Glucose molecules are of great significance being one of the most important molecules in metabolic chain.However,due to the small Raman scattering cross-section and weak/non-adsorption on bare metals,accurately obtain...Glucose molecules are of great significance being one of the most important molecules in metabolic chain.However,due to the small Raman scattering cross-section and weak/non-adsorption on bare metals,accurately obtaining their"fingerprint information"remains a huge obstacle.Herein,we developed a tip-enhanced Raman scattering(TERS)technique to address this challenge.Adopting an optical fiber radial vector mode internally illuminates the plasmonic fiber tip to effectively suppress the background noise while generating a strong electric-field enhanced tip hotspot.Furthermore,the tip hotspot approaching the glucose molecules was manipulated via the shear-force feedback to provide more freedom for selecting substrates.Consequently,our TERS technique achieves the visualization of all Raman modes of glucose molecules within spectral window of 400-3200 cm^(-1),which is not achievable through the far-field/surface-enhanced Raman,or the existing TERS techniques.Our TERS technique offers a powerful tool for accurately identifying Raman scattering of molecules,paving the way for biomolecular analysis.展开更多
The quality of the scanning tip is crucial for tip-enhanced Raman spectroscopy(TERS)experiments towards large signal enhancement and high spatial resolution.In this work,we report a controllable fabrication method to ...The quality of the scanning tip is crucial for tip-enhanced Raman spectroscopy(TERS)experiments towards large signal enhancement and high spatial resolution.In this work,we report a controllable fabrication method to prepare TERS-active tips by modifying the tip apex at the atomic scale,and propose two important criteria to in-situ judge the tip’s TERS activity for tip-enhanced Raman measurements.One criterion is based on the downshift of the first image potential state to monitor the coupling between the far-field incident laser and near-field plasmon;the other is based on the appearance of the low-wavenumber Raman peaks associated with an atomistic protrusion at the tip apex to judge the coupling efficiency of emissions from the near field to the far field.This work provides an effective method to quickly fabricate and judge TERS-active tips before real TERS experiments on target molecules and other materials,which is believed to be instrumental for the development of TERS and other tip-enhanced spectroscopic techniques.展开更多
Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible ...Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible for Raman to detect single molecule with nanometer resolution.However,due to technical diffculties,tip-enhanced CARS(TECARS)is not as successful as expected.For single molecular detection,high sensitivity and resolution are two main challenges.Here,we reported the first single atom layer TECARS imaging on Graphene with the highest resolution about 20 nm,which has ever been reported.The highest EF_(TECARS/CARS) is about 10^(4),the similar order of magnitude with SECARS(EF of tip is usually smaller than that of substrates).Such resolution and sensitivity is promising for medical,biology and chemical applications in the future.展开更多
A thorough understanding of biological species and emerging nanomaterials requires,among other efforts,their in-depth characterization through optical techniques capable of nanoresolution.Nanoscopy techniques based on...A thorough understanding of biological species and emerging nanomaterials requires,among other efforts,their in-depth characterization through optical techniques capable of nanoresolution.Nanoscopy techniques based on tip-enhanced optical effects have gained tremendous interest over the past years,given their potential to obtain optical information with resolutions limited only by the size of a sharp probe interacting with focused light,irrespective of the illumination wavelength.Although their popularity and number of applications is rising,tip-enhanced nanoscopy(TEN)techniques still largely rely on probes that are not specifically developed for such applications,but for atomic force microscopy.This limits their potential in many regards,e.g.,in terms of signal-to-noise ratio,attainable image quality,or extent of applications.We take the first steps toward next-generation TEN by demonstrating the fabrication and modeling of specialized TEN probes with known optical properties.The proposed framework is highly flexible and can be easily adjusted to be used with diverse TEN techniques,building on various concepts and phenomena,significantly augmenting their function.Probes with known optical properties could potentially enable faster and more accurate imaging via different routes,such as direct signal enhancement or facile and ultrafast optical signal modulation.We consider that the reported development can pave the way for a vast number of novel TEN imaging protocols and applications,given the many advantages that it offers.展开更多
In this review,we present a brief overview on the recent advances in Angstr6m-resolved tip-enhanced Raman spectromicroscopy.We first introduce the theoretical understanding of the confinement of light at the atomistic...In this review,we present a brief overview on the recent advances in Angstr6m-resolved tip-enhanced Raman spectromicroscopy.We first introduce the theoretical understanding of the confinement of light at the atomistic scale,and explain how the Raman scattering from a single molecule happens under the“illumination”of such an atomically confined light.Then we describe the latest developments on Angstr6m-resolved tipenhanced Raman spectromicroscopy,particularly on a new methodology called“scanning Raman picoscopy”for visually cons true ting the chemical st ruc ture of a single molecule in real space.Finally,we give a perspective of this technique in various applications where iden ti fying the chemical st ruc tu res of mat erials at the chemical bond level is required.展开更多
