Energy Filtering Research Articles

Evolution of C-rich SiOC ceramics

Abstract Carbon-rich Si –O–C polymer-derived ceramics (PDCs) were investigated by various spectroscopic techniques, in order to characterize the evolution of their predominantly amorphous microstructure upon thermal treatment up to 1450 °C. Particular attention was addressed to modifications of the excess free carbon phase present in these materials. Surprisingly, the carbon clusters exhibited high stability above the pyrolysis temperature. Despite the high volume fraction of carbon, only a very limited carbothermal reduction process was detected. This study is divided into two parts: Part I deals with characterization tools that reveal a rather low lateral resolution and are hence termed here as integral spectroscopic techniques, i. e., solid-state NMR and Raman spectroscopy. In contrast, Part II illustrates the experimental results obtained from the very same materials characterized by spectroscopic and imaging techniques with high lateral resolution, i. e., electron energy-loss spectroscopy (EELS), high-resolution transmission electron microscopy (HRTEM), and energy-filtered TEM. In addition to materials characterization, emphasize of both papers is also to compare the information gained by either integral or local spectroscopy techniques and to highlight the strengths and weaknesses of either approach.

Nucleic acid delivery of immune-focused SARS-CoV-2 nanoparticles drives rapid and potent immunogenicity capable of single-dose protection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines may target epitopes that reduce durability or increase the potential for escape from vaccine-induced immunity. Using synthetic vaccinology, we have developed rationally immune-focused SARS-CoV-2 Spike-based vaccines. Glycans can be employed to alter antibody responses to infection and vaccines. Utilizing computational modeling and in vitro screening, we have incorporated glycans into the receptor-binding domain (RBD) and assessed antigenic profiles. We demonstrate that glycan-coated RBD immunogens elicit stronger neutralizing antibodies and have engineered seven multivalent configurations. Advanced DNA delivery of engineered nanoparticle vaccines rapidly elicits potent neutralizing antibodies in guinea pigs, hamsters, and multiple mouse models, including human ACE2 and human antibody repertoire transgenics. RBD nanoparticles induce high levels of cross-neutralizing antibodies against variants of concern with durable titers beyond 6 months. Single, low-dose immunization protects against a lethal SARS-CoV-2 challenge. Single-dose coronavirus vaccines via DNA-launched nanoparticles provide a platform for rapid clinical translation of potent and durable coronavirus vaccines.

Surface Integrity of Wire Electrochemical Machined Inconel 718

Wire electrochemical machining (wire ECM) combines the advantages of wire electrical discharge machining (wire EDM) and electrochemical machining (ECM). The advantages of flexible 2.5 dimensional machining without the need for an application-specific fixture are combined with the excellent surface integrity properties of the ECM. These properties make the process particularly suitable for highly critical components, like fir tree slots in turbine discs. Knowledge of the resulting surface integrity in terms of microstructure formation, oxide layers, etc. is essential for such components. Therefore, in this paper modified rim zones are investigated by wire ECM e.g. with energy filtered transmission electron microscopy.

Low energy, long sustainable and high-speed FIR filter based on truncated multiplier with SCG-HSCG adder

In advancement technology and applications like processing sound signals, processing image signals, software define radio signals and so on. In processing of digital systems in all type of devices may be wide range of contraptions and clamors. The result of design the all the athematic devices and performing the addition and multiplication operations need larger space in very large scale implementation. Here, the latest proposed methodology progressed in the design of Finite impulse response filter by redesign the multipliers and adders to introduce new unsigned and signed truncated multiplier and new SCG-HSCG adders. Also different III-Vth semiconductor materials can be used to get high speed filtering operation. In this way to decreases the partials part reduction of design truncated multiplier have more number of adders. The new design handles to replace the SCG-HSCG Adders. This design decreases the logic gates in operations of athematic, additions and multiplications. It also gives the more efficient in the sign and unsigned designs of different digital signal processing applications. This proposed new finite impulse response filter has designed with help of VHDL and Xilinx FPGA-S6LX9. The efficiency of proposed filter with truncated multiplier and SCG-HSCG adder, is compare with the existing all CSLA – Carry Select adder in terms of area, delay, and power. The novel FIR filter design reduces power distribution to the environment while increasing hardware device performance. Furthermore, these kinds of designs take up less space, which means they use less energy and last longer.

