III-Nitride Quantum Devices—Microphotonics

Photonic devices based on III-nitrides offer benefits such as UV/blue emission, large band offsets of InN/GaN/AlN heterostructures allowing novel quantum well (QW) device design, and inherently high-emission efficiencies. Furthermore, due to their mechanical hardness and larger band gaps (when compared with conventional semiconductor devices), III-nitride-based devices may operate at much higher temperatures and voltages/power levels for any dimensional configuration and in harsher environments than other semiconductor devices and are expected to provide much lower temperature sensitivities. These are crucial advantages for many applications. Over the last decade, the physics of microsize photonic devices has been investigated. New physical phenomena and properties are expected to dominate as the device size scales down. The microsize light emitters offer benefits over edge emitters such as the ability to create arrays of individually controllable pixels on a single chip, enhanced quantum efficiency, and greatly reduced lasing threshold. Rapid progress in the area of III-nitride microphotonics has been made. The growth and fabrication of micron and submicron size photonic structures based on III-nitride wide bandgap semiconductors has been achieved, and the technology has made it possible to integrate arrays of optical elements to form active photonic-integrated devices. One example is an interconnected µ-LED with enhanced emission efficiency over the conventional LEDs for the same device area. Another example is a µ-LED array with independently addressed pixels or III-nitride microdisplay. III-nitride microdisplay may offer performance that is superior to microdisplays fabricated from liquid crystals and organic LEDs. The third example presented is III-nitride UV Focal Plane Arrays (UV-FPA) of detectors. So far, the operation of AlGaN UV-FPA with size up to 256×256 pixels with 30×30?μm² unit cells has been demonstrated. Together with the nature of their two-dimensional array, these active micro-photonic devices show promise in many important applications, such as optical communications, signal and image processing, optical interconnects, computing, enhanced energy conversion and storage, chemical, biohazard substances, and disease detection, missile and shellfire, atmospheric ozone-level, and flame sensing. III-nitride microlens arrays have been fabricated successfully for blue and UV wavelength applications on GaN and AlN. The successful fabrication of microlens arrays based on III-nitride materials opens the possibility for monolithically integrating nitride-based micro-size photonic devices, as well as coupling light into, out of, and between arrays of III-nitride emitters and detectors, especially for short wavelengths covering the green-blue to deep UV (200?nm) region. Nanofabrication and characterization of photonic crystals with diameter/periodicity as small as 100/180?nm on InGaN/GaN MQW has been achieved. An unprecedented maximum enhancement factor of 20 was obtained under optical pumping. Single-mode ridged optical waveguide devices using GaN/AlGaN heterostructures have been designed, fabricated, and characterized for operation in 1550?nm wavelength window. The feasibility of developing novel photonic integrated circuits based on III-nitride wide bandgap semiconductors for fiber-optical communications has been investigated.     

One-step hydrothermal synthesis of feather duster-like NiS@MoS<Subscript>2</Subscript> with hierarchical array structure for the Pt-free dye-sensitized solar cell

Novel feather duster-like nickel sulfide (NiS) @ molybdenum sulfide (MoS₂) with hierarchical array structure is synthesized via a simple one-step hydrothermal method, in which a major structure of rod-like NiS in the center and a secondary structure of MoS₂ nanosheets with a thickness of about 15–55 nm on the surface. The feather duster-like NiS@MoS₂ is employed as the counter electrode (CE) material for the dye-sensitized solar cell (DSSC), which exhibits superior electrocatalytic activity due to its feather duster-like hierarchical array structure can not only support the fast electron transfer and electrolyte diffusion channels, but also can provide high specific surface area (238.19 m² g^?1) with abundant active catalytic sites and large electron injection efficiency from CE to electrolyte. The DSSC based on the NiS@MoS₂ CE achieves a competitive photoelectric conversion efficiency of 8.58%, which is higher than that of the NiS (7.13%), MoS₂ (7.33%), and Pt (8.16%) CEs under the same conditions.

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Graphical abstract Novel feather duster-like NiS@MoS₂ hierarchical structure array with superior electrocatalytic activity was fabricated by a simple one-step hydrothermal method.

