A Si-based monolithic laser is highly desirable for full integration of Si-photonics. Lasing from direct bandgap group-IV GeSn alloy has opened a completely new venue from the traditional III-V integration approach. We demonstrated optically pumped GeSn lasers on Si with broad wavelength coverage from 2 to 3 μm. The GeSn alloys were grown using newly developed approaches with an industry standard chemical vapor deposition reactor and low-cost commercially available precursors. The achieved maximum Sn composition of 17.5% exceeded the generally acknowledged Sn incorporation limits for using similar deposition chemistries.The highest lasing temperature was measured as 180 K with the active layer thickness as thin as 2 260 nm. The unprecedented lasing performance is mainly due to the unique growth approaches, which offer high-quality epitaxial materials. The results reported in this work show a major advance towards Si-based mid-infrared laser sources for integrated photonics.Si-based electronics industry has driven the digital revolution for an unprecedented success.As a result, there has been tremendous effort to broaden the reach of Si technology to build integrated photonics 1-3 . Although great success has been made on Si-based waveguides 4 , modulators 5 , and photodetectors 6,7 , a monolithic integrated light source on Si with high efficiency and reliability remains missing and is seen as the most challenging task to form a complete set of Si photonic components. Currently, Si photonics utilizes direct bandgap III-V lasers as the light source through different integration approaches such as wafer-bonding or direct-growth, which has seen significant progress in the last decade [8][9][10][11] . From the other side, a low solid solubility of Sn in Ge (<1%), low temperature growth techniques under nonequilibrium conditions have been successfully developed 20,21 , leading to the first experimental demonstration of direct bandgap GeSn alloy 22 and the optically pumped GeSn interband lasers [23][24][25] . The recent engagement of mainstream industrial chemical vapor deposition (CVD) reactors for the development of GeSn growth techniques has enabled those significant results, which implies that the growth method is manufacturable and can be transferred to the foundry/fab 3 . In this paper, we demonstrate the first set of optically pumped GeSn edge-emitting lasers that covers an unprecedented broad wavelength range from 2 to 3 μm with lower lasing threshold and higher operation temperature than all previous reports. This superior laser performance is attributed to the unique epitaxial growth approaches that were developed based on newly discovered growth dynamics. Contrary to the common belief that growing GeSn with high Sn fabrication of a thicker, defect-free GeSn top layer to maximize the mode overlap with it.Moreover, the material growth study revealed that there is still room to further improve the material quality by optimizing the growth conditions. References

Acidic dissolution of transition metals from Pt based alloy catalysts for oxygen reduction reaction (ORR) is an unavoidable process during fuel cell operation. In this work we studied the effect of acid treatment of graphene-supported Pt 1 Ni x (x ) 0, 0.25, 0.5, 1, and 2) alloys on the kinetics of the ORR in both alkaline and acidic solutions together with the generation of OH radicals in alkaline solutions. The alloy nanoparticles were synthesized through coimpregnation and chemical reduction. The electronic and structural features of the alloy were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. The ORR performances were studied using cyclic voltammetry and rotating ring disk electrode techniques in 0.05 M H 2 SO 4 and 0.1 M NaOH, respectively. The alloy catalysts were more active than pure Pt toward ORR, and after acid treatment the ORR activity of Pt-Ni alloy was enhanced in both acidic and alkaline media. The maximum activity of the Pt-based catalysts was found with ca. 50 atom % Ni content in the alloys (Pt 1 Ni 1 @graphene). OH radicals were generated through dissociation of hydroperoxide at the catalysts' surface and detected by fluorescence technique using terephthalic acid as capture reagent, which readily reacts with OH radical to produce highly fluorescent product, 2-hydroxyterephthalic acid. More OH radicals were found to be generated at Pt 1 Ni 1 @graphene catalyst. This work may be valuable in the design of electrocatalysts with higher ORR activity but lower efficiency of OH radical generation.