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Improved reflection technique for the permittivity measurement of ferrites using slotted coaxial samples
摘要： This paper presents the effect of magnetic permeability on the permittivity measurement using coaxial line reflection technique. It discusses in detail about the design aspects, analysis and simulation of the slotted co-axial sample and fixture for dielectric characterization of the ferrites and garnets possessing both dielectric and magnetic properties. This technique makes use of improved coaxial fixture and APC 07 compatible slotted coaxial sample geometry to measure the complex permittivity of the ferrite material. Permittivity is calculated from the impedance of sample loaded fixture, which is independent of magnetic permeability, because of air slot cut in the coaxial hollow cylindrical sample along the length. Characterization data of dielectrics and ferrites is used in design of ferrite circulators, and pulse magnets for particle accelerator applications. This is also used in many other RF applications including design of dielectric resonator for spin wave line width measurement of ferrites. Design work is aimed at accurate measurement of complex permittivity; using reflection measurement in coaxial fixture over a wide frequency range of 20 kHz to 1 GHz. Reflection measurement technique is further explored for accurate measurement of complex permittivity.
关键词： Complex permittivity,Network analyzer,Coaxial open ended fixture,Wide band measurement technique
更新于2025-09-23 15:23:52
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Composition Dependence of the Band Gap Energy of the Sb-Rich GaBixSb1?x Alloy (0?≤?x?≤?0.26) Described by the Modified Band Anticrossing Model
摘要： The impurity–host interaction and the impurity–impurity interaction exist in the Sb-rich GaBixSb1?x alloy. It is found that the effect of impurity–impurity on the band gap energy can be neglected. The impurity–host interaction not only depends on the Bi content, but also on the content of the host material. In order to describe the band gap energy of the Sb-rich GaBixSb1?x, the virtual crystal approximation for conduction band minimum (CBM) and the modified valence band anticrossing model for valence band maximum (VBM) are applied. It is also found that when the Bi content is about 0.259, the band gap energy of GaBixSb1?x becomes 0 eV. In addition, it is found that the U CBM depending on Bi content is much stronger than that of the U VBM. It is relative to two factors. One is that the conduction band offset between GaSb and GaBi is much larger than the valence band offset. The other is that the energy difference between the Bi level and the U VBM of GaSb is very large. The large energy difference usually leads to a weak coupling interaction between the Bi level and the U VBM of GaSb, thus resulting in weak composition dependence of the U VBM in the Sb-rich range.
关键词： Bi level,band gap energy,Sb-rich,GaBixSb1?x
更新于2025-09-23 15:23:52
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Influence of In Doping on the Electronic Transport Properties of n-Type Cu0.008Bi2Te2.7Se0.3
摘要： Doping is an effective approach to enhance the thermoelectric figure of merit (zT) of thermoelectric alloys by modifying their electronic structure. In this study, we investigated the influence of In doping on the electronic and thermal transport properties of n-type Cu0.008Bi2-xInxTe2.7Se0.3 (x = 0, 0.005, 0.01, and 0.015) polycrystalline alloys. The electrical conductivity of the alloys showed a moderate decreased by In doping. The Seebeck coefficient also decreased slightly. The bandgap Eg of the alloys widened slightly according to the Goldsmid–Sharp Eg formula. The band parameters of the conduction and valence bands were estimated using a two-band model. In the case of the In-doped samples, the concentration and mobility of electrons decreased simultaneously, resulting in a reduction in the electrical conductivity. However, the level of bipolar conduction remained unchanged even after doping because of the compensation of Eg widening and the band parameter modification. Meanwhile, the effect of In doping on the thermal conductivity of n-type Cu0.008Bi2Te2.7Se0.3 was found to be insignificant. Consequently, the zT of the alloy increased slightly to 1.12 at x = 0.05, while it decreased at higher doping levels.
关键词： bipolar conduction,Thermoelectrics,single parabolic band model,bismuth telluride
更新于2025-09-23 15:23:52
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Energy diagram analysis of photoelectrochemical water splitting process
摘要： Photoelectrochemical (PEC) water splitting process is thoroughly revisited based on the energy diagram to elucidate the experimental observations. The TiO2 nanorod structure is studied as the model system for the photoanode of the PEC cell due to its stability in both acidic and basic solutions. The photocurrents with the external bias are examined under the various electrolytes of H2SO4, NaCl, and NaOH. The energy diagrams of the whole PEC system related to the water splitting process are interactively constructed in three-electrode configuration with the vacuum level as the common reference. Electrode potentials and photocurrents measured with the external bias in dark and under light are systematically correlated with the energy diagram of the PEC system. The pH dependent flat-band potential is explained by applying the pH dependent Helmholtz layer potential at the interface. In addition, the distribution of the applied potential in the PEC system during the water splitting process is understood by in-depth understanding of the energy band diagram.
