- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
European Microscopy Congress 2016: Proceedings || Graphite-to-diamond (13C) direct transition in a diamond anvil high-pressure cell
摘要： As the hardest material in nature, diamond is of great importance and interest for scientific studies. However, formation of a diamond is complicated process and requires extreme conditions. Bundy and Kasper (1967) for the first time synthesized a new form of carbon—hexagonal diamond – under conditions of static pressure exceeding about 13 GPa and temperature greater than about 1000°C [1]. At room temperature the crystal structure of graphite is stable up to pressure 15 GPa and loses some of the graphite features at higher pressure, forming metastable graphitic or amorphous phases [2]. Transition of polycrystalline graphite to diamond occurs after hydrostatic pressure treatment near 70 GPa [3]. The development of solid-state phase transitions, including those at the stage of nucleation and development of a new phase practically always is connected with the relaxation of elastic stress [4], and in case of graphite-diamond transformation the latter can play main role. The goal of the present work is the formation of diamond from graphite in direct phase transition in a diamond anvil high-pressure cell, where the relaxation of elastic stress can be realized by means of plastic deformation of the sample. The experiment was performed at room temperature without a catalyst.13С was subjected to the shear deformation under pressure of 25 GPa. The structure studies of the obtained material were made by transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). In order to prevent the confusion of the diamond obtained in the experiment with one of the diamond anvils we used graphite composed of 13C carbon isotope atoms as a precursor. The diamond anvils consisted of conventional 12C diamond. Before TEM examination of each sample a Raman spectroscopy was used to verify that it contains only 13 C (diamond) and no 12C. TEM and EELS were carried out using JEOL JEM-2010 high-resolution transmission electron microscope. TEM analysis has shown that the samples obtained in the series of our experiments contain several phases of carbon simultaneously. After the high pressure treatment in shear diamond anvil cell (SDAC) there were observed some fragments of the sample, which contained both hexagonal and rhombohedral graphite (significant amounts of the last one), and also diamond and lonsdaleite. Fig. 1 shows the fragment, where the rhombohedral graphite presents. Fig. 2a shows the diamond structure fragment with {111}-planes composing 70o. Interplanar distances are 0.206 nm. Fig. 2b shows the EELS-spectrum which can be unambiguously attributed to a diamond. Thus, it was shown that 13С-graphite directly transforms into 13С-diamond (at least particularly) without a catalyst at room temperature after treatment in SDAC under pressure of 25 GPa.
关键词： EELS,high pressure,shear diamond anvil cell,HRTEM
更新于2025-09-23 15:23:52
-
Vibrational electron energy loss spectroscopy in truncated dielectric slabs
摘要： Specially designed instrumentation for electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope makes it possible to probe very low-loss excitations in matter with a focused electron beam. Here we study the nanoscale interaction of fast electrons with optical phonon modes in silica. In particular, we analyze the spatial dependence of EEL spectra in two geometrical arrangements: a free-standing truncated slab of silica and a slab with a junction between silica and silicon. In both cases, we identify different loss channels, involving polaritonic and nonpolaritonic contributions to the total electron energy loss, and we obtain the corresponding energy-filtered maps. Furthermore, we present a comparison of the theoretical simulations for a silica-silicon junction with experimental results, and we discuss the spatial resolution attainable from the energy-filtered map considering optical phonon excitations in a conventional experimental arrangement.
关键词： optical phonon modes,nonpolaritonic,polaritonic,silica,electron energy loss spectroscopy,EELS,silicon
更新于2025-09-23 15:21:21
-
[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
-
Infrared plasmonics: STEM-EELS characterization of Fabry-P??rot resonance damping in gold nanowires
摘要： Materials possessing strong midinfrared responses are of current interest because of their potential application to long-wavelength metamaterials, photonic devices, molecular detection, and catalysis. Here, we utilize high-energy resolution (80 cm?1, 10 meV) electron-energy-loss spectroscopy (EELS) in a monochromated and aberration-corrected scanning transmission electron microscope (STEM) to resolve multipolar surface plasmon resonances (SPRs), sometimes called Fabry-Pérot (FP) resonances, in gold nanowires with mode energies spanning from ～1000 to 8000 cm?1. STEM-EELS provides access to these mid- to near-IR responses in a single acquisition, avoiding the difficulties inherent in obtaining the same data using near-field optical techniques. The experimentally measured FP resonance energies and linewidths, together with analytical modeling and full-wave numerical electrodynamics simulations, provide a comprehensive picture of the radiative and intrinsic contributions to the total damping rates. We find some FP modes with dephasing times >60 fs, which is almost twice the longest previously reported plasmon dephasing time for individual Au nanoparticles in the infrared. The long dephasing times and the broad tunability of the FP resonance energies throughout the infrared region suggest additional opportunities for harnessing infrared plasmonic energy before dephasing occurs.
