Investigation of reflection anisotropy induced by micropipe defects on the surface of a 4H-SiC single crystal using scanning anisotropy microscopy

Optical reflection anisotropy microscopy mappings of micropipe defects on the surface of a 4H-SiC single crystal are studied by the scanning anisotropy microscopy(SAM)system.The reflection anisotropy(RA)image with a'butterfly pattern'is obtained around the micropipes by SAM.The RA image of the edge dislocations is theoretically simulated based on dislocation theory and the photoelastic principle.By comparing with the Raman spectrum,it is verified that the micropipes consist of edge dislocations.The different patterns of the RA images are due to the different orientations of the Burgers vectors.Besides,the strain distribution of the micropipes is also deduced.One can identify the dislocation type,the direction of the Burgers vector and the optical anisotropy from the RA image by using SAM.Therefore,SAM is an ideal tool to measure the optical anisotropy induced by the strain field around a defect.

Phase-locked single-mode terahertz quantum cascade lasers array

We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback(DFB)grating,resulting in nearly five times amplification of the single-mode power.Due to the optimum length of Talbot cavity depends on wavelength,the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry-Perot(F-P)cavities.The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array,enabling phase-locked operation of ridges.We set the spacing between adjacent elements to be 220μm,much larger than the free-space wavelength,ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution.This scheme provides a new approach for enhancing the single-mode power of THz QCLs.

Quantum cascade lasers grown by MOCVD

Sharing the advantages of high optical power,high efficiency and design flexibility in a compact size,quantum cascade lasers(QCLs)are excellent mid-to-far infrared laser sources for gas sensing,infrared spectroscopic,medical diagnosis,and defense applications.Metalorganic chemical vapor deposition(MOCVD)is an important technology for growing high quality semiconductor materials,and has achieved great success in the semiconductor industry due to its advantages of high efficiency,short maintenance cycles,and high stability and repeatability.The utilization of MOCVD for the growth of QCL materials holds a significant meaning for promoting the large batch production and industrial application of QCL devices.This review summarizes the recent progress of QCLs grown by MOCVD.Material quality and the structure design together determine the device performance.Research progress on the performance improvement of MOCVD-grown QCLs based on the optimization of material quality and active region structure are mainly reviewed.

Influence of Frohlich Interaction on Intersubband Transitions of InGaAs/InAlAs-Based Quantum Cascade Detector Structures Investigated by Infrared Modulated Photoluminescence

We demonstrate the use of an infrared modulated photoluminescence(PL)method based on a step-scan Fourier-transform infrared spectrometer to analyze intersubband transition(ISBT)of InGaAs/InAlAs quantum cascade detector(QCD)structures.By configuring oblique and parallel excitation geometries,high signal-to-noise ratio PL spectra in near-to-far-infrared region are measured.With support from numerical calculations based on the k·p perturbation theory,the spectra is attributed to intraband and interband transitions of InGaAs/InAlAs QCD structures.Temperature evolution results show that the k-dependent transitions caused by longitudinal optical phonon-assisted scattering(Frohlich interaction)plays an important role in the ISBT.These results suggest that this infrared modulated-PL method has great potential in characterizing QCD devices and conducting performance diagnostics.

枝链有效聚集诱导型疏水缔合水凝胶的力学性能与溶胀行为

采用"胶束共聚"方法,设计合成一种以丙烯酰胺为亲水单体,"枝链"脂肪醇聚氧乙烯醚丙烯酸酯为疏水单体,十二烷基硫酸钠为表面活性剂共聚的疏水缔合水凝胶。其中长烷基"枝链"通过有效疏水缔合作用构筑内部交联点支撑整个凝胶网络,秉承着内部微观结构制约宏观力学性能,通过微调凝胶内部有效枝链的聚集状态,最终力学性能、溶胀性能等发生一系列变化。具体为通过改变不同配比的表面活性剂和疏水单元深入考察对凝胶内部枝链诱导聚集状态、微观结构以及对拉伸性能、溶胀性能的影响。在探索中发现有趣的规律,即在有效疏水缔合作用最强、最佳时刻、表面活性剂与疏水单体的摩尔比为3,此时凝胶网络的有效聚集最紧密、结构最均匀且强度最高,其形态在水中可维持半年以上,且良好的自愈合性质将拓宽其应用领域。

Maffucci syndrome with unilateral limb: a case report and review of the literature

Maffucci syndrome is a congenital, non-hereditary mesodermal dysplasia manifested by multiple enchondromas and hemangiomas. It is associated with diverse secondary musculoskeletal deformities, which is exceedingly rare. We report a case of hemangiomas and enchondromas localized in the unilateral limb in a patient with Maffucci syndrome. Treatment consists of orthopedic and surgical intervention to minimize deformities and for cosmetic purpose. Careful surveillance for malignant degeneration of both skeletal and non-skeletal tumors, especially in the brain and abdomen, is essential.