     

Sequence influence of nonidentical InGaAsP quantum wells on broadband characteristics of semiconductor optical amplifiers--superluminescent diodes

Extremely broadband emission is obtained from semiconductor optical amplifiers-superluminescent diodes with nonidentical quantum wells made of InGaAsP/InP materials. The well sequence is experimentally shown to have a significant influence on the emission spectra. With the three In(0.67) Ga(0.33) As(0.72) P(0.28) quantum wells near the n -cladding layer and the two In(0.53) Ga(0.47) As quantum wells near the p -cladding layer, all bounded by In(0.86) Ga(0.14) As(0.3)P(0.7) barriers, the emission spectrum could cover from less than 1.3 to nearly 1.55 microm, and the FWHM could be near 300 nm.     

EFFECT OF FLAME SUPPORT LAYER GEOMETRY AND MATERIALS ON THE RADIANT EFFICIENCY OF GAS RADIANT BURNERS

Parallel rods / tubes flame support layers were used to study variations in geometry and materials on radiant burner performance. An increased density of rods increased the efficiency, as more surface area was provided to extract the heat of combustion. This effect was attenuated far fraction closed areas above 0·33 because of increased interference of direct base-to-load radiation. Thinner rods (with fraction closed area constant), having a lower thermal conduction resistance, fostered higher efficiency. Greater distances between the base and rods decreased efficiency due to air entrainment. This functioned to cool the base, increasing the range of combustion intensities where a portion of combustion lifted from the burner base. Isolation of radiating materials from conducting to the burner housing resulted in a ～ 5% upward shift in efficiency. Low to high efficiency was measured for alumina, mullite, and oxidized stainless steel rods, respectively; this was related directly to the emittances of the materials used. SiC and MoSi₂ coatings on alumina rods resulted in burners which were as efficient as one with stainless steel rods. A burner designed as a restricted band spectral emitter was not as efficient in its high-emission range as a more graybody emitter under the same combustion intensity; the higher-temperature spectral emitter discouraged extraction of sensible heat from the combustion product stream.     

基于光谱法舌诊的脂肪肝快速诊断

提出了一种基于光谱技术的脂肪肝无创、快速诊断新方法。由于舌体能较客观的反映人体生理、病理变化,因此采集志愿者舌体舌尖部位的反射光谱,然后对数据进行分析,计算反射光谱的归一化反射率。建立3层BP网络模型,从采集来的115例样本中抽取32例健康人和44例脂肪肝患者的光谱归一化反射率作为神经网络的输入,再对未知的14例健康人样本和25例脂肪肝患者样本进行分类预测,分类正确率达到89.7%,实验结果表明了光谱法运用于脂肪肝快速无创诊断的可行性。同时,实验结果说明光谱法能更客观全面地反映人舌所携带的组织细胞、微循环等方面的信息,有可能为临床提供一种快速、简便的诊断手段,也为今后的中医证侯的度量提供借鉴。     

Organizing C60 molecules on a nanostructured Au(111) surface

We have studied, using scanning tunneling microscopy, the adsorption of C₆₀ molecules on a nanostructured Au(111) surface consisting of artificially created two-dimensional cavities. These cavities, one atomic layer deep, are found to be effective as molecular traps at room temperature. Gold atoms at step edges are found to respond to the adsorption of C₆₀ molecules and gross faceting is observed for steps connected with R30° oriented C₆₀ molecular islands. Structural models are proposed to establish the step structures related to all three types of molecular islands.     

Variational multiscale element-free Galerkin method for 2D Burgers’ equation

A new numerical method, which is based on the coupling between variational multiscale method and meshfree methods, is developed for 2D Burgers’ equation with various values of Re. The proposed method takes full advantage of meshfree methods, therefore, no mesh generation and mesh recreation are involved. Meanwhile, compared with the variational multiscale finite element method, a strong assumption, that is, the fine scale vanishes identically over the element boundaries although non-zero within the elements, is not needed. Subsequently two problems which have an available analytical solution of their own are solved to analyze the convergence behaviour of the proposed method. Finally a 2D Burgers’ equation having large Re is solved and the results have also been compared with the ones computed by two other methods. The numerical results show that the proposed method can indeed obtain accurate numerical results for 2D Burgers’ equation having large Re, which does not refer to the choice of a proper stabilization parameter.     