关键词： gold nanowires,plasmon dephasing times,Fabry-Pérot resonance,infrared plasmonics,STEM-EELS
更新于2025-09-23 15:19:57
-
European Microscopy Congress 2016: Proceedings || Revisiting the EELS analyses and its coupling with multi-wavelength Raman spectroscopy: the case of hydrogenated amorphous carbon thin films
摘要： Thanks to the long-term stability of their properties, hydrogenated amorphous carbon (a:C-H) thin films are very promising materials for numerous applications including coatings for spatial applications.1 In order to improve their performances, a full understanding of their local chemistry is highly required. Fifteen years ago, according to the seminal work of Ferrari et al.,2 EELS was the most used technique to get such kind of quantitative information on these materials. Nowadays the complexity of the physics phenomena behind EELS is well known3 and this technique is regarded as time-consuming and difficult to interpret properly. Other optical techniques such as Raman spectroscopy are now clearly favored by the scientific community. However they still lack of the spatial resolution that EELS in a STEM offers for getting direct chemical information. a-C:H thin films, with a thickness around 300 nm, were deposited on a Si wafer and submitted to isothermal annealing at 500°C with different annealing times up to 2500 minutes. The hydrogen content was monitored by multi-wavelength (MW) Raman using a set of reference materials. To determine the sp2 fraction (sp2 %) from core-loss EELS, the R ratio (R = Iπ*(ΔE)/I(π*(ΔE)+σ*(ΔE)) was determined first by taking into account the asymmetry of the π* character (Fig. 1a).4,5 This value was then normalized by the maximum R value (RREF) that could be obtained from a HOPG sample in the same experimental condition using relativistic calculations (Fig. 1b).6 When needed, this method was also slightly modified to take into account the contribution of heterospecies. In addition, the mass density and the oxygen content was derived from low-loss and core-loss spectra, respectively. The EELS C-K edge spectra (Fig. 2a) present all a typical signature of amorphous carbons. However, the intensity of the massif above 292 eV differs from sample to sample and clearly highlights a slight variation of the sp2 %. The samples annealed 2500 min also presents a supplementary peak (red arrow in Fig. 2a), which is related to the oxidation of the thin film. As expected, the sp2 % increases with the annealing time (Fig. 2b). This effect is related to the H desorption of the thin films as monitored by Raman spectroscopy. Two samples do not follow this trend: the as-deposited sample and the sample annealed 2500 minutes. This latter presents a strong oxidation, leading to a decrease of the sp2 %. On the other hand, the as-deposited sample shows variation of the C-K edge fine structures (Fig. 3a) highlighting chemical inhomogneities in the thin film. This sample presents a strong gradient of the sp2 % induced by the deposition process (Fig. 3b) which is cured with the annealing time. All these results will be detailed together with the influence of the oxidation on the chemical and physical properties. In addition, the coupling of MW Raman, infrared and EELS spectroscopies to extract a wealth of chemical information will be discussed. Our results provide a complete combination of C-hybridization, spatial elemental analyses and structural defects studies for shedding light on these complex materials.7,8
关键词： Raman,Hydrogenated Amorphous Carbon,EELS,sp2 fraction
更新于2025-09-19 17:15:36
-
Synthesis of Anatase (Core)/Rutile (Shell) Nanostructured TiO <sub/>2</sub> Thin Films by Magnetron Sputtering Methods for Dye-Sensitized Solar Cell Applications
