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Characterization of ultrafast plasmon dynamics in individual gold bowtie by time-resolved photoemission electron microscopy
摘要： We report on the investigation of ultrafast dynamics of the plasmonic field in individual gold bowtie nanostructure by combining interferometric time-resolved photoemission electron microscopy with a damped harmonic oscillator model. We experimentally obtain different plasmon dephasing times in the tips of the bowtie nanostructure. In the meantime, we demonstrate that the experimental time-resolved photoemission signal can be used to directly compare resonance frequency and dephasing time of different hot spots. In addition, we find that the plasmon field, which is extracted from the photoemission signal, initially oscillates at the laser field frequency, and finally develops into its eigenfrequency after experiencing a few periods of frequency fluctuation due to the competition between forced and autonomous oscillation of the plasmons.
关键词： ultrafast plasmon dynamics,gold bowtie,resonance frequency,plasmon dephasing times,time-resolved photoemission electron microscopy
更新于2025-09-09 09:28:46
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Experimental Investigations of Phase Equilibria in Ternary Ag-Cu-Ga System
摘要： Experimental study of phase equilibria in the ternary Ag-Cu-Ga system was carried out by using DTA/DSC, isothermal equilibration and microscopic as well as x-ray analyses. DTA experiments were conducted for alloys, whose concentrations varied along two cross-sections determined by the ratio of mole fractions xAg/xCu = 1:1 and xAg/xGa = 1:1. Equilibration of samples was carried out at 200, 450 and 650 (cid:3)C. The obtained information about phases in equilibrium was compared with the results of calculations of the phase diagram for conditions identical to our experiments. It was demonstrated that the results of calculations are compatible with the experimental data.
关键词： CALPHAD method,x-ray diffraction,DTA measurements,Ag-Cu-Ga system,phase equilibria,scanning electron microscopy
更新于2025-09-09 09:28:46
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Epitaxial Ge-rich silicon layers after dry oxidation of Ge implanted silicon
摘要： We report on formation of epi-layer of SixGe1-x by taking standard procedure in CMOS technology. The competitive process of solid solubility of Ge dopant into Si and SiO2 is the key to engineer atomically sharp, low defect very thin epitaxial layer at the interface of oxide-Si. Oxidation time process was used to control the distribution of the doped Ge ions at the interface of Si with oxide and in the oxide layer. Implanted samples (35 keV and 1 × 1016 Ge+/cm2) were oxidized at 1050 °C for 30–90 min. RBS-Channeling analysis shows two separate peaks of Ge corresponds to different depths after oxidation. Corroborate with high resolution microscopy and elemental analysis, we determined the first peak as enriched layer of SixGe1-x at the interface of SiO2eSi. Less than 10 nm epitaxially grown interfacial layer is very low in defects, and Ge ions are fully substituted into the host lattice. The second peak originated from diffusion of Ge into SiO2 resulted in a segregated layer containing Ge in oxide film. Technological demand on forming SixGe1-x layer for CMOS application through standard routes is what we address in this research.
关键词： High resolution electron microscopy,Point defects,Germanium silicon alloys,Ion implantation,Solid phase epitaxy
更新于2025-09-09 09:28:46
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Detection of oxygen sub-lattice ordering in A-site deficient perovskites through monochromated core-loss EELS mapping
摘要： Perovskite oxides are widely studied for a variety of applications, from thermoelectrics to fuel cells. Part of the attraction lies in the fact that perovskite ceramics are relatively easy to dope chemically over a wide range of compositions, resulting in various degrees of structural ordering. As a consequence, the properties and functionalities of such materials can be readily tailored. For instance in systems proposed for thermoelectric applications, the presence of superlattices, or domain boundaries vacancies can suppress the thermal conductivity due to increased phonon scattering. Understanding therefore the mechanisms behind the formation of such types of ordering in ceramic systems is crucial for their implementation in engineering applications. Here, we report on an A-site deficient perovskite system based on the Nd2/3xTiO3 double perovskite. This system, a candidate for thermoelectric applications, has attracted significant attention due to the presence of a peculiar superstructure originating in part in A-site cation vacancy ordering. Using aberration corrected Scanning Transmission Electron Microscopy we investigate a series of Nd2/3xTiO3 ceramics engineered to possess different degrees of A-site cation-vacancy ordering and as a result vastly different thermoelectric properties. Annular Bright Field Imaging of the [110] orientation, preformed in the Nion UltraSTEM 100TM reveals the presence of tilting domains in the TiO6 sub lattice, dependent on the A-site occupancy. Furthermore, advanced image analysis of the electron micrographs was used to measure local distortions in the TiO6 lattice. The presence of these octahedral distortions was further investigated by employing atomically resolved monochromated core loss Electron Energy Loss measurements, acquired with an energy resolution better than 0.100eV, using the Nion UltraSTEM 100MC TM instrument. With this approach it is not only possible to map individual components of the Ti L2,3 near edge fine structure, but also fine local changes in the ELNES; subtle changes Ti L2,3 pre-peak intensity – usually not discernible in conventional EELS measurements as well as changes in the Ti L3 eg/tg and tg L3/L2 intensity ratios all indicative of local TiO6 distortions.
