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The efficiency of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) is limited by the high absorption issue of the p-GaN contact layer or poor contact properties of the transparent p-AlGaN contact layer. Enhancement of the light output efficiency and thermal stability of DUV LEDs with an emission wavelength of 272 nm was investigated in this work. Ag nanodots on an 8-nm p-GaN cap layer were used to form ohmic contact, and Al and Mg reflective mirrors were employed to enhance the light output power (LOP) of DUV LEDs. However, serious deterioration of LOP occurred after the high-temperature process for the LEDs with Al and Mg reflective mirrors, which can be attributed to the damage to the ohmic contact properties. A Ti barrier layer was inserted between the Ag/p-GaN and Al layers to prevent the degeneration of ohmic contact. The wall-plug efficiency (WPE) of DUV LEDs fabricated by the Ag-nanodot/Ti/Al electrode is 1.38 times that of LEDs fabricated by adopting a thick Ag layer/Ti/Al at 10 mA after a high-temperature process. The Ag-nanodot/Ti/Al electrode on thin p-GaN is a reliable technology to improve the WPE of DUV LEDs. The experimental and simulated results show that the ohmic contact is important for the hole-injection efficiency of the DUV LEDs when p-GaN is thin, and a slight increase in the contact barrier height will decrease the WPE drastically. The results highlighted the importance of thermally stable ohmic contacts to achieve high-efficiency DUV LEDs and demonstrated a feasible route for improving the LOP of DUV LEDs with a thin p-GaN cap layer and stable reflective electrodes.

This study aimed to evaluate the effect of the number of lactations and litter size on the chemical composition, immunoglobulins, and cytokines of goat colostrum. The experiment was conducted at the Animal Research Base, Mianyang Academy of Agricultural Sciences, from February to March 2021. After delivery, 48 colostrum samples were obtained every 24 h by manual milking from both udders. The contents of colostrum proteins, IgA, and IgM increased markedly up to 48 h postpartum, reaching 250 and 1250 ��g/mL, respectively (p p p p

The effect of direct-feed microbial (DFM) treatment on body weight, serum biochemical indexes, serum immunoglobulins, and serum cytokines was studied. The study was a completely randomized design with 20 growing females Beichuan white goats, weighing 25.11 ± 1.96 kg, divided into two groups of 10 goats per treatment. Goats were offered (1) 10 mL saline solution (Control group) (2) or 10 mL microbials solution (DFM group) on days 0 and 7 for two times. No effect on final body weight and body size was observed between DFM and control group (

The hollow rod electric heating (HREH) technology can greatly increase the temperature of the fluid in wellbore and improve its fluidity, which is widely used in rod pump wells. Bohai offshore oilfields also have urgent application requirements for HREH technology due to the wide distribution of heavy oil and high waxy crude oil. However, more than 90% of the oil wells there are produced by electric submersible pumps (ESPs). None of these christmas trees in use are suitable for ESP wells using HREH technology. Based on the conventional christmas tree with only one main channel, a new type of eccentric christmas tree, with separated main channel and cable channel, is designed. As with the conventional ones, the main channel works as the flow passage of wellbore fluids. And the cable channel is used to run and pull out the heating cable. The eccentric design of the main channel provides the space for the cable channel. The separate cable channel avoids the cable crossing the main channel, so that the master valve of the christmas tree can be opened and closed normally, which contributes to ensuring safe production. In the meanwhile, the christmas tree can also seal the heating cable owing to some special design. This new device has been successfully tested on 6 ESP wells in Bohai Bay. After the installation of the christmas tree, the cable was smoothly run down to the predetermined depth. The construction operation was simple and convenient. There was no oil or gas leakage at wellhead after it was put into use. The wellhead temperature of all these wells reached above 50°C and no wax deposited in tubing any more, verifying its safety and reliability. This new type of safe and reliable christmas tree lays a solid foundation for the popularization and application of HREH technology, especially in those waxy oil wells and heavy oil wells with ESPs.