摘要： Currently, anatase/rutile core/shell structures are accepted as highly efficient building blocks for TiO2-based catalysts or photo-electrodes used in dye-sensitized solar cells (DSSCs). It is understood that a thin layer of rutile covering the core anatase pillar would improve the performance of DSSCs by retarding the charge recombination at the semiconductor/sensitizer/electrolyte interfaces. In this work, we report on the synthesis of core/shell nanostructured TiO2 thin films using reactive magnetron sputtering at a glancing angle with different power applying modes: well-separated pillars of pure anatase were synthesized using the DC mode, and then, high-pulse peak power was applied to the Ti target (high power impulse magnetron sputtering – HiPIMS) resulting in the covering of the anatase columns with a thin layer of rutile. The latter technique is well-known to increase the energy load during the growth of the film which is a key parameter to successfully obtain the TiO2 phase normally only achieved at high temperature, i.e. rutile. The peak current, the frequency and the pulse width were optimized in order to obtain the desired crystalline structure and thickness of the rutile top layer. Scanning Electron Microscopy (SEM) cross-section views of the synthesized films clearly show that the pillar-like structures are not affected by the energetic species striking the surface during the HiPIMS process. Grazing Incidence X-Ray Diffraction (GIXRD) suggests the presence of both anatase and rutile phases in the films. Further characterization of the anatase/rutile core/shell interface by electron transmission techniques such as Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS) mapping confirm the hypothesis and reveal that the anatase pillars are partly covered by a rutile crust.
关键词： EELS,Dye-Sensitized Solar Cells,TEM,TiO2,GLAD,Reactive Magnetron Sputtering,core/shell nanostructures,HiPIMS
更新于2025-09-12 10:27:22
-
Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy Studies of Hole-Selective Molybdenum Oxide Contacts in Silicon Solar Cells
摘要： In this study, sub-stochiometric hole-selective molybdenum oxide (MoOx) contacts in crystalline silicon (c-Si) solar cells were investigated by a combination of transmission electron microscopy (TEM) and spatially-resolved electron energy-loss spectroscopy (SR-EELS). It was observed that a ≈ 4 nm SiOx interlayer grows at the MoOx/c-Si interface during the evaporation of MoOx over c-Si substrate. SR-EELS analyses revealed the presence of 1.5 nm diffused MoOx/ITO (indium tin oxide) interface in both as-deposited and annealed samples. Moreover, the presence of a 1 nm thin layer with a lower oxidation state of Mo was detected at SiOx/MoOx interface in as-deposited state which disappears upon annealing. Overall, it was evident that no hole-blocking interlayer is formed at MoOx/ITO interface during annealing and homogenization of the MoOx layer takes place during the annealing process. Furthermore, device simulations revealed that efficient hole collection is dependent on MoOx work function and that reduction in work function of MoOx results in loss of band bending and negatively impacts hole-selectivity.
关键词： silicon,electron energy-loss spectroscopy (EELS),hole-selective,transmission electron microscopy (TEM),molybdenum oxide (MoOx)
更新于2025-09-12 10:27:22
-
Size-dependent dielectric function for electron-energy-loss spectra of plasmonic nanoparticles
摘要： A size-dependent complex dielectric function is proposed to describe the impact that size effects have on the dielectric response for electron energy loss spectroscopy (EELS) of plasmonic nanoparticles. Our implementation is based on experimental bulk complex refractive index and the modification of the Lorentz-Drude model. Our theoretical framework is verified and analysed by performing numerical simulation comparisons of EELS for Au spherical nanoparticles of different sizes. The results show that finite-size effects cannot be neglected for a broader size range of up to at least 200 nm for Au spherical nanoparticles. Moreover, the EELS regions in which contributions of surface or bulk energy loss are dominant are confirmed by the optical extinction spectra of Au spherical nanoparticles of different sizes, which takes into account the size-dependent dielectric function. The results provided here provide a suitable and versatile framework for the design of plasmonic elements on the nanometre scale.
