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Non-radiative processes in metal halide perovskite semiconductors probed by photoluminescence microscopy
摘要： Organo metal halide perovskites are solution processed semiconductors that recently attracted a great attention. They possess a rather “soft” and (photo) chemically active solid structure allowing for ion migration and other mass diffusion processes. This is a likely reason why non-radiative recombination centres in these materials are activated and de-activated on relatively slow time-scales. This dynamics reveals as photoluminescence (PL) fluctuations (blinking) of individual microcrystals and local areas of films and allows for application of a broad range of single molecule spectroscopy methods including optical super-resolution. Studying PL blinking resolves properties of individual non-radiative centres and helps to unravel their chemical nature.
关键词： perovskite,metal halide,Non-radiative processes,semiconductors,photoluminescence microscopy
更新于2025-09-23 15:21:21
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Selected mode mixing and interference visualized within a single optical nanoantenna
摘要： Interference-based directional antennas typically consist of multiple dipoles with properly set distances and phases, which cause constructive interferences towards certain directions in radiation or reception. For nano optical antennas, the directionality can be realized by superposition of multiple eigen modes in a single structure. Such mode mixing creates locally strong field enhancement, which should be properly controlled for energy-conversion or sensing applications. However, experimental verification of the nano optical field, or especially the hot-spots, created by interference of selected eigen modes is not trivial. We here visualize how optical fields are distributed when multiple modes interfere within a silver disk nano antenna. We use angle- and polarization-resolved cathodoluminescence based on scanning transmission electron microscopy to select specific modes and visualize the field distribution at the nanoscale. The interfered field distribution significantly changes depending on the detection angles even when the detection geometry is symmetric, which can be explained by the phase difference of the excited mode. The cathodoluminescence signals are also modeled as superpositions of analytical eigen mode functions consisting of multipoles in space and complex Lorentzians in frequency to reproduce the experimentally obtained photon maps.
关键词： Scanning Transmission Electron Microscopy,Surface Plasmon,Multipole,Cathodoluminescence,Nanodisk
更新于2025-09-23 15:21:21
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In-situ measurement of surface relief induced by Widmanst?tten and bainitic ferrites in low carbon steel by digital holographic microscopy
摘要： In-situ measurement by digital holographic microscopy (DHM) was employed to clarify the difference between the surface relief effects of Widmanst?tten ferrite (WF) and bainitic ferrite (BF) associated with their transformations from austenite in a low-carbon steel. It was clarified that the evolution of the surface relief is totally different between WF and BF. Only in BF, the observed ratio of the relief height to the plate width converged instantly to the value predicted by the phenomenological theory of martensite crystallography (PTMC). The ratio gradually increased with increasing plate thickness and never reached the value predicted by PTMC in WF.
关键词： Digital holographic microscopy,Phase transformations,Surface relief,Phenomenological theory of martensite crystallography
更新于2025-09-23 15:21:21
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Ultrathin Y <sub/>2</sub> O <sub/>3</sub> :Eu <sup>3+</sup> nanodiscs: spectroscopic investigations and evidence for reduced concentration quenching
摘要： Here, we report the synthesis and spectral properties of ultrathin nanodiscs (NDs) of Y2O3:Eu3+. It was found that the NDs of Y2O3:Eu3+ with a thickness of about 1 nm can be fabricated in a reproducible, facile and self-assembling process, which does not depend on the Eu3+ concentration. The thickness and morphology of these NDs were determined with small angle x-ray scattering and transmission electron microscopy. We found that the crystal field in these nanoparticles deviates from both the cubic and monoclinic characteristics, albeit the shape of the 5D0 → 7FJ (J = 0, 1, 2) transitions shows some similarity with the transitions in the monoclinic material. The Raman spectra of the non-annealed NDs manifest various vibration modes of the oleic acid molecules, which are used to stabilise the NDs. The annealed NDs show two very weak Raman lines, which may be assigned to vibrational modes of Y2O3 NDs. The concentration quenching of the Eu3+ luminescence of the NDs before annealing is largely suppressed and might be explained in terms of a reduction of the phonon density of states.
关键词： nanodiscs,small angle x-ray scattering,europium-doped yttrium oxide,Raman spectroscopy,concentration quenching,transmission electron microscopy,luminescence
更新于2025-09-23 15:21:21
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Coherent Tabletop EUV Ptychography of Nanopatterns
摘要： Coherent diffraction imaging (CDI) or lensless X-ray microscopy has become of great interest for high spatial resolution imaging of, e.g., nanostructures and biological specimens. There is no optics required in between an object and a detector, because the object can be fully recovered from its far-field diffraction pattern with an iterative phase retrieval algorithm. Hence, in principle, a sub-wavelength spatial resolution could be achieved in a high-numerical aperture configuration. With the advances of ultrafast laser technology, high photon flux tabletop Extreme Ultraviolet (EUV) sources based on the high-order harmonic generation (HHG) have become available to small-scale laboratories. In this study, we report on a newly established high photon flux and highly monochromatic 30 nm HHG beamline. Furthermore, we applied ptychography, a scanning CDI version, to probe a nearly periodic nanopattern with the tabletop EUV source. A wide-field view of about 15 × 15 μm was probed with a 2.5 μm?diameter illumination beam at 30 nm. From a set of hundreds of far-field diffraction patterns recorded for different adjacent positions of the object, both the object and the illumination beams were successfully reconstructed with the extended ptychographical iterative engine. By investigating the phase retrieval transfer function, a diffraction-limited resolution of reconstruction of about 32 nm is obtained.