Metal-supported ultrathin ferrous oxide(FeO)has attracted immense interest in academia and industry due to its widespread applications in heterogeneous catalysis.However,chemical insight into the local structural char...Metal-supported ultrathin ferrous oxide(FeO)has attracted immense interest in academia and industry due to its widespread applications in heterogeneous catalysis.However,chemical insight into the local structural characteristics of FeO,despite its critical importance in elucidating structure−property relationships,remains elusive.In this work,we report the nanoscale chemical probing of gold(Au)-supported ultrathin FeO via ultrahigh-vacuum tip-enhanced Raman spectroscopy(UHV-TERS)and scanning tunneling microscopy(STM).For comparative analysis,single-crystal Au(111)and Au(100)substrates are used to tune the interfacial properties of FeO.Although STM images show distinctly different moirésuperstructures on FeO nanoislands on Au(111)and Au(100),TERS demonstrates the same chemical nature of FeO by comparable vibrational features.In addition,combined TERS and STM measurements identify a unique wrinkled FeO structure on Au(100),which is correlated to the reassembly of the intrinsic Au(100)surface reconstruction due to FeO deposition.Beyond revealing the morphologies of ultrathin FeO on Au substrates,our study provides a thorough understanding of the local interfacial properties and interactions of FeO on Au,which could shed light on the rational design of metal-supported FeO catalysts.Furthermore,this work demonstrates the promising utility of combined TERS and STM in chemically probing the structural properties of metal-supported ultrathin oxides on the nanoscale.展开更多
Probing the optical properties of molybdenum disulfide(MoS_2) is vital to its application in plasmon-enhanced spectroscopy, catalysts, sensing, and optoelectronic devices. In this paper, we theoretically studied the R...Probing the optical properties of molybdenum disulfide(MoS_2) is vital to its application in plasmon-enhanced spectroscopy, catalysts, sensing, and optoelectronic devices. In this paper, we theoretically studied the Raman and fluorescence properties of monolayer MoS_2 using tip-enhanced spectroscopy(TES). In the strong-coupling TES system, the Raman and fluorescence enhancement factors can be turned to as high as 4.5 × 10~8 and 3.3 × 10~3,respectively, by optimizing the tip–MoS_2-film distance. Our theoretical results not only help to deeply understand the TES properties of monolayer MoS_2, but also provide better guidance on the applications of the novel two-dimensional material.展开更多
Tip-enhanced Raman spectroscopy(TERS)imaging is a super-resolution imaging technique that features the merits of both surface-enhanced Raman spectroscopy(SERS)and scanning probe microscopy(SPM),such as the high chemic...Tip-enhanced Raman spectroscopy(TERS)imaging is a super-resolution imaging technique that features the merits of both surface-enhanced Raman spectroscopy(SERS)and scanning probe microscopy(SPM),such as the high chemical sensitivity from the former and the nanoscale spatial resolution from the latter.These advantages make TERS an essential nanospectroscopic characterization technique for chemical analysis,materials science,bio-sensing,etc.TERS probes,the most critical factor determining the TERS imaging quality,are expected to provide a highly confined electromagnetic hotspot with a minimized scattering background for the generation of Raman signals with high spatial resolution.After two decades of development,numerous probe design concepts have been proposed and demonstrated.This review provides a comprehensive overview of the state-of-the-art TERS probe designs,from the working mechanism to the practical performance.We start with reviewing the recent development of TERS configurations and the corresponding working mechanisms,including the SPM platforms,optical excitation/collection techniques,and probe preparation methods.We then review the emerging novel TERS probe designs,including the remote-excitation probes,the waveguide-based nanofocusing probes,the metal-coated nanofocusing probes,the nanowire-assisted selective-coupling probes,and the tapered metal-insulator-metal probes.Our discussion focuses on a few critical aspects,including the surface-plasmon-polariton(SPP)hotspot excitation technique,conversion efficiency,working frequency,and controllability.In the end,we review the latest TERS applications and give a perspective on the future of TERS.展开更多
A novel approach of combining conventional infrared spectroscopy （IR） and atomic force microscopy （AFM） is presented to better understand the behavior of a drug adsorbed on a metal substrate at the nanoscale level...A novel approach of combining conventional infrared spectroscopy （IR） and atomic force microscopy （AFM） is presented to better understand the behavior of a drug adsorbed on a metal substrate at the nanoscale level. Tip-enhanced infrared nanospectroscopy （TEIRA） was used for the first time to investigate Lu AA33810, a selective brain-penetrating Y5 receptor antagonist, after immobilization on gold nanopartides （GNPs）. Here, a gold coated AFM tip and gold substrate were used to obtain the near-field electromagnetic field trapping effect. Because of the huge signal enhancement, it was possible to obtain the spectral information regarding the self-assembled monolayer of the investigated molecule. The effect of two orthogonal polarizations （p- and s-polarization modulations） of the excitation laser beam on the spectral patterns is also discussed. The results show that there is a strong relationship between the state of polarization of the incident radiation and the relative infrared band intensities. Another factor affecting the observed spectral differences is the topology of the metal substrate, which may result in the induction of a cross-polarization effect. The performed analysis indicates that the C--C bond from the cyclohexyl group is oriented almost parallel to the metal surface. Conversely, the p- and s-polarized spectral variations suggest that the O=S---O angle is high enough to enable the simultaneous interaction of both oxygen atoms with the GNPs.展开更多
Tip-enhanced Raman spectroscopy(TERS)is a powerful surface analysis technique that can provide subnanometer-resolved images of nanostructures with site-specific chemical fingerprints.However,due to the limitation of w...Tip-enhanced Raman spectroscopy(TERS)is a powerful surface analysis technique that can provide subnanometer-resolved images of nanostructures with site-specific chemical fingerprints.However,due to the limitation of weak Raman signals and the resultant difficulty in achieving TERS imaging with good signal-to-noise ratios(SNRs),the conventional single-peak analysis is unsuitable for distinguishing complex molecular architectures at the subnanometer scale.Here we demonstrate that the combination of subnanometer-resolved TERS imaging and advanced multivariate analysis can provide an unbiased panoramic view of the chemical identity and spatial distribution of different molecules on surfaces,yielding high-quality chemical images despite limited SNRs in individual pixel-level spectra.This methodology allows us to exploit the full power of TERS imaging and unambiguously distinguish between adjacent molecules with a resolution of~0.4 nm,as well as to resolve submolecular features and the differences in molecular adsorption configurations.Our results provide a promising methodology that promotes TERS imaging as a routine analytical technique for the analysis of complex nanostructures on surfaces.展开更多
