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Diamond field-effect transistor (FET) has great application potential for high frequency and high power electronic devices. In this work, diamond FETs were fabricated on (0 0 1) single crystal diamond with homoepitaxial layer. The nitrogen impurity content in the homoepitaxial layer is greatly decreased as measured by the Raman and photoluminescence spectra. The diamond field effect transistor with 100 nm Al2O3 as gate dielectric shows ohomic contact resistance of 35 Ω . mm, maximum drain saturation current density of 500 mA/mm, and maximum transconductance of 20.1 mS/mm. Due to the high quality of Al2O3 gate dielectric and single crystal diamond substrate, the drain work voltage of −58 V is achieved for the diamond FETs. A continuous wave output power density of 4.2 W/mm at 2 GHz is obtained. The output power densities at 4 and 10 GHz are also improved and achieve 3.1 and 1.7 W/mm, respectively. This work shows the application potential of single crystal diamond for high frequency and high power electronic devices.

The objective of this study was to identify the effects of 100 μM melatonin (MT), 1 μL/L 1-methylcyclopropene (1-MCP), and their combination treatments on the postharvest characteristics, nutritional quality, and antioxidant capacity of ‘Youhou’ persimmons during cold storage at 0°C. Compared with the control fruit, all three treatments suppressed ethylene production and respiration rate, leading to delayed softening, reduced peel discoloration, and soluble solid content loss. These treatments increased plasma membrane stability by inhibiting lipoxygenase activity and decreasing H2O2, electrolyte leakage, and malondialdehyde concentrations, resulting in higher tolerance to chilling injury (CI). At the end of storage, the CI index of fruit treated with MT, 1-MCP, and MT+1-MCP respectively exhibited 54.67%, 14.57%, and 5.54%, which were significantly lower than the control ones (78.36%). In addition, the phenolics, flavonoids, and ascorbic acid contents were also improved by the above treatments, which contributed to higher antioxidant activity than the control fruit at the late stage of storage. The combination of MT and 1-MCP treatment was more effective in improving the postharvest quality and preserving high antioxidant ability levels than either treatment alone, indicating a promising measure to preserve sweet persimmons up to 70 d.

β -Ga _2 O _3 Schottky barrier diodes (SBDs) with low-defect epitaxial surface and effective termination are essential for realizing excellent blocking characteristics. This work systematically studied oxygen annealing at various temperatures, optimizing the epitaxial surface by reducing the surface roughness and dislocation density. Combined with mesa termination, the results showed that the breakdown voltage ( V _br ) significantly increased from 845 V to 1532 V. The device with a 3 × 3 mm ^2 anode size was fabricated simultaneously, and the high forward currents of 8.7 A@2 V and V _br > 700 V were achieved. This work shows a possible solution for the commercialization of β -Ga _2 O _3 SBDs.

Downy mildew is a serious disease in cucumber production worldwide, which is caused by Pseudoperonospora cubensis (Berk. & Curt.) Rostov. Underlying the mechanism of cucumber response to downy mildew infection is important for breeding improvement and production; however, the research remains largely elusive. A comparative proteomic approach was used to reveal the differential accumulation of the proteomes from leaves of cucumber (susceptible line and resistant line) that were inoculated with P. cubensis or not by two-dimensional electrophoresis and MALDI-TOF/TOF MS. A total of 76 protein spots were successfully identified with significant changes in abundance (> 2-fold, P < 0.05) in downy mildew infected or not leaves for the susceptible line and resistant line. By the functional annotation, these proteins were classified into 8 groups including photosynthesis (29%), energy and metabolism (29%), cell rescue and defense (17%), and protein biosynthesis, folding and degradation (13%), unclassified (7%), nucleotide metabolism (3%), signal transduction (1%) and cellular process (1%). Among the 17 differentially expressed proteins between the resistant and susceptible cucumber line, most of the protein spots were concentrated in cell rescue and defense (4) and energy and metabolism (4). Moreover, a schematic diagram containing majority of the metabolic pathways of cucumber leaves in response to downy mildew was proposed. This network revealed the positive effect of several functional components in cucumber seedlings' resistant to downy mildew such as accumulation of energy supply and resistance-related proteins, hastened protein metabolism and photorespiratory, inhibited photosynthesis, and triggered photosystem repair and programmed cell death. Taken together, these results have advanced a further understanding of the key metabolic pathways of cucumber resistance to downy mildew and pathogen control in the proteomic level.

