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Highly reliable signal recording with low electrode-skin impedance makes the microneedle array electrode (MAE) a promising candidate for biosignal sensing. However, when used in long-term health monitoring for some incidental diseases, flexible microneedles with perfectly skin-tight fit substrates lead to sweat accumulation inside, which will not only affect the signal output but also trigger some skin allergic reactions. In this paper, a flexible MAE on a Miura-ori structured substrate is proposed and fabricated with two-directional in-plane bendability. The results from the comparison tests show enhanced performance in terms of (1) the device reliability by resisting peeling off of the metal layer from the substrate during the operation and (2) air ventilation, achieved from the air-circulating channels, to remove sweat. Bio-signal recordings of electrocardiography (ECG), as well as electromyography (EMG) of the biceps brachii, in both static and dynamic states, are successfully demonstrated with superior accuracy and long-term stability, demonstrating the great potential in health monitoring applications.

At present, uniform upscaling division methods are routinely used to upscale geologic model grids, resulting in overly fine grids in some areas of the model. To improve computational efficiency, we have examined the effect of model upscaling with different upscaling parameters with the goal of producing a nonuniform grid with uniform accuracy. We based our nonuniform upscaling grid method on geologic characteristics including reservoir thickness, physical properties, reservoir spacing, and water flooding. Most of the logging curves of thin reservoirs are finger-like, allowing us to define the grid size according to the reservoir thickness. We use two different strategies to discretize uniform and composite reservoirs and represent reservoir thickness that exhibit bell- and funnel-shaped logging curves. Although one grid point accurately represents a uniform reservoir, we find that composite reservoirs require four or five points to accurately represent the physical properties of a composite reservoir. For the thick reservoirs (>5 m) with box- or composite-type logging curves, the physical properties inside the reservoir do not change much; therefore, we use a grid point to represent the reservoir thickness information. Using these metrics, we constructed alternative “moderate” and “efficient” vertical grid upscaling strategies. Taking the 15 sedimentary units with a total thickness of 72 m as an example, the statistical results show that the computational efficiency using our data-adaptive grid can be increased more than five times compared to the traditional uniform fine-grid method while retaining the same accuracy.

The Mw 4.6 earthquake that occurred on 17 August 2015 northwest of Fort St. John, British Columbia, is considered the largest hydraulic-fracturing-induced event in Canada, based on its spatiotemporal relationship with respect to nearby injection operations. There is a ∼5 day delay of this Mw 4.6 mainshock from the onset of fluid injection at the closest well pad (W1). In contrast, other two nearby injection wells (W2 and W3) have almost instantaneous seismic responses. In this study, we first take a forward numerical approach to investigate the causative mechanisms for the Mw 4.6 event. Specifically, three finite-element 3D poroelastic models of various permeability structures and presence or absence of hydraulic conduits are constructed, to calculate the coupled evolution of elastic stress and pore pressure caused by multistage fluid injections. Our simulation results suggest that pore pressure increase associated with the migration of injected fluid is required to accumulate sufficient stress perturbations to trigger this Mw 4.6 earthquake. In contrast, the elastic stress perturbation caused by rock matrix deformation alone is not the main cause. Furthermore, injection and seismicity at W1 may have altered the local stress field and brought local faults closer to failure at sites W2 and W3. This process could probably shorten the seismic response time and, thus, explain the observed simultaneous appearance of injection and induced seismicity at W2 and W3.

The discovery of H3S and LaH10 is an important step towards the development of room temperature superconductors which fuels the enthusiasm for finding promising superconductors among hydrides at high pressure. In the present study, three new and stable stoichiometric MoH5, MoH6 and MoH11 compounds were found in the pressure range of 100–300 GPa. The highly hydrogen-rich phase of Cmmm-MoH11 has a layered structure that contains various forms of hydrogen: H, H2− and H3− units. It is a high-Tc material with an estimated Tc value in the range of 165–182 K at 250 GPa. The same structures are also found in NbH11, TaH11, and WH11, each material showing Tc ranging from 117 to 168 K. By combining the method of using two coupling constants λopt and λac, and two characteristic frequencies (optical and acoustic) with first-principle calculations, we found that the high values of Tc are mainly caused by the presence of high frequency optical modes, but the acoustic modes also play a noticeable role.

In this work, we report on the monolithic integrated photodetectors (PDs) in InGaN/GaN light-emitting diodes (LEDs) to monitor the fluctuation of LED intensity over time. The effect of PD position on the light-receiving performance is studied through ray-trace simulation. Three LED-PD devices with different PD positions are fabricated via standard microfabrication processes, and a series of experimental measurements are performed to examine their performances. The design of the PD located in the center of the LED exhibits a 58% increase in the detected photocurrent and has less influence on the emission profile of the LED, compared with the PD formed at the edge. The white light emission is demonstrated by encapsulating the LED-PD device with yellow phosphor and the on-chip PD shows highly similar sensing behaviors as the external Si-based photodiode. Compared with the traditional off-chip detection scheme, the optimal monolithic PD design can provide comparable sensing capabilities, higher compactness, insensitivity to ambient lighting, and less influence on the LED emission profile, making it highly suitable for real-time monitoring of LED intensity variations in various practical and scientific lighting applications.

