Manipulating metal-insulator transitions in strongly correlated materials is of great importance in condensed matter physics,with implications for both fundamental science and technology.Vanadium dioxide(VO_(2)),as an...Manipulating metal-insulator transitions in strongly correlated materials is of great importance in condensed matter physics,with implications for both fundamental science and technology.Vanadium dioxide(VO_(2)),as an ideal model system,is metallic at high temperatures and shown a typical metal-insulator structural phase transition at 341 K from rutile structure to monoclinic structure.This behavior has been absorbed tons of attention for years.However,how to control this phase transition is still challenging and little studied.Here we demonstrated that to control the Ag nanonet arrays(NAs)in monoclinic VO_(2)(M)could be effective to adjust this metal-insulator transition.With the increase of Ag NAs volume fraction by reducing the template spheres size,the transition temperature(Tc)decreased from 68°C to 51°C.The mechanism of Tc decrease was revealed as:the carrier density increases through the increase of Ag NAs volume fraction,and more free electrons injected into the VO_(2)films induced greater absorption energy at the internal nanometal-semiconductor junction.These results supply a new strategy to control the metal-insulator transitions in VO_(2),which must be instructive for the other strongly correlated materials and important for applications.展开更多
A new technique to reduce the influence of metallic carbon nanotubes(CNTs)relevant for large-scale integrated circuits based on CNT-nanonet transistorsis proposed and verified.Historically,electrical and chemical filt...A new technique to reduce the influence of metallic carbon nanotubes(CNTs)relevant for large-scale integrated circuits based on CNT-nanonet transistorsis proposed and verified.Historically,electrical and chemical filtering of the metallic CNTs have been used to improve the ON/OFF ratio of CNT-nanonet transistors;however,the corresponding degradation in ON-current has made these techniques somewhat unsatisfactory.Here,we abandon the classical approaches in favor of a new approach based on relocation of asymmetric percolation threshold of CNT-nanonet transistors by a technique called“striping”;this allows fabrication of transistors with ON/OFF ratio>1000 and ON-current degradation no more than a factor of 2.We offer first principle numerical models,experimental confirmation,and renormalization arguments to provide a broad theoretical and experimental foundation of the proposed method.展开更多
In this study, series of nanolayered structures of Zn–Al LDHs were prepared by urea hydrolysis. Nanofibers and nanonets of the Al-doped ZnO were formed via the decomposition of the nanolayers under high pressure and ...In this study, series of nanolayered structures of Zn–Al LDHs were prepared by urea hydrolysis. Nanofibers and nanonets of the Al-doped ZnO were formed via the decomposition of the nanolayers under high pressure and temperature. Nanospheres were also prepared for comparison. The different morphologies of the prepared nanomaterials were confirmed by several techniques. An improvement for the optical properties of the doped zinc oxides was observed through narrowing of their band gap energies because of transforming the nanolayers to nanonets and nanofibers. The photocatalytic activities of the prepared nanomaterials were studied through photocatalytic degradation of the pollutants of acid green dyes. Complete decolorization and mineralization of green dyes happened in the presence of the nanolayers and nanospheres within 4–6 h,while the nanonets and the nanofibers achieved the complete decolorization and degradation of the dyes at shorter time 1.3 h. These results could be explained though the kinetic study of the photocatalytic degradation of dyes. It was concluded that the nanonets and the nanofibers were very effective for the photocatalytic degradation of pollutants.展开更多
A Ga2O·11Al2O3 nanonet was synthesized by using Ga2O3 powder as the precursor to generate Ga2O vapor in H2 atmosphere which further reacted with Al2O3 at 730 °C to form Ga2O·11Al2O3 at the interfaces of...A Ga2O·11Al2O3 nanonet was synthesized by using Ga2O3 powder as the precursor to generate Ga2O vapor in H2 atmosphere which further reacted with Al2O3 at 730 °C to form Ga2O·11Al2O3 at the interfaces of a porous anodic aluminum oxide (AAO) template. The prepared Ga2O·11Al2O3 nanonet then served as a Ga2O-stablizing reservoir to fabricate single crystal GaN nanowires. The residual Ga2O3 powder at the surface of the produced Ga2O·11Al2O3 nanonet and the metallic Ga or Ga2O from the Ga2O·11Al2O3 decomposition reacted with ammonia to yield GaN nanowires at 780 °C. The reaction mechanisms were investigated.展开更多