This paper proposes an integrated technology of chemical sand control and stratified water injection in water injection well, which enlarge the inner diameter of injection well after sand control and achieve flexible stratification of injection layer. Mechanical sand control is the main method for injection wells in offshore oilfields. After sand control, the inner diameter of injection well is small and the number of injection layers is generally 3-4 layers. For reservoirs with strong longitudinal heterogeneity, it's difficult to get higher longitudinal sweep coefficient of driving and better effect of injection. The technology realizes completion by chemical sand control, without screens downhole. The ceramsite whose surface has been treated by crosslinking agent is injected into the well and heated. The crosslinking reaction occurs on the surface of the ceramsite, forming a cement layer with a thickness of 3-5cm and a certain compressive strength of 7.2MPa and a permeability of 5000mD on the wellbore. This cement layer not only can be used as a barrier to retain formation, but also can provide flow channels for fluids. Then, the stratified injection pipe string is run. The developed multi-functional packer contacts and seals the cemented layer to realize the stratification of the injection reservoir. The position and quantity of the packer are designed according to the target injection horizon to achieve flexible stratification. This technology has been successfully applied to 4 wells in the Bohai Oilfield, all of which have the characteristics of large reservoir thickness and strong vertical heterogeneity. The conventional sand control and injection technology makes it difficult for the actual injection volume to reach the target volume, and the water cut of the benefit well continues to rise. After applying the integrated technology, for a directional well with a bore diameter of 9.625 in, the maximum inner diameter can reach 9.625 in, while the inner diameter of traditional sand control methods is only 4.75 in. The number of injection layers exceeds 5, and the actual injection volume meets the designed requirement. The validity period has exceeded 40 months and continues to be effective. The water cut of the benefiting well decreases from 85% to 78%, and the oil production rate increased from 56 m3/d to 72 m3/d. The successful application of the integrated technology provides a new idea for subdivision water injection in offshore oilfields. The increase in the internal diameter of well can reduce the difficulty of operation and increase the water injection rate. The flexible stratification can improve the vertical production degree of reservoir water flooding and the overall effect of water injection.

This work reports on high-reflectivity Ag nanodot (AgND)/Mg/Al Ohmic contacts suitable for both p-GaN and n-GaN. The lowest specific contact resistances are found to be 2.25 × 10−2 Ω·cm2 on p-GaN and 2.56 × 10−5 Ω·cm2 on n-GaN. Ag was deposited and converted into AgNDs by annealing, and Mg/Al was then deposited. A second annealing process at different temperatures was performed to check the thermal stability of the contacts. Both the p-GaN and n-GaN contacts were Ohmic after annealing at 300 °C or below. The AgND/Mg/Al contacts annealed at 250 °C or less showed a reflectivity of over 91% for wavelengths from 400 to 550 nm. X-ray photoelectron spectroscopy and x-ray diffraction measurements were performed to investigate the contact mechanisms. We propose that in AgND/Mg/Al on p-GaN, the effective barrier is lowered due to the presence of an Ag2O intermedia layer and the tunneling effect enables Ohmic contact. When the annealing temperature is 350 °C or higher, the Ag2O changes to β-AgGaO2 or is decomposed and the height and width of the barrier for holes increase, which causes the Ohmic contact to deteriorate. The Ohmic behavior of AgND/Mg/Al contacts on n-GaN is assumed to be mainly due to the high direct coverage ratio of Mg and the good Ohmic contact behavior of Mg/n-GaN. These results show that AgND/Mg/Al Ohmic contacts can be fabricated simultaneously on both p-GaN and n-GaN, which is a possible solution for improving the density of both GaN-based ICs and micro-light emitting diodes (LEDs). This contact scheme can also improve the light output efficiency of GaN-based LEDs.