In this work, vertical NiO/Ga2O3 heterojunction diodes (HJDs) integrated with SiNx/Al2O3 double-layered insulating field plate (FP) structures have been demonstrated. With the additional post-annealing, the resultant diode exhibits a decreased differential specific on-resistance ( $\text{R}_{\mathrm{ on,sp}}$ ) of 5.4 $\text{m}\boldsymbol{\Omega } \cdot $ cm2 and an enhanced breakdown voltage (BV) of 1036 V. The improved performance is attributed by the combination of the FP-suppressed crowding electric field at the device edge and the reduced trap density at the NiO/Ga2O3 interface. In particular, the near-unity ideality factor has been achieved for this p-n HJD at an elevated temperature of 275 °C, indicating that the diffusion current is dominated. The high-temperature operation capability is owing to the quality improvement of NiO/Ga2O3 interface, where the Shockley-Read-Hall (SRH) recombination mediated by deep-level defects within the depletion region is thus suppressed.

Abstract Self-driven photodetectors that can detect light without any external voltage bias are important for low-power applications, including future internet of things, wearable electronics, and flexible electronics. While two-dimensional (2D) materials exhibit good optoelectronic properties, the extraordinary properties have not been fully exploited to realize high-performance self-driven photodetectors. In this paper, a metal–semiconductor–metal (MSM) photodetector with graphene and Au as the two contacts have been proposed to realize the self-driven photodetector. Van der Waals contacts are formed by dry-transfer methods, which is important in constructing the asymmetrical MSM photodetector to avoid the Fermi-level pinning effect. By choosing graphene and Au as the two contact electrodes, a pronounced photovoltaic effect is obtained. Without any external bias, the self-driven photodetector exhibits a high responsivity of 7.55 A W−1 and an ultrahigh photocurrent-to-dark current ratio of ~108. The photodetector also shows gate-tunable characteristics due to the field-induced Fermi-level shift in the constituent 2D materials. What is more, the high linearity of the photodetector over almost 60 dB suggests the easy integration with processing circuits for practical applications.

The traditional Born iterative method (BIM) and distorted Born iterative method (DBIM) are both effective for electromagnetic scattering inversion. But they are inefficient because of the computation of forward scattering problem in each iteration. In this paper, a modified forward-solver scheme based on Born series is proposed for improving the efficiency. By using this scheme, the traditional time-consuming forward scattering procedure, matrix inversion, is replaced by a simple multiplication with low computation complexity in each iteration. Numerical and experimental two-dimensional electromagnetic scattering models are used to validate the proposed method. The imaging results and CPU times indicate that the presented methods have good accuracy and can improve the efficiency greatly.

Abstract In this work, parametric investigations on structural optimization are systematically made for 4H-SiC-based separated absorption charge and multiplication (SACM) avalanche ultraviolet photodiode (UV APD). According to our results, the breakdown voltage can be strongly affected by the thickness for the multiplication layer and the doping concentration for the charge control layer. The thickness for the n-type ohmic contact layer, the absorption layer, and the charge control layer can remarkably affect the light penetration depth, which correspondingly influences the number of photo-generated electron-hole pairs, and therefore the aforementioned layer thickness has a strong impact on the responsivity for SACM APD. For enhancing the responsivity of the APD, we require a reduced energy band barrier height at the interface of the optical absorption layer and the charge control layer, so that the promoted carrier transport into the multiplication layer can be favored. In addition, we investigate positive beveled mesas with smaller angles so as to reduce the electric field at the mesa edge. Thus, the dark current is correspondingly suppressed.

Background: This study aimed to investigate the biomechanical behaviors of polyether ether ketone (PEEK) and traditional materials (titanium and fiber) when used to restore tooth defects in the form of prefabricated post or customized post via computational modelling. Methods: First, the prototype of natural tooth, and the prototypes of prefabricated post and customized post were established, respectively, whilst the residual root was restored with dentin ferrule using reverse engineering methods. Then, the stress and strain of CFR-PEEK (PEEK reinforced by 30% carbon fiber) and pure PEEK (PEEK without any reprocessing) post were compared with those made in traditional materials using the three-dimensional finite element method. Results: From the stress point of view, compared with metal and fiber posts, CFR-PEEK and pure PEEK prefabricated post both demonstrated reduced post-core interface stress, post stress, post-root cement stress and root cement stress; moreover, CFR-PEEK and pure PEEK customized post demonstrated reduced post stress, post-root cement stress and root cement stress, while the strain of CFR-PEEK post was the closest to that of dentin. Conclusions: Compared with the traditional posts, both the CFR-PEEK and pure PEEK posts could reduce the risk of debonding and vertical root fracture, whether they were used as prefabricated posts or customized posts, but the biomechanical behavior of carbon fiber-reinforced CFR-PEEK restorations was the closest to dentin, no matter if they were used as prefabricated post or customized post. Therefore, the CFR-PEEK post could be more suitable to restore massive tooth defects. Pure PEEK needs filler reinforcement to be used for post-retained restoration.

