A facile design of Pt nanostructures from submonolayer to monolayer has been realized by ion adsorption-in situ electrochemical reduction on Au nanoparticles supported on multiwall carbon nanotubes （CNTs）. The as pr...A facile design of Pt nanostructures from submonolayer to monolayer has been realized by ion adsorption-in situ electrochemical reduction on Au nanoparticles supported on multiwall carbon nanotubes （CNTs）. The as prepared Au@Pt/CNTs catalysts display coverage-specific electrocatalysis. Au@Pt/CNTs with low Pt coverage is inactive towards methanol oxidation whereas it oxidizes formic acid effectively through a direct pathway with mass specific activity 90 times that of a commercial Pt/C catalyst. Due to its inertness to methanol, it shows high performance in the oxygen reduction reaction （ORR） with high methanol tolerance. In contrast, simply increasing the Pt coverage to above 40% switches the formic acid oxidation process to both direct and indirect catalytic pathways, and also results in high methanol oxidation activity.展开更多
CuO/γ-Al2O3 catalysts were prepared by impregnation with different CuO loadings. The dispersion of CuO supported on γ-Al2O3 support was studied using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, ...CuO/γ-Al2O3 catalysts were prepared by impregnation with different CuO loadings. The dispersion of CuO supported on γ-Al2O3 support was studied using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and temperature programmed reduction （TPR）. The dispersion threshold of CuO in γ-Al2O3 determined by X-ray quantitative analysis was 0.275 g/g, i.e., 0.275CuAl. Highly dispersed CuO or crystalline CuO would appear on the γ-Al2O3 support when CuO loading was below or more than its dispersion threshold. TPR experiments show that reduction peak temperature ranges of 0.1CuAl and pure CuO are 420-690 °C and 290-380 °C, respectively. 0.1CuAl is not easily reduced due to interaction between CuO and γ-Al2O3. 0.5CuAl shows a two-step reduction range during 210-300 °C and 410-730 °C, which confirms the existence of highly dispersed CuO and crystalline CuO. The sulfation experiments show the optimal CuO loading amount is far below its dispersion threshold, and copper oxide supported on γ-Al2O3 is in the form of submonolayer.展开更多
The methanol oxidation reaction(MOR)is the limiting half-reaction in direct methanol fuel cell(DMFC).Although Pt is the most active single-metal electrocatalyst for MOR,it is hampered by high cost and CO poisoning.Con...The methanol oxidation reaction(MOR)is the limiting half-reaction in direct methanol fuel cell(DMFC).Although Pt is the most active single-metal electrocatalyst for MOR,it is hampered by high cost and CO poisoning.Constructing a Pt or Ru monolayer on a second metal substrate by means of galvanic replacement of underpotentially deposited(UPD)Cu monolayer has been shown as an efficient catalyst design strategy for the electrocatalysis of MOR because of the presumed 100%utilization of atoms and resistance to CO poisoning.Herein,we prepared one-dimensional surface-alloyed electrocatalyst from predominantly(111)faceted Au nanowires with high aspect ratio as the substrate of under-potential deposition.The electrocatalyst comprises a core of the Au nanowire and a shell of catalytically active Pt coated by Ru.Coverage-dependent electro-catalytic activity and stability is demonstrated on the Pt/Ru submonolayers on Au wires for MOR.Among all these catalysts,Au@Pt_(ML)@Ru_(ML)exhibits the best electrocatalytic activity and poisoning tolerance to CO.This presents a viable method for the rational catalyst design for achieving high noble-metal utilization efficiency and high catalytic performance.展开更多
With a chirped InAs/GaAs SML-QD （quantum dot） structure serving as the active region, the superluminescent diodes emitting at wavelength of around 970nm are fabricated. By using an active multimode interferometer co...With a chirped InAs/GaAs SML-QD （quantum dot） structure serving as the active region, the superluminescent diodes emitting at wavelength of around 970nm are fabricated. By using an active multimode interferometer configuration, these devices exhibit high continue-wave output powers from the narrow ridge waveguides. At continue-wave injection current of 800mA, an output power of 18.5mW, and the single Gaussian-like emission spectrum centered at 972nm with a full width at half maximum of 18nm are obtained.展开更多