A novel ohmic contact formation mechanism is revealed for the annealed Ta0.83 Al0.17/Au stacks on non-recessed i-AlGaN/GaN. It is demonstrated that the contact metal alloy mainly composed by Au penetrates the AlGaN layer without apparent Ta-related solid phase reactions, establishing a spike-free contact to the 2D electron gas. A low contact resistivity of $0.14\Omega ~\cdot $ mm (4.24E- $7~\Omega \cdot $ cm2) is then obtained after 900 °C/60s annealing.

This article reports on a design journey for Sc x Al1 – N -based dual-mode hybrid quasi-surface and bulk acoustic wave (quasi-SAW/BAW) resonators. Four types of acoustic excitation configurations are proposed in these designs based on Sc x Al1– x N/6H-SiC stack architectures. The influence of Sc x Al1– x N materials, film thickness, and device configurations on the performance is investigated. After design optimization, the final dual-mode hybrid quasi-SAW/BAW resonators comprise of top electrode, partially etched Sc x Al1– x N pillars, and bottom electrode, which are stacked on a 6H-SiC substrate. The coupled quasi-SAW and BAW excited in the hybrid resonators enhance the resonance for both quasi-Rayleigh and quasi-Sezawa modes which results in a high effective coupling coefficient ( K eff2) and phase velocity ( ${v}$ ). Simulation results show that the optimized hybrid quasi-SAW/BAW resonator based on Mo/Sc0.4 Al0.6N/Mo/6H-SiC configuration with SiO2 filling the grooves has a remarkable K eff2 value of 14.55% and a high ${v}$ above 7500 m/s, which make this kind of dual-mode hybrid quasi-SAW/BAW resonators have great potential in wideband and high-frequency applications.

On 17 August 2015, an Mw 4.6 earthquake occurred northwest of Fort St. John, British Columbia, possibly induced by hydraulic fracturing (HF). We use data from eight broadband seismometers located ∼50 km from the hypocenter to detect and estimate source parameters of more than 300 events proximal to the mainshock. Stress-drop values estimated using seismic moment and corner frequency from single-event spectra and spectral ratios range from ∼1 to 35 MPa, within the typical range of tectonic earthquakes. We observe an ∼5-day delay between the onset of fluid injection and the mainshock, a b-value of 0.78 for the sequence, and a maximum earthquake magnitude larger than the prediction based on the total injection volume, suggesting that the Mw 4.6 sequence occurred on a pre-existing fault and that the maximum magnitude is likely controlled by tectonic conditions. Results presented here show that pre-existing fault structures should be taken into consideration to better estimate seismic hazard associated with HF operations and to develop schemes for risk mitigation in close proximity to HF wells.

As an optical material, Y2O3 transparent ceramics are desirable for application as laser host materials. However, it is difficult to sinter and dense of Y2O3 hinders the preparation of high-quality optical ceramics via traditional processes. In this work, we use La2O3 as a sintering aid for fabricating high-transparency Y2O3 ceramics using a vacuum sintering process. It is demonstrated that the in-line optical transmittance of 15.0 at% La-doped Y2O3 at a wavelength of 1100 nm achieves a transmittance of 81.2%. A sintering kinetics analysis reveals that a grain-boundary-diffusion-controlled mechanism dominates the faster densification at high La3+ concentrations. It is also shown that both the mechanical and thermal properties of Y2O3 transparent ceramics are significantly improved upon the increase of La2O3 sintering additives. The results indicate that a La-doped Y2O3 transparent ceramic is a promising candidate for a laser host material.

Up-conversion (UC) luminescence properties of Nd:Y2O3transparent ceramics are investigated. It is shown that, under a laser excitation of 808 nm, the samples exhibit significant UC emission. With an increase in the Nd3+ concentration, the intensity of green emission decreases, while the intensity of red emission first increases and then decreases. In particular, both green and red UC emissions are found to be two-photon processes, but with different quantum transition mechanisms. In addition, the dependence of UC emission intensity on the pumping power is studied. Our studies indicate that Nd:Y2O3 transparent ceramics are promising candidates as short-wavelength UC laser material.

Harvesting the potential performance of GaN-based devices in terms of the areal power density and reliability, relies on the efficiency of their thermal management. Integration of extremely high thermal conductivity Single-crystalline CVD-diamond serves as an efficient solution to their strict thermal requirements. However, the major challenge lies in the Thermal Boundary Resistance (TBR) at the interface of GaN/Diamond or SiC/Diamond. Junction temperature of the device shows a sensitivity of 1.28°C for every unit of TBR for GaN-on-Diamond compared to 0.43°C for every 10 units of TBR for GaN/SiC-on-Diamond. Finite Volume Thermal Analysis has shown a limit of around 22 m2K/GW beyond which the merit of proximity to the heat-source for GaN-on-Diamond can no more outperform GaN/SiC-on-Diamond. Besides, due to the temperature dependency of the thermal conductivity K, an increase in the temperature causes an increase in the thermal resistivity of the device which is more significant in high power operations. Simplified assumption of constant K overestimates the device performance by resulting in 17.4°C lower junction temperature for the areal power density of 10W/mm. Other part of the project regarding the in-house growth of CVD-diamond to be bonded to the GaN device has been simultaneously in progress.