关键词： high-order harmonic generation,ptychography,lensless X-ray microscopy,Extreme Ultraviolet,Coherent diffraction imaging
更新于2025-09-23 15:21:21
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Structural identification of silicene on the Ag(111) surface by atomic force microscopy
摘要： Silicene is a two-dimensional atomic layer material with buckled honeycomb arrangements of Si atoms. The diversity of those arrangements, which expands its potential applications, makes it dif?cult to determine its structure in any particular case. In this paper, we show that atomic force microscopy (AFM) has the capability of structural determination of unknown phases of silicene. We carried out an AFM observation of (√13×√13)R13.9? silicene of unknown structures on Ag(111). Remarkably, it was shown that all constituent Si atoms forming a honeycomb lattice can be resolved by AFM whereas scanning tunneling microscopy (STM) can image only the topmost Si atoms. High-resolution AFM imaging allowed us to identify two types of buckled structure of (√13×√13)R13.9? silicene on Ag(111), which had not been previously discriminated. The structure models obtained by theoretical simulation reproduced AFM images as well as previous STM images. In addition, the mechanism of high-resolution AFM imaging was elucidated by force spectroscopy combined with ?rst-principles calculations. Namely, attractive interaction with the tip pulls up buckled down Si atoms, causing local ?ips of the buckled structures.
关键词： structural determination,buckled structures,Ag(111) surface,silicene,atomic force microscopy
更新于2025-09-23 15:21:21
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Accurate <i>ab initio</i> determination of ballistic electron emission spectroscopy: Application to Au/Ge
摘要： Ab initio nonequilibrium Keldysh formalism based on an N -order renormalization technique is used to compute I (V ) ballistic electron emission microscopy characteristics at the Au/Ge(001) interface. Such a formalism quantitatively reproduces precise experimental measurements under ultrahigh vacuum and low-temperature conditions. At T = 0 K, the ballistic current follows the law (V ? VSB)2.1, VSB being the Schottky barrier. At T > 0 K, temperature effects become signi?cant near the onset and must be taken into account to identify an accurate value for VSB from a best-?t procedure. We ?nd two values for VSB, 0.67 and 0.75 eV, which we associate with two different atomic registries at the interface.
关键词： Au/Ge interface,ab initio,nonequilibrium Keldysh formalism,ballistic electron emission microscopy,Schottky barrier
更新于2025-09-23 15:21:21
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Preferred orientation of 2,7-dioctyl[1]benzothieno[3,2- <i>b</i> ][1]benzothiophene molecules on inorganic single-crystal substrates with various orientations
摘要： The organic molecule 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) was deposited on quartz glass, e11 (cid:2)20T A-, (0001) C-, and e1 (cid:2)102T R-single-crystal Al2O3 (sapphire), and (100)-, and (111)-single-crystal MgO substrates by vacuum thermal evaporation, and structural characterizations were carried out by X-ray di?raction analysis and atomic force microscopy (AFM) observation. The (001) out-of-plane orientation with a similar in-plane orientation was obtained irrespective of the substrate material and orientation, and its formation was governed by π–π-stacking-induced molecular ordering. The degree of orientation was re?ected by the grain structure related to the substrate material. The growth model of the oriented C8-BTBT layer was speculated on the basis of experimental results.
关键词： π–π-stacking,vacuum thermal evaporation,X-ray diffraction,C8-BTBT,atomic force microscopy
更新于2025-09-23 15:21:21
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Pseudo-Continuous Flow FTIR System for Glucose, Fructose and Sucrose Identification in Mid-IR Range
摘要： In this paper, we present a new FTIR-based micro?uidic system for Glucose, Fructose and Sucrose detection. The proposed micro?uidic system is based on a pseudo-continuous ?ow coupled to a microscope-FTIR instrument. The detection and characterization of sugar samples were performed by recording their absorption spectrum in the wavelength range 700–1000 cm?1 of the Mid-IR region. The proposed pseudo-continuous ?ow system is designed to improve the uniformity of the sample distribution in the analyzed area versus conventional systems. The obtained results for different sugars concentrations, show a very low measurement error of 4.35% in the absorption peak intensity, which is ten times lower than the error obtained using the conventional measurements.
关键词： mid-IR absorption spectroscopy,absorption spectrum,FTIR spectroscopy,microscopy-FTIR spectrometer,sugars detection and quanti?cation,Glucose,Fructose,Sucrose,pseudo-continuous ?ow
更新于2025-09-23 15:21:21
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - New applications for ultra-high brightness LaB<inf>6</inf> nanowire cathode
摘要： Electron microscopy is probably the most demanding application for a high brightness electron source. This is because the electromagnetic lens is with both chromatic and spherical aberrations. Those lens imperfections put limits on the focusable electrons, which are required to, as much as possible, originate from a small area before spreading over a small angle as per unit velocity. Brightness and energy spread, two quantities closely related to such requirements, are therefore most important in predicting an achievable resolution for an electron optical system. A third crucial factor is stability, a general requirement from the perspective of commercial instruments, which must deliver guarantee-able performance in a repeatable manner. This work will introduce a nano-emitter which prevails over current electron sources in respect of the above-mentioned three qualities.
关键词： electron microscopy,EELS,field emission
更新于2025-09-23 15:21:21