Boron is an ambitious fuel in energetic materials since its high heat release values,but its application is prohibited by low combustion efficiency and oxidization during storage.The polydopamine(PDA)was introduced in...Boron is an ambitious fuel in energetic materials since its high heat release values,but its application is prohibited by low combustion efficiency and oxidization during storage.The polydopamine(PDA)was introduced into boron particles,investigating the impact of PDA content on the energetic behavior of boron.The results indicated that the PDA coating formed a fishing net structure on the surface of boron particles.The heat release results showed that the combustion calorific value of B@PDA was higher than that of the raw boron.Specifically,the actual combustion heat of boron powder in B@10%PDA increased by 38.08%.Meanwhile,the DSC peak temperature decreased by 100.65℃under similar oxidation rate compared to raw boron.Simultaneously,the B@PDA@AP and B@AP composites were prepared,and their combustion properties were evaluated.It was demonstrated that B@10%PDA@AP exhibited superior performance in terms of peak pressure and burning time,respectively.The peak pressure is 12.43 kPa more than B@AP and burning time is 2.22 times higher than B@AP.Therefore,the coating of PDA effectively inhibits the oxidization of boron during storage and enhances the energetic behavior of boron and corresponding composites.展开更多
Metamaterials with higher-order topological band gaps that exhibit topological physics beyond the bulkedge correspondence provide unique application values due to their ability of integrating topological boundary stat...Metamaterials with higher-order topological band gaps that exhibit topological physics beyond the bulkedge correspondence provide unique application values due to their ability of integrating topological boundary states at multiple dimensions in a single chip.On the other hand,in the past decade,micromechanical metamaterials are developing rapidly for various applications such as micro-piezoelectricgenerators,intelligent micro-systems,on-chip sensing and self-powered micro-systems.To empower these cutting-edge applications with topological manipulations of elastic waves,higher-order topological mechanical systems working at high frequencies(MHz)with high quality-factors are demanded.The current realizations of higher-order topological mechanical systems,however,are still limited to systems with large scales(centimetres)and low frequencies(k Hz).Here,we report the first experimental realization of an on-chip micromechanical metamaterial as the higher-order topological insulator for elastic waves at MHz.The higher-order topological phononic band gap is induced by the band inversion at the Brillouin zone corner which is achieved by configuring the orientations of the elliptic pillars etched on the silicon chip.With consistent experiments,theory and simulations,we demonstrate the emergence of coexisting topological edge and corner states in a single silicon chip as induced by the higher-order band topology.The experimental realization of on-chip micromechanical metamaterials with higherorder topology opens a new regime for materials and applications based on topological elastic waves.展开更多
The screw dislocations are intriguing defects that are often observed in natural and artificial materials. The dislocation spirals break the reflection and inversion symmetries of the lattices and modify the interlaye...The screw dislocations are intriguing defects that are often observed in natural and artificial materials. The dislocation spirals break the reflection and inversion symmetries of the lattices and modify the interlayer coupling in layer-structured materials, inducing additional complexity in layer stacking and thus novel properties in materials. Here, we report on the interlayer coupling of two-dimensional (2D) MoSe2 flakes with screw dislocations by atomic force microscopy (AFM), Raman spectra and photoluminescence (PL) spectra. By controlling the supersaturation conditions, 2D MoSe2 flakes with screw dislocations are grown on amorphous SiO2 substrates by chemical vapor deposition (CVD). AFM measurements reveal that the interlayer spacing in such 2D MoSe2 flakes with screw dislocation is slightly widened with respect to the normal AA- or AB-stacked ones due to the presence of the screw dislocations. Raman and PL spectra show that the interlayer coupling is weaker and thus the band gap is wider than that in the normal AA- or AB-stacked ones. Our work demonstrates that the interlayer coupling of 2D transition metal dichalcogenides (TMDCs) flakes can be tuned by the induction of screw dislocations, which is very helpful for developing novel catalysts and electronic devices.展开更多