This work reports a Mg (130 nm)/Al (50 nm) bilayer to realize high-reflectivity ohmic contact for n-GaN. The contact resistivity of $3.75\times 10 ^{ {-4}} \Omega \cdot $ cm $^{ {2}}$ with Mg/Al contact was achieved after annealing at 250 °C in ambient Ar for 1 min. The specific contact resistivity was found to change moderately when the annealing temperature was below 400 °C, but the ohmic characteristics deteriorated significantly when the annealing temperature was above 450 °C. X-ray photoemission spectroscopy revealed that the Ga 3d (Ga-N) peak decreased by 0.28 eV with the increase of the annealing temperature from 250 to 450 °C, which can increase the metal-semiconductor contact barrier height, leading to deteriorated current-voltage characteristics. The reflectivity of the samples was found to decrease with the increase of the annealing temperature, and decreased greatly when the temperature exceeded 350 °C. When the annealing temperature is below 300 °C, the reflectivities of the samples are greater than 90% for wavelengths from 350 to 550 nm. Mg/Al is therefore a promising candidate to serve as a reflective n-GaN electrode for GaN-based flip-chip LEDs to improve the light extraction efficiency.

Semi-polar micro-LEDs have gain increasing interests due to the advantages of polarization control and quantum efficiency improvement. In this work, a novel semi-polar (20–21)-plane micro-LEDs array has been designed and manufactured. In comparison with c-plane micro-LEDs, semi-polar micro-LEDs indicate better electrical and optical performance. The relative EQE of semi-polar micro-LEDs remains at 62% under the injected current density of 775.6 A/cm2, which indicates a reduced efficiency droop due to less polarization in MQWs. It has been further proved by a significant reduction of 55% in emission peak blue-shift under the injected current density from 11.1 A/cm2 to 775.6 A/cm2. In addition, the carrier recombination dynamics and spatial light distribution of semi-polar micro-LEDs with different pixel sizes have been studied. Fast recombination lifetime in smaller size semi-polar micro-LEDs indicates a promising way to be used as a high modulation bandwidth light source. Stable and uniform light distribution in a wider range of spatial azimuths further supports for the semi-polar micro-LEDs as a strong candidate for the applications of high-resolution display and high-speed visible light communication.

Current-voltage ( I-V ) characteristics of AlGaN ultraviolet light-emitting diodes (UV-LEDs) under the temperatures ranging from 50 K to 300 K are analyzed. The abnormal diode characteristics of UV-LEDs below the turn-on voltage indicate the existence of space-charge-limited (SCL) current transport in the presence of deep trap states, which induce a non-linear current leakage effect. The SCL current is gradually overwhelmed by Ohmic leakage as the temperature increases, which is mainly due to the thermally generated carrier concentration and traps deactivation. A modified three-diode circuit model is suggested with an additional series resistor and diode to emulate the forward-bias I-V characteristics of UV-LEDs. An excellent fit to the I-V curves of UV-LEDs is achieved, which illustrates the impact of deep trap states on the electrical characteristics of UV-LEDs.

This paper proposes a set of methods for selecting the type of sand control screen and optimizing the accuracy in heavy oil Wells, which take into account the requirements of sand control and productivity protection in heavy oil Wells. Sand retaining experiments are carried out with slotted screen, wire wrapped screen and metal filter screen under the condition of oil and water mixed sand carrying flow. In order to optimize the sand control screen suitable for heavy oil well, this paper uses the weighted average method to quantitatively evaluate the flow performance, sand retention performance and oil conductivity of the screen. Then, repeat the experiment by changing the accuracy of the screen to optimize the accuracy. The experimental results show that the permeability of the three kinds of sand control screens is about 5μm2 when only heavy oil plugging occurs. Under the combined plugging action of formation sand and heavy oil, the slotted screen has the highest permeability, and its conductivity to heavy oil is 10% higher than that of the other two screens. The slotted screen and wire wrapped screen have the higher sand retention performance, with a sand retention rate of about 90%. Through the quantitative evaluation of the sand control performance of three kinds of screens in different production stages of heavy oil Wells, the slotted screen is selected as the optimal screen. For simulated formation sand with a median particle size of 250μm, the optimal sand control accuracy is 200μm. This paper provides a quantitative optimization method of screen type and accuracy for sand control design of sand-producing heavy oil Wells, so as to maximize the productivity under the premise of ensuring sand-producing control of heavy oil Wells.