Abstract Background Radiation exposure negatively affects the regenerative ability and makes reconstruction of bone defects after tumor section difficult. miR-34a is involved in radiation biology and bone metabolism. The aim of this study was to investigate whether miR-34a could contribute to bone regeneration in irradiated bone defects. Methods The expression of miR-34a was analyzed during the osteoblastic differentiation of irradiated BMSCs and bone formation in irradiated bone defects. miR-34a mimics and miR-34a inhibitor were used to upregulate or suppress the expression of miR-34a in BMSCs irradiated with 2 or 4 Gy X-ray radiation. In vitro osteogenesis and subcutaneous osteogenesis were used to assess the effects of miR-34a on the osteogenic ability of radiation-impaired BMSCs. Collagen-based hydrogel containing agomiR-34a or antagomiR-34a were placed into the 3-mm defects of irradiated rat tibias to test the effect of miR-34a on bone defect healing after irradiation. Results miR-34a was upregulated in the process of bone formation after irradiation. Transfecting radiation-impaired BMSCs with miR-34a mimics enhanced their osteoblastic differentiation in vitro by targeting NOTCH1. Overexpression of miR-34a enhanced the ectopic bone formation of irradiated BMSCs. In situ delivery of miR-34a promoted bone regeneration in irradiated bone defects. Conclusions miR-34a promoted the osteoblastic differentiation of BMSCs and enhanced the ectopic bone formation after irradiation. miR-34a promoted bone defect healing in irradiated rat tibias. miR-34a-targeted therapy might be a promising strategy for promoting the reconstruction of bone defects after radiotherapy.

Diamonds are thought to be excellent candidates of next-generation semiconductor materials for high power and high frequency devices. A two-dimensional hole gas in a hydrogen-terminated diamond shows promising properties for microwave power devices. However, high sheet resistance and low carrier mobility are still limiting factors for the performance improvement of hydrogen-terminated diamond field effect transistors. In this work, the carrier scattering mechanisms of a two-dimensional hole gas in a hydrogen-terminated diamond are studied. Surface roughness scattering and ionic impurity scattering are found to be the dominant scattering sources. Impurity scattering enhancement was found for the samples after a high-temperature Al2O3 deposition process. This work gives some insight into the carrier transport of hydrogen-terminated diamonds and should be helpful for the development of diamond field effect transistors.

Mycobacterium tuberculosis (MTB) and non-tuberculous mycobacteria (NTM) are formidable causes of lung diseases throughout the world. While MTB is considered to be more virulent than NTM, host factors also play a key role in disease development. To elucidate whether there are differential immune responses to various mycobacteria, THP-1 macrophages were temporally infected with MTB H37Rv or with four different NTM species. We found that cells infected with MTB had greater bacterial burden and p65 nuclear factor-kappa B (NF-κB) activation than cells infected with NTM. There was also differential expression of mRNA for interleukin-1-β (IL-1β), IL-8, IL-10, and tumor necrosis factor-alpha (TNF-α) with no distinct pattern of mRNA expression among the different mycobacteria. In contrast, at the protein level, some generalizations can be made of the cytokines and chemokines expressed. Compared to uninfected cells, the rapid-growing Mycobacterium smegmatis but not Mycobacterium abscessus induced significantly greater pro-inflammatory cytokines and IL-10, whereas both NTM individually induced greater levels of chemokines. Compared to uninfected control cells, the two slow-growing NTM and MTB differentially induced cytokine expression with Mycobacterium avium inducing more pro-inflammatory cytokines and IL-10, whereas M. avium, Mycobacterium intracellulare, and MTB inducing greater but similar levels of chemokines. MTB-infected THP-1 cells also demonstrated lower level of phagosome–lysosome fusion and apoptosis than NTM-infected cells while there were differences in these macrophage functions among the NTM species. Interestingly, M. intracellulare, M. avium, and MTB have similar levels of autophagosome formation, but the levels displayed by all three were lower than for M. smegmatis and M. abscessus. This study demonstrates the differences in bacterial burden and macrophage effector functions among several clinically relevant mycobacterial species. Such disparities may, in part, account for differences in clinical outcomes among patients infected with various species of NTM as has been seen for different strains of MTB.