According to the InAs/GaAs submonolayer quantum dot active region, we demonstrate a bent-waveguide superluminescent diode emitting at a wavelength of around 970 nm. At a pulsed injection current of 0.5 A, the device e...According to the InAs/GaAs submonolayer quantum dot active region, we demonstrate a bent-waveguide superluminescent diode emitting at a wavelength of around 970 nm. At a pulsed injection current of 0.5 A, the device exhibits an output power of 24 mW and an emission spectrum centred at 971 nm with a full width at half maximum of 16 nm.展开更多
Two-dimensional(2D)magnetic materials promise unconventional properties and quantum phases as well as advances in ultracompact spintronics.Miniaturization of 2D magnets often reaches a single monolayer but in general ...Two-dimensional(2D)magnetic materials promise unconventional properties and quantum phases as well as advances in ultracompact spintronics.Miniaturization of 2D magnets often reaches a single monolayer but in general can go beyond this limit,as demonstrated by 2D magnetism of submonolayer Eu superstructures coupled with Si.The question is whether the submonolayer magnetism constitutes a general phenomenon.Herein,we demonstrate that regular Eu lattices form a class of 2D magnets displaying various structures,stoichiometries,and chemical bonding.We synthesized and studied a set of Eu superstructures on Ge(001).Their magnetic properties are consistent with the emergence of a magnetic order such as ferro-or ferrimagnetism.In particular,control over the magnetic transition temperature by weak magnetic fields indicates the 2D nature of the magnetism.Taken together,Eu/Ge and Eu/Si superstructures seed a nucleus of the research area addressing the emergence of magnetism in submonolayer chemical species.展开更多
Two-component submonolayer growth on triangular lattice is qualitatively studied by kinetic Monte Carlo techniques.The hopping barrier governing surface diffusion of the atoms is estimated using pair interaction poten...Two-component submonolayer growth on triangular lattice is qualitatively studied by kinetic Monte Carlo techniques.The hopping barrier governing surface diffusion of the atoms is estimated using pair interaction potentials.Several degrees of freedoms enhancing the surface diffusion of atoms are also introduced.The main advantages of the presented technique are the reduced number of free parameters and the clear diffusion activated mechanism for the segregation of different types of atoms.The potential of this method is exemplified by reproducing(i)phase-boundary creation and dynamics related to vacancies and stacking faults;(ii)a special co-deposition and segregation process where the segregated atoms of the second component surround the islands formed by the first type of atoms.展开更多
文摘A facile design of Pt nanostructures from submonolayer to monolayer has been realized by ion adsorption-in situ electrochemical reduction on Au nanoparticles supported on multiwall carbon nanotubes （CNTs）. The as prepared Au@Pt/CNTs catalysts display coverage-specific electrocatalysis. Au@Pt/CNTs with low Pt coverage is inactive towards methanol oxidation whereas it oxidizes formic acid effectively through a direct pathway with mass specific activity 90 times that of a commercial Pt/C catalyst. Due to its inertness to methanol, it shows high performance in the oxygen reduction reaction （ORR） with high methanol tolerance. In contrast, simply increasing the Pt coverage to above 40% switches the formic acid oxidation process to both direct and indirect catalytic pathways, and also results in high methanol oxidation activity.
基金Project (Jinchuan 201114) supported by the Pre-Research Foundation of Jinchuan Group Ltd., ChinaProject (2011148) supported by the Analysis and Testing Foundation of Kunming University of Science and Technology, China
文摘CuO/γ-Al2O3 catalysts were prepared by impregnation with different CuO loadings. The dispersion of CuO supported on γ-Al2O3 support was studied using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and temperature programmed reduction （TPR）. The dispersion threshold of CuO in γ-Al2O3 determined by X-ray quantitative analysis was 0.275 g/g, i.e., 0.275CuAl. Highly dispersed CuO or crystalline CuO would appear on the γ-Al2O3 support when CuO loading was below or more than its dispersion threshold. TPR experiments show that reduction peak temperature ranges of 0.1CuAl and pure CuO are 420-690 °C and 290-380 °C, respectively. 0.1CuAl is not easily reduced due to interaction between CuO and γ-Al2O3. 0.5CuAl shows a two-step reduction range during 210-300 °C and 410-730 °C, which confirms the existence of highly dispersed CuO and crystalline CuO. The sulfation experiments show the optimal CuO loading amount is far below its dispersion threshold, and copper oxide supported on γ-Al2O3 is in the form of submonolayer.