A robust process for Au-free ohmic contact formation is demonstrated by a direct contact of TixAly alloy film on non-recessed i-AlGaN/GaN. Using this novel TixAly alloy instead of multilayers as contact metals, an ultra-low contact resistivity of $ mm is achieved for Ti5Al1 alloy on i-AlGaN/GaN after 880 °C/60s annealing.

Recess processes for the fabrication of normally-off GaN HEMTs generally compromise devices’ on-state performance. In this work, recess-free quasi-normally-off GaN HEMTs with a threshold voltage of 0.24 V is realized by local control of two-dimensional electron gas (2DEG) density. The devices feature a $0.1~{\mu }\text{m}$ gate length, SiNx stress liner, and comb gate. SiNx liner can provide significant stress to AlGaN/GaN heterostructure in the scaled gate region. The additional stress translates to the additional electric field and depletes the 2DEG in the gate region. As a result, the quasi-normally-off operation is achieved. Furthermore, the comb gate structure is introduced to suppress the short channel effects, supported by TCAD simulation. The quasi-normally-off devices’ excellent on-state performances are benchmarked against the normally-off devices reported recently and a p-GaN HEMT purchased from a commercial foundry. The results support strain engineering as a promising technique to pursue the normally-off operation of GaN HEMTs.

This paper demonstrates a new fabrication process for gallium nitride high-electron mobility transistors (HEMTs) free of plasma damages in the sub-100 nm T-shape gate area. The common peeling-off problems of electron beam resists during gate metal deposition process were solved by introducing a fluorine plasma treatment process before gate metal deposition. By combining dry and wet etching processes appropriately, an on/off ratio of 107 at a drain-to-source voltage of 1 V was achieved. This work also investigated the short channel effect in devices with gate lengths from 70 to 440 nm. Reducing gate length results in decrease of threshold voltage due to the drain-induced barrier-lowering effect. Current gain cut-off frequency fT and maximum oscillation frequency fmax increase while gate length reduces till 250 nm. However, below 250 nm, fT and fmax no longer increase while gate length reduces till sub-100 nm, which reflect the short channel effect.

Hybrid heterojunctions based on two-dimensional (2D) and conventional three-dimensional (3D) materials provide a promising way toward nanoelectronic devices with engineered features. In this work, we investigated the band alignment of a mixed-dimensional heterojunction composed of transferred MoS2 on β-Ga2O3($$ 2- $$2-01) with and without nitridation. The conduction and valence band offsets for unnitrided 2D-MoS2/3D-β-Ga2O3 heterojunction were determined to be respectively 0.43 ± 0.1 and 2.87 ± 0.1 eV. For the nitrided heterojunction, the conduction and valence band offsets were deduced to 0.68 ± 0.1 and 2.62 ± 0.1 eV, respectively. The modified band alignment could result from the dipole formed by charge transfer across the heterojunction interface. The effect of nitridation on the band alignments between group III oxides and transition metal dichalcogenides will supply feasible technical routes for designing their heterojunction-based electronic and optoelectronic devices.

In this work, a thin-film transistor gas sensor based on the p-N heterojunction is fabricated by stacking chemical vapor deposition-grown tungsten disulfide (WS2) with a sputtered indium–gallium–zi...

Thermoelectric materials can effectively convert waste heat into electrical energy and receive more and more attention. Zintl phase Mg3Sb2 is a typical layered thermoelectric material and the anisotropy in crystalline structure induces strong anisotropy in its thermoelectric properties. As a result, polycrystalline Mg3Sb2 usually can not achieve the maximum thermoelectric performance. Our research proves that the dimensionality reduction in material structure can not only avoid certain crystalline direction's poor thermoelectric properties but also effectively reduce the lattice thermal conductivity. Within the framework of the density functional theory, the thermoelectric performance of two-dimensional Mg3Sb2 mono layer is accurately investigated. The ZT value of the Mg3Sb2 nano-thin film can reach 2.5 at 900 K, which is larger than that of the bulk. The theoretical results indicate that the process of nano-engineered structure can significantly enhance the energy conversion efficiency of thermoelectrics.

The search for high-temperature superconductivity is one of the research frontiers in physics. In the sulfur hydride system, an extremely high Tc (∼200 K) has been recently developed at pressure. However, the Meissner effect measurement above megabar pressures is still a great challenge. Here, we report the superconductivity identification of sulfur hydride at pressure, employing an in situ alternating-current magnetic susceptibility technique. We determine the superconducting phase diagram, finding that superconductivity suddenly appears at 117 GPa and Tc reaches 183 K at 149 GPa before decreasing monotonically with increasing pressure. By means of theoretical calculations, we elucidate the variation of Tc in the low-pressure region in terms of the changing stoichiometry of sulfur hydride and the further decrease in Tc owing to a drop in the electron–phonon interaction parameter λ. This work provides a new insight into clarifying superconducting phenomena and anchoring the superconducting phase diagram in the hydrides.