High powerλ~8.5μm quantum cascade laser grown by MOCVD operating continuous-wave up to 408 K

Robust quantum cascade laser(QCL)enduring high temperature continuous-wave(CW)operation is of critical importance for some applications.We report on the realization of lattice-matched InGaAs/InAlAs/InP QCL materials grown by metal-organic chemical vapor deposition(MOCVD).High interface quality structures designed for light emission at 8.5μm are achieved by optimizing and precise controlling of growth conditions.A CW output power of 1.04 W at 288 K was obtained from a 4 mm-long and 10μm-wide coated laser.Corresponding maximum wall-plug efficiency and threshold current density were 7.1%and 1.18 kA/cm2,respectively.The device can operate in CW mode up to 408 K with an output power of 160 mW.

Quantum cascade lasers: from sketch to mainstream in the mid and far infrared

Electrically-pumped semiconductor lasers based on monolithic chip configuration possess plenty of advantages such as small volume,light weight,long lifetime and stable performance.Nevertheless this type of lasers rely on the interband transition,which sets the bounds for emission wavelength typically below 4μm,and state of the art performance has been attained below 3μm.Attempts to employ small bandgap meterials like antimonide or lead salts ended with poor performance mainly due to imperfect crystal quality and severe Auger recombination.In view of the broad application prospects of infrared spectral range above 3μm,more attention was casted again on the low-dimensional quantum structure materials,such as quantum wells and quantum dots,which have been applied in the near infrared successfully decades ago.

Fabrication and characterization of AlGaN/GaN HEMTs with high power gain and efficiency at 8 GHz

State-of-the-art AlGaN/GaN high electron mobility structures were grown on semi-insulating 4H-SiC substrates by MOCVD and X-band microwave power high electron mobility transistors were fabricated and characterized.Hall mobility of 2291.1 cm^(2)/(V·s)and two-dimensional electron gas density of 9.954×10^(12)cm^(-2)were achieved at 300 K.The HEMT devices with a 0.45-μm gate length exhibited maximum drain current density as high as 1039.6 mA/mm and peak extrinsic transconductance of 229.7 mS/mm.The f_(T)of 30.89 GHz and f_(max)of 38.71 GHz were measured on the device.Load-pull measurements were performed and analyzed under(-3.5,28)V,(-3.5,34)V and(-3.5,40)V gate/drain direct current bias in class-AB,respectively.The uncooled device showed high linear power gain of 17.04 dB and high power-added efficiency of 50.56%at 8 GHz when drain biased at(-3.5,28)V.In addition,when drain biased at(-3.5,40)V,the device exhibited a saturation output power dens-ity up to 6.21 W/mm at 8 GHz,with a power gain of 11.94 dB and a power-added efficiency of 39.56%.Furthermore,the low f_(max)/f_(T)ratio and the variation of the power sweep of the device at 8 GHz with drain bias voltage were analyzed.

Quantum cascade superluminescent light emitters with high power and compact structure

Quantum cascade(QC)superluminescent light emitters(SLEs)have emerged as desirable broadband mid-infrared(MIR)light sources for growing number of applications in areas like medical imaging,gas sensing and national defense.However,it is challenging to obtain a practical high-power device due to the very low efficiency of spontaneous emission in the intersubband transitions in QC structures.Herein a design of^5μm SLEs is demonstrated with a two-phonon resonancebased QC active structure coupled with a compact combinatorial waveguide structure which comprises a short straight part adjacent to a tilted stripe and to a J-shaped waveguide.The as-fabricated SLEs achieve a high output power of 1.8 mW,exhibiting the potential to be integrated into array devices without taking up too much chip space.These results may facilitate the realization of SLE arrays to attain larger output power and pave the pathway towards the practical applications of broadband MIR light sources.

