Research on two-dimensional(2D)materials is one of the most active fields in materials science and nanotechnology.Among the members of the 2D family,layered hydroxides(LHs)represent an exceptional case of study due to...Research on two-dimensional(2D)materials is one of the most active fields in materials science and nanotechnology.Among the members of the 2D family,layered hydroxides(LHs)represent an exceptional case of study due to their unparalleled chemical versatility which allows the modulation of their physicochemical properties at will.Nowadays,LHs based on earth-abundant metals are key materials in the areas of energy storage and conversion,hybrid materials or magnetism.α-Co hydroxides(Simonkolleite-like structures)are promising phases with tuneable electronic and magnetic properties by ligand modification.However,even in the simple case ofα-Co^(Ⅱ)hydroxychlorides,the preparation of well-defined large 2D crystals is not straightforward,hindering the development of fundamental studies.Herein,we present the synthesis of 2D hexagonal crystals with outstanding sizethickness relationship(diameter>5μm and thickness of 20±7 nm)by a simple homogeneous synthesis taking place at room temperature.In structural terms,no differences are observed between our layered materials and those obtained hydrothermally.However,dynamic susceptibility measurements alert about different arrangements of the magnetic sublattices,which have been rationalized with structural DFT calculations.This work provides an extremely easy bottom-up method to obtain high-quality 2D crystals based onα-CoIIhydroxides,paving the way for the development of fundamental studies and applications.展开更多
This paper investigates the collision between two nonlinear waves with different propagation directions in two- dimensional dust crystals. Using the extended Poincare-Lighthill-Kuo perturbation method, two Korteweg-de...This paper investigates the collision between two nonlinear waves with different propagation directions in two- dimensional dust crystals. Using the extended Poincare-Lighthill-Kuo perturbation method, two Korteweg-de Vries equations for nonlinear waves in both the ξ and η directions are obtained, respectively, and the analytical phase shifts and trajectories after the collision of two nonlinear waves are derived. Finally, the effects of parameters of the lattice constant a, the arbitrary constant u0η, the forces f（r）, and the colliding angle θ on the phase shifts of both colliding nonlinear waves are examined.展开更多
Two-dimensional（2D） materials have recently received a great deal of attention due to their unique structures and fascinating properties,as well as their potential applications.2D hexagonal boron nitride（2D hBN）,a...Two-dimensional（2D） materials have recently received a great deal of attention due to their unique structures and fascinating properties,as well as their potential applications.2D hexagonal boron nitride（2D hBN）,an insulator with excellent thermal stability,chemical inertness,and unique electronic and optical properties,and a band gap of 5.97 e V,is considered to be an ideal candidate for integration with other 2D materials.Nevertheless,the controllable growth of high-quality 2D h-BN is still a great challenge.A comprehensive overview of the progress that has been made in the synthesis of 2D h-BN is presented,highlighting the advantages and disadvantages of various synthesis approaches.In addition,the electronic,optical,thermal,and mechanical properties,heterostructures,and related applications of 2D h-BN are discussed.展开更多
The thermal conduction of suspended few-layer hexagonal boron nitride （h-BN） sheets was experimentally investigated using a noncontact micro-Raman spectroscopy method. The first-order temperature coefficients for mo...The thermal conduction of suspended few-layer hexagonal boron nitride （h-BN） sheets was experimentally investigated using a noncontact micro-Raman spectroscopy method. The first-order temperature coefficients for monolayer （1L）, bilayer （2L） and nine-layer （9L） h-BN sheets were measured to be -（3.41 ± 0.12）× 10-2, -（3.15 ± 0.14） × 10-2 and -（3.78 ±0.16）× 10-2 cm-1.K-1, respectively. The room-temperature thermal conductivity of few-layer h-BN sheets was found to be in the range from 227 to 280 W.m-1-K-1, which is comparable to that of bulk h-BN, indicating their potential use as important components to solve heat dissipation problems in thermal management configurations.展开更多
Hexagonal boron nitride （h-BN） is believed to offer better passivation to metallic surfaces than graphene owing to its insulating nature, which facilitates blocking the flow of electrons, thereby preventing the occu...Hexagonal boron nitride （h-BN） is believed to offer better passivation to metallic surfaces than graphene owing to its insulating nature, which facilitates blocking the flow of electrons, thereby preventing the occurrence of galvanic reactions. Nevertheless, this may not be the case when an h-BN-protected material is exposed to aqueous environments. In this work, we analyzed the stability of mono and multilayer h-BN stacks exposed to H202 and atmospheric conditions. Our experiments revealed that monolayer h-BN is as inefficient as graphene as a protective coating when exposed to H202. Multilayer h-BN offered a good degree of protection. Monolayer h-BN was found to be ineffective in an air atmosphere as well. Even a 10-15 layers-thick h-BN stack could not completely protect the surface of the metal under consideration. By combining Auger electron spectroscopy and secondary ion mass spectrometry techniques, we observed that oxygen could diffuse through the grain boundaries of the h-BN stack to reach the metallic substrate. Fortunately, because of the diffusive nature of the process, the oxidized area did not increase with time once a saturated state was reached. This makes multflayer （not monolayer） h-BN a suitable long-term oxidation barrier. Oxygen infiltration could not be observed by X-ray photoelectron spectroscopy. This technique cannot assess the chemical composition of the deeper layers of a material. Hence, the previous reports, which relied on XPS to analyze the passivating properties of h-BN and graphene, may have ignored some important subsurface phenomena. The results obtained in this study provide new insights into the passivating properties of mono and multilayer h-BN in aqueous media and the degradation kinetics of h-BN-coated metals exposed to an air environment.展开更多