As high-performance dielectric material, small sizes of barium titanate (BaTiO3) are desirable for the application of multilayer ceramic capacitors. Herein, we synthesized ultrafine BaTiO3 powders with mean particle size of (dav.) 156 nm, tetragonality (c/a) of 1.0092 and specific surface area (SBET) of 6.09 m2/g by two-step sintering process. Kinetic analysis of solid-state reaction reveals that the phase-boundary-controlled mechanism dominated the reaction process in two-step sintering process compared with one-step sintering process dominated by the first-order mechanism. It is also shown that enhanced nucleation in two-step calcination is beneficial for improving the tetragonality. In particular, the dielectric constant and dielectric loss of BaTiO3 ceramics at the Curie temperature are found to be about 12800 and 0.003. This work demonstrates a strategy to trigger a method which can effectively improve the dielectric properties of BaTiO3 ceramic.

Transparent ceramic is considered to be a fascinating material with high photonic quality for a diverse range of applications. Here, we fabricated series of highly transparent Yb:Y2O3 (Yb:1.0, 3.0, 5.0, 7.0 and 9.0 at.%) ceramics via a vacuum solid-state reactive sintering. The room temperature up-conversion spectra for blue emissions are observed under the laser excitation of 980 nm. It is shown that the content of Yb3+ plays an important role in emission efficiency. Especially, the sample containing 7.0 at.% Yb3+ achieves the strongest cooperative luminescence. Analysis reveals that Yb3+-Yb3+ cluster cooperating in Y2O3 transparent ceramics takes place via phonon-assist energy transfer mechanism. Furthermore, the blue emission spectroscopy and decay lifetime of 7.0 at.% Yb:Y2O3 are also discussed.

The increasing decomposition temperature of solid ammonia borane under high pressure introduces a solid–solid phase transition preceding decomposition. An earlier X-ray diffraction experiment sugge...

Hydrogen-rich compounds are being extensively explored theoretically and experimentally as potential hydrogen storage materials. In this work, we predicted a hydrogen-rich compound rhodium trihydride ($\mathrm{Rh}{\mathrm{H}}_{3}$) with a high volumetric hydrogen density of 212.5 g/L by means of ab initio calculations. The $\mathrm{Rh}{\mathrm{H}}_{3}$ with Pnma symmetry is thermodynamically stable and accessible through synthesis above 40 GPa. The compound is dynamically and mechanically stable at ambient pressure. Further calculation suggests a probable dehydrogenation temperature ${T}_{\mathrm{des}}$ of $65{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ at ambient pressure with decomposition route to $\mathrm{Rh}+{\mathrm{H}}_{2}$. High volumetric hydrogen density and moderate dehydrogenation temperature place $\mathrm{Rh}{\mathrm{H}}_{3}$ as one of the best hydrogen storage materials. Our work encourages the experimental synthesis of $\mathrm{Rh}{\mathrm{H}}_{3}$ at high pressure.

The bilayer Al 2 O 3 /in-situ SiN x gate dielectric stacks were applied to fabricate high-performance AlGaN/GaN MIS-HEMTs. Both the normally-off and normally-on operations were realized on the ultrathin-barrier Al 0.05 Ga 0.95 N/GaN heterojunctions. Moreover, the low $V_{th}$ hysteresis of 50 mV and subthreshold swing of 70 mv/dec were achieved based on the in-situ SiN x /Al 0.05 Ga 0.95 N interface. The combination of Al 2 O 3 layer and in-situ SiN x layer can also increase the output current and suppress the gate current leakage.

In this paper, we demonstrated a gold-free Ti 5 Al 1 /TiN source and drain (S/D) contact on non-recessed AlGaN/AlN/GaN structure. Compared to the conventional gold-based (Ti/Al/Ti/ Au and Ta/ Al/Au) or multilayer gold-free (Ti/Al/TiN and Ta/Al/Ta) S/D contact metals, using a Ti 5 Al 1 /TiN (60 nm/60 nm) dual-layer contact metal, a low contact resistivity of $0.11 \Omega\cdot \text{mm}$ was achieved after 920 °C/ 60 s annealing in nitrogen ambient. It was found that Al out-diffusion from AlGaN was suppressed while a thin TiN layer and n-AlGaN layer was formed at the interface, which were beneficial for the low contact resistivity S/D contact formation.

The performance of perovskite photovoltaics is fundamentally impeded by the presence of undesirable defects that contribute to non-radiative losses within the devices. Although mitigating these losses has been extensively reported by numerous passivation strategies, a detailed understanding of loss origins within the devices remains elusive. Here, we demonstrate that the defect capturing probability estimated by the capture cross-section is decreased by varying the dielectric response, producing the dielectric screening effect in the perovskite. The resulting perovskites also show reduced surface recombination and a weaker electron-phonon coupling. All of these boost the power conversion efficiency to 22.3% for an inverted perovskite photovoltaic device with a high open-circuit voltage of 1.25 V and a low voltage deficit of 0.37 V (a bandgap ~1.62 eV). Our results provide not only an in-depth understanding of the carrier capture processes in perovskites, but also a promising pathway for realizing highly efficient devices via dielectric regulation., Performance of perovskite photovoltaics is greatly affected by undesirable defects that contribute to non-radiative losses. Here, the authors mitigate these losses by doping perovskite with KI to alter the dielectric response, thus defect capturing probability, resulting in inverted device with PCE of 22.3% and low voltage loss.