The electrical and optical properties of Ag/p–GaN contacts have been investigated as a function of the annealing temperature, oxygen concentration, and annealing time. Specific contact resistance (ρc) values as low as 1.2 × 10–4 Ω·cm2 were obtained from the Ag/p–GaN contact annealed at 400 °C for 60 s in ambient O2/N2 (1:10). We found that the participation of oxygen improves the formation of ohmic contacts. Oxygen might remove the H in Mg–H complexes to activate the Mg acceptors and enhance Ga out-diffusion to form an Ag–Ga solid solution. We also found that the reflectivity of the Ag layer decreases with increasing annealing temperature in the O2-containing ambient environment. Thus, an optimal annealing condition of Ag/p–GaN for blue and green LEDs is suggested based on these results. We also used the suggested annealing conditions to form ohmic contacts on DUV LEDs and achieved good electrical performance. The forward voltages of UVC LEDs fabricated with annealed Ag contacts were 6.60 V (7.66 V) at a 40 mA (100 mA) injection current.

Since the field test of polymer flooding technology was carried out in the Bohai Oilfield in 2003, problems such as plugging of polymer-response wells have become increasingly worse, and conventional acidizing and plugging removal measures have had poor results. Therefore, this paper carries out research to provide a basis for effective plug removal in oil wells, to improve the productivity of polymer flooding oil wells. In this paper, the component analysis of the plug samples from the benefit injection wells in the field was carried out. The clogging mechanism was studied through X-ray diffraction, scanning electron microscopy, energy spectrum analysis, infrared spectroscopy, and chromatography, as well as through dynamic simulation evaluation of plugs and dynamic displacement experiments of long cores. Through simulation experiments, the clogging mechanism is clarified and the blockage radius range was obtained by various methods such as inverse effect of comprehensive measures, well test interpretation, and empirical formula calculation. The analysis results of the plugs show that the inorganic components of the plugs are calcium and magnesium carbonate scales, clay minerals and iron salt precipitation, and the organic components are the micelles formed by the crosslinking of trivalent metal ions. The greater the concentration of polymer produced, the greater the strength of calcium-magnesium scale aggregates and aluminum-iron-colloid elastomer, the greater the degree and depth of reservoir pore throat clogging, the larger the screen clogging area, which will even block the inlet of electric submersible pump. This will result in poor acidizing plugging effect and rapid decline in oil well productivity. Through various methods such as the inverse effect of comprehensive measures, well test interpretation, and empirical formula calculation, the blockage radius of polymer flooding response wells is greater than 4 meters. Based on this understanding, in the five wells plug removal measures, the unblocking radius and unblocking chemical agent system were adjusted and optimized. On-site application effect tracking shows that the plug removal measures have achieved good oil incremental effects, and the measures are all effective. Through the classification and comparison of oil well productivity characteristics, formation water composition, output polymer properties and other characteristics, this paper established the identification mark of plugging of polymer-response wells. In addition, an analysis method for clogging was established to clarify the composition and formation mechanism of the clogging. Finally, the plug radius calculation method was established by means of backstepping the effects of plug removal measures and well test interpretation analysis.

Hybrid white light emitting diodes (LEDs) have been developed utilizing micro-LEDs radiatively pumping down-conversion phosphor materials. The cyan InGaN/GaN multiple quantum wells LEDs with 95 μm in square are fabricated into 4 × 4 pixels as one unit in 4 in wafer by photolithography and inductively coupled plasma etching techniques. The relatively low turn on voltage and low leakage of cyan micro-LEDs indicate good electrical performance. A significant reduction in the efficiency droop characteristics of cyan micro-LED has been observed in comparison with that of standard green LED. Finally, based on a systemic optimization for white emission indexes, high-quality hybrid white light emission has been demonstrated by the combination of blue and cyan micro-LEDs with two types of phosphors, which have a high color rendering index up to 87 at the correlated color temperatures of 6500 K. It also demonstrates a way to adjust the color component by modifying the output power of cyan micro-LED in hybrid LED, showing a promising candidate in a large range of applications including micro-displays, bioinstrumentation, photolithography, and lab-on-chip systems in the future.

