Graphene is the stiffest material known so far but, due to its one-atom thickness, it is also very bendable.Consequently, free-standing graphene exhibit ripples that has major effects on its elastic properties. Here w...Graphene is the stiffest material known so far but, due to its one-atom thickness, it is also very bendable.Consequently, free-standing graphene exhibit ripples that has major effects on its elastic properties. Here we will summarize three experiments where the influence of rippling is essential to address the results. Firstly, we observed that atomic vacancies lessen the negative thermal expansion coefficient(TEC) of free-standing graphene.We also observed an increase of the Young's modulus with global applied strain and with the introduction of small density defects that we attributed to the decrease of rippling. Here, we will focus on a surprising feature observed in the data: the experiments consistently indicate that only the rippling with wavelengths between 5 and 10 nm influences the mechanics of graphene. The rippling responsible of the negative TEC and anomalous elasticity is thought to be dynamic, i.e. flexural phonons. However, flexural phonons with these wavelengths should have minor effects on the mechanics of graphene, therefore other mechanisms must be considered to address our observations. We propose static ripples as one of the key elements to correctly understand the thermomechanics of graphene and suggest that rippling arises naturally due to a competition of symmetry breaking and anharmonic fluctuations.展开更多
The isolation of graphene and subsequent studies showed that obtaining atomically thin crystalline sheets was feasible and possessed extraordinary properties.This result opened the door to an entirely new family of ma...The isolation of graphene and subsequent studies showed that obtaining atomically thin crystalline sheets was feasible and possessed extraordinary properties.This result opened the door to an entirely new family of materials known as two-dimensional or 2D materials.Research in this field is intense:the emergence of new 2D materials,the properties of their combinations and the ability of graphene to reinvent itself,showing novel and exciting properties,make it likely that this field will continue to be one of the leading topics of materials science and condensed matter physics.展开更多
Perfect lenses,superlenses and time-reversal mirrors can support and spatially separate evanescent waves,which is the basis for detecting subwavelength information in the far field.However,the inherent limitations of ...Perfect lenses,superlenses and time-reversal mirrors can support and spatially separate evanescent waves,which is the basis for detecting subwavelength information in the far field.However,the inherent limitations of these methods have prevented the development of systems to dynamically distinguish subdiffraction-limited signals.Utilizing the physical merits of spoof surface plasmon polaritons(SPPs),we demonstrate that subdiffraction-limited signals can be transmitted on planar integrated SPP channels with low loss,low channel interference,and high gain and can be radiated with a very low environmental sensitivity.Furthermore,we show how deep subdiffraction-limited signals that are spatially coupled can be distinguished after line-of-sight wireless transmission.For a visualized demonstration,we realize the high-quality wireless communication of two movies on subwavelength channels over the line of sight in real time using our plasmonic scheme,showing significant advantages over the conventional methods.展开更多
A novel porous and crystalline two-dimensional(2D)electrochemically active covalent organic framework(COF)based on ortho-quinone units has been prepared as an innovative approach towards the development of organic cat...A novel porous and crystalline two-dimensional(2D)electrochemically active covalent organic framework(COF)based on ortho-quinone units has been prepared as an innovative approach towards the development of organic cathode materials with multiple redox sites as an efficient electrocatalyst for the oxygen reduction reaction(ORR).In contrast with most of the previously reported COFs as electrocatalysts for the ORR,the electrocatalytic application of this material towards ORR has been investigated without adding any metal or conductive supporting material and avoiding any additional carbonization step.Additionally,the electrochemical properties of the COF material have been compared with two analogue amorphous frameworks with similar chemical composition,which points out the important role of the enhanced crystallinity and porosity of the COF network in its superior performance as an electrocatalyst towards ORR.展开更多