Peroxisome proliferator-activated receptor gamma (PPARγ) is a valuable drug target for diabetic treatment and ligands of PPARγ have shown potent anti-diabetic efficacy. However, to overcome the severe side effects of current PPARγ-targeted drugs, novel PPARγ ligands need to be developed. Sulindac, an identified ligand of PPARγ, is widely used in clinic as a non-steroidal anti-inflammatory drug. To explore its potential application for diabetes, we designed and synthesized a series of sulindac derivatives to investigate their structure-activity relationship as PPARγ ligand and potential anti-diabetic effect. We found that meta-substitution in sulindac's benzylidene moiety was beneficial to PPARγ binding and transactivation. Z rather than E configuration of the benzylidene double bond endowed derivatives with the selectivity of PPARγ activation. The indene fluorine is essential for binding and regulating PPARγ. Compared with rosiglitazone, compound 6b with benzyloxyl meta-substitution and Z benzylidene double bond weakly induced adipogenesis and PPARγ-targeted gene expression. However, 6b potently improved glucose tolerance in a diabetic mice model. Unlike rosiglitazone, 6b was devoid of apparent toxicity to osteoblastic formation. Thus, we provided some useful guidelines for PPARγ-based optimization of sulindac and an anti-diabetic lead compound with less side effects.

We report a dramatic current reduction, or a resistance increase, by a few orders of magnitude of two common-anode Au/Ti/pGaN Schottky junctions annealed within a certain annealing condition window (600 - 700 oC, 1 - 4 min). Results from similar common-anode Schottky junctions made of Au/p-GaN, Al/Ti/p-GaN and Au/Ti/graphene/p-GaN junctions demonstrated that all the three layers (Au, Ti and p-GaN) are essential for the increased resistance. Raman characterization of the p-GaN showed a decrease of the Mg-N bonding, i.e., the deactivation of Mg, which is consistent with the Hall measurement results. Moreover, this high-resistance junction structure was employed in p-GaN gate AlGaN/GaN HEMTs. It was shown to be an effective gate technology that was capable to boost the gate breakdown voltage from 9.9 V to 13.8 V with a negligible effect on the threshold voltage or the sub-threshold slope.

The effective spin Hamiltonian method has drawn considerable attention for its power to explain and predict magnetic properties in various intriguing materials. In this review, we summarize different types of interactions between spins (hereafter, spin interactions, for short) that may be used in effective spin Hamiltonians as well as the various methods of computing the interaction parameters. A detailed discussion about the merits and possible pitfalls of each technique of computing interaction parameters is provided.

Understanding the fundamental properties of buried interfaces in perovskite photovoltaics is of paramount importance to the enhancement of device efficiency and stability. Nevertheless, accessing buried interfaces poses a sizeable challenge because of their non-exposed feature. Herein, the mystery of the buried interface in full device stacks is deciphered by combining advanced in situ spectroscopy techniques with a facile lift-off strategy. By establishing the microstructure-property relations, the basic losses at the contact interfaces are systematically presented, and it is found that the buried interface losses induced by both the sub-microscale extended imperfections and lead-halide inhomogeneities are major roadblocks toward improvement of device performance. The losses can be considerably mitigated by the use of a passivation-molecule-assisted microstructural reconstruction, which unlocks the full potential for improving device performance. The findings open a new avenue to understanding performance losses and thus the design of new passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.

In this paper, 600nm Z-cut lithium niobate (LiNbO 3 ) thin film based third-order antisymmetric (A3) mode resonators with different geometries has been investigated. Through a series of experiments, it has been found for the first time that effective electromechanical coupling coefficient $\left( {K_{{\text{eff}}}^2} \right)$ is influenced by the gap between electrodes (Ge), and $K_{{\text{eff}}}^2$ decreases with the increase of Ge when electrode pitch (P) higher than 5μm. Finally, a A3 mode resonator with a high $K_{{\text{eff}}}^2$ of 6.72% is obtained. This $K_{{\text{eff}}}^2$ is the highest reported value in similar acoustic resonators working about 9 GHz and will be beneficial to the construction of X-band filters.

The dynamic ON-resistance (Ron) of p-GaN HEMTs was reduced using the dual field plate (FP) structure combined with the source field plate (S-FP) and gate field plate (G-FP). The electric field redistribution at the gate edge reduces the electron trapping during the high voltage blocking, avoiding the Ron increase after the device switching on. The devices with the dual FPs attained the breakdown voltage over 600 V, and the Ron increased only 50% after 200 V blocking, outperforming the devices with single FP or without FPs. Moreover, a plasma surface treatment process was introduced to further improve dynamic Ron performance, which is a promising method to alleviate the current collapse effect. The electric field distribution was also simulated using TCAD to support the experimental results. The results support the dual field plate design a useful structure for high-voltage GaN based HEMTs.