Picosecond laser oscillator with a cavity design for stable CW mode-locking operation

A detailed design of a picosecond laser oscillator is made by using optical resonance theory and semiconductor saturable absorber mirror continuous wave mode-locked technology. Mode parameters in the optical resonance including beam sizes on the laser crystal and mode locker are calculated. By theoretical calculations, 3.7 W output power is obtained at a pump power of 11 W and the optical to optical efficiency is 34% in the designed model of picosecond laser. Based on the detailed design, an experiment is proceeded and a picosecond laser oscillator of about 3.5 W output power with 10.6 W pump power is fabricated. The optical to optical efficiency of the laser is 33%, the pulse duration is about 20 ps, and the repetition rate is about 80.3 MHz. The oscillator presents long-term stability in the experiment.     

Observation of B(s)(0) → D(s)(*)+ D(s)(*)- using e+ e- collisions and a determination of the B(s)-B(s) width difference ΔΓ(s)

We have made the first observation of B(s)(0)→D(s)(*)+ D(s)(*)- decays using 23.6 fb(-1) of data recorded by the Belle experiment running on the Υ(5S) resonance. The branching fractions are measured to be B(B(s)(0)→D(s)+ D(s)-)=(1.03(-0.32-0.25)(+0.39+0.26))%, B(B(s)(0)→D(s)(*±) D(s)(?))=(2.75(-0.71)(+0.83)±0.69)%, and B(B(s)(0)→D(s)*+ D(s)*-)=(3.08(-1.04-0.86)(+1.22+0.85))%; the sum is B[B(s)(0)→D(s)(*)+ D(s)(*)-]=(6.85(-1.30-1.80)(+1.53+1.79))%. Assuming B(s)(0)→D(s)(*)+ D(s)(*)- saturates decays to CP-even final states, the branching fraction determines the ratio ΔΓ(s)/cosφ, where ΔΓ(s) is the difference in widths between the two B(s)-B(s) mass eigenstates, and φ is a CP-violating weak phase. Taking CP violation to be negligibly small, we obtain ΔΓ(s)/Γ(s)=0.147(-0.030)(+0.036)(stat)(-0.041)(+0.042)(syst), where Γ(s) is the mean decay width.     

Sono-assisted preparation of highly-efficient peroxidase-like Fe3O4 magnetic nanoparticles for catalytic removal of organic pollutants with H2O2

Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) with much improved peroxidase-like activity were successfully prepared through an advanced reverse co-precipitation method under the assistance of ultrasound irradiation. The characterizations with XRD, BET and SEM indicated that the ultrasound irradiation in the preparation induced the production of Fe₃O₄ MNPs possessing smaller particle sizes (16.5 nm), greater BET surface area (82.5 m² g^?1) and much higher dispersibility in water. The particle sizes, BET surface area, chemical composition and then catalytic property of the Fe₃O₄ MNPs could be tailored by adjusting the initial concentration of ammonia water and the molar ratio of Fe²⁺/Fe³⁺ during the preparation process. The H₂O₂-activating ability of Fe₃O₄ MNPs was evaluated by using Rhodamine B (RhB) as a model compound of organic pollutants to be degraded. At pH 5.4 and temperature 40 °C, the sonochemically synthesized Fe₃O₄ MNPs were observed to be able to activate H₂O₂ and remove ca. 90% of RhB (0.02 mmol L^?1) in 60 min with a apparent rate constant of 0.034 min^?1 for the RhB degradation, being 12.6 folds of that (0.0027 min^?1) over the Fe₃O₄ MNPs prepared via a conventional reverse co-precipitation method. The mechanisms of the peroxidase-like catalysis with Fe₃O₄ MNPs were discussed to develop more efficient novel catalysts.