Abstract Background The reconstruction of bone defects is often impaired by radiotherapy since bone quality is compromised by radiation. This study aims to investigate the therapeutic efficacy of the composite cell sheets-bone marrow mesenchymal stem cell (BMSC) sheets cocultured with endothelial progenitor cells (EPCs)-in the healing of irradiated bone defects and the biological effects of EPCs on the osteogenic properties of BMSC sheets. Methods BMSCs and EPCs were isolated from rat bone marrow. BMSCs were used to form cell sheets by the vitamin C inducing method. EPCs were seeded on BMSC sheets to make EPCs–BMSC sheets. Osteogenesis of EPCs–BMSC sheets and BMSC sheets were tested. In vitro osteogenesis tests included ALP, Alizarin Red S, Sirius Red staining, qRT-PCR and Western blot analysis after 3 and 7 days of osteogenic incubation. Subcutaneous osteogenesis was tested by H&E staining and immunohistochemical staining 8 weeks after transplantation. EPCs–BMSC sheets and BMSC sheets were used in the 3 mm defects of non-irradiated and irradiated rat tibias. Micro-CT and histological analysis were used to test the healing of bone defects 4 and 8 weeks after transplantation. Results EPCs–BMSC sheets showed enhanced osteogenic differentiation in vitro with increased expression of osteoblastic markers and osteogenesis related staining compared with BMSC sheets. In subcutaneous osteogenesis test, EPCs–BMSC sheets formed larger areas of new bone and blood vessels. The EPCs–BMSC group had the highest volume of newly formed bone in the defect area of irradiated tibias. Conclusions EPCs improved the osteogenic differentiation of BMSC Sheets and enhanced the ectopic bone formation. EPCs–BMSC sheets promoted bone healing in irradiated rat tibias. EPCs–BMSC sheets are potentially useful in the reconstruction of bone defect after radiotherapy.

In this paper, we report on a novel E-mode AlGaN/GaN gates-seperating groove heterostructure field-effect transistor (GSG HFET). The current turn-on/off is controlled by changing gate voltage to regulate the horizontal energy band between the double gates. A threshold voltage of 0.23 V and a high drain current density of 851 mA/mm are obtained in GSG HFET. Compared with the proposed depletion-mode device, the maximum drain current of the GSG HFET deceases slightly (about 7%). It is noteworthy that the threshold voltage is less sensitive to the etching time. The devices show high-uniformity threshold voltage of 0.23 V within wide etching time range from 5 to 9 min.

Abstract Irradiated bone has a greater risk of implant failure than nonirradiated bone. The purpose of this study was to investigate the influence of cell sheets composed of co-cultured bone marrow mesenchymal stromal cells (BMSCs) and endothelial progenitor cells (EPCs) on implant osseointegration in irradiated bone. Cell sheets (EPCs, BMSCs or co-cultured EPCs and BMSCs) were wrapped around titanium implants to make cell sheet-implant complexes. The co-cultured group showed the highest osteogenic differentiation potential in vitro, as indicated by the extracellular matrix mineralization and the expression of osteogenesis related genes at both mRNA and protein levels. The co-cultured cells promoted ectopic bone formation as indicated by micro-computed tomography (Micro-CT) and histological analysis. In the irradiated tibias of rats, implants of the co-cultured group showed enhanced osseointegration by Micro-CT evaluation and histological observation. Co-cultured EPCs and BMSCs also up-regulated the expression of osteogenesis related genes in bone fragments in close contact with implants. In conclusion, cell sheets of co-cultured EPCs and BMSCs could promote osseous healing around implants and are potentially useful to improve osseointegration process for patients after radiotherapy.