Structure prediction studies on Ca-H binary systems under high pressures were carried out, and the structures of calcium hydrides in earlier works were reproduced. The previously unreported composition of CaH

MOSFET power device with beta-Ga 2 O 3 substrate are simulated via TCAD and discussed in this paper. Material models are established and calibrated based on the existing experimental results. Device design specifications like channel doping profile, gate-source distance, selective doping, field plate enhancement, and ion-implantation profile are evaluated and discussed. The results serve as a guide and reference for the beta-Ga 2 O 3 , MOSFET device design.

Normally-off Gallium Nitride (GaN) transistors with p-GaN gated technology for power applications are studied for the optimization of off-state breakdown performance. The gate-drain distance, gate length, field plate length and its configuration have been studied. Increase gate-drain distance will not only enhance the breakdown performance but also increase the $\mathrm{R}_{\mathrm{on}},\ \mathrm{L}_{\mathrm{GD}}$ between $10 -20\ \mu\mathrm{m}$ is recommended. Extra gate length will lead to the rising of the gate leakage current under high voltage. The overhang length of the field plate is a critical factor for breakdown performance, over placing the length of overhang may result in an additional current leakage path.

The quasi-normally-off operation of AlGaN/GaN HEMTs was realized using strain engineering. The dual-layer silicon nitride (SiNx) stressors applied compression to the gate region in devices, and the introduced compression translated to piezoelectric polarization charges and hence, increased the threshold voltage of devices. The devices with dual-layer stressors showed quasi-normally-off characteristics and the threshold voltage of 0.17 V. Besides, the comb-gate structure was introduced to suppress the short channel effects. The on-state performance of the comb-gate devices, including on-resistance $(\pmb{R}_{\pmb{on}})$ and saturation current $(\pmb{I}_{\pmb{d},\pmb{sat}})$ , was benchmarked against that of p-GaN gate HEMTs from a commercial foundry. The dual-layer stressor and comb-gate structure further improved the feasibility of strain engineering as a practical approach in the pursuit of the normally-off operation of AIGaN/GaN HEMTs in power electronics applications.

One of the main motivations for studying superconductivity is to search for high-temperature superconductors, especially room-temperature superconductors. During the long history of more than 100 years since the discovery of superconductivity, a number of high-temperature superconductors were found and several great breakthroughs were achieved. Recently, thanks to advances in computing power, progress in crystal structure prediction, and developments in density functional theory, computations have been carried out to predict the structures and an appearance of superconductivity of hydrides at high pressure. More exciting, it is been the first time when a simple, perfect cubic phase of H3S which become superconductor at Tc = 200 K under high pressure was successfully predicted by means of ab initio calculation, and then confirmed experimentally. This observation breaks the temperature record of cuprate with Tc = 164 K and further stimulates the studies of hydrides under pressure. Very recently, the high value of Tc = 286 K was theoretically predicted for LaH10 at 210 GPa and this prediction has been confirmed experimentally. These two successful examples demonstrate the importance of ab initio approach to superconductivity.

Water scarcity has become a global issue of severe concern. Great efforts have been undertaken to develop low-cost and highly efficient condensation strategies to relieve water shortages in arid regions. However, the rationale for design of an ideal condensing surface remains lacking due to the conflicting requirements for water nucleation and transport. In this work, we demonstrate that a biphilic nanoscale topography created by a scalable surface engineering method can achieve an ultraefficient water harvesting performance. With hydrophilic nanobumps on top of a superhydrophobic substrate, this biphilic topography combines the merits of biological surfaces with distinct wetting features (e.g., fog-basking beetles and water-repellent lotus), which enables a tunable water nucleation phenomenon, in contrast to the random condensation mode on their counterparts. By adjusting the contrasting wetting features, the characteristic water nucleation spacing can be tuned to balance the nucleation enhancement and water transport to cope with various environments. Guided by our nucleation density model, we show an optimal biphilic topography by tuning the nanoscale hydrophilic structure density, which allows an ∼349% water collection rate and ∼184% heat transfer coefficient as compared to the state-of-the-art superhydrophobic surface in a moisture-lacking atmosphere, offering a very promising strategy for improving the efficiency of water harvesting in drought areas.

To assess the potential of catastrophic megathrust earthquakes (M W > 8) along the Manila Trench, the eastern boundary of the South China Sea, we incorporate a 3D non-planar fault geometry in the framework of rate-state friction to simulate earthquake rupture sequences along the fault segment between 15°N-19°N of northern Luzon. Our simulation results demonstrate that the first-order fault geometry heterogeneity, the transitional-segment (possibly related to the subducting Scarborough seamount chain) connecting the steeper south segment and the flatter north segment, controls earthquake rupture behaviors. The strong along-strike curvature at the transitional-segment typically leads to partial ruptures of M W ~8.3 and M W ~7.8 along the southern and northern segments respectively. The entire fault occasionally ruptures in M W ~8.8 events when the cumulative stress in the transitional-segment is sufficiently high to overcome the geometrical inhibition. Fault shear stress evolution, represented by the S -ratio, is clearly modulated by the width of seismogenic zone ( W ). At a constant plate convergence rate, a larger W indicates on average lower interseismic stress loading rate and longer rupture recurrence period, and could slow down or sometimes stop ruptures that initiated from a narrower portion. Moreover, the modeled interseismic slip rate before whole-fault rupture events is comparable with the coupling state that was inferred from the interplate seismicity distribution, suggesting the Manila trench could potentially rupture in a M8+ earthquake.