We investigate the electrical and optical properties of graphene–Ag nanodot compounds as transparent conductive layers (TCLs) for gallium nitride (GaN)-based ultraviolet light-emitting diodes (UV-LEDs) with different Ag thicknesses. As the thickness of Ag increases from 2 to 5 nm on the 365-nm UV-LEDs, the transmittance decreases from 82.5% to 65.2% and ohmic contact resistance decreases from 0.2 to ${1.3}{\times} {10}^{-5} \Omega \text {cm}^{2}$ . At a wavelength of about 320 nm, the TCLs exhibit high transparency, which is also confirmed by the simulation data of the finite-difference time-domain solution. The simulation and experimental results suggest that Ag with a thickness of 5 nm can potentially obtain both low ohmic contact resistance and high transmittance at the wavelength of about 320 nm, which is important for medical applications. We also study the nanodot migration and coalescence mechanism of 2- and 5-nm Ag samples by scanning electron microscopy, as well as the influence of the existence of graphene. The 5-nm Ag sample has smaller and denser Ag nanodots and thus exhibits better electrical properties. In addition, the Ag nanodots after the second annealing procedure with graphene covering are larger than those without graphene covering.

Junction temperature (Tj) and current have important effects on light-emitting diode (LED) properties. Therefore, the electroluminescence (EL) spectra of blue and green LEDs were investigated in a Tj range of 120&ndash, 373 K and in a current range of 80&ndash, 240 mA based on accurate real-time measurements of Tj using an LED with a built-in sensor unit. Two maxima of the emission peak energy with changing Tj were observed for the green LED, while the blue LED showed one maximum. This was explained by the transition between the donor-bound excitons (DX) and free excitons A (FXA) in the green LED. At low temperatures, the emission peak energy, full width at half maximum (FWHM), and radiation power of the green LED increase rapidly with increasing current, while those of the blue LED increase slightly. This is because when the strong spatial potential fluctuation and low exciton mobility in the green LED is exhibited, with the current increasing, more bonded excitons are found in different potential valleys. With a shallower potential valley and higher exciton mobility, excitons are mostly bound around the potential minima. The higher threshold voltage of the LEDs at low temperatures may be due to the combined effects of the band gap, dynamic resistance, piezoelectric polarization, and electron-blocking layer (EBL).

This paper investigates the problem of position tracking control for a medium density fiberboard (MDF) continuous hot pressing electro-hydraulic servo system (EHSS). A novel adaptive neural output feedback control scheme is proposed that seeks to achieve high-precision tracking control with guaranteed transient performance, in the presence of unmeasured states, unknown nonlinearities, and external disturbance. Specifically, in the proposed control framework, a reduced-order observer (ROO) is first designed to estimate the unmeasured system states. Subsequently, an adaptive controller is constructively synthesized by incorporating the designed ROO into dynamic surface control design. It is shown that the derived controller can enable the tracking error to converge to a preset arbitrarily small residual set with prescribed convergence rate and maximum overshoot. Finally, simulation results are given to verify the effectiveness of the developed approach.

Recently, the emerging inorganic perovskites CsPbX 3 (X = Br, I) have received great attention in the photovoltaic community due to their excellent photoelectric property and good thermal stability. However, most of the reported CsPbX 3 films are fabricated by the uncontrolled solution method, and it is challenging to generate pinhole-free Br-rich films due to the over-rapid liquid-phase reaction feature and the solubility limitation of bromide. Herein, we develop a sequential chemical vapor deposition (CVD) method to fabricate colorful, band-gap tunable, and stable CsPb(I x Br 1-x ) 3 films. First, air-stable CsPbBr 3 precursor films are fabricated via a Br 2 -assisted CVD process. Second, a series of CsPb(I x Br 1-x ) 3 (x = 0, 0.2, 0.33, 0.5, 0.67, 0.8, 1) high-quality films with consistent compositions are then obtained by another MAI/MABr-assisted CVD process. Experimental results show that all of the CsPb(I x Br 1-x ) 3 films have the same cubic structure and (100) preferred orientation. With the increase of MAI component, the colors of films darken gradually, the main diffraction peaks at (100) and (200) planes shift to small angle, their optical bandgaps monotonously decrease from 2.34 eV to 1.67 eV, the grains of films grow up, and the porous films become more compact. Strikingly, it is found that CsPb(I x Br 1-x ) 3 films become very stable in air ambient when x is less or equal to 0.5. Therefore, we first employ a cost-effective CVD technology to modulate the anion compositions of CsPbX 3 inorganic perovskite films, which shows a high potential for the photovoltaic applications such as highly efficient tandem perovskite solar cells (PSCs) and colorful smart photovoltaic windows.

