GaN‐based top‐emitting micro‐blue‐light‐emitting diode chips with different current spreading layers (CSLs) and different sizes are fabricated, analyzed at different ambient temperatures, and their ...performances are compared. The observed behaviors are attributed mainly to the thermal effects, determined by the ambient temperature and internal heat from the injected current. For any chip size and ambient temperature, an indium tin oxide (ITO) CSL induces higher light‐output power (LOP) and external quantum efficiency (EQE), making it the better choice in illumination scenarios; a Ni/Au CSL leads to a smaller amount of internal heat and can sustain a higher saturation current density, making it preferred in high‐bandwidth visible‐light communication systems. Moreover, if the ITO CSL is replaced by the Ni/Au CSL, owing to the faster decrease in the internal heat, the temperature stabilities of the LOP, EQE, and equilibrium point of the peak wavelength can be improved. In addition, the size effects are discussed based on the internal heat.
GaN‐based top‐emitting micro‐blue‐light‐emitting diode chips with different current spreading layers (CSLs) and different sizes are fabricated. The thermal effects, determined by the ambient temperature and internal heat from the injected current, on the electrical and optical characteristics are analyzed. The indium tin oxide CSL is suggested in illumination scenarios, while the Ni/Au CSL is preferred in high‐bandwidth visible‐light communication systems.
The GaN-based white light-emitting diode (LED), in which 4
×
4 arrayed micro-pixels are packaged using chip-on-board technique, is fabricated for both illumination and visible light communication. ...The features of the electrical, optical, and communication characteristics related to the injected current are analysed. It is implied that the saturated injected current could be the optimised injected current for both illumination and communication, if the highest light-output power (LOP) and the largest 3-dB modulation bandwidth are desired. However, in order to improve the electro-optic conversion efficiency (EOC) and the lifetime for practical devices, the huge current density should be avoided and a small injected current should be better. In our experiments, if the injected current is reduced from the saturated injected current of 130 mA (4597.8 A/
cm
2
) to 20 mA (707.4 A/
cm
2
), the EOC and the lifetime of 95% LOP are improved from 3.1 to 11.4% and extended from 16.5 to 1560 h, respectively, while the total LOP of arrayed pixels and the 3-dB modulation bandwidth are still good values. The characteristics before and after the ageing process with different injected current are also discussed. It is shown that the ageing process has permanent degradation of the electrical and optical performance but has little effects on the modulation bandwidth of the 60-μm-diameter micro-LEDs in the experiments. Moreover, the small injected current leads to minimal degradation and would be the preferred choice.
In this work, anodic aluminum oxide (AAO) over Al mesh was fabricated as a support for monolithic catalyst for ozone decomposition. AAO with the pore sizes of about 9–38 nm could be obtained by ...increasing the voltage from 20 to 40 V. A mechanism was proposed to address the formation of AAO over Al mesh. Different with the case over Al plate, the key of the formation of porous AAO over Al mesh is to seal the edges of the Al mesh immersed in the electrolyte to keep the conductivity of the interlaced Al wires. Mn–Co nanospheres with the size of about 80 nm were decorated on AAO through a simple dip-coating process. The obtained material then was used as monolithic catalyst for ozone decomposition. It was found out that the developed material showed much better activity than Mn–Co composite decorated on Al mesh only, which is possibly due to the combination of the adsorption ability of AAO and the catalytic property of Mn–Co composite.
Controlling the size and uniform dispersion of noble metal nanoclusters on the metal oxide based semiconductor are difficult due to the natural tendency for metal atoms to agglomerate. Here, we ...present the protocol for an “irradiation-dark” photochemical deposition to obtain uniform metal nanoclusters on semiconductor support, and the protocol for measuring the size and size distribution of metal nanoclusters.
For complete details on the use and execution of this protocol, please refer to Wu et al. (2022).
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•Detailed protocol for the“irradiation-dark” photochemical deposition•Optimized approach for high loading amount•Characterization protocol of the size and size distribution of metal nanoclusters
Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.
Controlling the size and uniform dispersion of noble metal nanoclusters on the metal oxide based semiconductor are difficult due to the natural tendency for metal atoms to agglomerate. Here, we present the protocol for an “irradiation-dark” photochemical deposition to obtain uniform metal nanoclusters on semiconductor support, λ and the protocol for measuring the size and size distribution of metal nanoclusters. For complete details on the use and execution of this protocol, please refer to (Wu et al., 2022).