Energy efficient buildings require novel thermal insulators accompanied by lightweight,mechanically robust,fire resistant,and low thermal conductivity.Ceramic fibrous aerogels have emerged as promising candidates,howe...Energy efficient buildings require novel thermal insulators accompanied by lightweight,mechanically robust,fire resistant,and low thermal conductivity.Ceramic fibrous aerogels have emerged as promising candidates,however it’s difficult for these materials to achieve exceptional mechanical and thermal insulation performance simultaneously.Here,we demonstrate a unique semi-template method to fabricate biomimetic-architectured silica/carbon dual-fibrous aerogel with robust mechanical performance.Specifically,aerogels with honeycomb-like cellular and nanofiber/nanonet cell wall were constructed by freezedrying the homogeneous dispersion of SiO_(2)nanofibers and cellulose nanofibers co-suspensions.It is worth noting that the biomimetic structure has been perfectly inherited even subjected to high-temperature carbonization.As a result,the excellent structural stability brought by the novel structure enables the aerogel to completely recover under large compression and buckling strain of 80%,and exhibit robust fatigue resistance over 200,000 cycles.More importantly,the aerogels exhibit ultralow thermal conductivity(0.023 W·m^(−1)·K^(−1)),superior flame retardancy,together with excellent thermal insulation performance over a wide temperature ranging from−196 to 350°C.The fabrication of such materials may provide new ideas for the development of next-generation thermal insulators for harsh conditions.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11904299 and U1930124)the Foundation of China Academy of Engineering Physics(Grant No.2018AB02)。
文摘Manipulating metal-insulator transitions in strongly correlated materials is of great importance in condensed matter physics,with implications for both fundamental science and technology.Vanadium dioxide(VO_(2)),as an ideal model system,is metallic at high temperatures and shown a typical metal-insulator structural phase transition at 341 K from rutile structure to monoclinic structure.This behavior has been absorbed tons of attention for years.However,how to control this phase transition is still challenging and little studied.Here we demonstrated that to control the Ag nanonet arrays(NAs)in monoclinic VO_(2)(M)could be effective to adjust this metal-insulator transition.With the increase of Ag NAs volume fraction by reducing the template spheres size,the transition temperature(Tc)decreased from 68°C to 51°C.The mechanism of Tc decrease was revealed as:the carrier density increases through the increase of Ag NAs volume fraction,and more free electrons injected into the VO_(2)films induced greater absorption energy at the internal nanometal-semiconductor junction.These results supply a new strategy to control the metal-insulator transitions in VO_(2),which must be instructive for the other strongly correlated materials and important for applications.
基金the Network for Computational Nanotechnology and the Lilly Foundation for financial supportthe National Science Foundation(NIRT-0403489)+1 种基金the Department of Energy(DE-FG02-07ER46471)Motorola,Inc.,the Frederick-Seitz Materials Research Laboratory,and the Center for Microanalysis of Materials(DE-FG02-07ER46453 and DE-FG02-07ER46471)at the University of Illinois.
文摘A new technique to reduce the influence of metallic carbon nanotubes(CNTs)relevant for large-scale integrated circuits based on CNT-nanonet transistorsis proposed and verified.Historically,electrical and chemical filtering of the metallic CNTs have been used to improve the ON/OFF ratio of CNT-nanonet transistors;however,the corresponding degradation in ON-current has made these techniques somewhat unsatisfactory.Here,we abandon the classical approaches in favor of a new approach based on relocation of asymmetric percolation threshold of CNT-nanonet transistors by a technique called“striping”;this allows fabrication of transistors with ON/OFF ratio>1000 and ON-current degradation no more than a factor of 2.We offer first principle numerical models,experimental confirmation,and renormalization arguments to provide a broad theoretical and experimental foundation of the proposed method.
