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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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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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Tunability and enlargement of omnidirectional transmission frequency range in a photonic heterostructure containing Dirac semimetal
摘要： In this study, We theoretically realized the enlargement of the photonic crystal band gap by a photonic heterostructure containing Dirac semimetal layer. At the same time, since the dielectric constant of the Dirac semimetal changes with its Fermi level, based on this characteristic, we have realized the adjustment of the band gap of the enlarged photonic crystal. Comparing a single photonic crystal with a heterostructure photonic crystal, it is found that the photonic band gap of the heterostructure photonic crystal is signi?cantly enlarged, and then the effects of different incident angles and polarized waves on the photonic band gap are analyzed. Based on the above properties, it has potential applications in tunable photonic crystal devices.
关键词： omnidirectional transmission frequency range,photonic heterostructure,enlargement,Dirac semimetal,tunability
更新于2025-09-09 09:28:46
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Design of Dual-Band Bandpass Filter With Multiple Transmission Zeros Using Transversal Signal Interaction Concepts
摘要： In this letter, a compact dual-band bandpass ?lter (BPF) based on the transversal signal interaction concepts is presented. The center frequencies of dual-band BPF are centered at 3.8 and 4.8 GHz with 3-dB fraction bandwidths of 11.3% and 10.7%, respectively. Transversal ?ltering structure is introduced in the proposed dual-band BPF, which provides two signal propagation paths from input to output. Thus, a dozen of transmission zeros are yielded to obtain wide stopband suppression ranging from 5.2 to 16 GHz. To validate the design scheme, a dual-band BPF with high selectivity, compact size, independently controllable bandwidth, and wide stopband suppression is fabricated and measured.
关键词： Bandpass ?lter (BPF),transmission zeros,dual band,transversal signal interaction (TSI)
更新于2025-09-09 09:28:46
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Synthesis, Characterization and Photocatalytic Efficiency of ZnO/MWCNT Nanocomposites Prepared Under Different Solvent Conditions
摘要： Here we report the application of zinc oxide (ZnO) coated multi-walled carbon nanotube (MWCNT) composites in the photocatalytic decomposition of acetaldehyde (AA). Zinc oxide nanoparticles were successfully coated on the multi-walled carbon nanotube via impregnation process using zinc acetate (Zn(CH3COO)2 × 2H2O) as precursor and sodium dodecyl sulfate (SDS) treated multi-walled carbon nanotube as raw material under different solvent conditions. The applied solvents during preparation were ethanol (EtOH) and water (H2O). As-prepared materials were characterized by thermal analysis (TG), X-ray diffraction (XRD), specific surface area measurement (BET) and transmission electron microscopy (TEM) techniques. Photocatalytic efficiencies of as-prepared composites were investigated in a stationary reactor equipped with UV lamp. Decomposition of acetaldehyde was followed by using gas chromatography (GC). Observations revealed that using impregnation method and different solvents the preparation of ZnO/MWCNT nanocomposites can be controlled easily. The highest degradation rate was achieved with the nanocomposite was synthetized using ethanol as solvent. The photocatalytic experiments revealed that the composite has higher photocatalytic activity than that of both the zinc oxide nanoparticles and the mechanical mixture of multi-walled carbon nanotube and zinc oxide.
关键词： Transmission Electron Microscopy,Zinc Oxide,Photocatalysis,Gas Chromatography,Nanocomposite
更新于2025-09-09 09:28:46
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Signal transmission at invaginating cone photoreceptor synaptic contacts following deletion of the presynaptic cytomatrix protein Bassoon in mouse retina
摘要： A key feature of the mammalian retina is the segregation of visual information in parallel pathways, starting at the photoreceptor terminals. Cone photoreceptors establish synaptic contacts with On bipolar and horizontal cells at invaginating, ribbon-containing synaptic sites, whereas Off bipolar cells form flat, non-ribbon-containing contacts. The cytomatrix protein Bassoon anchors ribbons at the active zone, and its absence induces detachment of ribbons from the active zone. In this study we investigate the impact of a missing Bassoon on synaptic transmission at the first synapse of the visual system. Release properties of cone photoreceptors were studied in wild-type and mutant mouse retinae with a genetic disruption of the presynaptic cytomatrix protein Bassoon using whole-cell voltage-clamp recordings. Light and electron microscopy revealed the distribution of Ca2+ channels and synaptic vesicles, respectively, in both mouse lines. Whole-cell recordings from postsynaptic horizontal cells of the two mouse lines showed that the presence of Bassoon (and a ribbon) enhanced the rate of exocytosis during tonic and evoked release by increasing synaptic vesicle pool size and replenishment rate, while at the same time slowing synaptic vesicle release. Furthermore, the number of Cav1.4 channels and synaptic vesicles was significantly higher at wild-type than at Bassoon mutant synaptic sites. The results of our study demonstrate that glutamate release from cone photoreceptor terminals can occur independent of a synaptic ribbon, but seems restricted to active zones, and they show the importance of a the synaptic ribbon in sustained and spatially and temporally synchronized neurotransmitter release.