Topological metals(TMs)are a kind of special metallic materials,which feature nontrivial band Cross-ings near the Fermi energy,giving rise to peculiar quasiparticle excitations.TMs can be classified based on the chara...Topological metals(TMs)are a kind of special metallic materials,which feature nontrivial band Cross-ings near the Fermi energy,giving rise to peculiar quasiparticle excitations.TMs can be classified based on the characteristics of these band crossings.For example,according to the dimensionality of the crossing,TMs can be classifed into nodal-point,nodal-line,and nodal-surface metals.Another important property is the type of dispersion.According to degree of the tilt of the local dispersion around the crossing,we have typeI and type-II dispersions.This leads to significant distinctions in the physical properties of the materials,owing to their contrasting Fermi surface topologies.In this article,we briefly review the recent advances in this research direction,focusing on the concepts,the physical properties,and the material realizations of the type-Il nodal-point and nodal-line TMs.展开更多
Recently,fragile topology[1–11]and its important role in the properties of twisted bilayer graphene[8],non-Abelian topology[9],flat bands[10]and related emergent phases have attracted much attention,and led to discov...Recently,fragile topology[1–11]and its important role in the properties of twisted bilayer graphene[8],non-Abelian topology[9],flat bands[10]and related emergent phases have attracted much attention,and led to discoveries that connect band topology with correlated electron states[11,12]such as superconductivity[12].Interestingly,the band topology can impose constraints on the superconducting order parameters as revealed by recent studies[12].Fragile topological phases are characterized by nontrivial signatures in either the Wilson loops[3,6]or the band representations[2,3,13]but can be connected with some obstructed atomic insulator phases,which are trivial insulators with charge centers away from atoms,via adding some trivial bands[2].It has been shown that fragile topological insulators do not have robust edge states,imposing challenges on their experimental signatures.Later,it was proposed that local gauge flux insertion[4]or twisted boundary conditions[14,15]can be a useful tool to probe the fragile topology.However,neither local gauge flux insertion nor the twisted boundary condition is feasible in genuine condensed matter experimental conditions.展开更多
文摘Boron is an ambitious fuel in energetic materials since its high heat release values,but its application is prohibited by low combustion efficiency and oxidization during storage.The polydopamine(PDA)was introduced into boron particles,investigating the impact of PDA content on the energetic behavior of boron.The results indicated that the PDA coating formed a fishing net structure on the surface of boron particles.The heat release results showed that the combustion calorific value of B@PDA was higher than that of the raw boron.Specifically,the actual combustion heat of boron powder in B@10%PDA increased by 38.08%.Meanwhile,the DSC peak temperature decreased by 100.65℃under similar oxidation rate compared to raw boron.Simultaneously,the B@PDA@AP and B@AP composites were prepared,and their combustion properties were evaluated.It was demonstrated that B@10%PDA@AP exhibited superior performance in terms of peak pressure and burning time,respectively.The peak pressure is 12.43 kPa more than B@AP and burning time is 2.22 times higher than B@AP.Therefore,the coating of PDA effectively inhibits the oxidization of boron during storage and enhances the energetic behavior of boron and corresponding composites.
基金supported by the Natural Science Foundation of Guangdong Province(2020A1515010549)China Postdoctoral Science Foundation(2020M672615 and 2019M662885)+1 种基金National Postdoctoral Program for Innovative Talents(BX20190122)the Jiangsu specially-appointed professor funding。
文摘Metamaterials with higher-order topological band gaps that exhibit topological physics beyond the bulkedge correspondence provide unique application values due to their ability of integrating topological boundary states at multiple dimensions in a single chip.On the other hand,in the past decade,micromechanical metamaterials are developing rapidly for various applications such as micro-piezoelectricgenerators,intelligent micro-systems,on-chip sensing and self-powered micro-systems.To empower these cutting-edge applications with topological manipulations of elastic waves,higher-order topological mechanical systems working at high frequencies(MHz)with high quality-factors are demanded.The current realizations of higher-order topological mechanical systems,however,are still limited to systems with large scales(centimetres)and low frequencies(k Hz).Here,we report the first experimental realization of an on-chip micromechanical metamaterial as the higher-order topological insulator for elastic waves at MHz.The higher-order topological phononic band gap is induced by the band inversion at the Brillouin zone corner which is achieved by configuring the orientations of the elliptic pillars etched on the silicon chip.With consistent experiments,theory and simulations,we demonstrate the emergence of coexisting topological edge and corner states in a single silicon chip as induced by the higher-order band topology.The experimental realization of on-chip micromechanical metamaterials with higherorder topology opens a new regime for materials and applications based on topological elastic waves.