Tip-enhanced Raman spectroscopy (TERS) has been used to obtain the Raman signal of surface species on silicon single crystal surfaces without the necessity for surface enhancement by addition of Ag nanoparticles. By i...Tip-enhanced Raman spectroscopy (TERS) has been used to obtain the Raman signal of surface species on silicon single crystal surfaces without the necessity for surface enhancement by addition of Ag nanoparticles. By illuminating the hydrogen terminated silicon surface covered with a droplet of 4-vinylpyridine with UV light, a 4-ethylpyridine modified silicon surface can be easily obtained. By bringing a scanning tunneling microscope (STM) Au tip with a nanoscale tip apex to a distance of ca. 1 nm from the modified silicon surface, enhanced Raman signals of the silicon phonon vibrations and the surface-bonded 4-ethylpyridine were obtained. The Raman enhancement factor was estimated to be close to 107. By comparing the surface enhanced Raman scattering (SERS) signal obtained after surface enhancement with Ag nanoparticles and the TERS signal of the surface, the advantage of TERS over SERS for characterizing the surface species on substrates becomes apparent: TERS readily affords vibrational information about the system without disturbing it by surface enhancement. In this sense, TERS can be considered a truly non-invasive tool which is ideal for characterizing the actual surface species on substrates.展开更多
Chemistry on solid surfaces is central to many research areas of practical interest,such as synthesis,catalysis,electrochemistry,photochemistry,and materials science.A comprehensive understanding of the nanoscale on-s...Chemistry on solid surfaces is central to many research areas of practical interest,such as synthesis,catalysis,electrochemistry,photochemistry,and materials science.A comprehensive understanding of the nanoscale on-surface chemistry involved in these areas is important for establishing composition-structure-performance relationships.With the rapid development of tip-enhanced Raman spectroscopy(TERS),it has become possible to investigate physical and chemical processes on suitable surfaces at the nanoscale level and in real space.In this review,after a brief introduction of the background of onsurface chemistry and TERS,we systematically discuss the progress in the application of TERS in this field.Our focus is the applications of TERS to nanoscale coordination processes,decomposition reactions,polymerization processes,electrochemical reactions,catalytic chemistry,and functionalization chemistry on solid surfaces.We conclude by discussing the future challenges and development of TERS techniques and related applications in on-surface chemistry.展开更多
Surface with well-defined components and structures possesses unique electronic,magnetic,optical and chemical properties.As a result,surface chemistry research plays a crucial role in various fields such as catalysis,...Surface with well-defined components and structures possesses unique electronic,magnetic,optical and chemical properties.As a result,surface chemistry research plays a crucial role in various fields such as catalysis,energy,materials,quantum,and microelectronics.Surface science mainly investigates the correspondence between surface property and functionality.Scanning probe microscopy(SPM)techniques are important tools to characterize surface properties because of the capability of atomic-scale imaging,spectroscopy and manipulation at the single-atom level.In this review,we summarize recent advances in surface electronic,magnetic and optical properties characterized mainly by SPM-based methods.We focus on elucidating theπ-magnetism in graphene-based nanostructures,construction of spin qubits on surfaces,topology properties of surface organic structures,STM-based light emission,tip-enhanced Raman spectroscopy and integration of machine learning in SPM studies.展开更多
One dimensional(1D)semiconductor is a class of extensively attractive materials for many emerging solar energy conversion technologies.However,it is still of shortage to assess the impact of 1D structural symmetry on ...One dimensional(1D)semiconductor is a class of extensively attractive materials for many emerging solar energy conversion technologies.However,it is still of shortage to assess the impact of 1D structural symmetry on spatial charge separation and understand its underlying mechanism.Here we take controllably-synthesized 1D BiVO_(4)nanocones and nanorods as prototypes to study the influence of 1D symmetry on charge separation.It is found that the asymmetric BiVO_(4)nanocones enable more effective charge separation compared with the symmetric nanorods.The unexpected spatial charge separation on the nanocones is mainly ascribed to uneven light absorption induced diffusion-controllable charge separation due to symmetry breaking of 1D nanostructure,as evidenced by spatial and temporal resolved spectroscopy.Moreover,the promotion effect of charge separation on the nanocones was quantitatively evaluated to be over 20 times higher than that in BiVO_(4)nanorods.This work gives the first demonstration of the influence of 1D structural symmetry on the charge separation behavior,providing new insights to design and fabricate semiconductor materials for efficient solar energy conversion.展开更多
Single-molecule tip-enhanced Raman spectroscopy(TERS)has emerged as an important technique for structural analysis at sub-molecular scale.Here in this work,we report a TERS study of an isolated free-base porphyrin mol...Single-molecule tip-enhanced Raman spectroscopy(TERS)has emerged as an important technique for structural analysis at sub-molecular scale.Here in this work,we report a TERS study of an isolated free-base porphyrin molecule adsorbed on the Ag(100)surface at cryogenic temperature(~7 K).Site-dependent TERS spectra reveal distinct local vibrational information for the chemical constituents within a single molecule.Moreover,distinct spatial features among different Raman peaks can be resolved from the TERS mapping images.These images are found to associate with related vibrational modes,enabling to resolve the mode associated with N-H bonds at the sub-nanometer level.This study will provide deep insights into the symmetry of adsorption configurations and local vibrational information within a single molecule.展开更多