We propose theoretically and demonstrate experimentally the generation of light pulses whose polarization varies temporally to cover selected areas of the Poincare´sphere with both tunable swirling speed and tota...We propose theoretically and demonstrate experimentally the generation of light pulses whose polarization varies temporally to cover selected areas of the Poincare´sphere with both tunable swirling speed and total duration(1 ps and 10 ps,respectively,in our implementation).The effect relies on the Rabi oscillations of two polariton polarized fields excited by two counter-polarized and delayed pulses.The superposition of the oscillating fields result in the precession of the Stokes vector of the emitted light while polariton lifetime imbalance results in its drift from a circle of controllable radius on the Poincare´sphere to a single point at long times.The positioning of the initial circle and final point allows to engineer the type of polarization spanning,including a full sweeping of the Poincare´sphere.The universality and simplicity of the scheme should allow for the deployment of time-varying full-Poincare´polarization fields in a variety of platforms,timescales,and regimes.展开更多
By combining ab initio calculations and experiments, we demonstrate how the band gap of the transition metal trichalcogenide TiS3 can be modified by inducing tensile or compressive strain. In addition, using our calcu...By combining ab initio calculations and experiments, we demonstrate how the band gap of the transition metal trichalcogenide TiS3 can be modified by inducing tensile or compressive strain. In addition, using our calculations, we predicted that the material would exhibit a transition from a direct to an indirect band gap upon application of a compressive strain in the direction of easy electrical transport. The ability to control the band gap and its nature could have a significant impact on the use of TiS3 for optical applications. We go on to verify our prediction via optical absorption experiments that demonstrate a band gap increase of up to 9% (from 0.99 to 1.08 eV) upon application of tensile stress along the easy transport direction.展开更多
The writings of the text on the last line,left column on the 4^th page and the text on lines 8^th,10^th,11^th and 16^th in the 4^th paragraph,left column and on lines from 1st to 8^th in the 1st paragraph,right column...The writings of the text on the last line,left column on the 4^th page and the text on lines 8^th,10^th,11^th and 16^th in the 4^th paragraph,left column and on lines from 1st to 8^th in the 1st paragraph,right column on the 5^th page,and the text on line 4^th in the 1^st paragraph,left column on the 9^th page,and Fig.3 and its caption on the 5^th page in the original version of this article were unfortunately incorrect.展开更多
Predicting the properties of two-dimensional (2D) materials as graphene and hexagonal boron nitride (h-BN) monolayers after their growth on any given substrate is a major challenge. While the influence of the elec...Predicting the properties of two-dimensional (2D) materials as graphene and hexagonal boron nitride (h-BN) monolayers after their growth on any given substrate is a major challenge. While the influence of the electron configuration of the atoms of the underlying surface is well-understood, the effect of substrate geometry still remains unclear. The structural properties of h-BN monolayers grown on a rectangularly packed Rh(110) surface were characterized in situ by ultrahigh vacuum scanning tunneling microscopy and were compared to those that this material exhibits when grown on substrates showing different crystallographic orientations. Although the h-BN monolayer grown on Rh(110) was dominated by a unique quasiunidimensional moir6 pattern, suggesting considerable interface interaction, the moir6 corrugation was unexpectedly smaller than those reported for strongly interacting interfaces with hexagonal-terminated substrates, owing to differences in the possible binding landscapes at interfaces with differently oriented substrates. Moreover, a rule was derived for predicting how interface corrugation and the existence and extent of subregions within moir6 supercells containing favorable sites for orbital mixing between h-BN monolayers and their supports depend on substrate symmetry. These general symmetry considerations can be applied to numerous 2D materials, including graphene, thereby enabling the prediction of how substrate choice determines the properties of these materials. Furthermore, they could also provide new routes for tuning 2D material properties and for developing nanotemplates showing different geometries for Krowing adsorbate superlattices.展开更多
Though it is well recognized that the space between graphene cover and the metal substrate canact as a two-dimensional(2D)nanoreactor,several issues are still unresolved,including the role of the metal substrate,the m...Though it is well recognized that the space between graphene cover and the metal substrate canact as a two-dimensional(2D)nanoreactor,several issues are still unresolved,including the role of the metal substrate,the mechanisms ruling water intercalation and the identification ofsites at which water is decomposed.Here,we solve these issues by means of density functional theory and high-resolution electron energyloss spectroscopy experiments carried out on graphene grown on(111)-oriented Cu foils.Specifically,we observe decomposition of H2O atroom temperature with only H atoms forming bonds with graphene and with buried OH groups underneath the graphene cover.Ourtheoretical model discloses physicochemical mechanisms ruling the migration and decomposition of water on graphene/Cu.We discover thatthe edge of graphene can be easily saturated by H through decomposition of H2O,which allows H2O to migrate in the subsurface region from thedecoupled edge,where H2O decomposes at room temperature.Hydrogen atoms produced by the decomposition of H2O initially form a chemicalbond with graphene for the lower energy barrier compared with other routes.These findings are essential to exploit graphene/Cu interfaces incatalysis and in energy-related applications.展开更多