We present molecular dynamics simulation evidence for a freezing transition from liquid silicon to quasi-two-dimensional(quasi-2D)bilayer silicon in a slit nanopore.This new quasi-2D polymorph of silicon exhibits a bi...We present molecular dynamics simulation evidence for a freezing transition from liquid silicon to quasi-two-dimensional(quasi-2D)bilayer silicon in a slit nanopore.This new quasi-2D polymorph of silicon exhibits a bilayer hexagonal structure in which the covalent coordination number of every silicon atom is four.Quantum molecular dynamics simulations show that the stand-alone bilayer silicon(without the confinement)is still stable at 400 K.Electronic band-structure calculations suggest that the bilayer hexagonal silicon is a quasi-2D semimetal,similar to a graphene monolayer,but with an indirect zero band gap.展开更多
Quantum information technology requires bright and stable single-photon emitters(SPEs).As a promising single-photon source,SPEs in layered hexagonal boron nitride(hBN)have attracted much attention recently for their h...Quantum information technology requires bright and stable single-photon emitters(SPEs).As a promising single-photon source,SPEs in layered hexagonal boron nitride(hBN)have attracted much attention recently for their high brightness and excellent optical stability at room temperature.In this review,the physical mechanisms and the recent progress of the quantum emission of hBN are reviewed,and the various techniques to fabricate high-quality SPEs in hBN are summarized.The latest development and applications based on SPEs in hBN in emerging areas are discussed.This review focuses on the modulation of SPEs in hBN and discusses possible research directions for future device applications.展开更多
Among the various two-dimensional(2D)materials,more than 99%of them are noncentrosymmetric.However,since the commonly used substrates are generally centrosymmetric,antiparallel islands are usually inevitable in the gr...Among the various two-dimensional(2D)materials,more than 99%of them are noncentrosymmetric.However,since the commonly used substrates are generally centrosymmetric,antiparallel islands are usually inevitable in the growth of noncentrosymmetric 2D materials because of the energetic equivalency of these two kinds of antiparallel islands on centrosymmetric substrates.Therefore,achieving the growth of noncentrosymmetric 2D single crystals has long been a great challenge compared with the centrosymmetric ones like graphene.In this review,we presented the remarkable efforts and progress in the past decade,through precise chemical processes.We first discussed the great challenge and possible strategies in the growth of noncentrosymmetric 2D single crystals.Then,we focused on the advancements made in producing representative noncentrosymmetric 2D single crystals,including hexagonal boron nitride(hBN),transition metal dichalcogenides(TMDs),and other noncentrosymmetric 2D materials.At last,we summarized and looked forward to future research on the growth of layer-,stacking-,and twist-controlled noncentrosymmetric 2D single crystals and their heterostructures.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
Two-dimensional （2D） crystals have a multitude of forms, including semi-metals, semiconductors, and insulators, which are ideal for assembling isolated 2D atomic materials to create van der Waals （vdW） heterostruc...Two-dimensional （2D） crystals have a multitude of forms, including semi-metals, semiconductors, and insulators, which are ideal for assembling isolated 2D atomic materials to create van der Waals （vdW） heterostructures. Recently, artificially-stacked materials have been considered promising candidates for nanoelectronic and optoelectronic applications. In this study, we report the vertical integration of layered structures for the fabrication of prototype non-volatile memory devices. A semiconducting-tungsten-disulfide-channel-based memory device is created by sandwiching high-density-of-states multi-layered graphene as a carrier-confining layer between tunnel barriers of hexagonal boron nitride （hBN） and silicon dioxide. The results reveal that a memory window of up to 20 V is opened, leading to a high current ratio （〉103） between programming and erasing states. The proposed design combination produced layered materials that allow devices to attain perfect retention at 13% charge loss after 10 years, offering new possibilities for the integration of transparent, flexible electronic systems.展开更多
基金supported by the European Research Council(ERC Starting Grant No.2D-Pnicto Chem 804110)the Spanish MICINN(PID2019-111742GA-I00 and Unit of Excellence“María de Maeztu”CEX2019-000919-M)+2 种基金the Deutsche Forschungsgemeinschaft DFG(FLAG-ERA AB694/2-1)the Generalitat Valenciana(CIDEGENT/2018/001 and i Di FEDER/2018/061 co-financed by FEDER)CONICET for financial support and CNEA Computing Clusters for computer time(density functional theory calculations).