关键词： Annular Bright Field Imaging,aberration corrected Scanning Transmission Electron Microscopy,Nd2/3xTiO3,structural ordering,Electron Energy Loss measurements,thermoelectrics,fuel cells,A-site deficient perovskite,phonon scattering,perovskite oxides
更新于2025-09-09 09:28:46
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Sharpening emitter localization in front of a tuned mirror
摘要： Single-molecule localization microscopy (SMLM) aims for maximized precision and a high signal-to-noise ratio. Both features can be provided by placing the emitter in front of a metal-dielectric nanocoating that acts as a tuned mirror. Here, we demonstrate that a higher photon yield at a lower background on biocompatible metal-dielectric nanocoatings substantially improves SMLM performance and increases the localization precision by up to a factor of two. The resolution improvement relies solely on easy-to-fabricate nanocoatings on standard glass coverslips and is spectrally and spatially tunable by the layer design and wavelength, as experimentally demonstrated for dual-color SMLM in cells.
关键词： localization precision,metal-dielectric nanocoatings,dual-color SMLM,Single-molecule localization microscopy
更新于2025-09-09 09:28:46
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Charge-stripe crystal phase in an insulating cuprate
摘要： High-temperature (high-Tc) superconductivity in cuprates arises from carrier doping of an antiferromagnetic Mott insulator. This carrier doping leads to the formation of electronic liquid-crystal phases. The insulating charge-stripe crystal phase is predicted to form when a small density of holes is doped into the charge-transfer insulator state, but this phase is yet to be observed experimentally. Here, we use surface annealing to extend the accessible doping range in Bi-based cuprates and realize the lightly doped charge-transfer insulating state of the cuprate Bi2Sr2CaCu2O8+x. In this insulating state with a charge transfer gap on the order of ~1 eV, our spectroscopic imaging scanning tunnelling microscopy measurements provide strong evidence for a unidirectional charge-stripe order with a commensurate 4a0 period along the Cu–O–Cu bond. Notably, this insulating charge-stripe crystal phase develops before the onset of the pseudogap and formation of the Fermi surface. Our work provides fresh insight into the microscopic origin of electronic inhomogeneity in high-Tc cuprates.
关键词： spectroscopic imaging scanning tunnelling microscopy,electronic inhomogeneity,cuprates,charge-stripe crystal phase,high-temperature superconductivity
更新于2025-09-09 09:28:46
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Effects of N2 and NH3 plasma exposure on the surface topography of p-GaN under quasi-atmospheric pressure
摘要： We used atomic force microscopy to characterize the surface topography of p-GaN exposed to N2 and NH3 plasma under quasi-atmospheric pressure using a microwave-excited plasma source with a microstrip line structure. The exposure time was varied from 2 to 20 min at a substrate temperature of 700 °C. Under both N2 and NH3 plasma exposure for 2 min, the ridge-shaped features on the surface of as-grown p-GaN dulled immediately and the surface roughness decreased remarkably, whereas the atomic step structure of the surface was maintained. The step crossing and bunching of the surface disappeared with increasing exposure time to both types of plasma. However, increasing the NH3 plasma exposure time to 20 min led to the formation of pits and appearance of particles along the step edges, resulting in drastic roughening of the surface. Thus, GaN surfaces can be smoothed without the destruction of their step structures via moderate plasma exposure under quasi-atmospheric pressure, and these plasma sources could prospectively be used in metal-organic chemical vapor deposition systems for nitride semiconductor growth.