Investigation of the excitations of plasmons and surface exciton polaritons in monoclinic gadolinium sesquioxide by electron energy-loss spectroscopy and plasmon spectroscopic imaging.

The monoclinic gadolinium sesquioxide (denoted as m-Gd2O3) with its lower crystal symmetry exhibits larger dielectric permittivity (κ) than the cubic Gd2O3 (denoted as c-Gd2O3). Recently, a few nanometers thick m-Gd2O3 thin film has been successfully epitaxially grown on a GaN substrate as a promising candidate gate oxide in metal-oxide-semiconductor field-effect transistors (MOSFETs). Thus, it is important to understand the electronic excitations in m-Gd2O3 and investigate them by electron energy loss spectroscopy (EELS) performed with aloof electron beams and electron diffraction to gain the spatial and momentum resolutions. In this study, using scanning transmission electron microscopy combined with EELS (STEM-EELS) in the aloof electron beam setup, we observed low-loss spectral features at 13 eV and 14.5 eV at the specimen edge in a grazing incidence and the material interior, which can be interpreted as a surface plasmon (SP) and a volume plasmon (VP), respectively. Surface exciton polaritons (SEPs), which represents surface resonances associated with excitonic onsets above the bandgap, were also observed at about 7, 10.2, and 36 eV energy loss. Their surface excitation character was confirmed by energy-filtered transmission electron microscopy spectrum imaging (EFTEM-SI) and using relativistic energy versus-momentum (E–k) map calculations. The momentum (q)-dependent EELS indicates that the SEP features near the bandgap represented a function of q and revealed a nondispersive behavior for VP and SEP at 36 eV. The oscillator strengths for VP and SEP at 36 eV dropped at different q values along with different q directions, revealing the anisotropic electronic structures of m-Gd2O3.

Observing secondary-electron yield and charging in an insulating material by ultralow-voltage scanning electron microscope

Secondary-electron yield (SEY) and surface charging of various insulating materials under irradiation of primary electrons (PEs) with energy of lower than 100 eV were investigated. Irradiation energy of the PEs with SEY of 1 (E1) for SiO2 and Si3N4 was about 20 eV and that for the resist using in extreme ultraviolet (EUV) lithography was about 40 eV. Additionally, it was found that E1 corresponds to the lower limit for obtaining scanning electron microscope images of the EUV resist pattern. The surface potential of the pattered EUV resist modulated by PE irradiation was estimated by using a retarding-field energy filter. It was found that the surface potential varies with the width and pitch of the EUV resist pattern. The variation of surface potential depends on the width and pitch due to the fact that the secondary electrons emitted from the space of the resist pattern are absorbed in the sidewalls of the resist pattern as it becomes denser.

Synthesis of gold nanoparticles using silk sericin as a green reducing and capping agent

Various natural materials were used recently for the synthesis of gold nanoparticles (AuNPs). These natural materials are attracting attention because they are more environmentally friendly than conventional chemicals used for AuNP synthesis. Silk sericin (SS) is a protein that is removed during the silk degumming process, and it has been studied for the synthesis of several inorganic materials, such as hydroxyapatite and silica. The present study synthesized AuNPs using SS. To optimize the conditions for the synthesis of AuNPs, the effects of reaction pH, SS concentration, reaction time and temperature during the formation of AuNPs were monitored using visual observation, a UV–Vis spectrophotometer, and energy-filtered transmission electron microscopy (EF-TEM) analysis. When the concentration of HAuCl4 was 1 mM, the optimal conditions for synthesizing AuNPs were an SS concentration of 1 mg/ml, a reaction pH of 7, a reaction temperature of 70 °C and a reaction time of 12 h. The AuNPs prepared under the optimal conditions had a size of approximately 17 nm, and the particles were well dispersed. When ethanol was added, the secondary structure of SS transitioned to β-sheets, the size of the gold nanoparticles increased to approximately 20 nm, and the amount of AuNPs increased. Amino acids bearing a hydroxyl group or negative charge were effective in the synthesis of AuNPs, and SS has a high content of these amino acids. Therefore, SS reduced gold ions and induced the synthesis of AuNPs. High-resolution TEM (HR-TEM), energy-dispersive X-ray spectroscopy (EDS), and thermogravimetric analysis (TGA) revealed that SS remained in a form that capped the synthesized AuNPs.

