Flexible Hard Coating: Glass‐Like Wear Resistant,Yet Plastic‐Like Compliant,Transparent Protective Coating for Foldable Displays

A flexible hard coating for foldable displays is realized by the highly cross‐linked siloxane hybrid using structure–property relationships in organic–inorganic hybridization. Glass‐like wear resistance, plastic‐like flexibility, and highly elastic resilience are demonstrated together with outstanding optical transparency. It provides a framework for the application of siloxane hybrids in protective hard coatings with high scratch resistance and flexibility for foldable displays.     

Exploiting Colloidal Metamaterials for Achieving Unnatural Optical Refractions

The scaling down of meta-atoms or metamolecules (collectively denoted as metaunits) is a long-lasting issue from the time when the concept of metamaterials was first suggested. According to the effective medium theory, which is the foundational concept of metamaterials, the structural sizes of meta-units should be much smaller than the working wavelengths (e.g., << 1/5 wavelength). At relatively low frequency regimes (e.g., microwave and terahertz), the conventional monolithic lithography can readily address the materialization of metamaterials. However, it is still challenging to fabricate optical metamaterials (metamaterials working at optical frequencies such as the visible and near-infrared regimes) through the lithographic approaches. This serves as the rationale for using colloidal self-assembly as a strategy for the realization of optical metamaterials. Colloidal self-assembly can address various critical issues associated with the materialization of optical metamaterials, such as achieving nanogaps over a large area, increasing true 3D structural complexities, and cost-effective processing, which all are difficult to attain through monolithic lithography. Nevertheless, colloidal self-assembly is still a toolset underutilized by optical engineers. Here, the design principle of the colloidally self-assembled optical metamaterials exhibiting unnatural refractions, the practical challenge of relevant experiments, and the future opportunities are critically reviewed.     

A neural network constitutive model for hyperelasticity based on molecular dynamics simulations

Numerical analysis of the hyperelastic behavior of polymer materials has drawn significant interest from within the field of mechanical engineering. Currently, hyperelastic models based on the energy density function, such as the Neo-Hookean, Mooney-Rivlin, and Ogden models, are used to investigate the hyperelastic responses of materials. Conventionally, constants relating to materials were determined from experimental data by using global least-squares fitting. However, formulating a constitutive equation to capture the complex behavior of hyperelastic materials was difficult owing to the limitations of the analytical model and experimental data. This study addresses these limitations by using a system of neural networks (NNs) to design a data-driven surrogate model without a specific function formula, and employs molecular dynamics (MD) simulations to calculate the massive amount of combined loading data of hyperelastic materials. Thus, MD simulations were used to propose an NN constitutive model for hyperelasticity to derive the constitutive equation to model the complex hyperelastic response. In addition, the probability distributions of the numerical solutions of hyperelasticity are used to characterize the uncertainty of the MD models. These statistical finite element results not only present numerical results with reliability ranges but also scattered distributions of the solution obtained from the MD-based probability distributions.     

High Performance β-Ga2O3 Schottky Barrier Transistors with Large Work Function TMD Gate of NbS2 and TaS2

Gallium trioxide, β-Ga₂O₃, has been recently studied due to its promising semiconducting properties as active material in transistors or Schottky diodes. Transistors with β-Ga₂O₃ channels are mostly metal oxide field effect transistors (MOSFET), and they show very negative threshold voltages (V_th) in general. Metal semiconductor field effect transistors (MESFETs) with top gate are also reported with less negative V_th. Still, β-Ga₂O₃ MESFETs are only a few. Here, bottom gate architecture β-Ga₂O₃ MESFETs using transition metal dichalcogenide (TMD) NbS₂ and TaS₂ are reported. Due to the large work functions of those metallic TMDs, the MESFETs display minimum subthreshold swing of 61 mV dec⁻¹, small V_th of −1.2 V, minimum OFF I_D of ≈100 fA, and maximum ON/OFF current ratio of ≈10⁸. Both β-Ga₂O₃ Schottky diodes with TaS₂ and NbS₂ display good junction stability even after 300 °C measurements in 10 mTorr vacuum. When the β-Ga₂O₃ MESFET with TaS₂ gate is integrated as a switching FET into an organic light emitting diode (OLED) circuit, it demonstrates long-term leakage endurance performance, maintaining an OLED brightness higher than 58% of the initial intensity after 100 s passes since the ON-switching point, which is even superior to the performance of conventional a-IGZO MOSFET switch.     

Highly Reliable Charge Trap-Type Organic Non-Volatile Memory Device Using Advanced Band-Engineered Organic-Inorganic Hybrid Dielectric Stacks

With the recent interest in data storage in flexible electronics, highly reliable charge trap-type organic-based non-volatile memory (CT-ONVM) has attracted much attention. CT-ONVM should have a wide memory window, good endurance, and long-term retention characteristics, as well as mechanical flexibility. This paper proposed CT-ONVM devices consisting of band-engineered organic–inorganic hybrid films synthesized via an initiated chemical vapor deposition process. The synthesized poly(1,3,5-trimethyl-1,3,5,-trivinyl cyclotrisiloxane) and Al hybrid films are used as a tunneling dielectric layer and a blocking dielectric layer, respectively. For the charge trapping layer, different Hf, Zr, and Ti hybrids are examined, and their memory performances are systematically compared. The best combination of hybrid dielectric stacks showed a wide memory window of 6.77 V, good endurance of up to 10⁴ cycles, and charge retention of up to 71% after 10⁸ s even under the 2% strained condition. The CT-ONVM device using the hybrid dielectric stacks outperforms other organic-based charge trap memory devices and is even comparable in performance to conventional inorganic-based poly-silicon/oxide/nitride/oxide/silicon structures devices. The CT-ONVM using hybrid dielectrics can overcome the inherent low reliability and process complexity limitations of organic electronics and expedite the realization of wearable organic electronics.     