关键词： microwave-assisted plasma,surface topography,N2 and NH3 plasma,atomic force microscopy,metal organic chemical vapor deposition,GaN
更新于2025-09-09 09:28:46
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Analyzing the Influence of Substituents on Proton Tautomerization - a Comparison of tetra- <i>tert</i> -Butyl Phthalocyanine Isomers
摘要： We present a comparative study of tetra-tert-butyl phthalocyanine (ttbPc) isomers on a Ag(111) surface by means of low temperature scanning tunneling microscopy to analyze the influence of substituents on the tautomerization, a proton transfer reaction, in single molecules. By comparing ttbPc with the well studied phthalocyanine (H2Pc) molecule, we demonstrate a decoupling from the surface by the tert-butyl substituents. A comparison between the four ttbPc isomers, which naturally exist due to different bonding positions of the tert-butyl groups on the macrocycle, reveals a significant influence of the structural differences on their tautomerization behavior, as evidenced by a switching rate which varies by up to a factor of four between ttbPc isomers. These findings can be understood by an energetic landscape of the proton switch which links the binding distance of tert-butyl groups with the height of potential barriers. This model is supported by the analysis of two types of deprotonated ttbPc molecules with the molecular nanoprobe (MONA) technique.
关键词： tetra-tert-butyl phthalocyanine,proton transfer,scanning tunneling microscopy,tautomerization,isomers
更新于2025-09-09 09:28:46
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Direct Imaging of Photo-Switching Molecular Conformations Using Individual Metal Atom Markers
摘要： Photo-switching behavior of individual organic molecules was imaged by annular dark-field scanning transmission electron microscopy (ADF-STEM) using a highly electron beam transparent graphene support. Photo-switching azobenzene derivatives with ligands at each ends containing single transition metal atoms (Pt) were designed (Pt-complex), and the distance between the strong ADF-STEM contrast from the two Pt atoms in each Pt-complex is used to track molecular length changes. UV irradiation was used to induce photo-switching of the Pt complex on graphene, and we show that the measured Pt-Pt distances within isolated molecules decreases from ~2.1 nm to ~1.4 nm, indicative of a trans-to-cis isomerization. Light illumination of the Pt-complex on the graphene support also caused their diffusion out from initial clusters to the surrounding area of graphene, indicating that the light-activated mobilization overcomes the inter-molecular van der Waals interactions. This approach shows how individual isolated heavy metal atoms can be included as markers into complex molecules to track their structural changes using ADF-STEM on graphene supports, providing an effective method to study a diverse range of complex organic materials at the single molecule level.
关键词： annular dark-field scanning transmission electron microscopy,photo-switch,direct imaging,graphene support,heavy atom marker,azobenzene
更新于2025-09-09 09:28:46
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Metal-insulator transition in V <sub/>2</sub> O <sub/>3</sub> thin film caused by tip-induced strain
摘要： We have demonstrated pressure-induced transition in a c-axis oriented vanadium sesquioxide (V2O3) thin film from a strongly correlated metal to a Mott insulator in a submicrometric region by inducing a local stress using contact atomic force microscopy. To have an access to a pressure range of sub-gigapascal, a tip with a large radius of 335 nm was prepared by chemical vapour deposition of platinum onto a commercial tip with a focused ion beam (FIB). The FIB-modified tip gives a good electrical contact at low working pressures (0.25–0.4 GPa) allowing unambiguously to evidence reversible metal-insulator transition in a pulsed laser-deposited V2O3 thin film by means of local investigations of current-voltage characteristics. A finite element method has confirmed that the diminution of the c/a ratio under this tip pressure explains the observed phase transition of the electron density of states in the film.
关键词： tip-induced strain,Mott insulator,metal-insulator transition,V2O3 thin film,atomic force microscopy
更新于2025-09-09 09:28:46