There has been much interest in developing multilayered or nanolayered physical vapor deposition（PVD） coatings identified as a group of promising protective coatings for their excellent mechanical properties and cor...There has been much interest in developing multilayered or nanolayered physical vapor deposition（PVD） coatings identified as a group of promising protective coatings for their excellent mechanical properties and corrosion resistance. In this study, the multilayered Cr N/Cr2O3 coatings with different bilayer periods（L） were synthesized on the polished high speed steel substrates from a Cr target with the alternative atmosphere of pure nitrogen and pure oxygen by arc ion plating（AIP） technique. The results revealed that the microstructure,morphologies and properties of the multilayered coatings were strongly influenced by the bilayer period（L）.There were two kinds of interfaces in the multilayered Cr N/Cr2O3coatings： the sharp ones and the blurry ones. With reducing the value of L, the macro-particles densities decreased gradually, whereas the coating microhardness, adhesive strength and wear resistance first increased, and then decreased slightly or remained stable as the bilayer period L 〈 590 nm. The multilayered Cr N/Cr2O3 coating with the bilayer period L of 590 nm possessed the best comprehensive properties, namely the highest microhardness, the strongest adhesion, and the lowest wear rate.展开更多
Herein,we report the synthesis and structures of two novel mixed-metal clusters denoted as Th_(9)Ag_(6)and Th_(9)Ag_(12).Both clusters feature unprecedented Th_(9)cores.The cores are tricapped trigonal prism moieties ...Herein,we report the synthesis and structures of two novel mixed-metal clusters denoted as Th_(9)Ag_(6)and Th_(9)Ag_(12).Both clusters feature unprecedented Th_(9)cores.The cores are tricapped trigonal prism moieties that are novel among actinides.Attempted alternative synthesis routes indicate that the Th_(9)clusters are accessible only through slow introduction of Ag_(+)into a solution containing a Th6 cluster modified with 2-picolinic acid.Alternative rapid addition of Ag_(+)leads to dissociation of the Th6 cluster with formation of a high-purity(ThAg)_(∞)two-dimensional layered structure material.A mechanism for cluster dissociation and reassembly to yield Th_(9)from Th6 is proposed that is consistent with spectroscopic observations and computational results.Because of Ag⋯Ag andπ–πinteractions,the Th_(9)Ag_(12)cluster exhibits high stability in air,at elevated temperature,underγ-irradiation,and in common solvents.展开更多
In this study, CrN/Cr2O3 double-layered coatings with various thickness ratios of CrN vs Cr2O3 layer were prepared by arc ion plating technology. The influences of the thickness ratio of CrN vs Cr2O3 layer on the micr...In this study, CrN/Cr2O3 double-layered coatings with various thickness ratios of CrN vs Cr2O3 layer were prepared by arc ion plating technology. The influences of the thickness ratio of CrN vs Cr2O3 layer on the microstructural characteristics as well as the mechanical and tribological properties of the CrN/Cr2O3 doublelayered coatings were investigated. The corresponding mechanisms were also discussed. The results indicated that the insertion of CrN layer between the Cr2O3 layer and substrate can effectively decrease the internal stress level of the coating. With increasing the thickness ratio of CrN vs Cr2O3 layer, the surface roughness of double-layered coatings decreased gradually, which had a certain influence on the friction coefficient. In addition, the microhardness also declined gradually, the adhesive strength almost increased linearly, whereas the wear rate declined firstly and then increased slightly. As the thickness ratio was 2：1, the double-layered coating exhibited the best wear resistance.展开更多
We experimentally demonstrate a high power nanosecond pulsed terahertz(THz)-wave parametric oscillator(TPO)by using a wide pump beam.A surface emitted cavity configuration is employed to reduce the THz absorption in M...We experimentally demonstrate a high power nanosecond pulsed terahertz(THz)-wave parametric oscillator(TPO)by using a wide pump beam.A surface emitted cavity configuration is employed to reduce the THz absorption in MgO:LiNbO_(3) crystal.The THz wave can be tuned from 1 THz to 3 THz.A maximum THz output energy of 438 nJ/pulse is achieved at 1.56 Hz using a 4.5-mm-diameter pump beam with a pulse energy of 226 mJ pump energy with the repetition of 10 Hz,corresponding to the energy conversion efficiency of 1.94×10^(-6).展开更多
In this work,we report a novel octa-nuclear uranyl(U8)motif[(UO2)8O4(μ3-OH)2(μ2-OH)2]4+embedded in a uranyl-oxalate coordination polymer(compound 1)based on a U-shaped linker with extra-long xylylene chains for stab...In this work,we report a novel octa-nuclear uranyl(U8)motif[(UO2)8O4(μ3-OH)2(μ2-OH)2]4+embedded in a uranyl-oxalate coordination polymer(compound 1)based on a U-shaped linker with extra-long xylylene chains for stabilizing the resulting high-nuclear motif through additional cross-linking connectivity.A comparison with dimeric and monomeric uranyl compounds obtained at different pH value from the same hydrothermal system reveals that,solution pH plays a vital role in formation of this octa-nuclear uranyl motif by promoting hydrolysis of uranyl source.Since high similarity of eight uranium centers in this nearly planar U8 motif here,overlapping and broadening of signals in fluorescence,infra-red(IR)and Raman spectra can be found.展开更多
基金financial supports from the National Key Basic Research Program of China (973 Program, No. 2012CB625100)the National Natural Science Foundation of China (Nos. 51001106 and 51301181)the Doctoral Starting up Foundation of Liaoning Province Science and Technology Agency, China (No. 20131118)
文摘There has been much interest in developing multilayered or nanolayered physical vapor deposition（PVD） coatings identified as a group of promising protective coatings for their excellent mechanical properties and corrosion resistance. In this study, the multilayered Cr N/Cr2O3 coatings with different bilayer periods（L） were synthesized on the polished high speed steel substrates from a Cr target with the alternative atmosphere of pure nitrogen and pure oxygen by arc ion plating（AIP） technique. The results revealed that the microstructure,morphologies and properties of the multilayered coatings were strongly influenced by the bilayer period（L）.There were two kinds of interfaces in the multilayered Cr N/Cr2O3coatings： the sharp ones and the blurry ones. With reducing the value of L, the macro-particles densities decreased gradually, whereas the coating microhardness, adhesive strength and wear resistance first increased, and then decreased slightly or remained stable as the bilayer period L 〈 590 nm. The multilayered Cr N/Cr2O3 coating with the bilayer period L of 590 nm possessed the best comprehensive properties, namely the highest microhardness, the strongest adhesion, and the lowest wear rate.