Enhanced thermoelectric properties of atomic-layer-deposited ZnO-Based superlattice thin films by tuning the composition and structure of interlayers

Superlattice thin films composed of a lightly Hf-doped ZnO matrix and various periodically inserted interlayers—including TiO2, ZrO2, HfO2, and their combinations, with various thicknesses—were prepared by atomic layer deposition (ALD) and characterized in terms of thermoelectric properties. The effects of interlayer type and thickness on the comprehensive thermoelectric properties of the superlattice films were determined, including electron mobility (μe), electron concentration (ne), electrical conductivity (σ), Seebeck coefficient (S), power factor (PF), thermal conductivity (κ), and ZT value. The TiO2, ZrO2, and HfO2 interlayers provided different potential barriers (HfO2 > ZrO2 ≫ TiO2) and atomic-mass mismatches (HfO2 > ZrO2 > TiO2) with the matrix, resulting in differing trade-off’s among energy filtering (raising S), carrier blocking (lowering σ), and phonon scattering (reducing κ) effects. Favorable balances of the effects were obtained by combining the single-content interlayers into composite interlayers, where the ALD preparation method enabled precise tuning of the interlayer composition and structure for optimal thermoelectric properties of the superlattice films. Specifically, superlattice films with a composite interlayer consisting of an alternating 1 cycle TiO2/1 cycle HfO2 structure at 1.5 nm thickness achieved a maximum of approximately 17-fold increase in ZT over that of bulk ZnO films. The results presented a quantitative guide for designing interlayer structures in superlattice films for enhanced thermoelectric properties.

Computational Discovery of TTF Molecules with Deep Generative Models.

We present a computational workflow based on quantum chemical calculations and generative models based on deep neural networks for the discovery of novel materials. We apply the developed workflow to search for molecules suitable for the fusion of triplet-triplet excitations (triplet-triplet fusion, TTF) in blue OLED devices. By applying generative machine learning models, we have been able to pinpoint the most promising regions of the chemical space for further exploration. Another neural network based on graph convolutions was trained to predict excitation energies; with this network, we estimate the alignment of energy levels and filter molecules before running time-consuming quantum chemical calculations. We present a comprehensive computational evaluation of several generative models, choosing a modification of the Junction Tree VAE (JT-VAE) as the best one in this application. The proposed approach can be useful for computer-aided design of materials with energy level alignment favorable for efficient energy transfer, triplet harvesting, and exciton fusion processes, which are crucial for the development of the next generation OLED materials.

Insights from microstructure and mechanical property comparisons of three pilgered ferritic ODS tubes

To develop advanced nuclear fuel claddings, two oxide dispersion strengthened (ODS) alloys were designed, manufactured, and evaluated. First, 12 %Cr alloy, is an ODS-version of ferritic steel, and second, 10 %Cr-6 %Al alloy, is a high-strength version of accident tolerant iron-chrome-aluminum alloy. Their properties and performance were compared with “classical” ODS material, 14 %Cr alloy 14WYT. Thin-walled (∼500 µm wall thickness) tubes were manufactured successfully using the pilgering technique. For all alloys, axial tensile specimens exhibited high tensile strength (>1 GPa) and reasonable plastic strains (10–17%). Ring tensile specimens, conversely, showed limited ductility (∼1%) with similar strengths to those measured in the axial orientation. The grain size, precipitate dispersion characteristics, and dislocation densities were then used to estimate yield strengths that were compared against room temperature axial and ring-pull tensile test data. The strengthening models showed mixed agreement with experimentally measured values due to the highly anisotropic microstructures of all three ODS tubes. These results illustrate the need for future model optimization to accommodate non-isotropic microstructures associated with components processed using rolling/pilgering approaches. In all cases, atom probe tomography and energy-filtered transmission electron microscopy demonstrated that ODS structure survived multiple pilgering operations, and precipitate microstructure evolution matched well the state-of-the-art nanoprecipitate coarsening models.