Rationale: The association between non-tuberculous mycobacterial lung disease and alpha-1-antitrypsin (AAT) deficiency is likely due, in part, to underlying emphysema or bronchiectasis. But there is increasing evidence that AAT itself enhances host immunity against microbial pathogens and thus deficiency could compromise host protection.Objectives: The goal of this project is to determine if AAT could augment macrophage activity against non-tuberculous mycobacteria.Methods: We compared the ability of monocyte-derived macrophages cultured in autologous plasma that were obtained immediately before and soon after AAT infusion—given to individuals with AAT deficiency—to control an ex vivo Mycobacterium intracellulare infection.Measurements and Main Results: We found that compared to pre-AAT infused monocyte-derived macrophages plus plasma, macrophages, and contemporaneous plasma obtained after a session of AAT infusion were significantly better able to control M. intracellulare infection; the reduced bacterial burden was linked with greater phagosome-lysosome fusion and increased autophagosome formation/maturation, the latter due to AAT inhibition of both M. intracellulare–induced nuclear factor-kappa B activation and A20 expression. While there was a modest increase in apoptosis in the M. intracellulare-infected post-AAT infused macrophages and plasma, inhibiting caspase-3 in THP-1 cells, monocyte-derived macrophages, and alveolar macrophages unexpectedly reduced the M. intracellulare burden, indicating that apoptosis impairs macrophage control of M. intracellulare and that the host protective effects of AAT occurred despite inducing apoptosis.Conclusion: AAT augments macrophage control of M. intracellulare infection through enhancing phagosome-lysosome fusion and autophagy.

We aimed to investigate the efficacy of four severity-of-disease scoring systems in predicting the 28-day survival rate among patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD) requiring emergency care. Clinical data of patients with AECOPD who required emergency care were recorded over 2 years. APACHE II, SAPS II, SOFA, and MEDS scores were calculated from severity-of-disease indicators recorded at admission and compared between patients who died within 28 days of admission (death group; 46 patients) and those who did not (survival group; 336 patients). Compared to the survival group, the death group had a significantly higher GCS score, frequency of comorbidities including hypertension and heart failure, and age (P

Polyether-ether-ketone (peek) is one of the most common materials used for load-bearing orthopedic devices owing to its radiolucency and favorable mechanical properties. However, current smooth-surfaced peek implants can lead to fibrous capsule formation. To overcome this issue, here, peek specimens with well-defined internal cross-linked structures (macropore diameters of 1.0−2.0 mm) were fabricated using a three-dimensional (3D) printer, and an acid-etched microporous surface was achieved using injection-molding technology. The cell adhesion properties of smooth and microporous peek specimens was compared in vitro through a scanning electron microscope (SEM), and the soft tissue responses to the both microporous and cross-linked structure of different groups were determined in vivo using a New Zealand white rabbit model, and examined through histologic staining and separating test. The results showed that the acid-etched microporous surface promoted human skin fibroblasts (HSF) adherence, while internal cross-linked structure improved the ability of the peek specimen to form a mechanical combination with soft tissue, especially with the 1.5 mm porous specimen. The peek specimens with both the internal cross-linked structure and external acid-etched microporous surface could effectively promote the close integration of soft tissue and prevent formation of fibrous capsules, demonstrating the potential for clinical application in surgical repair.

This paper reports on the design, fabrication and preliminary test results of a novel microelectromechanical systems (MEMS) device—the acoustic gyroscope. The unique operating mechanism is based on the “acoustic version” of the Sagnac effect in fiber-optic gyros. The device measures the phase difference between two sound waves traveling in opposite directions, and correlates the signal to the angular velocity of the hosting frame. As sound travels significantly slower than light and develops a larger phase change within the same path length, the acoustic gyro can potentially outperform fiber-optic gyros in sensitivity and form factor. It also promises superior stability compared to vibratory MEMS gyros as the design contains no moving parts and is largely insensitive to mechanical stress or temperature. We have carried out systematic simulations and experiments, and developed a series of processes and design rules to implement the device.

Using the Quasi-Two-Dimensional (quasi-2D) model, the current-voltage (I-V) characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with different gate length were simulated based on the measured capacitance-voltage (C-V) characteristics and I-V characteristics. By analyzing the simulation results, we found that the different polarization charge distribution generated by the different channel electric field distribution can result in different polarization Coulomb field scattering, and the difference of the electron mobility mostly caused by the polarization Coulomb field scattering can reach up to 1829.9 cm2/V·s for the prepared AlGaN/AlN/GaN HFET. In addition, it was also found that when the two-dimension electron gas (2DEG) sheet density is modulated by the drain-source bias, the electron mobility appears peak with the variation of the 2DEG sheet density, and the ratio of gate length to drain-source distance is smaller, the 2DEG sheet density corresponding to the peak point is higher.