Green resonant-cavity light-emitting diode (RCLED) has great potential in optical communication but suffers low efficiency. In this study, GaN-based flip-chip green RCLED incorporated with nitrogen ...face-oriented inclination asymmetric trapezoidal quantum wells (NOAT-QWs) is proposed to enhance the light-output power (LOP). Samples with NOAT-QWs and normal symmetric square quantum wells (SS-QWs) were fabricated and characterized. Although their electrical characteristics and emission spectra are similar, the LOP and emission efficiency are significantly improved. At a driving current of 450 mA, the improvement of LOP for RCLED with NOAT-QWs can be as high as 1.44 times in comparison to the sample with SS-QWs. The unprecedented high output power of 115 mW and the narrow full-width-at-half-maximum (FWHM) of 6.4 nm in the emission spectrum give great potential in optical communication. The inherent mechanism was investigated by the finite element analysis, from which the simulation results match well with the experimental measurements. The simulation results reveal that the NOAT-QWs are beneficial in alleviating the quantum confined stark effect and facilitating easier hole carriers' flow across the barriers, leading to more electron-hole wave function overlaps and higher radiative recombination rate.
The equalization circuit in the visible light communication (VLC) system has large impacts on the frequency response and can greatly improve the 3-dB modulation bandwidth. The optimization of the ...two-stage common-emitter transistor amplifier for equalization circuit is presented in detail and the design rules are disclosed. At first, the frequency response of the single-stage amplifier is derived and the simulated characteristic curves illustrated the changing regularity of four main factors are given. Subsequently, the frequency response of the two-stage amplifier is investigated by simulation. It is shown that the capacitors in the resistance–capacitance (RC) network has large impacts on the low-frequency range, while the resistors in the RC network can adjust the high-frequency, and the resistors in the emitter can adjust the low-frequency. Experimental measurements of the fabricated equalization circuit demonstrated the simulation results. Then, the two-stage amplifier is induced as post-equalization circuit (post-EQC) or pre-equalization circuit (pre-EQC) and the measured frequency response curves are given. The equalization circuit with proper sets of capacitors and resistors would flatten the frequency response curve of the VLC system. It is shown that the 3-dB modulation bandwidth of the VLC system equipped with post-EQC or pre-EQC can be expanded to 292 MHz or 304 MHz, respectively. Moreover, if the photoelectric receiver and the post-EQC are combined in the optimization, the 3-dB modulation bandwidth can be expanded to 375 MHz.
Noble metal nanoclusters/oxides have been attracting close attention in heterogeneous catalysis due to their unique physical and chemical properties. However, due to the effect of the Schottky ...heterojunction, the deposited particles are easy to aggregate, and the size is difficult to control. In this work, we report a surface-confined photodeposition process to load ultrafine noble nanoclusters on semiconductor oxides, e.g., titanium oxide (TiO2), in a fluidized bed (F method). Different from the traditional photodeposition in solution (L method), the metal precursors which are absorbed on the semiconductor are difficult to migrate via the F method, therefore effectively inhibiting the agglomeration of nanoparticles. Noble metal nanoclusters with a uniform size smaller than 2 nm are obtained. In the model reaction of the catalytic oxidation of formaldehyde (HCHO), Pt/TiO2 with an ultralow loading amount (0.08 wt% Pt) showed excellent performance for the catalytic oxidation of HCHO at room temperature, which is benefited from the small and uniform size of nanoclusters. This work brings an effective strategy in the fabrication of size-controlled noble metals on oxide supports for heterogeneous catalysis.
Light‐Emitting Diodes
The GaN‐based blue‐light‐emitting diodes (LED) chips with 4 × 4 arrayed pixels are fabricated and packaged by chip‐on‐board (COB) technique and welded on printed circuit board ...(PCB) as white‐LED modules. The size of the mesa and the electrodes are carefully selected to get a compromise between the luminous flux and the modulation bandwidth for the dual function of illumination and communication. More details can be found in article number 1800484 by Huamao Huang, Hong Wang and co‐workers.
Exploring accurate, noninvasive, and inexpensive disease diagnostic sensors is a critical task in the fields of chemistry, biology, and medicine. The complexity of biological systems and the ...explosive growth of biomarker data have driven machine learning to become a powerful tool for mining and processing big data from disease diagnosis sensors. With the development of bioinformatics and artificial intelligence (AI), machine learning models formed by data mining have been able to guide more sensitive and accurate molecular computing. This review presents an overview of big data collection approaches and fundamental machine learning algorithms and discusses recent advances in machine learning and molecular computational disease diagnostic sensors. More specifically, we highlight existing modular workflows and key opportunities and challenges for machine learning to achieve disease diagnosis through big data mining.
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