Coupled-ridge waveguide quantum cascade laser array lasing at λ~5μm

In this work,we demonstrated high-power quantum cascade laser(QCL)arrays lasing at λ~5μm by employing an optimized coupled-ridge waveguide(CRW)structure.Five-element QCL arrays were simulated and fabricated through a two-step etching method to extend the CRW structure to a mid-wave infrared regime.A lateral far-field with the main peak near a diffraction-limited intensity curve of about 10°was observed by properly designing a geometric shape of the ridges and interspaces.By introducing a buried 2nd-order distributed feedback(DFB)grating,substrate emission with a radiation power above 1 W at 25℃ is achieved.Single longitudinal mode operation is obtained by changing the temperature of the heatsink with a good linear wavelength tuning coefficient of -0.2 cm^(-1)/K.

氧化物气凝胶高温红外改性研究

氧化物气凝胶是一类具有超低热导率的新型纳米多孔材料,在航空航天等高温隔热领域具有广阔的应用前景。然而目前常见的氧化硅、氧化铝等氧化物气凝胶受材料/结构单元固有性质的限制,其通常具有红外透明性,而高温下辐射传热占据主导地位,大量红外辐射会透过气凝胶,热导率急剧攀升,导致其高温隔热性能较差,因此需要对其进行高温红外改性,从而满足更高的隔热性能需求。本文综述了近年来添加遮光剂、纤维及调整气凝胶的结构/形貌在提高氧化物气凝胶高温隔热性能方面的研究进展,并对未来研究方向进行展望。

Mode-switchable dual-color infrared quantum cascade detector

In this paper,a patch-antenna-array enhanced quantum cascade detector with freely switchable operating modes among mid-wave,long-wave,and dual-color was proposed and discussed.The dual-color absorption occurs in a single active region through an optimized coupled miniband diagonal-transition subbands arrangement,and a successful separation of the operation regimes was realized by two nested antenna arrays with different patch sizes up to room temperature.At 77 K,the 5.7-μm channel achieved a peak responsivity of 34.6 mA/W and exhibited a detectivity of 2.0×10^(10)Jones,while the 10.0-μm channel achieved a peak responsivity of 87.5 mA/W,giving a detectivity of 5.0×10^(10)Jones.Under a polarization modulation of the incident light,the minimum cross talk of the mid-wave and the long-wave operating modes was 1:22.5 and 1:7.6,respectively.This demonstration opens a new prospect for multicolor infrared imaging chip integration technology.

Benefit-risk assessment of incretin and other anti-diabetic agents in type 2 diabetes using a stochastic multicriteria acceptability analysis model

To the Editor:Incretin-based therapies for type 2 diabetes mellitus(T2DM)include incretin mimetics of glucagonlike peptide-1 receptor agonists(GLP-1 RAs)and incretin enhancers of dipeptidyl peptidase-4(DPP-4)inhibitors.[1]With good hypoglycemic effects of incretin-based drugs that show no weight gain or hypoglycemia risk,these drugs are increasingly used in patients with T2DM.

High-power distributed feedback lasers based on InP corrugated sidewalls atλ~2μm

We report a high-power single-mode InP-based 2μm distributed feedback(DFB)laser with a second-order buried grating and corrugated sidewalls.A second-order semiconductor grating is used for in-plane feedback and vertical out-coupling.The corrugated sidewalls are used to eliminate higher-order transverse modes.For the DFB laser with a 2 mm long cavity and 15μm wide ridge,the maximum continuous-wave edge-emitting and surface-emitting single-mode powers at 300 K are up to 81 and 42 m W,respectively.A single-lobed far-field radiation pattern with a low divergence angle of approximately 8.6°is achieved by a device with a ridge width of 15μm.The single-longitudinal-mode emission wavelength of the fabricated laser can be adjusted from2003.8 nm at 288 K to 2006.9 nm at 313 K without any mode hopping.Robust single-mode emission with a side-mode suppression ratio of 30 dB is achieved under all injection currents and temperature conditions.