A new circularly polarized (CP) array using the filtering phase shifting theory is designed. First, a phase-designable filter is designed by adjusting the position of the transmission zero (TZ) of the doublet topology filter. Next, a phase-designable 3rd-order filtering antenna element can be obtained by using a stub-loaded resonator (SLR) as the physical structure of the doublet topology, and the patch is treated as the last resonating mode. Then, two 3rd-order filtering antenna elements with 90° phase difference are designed. Finally, by using the slot-coupled feed structure, four elements with phases of 0°, 90°, 180°, 270° are rotated sequentially to form a circularly polarized array. The measured results show that the impedance bandwidth is 8.1% (5.07-5.5 GHz); the axial ratio (AR) bandwidth is 6.7% (5.05-5.4 GHz); the maximum CP realized gain is 10.5 dBic; and the good filtering function is implanted. [ABSTRACT FROM AUTHOR]

The AlGaN/GaN heterostructure field-effect transistor (HFET) with 100 nm gate length was fabricated. An improved method is proposed to determine the value of the source access resistance corresponding to each direct current quiescent points in the saturation region of the current-voltage characteristics. The increase in the source access resistance with drain-source current has been studied, taking into account several main scattering mechanisms, including polarization Coulomb field (PCF) scattering, polar-optical-phonon scattering, piezoelectric scattering, and interface roughness scattering. It is found that PCF scattering plays a very important role in the source access resistance of AlGaN/GaN HFETs. The PCF scattering component of source access resistance decreases with the increase in drain-source current. [ABSTRACT FROM AUTHOR]

The electron mobility scattering mechanisms in AlN/GaN heterostuctures with 3 nm and 6 nm AlN barrier thicknesses were investigated by temperature-dependent Hall measurements. The effect of interface roughness (IFR) scattering on the electron mobility was found to be enhanced by increasing AlN barrier thickness. Moreover, using the measured capacitance-voltage and current-voltage characteristics of the fabricated heterostructure field-effect transistors (HFETs) with different Schottky areas on the two heterostuctures, the variations of electron mobility with different gate biases were investigated. Due to enhanced IFR scattering, the influence of polarization Coulomb field (PCF) scattering on electron mobility was found to decrease with increasing AlN barrier layer thickness. However, the PCF scattering remained an important scattering mechanism in the AlN/GaN HFETs. [ABSTRACT FROM AUTHOR]

A gate length of 0.2 μm InAlN/GaN high electron mobility transistor on SiC substrate is obtained with a maximum current gain cutoff frequency (fT) of 65.8GHz and a maximum power gain cutoff frequency (fmax) of 143.6GHz. Lombardi model, which takes interface roughness scattering into consideration, has been introduced to model the transconductance (gm) degradation. The simulated gm and fT with Lombardi model are 69% and 58% lower than the ones without considering interface roughness scattering, respectively. Further analysis show experimental gm, gate capacitance (Cg), and fT are consistent with results based on Lombardi model. [ABSTRACT FROM AUTHOR]

A reduced surface field (RESURF) AlGaN/GaN high-electron-mobility transistor (HEMT) with graded doping buffer (GDB) and slant back electrode (SBE) is proposed. In the GDB, the p-dopant density increases linearly both from top to bottom and right to left. The concentrated negative space charges in the lower-left corner of GDB attract the electric field lines from the channel and barrier towards the gate under OFF-state, which flats the electric field and enhances the breakdown voltage (Vbr). Additionally, the low p-dopant density near the top of GDB achieves the device with low ON-state resistance (RON). The SBE flats the electric field along the channel above it and introduces a peak electric field near its edge. Simulation results show a Vbr of 2150 V and RON of 7.05 Ωmm for the proposed device, compared with 1701 V and 7.73 Omm for the conventional back electrode RESURF HEMT (BE-RESURF HEMT) with the same gate -drain spacing. Moreover, due to the reduced depletion of 2DEG from the GDB, the proposed device shows slight increases in fT and fmax (8.76 and 14.80 GHz), comparing with the conventional BE-RESURF HEMT (8.24 and 13.84 GHz). [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) measurements are performed on the single CH(sub 3)(super +) ion-beam deposited films, violet/blue emission was observed and the ion bombardment effect on the PL behavior is investigated. Increasing substrate temperature or lowering ion energy leads to strengthening of the red part of the PL spectrum, due to the healing of ion-bombardment-induced effects in the film.