Achieving superior performance of nanoparticle systems is one of the biggest challenges in catalysis.Two major phenomena,occurring during the reactions,hinder the development of the full potential of nanoparticle cata...Achieving superior performance of nanoparticle systems is one of the biggest challenges in catalysis.Two major phenomena,occurring during the reactions,hinder the development of the full potential of nanoparticle catalysts:sintering and contamination with carbon containing species,sometimes called coking.Here,we demonstrate that Ir nanocrystals,arranged into periodic networks on hexagonal boron nitride(h-BN)supports,can be restored without sintering after contamination by persistent carbon.This restoration yields the complete removal of carbon from the nanocrystals,which keep their crystalline structure,allowing operation without degradation.These findings,together with the possibility of fine tuning the nanocrystals size,confer this nanoparticle system a great potential as a testbed to extract key information about catalysis-mediated oxidation reactions.For the case of the CO oxidation by O2,reaction of interest in environmental science and green energy production,the existence of chemical processes not observed before in other nanoparticle systems is demonstrated.展开更多
Extracting the light trapped in a waveguide,or the opposite effect of trapping light in a thin region and guiding it perpendicular to its incident propagation direction,is essential for optimal energetic performance i...Extracting the light trapped in a waveguide,or the opposite effect of trapping light in a thin region and guiding it perpendicular to its incident propagation direction,is essential for optimal energetic performance in illumination,display or light harvesting devices.Here we demonstrate that the paradoxical goal of letting as much light in or out while maintaining the wave effectively trapped can be achieved with a periodic array of interpenetrated fibers forming a photonic fiber plate.Photons entering perpendicular to that plate may be trapped in an intermittent chaotic trajectory,leading to an optically ergodic system.We fabricated such a photonic fiber plate and showed that for a solar cell incorporated on one of the plate surfaces,light absorption is greatly enhanced.Confirming this,we found the unexpected result that a more chaotic photon trajectory reduces the production of photon scattering entropy.展开更多
Expanding the functionalities of plasmon-assisted lasers is essential for emergent applications in nanoscience and nanotechnology.Here,we report on a novel ability of plasmonic structures to induce dual-wavelength las...Expanding the functionalities of plasmon-assisted lasers is essential for emergent applications in nanoscience and nanotechnology.Here,we report on a novel ability of plasmonic structures to induce dual-wavelength lasing in the near-infrared region in a Yb^(3+) solid-state laser.By means of the effects of disordered plasmonic networks deposited on the surface of a Yb^(3+)-doped nonlinear RTP crystal,room-temperature dual-wavelength lasing,with a frequency difference between the lines in the THz range,is realized.The dual-wavelength laser is produced by the simultaneous activation of two lasing channels,namely,an electronic-and a phonon-terminated laser transition.The latter is enabled by the out-of-plane field components that are generated by the plasmonic structures,which excite specific Raman modes.Additionally,multiline radiation at three different wavelengths is demonstrated in the visible spectral region via two self-frequency conversion processes,which occur in the vicinities of the plasmonic structures.The results demonstrate the potential of plasmonic nanostructures for inducing drastic modifications in the operational mode of a solid-state laser and hold promise for applications in a variety of fields,including multiplexing,precise spectroscopies,and THz radiation generation via a simple and cost-effective procedure.展开更多
基金financial support from the Spanish MINECO through PID2019-106268 GB-C31from Comunidad de Madrid (S2018/NMT-4511, NMAT2D-CM)+1 种基金support from the Spanish Ministry of Science and Innovation, through the "María de Maeztu" Programme for Units of Excellence in R&D (CEX2018-000805-M)support from the Spanish Ministry of Science and Innovation for the Jd C Fellowship FJCI-2017-32370.