In 2013,a breakthrough experiment pushed the Raman mapping of molecules via the tip-enhanced Raman scattering（TERS） technique to a sub-nanometer spatial resolution,going into the single-molecule level.This surprisin...In 2013,a breakthrough experiment pushed the Raman mapping of molecules via the tip-enhanced Raman scattering（TERS） technique to a sub-nanometer spatial resolution,going into the single-molecule level.This surprising result was well explained by accounting for the critical role of elastic molecule Rayleigh scattering within a plasmonic nanogap in enhancing both the localization and the intensity level of the Raman scattering signal.In this paper,we theoretically explore the influence of various geometric factors of the TERS system on the spatial resolution of Raman mapping,such as the tip curvature radius,tip conical angle,tip–substrate distance,and tip–molecule vertical distance.This investigation can help to find out the most critical geometric factor influencing the spatial resolution of TERS and march along in the right direction for further improving the performance of the TERS system.展开更多
Topological semimetals,possessing topologically non-trivial band structures,serve as excellent platforms for realizing topological superconductivity through hard point-contact experiments.In this study,we successfully...Topological semimetals,possessing topologically non-trivial band structures,serve as excellent platforms for realizing topological superconductivity through hard point-contact experiments.In this study,we successfully induce superconductivity in the three-dimensional Dirac semimetal,cubic PtBi_(2),using ferromagnetic and paramagnetic tips in hard point contact experiments.The induced superconductivity is proven to be insensitive to ferromagnetism and exhibits unconventional features in the point-contact spectra.The highest superconducting transition temperature(T_(c))reaches approximately 5.1 K,and the T_(c)values are proven to have a positive correlation with the coupling between the tip and the sample.Furthermore,we extend our point-contact experiments to trigonal PtBi_(2),a material possessing a type-ⅠWeyl semimetal band structure and triply degenerate points proximate to the Fermi level.Utilizing both ferromagnetic Ni tips and paramagnetic Ag tips,we successfully enhance superconductivity with a T_(c)of up to 3.0 K in this material.The findings from point-contact measurements reveal that the enhanced superconductivity is compatible with ferromagnetism and the magnetism of the tip can affect the symmetry of the enhanced superconducting state.Given that the lattice structure remains stable under pressure up to 51.2 GPa for cubic PtBi_(2)and 12.9 GPa for trigonal PtBi_(2),the emergent superconducting states observed in these two PtBi_(2)materials could inherit their topological nontrivial nature and be promising candidates for topological superconductor.展开更多
In this Letter,we use electromagnetic simulations to systematically investigate the influence of a thin dielectric layer on the local electric field and molecular spectroscopy in the plasmonic junction.It is found tha...In this Letter,we use electromagnetic simulations to systematically investigate the influence of a thin dielectric layer on the local electric field and molecular spectroscopy in the plasmonic junction.It is found that both the intensity and spatial confinement of the electric field and molecular spectroscopy can be significantly enhanced by applying a dielectric layer with large dielectric constant.We also discuss the optimal dielectric layer thickness to obtain the largest quantum efficiency of a dipole emitter.These results may be instructive for further studies in molecular spectroscopy and optoelectronics in plasmonic junctions.展开更多
The use of single-layer MoS2 in light emitting devices requires innovative methods to enhance its low photoluminescence （PL） quantum yield. In this work, we report that single-layer MoS2 with a strong PL can be prep...The use of single-layer MoS2 in light emitting devices requires innovative methods to enhance its low photoluminescence （PL） quantum yield. In this work, we report that single-layer MoS2 with a strong PL can be prepared by oxidizing bilayer MoS2 using W-ozone oxidation. We show that as compared to mechanically-exfoliated single-layer MoS2, the PL intensity of the single-layer MoS2 prepared by W-ozone oxidation is enhanced by 20-30 times. We demonstrate that the PL intensity of both neutral excitons and trions （charged excitons） can be greatly enhanced in the oxidized MoS2 samples. These results provide novel insights into the PL enhancement of single-layer MoS2.展开更多
Topological materials, hosting topological nontrivial electronic band, have attracted widespread attentions. As an application of topology in physics, the discovery and study of topological materials not only enrich t...Topological materials, hosting topological nontrivial electronic band, have attracted widespread attentions. As an application of topology in physics, the discovery and study of topological materials not only enrich the existing theoretical framework of physics, but also provide fertile ground for investigations on low energy excitations, such as Weyl fermions and Majorana fermions, which have not been observed yet as fundamental particles. These quasiparticles with exotic physical properties make topological materials the cutting edge of scientific research and a new favorite of high tech. As a typical example, Majorana fermions, predicted to exist in the edge state of topological superconductors, are proposed to implement topological error-tolerant quantum computers. Thus, the detection of topological superconductivity has become a frontier in condensed matter physics and materials science. Here, we review a way to detect topological superconductivity triggered by the hard point contact: tip-induced superconductivity(TISC) and tip-enhanced superconductivity(TESC). The TISC refers to the superconductivity induced by a non-superconducting tip at the point contact on non-superconducting materials. We take the elaboration of the chief experimental achievement of TISC in topological Dirac semimetal Cd_3As_2 and Weyl semimetal Ta As as key components of this article for detecting topological superconductivity. Moreover, we also briefly introduce the main results of another exotic effect, TESC, in superconducting Au_2Pb and Sr_2RuO_4 single crystals, which are respectively proposed as the candidates of helical topological superconductor and chiral topological superconductor. Related results and the potential mechanism are conducive to improving the comprehension of how to induce and enhance the topological superconductivity.展开更多
基金supported by National Natural Science Foundation of China(12374358,91950207)Guangdong Basic and Applied Basic Research Foundation(2024A1515010420).