Nowadays, inorganic perovskites such as CsPbI3 and CsPbBr3 with excellent photoelectric property and superior thermal stability have triggered strong interest in the photovoltaic community. However, all of the inorganic perovskite absorbers reported in literatures are fabricated by the complicated solution process. Meanwhile, CsPbI3 exists serious structural phase-transition; while stable CsPbBr3 suffers solubility limitation of bromide in conventional solution route. Herein, we develop a smart Br2-vapor-assisted chemical vapor deposition (CVD) method to realize the fast anion-exchange from CsPbI3 to CsPbBr3. With the substitution of small Br− anions, the undesirable phase-transition of CsPbI3 is heavily restrained and its structural stability is tremendously enhanced; and thus here we open a new avenue to solve the solubility issue of bromide. Consequently, CsPbBr3 all-inorganic perovskite solar cells (PSCs) with Carbon top electrode are first achieved by cost-effective CVD technology, showing a relatively high power conversion efficiency (PCE) of 5.38%. The charge transport mechanism of CsPbBr3 PSCs is correspondingly elucidated in-depth. We find that the interface of TiO2 and CsPbBr3 might be the root cause of hysteresis phenomenon, while another interface between Carbon and CsPbBr3 is not a rectifying contact but only increases the ohmic resistance of electrode. Moreover, our PSCs demonstrate a good long-term stability and give ∼90% of initial efficiencies after exposure to air for 21 days.

This paper presents a novel nonlinear control approach for medium-density fiberboard continuous hot pressing electro-hydraulic servo system (EHSS). The EHSS is subject to input saturation and unknown external disturbance. The approach is developed in the framework of the prescribed performance control design. The transient and steady behaviors are both considered by virtue of an appropriate performance function. A new robust adaptive neural control algorithm is then developed by introducing a dynamic surface control scheme. Moreover, the compensation control is designed for the nonlinear term arising from the input saturation. It is shown with the Lyapunov stability analysis that all the signals in the closed-loop system are semi-globally uniformly ultimately bounded. In addition, the system tracking performance regarding transient and steady-state behaviors is guaranteed effectively with input saturation via the designed control approach. Finally, numerical simulation results are presented to authenticate and validate the effectiveness of the proposed control scheme.

Over the past few years, significant attention has been focused on HC(NH2)2PbI3 (FAPbI3) perovskite due to its reduced band gap and enhanced thermal stability compared with the most studied CH3NH3PbI3 (MAPbI3). However, FAPbI3 is sensitive to moisture and also encounters a serious structural phase-transition from photoactive α-phase to photoinactive δ-phase. Herein, we first develop a novel FAI gas-phase-assisted mixed-cation compositional modulation method to fabricate CsxFA1–xPbI3 perovskite solar cells (PSCs), and realize the structural stabilization of α-phase FAPbI3 with the incorporation of smaller inorganic Cs+ ions. Through the setting of different Cs+ contents (x = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.50) along with a moderate FAI vapor deposition process, a series of CsxFA1–xPbI3 films with consistent compositions are fabricated, which perfectly resolves the main blocking problems of the conventional solution approach, such as difficulty in compositional control and rough film morphology. Me...

This study developed an LED thermal resistance and thermal interface material evaluation method using LEDs with an internal sensor unit by both steady-state and transient thermal measurements. The problem of the measurement delay time caused by the current switching, which exist in conventional methods can be avoided in both steady-state and transient thermal measurements. Slight error in junction temperature measurement caused by the self-illumination effect can be identified without the current switching issue. The error is compensated in steady-state thermal measurement and is insignificant in transient measurement. Compared with conventional methods, this method uses low-cost equipment, while realizing improved accuracy.

