically <5 Hz) encountered there, coupled with the low levels of voltage generation. The vast majority of PEH‐related studies have only focused on PEH configurations and geometries, Often entailing secondary structures. d₃₁ mode, which is the most natural mode of excitation, has not been investigated in depth for piezo‐patches directly bonded on the main structure. Studies, which have focused on electronic conditioning circuitry, have been restricted to typically high‐voltage and high‐frequency scenarios only. This paper focuses on systematically studying the issues inflicting energy harvesting from the ambient vibrations induced flexural strains civil structures, such as city flyovers, using piezo elements in d₃₁ mode. Vibration measurements are first undertaken from a typical city flyover consisting of steel girders supporting a reinforced concrete (RC) deck. The basic site measurements are employed to perform a laboratory‐based parametric study to investigate the influence of parameters such as vibration frequency, voltage, and circuit components like diodes on PEH. On the basis of the experimental results, it can be concluded that power in microwatts range can be typically harvested from these civil structures through directly bonded piezo patches in d₃₁ mode. However, there are still issues associated with electronic circuitry accompanying harvesters, such as diodes and storage elements. The same are summarised and future directions envisioned.     

Nutzung von Low‐Transformation‐Temperature‐Werkstoffen (LTT) zur Eigenspannungsreduzierung im Elektronenstrahlschweißprozess

Low‐Transformation‐Temperature materials (LTT) were designed to reduce delay as well as residual tensile stress in welds on carbon‐manganese steels. Using the volume expansion effect during a martensitic transformation these materials counteract the volume shrinkage during cooling. While this positive effects on residual stress relief by Low‐Transformation‐Temperature‐alloys has been proven in various studies, these alloys have always been used in large volumes as additional filler material in electric arc welding processes. Modular heat fields initiated by an electron‐beam‐welding‐process offers the potential of a time‐activated initiation of compressive stresses triggered by phase transformation of Low‐Transformation‐Temperature‐alloys. Developing a technology able to reduce residual stress and thus the deformation of complex welded components is the aim. The first approach of Low‐Transformation‐Temperature‐material used in the electron beam process and its behaviour is presented here.     

PM‐Composites with Nickel‐Titanium Shape Memory Alloys

Starting from NiTi‐powders, composites of nickel‐titanium shape memory alloys (NiTi‐SMA) and different stainless steels as well as of different NiTi‐SMAs were produced by using the process of hot isostatic pressing (HIP). Metallographic investigations focussed on the interface between NiTi‐SMA and stainless steel with special emphasis placed on the characterization of the typical structure of the diffusion zones in both components.