Combined electrostatic analyzer—Wien filter probe for characterization of species distributions in Hall thrusters

We present a combined electrostatic and magnetostatic plasma diagnostic tool used to measure current fractions of ion species in a Hall-effect thruster plume. Hall thrusters produce thrust by accelerating singly and multiply charged ions to high velocity. Singly charged ions fall through potential differences from their point of creation to the location of measurement, which varies as a function of time and position resulting in a relatively wide distribution of energy. This process is further complicated by both direct and multi-step creation of multiply charged ions and by ion-neutral collisions. The result is that Wien velocity filter (ExB) spectra typically have overlapping peaks. Analysis of these spectra requires assumptions about the velocity distribution function (VDF) that are hard to verify and can result in the incorrect species current distribution used to calculate thruster performance efficiencies. We present how adding an energy filter in line with an ExB probe can result in a more accurate measurement of the species current fraction while also providing information about the ion energy distribution of each species. The combined diagnostic was used to measure the species current distribution in a 1.5 kW Hall thruster operating on krypton. The diagnostic setup and data analysis of the probe measurements are presented and compared against results utilizing established VDF-fit and integration techniques applied to standard spectra measured by a standalone ExB probe.

Excellent dispersion effects of carbon nanodots on the thermoelectric properties of Bi2Te2.7Se0.3 with excessive Te

With excellent performance at room temperature as well as being the most mature n-type thermoelectric material in commercialization, Bi2Te2.7Se0.3 has been attracting increased attention. In this study, its carrier concentration and mobility were optimized by introducing excessive Te. When the excessive content of Te was 0.4, its power factor was the largest, and its thermal conductivity declined slightly. Based on Te excess, carbon nanodots were introduced as the dispersed nanosecond phase. The power factors were improved further due to the energy filter effect. In particular, the lattice thermal conductivity was depressed remarkably due to enhanced phonon scattering. Finally, at 423 K, the maximum ZT value of the sample reached 0.91, which was approximately 42% higher than that of the pure Bi2Te2.7Se0.3. The experimental results demonstrate that carbon nanodots dispersion acting as a nanosecond phase is an effective method to improve the thermoelectric performance of n-type Bi2Te2.7Se0.3-based materials.

Design and validation of a synchrotron proton beam line for FLASH radiotherapy preclinical research experiments.

The main purpose of this work was to generate and validate the dosimetric accuracy of proton beams of dimensions that are appropriate for in vivo small animal and in vitro ultrahigh dose rate (FLASH) radiotherapy experiments using a synchrotron-based treatment delivery system. This study was performed to enable future investigations of the relevance of a spread-out Bragg peak (SOBP) under FLASH conditions. The spill characteristics of the small field fixed horizontal beam line were modified to deliver accelerated protons in times as short as 2ms and to control the dose delivered. A Gaussian-like transverse beam profile was transformed into a square uniform one at FLASH dose rates, while avoiding low-dose regions, a crucial requirement to protect normal tissue during FLASH irradiation. Novel beam-shaping devices were designed using Monte Carlo techniques to produce up to about 6cm3 of uniform dose in SOBPs while maximizing the dose rate. These included a scattering foil, a conical flattening filter to maximize the flux of protons into the region of interest, energy filters, range compensators, and collimators. The shapes, sizes, and positions of the components were varied to provide the required field sizes and SOBPs. The designed and fabricated devices were used to produce 10-, 15-, and 20-mm diameter, circular field sizes and 10-, 15-, and 20-mm SOBP modulation widths at uniform physical dose rates of up to 375Gy/s at the center of the SOBP and a minimum dose rate of about 255Gy/s at the entrance, respectively, in cylindrical volumes. The flatness of lateral dose profiles at the center could be adjusted to within ±1.5% at the center of the SOBP. Assessment of systematic uncertainties, such as impact of misalignments and positioning uncertainties, was performed using simulations, and the results were used to provide appropriate adjustments to ensure high-accuracy FLASH beam delivery for both in vitro and in vivo preclinical experiments. It is feasible to use synchrotron-generated proton beams of sufficient dimensions for FLASH radiobiology experiments. We expect to use the system we developed to acquire in vitro and in vivo small animal FLASH radiobiology data as a function of dose, dose rate, oxygen content, and linear energy transfer to help us understand the underlying mechanisms of the FLASH phenomenon.