Highly efficient lead halide perovskites with tunable emission performance have become new candidate materials for light‐emitting devices and displays; however, the toxicity of lead and instability of halide perovskites greatly limits their application. Herein, rapid and large‐scale synthesis of highly emissive organic–inorganic manganese halide perovskites, (C5H6N)2MnBr4 and C5H6NMnCl3, are presented by a one‐pot solution‐based method, of which (C5H6N)2MnBr4 displays a high absolute photoluminescence quantum yield (95%) in the solid‐state. The developed (C5H6N)2MnBr4 perovskite noticeably exhibits high stability. Therefore both as‐synthesized green and red emissive manganese‐based phosphors with superior optical properties are used to fabricate blue light pumped white light‐emitting diodes (WLEDs), displaying excellent quality white light with a high color rendering index value of 91 and a correlated color temperature of 5331 K. This study not only presents the robust large‐scale production synthetic approach for organic–inorganic manganese halide perovskites, but also facilitates the development of high‐performance phosphors for future lighting and display technologies.

GaN pyramid arrays have been successfully synthesized by selective photo-assisted chemical etching in a K2S2O8/KOH solution. A detailed analysis of time evolution of surface morphology has been conducted, which describes an etching process of GaN pyramids. Room temperature cathodoluminescence images indicate that these pyramids are composed of crystalline GaN surrounding dislocations, which is caused by the greater recombination rate of electrons and holes at dislocation than that of crystalline GaN. The Raman results show a stress relaxation in GaN pyramids compared with unetched GaN. The optical property of both unetched GaN and GaN pyramids has been studied by photoluminescence. The formation mechanism and feature of GaN pyramids are also rationally explained.

The InGaN/GaN multiple quantum wells (MQWs) with truncated pyramid structure have been successfully epitaxially grown on the GaN hexagonal pyramids template through a simple and low-cost etch-regrown process. GaN hexagonal pyramids template was contained by a convenient photo-assisted chemical (PAC) etching method. The truncated pyramids are composed of { 10 1 ¯ 1 ¯ } and { 11 2 ¯ 2 } semi-polar facets as well as (0001) polar facet. It was observed that the InGaN/GaN MQWs substantially emitted broad spectrum with multiple peaks by room temperature photoluminescence (PL). The cathodoluminescence of MQWs red-shifts as the location moves from bottom to top on the facets due to the indium diffusion mechanism.

The formation sands of natural gas hydrate (NGH) reservoirs in the South China Sea are fine silty sands with a high content of clay, and it is difficult to be controlled effectively. We carried out a series of experiments to investigate the microcosmic retaining and plugging behavior of screen media with highly argillaceous fine sand samples, with median size of 10.13 μm. The screen sand-retention media and joint involved four types with slot width or accuracy of 20–60 μm. The screen media/joint sample was placed in the linear/radial flowing apparatus, and then the mixture of gas, water and sand were displaced flowing into the media to simulate the sand retaining process. The Microscopic imaging system was used to visually observe the dynamics of sand particle deposition and plugging inside the media as well as on its surface. The plugging permeability and the amount of the passed sand were also analyzed. According to the result, three microcosmic mechanisms of sand retaining and plugging were proposed, concerning fine sand invading and coarse sand bridge, partial sand block, and integrated sand bridge. The plugging permeability performance of screen media generally shows three stages of slow decreasing, rapid increasing and balance. At the balance stage of displacement, the plugging permeability of media sample mostly decreases more than 90%. During the whole test, the sand passing rate tends to slow down gradually, and the final retained sand ratio were more than 85%. Different configurations of sand retraining test show a little difference in plugging performance, depending on the factors of medium type, accuracy, sand characteristics, and flow conditions. Based on the effect of sand retaining and final flow ability observed in these experiments, the sand control in NGH reservoirs with highly argillaceous fine sands is practicable.

Hybrid white micro-pillar structure light emitting diodes (LEDs) have been manufacture utilizing blue micro-LEDs arrays integrated with 580 nm CIS ((CuInS2-ZnS)/ZnS) core/shell quantum dots. The fabricated hybrid white micro-LEDs have good electrical properties, which are manifested in relatively low turn-on voltage and reverse leakage current. High-quality hybrid white light emission has been demonstrated by the hybrid white micro-LEDs after a systemic optimization, in which the corresponding color coordinates are calculated to be (0.3303, 0.3501) and the calculated color temperature is 5596 K. This result indicates an effective way to achieve high-performance white LEDs and shows great promise in a large range of applications in the future including micro-displays, bioinstrumentation and visible light communication.