文摘Glucose molecules are of great significance being one of the most important molecules in metabolic chain.However,due to the small Raman scattering cross-section and weak/non-adsorption on bare metals,accurately obtaining their"fingerprint information"remains a huge obstacle.Herein,we developed a tip-enhanced Raman scattering(TERS)technique to address this challenge.Adopting an optical fiber radial vector mode internally illuminates the plasmonic fiber tip to effectively suppress the background noise while generating a strong electric-field enhanced tip hotspot.Furthermore,the tip hotspot approaching the glucose molecules was manipulated via the shear-force feedback to provide more freedom for selecting substrates.Consequently,our TERS technique achieves the visualization of all Raman modes of glucose molecules within spectral window of 400-3200 cm^(-1),which is not achievable through the far-field/surface-enhanced Raman,or the existing TERS techniques.Our TERS technique offers a powerful tool for accurately identifying Raman scattering of molecules,paving the way for biomolecular analysis.
基金supported by the National Key R&D Program of China(No.2016YFA0200600)the National Natural Science Foundation of China(No.21790352,No.22174135)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB36000000)Anhui Initiative in Quantum Information Technologies(No.AHY090100)。
文摘The quality of the scanning tip is crucial for tip-enhanced Raman spectroscopy(TERS)experiments towards large signal enhancement and high spatial resolution.In this work,we report a controllable fabrication method to prepare TERS-active tips by modifying the tip apex at the atomic scale,and propose two important criteria to in-situ judge the tip’s TERS activity for tip-enhanced Raman measurements.One criterion is based on the downshift of the first image potential state to monitor the coupling between the far-field incident laser and near-field plasmon;the other is based on the appearance of the low-wavenumber Raman peaks associated with an atomistic protrusion at the tip apex to judge the coupling efficiency of emissions from the near field to the far field.This work provides an effective method to quickly fabricate and judge TERS-active tips before real TERS experiments on target molecules and other materials,which is believed to be instrumental for the development of TERS and other tip-enhanced spectroscopic techniques.
基金We gratefully acknowledge the support from the National Natural Science Foundation of China(Nos.21735006 and 21127901),and the CAS Key Technology Talent Program.
文摘Coherent anti-Stokes Raman scattering(CARS)is able to enhance molecular signals by vibrational coherence compared to weak Raman signal.The surface or tip enhancement are successful technologies,which make it possible for Raman to detect single molecule with nanometer resolution.However,due to technical diffculties,tip-enhanced CARS(TECARS)is not as successful as expected.For single molecular detection,high sensitivity and resolution are two main challenges.Here,we reported the first single atom layer TECARS imaging on Graphene with the highest resolution about 20 nm,which has ever been reported.The highest EF_(TECARS/CARS) is about 10^(4),the similar order of magnitude with SECARS(EF of tip is usually smaller than that of substrates).Such resolution and sensitivity is promising for medical,biology and chemical applications in the future.
基金support of the Romanian Executive Agency for Higher Education,Research,Development and Innovation Funding(Grant Nos.RO-NO-2019-0601 MEDYCONAI and PN-III-P1-1.1-TE-2019-1339 OPTIGAN)the support of Horizon 2020 Attract(Phase 1)via the TEFPLASNOM project.
文摘A thorough understanding of biological species and emerging nanomaterials requires,among other efforts,their in-depth characterization through optical techniques capable of nanoresolution.Nanoscopy techniques based on tip-enhanced optical effects have gained tremendous interest over the past years,given their potential to obtain optical information with resolutions limited only by the size of a sharp probe interacting with focused light,irrespective of the illumination wavelength.Although their popularity and number of applications is rising,tip-enhanced nanoscopy(TEN)techniques still largely rely on probes that are not specifically developed for such applications,but for atomic force microscopy.This limits their potential in many regards,e.g.,in terms of signal-to-noise ratio,attainable image quality,or extent of applications.We take the first steps toward next-generation TEN by demonstrating the fabrication and modeling of specialized TEN probes with known optical properties.The proposed framework is highly flexible and can be easily adjusted to be used with diverse TEN techniques,building on various concepts and phenomena,significantly augmenting their function.Probes with known optical properties could potentially enable faster and more accurate imaging via different routes,such as direct signal enhancement or facile and ultrafast optical signal modulation.We consider that the reported development can pave the way for a vast number of novel TEN imaging protocols and applications,given the many advantages that it offers.
基金This work was supported by the National Key R&D Program of China(No.2016YFA0200600)the National Natural Science Foundation of China,the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB36000000)the Anhui Initiative in Quantum Information Technologies.
文摘In this review,we present a brief overview on the recent advances in Angstr6m-resolved tip-enhanced Raman spectromicroscopy.We first introduce the theoretical understanding of the confinement of light at the atomistic scale,and explain how the Raman scattering from a single molecule happens under the“illumination”of such an atomically confined light.Then we describe the latest developments on Angstr6m-resolved tipenhanced Raman spectromicroscopy,particularly on a new methodology called“scanning Raman picoscopy”for visually cons true ting the chemical st ruc ture of a single molecule in real space.Finally,we give a perspective of this technique in various applications where iden ti fying the chemical st ruc tu res of mat erials at the chemical bond level is required.
基金support from the National Science Foundation(DMR-2211474).