Dual-mode distributed feedback quantum cascade laser based on stacked 3D monolithic integration for on-chip multi-channel gas sensing

To facilitate the development of on-chip integrated mid-infrared multi-channel gas sensing systems,we propose a high-power dual-mode(7.01 and 7.5μm)distributed feedback quantum cascade laser based on stacked 3D monolithic integration.Longitudinal mode control is achieved by preparing longitudinal nested bi-periodic compound one-dimensional Bragg gratings along the direction of the cavity length in the confinement layer.Additionally,transverse coherent coupling ridges perpendicular to the cavity length direction are fabricated in the upper waveguide layer to promote the fundamental transverse mode output when all ridges are in phase.Stable dual-wavelength simultaneous emission with a side-mode suppression ratio of more than 20 dB was achieved by holographic exposure and wet etching.The entire spectral tuning range covers nearly 100 nm through joint tuning of the injection current and heat-sink temperature.High peak power and beam quality are guaranteed by the parallel coherent integration of seven-element ridge arrays.The device operates in a fundamental supermode with a single-lobed far-field pattern,and its peak output power reaches 3.36 W in pulsed mode at 20℃.This dual-mode laser chip has the potential for in-situ on-chip simultaneous detection of CH4and C2H6gases in leak monitoring.

中国城市圈层空间经济结构变迁的内在机理研究

本文研究了城市和圈层空间经济结构变动的内在机理。结论表明,城市向圈层地区知识溢出效应的增强,能够缩小城市与圈层之间的经济差距。异质性分析和机制检验结果显示,更高强度的劳动力自由流动并没有加快地区间经济增长的收敛,而是扩大了城市与圈层之间经济产出的差异。在城市向圈层地区知识溢出程度提高的过程中,政府在公共支出决策时会将更多的资源配置到城市中,强化了城市与圈层地区之间的"二元经济"结构。

超轻纳米纤维气凝胶的制备及其应用

超轻纳米纤维气凝胶是一种以一维纳米纤维为基本构筑单元的新型气凝胶材料,相比于传统气凝胶,其不仅具有更高的孔隙率和更低的密度,还拥有更优异的机械性能和理化性质,因此该材料的先进制备技术和在新兴领域的创新性应用是近年来超轻气凝胶领域的研究热点。本文结合国内外研究现状,按照材料体系分类系统综述了超轻纤维气凝胶的制备方法、结构特点以及在隔热、吸附、电化学、传感和生物医学等领域的重要应用,提出了现阶段该材料面临的一些挑战,并展望了其在未来的发展方向。

A review of third generation SiC fibers and SiC_f/SiC composites

Compared with the first and second generations SiC fibers, the third generation SiC fibers have obvious improvement in heat-resistance, oxidation-resistance and creep-resistance, which promote the development of SiCf/SiC composite materials. Therefore, the third generation SiC fibers have more advantages and broader prospects in engineering applications. In this paper, the fabrication and properties of the third generation SiC fibers are compared and discussed. The preparation processes of the third generation SiC fibers reinforced SiC matrix composites and their application in aeroengine and nuclear energy fields are summarized, while their future development is prospected as well.

Gut microbiome alterations and its link to corticosteroid resistance in immune thrombocytopenia

Quantitative metagenomic studies have linked the gut microbiota to autoimmune disorders.Here,we performed deep shotgun metagenomic sequencing of fecal samples from 99 immune thrombocytopenia(ITP)patients and 52 healthy controls.Dysbiosis in the gut microbiome of ITP was detected phylogenetically and functionally,and classifier based on species markers distinguished individuals with ITP from healthy controls.In particular,the abundance of Ruminococcus gnavus,Bifidobacterium longum and Akkermansia muciniphila was markedly increased in treatment-na?ve ITP patients,and the alterations of microbial species were correlated with clinical indices.Functionally,the secondary bile acid biosynthesis and flagellar assembly were depleted in the gut microbiota of ITP,which may contribute to the onset of ITP by affecting the immune system.Furthermore,we found that corticosteroid treatment affected the gut microbiome of ITP.Compared with corticosteroid-sensitive ITP patients,we identified that the corticosteroid-resistant ITP patients displayed a distinct gut microbiome,which was different from that of the treatment-na?ve ITP patients.Together,we provided support for the critical role of gut microbiota in the development of ITP and established a foundation for further research characterizing gut microbiota in relation to corticosteroid resistance of ITP.