In order to guarantee slab thickness precision of medium density fiberboard (MDF), the continuous hot-pressing process based on intelligent dynamic surface control (DSC) was investigated. Firstly, a mathematic model for hydraulic servo system of the continuous hot-pressing machine was proposed. Due to the uncertain function in the model, a fuzzy logic system was introduced to approximate it. Subsequently, a slab thickness tracking controller with less complexity was developed with the help of the DSC approach. Simultaneously, an on-line adaptive law was applied to estimate the adjustable parameter vector in the fuzzy system. Finally, experimental results validated that the proposed method can ensure the MDF slab thickness precision in the hot-pressing process.

We numerically investigated the optical/electrical characteristics of blue light-emitting-diodes (LEDs) and developed some optimization strategies. Our aim is to increase the optical performance of LEDs at low current density (0.02–2 A cm−2) for micro-LEDs used in display applications. First, we investigated the effects of quantum well (QW) number in blue In0.225Ga0.775N/In0.10Ga0.90N LEDs. We found that at low current density LEDs with lower QW number have much higher internal quantum efficiency (IQE) than those with higher QW number. Second, we also numerically investigated the effects of the electron blocking layer, n-side quantum barrier (QB) doping concentration, QB material and QW width with single quantum well (SQW) structure. For SQW LEDs at low current density, the electron injection efficiency was nearly one. In terms of the QB doping concentration, we found that an appropriate n-side QB doping can ensure Shockley-Read-Hall recombination appropriately equal Auger recombination, which ultimately results in high IQE. For QB material, we choose In0.05Ga0.95N as QB material to achieve both high IQE and low forward voltage. Regarding the QW width, we found that although LEDs with wide QW had high IQE, there were also two peaks in the electroluminescence (EL) spectrum, thus 3 nm was used as an optimal QW width. The original 5-QW structure showed a lower IQE range from 50 to 80% at the current density range from 0.01 to 2 A cm−2 and a forward voltage of 3.06 V at 1 A cm−2. In contrast, our optimized LED structure achieved an IQE of 92.3% at the current density range from 0.01 to 2 A cm−2 and a forward voltage of 2.72 V at 1 A/cm2.

Over the past few years, significant attention has been focused on HC(NH

GaN-based micro light emitting diodes (micro-LEDs) on silicon (Si) substrates with 40 μm in diameter are developed utilizing standard photolithography and inductively coupled plasma etching techniques. From current-voltage curves, the relatively low turn-on voltage of 2.8 V and low reverse leakage current in the order of 10 −8 A/cm 2 indicate good electrical characteristics. As the injection current increases, the electroluminescence emission wavelength hardly shifts at around 433 nm, and the relative external quantum efficiency slightly decays, because the impact of quantum-confined Stark effect is not serious in violet-blue micro-LEDs. Since GaN-LEDs are cost effective on large-area Si and suitable for substrate transfer or vertical device structures, the fabricated micro-LEDs on Si should have promising applications in the fields of high-resolution display and optical communication.

The performance of GaN based devices could possibly be improved by utilizing the good p-type properties of GaP layer and it provides the possibility of the integration of InAlGaN and AlGaInP materials to produce new devices, if high quality GaP compounds can be grown on III-nitride compounds. In this paper, the growth of GaP layers on GaN by metalorganic chemical vapor deposition (MOCVD) has been investigated. The results show that the GaP low temperature buffer layer can provide a high density of nucleation sites for high temperature GaP growth. Using a 40 nm thick GaP buffer layer, a single crystal GaP layer, whose full-width at half-maximum of the (1 1 1) plane measured by double crystal X-ray diffraction is 580″, can be grown on GaN. The V/III ratio plays an important role in the GaP layer growth and an appropriate V/III ratio can improve the quality of GaP layer. The GaP:Mg layer with hole carrier concentration of 4.2 × 10 18 cm −3 has been obtained.