基金financially supported by the Natural Science Foundation of Tianjin,China(No.18JCYBJC20600)the National Natural Science Foundation of China(Nos.62074123,61701543)Institute of Energy,Hefei Comprehensive National Science Center(No.19KZS207)。
文摘The methanol oxidation reaction(MOR)is the limiting half-reaction in direct methanol fuel cell(DMFC).Although Pt is the most active single-metal electrocatalyst for MOR,it is hampered by high cost and CO poisoning.Constructing a Pt or Ru monolayer on a second metal substrate by means of galvanic replacement of underpotentially deposited(UPD)Cu monolayer has been shown as an efficient catalyst design strategy for the electrocatalysis of MOR because of the presumed 100%utilization of atoms and resistance to CO poisoning.Herein,we prepared one-dimensional surface-alloyed electrocatalyst from predominantly(111)faceted Au nanowires with high aspect ratio as the substrate of under-potential deposition.The electrocatalyst comprises a core of the Au nanowire and a shell of catalytically active Pt coated by Ru.Coverage-dependent electro-catalytic activity and stability is demonstrated on the Pt/Ru submonolayers on Au wires for MOR.Among all these catalysts,Au@Pt_(ML)@Ru_(ML)exhibits the best electrocatalytic activity and poisoning tolerance to CO.This presents a viable method for the rational catalyst design for achieving high noble-metal utilization efficiency and high catalytic performance.
基金Project supported by the National Basic Research Program of China (Grant No. 2006CB604904)the National Natural Science Foundation of China (Grant Nos. 60976057, 61274072, and 60876086)
文摘With a chirped InAs/GaAs SML-QD （quantum dot） structure serving as the active region, the superluminescent diodes emitting at wavelength of around 970nm are fabricated. By using an active multimode interferometer configuration, these devices exhibit high continue-wave output powers from the narrow ridge waveguides. At continue-wave injection current of 800mA, an output power of 18.5mW, and the single Gaussian-like emission spectrum centered at 972nm with a full width at half maximum of 18nm are obtained.
基金supported by the National Basic Research Program of China (Grant No.2006CB604904)the National Natural Science Foundation of China (Grant Nos.60876086,60976057,and 60776037)
文摘According to the InAs/GaAs submonolayer quantum dot active region, we demonstrate a bent-waveguide superluminescent diode emitting at a wavelength of around 970 nm. At a pulsed injection current of 0.5 A, the device exhibits an output power of 24 mW and an emission spectrum centred at 971 nm with a full width at half maximum of 16 nm.
基金This work is supported by NRC“Kurchatov Institute”,the Ministry of Science and Higher Education of Russia(Agreement No.075-15-2021-1351)the Russian Science Foundation(grants No.22-13-00004(synthesis)+1 种基金20-79-10028(structural characterization)19-19-00009(studies on magnetism)).
文摘Two-dimensional(2D)magnetic materials promise unconventional properties and quantum phases as well as advances in ultracompact spintronics.Miniaturization of 2D magnets often reaches a single monolayer but in general can go beyond this limit,as demonstrated by 2D magnetism of submonolayer Eu superstructures coupled with Si.The question is whether the submonolayer magnetism constitutes a general phenomenon.Herein,we demonstrate that regular Eu lattices form a class of 2D magnets displaying various structures,stoichiometries,and chemical bonding.We synthesized and studied a set of Eu superstructures on Ge(001).Their magnetic properties are consistent with the emergence of a magnetic order such as ferro-or ferrimagnetism.In particular,control over the magnetic transition temperature by weak magnetic fields indicates the 2D nature of the magnetism.Taken together,Eu/Ge and Eu/Si superstructures seed a nucleus of the research area addressing the emergence of magnetism in submonolayer chemical species.
基金the Hungarian National Science Foundation under contract No.OTKA T048699INNOVATIAL 6th Framework Program Project IP 515844-21 and by Romanian CNCSIS 41/183 and CEEX/Nanobiospec grant.
文摘Two-component submonolayer growth on triangular lattice is qualitatively studied by kinetic Monte Carlo techniques.The hopping barrier governing surface diffusion of the atoms is estimated using pair interaction potentials.Several degrees of freedoms enhancing the surface diffusion of atoms are also introduced.The main advantages of the presented technique are the reduced number of free parameters and the clear diffusion activated mechanism for the segregation of different types of atoms.The potential of this method is exemplified by reproducing(i)phase-boundary creation and dynamics related to vacancies and stacking faults;(ii)a special co-deposition and segregation process where the segregated atoms of the second component surround the islands formed by the first type of atoms.