文摘Research on two-dimensional(2D)materials is one of the most active fields in materials science and nanotechnology.Among the members of the 2D family,layered hydroxides(LHs)represent an exceptional case of study due to their unparalleled chemical versatility which allows the modulation of their physicochemical properties at will.Nowadays,LHs based on earth-abundant metals are key materials in the areas of energy storage and conversion,hybrid materials or magnetism.α-Co hydroxides(Simonkolleite-like structures)are promising phases with tuneable electronic and magnetic properties by ligand modification.However,even in the simple case ofα-Co^(Ⅱ)hydroxychlorides,the preparation of well-defined large 2D crystals is not straightforward,hindering the development of fundamental studies.Herein,we present the synthesis of 2D hexagonal crystals with outstanding sizethickness relationship(diameter>5μm and thickness of 20±7 nm)by a simple homogeneous synthesis taking place at room temperature.In structural terms,no differences are observed between our layered materials and those obtained hydrothermally.However,dynamic susceptibility measurements alert about different arrangements of the magnetic sublattices,which have been rationalized with structural DFT calculations.This work provides an extremely easy bottom-up method to obtain high-quality 2D crystals based onα-CoIIhydroxides,paving the way for the development of fundamental studies and applications.
基金Project supported by the National Natural Science Foundation of China(Grant No.10875098)the Scientific and Technical Innovation Foundation of Northwest Normal University(Grant No.NWNU-KJCXGC-0348)
文摘This paper investigates the collision between two nonlinear waves with different propagation directions in two- dimensional dust crystals. Using the extended Poincare-Lighthill-Kuo perturbation method, two Korteweg-de Vries equations for nonlinear waves in both the ξ and η directions are obtained, respectively, and the analytical phase shifts and trajectories after the collision of two nonlinear waves are derived. Finally, the effects of parameters of the lattice constant a, the arbitrary constant u0η, the forces f（r）, and the colliding angle θ on the phase shifts of both colliding nonlinear waves are examined.
基金Project supported by the National Natural Science Foundation of China(Nos.61376007,61674137)the National Key Research and Development Program of China(No.2016YFB0400802)
文摘Two-dimensional（2D） materials have recently received a great deal of attention due to their unique structures and fascinating properties,as well as their potential applications.2D hexagonal boron nitride（2D hBN）,an insulator with excellent thermal stability,chemical inertness,and unique electronic and optical properties,and a band gap of 5.97 e V,is considered to be an ideal candidate for integration with other 2D materials.Nevertheless,the controllable growth of high-quality 2D h-BN is still a great challenge.A comprehensive overview of the progress that has been made in the synthesis of 2D h-BN is presented,highlighting the advantages and disadvantages of various synthesis approaches.In addition,the electronic,optical,thermal,and mechanical properties,heterostructures,and related applications of 2D h-BN are discussed.
文摘The thermal conduction of suspended few-layer hexagonal boron nitride （h-BN） sheets was experimentally investigated using a noncontact micro-Raman spectroscopy method. The first-order temperature coefficients for monolayer （1L）, bilayer （2L） and nine-layer （9L） h-BN sheets were measured to be -（3.41 ± 0.12）× 10-2, -（3.15 ± 0.14） × 10-2 and -（3.78 ±0.16）× 10-2 cm-1.K-1, respectively. The room-temperature thermal conductivity of few-layer h-BN sheets was found to be in the range from 227 to 280 W.m-1-K-1, which is comparable to that of bulk h-BN, indicating their potential use as important components to solve heat dissipation problems in thermal management configurations.