文摘Graphene is the stiffest material known so far but, due to its one-atom thickness, it is also very bendable.Consequently, free-standing graphene exhibit ripples that has major effects on its elastic properties. Here we will summarize three experiments where the influence of rippling is essential to address the results. Firstly, we observed that atomic vacancies lessen the negative thermal expansion coefficient(TEC) of free-standing graphene.We also observed an increase of the Young's modulus with global applied strain and with the introduction of small density defects that we attributed to the decrease of rippling. Here, we will focus on a surprising feature observed in the data: the experiments consistently indicate that only the rippling with wavelengths between 5 and 10 nm influences the mechanics of graphene. The rippling responsible of the negative TEC and anomalous elasticity is thought to be dynamic, i.e. flexural phonons. However, flexural phonons with these wavelengths should have minor effects on the mechanics of graphene, therefore other mechanisms must be considered to address our observations. We propose static ripples as one of the key elements to correctly understand the thermomechanics of graphene and suggest that rippling arises naturally due to a competition of symmetry breaking and anharmonic fluctuations.
文摘The isolation of graphene and subsequent studies showed that obtaining atomically thin crystalline sheets was feasible and possessed extraordinary properties.This result opened the door to an entirely new family of materials known as two-dimensional or 2D materials.Research in this field is intense:the emergence of new 2D materials,the properties of their combinations and the ability of graphene to reinvent itself,showing novel and exciting properties,make it likely that this field will continue to be one of the leading topics of materials science and condensed matter physics.
基金funded by the National Key Research and Development Program of China(Grant Nos.2017YFA0700201,2017YFA0700202,and 2017YFA0700203)by the National Natural Science Foundation of China(Grant Nos.61571117,61631007,61701108,and 61871127)+2 种基金by the 111 Project(Grant No.111-2-05)support from the QuantERA program of the European Commission with funding by the Spanish AEI through project PCI2018-09314from the“Maria de Maeztu”program for Units of Excellence in R&D(MDM-2014-0377).
文摘Perfect lenses,superlenses and time-reversal mirrors can support and spatially separate evanescent waves,which is the basis for detecting subwavelength information in the far field.However,the inherent limitations of these methods have prevented the development of systems to dynamically distinguish subdiffraction-limited signals.Utilizing the physical merits of spoof surface plasmon polaritons(SPPs),we demonstrate that subdiffraction-limited signals can be transmitted on planar integrated SPP channels with low loss,low channel interference,and high gain and can be radiated with a very low environmental sensitivity.Furthermore,we show how deep subdiffraction-limited signals that are spatially coupled can be distinguished after line-of-sight wireless transmission.For a visualized demonstration,we realize the high-quality wireless communication of two movies on subwavelength channels over the line of sight in real time using our plasmonic scheme,showing significant advantages over the conventional methods.
基金This work was financially supported by MICINN(Nos.PID2019-106268GB-C33,CTQ2017-84309-C2-1-R,RED2018-102412-T,and FIS2017-82415-R)Comunidad Autónoma de Madrid Transnanoavansens Program(No.S2018/NMT-4349)。
文摘A novel porous and crystalline two-dimensional(2D)electrochemically active covalent organic framework(COF)based on ortho-quinone units has been prepared as an innovative approach towards the development of organic cathode materials with multiple redox sites as an efficient electrocatalyst for the oxygen reduction reaction(ORR).In contrast with most of the previously reported COFs as electrocatalysts for the ORR,the electrocatalytic application of this material towards ORR has been investigated without adding any metal or conductive supporting material and avoiding any additional carbonization step.Additionally,the electrochemical properties of the COF material have been compared with two analogue amorphous frameworks with similar chemical composition,which points out the important role of the enhanced crystallinity and porosity of the COF network in its superior performance as an electrocatalyst towards ORR.
基金We acknowledge funding from the MIUR project Beyond Nano,the ERC Grant POLAFLOW(308136)the IEF project SQUIRREL(623708)and the support from IRSES project POLAPHEN.
