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Emergence of point defect states in a plasmonic crystal
摘要： Plasmonic crystals are well known to have band structure including a band gap, enabling the control of surface plasmon propagation and con?nement. The band dispersion relation of bulk crystals has been generally measured by momentum-resolved spectroscopy using far ?eld optical techniques while the defects introduced in the crystals have separately been investigated by near ?eld imaging techniques so far. Particularly, defect related energy levels introduced in the plasmonic band gap have not been observed experimentally. In order to investigate such a localized mode, we performed electron energy-loss spectroscopy (EELS) on a point defect introduced in a plasmonic crystal made up of ?at cylinders protruding out of a metal ?lm and arranged on a triangular lattice. The energy level of the defect mode was observed to lie within the full band-gap energy range. This was con?rmed by a momentum-resolved EELS measurement of the band gap performed on the same plasmonic crystal. Furthermore, we experimentally and theoretically investigated the emergence of the defect states by starting with a corral of ?at cylinders protrusions and adding sequentially additional shells of those in order to eventually form a plasmonic band-gap crystal encompassing a single point defect. It is demonstrated that a defectlike state already forms with a crystal made up of only two shells.
关键词： point defect,band gap,Plasmonic crystals,momentum-resolved spectroscopy,electron energy-loss spectroscopy
更新于2025-09-11 14:15:04
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Time-of-flight electron energy loss spectroscopy by longitudinal phase space manipulation with microwave cavities
摘要： The possibility to perform high-resolution time-resolved electron energy loss spectroscopy has the potential to impact a broad range of research fields. Resolving small energy losses with ultrashort electron pulses, however, is an enormous challenge due to the low average brightness of a pulsed beam. In this paper, we propose to use time-of-flight measurements combined with longitudinal phase space manipulation using resonant microwave cavities. This allows for both an accurate detection of energy losses with a high current throughput and efficient monochromation. First, a proof-of-principle experiment is presented, showing that with the incorporation of a compression cavity the flight time resolution can be improved significantly. Then, it is shown through simulations that by adding a cavity-based monochromation technique, a full-width-at-half-maximum energy resolution of 22 meV can be achieved with 3.1 ps pulses at a beam energy of 30 keV with currently available technology. By combining state-of-the-art energy resolutions with a pulsed electron beam, the technique proposed here opens up the way to detecting short-lived excitations within the regime of highly collective physics.
关键词： electron energy loss spectroscopy,longitudinal phase space manipulation,ultrashort electron pulses,time-of-flight,microwave cavities
更新于2025-09-10 09:29:36
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Solar e-Cooking: A Proposition for Solar Home System Integrated Clean Cooking
摘要： This paper presents the feasibility of using solar photovoltaics (Solar PV) as the energy source for cooking with special focus on the loss mechanisms and possible remedial measures. If the heat loss is minimized, to reduce the temperature losses, it is possible to cook with a low power source less than 500 W. A slogan has been adopted by the researchers—‘It is temperature that cooks food not heat’, meaning that it is not the flow of energy that cooks food, but rather, that food is cooked when held at a key temperature for a time. The slogan draws attention to the core concept that if heat loss is minimized, maintaining the temperature inside the cooker and the cooking pan, then the cooking process becomes very energy efficient. The paper considers ways to maintain temperature, but with due reference to the ‘art of cooking’, those all-important cultural processes that determine how meals are made. A prototype solar home system e-cooker was designed, fabricated and tested for cooking different foods in Bangladesh. Experimental results are presented to show that cooking is possible using much less power and energy than is commonly thought. A cost analysis is also presented to show that such a cooker can be cost effective in off-grid areas if connected to a properly designed Solar Home System.
关键词： Solar Home System,clean cooking,solar e-cooker,energy loss in cooking,science and art of cooking
更新于2025-09-10 09:29:36
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Effect of hydrogen concentration on graphene synthesis using microwave-driven plasma-mediated methane cracking
摘要： Gas phase graphene forms as an aerosol in a microwave plasma among other carbon forms. Consisting of 2-6 sheets per stack with dimensions between 100 – 500 nm, it is referred to as nanographene (NG). Surprisingly, increasing H/C ratio in the feedstock increases the relative graphitic content of the product. Dependence of the different carbon forms upon H/C ratio of the gas feed mixture is shown across multiple analytical characterizations. Attributes of (a) phase quality (pristine nature of NG) and (b) phase quantity (how much NG forms relative to other carbon sp2 phases) are addressed. Phase identification of the forms is performed via transmission electron microscopy with quantification by thermogravimetric analysis, assessing their respective oxidative reactivity benchmarked to commercially available similar carbon products applied as standards. X-ray diffraction differentiates these forms based on varied extent of graphitic structure. Electron energy loss spectroscopy assesses graphitic content by the ratio of sp2/sp3 bonding. Raman spectroscopy supports the observed shift in relative proportions of the carbon forms towards preferential graphitic content with increasing H/C. Selected area diffraction illustrates this for NG. Fringe analyses of nanostructure quantifies this shift for carbon particles. Infra-red spectroscopy reveals complementary C-H bonding as a measure of graphitic quality.
关键词： electron energy loss spectroscopy,thermogravimetric analysis,hydrogen concentration,methane cracking,graphene synthesis,X-ray diffraction,nanographene,microwave-driven plasma,Raman spectroscopy,infra-red spectroscopy
更新于2025-09-10 09:29:36
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<i>Ab initio</i> optical and energy loss spectra of transition metal monopnictides TaAs, TaP, NbAs, and NbP
摘要： Transition metal monopnictides represent a new class of topological semimetals with low-energy excitations, namely, Weyl fermions. We report optical properties across a wide spectral energy range for TaAs, TaP, NbAs, and NbP, calculated within density functional theory. Spectra are found to be somewhat independent of the anion and the light polarization. Their features are explained in terms of the upper s, p, d, and f electrons. Characteristic absorption features are related to the frequency dependence of the Fresnel re?ectivity. While the lower part of the energy loss spectra is dominated by plasmonic features, the high-energy structures are explained by interband transitions.
关键词： Topological semimetals,Energy loss spectra,Optical properties,Transition metal monopnictides,Weyl fermions
更新于2025-09-09 09:28:46
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Silicide phase formation by Mg deposition on amorphous Si. Ab initio calculations, growth process and thermal stability
摘要： Formation of magnesium silicides on amorphous silicon by deposition of Mg at room temperature is studied by electron energy loss spectroscopy, differential reflectance spectroscopy and high resolution transmission electron microscopy. Optimal crystal structures of Mg silicides under high pressure are found by ab initio DFT calculations. These structures are related to the particular minima of enthalpy. Dielectric functions are calculated for these structures. The transitions from the cubic phase c-Mg2Si to orthorhombic o-Mg2Si at 5.6 GPa and then from o-Mg2Si to hexagonal h-Mg2Si at 22.3 GPa are predicted using the USPEX code. The experimental spectra and the data obtained from the calculated dielectric functions are mutually consistent. Optical reflectance is suitable for monitoring the growth and transformations of the phases during experiments. During Mg deposition onto amorphous Si, the o-Mg2Si phase forms first, then the c-Mg2Si phase grows upon it. The observed sequence of phase formation is related with the compression stress arising in the depth of the Mg-Si mixture.
关键词： optical reflection spectroscopy,electron energy loss spectroscopy,solid state reactions,thin films,high resolution transmission electron spectroscopy,ab initio calculations
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