关键词： band analysis,TiO2 nanorod,photoelectrochemical water splitting
更新于2025-09-23 15:23:52
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Band Alignment of MoTe <sub/>2</sub> /MoS <sub/>2</sub> Nanocomposite Films for Enhanced Nonlinear Optical Performance
摘要： Band alignment is a key issue for the optoelectronics based on 2D layered transition metal dichalcogenides (TMDs) heterostructures. Herein, band alignment of MoTe2/MoS2 mixed heterostructure is measured with high-resolution X-ray photoelectron spectroscopy. The MoTe2/MoS2 heterostructure belongs to type-II heterostructure with the conduction band offset of 0.46 eV and the valence band offset of 0.9 eV. The stronger saturable absorption is observed in MoTe2/MoS2 heterostructure film compared with that of pure MoTe2 and MoS2 nanofilms at the same condition. An energy-level model combined with Runge–Kutta algorithm is used to understand the enhancement mechanism. It is found that the interlayer transition from MoTe2/MoS2 heterojunction plays an important role in the nonlinear optical enhancement. Meanwhile, band structure of MoTe2/MoS2 heterostructure is calculated by the first principles. The contributions of the MoTe2 and MoS2 to the heterojunction are almost equal and the valence band maximum and conduction band minimum exist in MoTe2 and MoS2 separately. This structure can form the interlayer carriers easily. The results suggest that the band alignment of TMDs paves the way for the type-II heterostructure for enhanced nonlinear response in the development of optical modulator, ultrafast laser mode lockers, saturable absorbers, and optical switches.
关键词： molybdenum disulfide (MoS2),band alignment,saturable absorption,heterostructure,molybdenum telluride (MoTe2)
更新于2025-09-23 15:23:52
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In-band phase deviation minimization method for wideband tunable phase shifter
摘要： This article provides a novel approach to analyze and design wideband tunable reflection-type phase shifter (RTPS) with low in-band phase deviation (IBPD) error. The proposed RTPS consists of coupled lines where through and coupled ports are terminated with varactor diodes. The coupled lines can minimize the parasitic elements of varactor diode to achieve high phase shift range (PSR). In addition, the measured frequency-dependent capacitance of varactor diode was used in the analytical analysis to obtain minimum IBPD error and high PSR. For experimental demonstration, phase shifter was fabricated at the center frequency of 2.5 GHz. The measured results show that the fabricated circuit achieved 126.85° PSR with ±6.48° IBPD error for 500 MHz bandwidth (BW). In addition, the measured maximum insertion loss variation and input/output return losses are within ±0.34 dB and higher than 16.85 dB within 500 MHz BW, respectively.
关键词： varactor diode,coupled line,low in-band phase deviation error,wideband tunable reflection-type phase shifter
更新于2025-09-23 15:23:52
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Study on Band-Gap Behaviors of 2D Hierarchical Re-Entrant Lattice Structures
摘要： An investigation of Poisson’s ratios and band gap behaviors of 2D hierarchical re-entrant lattice structures is conducted using finite element method (FEM). The structure with a hierarchy order n (n≥1) is constructed by replacing each outmost vertex of the re-entrant octagons of a hierarchical structure of hierarchy order n?1 with a smaller self-similar re-entrant octagon. The dispersion relation and transmission spectrum of the proposed hierarchical structures are analyzed based on the Bloch’s theorem. The effects of geometrical parameters, order of rotational symmetry and orientation angle of some types of re-entrant polygon cores on the lattice Poisson’s ratio and band gap structures are also investigated. Results show that the re-entrant structures with first order hierarchy exhibit a wider band gap and a stronger attenuation effect compared with structures without structural hierarchy. The first order 2D hierarchical re-entrant structure with a negative Poisson’s ratio of ?0.032 exhibits the widest band gap, 17.8% wider than that of the zeroth order 2D re-entrant structure. The order of rotational symmetry and the orientation angle of the re-entrant polygon cores of the lattice have a strong impact on the lattice Poisson’s ratio and band structures.