文摘We propose theoretically and demonstrate experimentally the generation of light pulses whose polarization varies temporally to cover selected areas of the Poincare´sphere with both tunable swirling speed and total duration(1 ps and 10 ps,respectively,in our implementation).The effect relies on the Rabi oscillations of two polariton polarized fields excited by two counter-polarized and delayed pulses.The superposition of the oscillating fields result in the precession of the Stokes vector of the emitted light while polariton lifetime imbalance results in its drift from a circle of controllable radius on the Poincare´sphere to a single point at long times.The positioning of the initial circle and final point allows to engineer the type of polarization spanning,including a full sweeping of the Poincare´sphere.The universality and simplicity of the scheme should allow for the deployment of time-varying full-Poincare´polarization fields in a variety of platforms,timescales,and regimes.
文摘By combining ab initio calculations and experiments, we demonstrate how the band gap of the transition metal trichalcogenide TiS3 can be modified by inducing tensile or compressive strain. In addition, using our calculations, we predicted that the material would exhibit a transition from a direct to an indirect band gap upon application of a compressive strain in the direction of easy electrical transport. The ability to control the band gap and its nature could have a significant impact on the use of TiS3 for optical applications. We go on to verify our prediction via optical absorption experiments that demonstrate a band gap increase of up to 9% (from 0.99 to 1.08 eV) upon application of tensile stress along the easy transport direction.
文摘The writings of the text on the last line,left column on the 4^th page and the text on lines 8^th,10^th,11^th and 16^th in the 4^th paragraph,left column and on lines from 1st to 8^th in the 1st paragraph,right column on the 5^th page,and the text on line 4^th in the 1^st paragraph,left column on the 9^th page,and Fig.3 and its caption on the 5^th page in the original version of this article were unfortunately incorrect.
文摘Predicting the properties of two-dimensional (2D) materials as graphene and hexagonal boron nitride (h-BN) monolayers after their growth on any given substrate is a major challenge. While the influence of the electron configuration of the atoms of the underlying surface is well-understood, the effect of substrate geometry still remains unclear. The structural properties of h-BN monolayers grown on a rectangularly packed Rh(110) surface were characterized in situ by ultrahigh vacuum scanning tunneling microscopy and were compared to those that this material exhibits when grown on substrates showing different crystallographic orientations. Although the h-BN monolayer grown on Rh(110) was dominated by a unique quasiunidimensional moir6 pattern, suggesting considerable interface interaction, the moir6 corrugation was unexpectedly smaller than those reported for strongly interacting interfaces with hexagonal-terminated substrates, owing to differences in the possible binding landscapes at interfaces with differently oriented substrates. Moreover, a rule was derived for predicting how interface corrugation and the existence and extent of subregions within moir6 supercells containing favorable sites for orbital mixing between h-BN monolayers and their supports depend on substrate symmetry. These general symmetry considerations can be applied to numerous 2D materials, including graphene, thereby enabling the prediction of how substrate choice determines the properties of these materials. Furthermore, they could also provide new routes for tuning 2D material properties and for developing nanotemplates showing different geometries for Krowing adsorbate superlattices.
基金This work was supported by the National Natural Science Foundation of China(Nos.21676232 and 21673206).A.P.thanks Danil W.Boukhvalov for scientific discussions and Vito Fabio for technical support for the HREELS experiments.D.F.acknowledges financial support from the Spanish Ministry of Economy and Competitiveness,through the Maria de Maeztu Programme for Units of Excellence in R&D(No.MDM-2014-0377)and MINECO project MAT2015-65356-C3-3-R.
文摘Though it is well recognized that the space between graphene cover and the metal substrate canact as a two-dimensional(2D)nanoreactor,several issues are still unresolved,including the role of the metal substrate,the mechanisms ruling water intercalation and the identification ofsites at which water is decomposed.Here,we solve these issues by means of density functional theory and high-resolution electron energyloss spectroscopy experiments carried out on graphene grown on(111)-oriented Cu foils.Specifically,we observe decomposition of H2O atroom temperature with only H atoms forming bonds with graphene and with buried OH groups underneath the graphene cover.Ourtheoretical model discloses physicochemical mechanisms ruling the migration and decomposition of water on graphene/Cu.We discover thatthe edge of graphene can be easily saturated by H through decomposition of H2O,which allows H2O to migrate in the subsurface region from thedecoupled edge,where H2O decomposes at room temperature.Hydrogen atoms produced by the decomposition of H2O initially form a chemicalbond with graphene for the lower energy barrier compared with other routes.These findings are essential to exploit graphene/Cu interfaces incatalysis and in energy-related applications.