Distributed Virtual Inertia Based Control of Multiple Photovoltaic Systems in Autonomous Microgrid

The large inertia of a traditional power system slows down system's frequency response but also allows decent time for controlling the system. Since an autonomous renewable microgrid usually has much smaller inertia, the control system must be very fast and accurate to fight against the small inertia and uncertainties. To reduce the demanding requirements on control, this paper proposes to increase the inertia of photovoltaic (PV) system through inertia emulation. The inertia emulation is realized by controlling the charging/discharging of the direct current (DC)-link capacitor over a certain range and adjusting the PV generation when it is feasible and/or necessary. By well designing the inertia, the DC-link capacitor parameters and the control range, the negative impact of inertia emulation on energy efficiency can be reduced. The proposed algorithm can be integrated with distributed generation setting algorithms to improve dynamic performance and lower implementation requirements. Simulation studies demonstrate the effectiveness of the proposed solution.      

Effects of Al<Superscript>3+</Superscript> substitution on the luminescence properties of LuNbO<Subscript>4</Subscript> doped with Eu<Superscript>3+</Superscript> and Tb<Superscript>3+</Superscript> ions

The effect of Al³⁺ substitution on the enhancement of the luminescence of Lu_1–xAl_xNbO₄:Eu³⁺ and Lu_1–xAl_xNbO₄:Tb³⁺ was investigated. X-ray diffraction patterns confirmed that the Eu³⁺, Tb³⁺, and Al³⁺ ions were fully incorporated into the Lu³⁺ sites. In the case of Lu_1–xAl_xNbO₄:Eu³⁺, the predominant red emission (614 nm) was assigned to the ⁵D₀?→?⁷F₂ transition of Eu³⁺ and for x?=?0–0.05, its intensity increased up to ~125 and 108% under 395 nm (⁷F₀ → ⁵L₆) and a charge transfer band excitation, respectively. For Lu_1–xAl_xNbO₄:Tb³⁺, the strongest emission band peaking at 551 nm was attained in the green region among multiple emission bands corresponding to the ⁵D₄?→?⁷F_J transitions of Tb³⁺. Increasing the x values from 0 to 0.05 increased the green emission significantly by ~137%. These phenomena were explained by the local structural distortions and crystal field asymmetry surrounding Eu³⁺ and Tb³⁺, which were attributed to a large difference in the ionic radii of Al³⁺ and Lu³⁺.     

Detection of Foot‐and‐Mouth Disease Virus Using a Polydiacetylene Immunosensor on Solid‐Liquid Phase

The rapid detection of foot‐and‐mouth disease virus (FMDV) is vital for the prevention of foot‐and‐mouth disease outbreaks. In this study, a polyvinylidene difluoride (PVDF)‐supported polydiacetylene (PDA) immunosensor is developed to detect FMDV, in which a polyclonal antibody against the FMDV VP1 antigen is conjugated as a specific virus‐binding module without a linker. First, a liposome‐based immunosensor is generated for the FMDV VP1 protein in the form of photopolymerized PDA colloids. Then, the VP1‐specific PDA immunosensors are modified onto PVDF strip to enable the rapid and portable detection of FMDV. Detailed analyses are performed using ultraviolet‐visible spectroscopy, dynamic light scattering, transmission electron microscopy, and scanning electron microscopy. A blue‐to‐red color transition is observed in the presence of FMDV particles, indicating the potential applications of FMDV‐specific PDA immunosensors for use in solid‐phase detection as well as via liquid‐phase liposome platforms. Thus, this work provides a rapid and simple detection for FMDV.     

QFT Parameter-Scheduling control design for linear Time-Varying systems based on RBF networks

For most of linear time-varying (LTV) systems, it is difficult to design time-varying controllers in analytic way. Accordingly, by approximating LTV systems as uncertain linear time-invariant, control design approaches such as robust control have been applied to the resulting uncertain LTI systems. In particular, a robust control method such as quantitative feedback theory (QFT) has an advantage of guaranteeing the frozen-time stability and the performance specification against plant parameter uncertainties. However, if these methods are applied to the approximated linear time-invariant (LTI) plants with large uncertainty, the resulting control law becomes complicated and also may not become ineffective with faster dynamic behavior. In this paper, as a method to enhance the fast dynamic performance of LTV systems with bounded time-varying parameters, the approximated uncertainty of time-varying parameters are reduced by the proposed QFT parameter-scheduling control design based on radial basis function (RBF) networks.     

Long‐term stable hydrophilic surface modification of poly(ether ether ketone) via the multilayered chemical grafting method

The aging phenomena of a poly(ether ether keton) (PEEK) surface hydrophilically modified via various protocols was investigated. The use of plasma treatment or chemical etching methods offers a relatively convenient surface modification route. However, the effects of hydrophilic treatment quickly disappeared and its original surface property was recovered within a few hours or a few days when stored at ambient conditions. Surface treatment based on a single‐layered chemical grafting method rendered an excellent hydrophilic surface with an initial contact angle of <15° and an improved retardation of surface aging. However, the contact angle of the modified PEEK specimen gradually increased with time and eventually reached ～50° after 23 days. A new method for the long‐term stable hydrophilic surface treatment of PEEK using a multilayered chemical grafting strategy was also developed. With this regard, aging of the modified surface could be significantly retarded over ～90 days. It was believed that the effectiveness of the surface modification and the retarded aging phenomena via the multilayered hydrophilic treatment could be attributed to mechanical and chemical stability of the covalently bonded active surface groups on the grafted polymer networks. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46042.