We report on a first-principles study of a novel band modulation in zigzag double-walled boron nitride nan- otubes （DBNNTs） by applying radial strain and coupled ex- ternal electric field. We show that the band alig...We report on a first-principles study of a novel band modulation in zigzag double-walled boron nitride nan- otubes （DBNNTs） by applying radial strain and coupled ex- ternal electric field. We show that the band alignment be- tween the inner and outer walls of the DBNNTs can be tuned from type I to type II with increasing radial strain, accompa- nied with a direct to indirect band gap transition and a sub- stantial gap reduction. The band gap can be further signifi- cantly reduced by applying a transverse electric field. The coupling of electric field with the radial strain makes the field-induced gap reduction being anisotropic and more re- markable than that in undeformed DBNNTs. In particular, the gap variation induced by electric field perpendicular to the radial strain is the most remarkable among all the modu-lations. These tunable properties by electromechanical cou- pling in DBNNTs will greatly enrich their versatile applica- tions in future nanoelectronics.展开更多
In this short review, we will briefly discuss the story of hydrogen storage, its impact on clean energy application, especially the challenges of using hydrogen adsorption for onboard application. After a short compar...In this short review, we will briefly discuss the story of hydrogen storage, its impact on clean energy application, especially the challenges of using hydrogen adsorption for onboard application. After a short comparison of the main methods of hydrogen storage （high pressure tank, metal hydride and adsorption）, we will focus our discussion on adsorption of hydrogen in graphitie carbon based large surface area adsorbents including carbon nanotubes, graphene and metal organic frameworks. The mechanisms, advantages, disadvantages and recent progresses will be discussed and reviewed for physisorption, metal-assisted storage and chemisorption. In the last section, we will discuss hydrogen spillover chemisorption in detail for the mechanism, status, challenges and perspectives. We hope to present a clear picture of the present technologies, challenges and the perspectives of hydrogen storage for the future studies.展开更多
Single-crystal graphene domains grown by chemical vapor deposition （CVD） intrinsically tend to have a six-fold symmetry; however, several factors can influence the growth kinetics, which can in turn lead to the form...Single-crystal graphene domains grown by chemical vapor deposition （CVD） intrinsically tend to have a six-fold symmetry; however, several factors can influence the growth kinetics, which can in turn lead to the formation of graphene with different shapes. Here we report the growth of oriented large-area pentagonal single-crystal graphene domains on Cu foils by CVD. We found that high-index Cu planes contributed selectively to the formation of pentagonal graphene. Our results indicated that lattice steps present on the crystalline surface of the underlying Cu promoted graphene growth in the direction perpendicular to the steps and finally led to the disappearance of one of the edges forming a pentagon. In addition, hydrogen promoted the formation of pentagonal domains. This work provides new insights into the mechanism of graphene growth.展开更多
Boron （B）, the one-electron-lacking neighbor of carbon in theperiodic table （and in the Latin alphabet）, is identified by ratherdifferent chemistry as compared to C. This gives rise to rich allo-tropy of boron, wh...Boron （B）, the one-electron-lacking neighbor of carbon in theperiodic table （and in the Latin alphabet）, is identified by ratherdifferent chemistry as compared to C. This gives rise to rich allo-tropy of boron, which is seen in the possibility of its multiple bulkphases, diverse clusters, cage-like fullerenes。展开更多
Crystalline nanostructures possess defects/vacancies that affect their physical and chemical properties. In this regard, the electronic structure of materials can be effectively regulated through defect engineering; t...Crystalline nanostructures possess defects/vacancies that affect their physical and chemical properties. In this regard, the electronic structure of materials can be effectively regulated through defect engineering; therefore, the correlation between defects/vacancies and the properties of a material has attracted extensive attention. Here, we report the synthesis of Bi2S3 microspheres by nanorod assemblies with exposed {211} facets, and the investigation of the types and concentrations of defects/vacancies by means of positron annihilation spectrometry. Our studies revealed that an increase in the calcined temperature, from 350 to 400 ℃, led the predominant defect/vacancy densities to change from isolated bismuth vacancies （VBi） to septuple Bi3＋-sulfur vacancy associates （VBiBiBiSSSS）. Furthermore, the concentration of septuple BiB＋-sulfur vacancy associates increased as the calcined temperature was increased from 400 to 450 ℃. The characterized transient photocurrent spectrum demonstrates that the photocurrent values closely correlate with the types and concentrations of the predominant defects/vacancies. Our theoretical computation, through first principles, showed that VBiBiBiSSSS strongly absorbs I2（sol）, easily desorbs I-（sol）, and enhances the electrocatalytic activity of the nanostructures.展开更多
The presence of defects/vacancies in nanomaterials influences the electronic structure of materials, and thus, it is necessary to study the correlation between the optoelectronic properties of a nanomaterial and its d...The presence of defects/vacancies in nanomaterials influences the electronic structure of materials, and thus, it is necessary to study the correlation between the optoelectronic properties of a nanomaterial and its defects/vacancies. Herein, we report a facile solvothermal route to synthesize three-dimensional （3D） SnS nanostructures formed by {131} faceted nanosheet assembly. The 3D SnS nanostructures were calcined at temperatures of 350, 400, and 450 ~C and used as counter electrodes, before their photocurrent properties were investigated. First principle computation revealed the photocurrent properties depend on the defect/vacancy concentration within the samples. It is very interesting that characterization with positron annihilation spectrometry confirmed that the density of defects/vacancies increased with the calcination temperature, and a maximum photocurrent was realized after treatment at 400 ℃. Further, the defect/vacancy density decreased when the calcination temperature reached 450℃ as the higher calcination temperature enlarged the mesopores and densified the pore walls, which led to a lower photocurrent value at 450℃ than at 400℃.展开更多
基金supported by the 973 Program(2012CB933403 and 2013CB932604)the National Natural Science Foundation of China(11172124 and 91023026)+5 种基金Jiangsu Province Natural Science Foundation(BK2011722)MOE doctoral discipline Foundation(20113218120033)China and Jiangsu Province Postdoctoral Science Foundation(2012T50494,20110490132 and 1002015B)the Fundamental Research Funds for the Central Universities(NS2012067)supported by the National Science Foundation(CMMI and NIRT)the U.S.Army Research Office MURI(W911NF-11-1-0362)
文摘We report on a first-principles study of a novel band modulation in zigzag double-walled boron nitride nan- otubes （DBNNTs） by applying radial strain and coupled ex- ternal electric field. We show that the band alignment be- tween the inner and outer walls of the DBNNTs can be tuned from type I to type II with increasing radial strain, accompa- nied with a direct to indirect band gap transition and a sub- stantial gap reduction. The band gap can be further signifi- cantly reduced by applying a transverse electric field. The coupling of electric field with the radial strain makes the field-induced gap reduction being anisotropic and more re- markable than that in undeformed DBNNTs. In particular, the gap variation induced by electric field perpendicular to the radial strain is the most remarkable among all the modu-lations. These tunable properties by electromechanical cou- pling in DBNNTs will greatly enrich their versatile applica- tions in future nanoelectronics.