基金the Agencia Estatal de Investigación(AEI)and Fondo Europeo de Desarrollo Regional(FEDER)(AEI/FEDER,UE)(project No.MAT2016-77852-C2-2-R)the Comunidad de Madrid and the Universidad Autónoma de Madrid under project No.SI3/PJI/2021-00500,and the CERICERIC Consortium(No.20187040)。
文摘Achieving superior performance of nanoparticle systems is one of the biggest challenges in catalysis.Two major phenomena,occurring during the reactions,hinder the development of the full potential of nanoparticle catalysts:sintering and contamination with carbon containing species,sometimes called coking.Here,we demonstrate that Ir nanocrystals,arranged into periodic networks on hexagonal boron nitride(h-BN)supports,can be restored without sintering after contamination by persistent carbon.This restoration yields the complete removal of carbon from the nanocrystals,which keep their crystalline structure,allowing operation without degradation.These findings,together with the possibility of fine tuning the nanocrystals size,confer this nanoparticle system a great potential as a testbed to extract key information about catalysis-mediated oxidation reactions.For the case of the CO oxidation by O2,reaction of interest in environmental science and green energy production,the existence of chemical processes not observed before in other nanoparticle systems is demonstrated.
基金support from the Spanish MINECO(Severo Ochoa Program,grant no.SEV-2015-0522)the MINECO and the Fondo Europeo de Desarrollo Regional FEDER(grant no.MAT2014-52985-R)+3 种基金the Fundacio Privada Cellex,and from the EC FP7 Program(ICT-2011.35)under grant no.NMP3-SL-2013-604506support from the Spanish MINECO/FEDER(grant no.MAT2015-66128-R)support from the Spanish MINECO(grant no.ENE2014-56237-C4)Mexico’s grant program CONACyT.
文摘Extracting the light trapped in a waveguide,or the opposite effect of trapping light in a thin region and guiding it perpendicular to its incident propagation direction,is essential for optimal energetic performance in illumination,display or light harvesting devices.Here we demonstrate that the paradoxical goal of letting as much light in or out while maintaining the wave effectively trapped can be achieved with a periodic array of interpenetrated fibers forming a photonic fiber plate.Photons entering perpendicular to that plate may be trapped in an intermittent chaotic trajectory,leading to an optically ergodic system.We fabricated such a photonic fiber plate and showed that for a solar cell incorporated on one of the plate surfaces,light absorption is greatly enhanced.Confirming this,we found the unexpected result that a more chaotic photon trajectory reduces the production of photon scattering entropy.
基金support from the Spanish Government under project MAT2016-76106-RComunidad de Madrid under grant S2013/MIT-2740+4 种基金funding from the Spanish Government under projects MAT2016-75716-C2-1-R(AEI/FEDER,UE)TEC2014-55948-RGeneralitat de Catalunya under project 2017SGR755grant FPU13/02476 from the Spanish Ministry of Educationfinancial support from the Spanish Government,through The“Maria de Maeztu”Programme for Units of Excellence in R&D(MDM-2014-0377)”.
文摘Expanding the functionalities of plasmon-assisted lasers is essential for emergent applications in nanoscience and nanotechnology.Here,we report on a novel ability of plasmonic structures to induce dual-wavelength lasing in the near-infrared region in a Yb^(3+) solid-state laser.By means of the effects of disordered plasmonic networks deposited on the surface of a Yb^(3+)-doped nonlinear RTP crystal,room-temperature dual-wavelength lasing,with a frequency difference between the lines in the THz range,is realized.The dual-wavelength laser is produced by the simultaneous activation of two lasing channels,namely,an electronic-and a phonon-terminated laser transition.The latter is enabled by the out-of-plane field components that are generated by the plasmonic structures,which excite specific Raman modes.Additionally,multiline radiation at three different wavelengths is demonstrated in the visible spectral region via two self-frequency conversion processes,which occur in the vicinities of the plasmonic structures.The results demonstrate the potential of plasmonic nanostructures for inducing drastic modifications in the operational mode of a solid-state laser and hold promise for applications in a variety of fields,including multiplexing,precise spectroscopies,and THz radiation generation via a simple and cost-effective procedure.