文摘Hexagonal boron nitride （h-BN） is believed to offer better passivation to metallic surfaces than graphene owing to its insulating nature, which facilitates blocking the flow of electrons, thereby preventing the occurrence of galvanic reactions. Nevertheless, this may not be the case when an h-BN-protected material is exposed to aqueous environments. In this work, we analyzed the stability of mono and multilayer h-BN stacks exposed to H202 and atmospheric conditions. Our experiments revealed that monolayer h-BN is as inefficient as graphene as a protective coating when exposed to H202. Multilayer h-BN offered a good degree of protection. Monolayer h-BN was found to be ineffective in an air atmosphere as well. Even a 10-15 layers-thick h-BN stack could not completely protect the surface of the metal under consideration. By combining Auger electron spectroscopy and secondary ion mass spectrometry techniques, we observed that oxygen could diffuse through the grain boundaries of the h-BN stack to reach the metallic substrate. Fortunately, because of the diffusive nature of the process, the oxidized area did not increase with time once a saturated state was reached. This makes multflayer （not monolayer） h-BN a suitable long-term oxidation barrier. Oxygen infiltration could not be observed by X-ray photoelectron spectroscopy. This technique cannot assess the chemical composition of the deeper layers of a material. Hence, the previous reports, which relied on XPS to analyze the passivating properties of h-BN and graphene, may have ignored some important subsurface phenomena. The results obtained in this study provide new insights into the passivating properties of mono and multilayer h-BN in aqueous media and the degradation kinetics of h-BN-coated metals exposed to an air environment.
基金This work was supported by grants from the De-partment of Energy(DOE)(No.DE-FG02-04ER46164)。
文摘We present molecular dynamics simulation evidence for a freezing transition from liquid silicon to quasi-two-dimensional(quasi-2D)bilayer silicon in a slit nanopore.This new quasi-2D polymorph of silicon exhibits a bilayer hexagonal structure in which the covalent coordination number of every silicon atom is four.Quantum molecular dynamics simulations show that the stand-alone bilayer silicon(without the confinement)is still stable at 400 K.Electronic band-structure calculations suggest that the bilayer hexagonal silicon is a quasi-2D semimetal,similar to a graphene monolayer,but with an indirect zero band gap.
基金This work was supported by the National Key Research and Development Program of China(No.2017YFA0206000)Beijing Natural Science Foundation(No.Z180011)National Natural Science Foundation of China(Nos.12027807 and 61521004)。
文摘Quantum information technology requires bright and stable single-photon emitters(SPEs).As a promising single-photon source,SPEs in layered hexagonal boron nitride(hBN)have attracted much attention recently for their high brightness and excellent optical stability at room temperature.In this review,the physical mechanisms and the recent progress of the quantum emission of hBN are reviewed,and the various techniques to fabricate high-quality SPEs in hBN are summarized.The latest development and applications based on SPEs in hBN in emerging areas are discussed.This review focuses on the modulation of SPEs in hBN and discusses possible research directions for future device applications.
基金This work was supported by Guangdong Major Project of Basic and Applied Basic Research(2021B030103000)the National Natural Science Foundation of China(12322406,52102043,52025023,51991342,52021006 and 61905215)+5 种基金the Key R&D Program of Guangdong Province(2020B010189001,2019B010931001,2018B010109009 and 2018B030327001)the Pearl River Talent Recruitment Program of Guangdong Province(2019ZT08C321)the Key Project of Science and Technology of Guangzhou(202201010383)the Natural Science Foundation o f Guangdong Provinces(2023A1515012743)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB3300000)the New Cornerstone Science Foundation through the XPLORER PRIZE.
文摘Among the various two-dimensional(2D)materials,more than 99%of them are noncentrosymmetric.However,since the commonly used substrates are generally centrosymmetric,antiparallel islands are usually inevitable in the growth of noncentrosymmetric 2D materials because of the energetic equivalency of these two kinds of antiparallel islands on centrosymmetric substrates.Therefore,achieving the growth of noncentrosymmetric 2D single crystals has long been a great challenge compared with the centrosymmetric ones like graphene.In this review,we presented the remarkable efforts and progress in the past decade,through precise chemical processes.We first discussed the great challenge and possible strategies in the growth of noncentrosymmetric 2D single crystals.Then,we focused on the advancements made in producing representative noncentrosymmetric 2D single crystals,including hexagonal boron nitride(hBN),transition metal dichalcogenides(TMDs),and other noncentrosymmetric 2D materials.At last,we summarized and looked forward to future research on the growth of layer-,stacking-,and twist-controlled noncentrosymmetric 2D single crystals and their heterostructures.
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.
文摘Two-dimensional （2D） crystals have a multitude of forms, including semi-metals, semiconductors, and insulators, which are ideal for assembling isolated 2D atomic materials to create van der Waals （vdW） heterostructures. Recently, artificially-stacked materials have been considered promising candidates for nanoelectronic and optoelectronic applications. In this study, we report the vertical integration of layered structures for the fabrication of prototype non-volatile memory devices. A semiconducting-tungsten-disulfide-channel-based memory device is created by sandwiching high-density-of-states multi-layered graphene as a carrier-confining layer between tunnel barriers of hexagonal boron nitride （hBN） and silicon dioxide. The results reveal that a memory window of up to 20 V is opened, leading to a high current ratio （〉103） between programming and erasing states. The proposed design combination produced layered materials that allow devices to attain perfect retention at 13% charge loss after 10 years, offering new possibilities for the integration of transparent, flexible electronic systems.
