Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible ...Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible for Raman to detect single molecule with nanometer resolution.However,due to technical diffculties,tip-enhanced CARS(TECARS)is not as successful as expected.For single molecular detection,high sensitivity and resolution are two main challenges.Here,we reported the first single atom layer TECARS imaging on Graphene with the highest resolution about 20 nm,which has ever been reported.The highest EF_(TECARS/CARS) is about 10^(4),the similar order of magnitude with SECARS(EF of tip is usually smaller than that of substrates).Such resolution and sensitivity is promising for medical,biology and chemical applications in the future.展开更多
Exploring facile and easily-scalable methods for synthesizing earth-abundant, cost-effective and efficient hy- drogen evolution reaction (HER) electrocatalysts is essential for the mass production of hydrogen as a c...Exploring facile and easily-scalable methods for synthesizing earth-abundant, cost-effective and efficient hy- drogen evolution reaction (HER) electrocatalysts is essential for the mass production of hydrogen as a clean and sustainable energy carrier. We report here a simple strategy to produce Mo2C nanocrystals embedded in carbon network (Mo2C@C) by the direct pyrolysis of ammonium molybdate and polyvinylpyrrolidone (PVP). It is found that PVP can be effectively used as a single source to form carbides and carbon network. The long polymer chain and coordinating capability with transition metal of PVP make it possible to form connected porous carbon network and well-dispersed MozC nanocrystals in several nanometers. The carbonization of PVP not only effectively in-situ prevents the aggregation of Mo2C nanocrystals during their formation, but also provides conductive porous matrix. As a result, the Mo2C@C composite exhibits the superior electrocatalytic performance for HER, which can be as- cribed to the large number of active sites from plenty of small MORC nanocrystals and the efficient mass and elec- tron transport network from carbon matrix. This strategy may inspire the exploration of cost-effective functional polymer as single source for both carbon precursor and nanostructure-directed reagent to mass-produce well-defined metal carbides nanostructures embedded in porous carbon network for energy applications.展开更多
The self-assemblies of 4-hexadecyloxybenzoic acid and 3,4,5-trihexadecyloxybenzoic acid have been studied by using scanning tunneling microscopy (STM). The well-ordered assemblies with different arrangement have been ...The self-assemblies of 4-hexadecyloxybenzoic acid and 3,4,5-trihexadecyloxybenzoic acid have been studied by using scanning tunneling microscopy (STM). The well-ordered assemblies with different arrangement have been investigated. The structural change is attributed to the different number of substituted alkyl chains on periphery.展开更多
基金We gratefully acknowledge the support from the National Natural Science Foundation of China(Nos.21735006 and 21127901),and the CAS Key Technology Talent Program.
文摘Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible for Raman to detect single molecule with nanometer resolution.However,due to technical diffculties,tip-enhanced CARS(TECARS)is not as successful as expected.For single molecular detection,high sensitivity and resolution are two main challenges.Here,we reported the first single atom layer TECARS imaging on Graphene with the highest resolution about 20 nm,which has ever been reported.The highest EF_(TECARS/CARS) is about 10^(4),the similar order of magnitude with SECARS(EF of tip is usually smaller than that of substrates).Such resolution and sensitivity is promising for medical,biology and chemical applications in the future.
文摘Exploring facile and easily-scalable methods for synthesizing earth-abundant, cost-effective and efficient hy- drogen evolution reaction (HER) electrocatalysts is essential for the mass production of hydrogen as a clean and sustainable energy carrier. We report here a simple strategy to produce Mo2C nanocrystals embedded in carbon network (Mo2C@C) by the direct pyrolysis of ammonium molybdate and polyvinylpyrrolidone (PVP). It is found that PVP can be effectively used as a single source to form carbides and carbon network. The long polymer chain and coordinating capability with transition metal of PVP make it possible to form connected porous carbon network and well-dispersed MozC nanocrystals in several nanometers. The carbonization of PVP not only effectively in-situ prevents the aggregation of Mo2C nanocrystals during their formation, but also provides conductive porous matrix. As a result, the Mo2C@C composite exhibits the superior electrocatalytic performance for HER, which can be as- cribed to the large number of active sites from plenty of small MORC nanocrystals and the efficient mass and elec- tron transport network from carbon matrix. This strategy may inspire the exploration of cost-effective functional polymer as single source for both carbon precursor and nanostructure-directed reagent to mass-produce well-defined metal carbides nanostructures embedded in porous carbon network for energy applications.
基金This work was supported by the National Natural Science Foundation of China (Grant No. G2000077501) the Foundation of the Chinese Academy of Sciences.
文摘The self-assemblies of 4-hexadecyloxybenzoic acid and 3,4,5-trihexadecyloxybenzoic acid have been studied by using scanning tunneling microscopy (STM). The well-ordered assemblies with different arrangement have been investigated. The structural change is attributed to the different number of substituted alkyl chains on periphery.