基金supported by the National Natural Science Foundation of China (Nos.11574029, 51661135026, 2177300&11704027, 11574361, and 11834017)the National Key R&D Program of China (Nos.2016YFA0300600 and 2016YFA0300904)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences (Nos.XDB30000000)the Key Research Program of Frontier Sciences (No.QYZDB-SSW-SLH004)the Youth Innovation Promotion Association CAS (No.2018013).
文摘The screw dislocations are intriguing defects that are often observed in natural and artificial materials. The dislocation spirals break the reflection and inversion symmetries of the lattices and modify the interlayer coupling in layer-structured materials, inducing additional complexity in layer stacking and thus novel properties in materials. Here, we report on the interlayer coupling of two-dimensional (2D) MoSe2 flakes with screw dislocations by atomic force microscopy (AFM), Raman spectra and photoluminescence (PL) spectra. By controlling the supersaturation conditions, 2D MoSe2 flakes with screw dislocations are grown on amorphous SiO2 substrates by chemical vapor deposition (CVD). AFM measurements reveal that the interlayer spacing in such 2D MoSe2 flakes with screw dislocation is slightly widened with respect to the normal AA- or AB-stacked ones due to the presence of the screw dislocations. Raman and PL spectra show that the interlayer coupling is weaker and thus the band gap is wider than that in the normal AA- or AB-stacked ones. Our work demonstrates that the interlayer coupling of 2D transition metal dichalcogenides (TMDCs) flakes can be tuned by the induction of screw dislocations, which is very helpful for developing novel catalysts and electronic devices.
基金The authors thank D.L.Deng for valuable discussions.The work was supported by the National Natural Sei-ence Foundation of China(Grants No.11734003)the National Key R&D Program of China(Grant No.2016YFA0300600)+1 种基金the Strategic P rorty Researei Prugram uf Chimese Aeadeny uf seenes(GraIL No.XD3000000)the Singapore Ministry of Education AcRF Tier 2(Grant Nos.MOE2017-T2-2-108 and MOE2019-T2-1-001).
文摘Topological metals(TMs)are a kind of special metallic materials,which feature nontrivial band Cross-ings near the Fermi energy,giving rise to peculiar quasiparticle excitations.TMs can be classified based on the characteristics of these band crossings.For example,according to the dimensionality of the crossing,TMs can be classifed into nodal-point,nodal-line,and nodal-surface metals.Another important property is the type of dispersion.According to degree of the tilt of the local dispersion around the crossing,we have typeI and type-II dispersions.This leads to significant distinctions in the physical properties of the materials,owing to their contrasting Fermi surface topologies.In this article,we briefly review the recent advances in this research direction,focusing on the concepts,the physical properties,and the material realizations of the type-Il nodal-point and nodal-line TMs.
基金supports from the National Key R&D Program of China(2022YFA1404400)the National Natural Science Foundation of China(12125504 and 12074281)+5 种基金the“Hundred Talents Program”of the Chinese Academy of Sciencesthe Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institutionssupported by the National Natural Science Foundation of China(12274005)National Key R&D Program of China(2021YFA1401900)supported by the Fundamental Research Funds for the Central Universities(30923010207)the National Natural Science Foundation of China(12302112)。
文摘Recently,fragile topology[1–11]and its important role in the properties of twisted bilayer graphene[8],non-Abelian topology[9],flat bands[10]and related emergent phases have attracted much attention,and led to discoveries that connect band topology with correlated electron states[11,12]such as superconductivity[12].Interestingly,the band topology can impose constraints on the superconducting order parameters as revealed by recent studies[12].Fragile topological phases are characterized by nontrivial signatures in either the Wilson loops[3,6]or the band representations[2,3,13]but can be connected with some obstructed atomic insulator phases,which are trivial insulators with charge centers away from atoms,via adding some trivial bands[2].It has been shown that fragile topological insulators do not have robust edge states,imposing challenges on their experimental signatures.Later,it was proposed that local gauge flux insertion[4]or twisted boundary conditions[14,15]can be a useful tool to probe the fragile topology.However,neither local gauge flux insertion nor the twisted boundary condition is feasible in genuine condensed matter experimental conditions.