文摘In this short review, we will briefly discuss the story of hydrogen storage, its impact on clean energy application, especially the challenges of using hydrogen adsorption for onboard application. After a short comparison of the main methods of hydrogen storage （high pressure tank, metal hydride and adsorption）, we will focus our discussion on adsorption of hydrogen in graphitie carbon based large surface area adsorbents including carbon nanotubes, graphene and metal organic frameworks. The mechanisms, advantages, disadvantages and recent progresses will be discussed and reviewed for physisorption, metal-assisted storage and chemisorption. In the last section, we will discuss hydrogen spillover chemisorption in detail for the mechanism, status, challenges and perspectives. We hope to present a clear picture of the present technologies, challenges and the perspectives of hydrogen storage for the future studies.
基金This work was supported by the National Natural Science Foundation of China （Nos. 51422204 and 51372132） and the National Basic Research Program of China （No. 2013CB228506）.
文摘Single-crystal graphene domains grown by chemical vapor deposition （CVD） intrinsically tend to have a six-fold symmetry; however, several factors can influence the growth kinetics, which can in turn lead to the formation of graphene with different shapes. Here we report the growth of oriented large-area pentagonal single-crystal graphene domains on Cu foils by CVD. We found that high-index Cu planes contributed selectively to the formation of pentagonal graphene. Our results indicated that lattice steps present on the crystalline surface of the underlying Cu promoted graphene growth in the direction perpendicular to the steps and finally led to the disappearance of one of the edges forming a pentagon. In addition, hydrogen promoted the formation of pentagonal domains. This work provides new insights into the mechanism of graphene growth.
基金support from the DOE grant DESC0012547the ONR grant N00014-15-1-2372
文摘Boron （B）, the one-electron-lacking neighbor of carbon in theperiodic table （and in the Latin alphabet）, is identified by ratherdifferent chemistry as compared to C. This gives rise to rich allo-tropy of boron, which is seen in the possibility of its multiple bulkphases, diverse clusters, cage-like fullerenes。
文摘Crystalline nanostructures possess defects/vacancies that affect their physical and chemical properties. In this regard, the electronic structure of materials can be effectively regulated through defect engineering; therefore, the correlation between defects/vacancies and the properties of a material has attracted extensive attention. Here, we report the synthesis of Bi2S3 microspheres by nanorod assemblies with exposed {211} facets, and the investigation of the types and concentrations of defects/vacancies by means of positron annihilation spectrometry. Our studies revealed that an increase in the calcined temperature, from 350 to 400 ℃, led the predominant defect/vacancy densities to change from isolated bismuth vacancies （VBi） to septuple Bi3＋-sulfur vacancy associates （VBiBiBiSSSS）. Furthermore, the concentration of septuple BiB＋-sulfur vacancy associates increased as the calcined temperature was increased from 400 to 450 ℃. The characterized transient photocurrent spectrum demonstrates that the photocurrent values closely correlate with the types and concentrations of the predominant defects/vacancies. Our theoretical computation, through first principles, showed that VBiBiBiSSSS strongly absorbs I2（sol）, easily desorbs I-（sol）, and enhances the electrocatalytic activity of the nanostructures.
文摘The presence of defects/vacancies in nanomaterials influences the electronic structure of materials, and thus, it is necessary to study the correlation between the optoelectronic properties of a nanomaterial and its defects/vacancies. Herein, we report a facile solvothermal route to synthesize three-dimensional （3D） SnS nanostructures formed by {131} faceted nanosheet assembly. The 3D SnS nanostructures were calcined at temperatures of 350, 400, and 450 ~C and used as counter electrodes, before their photocurrent properties were investigated. First principle computation revealed the photocurrent properties depend on the defect/vacancy concentration within the samples. It is very interesting that characterization with positron annihilation spectrometry confirmed that the density of defects/vacancies increased with the calcination temperature, and a maximum photocurrent was realized after treatment at 400 ℃. Further, the defect/vacancy density decreased when the calcination temperature reached 450℃ as the higher calcination temperature enlarged the mesopores and densified the pore walls, which led to a lower photocurrent value at 450℃ than at 400℃.