Si-substrate-based AlGaN/GaN high-electron mobility power transistors with low pressure chemical vapor deposition (LPCVD) SiN x as gate isolation material are fabricated on a 6-in wafer by CMOS compatible process. The dielectric failure by forward-biased constant-voltage stress time-dependent dielectric breakdown (TDDB) measurements at various temperatures (from room temperature to 250 °C) and their statistical Weibull analysis are compared. Impact of gate dielectric area and multifinger on the SiN x TDDB characteristics is also discussed. Using thermal microscope imager, the leakage current spots have been identified. The mean time to failure decreases with the increasing finger numbers in exponential form. We also predict the device ( ${W}_{G}= {0.25}$ mm) with 35-nm-thick LPCVD SiN x gate dielectric can survive at a positive gate voltage of ${V}_{\text {GS}}= {15}$ V for a 10-year time-to-breakdown lifetime (100 ppm and ${T}= {25}$ °C) and ${V}_{\text {GS}}= {7.5}$ V for a 10-year time-to-breakdown lifetime (100 ppm and ${T}= {250}$ °C).

In this work, a charge storage based enhancement mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMT) is proposed and studied. A stacked gate dielectrics, consisting of a tunnel oxide, a charge trap layer and a blocking oxide are applied in the HEMT structure. The E-mode can be realized by negative charge storage within the charge trap layer during the programming process. The impact of the programming condition and the thickness of the dielectrics on the threshold voltage (Vth) are simulated systematically. It is found that the Vth increases with the increasing programming voltage and time due to the increase of the storage charge. Under proper programming condition, the Vth can be increased to more than 2 V. Moreover, It is also found that the Vth increases with the decrease of the thickness of the dielectrics. In addition, it is found that the breakdown voltage of such HEMT can be adjusted by varying the gate dielectric stacks.

The phase diagram, electronic properties and superconductivity of an At-H system at high pressure are investigated through first principles calculation considering the effect of spin-orbit coupling (SOC). The Cmcm-AtH2, Pnma-AtH2, P6/mmm-AtH4, and Cmmm-AtH4 phases are uncovered above 50 GPa. Metallization is realized at 50 GPa for AtH2 and 60 GPa for AtH4, with Tc values of approximately 5-10 K and 30-50 K, respectively. In P6/mmm-AtH4, phonon softening induced by Fermi surface nesting occurs as the pressure increases, which is closely related to the structural phase transition of P6/mmm → Cmmm and plays a crucial role in the superconductivity of the P6/mmm phase. In addition, the spin-orbit coupling effect considerably influences the energy of ground states, pressure points of phase transitions, electronic structures, and even the electron-phonon coupling of the At-H system. Such an influence may also occur in other heavy atomic hydrides.

Hard materials are being investigated all the time by combining transition metals with light elements. Combining a structure search with first-principles functional calculations, we first discovered three stable stoichiometric C-rich ruthenium carbides in view of three synthesis routes, namely, the ambient phases of Ru2C3 and RuC, and two high pressure phases of RuC4. There is a phase transition of RuC4 from the P3[combining macron]m1 structure to the R3[combining macron]m structure above 98 GPa. The calculations of elastic constants and phonon dispersions show their mechanical and dynamical stability. The large elastic modulus, high Debye temperature and the estimated hardness values suggest that these hard ruthenium carbides have good mechanical properties. The analyses of electronic structure and chemical bonding indicate that chemical bonding, not carbon content, is the key factor for the hardness in these metallic C-rich ruthenium carbides. The partial covalent Ru-C bonds and strong covalent C-C bonds are responsible for the high hardness. Moreover, the emergence of partial covalent Ru-Ru bonds can enhance the hardness of RuC, while the ionic Ru-Ru bonds can weaken the hardness of Ru2C3.

In this study, we predict two kinds of stable structural models of B–S co-doped diamond through molecular dynamic simulations and geometrical optimization by density functional theory. The bond lengths and electron distribution near the dopants are similar with those of substitutional S in diamond with C3v symmetry. The B–S co-doped diamond shows the deep donor level, which is mainly contributed by the dopants and adjacent C atoms. Furthermore, the structures show the localized electron distribution near the dopants from the lone-pair electron around S atom.

Buckling of rigid thin films on elastomer substrates underlies the fabrication foundation of stretchable soft electronics. Here we demonstrate an optical approach to in situ characterize the buckling of silicon microribbon driven by releasing the pre-stretched poly-dimethylsiloxane (PDMS) substrate at a controllable strain rate. The method, based on quantitative differential interference microscopy, directly captures the space–time evolution of the surface topography at a frame rate of 100 fps in a large field of view of 50 × 195 μ m 2 . The nucleation, propagation and stabilization of the buckled structure during the buckling and unbuckling processes are observed and quantified. Our experiment reveals that a sequence of partially buckled patterns are energetically stable to bridge the unbuckled and fully buckled states. This work opens a new experimental scheme for the research on stretchable soft electronics and provides new evidence for the theoretical study of the buckling dynamics.