文摘Metal-supported ultrathin ferrous oxide(FeO)has attracted immense interest in academia and industry due to its widespread applications in heterogeneous catalysis.However,chemical insight into the local structural characteristics of FeO,despite its critical importance in elucidating structure−property relationships,remains elusive.In this work,we report the nanoscale chemical probing of gold(Au)-supported ultrathin FeO via ultrahigh-vacuum tip-enhanced Raman spectroscopy(UHV-TERS)and scanning tunneling microscopy(STM).For comparative analysis,single-crystal Au(111)and Au(100)substrates are used to tune the interfacial properties of FeO.Although STM images show distinctly different moirésuperstructures on FeO nanoislands on Au(111)and Au(100),TERS demonstrates the same chemical nature of FeO by comparable vibrational features.In addition,combined TERS and STM measurements identify a unique wrinkled FeO structure on Au(100),which is correlated to the reassembly of the intrinsic Au(100)surface reconstruction due to FeO deposition.Beyond revealing the morphologies of ultrathin FeO on Au substrates,our study provides a thorough understanding of the local interfacial properties and interactions of FeO on Au,which could shed light on the rational design of metal-supported FeO catalysts.Furthermore,this work demonstrates the promising utility of combined TERS and STM in chemically probing the structural properties of metal-supported ultrathin oxides on the nanoscale.
基金National Natural Science Foundation of China(NSFC)(11704222,11374353,91436102)Scientific Research Funds for Qufu Normal University(611601)
文摘Probing the optical properties of molybdenum disulfide(MoS_2) is vital to its application in plasmon-enhanced spectroscopy, catalysts, sensing, and optoelectronic devices. In this paper, we theoretically studied the Raman and fluorescence properties of monolayer MoS_2 using tip-enhanced spectroscopy(TES). In the strong-coupling TES system, the Raman and fluorescence enhancement factors can be turned to as high as 4.5 × 10~8 and 3.3 × 10~3,respectively, by optimizing the tip–MoS_2-film distance. Our theoretical results not only help to deeply understand the TES properties of monolayer MoS_2, but also provide better guidance on the applications of the novel two-dimensional material.
基金supported by the National Science Foundation(Nos.1654746 and 1810453).
文摘Tip-enhanced Raman spectroscopy(TERS)imaging is a super-resolution imaging technique that features the merits of both surface-enhanced Raman spectroscopy(SERS)and scanning probe microscopy(SPM),such as the high chemical sensitivity from the former and the nanoscale spatial resolution from the latter.These advantages make TERS an essential nanospectroscopic characterization technique for chemical analysis,materials science,bio-sensing,etc.TERS probes,the most critical factor determining the TERS imaging quality,are expected to provide a highly confined electromagnetic hotspot with a minimized scattering background for the generation of Raman signals with high spatial resolution.After two decades of development,numerous probe design concepts have been proposed and demonstrated.This review provides a comprehensive overview of the state-of-the-art TERS probe designs,from the working mechanism to the practical performance.We start with reviewing the recent development of TERS configurations and the corresponding working mechanisms,including the SPM platforms,optical excitation/collection techniques,and probe preparation methods.We then review the emerging novel TERS probe designs,including the remote-excitation probes,the waveguide-based nanofocusing probes,the metal-coated nanofocusing probes,the nanowire-assisted selective-coupling probes,and the tapered metal-insulator-metal probes.Our discussion focuses on a few critical aspects,including the surface-plasmon-polariton(SPP)hotspot excitation technique,conversion efficiency,working frequency,and controllability.In the end,we review the latest TERS applications and give a perspective on the future of TERS.
文摘A novel approach of combining conventional infrared spectroscopy （IR） and atomic force microscopy （AFM） is presented to better understand the behavior of a drug adsorbed on a metal substrate at the nanoscale level. Tip-enhanced infrared nanospectroscopy （TEIRA） was used for the first time to investigate Lu AA33810, a selective brain-penetrating Y5 receptor antagonist, after immobilization on gold nanopartides （GNPs）. Here, a gold coated AFM tip and gold substrate were used to obtain the near-field electromagnetic field trapping effect. Because of the huge signal enhancement, it was possible to obtain the spectral information regarding the self-assembled monolayer of the investigated molecule. The effect of two orthogonal polarizations （p- and s-polarization modulations） of the excitation laser beam on the spectral patterns is also discussed. The results show that there is a strong relationship between the state of polarization of the incident radiation and the relative infrared band intensities. Another factor affecting the observed spectral differences is the topology of the metal substrate, which may result in the induction of a cross-polarization effect. The performed analysis indicates that the C--C bond from the cyclohexyl group is oriented almost parallel to the metal surface. Conversely, the p- and s-polarized spectral variations suggest that the O=S---O angle is high enough to enable the simultaneous interaction of both oxygen atoms with the GNPs.
基金supported by the National Natural Science Foundation of Chinathe National Basic Research Program of China+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciencessupport from the NSFC’s 1000 Young Talents Recruitment Plan for Global Experts.
文摘Tip-enhanced Raman spectroscopy(TERS)is a powerful surface analysis technique that can provide subnanometer-resolved images of nanostructures with site-specific chemical fingerprints.However,due to the limitation of weak Raman signals and the resultant difficulty in achieving TERS imaging with good signal-to-noise ratios(SNRs),the conventional single-peak analysis is unsuitable for distinguishing complex molecular architectures at the subnanometer scale.Here we demonstrate that the combination of subnanometer-resolved TERS imaging and advanced multivariate analysis can provide an unbiased panoramic view of the chemical identity and spatial distribution of different molecules on surfaces,yielding high-quality chemical images despite limited SNRs in individual pixel-level spectra.This methodology allows us to exploit the full power of TERS imaging and unambiguously distinguish between adjacent molecules with a resolution of~0.4 nm,as well as to resolve submolecular features and the differences in molecular adsorption configurations.Our results provide a promising methodology that promotes TERS imaging as a routine analytical technique for the analysis of complex nanostructures on surfaces.