基金the National Science Fund for Distinguished Young Scholars(grant no.21925603)support of the National Natural Science Foundation of China(grant nos.22076187,11975152,11875057).The work of J.K.G.was supported by the U.S.Departme。
文摘Herein,we report the synthesis and structures of two novel mixed-metal clusters denoted as Th_(9)Ag_(6)and Th_(9)Ag_(12).Both clusters feature unprecedented Th_(9)cores.The cores are tricapped trigonal prism moieties that are novel among actinides.Attempted alternative synthesis routes indicate that the Th_(9)clusters are accessible only through slow introduction of Ag_(+)into a solution containing a Th6 cluster modified with 2-picolinic acid.Alternative rapid addition of Ag_(+)leads to dissociation of the Th6 cluster with formation of a high-purity(ThAg)_(∞)two-dimensional layered structure material.A mechanism for cluster dissociation and reassembly to yield Th_(9)from Th6 is proposed that is consistent with spectroscopic observations and computational results.Because of Ag⋯Ag andπ–πinteractions,the Th_(9)Ag_(12)cluster exhibits high stability in air,at elevated temperature,underγ-irradiation,and in common solvents.
基金the National Key Basic Research Program of China("973 Program",No.2012CB625100)the National Natural Science Foundation of China(No.51001106&No.51301181)the Doctoral Starting up Foundation of Liaoning Province Science and Technology Agency,China(No.20131118)
文摘In this study, CrN/Cr2O3 double-layered coatings with various thickness ratios of CrN vs Cr2O3 layer were prepared by arc ion plating technology. The influences of the thickness ratio of CrN vs Cr2O3 layer on the microstructural characteristics as well as the mechanical and tribological properties of the CrN/Cr2O3 doublelayered coatings were investigated. The corresponding mechanisms were also discussed. The results indicated that the insertion of CrN layer between the Cr2O3 layer and substrate can effectively decrease the internal stress level of the coating. With increasing the thickness ratio of CrN vs Cr2O3 layer, the surface roughness of double-layered coatings decreased gradually, which had a certain influence on the friction coefficient. In addition, the microhardness also declined gradually, the adhesive strength almost increased linearly, whereas the wear rate declined firstly and then increased slightly. As the thickness ratio was 2：1, the double-layered coating exhibited the best wear resistance.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61107086,61172010 and 61101058,Science and Technology Committee of TianJin(No 11JCYBJC01100)the National High Technology Research and Development Program of China(No 2011AA010205)the Open-Fund of the Key Laboratory of Opto-electronic Information Technology(Ministry of Education)at Tianjin University。
文摘We experimentally demonstrate a high power nanosecond pulsed terahertz(THz)-wave parametric oscillator(TPO)by using a wide pump beam.A surface emitted cavity configuration is employed to reduce the THz absorption in MgO:LiNbO_(3) crystal.The THz wave can be tuned from 1 THz to 3 THz.A maximum THz output energy of 438 nJ/pulse is achieved at 1.56 Hz using a 4.5-mm-diameter pump beam with a pulse energy of 226 mJ pump energy with the repetition of 10 Hz,corresponding to the energy conversion efficiency of 1.94×10^(-6).
基金National Natural Science Foundation of China(21671191,21577144,11405186)。
文摘In this work,we report a novel octa-nuclear uranyl(U8)motif[(UO2)8O4(μ3-OH)2(μ2-OH)2]4+embedded in a uranyl-oxalate coordination polymer(compound 1)based on a U-shaped linker with extra-long xylylene chains for stabilizing the resulting high-nuclear motif through additional cross-linking connectivity.A comparison with dimeric and monomeric uranyl compounds obtained at different pH value from the same hydrothermal system reveals that,solution pH plays a vital role in formation of this octa-nuclear uranyl motif by promoting hydrolysis of uranyl source.Since high similarity of eight uranium centers in this nearly planar U8 motif here,overlapping and broadening of signals in fluorescence,infra-red(IR)and Raman spectra can be found.
