Optical facet coatings for high-performance LWIR quantum cascade lasers atλ∼8.5μm

We report on the performance improvement of long-wave infrared quantum cascade lasers(LWIR QCLs)by studying and optimizing the anti-reflection(AR)optical facet coating.Compared to the Al2O3 AR coat⁃ing,the Y_(2)O_(3)AR coating exhibits higher catastrophic optical mirror damage(COMD)level,and the optical facet coatings of both material systems have no beam steering effect.A 3-mm-long,9.5-μm-wide buried-heterostruc⁃ture(BH)LWIR QCL ofλ~8.5μm with Y_(2)O_(3)metallic high-reflection(HR)and AR of~0.2%reflectivity coating demonstrates a maximum pulsed peak power of 2.19 W at 298 K,which is 149%higher than that of the uncoated device.For continuous-wave(CW)operation,by optimizing the reflectivity of the Y_(2)O_(3)AR coating,the maximum output power reaches 0.73 W,which is 91%higher than that of the uncoated device.

Effect of hot rolling on microstructure and tribology behaviors of Ti-50.8Ni alloy

We link different microstructures to tribological behaviors of Ti-50.8 Ni(mole fraction, %) in reciprocating mode at room temperature(20 ℃). Hot-rolled alloys with B2 phase exhibit lower coefficient of friction and wear rate compared to the ones with B19?. Stress-induced martensitic transformation occurs during sliding. However, multi-pass hot rolling weakens the wear resistance. In this study, microstructures were characterized through electron backscatter diffraction and transmission electron microscopy(EBSD/TEM). From the concept of energy conservation, the effects of weak intensity of hot-rolled textures on the wear resistance are minimal. Based on the result that the alloy with a higher portion of coincidence site lattice boundaries shows lower martensitic start transformation temperature in the DSC curves than that with higher KAM values, the delay on B2-B19? transformation from {112}B2 twins outweighs dislocations. Moreover, widely distributed small-angle grain boundaries owing to dynamic recovery improve the wear resistance effectively compared to those that are well-recrystallized.

Photocatalytic-controlled olefin isomerization over WO_(3-x)using low-energy photons up to 625 nm

WO_(3-X)(W-l)was used to achieve controllable photoisomerization of linear olefins without substituents under 625 nm light irradiation.Thermodynamic and kinetic isomers were obtained by regulating the carbon chain length of the olefins.Terminal olefins were converted into isomerized products,and the internal olefin mixtures present in petroleum derivatives were transformed into valuable pure olefin products.Oxygen vacancies(OVs)in W-1 altered the electronic structure of W-1 to improve its light-harvesting ability,which accounted for the high activity of olefin isomerization under light irradiation up to 625 nm.Additionally,OVs on the W-1 surface generated unsaturated W^(5+)sites that coordinated with olefins for the efficient adsorption and activation of olefins.Mechanistic studies reveal that the in situ formation of surface Ti-complexes and ir-allylic W intermediates originating from the coordination of coordinated unsaturated W^(5+)sites and olefins ensure high photocatalytic activity and selectivity of W-1 for the photocatalytic isomerization of olefins via a radical mechanism.

Iron-induced 3D nanoporous iron-cobalt oxyhydroxide on carbon cloth as a highly efficient electrode for oxygen evolution reaction

The development of highly efficient and cost-effective electrode materials for catalyzing the oxygen evolution reaction(OER)is crucial for water splitting technology.The increase in the number of active sites by tuning the morphology and structure and the enhancement of the reactivity of active sites by the incorporation of other components are the two main strategies for the enhancement of their catalytic performance.In this study,by combining these two strategies,a unique three-dimensional nanoporous Fe-Co oxyhydroxide layer coated on the carbon cloth(3D-FeCoOOH/CC)was successfully synthesized by in situ electro-oxidation methods,and directly used as a working electrode.The electrode,3D-FeCoOOH/CC,was obtained by the Fe doping process in(NH4)2Fe(SO4)2,followed by continuous in situ electro-oxidization in alkaline medium of“micro go chess piece”arrays on the carbon cloth(MCPAs/CC).Micro characterizations illustrated that the go pieces of MCPAs/CC were completely converted into a thin conformal coating on the carbon cloth fibers.The electrochemical test results showed that the as-synthesized 3D-FeCoOOH/CC exhibited enhanced activity for OER with a low overpotential of 259 mV,at a current density of 10 mA cm^–2,and a small Tafel slope of 34.9 mV dec^–1,as well as superior stability in 1.0 mol L^–1 KOH solution.The extensive analysis revealed that the improved electrochemical surface area,conductivity,Fe-Co bimetallic composition,and the unique 3D porous structure together contributed to the enhanced OER activity of 3D-FeCoOOH/CC.Furthermore,the synthetic strategy applied in this study could be extended to fabricate a series of Co-based electrode materials with the dopant of other transition elements.

Impact of Channel Length and Width for Charge Transportation of Graphene Field Effect Transistor

The effect of channel length and width on the large and small-signal parameters of the graphene field effect transistor have been explored using an analytical approach.In the case of faster saturation as well as extremely high transit frequency,the graphene field effect transistor shows outstanding performance.From the transfer curve,it is observed that there is a positive shift of Dirac point from the voltage of 0.15 V to 0.35 V because of reducing channel length from 440 nm to 20 nm and this curve depicts that graphene shows ambipolar behavior.Besides,it is found that because of widening channel the drain current increases and the maximum current is found approximately 2.4 mA and 6 mA for channel width 2μm and 5μm respectively.Furthermore,an approximate symmetrical capacitance-voltage(C-V)characteristic of the graphene field effect transistor is obtained and the capacitance reduces when the channel length decreases but the capacitance can be increased by raising the channel width.In addition,a high transconductance,that demands high-speed radio frequency(RF)applications,of 6.4 mS at channel length 20 nm and 4.45 mS at channel width 5μm along with a high transit frequency of 3.95 THz have been found that demands high-speed radio frequency applications.

高纯半绝缘SiC材料上缺陷的发光特性的研究

我们研究了采用电子辐照方法在高纯半绝缘4H-SiC材料表面上制备缺陷,获得了近似单个缺陷的发光特性。我们证明了碳化硅晶片上的缺陷的发光位于材料表面,而非材料内部。通过采用532nm激光泵浦碳化硅的表面,我们得到了一条波长在可见光范围内的光谱。通过设计两种不同电子能量的电子辐照、不同的电子辐照剂量以及退火时不同的氧含量,我们发现合理的电子辐照剂量和氧含量对高纯半绝缘4H-SiC材料的缺陷的产生以及发光特性将产生很大的影响,并得出了退火气体氛围中有氧气的成份将影响单个缺陷的形成和表面缺陷的发光强度的结论。有氧气的成份下,样品表面缺陷的发光强度低于退火时保护气体中无氧时的缺陷的发光强度,并且还会造成片上缺陷密度的增加。我们还分析了影响单个缺陷产生的主要因素与次要因素,以及影响缺陷发光稳定性原因的结论。这为在碳化硅材料上成功地制备出稳定可靠的量子器件提供了一个参考的价值。