基金supported by the National Natural Science Foundation of China (Grant Nos. 20673086, 20827003 and 20825313)the 973 Program(2009CB930703 and 2007CB935603)the Fok Ying Tung Foundation (101015)
文摘Tip-enhanced Raman spectroscopy (TERS) has been used to obtain the Raman signal of surface species on silicon single crystal surfaces without the necessity for surface enhancement by addition of Ag nanoparticles. By illuminating the hydrogen terminated silicon surface covered with a droplet of 4-vinylpyridine with UV light, a 4-ethylpyridine modified silicon surface can be easily obtained. By bringing a scanning tunneling microscope (STM) Au tip with a nanoscale tip apex to a distance of ca. 1 nm from the modified silicon surface, enhanced Raman signals of the silicon phonon vibrations and the surface-bonded 4-ethylpyridine were obtained. The Raman enhancement factor was estimated to be close to 107. By comparing the surface enhanced Raman scattering (SERS) signal obtained after surface enhancement with Ag nanoparticles and the TERS signal of the surface, the advantage of TERS over SERS for characterizing the surface species on substrates becomes apparent: TERS readily affords vibrational information about the system without disturbing it by surface enhancement. In this sense, TERS can be considered a truly non-invasive tool which is ideal for characterizing the actual surface species on substrates.
基金We acknowledge financial support from the ERC program(Grant No.741431-2DNanoSpec).
文摘Chemistry on solid surfaces is central to many research areas of practical interest,such as synthesis,catalysis,electrochemistry,photochemistry,and materials science.A comprehensive understanding of the nanoscale on-surface chemistry involved in these areas is important for establishing composition-structure-performance relationships.With the rapid development of tip-enhanced Raman spectroscopy(TERS),it has become possible to investigate physical and chemical processes on suitable surfaces at the nanoscale level and in real space.In this review,after a brief introduction of the background of onsurface chemistry and TERS,we systematically discuss the progress in the application of TERS in this field.Our focus is the applications of TERS to nanoscale coordination processes,decomposition reactions,polymerization processes,electrochemical reactions,catalytic chemistry,and functionalization chemistry on solid surfaces.We conclude by discussing the future challenges and development of TERS techniques and related applications in on-surface chemistry.
文摘Surface with well-defined components and structures possesses unique electronic,magnetic,optical and chemical properties.As a result,surface chemistry research plays a crucial role in various fields such as catalysis,energy,materials,quantum,and microelectronics.Surface science mainly investigates the correspondence between surface property and functionality.Scanning probe microscopy(SPM)techniques are important tools to characterize surface properties because of the capability of atomic-scale imaging,spectroscopy and manipulation at the single-atom level.In this review,we summarize recent advances in surface electronic,magnetic and optical properties characterized mainly by SPM-based methods.We focus on elucidating theπ-magnetism in graphene-based nanostructures,construction of spin qubits on surfaces,topology properties of surface organic structures,STM-based light emission,tip-enhanced Raman spectroscopy and integration of machine learning in SPM studies.
基金financially supported by the National Natural Science Foundation of China(21925206,21633009,21902156)the National Key R&D Program of China(2020YFA0406102)+2 种基金the DICP Foundation of Innovative Research(DICP I201927)the Dalian Science and Technology Innovation Fund(2020JJ26GX032)the Liaoning Doctor Scientific Research Initiation Fund(2019-BS-241)。
文摘One dimensional(1D)semiconductor is a class of extensively attractive materials for many emerging solar energy conversion technologies.However,it is still of shortage to assess the impact of 1D structural symmetry on spatial charge separation and understand its underlying mechanism.Here we take controllably-synthesized 1D BiVO_(4)nanocones and nanorods as prototypes to study the influence of 1D symmetry on charge separation.It is found that the asymmetric BiVO_(4)nanocones enable more effective charge separation compared with the symmetric nanorods.The unexpected spatial charge separation on the nanocones is mainly ascribed to uneven light absorption induced diffusion-controllable charge separation due to symmetry breaking of 1D nanostructure,as evidenced by spatial and temporal resolved spectroscopy.Moreover,the promotion effect of charge separation on the nanocones was quantitatively evaluated to be over 20 times higher than that in BiVO_(4)nanorods.This work gives the first demonstration of the influence of 1D structural symmetry on the charge separation behavior,providing new insights to design and fabricate semiconductor materials for efficient solar energy conversion.
基金supported by the National Key R&D Program of China(No.2016YFA0200600)the National Natural Science Foundation of China,the Chinese Academy of Sciences+1 种基金Anhui Initiative in Quantum Information TechnologiesAtif Ghafoor acknowledges support by the China Scholarship Council
文摘Single-molecule tip-enhanced Raman spectroscopy(TERS)has emerged as an important technique for structural analysis at sub-molecular scale.Here in this work,we report a TERS study of an isolated free-base porphyrin molecule adsorbed on the Ag(100)surface at cryogenic temperature(~7 K).Site-dependent TERS spectra reveal distinct local vibrational information for the chemical constituents within a single molecule.Moreover,distinct spatial features among different Raman peaks can be resolved from the TERS mapping images.These images are found to associate with related vibrational modes,enabling to resolve the mode associated with N-H bonds at the sub-nanometer level.This study will provide deep insights into the symmetry of adsorption configurations and local vibrational information within a single molecule.