关键词： metallic nanoparticles,Plasmonics,size-dependent dielectric function,surface plasmon,electron energy loss spectroscopy (EELS)
更新于2025-09-12 10:27:22
-
European Microscopy Congress 2016: Proceedings || Discrete spectroscopic electron tomography: using prior knowledge of reference spectra during the reconstruction
摘要： A three-dimensional (3D) characterization of the morphology of nanostructures can nowadays routinely be obtained using electron tomography. Nevertheless, resolving the chemical composition of complex nanostructures in 3D remains challenging and the number of studies in which electron energy loss spectroscopy (EELS) is combined with tomography is limited. In most of these studies, two dimensional (2D) elemental maps of the object are first extracted at each tilt angle and used as an input for tomographic reconstruction. An alternative approach is to reconstruct each energy loss separately yielding a 4D data cube where an EELS spectrum can be extracted from each 3D voxel. During the last decade, dedicated reconstruction algorithms have been developed for HAADF-STEM tomography which use prior knowledge about the investigated sample. For example, the discrete algebraic reconstruction technique (DART) is based on the idea that a 3D HAADF-STEM reconstruction of a (nano)material only contains a limited number of grey values. In this manner, several artefacts, typical to electron tomography, are mininized leading to reconstructions with a higher reliability. An additional advantage of discrete tomography is that the quantification of the final reconstruction is straightforward since the segmentation is part of the reconstruction algorithm. Here, we will extend discrete tomography to its application for spectroscopic datasets where it is assumed that the experimental spectrum of each reconstructed voxel is a linear combination of a well-known set of references spectra.
关键词： Electron tomography,EELS,discrete tomography,valency
更新于2025-09-11 14:15:04
-
European Microscopy Congress 2016: Proceedings || Can transverse plasmonic fields be revealed by differential phase contrast?
摘要： Surface plasmons give rise to a wide range of applications from molecular sensors [1] over novel circuit designs [2] to the design of meta-materials with highly unusual optical properties [3]. Of particular importance are localized surface plasmons (LSPs) that are confined to the surface of nanoparticles as they can give rise to a significant enhancement of electromagnetic fields in the vicinity of the nanostructure. Because LSPs typically are confined to the nanometer regime, TEM is ideally suited for mapping those charge oscillations. So far, the predominant method of studying plasmon oscillations has been EELS, which allows mapping the strength of selected resonance modes by measuring the energy loss probability of the probe beam for different LSP energies. In a non-relativistic approximation, this energy loss is brought about by the component of the electric field along the optical axis (and, in principle, the magnetic component perpendicular to the optical axis) of the excited plasmon resonance. Thus, it is impossible to gain any information about the electric field in the viewing plane (i.e., perpendicular to the optical axis). Precisely this component can, however, be studied using differential phase contrast (DPC) [4,5]. DPC exploits the fact that electrons subject to an electromagnetic field are deflected according to the Lorentz force. Any deflection along the optical axis gives rise to a change in kinetic energy and, hence, shows up in EELS. Any deflection perpendicular to the optical axis, however, changes the direction of the electron's momentum, but not its magnitude (in first order approximation). This gives rise to a shift in the electron's momentum distribution. The final momentum distribution, after passing the nanostructure, can then conveniently be measured in the TEM's diffraction plane. Compared to a reference measured without field, the displacement of the transmitted beam shows a shift that is proportional to the field integrated along the electron trajectory. Here, we used the MNPBEM toolbox [6,7] to simulate the plasmonic response of a 200x50x50 nm3 Ag nanorod to the electron beam (see fig. 1). From the data of the surface charges and currents, we then calculated the EELS maps (see fig. 1) and in-plane deflections along a line parallel to the nanorod (see fig. 2) for different plasmonic modes. The EELS maps show the typical excitation probabilities for the first two modes with two and three maxima. The in-plane electric field components show a similar behavior in general, although the local extrema are less pronounced. The DPC deflections are found to be in good agreement with the electric field with some small differences close to the center of the rod which can be attributed to the cumulative nature of the DPC deflections as well as retardation effects. The absolute magnitude of the DPC deflections in fig. 2 is of the order of 0.1 μrad at 300 keV which, albeit small, should be measurable with latest generation TEMs when using large camera lengths and/or the LACBED technique. In addition, the deflections can be increased, e.g., by using a lower acceleration voltage. This work shows that it should be feasible to determine all three components of the electromagnetic field caused by plasmons using a combination of DPC and EELS using state-of-the-art TEMs. This will open up new possibilities for understanding and designing novel plasmonic devices.
关键词： DPC,electric field,EELS,surface plasmon
更新于2025-09-11 14:15:04