An extensive investigation of fabricated AlGaN/GaN fin-shaped metal-insulator-semiconductor high-electron-mobility transistors (Fin-MISHEMTs) with Al2O3 dielectric is presented in this paper. Based on the pulsed I-V measurements and numerical simulation, the dynamic characteristics of GaN-based Fin-MISHEMTs were carried out under various quiescent bias conditions and temperatures. Moreover, the physical mechanisms of current collapse and dynamic on-resistance increase induced by trapping effects were analyzed. The results show that the observed nonmonotonic variation of current collapse with the gate quiescent bias voltage is resulted from the combination of gate leakage injection-related and hot-electron injection-related trapping effects. Compared with the conventional planar MISHEMTs, the current collapse of AlGaN/GaN Fin-MISHEMTs is smaller due to lower gate leakage and smaller threshold voltage shift, which is benefited from its enhanced gate controllability. The current collapse and dynamic on-resistance increase of Fin-MISHEMTs can be further suppressed by optimizing the device structure, such as designing the fin channels only under the gate. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) semiconducting materials have recently attracted wide attention and been regarded as promising building blocks for chemical sensors due to their high surface-to-volume ratio. However, their low response hinders the realization of high-performance 2D TMDCs chemical sensors. Here, we demonstrate the improvement of sensing performance of molybdenum ditelluride (MoTe2) gas sensor through continuous light illumination. The dependence of sensing performance on the energy of photons and light intensity is systematically studied. The response to NH3 is dramatically enhanced by more than 25 times under 254 nm ultraviolet (UV) light illumination with intensity of 2.5 mW/cm². Moreover, a remarkable low detection limit of 3 ppb is achieved, which is improved by 80 times compared with that in dark condition. The results demonstrate that light illumination is a promising method to improve the sensitivity of 2D TMDCs chemical sensors. [ABSTRACT FROM AUTHOR]

This paper reports on the design, fabrication and preliminary test results of a novel microelectromechanical systems (MEMS) device--the acoustic gyroscope. The unique operating mechanism is based on the "acoustic version" of the Sagnac effect in fiber-optic gyros. The device measures the phase difference between two sound waves traveling in opposite directions, and correlates the signal to the angular velocity of the hosting frame. As sound travels significantly slower than light and develops a larger phase change within the same path length, the acoustic gyro can potentially outperform fiber-optic gyros in sensitivity and form factor. It also promises superior stability compared to vibratory MEMS gyros as the design contains no moving parts and is largely insensitive to mechanical stress or temperature. We have carried out systematic simulations and experiments, and developed a series of processes and design rules to implement the device. [ABSTRACT FROM AUTHOR]

A graphene/LiNbO3 hybrid device is used to investigate the acoustic induced charge transport in chemical doped graphene. The chemical doping of graphene via its physisorption of gas molecules affects the surface acoustic wave (SAW) charge carrier transport in a manner different from electric field drift. That transport induces doping dependent macroscopic acoustoelectric current. The chemical doping can manipulate majority carriers and induces unique acoustoelectric features. The observation is explained by a classical relaxation model. Eventually the device based on acoustoelectric current is proved to outperform the common chemiresistor for chemicals. Our finding provides insight into acoustic charge carrier transport during chemical doping. The doping affects interaction of carriers with SAW phonon and facilitates the understanding of nanoscale acoustoelectric effect. The exploration inspires potential acoustoelectric application for chemical detection involving emerging 2D nanomaterials. [ABSTRACT FROM AUTHOR]

We report on the excitation of acousto-eletric (AE) charge transport in monolayer graphene by acoustic transducers based on aluminum nitride thin films. The acoustic waves induced macroscopic current flow that linearly scaled with input power. The AE current exhibited unique frequency dependence due to special configuration and piezoelectric properties of the transducer, which led to transitions between traveling and standing acoustic waves across a characteristic frequency. A Finite Element model was built to investigate and understand the phenomena and the underlying mechanisms. [ABSTRACT FROM AUTHOR]