基金the Deanship of Scientific Research in King Faisal University (Saudi Arabia) for funding and providing the facilities required for this research as a part of Annual Research Grants Program (No. 170047)
文摘In this study, series of nanolayered structures of Zn–Al LDHs were prepared by urea hydrolysis. Nanofibers and nanonets of the Al-doped ZnO were formed via the decomposition of the nanolayers under high pressure and temperature. Nanospheres were also prepared for comparison. The different morphologies of the prepared nanomaterials were confirmed by several techniques. An improvement for the optical properties of the doped zinc oxides was observed through narrowing of their band gap energies because of transforming the nanolayers to nanonets and nanofibers. The photocatalytic activities of the prepared nanomaterials were studied through photocatalytic degradation of the pollutants of acid green dyes. Complete decolorization and mineralization of green dyes happened in the presence of the nanolayers and nanospheres within 4–6 h,while the nanonets and the nanofibers achieved the complete decolorization and degradation of the dyes at shorter time 1.3 h. These results could be explained though the kinetic study of the photocatalytic degradation of dyes. It was concluded that the nanonets and the nanofibers were very effective for the photocatalytic degradation of pollutants.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50821061, 20773001, 20827002)Ministry of Sceince and Technology of China (2006CB806102, 2007CB936202, 2009CB929403)
文摘A Ga2O·11Al2O3 nanonet was synthesized by using Ga2O3 powder as the precursor to generate Ga2O vapor in H2 atmosphere which further reacted with Al2O3 at 730 °C to form Ga2O·11Al2O3 at the interfaces of a porous anodic aluminum oxide (AAO) template. The prepared Ga2O·11Al2O3 nanonet then served as a Ga2O-stablizing reservoir to fabricate single crystal GaN nanowires. The residual Ga2O3 powder at the surface of the produced Ga2O·11Al2O3 nanonet and the metallic Ga or Ga2O from the Ga2O·11Al2O3 decomposition reacted with ammonia to yield GaN nanowires at 780 °C. The reaction mechanisms were investigated.
基金supported by the National Natural Science Foundation of China(Nos.51925302,21961132024,and 51873029)the Science and Technology Commission of Shanghai Municipality(No.20QA1400500)+1 种基金China Postdoctoral Science Foundation(Nos.2021TQ0163 and 2021M101821)Shuimu Tsinghua Scholar Program.
文摘Energy efficient buildings require novel thermal insulators accompanied by lightweight,mechanically robust,fire resistant,and low thermal conductivity.Ceramic fibrous aerogels have emerged as promising candidates,however it’s difficult for these materials to achieve exceptional mechanical and thermal insulation performance simultaneously.Here,we demonstrate a unique semi-template method to fabricate biomimetic-architectured silica/carbon dual-fibrous aerogel with robust mechanical performance.Specifically,aerogels with honeycomb-like cellular and nanofiber/nanonet cell wall were constructed by freezedrying the homogeneous dispersion of SiO_(2)nanofibers and cellulose nanofibers co-suspensions.It is worth noting that the biomimetic structure has been perfectly inherited even subjected to high-temperature carbonization.As a result,the excellent structural stability brought by the novel structure enables the aerogel to completely recover under large compression and buckling strain of 80%,and exhibit robust fatigue resistance over 200,000 cycles.More importantly,the aerogels exhibit ultralow thermal conductivity(0.023 W·m^(−1)·K^(−1)),superior flame retardancy,together with excellent thermal insulation performance over a wide temperature ranging from−196 to 350°C.The fabrication of such materials may provide new ideas for the development of next-generation thermal insulators for harsh conditions.
