Low‐Noise and Large‐Linear‐Dynamic‐Range Photodetectors Based on Hybrid‐Perovskite Thin‐Single‐Crystals

Organic–inorganic halide perovskites are promising photodetector materials due to their strong absorption, large carrier mobility, and easily tunable bandgap. Up to now, perovskite photodetectors are mainly based on polycrystalline thin films, which have some undesired properties such as large defective grain boundaries hindering the further improvement of the detector performance. Here, perovskite thin‐single‐crystal (TSC) photodetectors are fabricated with a vertical p–i–n structure. Due to the absence of grain‐boundaries, the trap densities of TSCs are 10–100 folds lower than that of polycrystalline thin films. The photodetectors based on CH₃NH₃PbBr₃ and CH₃NH₃PbI₃ TSCs show low noise of 1–2 fA Hz^?1/2, yielding a high specific detectivity of 1.5 × 10¹³ cm Hz^1/2 W^?1. The absence of grain boundaries reduces charge recombination and enables a linear response under strong light, superior to polycrystalline photodetectors. The CH₃NH₃PbBr₃ photodetectors show a linear response to green light from 0.35 pW cm^?2 to 2.1 W cm^?2, corresponding to a linear dynamic range of 256 dB.     

Clay‐Inspired MXene‐Based Electrochemical Devices and Photo‐Electrocatalyst: State‐of‐the‐Art Progresses and Challenges

MXene, an important and increasingly popular category of postgraphene 2D nanomaterials, has been rigorously investigated since early 2011 because of advantages including flexible tunability in element composition, hydrophobicity, metallic nature, unique in‐plane anisotropic structure, high charge‐carrier mobility, tunable band gap, and favorable optical and mechanical properties. To fully exploit these potentials and further expand beyond the existing boundaries, novel functional nanostructures spanning monolayer, multilayer, nanoparticles, and composites have been developed by means of intercalation, delamination, functionalization, hybridization, among others. Undeniably, the cutting‐edge developments and applications of clay‐inspired 2D MXene platform as electrochemical electrode or photo‐electrocatalyst have conferred superior performance and have made significant impact in the field of energy and advanced catalysis. This review provides an overview of the fundamental properties and synthesis routes of pure MXene, functionalized MXene and their hybrids, highlights the state‐of‐the‐art progresses of MXene‐based applications with respect to supercapacitors, batteries, electrocatalysis and photocatalysis, and presents the challenges and prospects in the burgeoning field.     

High‐Performance n‐Channel Organic Transistors Using High‐Molecular‐Weight Electron‐Deficient Copolymers and Amine‐Tailed Self‐Assembled Monolayers

While high‐performance p‐type semiconducting polymers are widely reported, their n‐type counterparts are still rare in terms of quantity and quality. Here, an improved Stille polymerization protocol using chlorobenzene as the solvent and palladium(0)/copper(I) as the catalyst is developed to synthesize high‐quality n‐type polymers with number‐average molecular weight up to 10⁵ g mol^?1. Furthermore, by sp²‐nitrogen atoms (sp²‐N) substitution, three new n‐type polymers, namely, pBTTz, pPPT, and pSNT, are synthesized, and the effect of different sp²‐N substitution positions on the device performances is studied for the first time. It is found that the incorporation of sp²‐N into the acceptor units rather than the donor units results in superior crystalline microstructures and higher electron mobilities. Furthermore, an amine‐tailed self‐assembled monolayer (SAM) is smoothly formed on a Si/SiO₂ substrate by a simple spin‐coating technique, which can facilitate the accumulation of electrons and lead to more perfect unipolar n‐type transistor performances. Therefore, a remarkably high unipolar electron mobility up to 5.35 cm² V^?1 s^?1 with a low threshold voltage (≈1 V) and high on/off current ratio of ≈10⁷ is demonstrated for the pSNT‐based devices, which are among the highest values for unipolar n‐type semiconducting polymers.     

Micrometer‐ and Nanometer‐Sized Organic Single‐Crystalline Transistors

The use of micrometer and nanometer‐sized organic single crystals to fabricate devices can retain all the advantages of single crystals, avoid the difficulties of growing large crystals, and provide a way to characterize organic semiconductors more efficiently. Moreover, the effective use of such “small” crystals will be beneficial to nanoelectronics. Here we review the recent progress of organic single‐crystalline transistors based on micro‐/nanometer‐sized structures, namely fabrication methods and related technical issues, device properties, and current challenges.     