关键词： signal transmission,retina,cone photoreceptor,horizontal cell,ribbon synapse,Bassoon
更新于2025-09-09 09:28:46
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Selectively exciting quasi-normal modes in open disordered systems
摘要： Transmission through disordered samples can be controlled by illuminating a sample with waveforms corresponding to the eigenchannels of the transmission matrix (TM). But can the TM be exploited to selectively excite quasi-normal modes and so control the spatial profile and dwell time inside the medium? We show in microwave and numerical studies that spectra of the TM can be analyzed into modal transmission matrices of rank unity. This makes it possible to enhance the energy within a sample by a factor equal to the number of channels. Limits to modal selectivity arise, however, from correlation in the speckle patterns of neighboring modes. In accord with an effective Hamiltonian model, the degree of modal speckle correlation grows with increasing modal spectral overlap and non-orthogonality of the modes of non-Hermitian systems. This is observed when the coupling of a sample to its surroundings increases, as in the crossover from localized to diffusive waves.
关键词： non-Hermitian systems,transmission matrix,disordered systems,quasi-normal modes,modal transmission matrices
更新于2025-09-04 15:30:14
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[IEEE 2018 37th Chinese Control Conference (CCC) - Wuhan (2018.7.25-2018.7.27)] 2018 37th Chinese Control Conference (CCC) - Maximum Power Tracking of Wireless Power Transmission Systems Based on Critical Coupling Point Tracking
摘要： Power transmission is one of the key issues in wireless power transmission (WPT) systems and the maximum power transmission problem is considered in this paper. A load power model for the magnetic resonant coupling WPT system with string-to-string structure is carried out at first. And then, using the power normalization method, the theoretical performance is analyzed and a special working point called critical coupling point (CCP) is found. At this point, the system can transfer the possible maximum power. Thus, maximum power tracking (MPT) problem can be transformed into the critical coupling point tracking (CCPT) problem. Further, relationship between CCP and load resistance is analyzed. To achieve the maximum transmission power under any load, a DC-DC impedance conversion circuit is added at the receiving side so that the maximum power can be tracked by adjusting the equivalent load resistance dynamically. Simulation results show the effectiveness of the proposed method.
关键词： maximum power tracking,critical coupling point,wireless power transmission
更新于2025-09-04 15:30:14
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BANDPASS FILTERS WITH IMPROVED SELECTIVITY BASED ON DUAL-MODE RING RESONATORS
摘要： Two novel microstrip bandpass ?lters with improved selectivity based on dual-mode ring resonators are proposed. Tow and four transmission zeros close to the passband are realized to improve the selectivity for the passband. Sixth-order passband is realized with two open/shorted stubs and a dual-mode ring resonator. The transmission zeros near the passband can be adjusted conveniently by changing the characteristic impedances of the coupled lines. For demonstration, two planar bandpass ?lters (3-dB bandwidths 20.9%, 20.2%) are designed and fabricated.
关键词： dual-mode ring resonators,transmission zeros,microstrip bandpass filters,selectivity
更新于2025-09-04 15:30:14
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LOW-LOSS COMPLEX PERMITTIVITY AND PERMEABILITY DETERMINATION IN TRANSMISSION/REFLECTION MEASUREMENTS WITH TIME-DOMAIN SMOOTHING
摘要： An approach is proposed for determination of the complex permittivity and permeability of low-loss materials, eliminating half-wavelength resonances occurring in transmission/re?ection (T/R) measurements. To this end, we apply time-domain smoothing for removing resonant artifacts from the wave impedance obtained with the conventional T/R method, assuming that we do not have such artifacts in the refractive index. Accordingly, the permittivity and permeability are found from the smoothed wave impedance and conventional refractive index. Our method is validated by measurements for two di?erent low-loss materials, nylon and lithium ferrite, and those results are discussed. Further, results from the present approach are compared to those from the approximate approach derived in our previous work.
关键词： complex permittivity,transmission/re?ection measurements,permeability,low-loss materials,time-domain smoothing
更新于2025-09-04 15:30:14