Understanding the individual contributions of the factors that influence the electrical properties of a material is important for controlling these properties. In this study, the effects of multiple factors on the electrical properties of thin-barrier AlGaN/GaN heterojunctions with in-situ SiNx caps were investigated using step etching and annealing treatments. The sheet density of the two-dimensional electron gas decreased by 5.9% and 29.5% due to the decrease in the piezoelectric polarization of the AlGaN barrier and the variations in interface charges during SiNx removal, respectively, and it recovered greatly by 72% after annealing-induced surface reconstruction. Capacitance-voltage results clearly revealed few interface traps on the heterojunction with the in-situ SiNx cap. Moreover, a maximum output current of 705 mA/mm and threshold voltage hysteresis below 50 mV were achieved by optimizing the in-situ SiNx interlayer on a thin-barrier metal-insulator-semiconductor structure. This study presents an efficient method for modulating the properties of two-dimensional electron gas and provides insights into the functionality of in-situ SiNx passivation on thin-barrier AlGaN/GaN heterojunctions.

Barium titanate (BaTiO 3 ) powders were synthesized through hydrothermal process with Ba(OH) 2 ·8H 2 O and TiO 2 . By increasing the feedstock concentration (FC) from 0.25 to 1.50 M, BaTiO 3 powders maintain a stable average particle size (~180 nm and ~6.4441 m 2 /g) with an increasing tetragonality ( c/a : 1.0065–1.0075). Johnson-Mehl-Avrami and standard reaction rate equations were adopted to analyze the kinetic process of BaTiO 3 formation. The reaction is governed by first-order and phase-boundary-controlled mechanism for 0.25 M and 1.50 M, respectively. Lower extent of reaction is believed to lead to the better tetragonality for BaTiO 3 powders fabricated with higher FC. On the other hand, the relative stable particle size is correlated with the unvaried nucleation frequency and grain growth rate with various FC. This work can provide a guideline to manipulate the properties of BaTiO 3 powders used in electronic industry.

In this work, the charge storage based split floating gates (FGs) enhancement mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) are studied. The simulation results reveal that under certain density of two dimensional electron gas, the variation tendency of the threshold voltage (Vth) with the variation of the blocking dielectric thickness depends on the FG charge density. It is found that when the length sum and isolating spacing sum of the FGs both remain unchanged, the Vth shall decrease with the increasing FGs number but maintaining the device as E-mode. It is also reported that for the FGs HEMT, the failure of a FG will lead to the decrease of Vth as well as the increase of drain current, and the failure probability can be improved significantly with the increase of FGs number.

An analytical model is developed for the fluctuation of the electrostatic potential induced by a charged trap in the gate oxide in tunneling field effect transistor (TFET). The model is applied to get the fluctuation of the drain current induced by an interface trap in TFET. A low frequency noise model based on the current transportation through the tunneling and the channel is proposed. The dependency of the normalized power spectra SId/Id2 on the frequency f and the gate bias Vg for TFET is obtained. The noise spectra in TFET are found to be very different from those of conventional MOSFETs, and have the superposition of Lorentzian and 1/f lineshapes with the former associated with tunneling and the later with channel transportation. The potential and current models are compared with TCAD simulation. The calculated IdVg and the noise spectra are also compared with our experimental observations. The results show that the normalized spectra of the current noise due to the tunneling are more significantly affected by Vg than that due to the transportation through the channel. The results also show that the noise from the channel is dominated by the mobility fluctuation rather than the carrier number fluctuation.

The present work reports on the hydrogen gas detection properties of Pt-AlGaN/GaN high electron mobility transistor (HEMT) sensors with recessed gate structure. Devices with gate recess depths from 5 to 15 nm were fabricated using a precision cyclic etching method, examined with AFM, STEM and EDS, and tested towards H2 response at high temperature. With increasing recess depth, the threshold voltage ( ${V}_{\textit {TH}}$ ) shifted from −1.57 to 1.49 V. A shallow recess (5 nm) resulted in a 1.03 mA increase in signal variation ( $\Delta {I}_{\textit {DS}}$ ), while a deep recess (15 nm) resulted in the highest sensing response ( ${S}$ ) of 145.8% towards 300 ppm H2 as compared to reference sensors without gate recess. Transient measurements demonstrated reversible H2 response for all tested devices. The response and recovery time towards 250 ppm gradually decreased from 7.3 to 2.5 min and from 29.2 to 8.85 min going from 0 nm to 15 nm recess depth. The power consumption of the sensors reduced with increasing recess depth from 146.6 to 2.95 mW.

This paper introduces a tilting sensor based on Molecular Electronic Transducer (MET) technology. By applying electrical potential between two electrodes covered by lithium iodide electrolyte, the output current from the sensor reflects the covered area of electrodes. The continuously change of electrode area with tilting angle is achieved by patterning metal traces on top of a SiO 2 encapsulated silicon wafer. Polydimethylsiloxane (PDMS) is used as the electrolyte chamber which has high bond strength with SiO 2 after the surface treatment with O 2 plasma. The MET tilting sensor achieves a promising performance with a linear range of ± 90°, resolution of 0.184° and time constant of 40s.