Synchrotron‐Based Micro‐CT and Refraction‐Enhanced Micro‐CT for Non‐Destructive Materials Characterisation

X‐ray computed tomography is an important tool for non‐destructively evaluating the 3‐D microstructure of modern materials. To resolve material structures in the micrometer range and below, high brilliance synchrotron radiation has to be used. The Federal Institute for Materials Research and Testing (BAM) has built up an imaging setup for micro‐tomography and ‐radiography (BAMline) at the Berliner storage ring for synchrotron radiation (BESSY). In computed tomography, the contrast at interfaces within heterogeneous materials can be strongly amplified by effects related to X‐ray refraction. Such effects are especially useful for materials of low absorption or mixed phases showing similar X‐ray absorption properties that produce low contrast. The technique is based on ultra‐small‐angle scattering by microstructural elements causing phase‐related effects, such as refraction and total reflection. The extraordinary contrast of inner surfaces is far beyond absorption effects. Crack orientation and fibre/matrix debonding in plastics, polymers, ceramics and metal‐matrix‐composites after cyclic loading and hydro‐thermal aging can be visualized. In most cases, the investigated inner surface and interface structures correlate to mechanical properties. The technique is an alternative to other attempts on raising the spatial resolution of CT machines.     

Progress in Piezo‐Phototronic‐Effect‐Enhanced Light‐Emitting Diodes and Pressure Imaging

Wurtzite materials exhibit both semiconductor and piezoelectric properties under strains due to the non‐central symmetric crystal structures. The three‐way coupling of semiconductor properties, piezoelectric polarization and optical excitation in ZnO, GaN, CdS and other piezoelectric semiconductors leads to the emerging field of piezo‐phototronics. This effect can efficiently manipulate the emission intensity of light‐emitting diodes (LEDs) by utilizing the piezo‐polarization charges created at the junction upon straining to modulate the energy band diagrams and the optoelectronic processes, such as generation, separation, recombination and/or transport of charge carriers. Starting from fundamental physics principles, recent progress in piezo‐phototronic‐effect‐enhanced LEDs is reviewed; following their development from single‐nanowire pressure‐sensitive devices to high‐resolution array matrices for pressure‐distribution mapping applications. The piezo‐phototronic effect provides a promising method to enhance the light emission of LEDs based on piezoelectric semiconductors through applying static strains, and may find perspective applications in various optoelectronic devices and integrated systems.     

Single‐layer and multi‐layer wear‐resistant coatings

In this paper the formation of wear‐resistant coatings based on titanium and aluminum compounds using vacuum arc discharge and molecular nitrogen as a working gas is discussed. The experiments were carried out using an installation containing two independent evaporators and a system for attenuation and purification of the plasma flow. To obtain a high‐quality coating, it is necessary to ensure the equality of the ion flux densities coming to the substrate. The results of the experiments show that by changing the bias voltage on the substrate it is possible to adjust the content of elements in the coating and thus to control its parameters. Multi‐layer coatings have better performance characteristics, but require an improved degree of purification of the plasma flow from the droplet fraction.     

Nanocatalysts‐Augmented and Photothermal‐Enhanced Tumor‐Specific Sequential Nanocatalytic Therapy in Both NIR‐I and NIR‐II Biowindows

The tumor microenvironment (TME) has been increasingly recognized as a crucial contributor to tumorigenesis. Based on the unique TME for achieving tumor‐specific therapy, here a novel concept of photothermal‐enhanced sequential nanocatalytic therapy in both NIR‐I and NIR‐II biowindows is proposed, which innovatively changes the condition of nanocatalytic Fenton reaction for production of highly efficient hydroxyl radicals (?OH) and consequently suppressing the tumor growth. Evidence suggests that glucose plays a vital role in powering cancer progression. Encouraged by the oxidation of glucose to gluconic acid and H₂O₂ by glucose oxidase (GOD), an Fe₃O₄/GOD‐functionalized polypyrrole (PPy)‐based composite nanocatalyst is constructed to achieve diagnostic imaging‐guided, photothermal‐enhanced, and TME‐specific sequential nanocatalytic tumor therapy. The consumption of intratumoral glucose by GOD leads to the in situ elevation of the H₂O₂ level, and the integrated Fe₃O₄ component then catalyzes H₂O₂ into highly toxic ?OH to efficiently induce cancer‐cell death. Importantly, the high photothermal‐conversion efficiency (66.4% in NIR‐II biowindow) of the PPy component elevates the local tumor temperature in both NIR‐I and NIR‐II biowindows to substaintially accelerate and improve the nanocatalytic disproportionation degree of H₂O₂ for enhancing the nanocatalytic‐therapeutic efficacy, which successfully achieves a remarkable synergistic anticancer outcome with minimal side effects.     

