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The ever‐increasing power density and operation frequency in electrical power conversion systems require the development of power devices that can outperform conventional Si‐based devices. Gallium nitride (GaN) has been regarded as the candidate for next‐generation power devices to improve the conversion efficiency in high‐power electric systems. GaN‐based high electron mobility transistors (HEMTs) with normally‐off operation is an important device structure for different application scenarios. In this review, an overview of a series of effective approaches to improve the performance of GaN‐based power HEMT devices is given. Modified epistructures are presented to suppress defects and current leakage, and low‐damage recess‐free processes are discussed in fabricating normally‐off HEMTs. Possible effects of dielectrics on a metal–insulator–semiconductor (MIS) structure are also intensively introduced. Metal/semiconductor contact engineering is investigated, and fabrication of Au‐free ohmic contact and graphene insertion layer to enhance the device performance is emphasized. Finally, the effects of field plates are studied through the use of simulated and fabricated devices.

Intrinsically stretchable organic photovoltaic (is-OPV) with high efficiency and transparency remains a grand challenge for wearable applications. Herein, we report a full-solution processed device framework for semi-transparent is-OPV. A ferroconcrete-liked...

The decomposition of pyrolytic boron nitride (p-BN) during milling is studied as a function of the milling time. It has been found that the p-BN compound can be partially decomposed by milling until an amorphous p-BN phase is formed so that the content of nitrogen in the p-BN system will not continue to be changed by the milling process. Furthermore, the structure and magnetic properties of Nd2Fe14BNx-based alloys prepared by mechanical alloying using either p-BN or milled p-BN as starting material have been investigated. The Nd2Fe14BNx phase with x up to 0.25 coexists with some amounts of NdN, the Nd-rich phase and -Fe. A pre-milling process of p-BN favours the formation of the Nd2Fe14BNx phase. The magnetic properties of Nd16Fe76B8Nx alloys prepared by using milled p-BN are better than those made of non-milled p-BN. The Curie temperature of the Nd2Fe14BN0.25 phase is 335 °C, which is slightly higher than that of the Nd2Fe14B compound. A coercivity higher than 20 kOe is achieved for Nd2Fe14BNx-based alloys by adding excess Nd, which is close to the value of Nd16Fe76B8 prepared by using pure B.

Ultrasound and electromyography (EMG) are two of the most commonly used diagnostic tools for the assessment of muscles. Recently, many studies reported the simultaneous collection of EMG signals and ultrasound images, which were normally amplified and digitized by different devices. However, there is lack of a systematic method to synchronize them and no study has reported the effects of ultrasound gel to the EMG signal collection during the simultaneous data collection. In this paper, we introduced a new method to synchronize ultrasound B-scan images, EMG signals, joint angles and other related signals (e.g. force and velocity signals) in real-time. The B-mode ultrasound images were simultaneously captured by the PC together with the surface EMG (SEMG) and the joint angle signal. The deformations of the forearm muscles induced by wrist motions were extracted from a sequence of ultrasound images, named as Sonomyography (SMG). Preliminary experiments demonstrated that the proposed method could reliably collect the synchronized ultrasound images, SEMG signals and joint angle signals in real-time. In addition, the effect of ultrasound gel on the SEMG signals when the EMG electrodes were close to the ultrasound probe was studied. It was found that the SEMG signals were not significantly affected by the amount of the ultrasound gel. The system is being used for the study of contractions of various muscles as well as the muscle fatigue.

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An internal quantum efficiency (IQE) as high as 39% was achieved with the nonpolar a-plane AlGaN-based multiple quantum wells (MQWs) grown on the r-plane sapphire substrate with metal organic chemical vapor deposition technology. Evident fourth order X-ray diffraction satellite peak and intense MQW-related exciton emission peak at a wavelength of 279.2 nm were observed, implying the successful growth of high quality nonpolar aplane AlGaN-based MQWs. It was found that the employment of the trimethyl-aluminum (TMAl) flow duty-ratio modulation method played a crucial role in the epitaxial growth of the nonpolar a-plane AlGaN MQWs with sharp heterointerfaces and high IQE. Moreover, the unambiguous absence of the blue-shift in the MQWs-related exciton emission peak was verified in spite of the increase in the excitation power during the measurement of the excitation power-modulated photoluminescence spectra, indicating a complete elimination of the quantum confined Stark effect in the nonpolar AlGaN-based MQWs.

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