关键词： re-entrant,negative Poisson’s ratio,band gap,hierarchical structure,transmission spectrum
更新于2025-09-23 15:23:52
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Feasibility of a simplified narrow-band imaging classification system for Barrett’s esophagus for novice endoscopists
摘要： Background Narrow-band imaging (NBI) classifications for Barrett’s esophagus have been proposed for the detection of early esophageal adenocarcinoma. We developed a simplified classification system with demonstrated high diagnostic accuracy and reproducibility among experienced endoscopists, but the feasibility of this system among novice endoscopists was unclear. Methods In the present study, eight novice endoscopists with no experience of magnification endoscopy were asked to review 248 images of Barrett’s esophagus (72 dysplastic, 176 non-dysplastic) obtained using high-definition magnification endoscopy with NBI 6 weeks before (1st test), immediately after (2nd test), and 6 weeks after (3rd test) being taught the simplified classification system. The primary outcomes were differences in diagnostic accuracy for dysplasia among the three tests. Results The specificity and overall accuracy improved significantly in the 2nd vs. 1st test [97% vs. 80% (p < 0.001) and 94% vs. 82% (p < 0.001), respectively], sensitivity was comparable (87% in both tests; p = 0.42). In the 3rd test, the sensitivity and overall accuracy decreased significantly compared with the 2nd test [82% vs. 87% (p < 0.001) and 93% vs. 94% (p < 0.05), respectively], but there was no significant difference in specificity (97% in both tests; p = 0.16). The kappa values for interobserver agreement for the mucosal pattern, vascular pattern, and predicted histology were substantial, and improved significantly in the 2nd vs. 1st test (0.78 vs. 0.59, 0.70 vs. 0.53, and 0.79 vs. 0.66, respectively; p < 0.001 for all). Conclusions The simplified NBI classification system may be appropriate for novice endoscopists to use in providing high accuracy and reproducibility.
关键词： Narrow-band imaging,Magnification endoscopy,Barrett’s esophagus,Classification,Esophageal adenocarcinoma
更新于2025-09-23 15:23:52
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Zn <sub/>3</sub> Ga <sub/>2</sub> Ge <sub/>2</sub> O <sub/>10</sub> :Cr <sup>3+</sup> Uniform Microspheres: Template-Free Synthesis, Tunable Bandgap/Trap Depth, and <i>In Vivo</i> Rechargeable Near-Infrared-Persistent Luminescence
摘要： Near-infrared (NIR) emitting persistent phosphors of Cr3+-doped zinc gallogermanate have emerged for in vivo bio-imaging with the advantages of no need for in situ excitation. However, it is challenging to synthesize well-dispersed and uniform spherical particles with high brightness, high resolution, and distinguished NIR long afterglow. In this work, Zn3Ga2Ge2O10:Cr3+ (ZGGC) monospheres were directly synthesized by a facile hydrothermal method with the assistance of citric anions (Cit3-), which emit a NIR emission at ~696 nm and exhibit excellent NIR persistent luminescence with rechargeability. Controlled experiments indicated that the shape evolution of ZGGC product is significantly affected by Cit3-, solution pH, and the duration and temperature of hydrothermal reaction. Furthermore, compositional influence on the crystal structure, bandgap, trap depth, and luminescence characteristics of ZnyGa2Ge2O10-δ:Cr3+ (y = 2.8, 3.0, 3.2) were investigated in details, which allows to construct an energy level diagram of the ZGGC host, Cr3+ ions, and electron traps. It was found that the bandgap and conduction-band minimum (CBM) are significantly affected by the Zn content, while the valence-band maximum (VBM) is not. The y = 3.0 sample exhibited the best persistent luminescence, owing to its deepest defects. The ZGGC-NH2 prepared through surface functionalization of ZGGC spheres showed distinguished NIR long afterglow, low toxicity, and great potential for in vitro cell imaging and in vivo bio-imaging in the absence of excitation. Moreover, the persistent-luminescence signal from the ZGGC-NH2 can be repeated in vivo through in situ recharge with external excitation of a red LED lamp, indicating that the ZGGC-NH2 is suitable for applications in long-term in vivo imaging.
关键词： in vivo imaging,Near infrared persistent luminescence,conduction band minimum,monospheres
更新于2025-09-23 15:23:52
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Facet-Dependent Photocatalytic Behaviors of ZnS-Decorated Cu <sub/>2</sub> O Polyhedra Arising from Tunable Interfacial Band Alignment
摘要： ZnS particles were grown over Cu2O cubes, octahedra, and rhombic dodecahedra for examination of their facet-dependent photocatalytic behaviors. After ZnS growth, Cu2O cubes stay photocatalytically inactive. ZnS-decorated Cu2O octahedra show enhanced photocatalytic activity resulting from better charge carrier separation upon photoexcitation. Surprisingly, Cu2O rhombic dodecahedra give greatly suppressed photocatalytic activity after ZnS deposition. Electron paramagnetic resonance (EPR) spectra agree with these experimental observations. Time-resolved photoluminescence (TRPL) profiles provide charge transfer insights. The decrease in the photocatalytic activity is attributed to an unfavorable band alignment caused by significant band bending within the Cu2O (110)/ZnS (200) plane interface. A modified Cu2O–ZnS band diagram is presented. Density functional theory (DFT) calculations generating plane-specific band energy diagrams of Cu2O and ZnS match well with the experimental results, showing charge transfer across the Cu2O (110)/ZnS (200) plane interface would not happen. This example further illustrates that the actual photocatalysis outcome for semiconductor heterojunctions cannot be assumed because interfacial charge transfer is strongly facet-dependent.
关键词： interfacial charge transfer,zinc sulfide,cuprous oxide,facet-dependent properties,heterojunctions,band alignment
更新于2025-09-23 15:23:52