Ultrahigh‐Water‐Content,Superelastic, and Shape‐Memory Nanofiber‐Assembled Hydrogels Exhibiting Pressure‐Responsive Conductivity

High‐water‐content hydrogels that are both mechanically robust and conductive could have wide applications in fields ranging from bioengineering and electronic devices to medicine; however, creating such materials has proven to be extremely challenging. This study presents a scalable methodology to prepare superelastic, cellular‐structured nanofibrous hydrogels (NFHs) by combining alginate and flexible SiO₂ nanofibers. This approach causes naturally abundant and sustainable alginate to assemble into 3D elastic bulk NFHs with tunable water content and desirable shapes on a large scale. The resultant NFHs exhibit the integrated properties of ultrahigh water content (99.8 wt%), complete recovery from 80% strain, zero Poisson's ratio, shape‐memory behavior, injectability, and elastic‐responsive conductivity, which can detect dynamic pressure in a wide range (>50 Pa) with robust sensitivity (0.24 kPa^?1) and durability (100 cycles). The fabrication of such fascinating materials may provide new insights into the design and development of multifunctional hydrogels for various applications.     

Variational‐based modeling of micro‐electro‐elasticity with electric field‐driven and stress‐driven domain evolutions

Recently, increasing interest in so‐called functional or smart materials with electromechanical coupling has been shown such as ferroelectric piezoceramics. These materials are characterized by microstructural properties, which can be changed by external stress and electric field stimuli, and hence find use as the active components in sensors and actuators. The electromechanical coupling effects result from the existence and rearrangement of microstructural domains with uniformly oriented electric polarization. The understanding and efficient simulation of these highly nonlinear and dissipative mechanisms, which occur on the microscale of ferroelectric piezoceramics, are a key challenge of the current research. This paper does not offer a substantially new physical model of these phenomena but a new mathematical modeling approach based on a rigorous exploitation of rate‐type variational principles. This provides a new insight in the structure of the coupled problem, where the governing field equations appear as the Euler equations of a variational statement. We outline a variational‐based micro‐electro‐elastic model for the microstructural evolution of both electrically and mechanically driven electric domains in ferroelectric ceramics, which also incorporates the surrounding free space. To this end, we extend recently developed multifield incremental variational principles of electromechanics from local to gradient‐extended dissipative response and specialize it by a Ginzburg–Landau‐type phase field model, where the thickness of the domain walls enters the formulation as a length scale. This serves as a natural starting point for a canonical compact, symmetric finite element implementation, considering the mechanical displacement, the microscopic polarization, and the electric potential induced by the polarization as the primary fields. The latter is defined on both the solid domain and a surrounding free space. Numerical simulations treat domain wall motions for electric field‐driven and stress‐driven loading processes, including the expansion of the electric potential into the free space. Copyright © 2012 John Wiley & Sons, Ltd.     

Functional Single‐Walled Carbon Nanotubes and Nanoengineered Networks for Organic‐ and Perovskite‐Solar‐Cell Applications

Carbon nanotubes have a variety of remarkable electronic and mechanical properties that, in principle, lend them to promising optoelectronic applications. However, the field has been plagued by heterogeneity in the distributions of synthesized tubes and uncontrolled bundling, both of which have prevented nanotubes from reaching their full potential. Here, a variety of recently demonstrated solution‐processing avenues is presented, which may combat these challenges through manipulation of nanoscale structures. Recent advances in polymer‐wrapping of single‐walled carbon nanotubes (SWNTs) are shown, along with how the resulting nanostructures can selectively disperse tubes while also exploiting the favorable properties of the polymer, such as light‐harvesting ability. New methods to controllably form nanoengineered SWNT networks with controlled nanotube placement are discussed. These nanoengineered networks decrease bundling, lower the percolation threshold, and enable a strong enhancement in charge conductivity compared to random networks, making them potentially attractive for optoelectronic applications. Finally, SWNT applications, to date, in organic and perovskite photovoltaics are reviewed, and insights as to how the aforementioned recent advancements can lead to improved device performance provided.     

Economic‐statistical design of 2‐of‐2 and 2‐of‐3 runs rule scheme

In this paper, we investigate the economic‐statistical design method for the 2‐of‐2 runs rule and the 2‐of‐3 runs rule. The Markov chain approach is used to obtain the average run length and the process cycle time. In addition, a simplified algorithm is presented to search the optimal setting of the design parameters. A numerical example and sensitivity analysis are also provided to compare the performances of the runs rules. The results show that the use of runs rule scheme can reduce operating cost comparing with the Shewhart control chart while maintaining a good statistical performance. Copyright © 2008 John Wiley & Sons, Ltd.