基金Project supported by the National Natural Science Foundation of China(Grant No.11434017)the National Basic Research Program of China(Grant No.2013CB632704)
文摘In 2013,a breakthrough experiment pushed the Raman mapping of molecules via the tip-enhanced Raman scattering（TERS） technique to a sub-nanometer spatial resolution,going into the single-molecule level.This surprising result was well explained by accounting for the critical role of elastic molecule Rayleigh scattering within a plasmonic nanogap in enhancing both the localization and the intensity level of the Raman scattering signal.In this paper,we theoretically explore the influence of various geometric factors of the TERS system on the spatial resolution of Raman mapping,such as the tip curvature radius,tip conical angle,tip–substrate distance,and tip–molecule vertical distance.This investigation can help to find out the most critical geometric factor influencing the spatial resolution of TERS and march along in the right direction for further improving the performance of the TERS system.
基金supported by the National Natural Science Foundation of China[Grant No.12488201(J.W.)]the Innovation Program for Quantum Science and Technology[2021ZD0302403(J.W.)]+2 种基金the National Key R&D Program of the MOST of China[Grant No.2022YFA1602603(M.T.)]the Capacity Building for Sci-Tech Innovation-Fundamental Scientific Research Funds[Grant No.20530290057(H.W.)]the Science and Technology Project of Beijing Municipal Education Commission[KM202010028014(H.W.)].
文摘Topological semimetals,possessing topologically non-trivial band structures,serve as excellent platforms for realizing topological superconductivity through hard point-contact experiments.In this study,we successfully induce superconductivity in the three-dimensional Dirac semimetal,cubic PtBi_(2),using ferromagnetic and paramagnetic tips in hard point contact experiments.The induced superconductivity is proven to be insensitive to ferromagnetism and exhibits unconventional features in the point-contact spectra.The highest superconducting transition temperature(T_(c))reaches approximately 5.1 K,and the T_(c)values are proven to have a positive correlation with the coupling between the tip and the sample.Furthermore,we extend our point-contact experiments to trigonal PtBi_(2),a material possessing a type-ⅠWeyl semimetal band structure and triply degenerate points proximate to the Fermi level.Utilizing both ferromagnetic Ni tips and paramagnetic Ag tips,we successfully enhance superconductivity with a T_(c)of up to 3.0 K in this material.The findings from point-contact measurements reveal that the enhanced superconductivity is compatible with ferromagnetism and the magnetism of the tip can affect the symmetry of the enhanced superconducting state.Given that the lattice structure remains stable under pressure up to 51.2 GPa for cubic PtBi_(2)and 12.9 GPa for trigonal PtBi_(2),the emergent superconducting states observed in these two PtBi_(2)materials could inherit their topological nontrivial nature and be promising candidates for topological superconductor.
基金supported by the National Natural Science Foundation of China(Nos.12004343 and 11874268)。
文摘In this Letter,we use electromagnetic simulations to systematically investigate the influence of a thin dielectric layer on the local electric field and molecular spectroscopy in the plasmonic junction.It is found that both the intensity and spatial confinement of the electric field and molecular spectroscopy can be significantly enhanced by applying a dielectric layer with large dielectric constant.We also discuss the optimal dielectric layer thickness to obtain the largest quantum efficiency of a dipole emitter.These results may be instructive for further studies in molecular spectroscopy and optoelectronics in plasmonic junctions.
文摘The use of single-layer MoS2 in light emitting devices requires innovative methods to enhance its low photoluminescence （PL） quantum yield. In this work, we report that single-layer MoS2 with a strong PL can be prepared by oxidizing bilayer MoS2 using W-ozone oxidation. We show that as compared to mechanically-exfoliated single-layer MoS2, the PL intensity of the single-layer MoS2 prepared by W-ozone oxidation is enhanced by 20-30 times. We demonstrate that the PL intensity of both neutral excitons and trions （charged excitons） can be greatly enhanced in the oxidized MoS2 samples. These results provide novel insights into the PL enhancement of single-layer MoS2.
基金financially supported by the National Program on Key Basic Research Project(2018YFA0305604 and 2017YFA0303302)National Natural Science Foundation of China(11774008,381/0401210001)+2 种基金the Key Research Program of the Chinese Academy of Sciences(XDPB08-2)the Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics,Tsinghua University(KF201703)China Postdoctoral Science Foundation(130/0401130005)
文摘Topological materials, hosting topological nontrivial electronic band, have attracted widespread attentions. As an application of topology in physics, the discovery and study of topological materials not only enrich the existing theoretical framework of physics, but also provide fertile ground for investigations on low energy excitations, such as Weyl fermions and Majorana fermions, which have not been observed yet as fundamental particles. These quasiparticles with exotic physical properties make topological materials the cutting edge of scientific research and a new favorite of high tech. As a typical example, Majorana fermions, predicted to exist in the edge state of topological superconductors, are proposed to implement topological error-tolerant quantum computers. Thus, the detection of topological superconductivity has become a frontier in condensed matter physics and materials science. Here, we review a way to detect topological superconductivity triggered by the hard point contact: tip-induced superconductivity(TISC) and tip-enhanced superconductivity(TESC). The TISC refers to the superconductivity induced by a non-superconducting tip at the point contact on non-superconducting materials. We take the elaboration of the chief experimental achievement of TISC in topological Dirac semimetal Cd_3As_2 and Weyl semimetal Ta As as key components of this article for detecting topological superconductivity. Moreover, we also briefly introduce the main results of another exotic effect, TESC, in superconducting Au_2Pb and Sr_2RuO_4 single crystals, which are respectively proposed as the candidates of helical topological superconductor and chiral topological superconductor. Related results and the potential mechanism are conducive to improving the comprehension of how to induce and enhance the topological superconductivity.