3D Nanoscale Morphology Characterization of Ternary Organic Solar Cells

It is highly desired to develop advanced characterization techniques to explore the 3D nanoscale morphology of the complicated blend film of ternary organic solar cells (OSCs). Here, ternary OSCs are constructed by incorporating the nonfullerene acceptor perylenediimide (PDI)-diketopyrrolopyrrole (DPP)-PDI and their morphology is characterized in depth to understand the performance variation. In particular, photoinduced force microscopy (PiFM) coupled with infrared laser spectroscopy is conducted to qualitatively study the distribution of donor and acceptors in the blend film by chemical identification and to quantitatively probe the segmentation of domains and the domain size distribution after PDI-DPP-PDI acceptor incorporation by PiFM imaging and data processing. In addition, the energy-filtered transmission electron microscopy with energy loss spectra is utilized to visualize the nanoscale morphology of ultrathin cross-sections in the configuration of the real ternary device for the first time in the field of photovoltaics. These measurements allow to "view" the surface and cross-sectional morphology and provide strong evidence that the PDI-DPP-PDI acceptor can suppress the aggregation of the fullerene molecules and generate the homogenous morphology with a higher-level of the molecularly mixed phase, which can prevent the charge recombination and stabilize the morphology of photoactive layer.

Crystallographical and morphological changes in charge-ordering transition of RFe2O4 (R: Y, Lu) investigated by transmission electron microscopy

Temperature dependence of charge-ordered crystal structures and domain structures in RFe2O4 (R: Y and Lu) was investigated by energy-filtered transmission electron microscopy, combined with conventional transmission electron microscopy. The presence of three-dimensional to two-dimensional charge ordering transition were observed in both YFe2O4 and LuFe2O4 on heating. Furthermore, real-space images obtained with the energy-filtered transmission electron microscopy revealed that YFe2O4 has less anisotropic nanometer-scale charge-ordered domains than LuFe2O4. These findings in RFe2O4 indicate the importance of the interchange interactions between Fe-O bilayers in addition to those within bilayers in the structural phase transitions associated with charge ordering in this system.

Ultrahigh In-Plane Thermoelectric Performance in Self-Assembled PbSe:Au Films With Vertically Aligned Nanopillar

Self-assembled nanocomposites with tunable physical properties have potential applications in advanced devices. In this work, self-assembled PbSe:Au films with vertically aligned nanopillars (VAN) were fabricated by pulsed laser deposition. Detailed heterostructures with atomic-resolution have been investigated by cross-sectional scanning tunnelling microscopy. The results show that self-assembled Au nanopillars in a PbSe matrix is realized. Compared with PbSe matrix, PbSe:Au vertical interface can facilitate energy filter effect and lower the in-plane thermal conductivity. The maximum ZT values for n-type self-assembled VAN film is ~2.6 at 523 K, which is ~400% higher than that of pure PbSe film (ZT=0.5). This study suggests that the vertical interface in the unique VAN provide a viable route to manipulate the thermoelectric properties for the thermoelectric materials.