The fabrication processes of heterostructure field-effect transistors (HFETs) often introduce stresses into the device structures. These stresses can significantly affect the electrical characteristics of the device. We investigated the additional strain induced by the gate metals (in this study, Au, Cu, Fe, Al, and Ni) in AlGaN/AlN/GaN HFETs using the measured capacitance-voltage and current-voltage characteristics. We found that the intensity of the additional strain of the AlGaN barrier layer is greatly affected by the types of gate metals. For those metals that mainly undergo a physical interaction with the AlGaN barrier layer, there is a negative correlation between the intensity of the additional strain and the Young's modulus of the gate metal. Therefore, the gate metal with a larger Young's modulus will be more favorable for weakening polarization Coulomb field scattering and increasing both the carrier mobility and the sheet carrier density in AlGaN/AlN/GaN HFETs. [ABSTRACT FROM AUTHOR]

We have investigated the variation of electron velocity in AlGaN/GaN heterostructures depending on illuminating light intensity and wavelength. It is shown that the electron velocity at high electric field increases under above-band light illumination. This electron velocity enhancement is found to be related to the photo-generated cold holes which interact with hot electrons and thus accelerate the energy relaxation at high electric field. The results suggest an alternative way to improve the electron energy relaxation rate and hence the electron velocity in GaN based heterostructures. [ABSTRACT FROM AUTHOR]

We investigate the temperature dependent electrical transport properties of quasi-free standing bilayer graphene on 4H-SiC (0001) substrate. Three groups of monolayer epitaxial graphene and corresponding quasi-free standing bilayer graphene with different crystal quality and layer number homogeneity are prepared. Raman spectroscopy and atomic-force microscopy are used to obtain their morphologies and layer number, and verify the complete translation of buffer layer into graphene. The highest room temperature mobility reaches 3700 cm²/V-s for the quasi-free standing graphene. The scattering mechanism analysis shows that poor crystal quality and layer number inhomogeneity introduce stronger interacting of SiC substrate to the graphene layer and more impurities, which limit the carrier mobility of the quasi-free standing bilayer graphene samples. [ABSTRACT FROM AUTHOR]

The impact of bulk traps in GaN buffer on the transient characteristics of AlGaN/GaN HEMTs is studied based on two-dimensional (2-D) numerical simulations. Starting from the calibration of simulation model compared with the experimentally measured data, we carried out both the pulse-on and pulse-off gate-lag transient simulations. The simulation reproduced the experimental result, suggesting that the rising trend of the turn-on pulsed gate-lag transient current in the experiment can be explained with bulk traps. It is proved that the bulk acceptor trap in GaN buffer can play an important role in the gate-lag transient response of GaN-based HEMTs besides the surface and interface traps. Bulk traps which cannot be eliminated by passivation should be taken into account for modeling. The mechanism of bulk trapping effect in buffer is analyzed in this paper, which may benefit the future work for design and model development of these devices. Furthermore, the influence of trap filling time on the drain current collapse is investigated. [ABSTRACT FROM AUTHOR]

In this study, we investigated the electrical properties of the AlGaN/AlN/GaN heterostructure fieldeffect transistors (HFETs) with Ti/Al/Ni/Au gate electrodes using the measured capacitancevoltage, current-voltage characteristics, and micro-Raman spectroscopy. We found that the uneven distribution of the strain caused by the Schottky metals was a major factor that generates the polarization Coulomb field scattering in AlGaN/AlN/GaN HFETs, and after appropriate rapid thermal annealing (RTA) processes, the polarization Coulomb field scattering was greatly weakened and the two-dimensional electron gas electron mobility was improved. We also found that the Schottky barrier height and the DC characteristics of the devices became better after appropriate RTA. Of course, the electrical performances mentioned above became deteriorated after excessive annealing. [ABSTRACT FROM AUTHOR]

Abstract: With a large number of applications of large steel plate, in order to ensure the engineering and product quality, it is necessary to test the quality of large plate. In the domestic, large steel is detected mainly by hand, there are some defects such as low efficiency, large strength, easy to misjudge and leakage judgment. This paper presents an ultrasonic automatic detection system design of large steel plate, multi-channel tests steel plate, stepper motor controls motion, Ethernet transmits data; Designing the system circuit, giving probe scanning method, defects determination method and selection and arrangement of probes. The system has high detection efficiency and high precision, simple mechanical structure, small size, low cost, and has an important application. [Copyright &y& Elsevier]

Presents a study which dealt with determination of preventive and corrective control strategies to contain voltage collapse in stressed power systems. Introduction of the system modeling; Framework for preventive and corrective control; Formulation for preventive control; Numerical results.