High-performance in n-type PbTe-based thermoelectric materials achieved by synergistically dynamic doping and energy filtering

The development of n-type high-performance PbTe thermoelectric materials for matching its p-type counterparts is an urgent matter to expand its practical applications. Here, we introduce Ag2Te into n-type Pb0.975Cr0.025Te for achieving a high peak figure of merit of 1.5 at 773 K. Such a high value is attributed to the synergistic optimization of carrier and phonon transports by Ag2Te introducing and the dynamic doping of Ag. From the detailed structure and property analysis, we found that Ag2Te nanoprecipitates establish coherent interfaces and hence potential barriers with the matrix to induce energy-dependent carrier scattering and maintain relatively high carrier mobility, leading to an optimal electrical-transport properties over a wide temperature range. Moreover, we employ comprehensive electron microscopy investigations and approximate Debye-Callaway model to reveal the origin of the significantly reduced lattice thermal conductivity in Ag2Te-alloyed Pb0.975Cr0.025Te. The strategies used here provide an effective method for designing high-performance thermoelectric material systems.

Ultrastructure of spherites in the midgut diverticula and Malpighian tubules of the harvestman Amilenus aurantiacus during the winter diapause

Amilenus aurantiacus overwinter in diapause, a natural starvation period, in hypogean habitats. The structure of spherites in the midgut diverticula (MD) and Malpighian tubules (MT) has been studied comparatively by light microscopy and TEM to detect eventual differences in mineral consumption in the beginning and at the end of the starvation period in these organs (MD and MT) associated with digestive processes. The chemical composition of spherites was examined by combining energy-dispersive X-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS) and energy-filtered TEM (EFTEM). The structure of the spherites changed during overwintering in both organs. At the beginning of overwintering, the spherites were composed of densely packed concentric layers of electron-dense and electron-lucent material. In the middle and at the end of overwintering, the electron-lucent layers between the layers of material indicated the loss of some material. The chemical composition of the spherites changed only in the MD; at the beginning of overwintering, these contained Si, O, C and Fe, while later there was no more Fe. In contrast, spherites in the MT were composed of Si, O, C and Ca throughout overwintering. A less intensive exploitation of the MD spherites was probably due to complete cessation of digestive and other cell activity in this organ during the winter diapause; activity of the MT slowed, but continued removing the cell metabolites.

Simulation method for investigating the use of transition-edge sensors as spectroscopic electron detectors

Transition-edge sensors (TESs) are capable of highly accurate single particle energy measurement. TESs have been used for a wide range of photon detection applications, particularly in astronomy, but very little consideration has been given to their capabilities as electron calorimeters. Existing electron spectrometers require electron filtering optics to achieve energy discrimination, but this step discards the vast majority of electrons entering the instrument. TESs require no such energy filtering, meaning they could provide orders of magnitude improvement in measurement rate. To investigate the capabilities of TESs in electron spectroscopy, a simulation pipeline has been devised. The pipeline allows the results of a simulated experiment to be compared with the actual spectrum of the incident beam, thereby allowing measurement accuracy and efficiency to be studied. Using Fisher information, the energy resolution of the simulated detectors was also calculated, allowing the intrinsic limitations of the detector to be separated from the specific data analysis method used. The simulation platform has been used to compare the performance of TESs with existing x-ray photoelectron spectroscopy (XPS) analysers. TESs cannot match the energy resolution of XPS analysers for high-precision measurements but have comparable or better resolutions for high count rate applications. The measurement rate of a typical XPS analyser can be matched by an array of ten TESs with 120 response times and there is significant scope for improvement, without compromising energy resolution, by increasing array size.

Photonic crystal nanobeam cavities with lateral fins

Abstract We present the design, fabrication, and characterization of suspended arrays of small volume, high quality factor (Q) silicon nitride photonic crystal nanobeam (PCNB) cavities with lateral nanorod fin structures. By controlling the alignment position of the fins with respect to the air holes, the resonance wavelength and Q-factor of the PCNB cavities can be tuned to realize the desired performance. Measured tunable range of 2 × 104 and 10 nm is achieved for Q-factor and resonance wavelength, respectively, with the highest Q-factor measured at 2.5 × 104. Incorporating such nanorod fins into the nanobeam cavity is demonstrated to provide improved mechanical support, thermal transport, and channels of lateral carrier injection for the suspended PCNB. The proposed PCNB cavities with lateral fins are advantageous for energy efficient, ultra-compact lasers, modulators, filters, and sensors.