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A Low-Cost Compact Planar Dual-Band 3?dB Branch Line Coupler Using an Unbalanced CRLH
摘要： In this work, a compact dual-band 3 dB branch line coupler (BLC) is designed with center frequency at 2.45 GHz and 5.08 GHz using an unbalanced composite right/left-handed transmission line. Based on the two-port ABCD parameters, the lumped equivalent circuit of the proposed TL is extracted and optimized to obtain characteristic impedance at 2.45 GHz and 5.08 GHz. The right- and left-handed characteristics of the proposed TL are examined. Incorporating the proposed TL, a dual-band BLC with 0.29λg × 0.3λg size is obtained. The frequency response has magnitude imbalance of 0.8 dB, phase imbalance of 1.8° and 160 MHz bandwidth at 2.45 GHz and magnitude imbalance of 0.81 dB, phase imbalance of 0.006° and 100 MHz bandwidth at 5.08 GHz.
关键词： Branch line coupler (BLC),CRLH TL,Dual band,Unbalanced CRLH TL,Open stub,Interdigital capacitor
更新于2025-09-09 09:28:46
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Precise determination of electron-affinity and band gap via optical response and optical spectra
摘要： In order to obtain both the band gap and a?nity of semiconductor by photoelectric e?ect and optical spectra, Lee A. DuBridge`s formula which describes the mathematical relationship between photocurrent and photon energy in metal is extended in semiconductor. Thus cut-o? energy of photon can be ?gured out via this formula, at the same time, the a?nity of semiconductor can be determined from the di?erence between cut-o? energy and band gap detected by optical spectra in semiconductor. The results of application on ?ve semiconductors prove that the method proposed in this paper is credible, the good agreements between experimental light energy-photoelectric yield curves and theoretical curves demonstrate that the classic Lee A. DuBridge`s theory of surface photoemission does an excellent job of ?tting the photo absorption pro?le shapes of semiconductor as an earlier application on metals, these results suggest that the Lee A. DuBridge`s formalism, which is straightforward and physical, may be of signi?cant utility in semiconductor spectroscopy. It is hoped also that the results will encourage a comprehensive theoretical analysis of the applicability of semiconductor. Beside, how the band gap of Cr3+ doped n-type TiO2 is controlled by composition of Ti is express with mathematical way.
关键词： Semiconductor,Determination,Band gap,Cut-o? energy,A?nity
更新于2025-09-09 09:28:46
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Peculiarities of band structure of one-dimensional photonic crystals
摘要： In this paper, the peculiarities of the band structure of one-dimensional photonic crystals are studied, when the periodic (quasiperiodic) medium is inhomogeneous in relation to both the dielectric and magnetic properties. It is shown that the photonic band gap does not appear at small angles of incidence, in the case when the modulation depths of the dielectric permittivity and magnetic permeability coincide. The possibilities of obtaining photonic bandgaps in the terahertz radiation region are considered. The features of the band structure of photonic crystal with different spatial periods of the dielectric permittivity and magnetic permeability are investigated. It is shown that in this case, four PBGs appear in each diffraction reflection order.
关键词： Dielectric permittivity,Band structure,Magnetic permeability,Photonic crystals,Terahertz radiation
更新于2025-09-09 09:28:46
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Ultrapure NIR-to-NIR Single Band Emission of β-PbF2: Yb3+/Tm3+ in Glass Ceramics
摘要： An ultrapure near infrared (NIR) emission entered at 800 nm upon 976 nm laser excitation (NIR-to-NIR) was observed in β-PbF2: Yb3+/Tm3+ glass ceramics (GCs). The ultrapure NIR-to-NIR single band emission originated from the 3H4 → 3H6 transition of Tm3+ with the ratio of NIR emission, and a blue band up to 9,633 was obtained. Through detailed analysis of the crystal structure and the energy transfer between Tm3+ and Yb3+, it is elucidated that the host lattice with low phonon energy cooperative with the energy mismatch results in a dramatic population of the 3H4 state as well as ultrapure NIR-to-NIR single band emission. Moreover, up-conversion (UC) emission properties and the decay lifetimes of β-PbF2: Yb3+/Tm3+ in GCs were explored thoroughly. The results illustrate that efficient cross relaxation (CR) processes between Tm3+ generate the energy redistribution in UC emission spectra, further concentrating energy to NIR emission. These two issues can be treated as crucial factors on ultrapure NIR-to-NIR single band emission in β-PbF2: Yb3+/Tm3+ in GCs. The ultrapure NIR-to-NIR single band emission through 976 nm laser excitation is advantageous for enhancing resolution and has potential application in bio-imaging fields.
关键词： Energy mismatch,Fluoride nanocrystal doped with Tm3+,Glass ceramics,Single band,Cross relaxation
更新于2025-09-09 09:28:46
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A Facile Strategy for Preparation and Application of Squaraine Nanometer Hybrids with Broad Band Absorption
摘要： Organic materials are receiving more attention in the solar cell due to their better solution process, controllable synthesis, tunable chemical and physical properties. However, the focus problem of compatibility and aggregation is to be solved urgently in organic materials, which inevitably limits them widely application. To this end, an inorganic-organic hybrid materials with wide-band absorption is designed and prepared, that incorporates octavinyl-polyhedral oligomeric silsesquioxane with 6-bromoquanaldine to produce H1, then reacts with squaric acid to design H2, which efficiently avoids the fluorescence quenching due to the steric hindrance. The electrochemical results shows that the energy level of H2 is match well with the commercial dye N719. Hence it shows a better photovoltaic performance based on dye-sensitized solar cell, along with power conversion efficiency up to 7.73 % when it is co-sensitized with N719. The hybrid system exhibits good performances in solar cell and long-term stability.
关键词： dye-sensitized solar cell,disaggregation,broad-band absorption,co-sensitizer
更新于2025-09-09 09:28:46
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ion bombardment effect on the band gap of anatase TiO2 ultrathin films
摘要： We report a study of the effect of nitrogen ion bombardment on the optical properties of anatase TiO2 ultrathin films, particularly the band gap energy. The TiO2 films were prepared by a sol-gel method and dip-coating process. The as-prepared TiO2 films were then exposed to a +N2 low-energy ion beam from a microwave electron cyclotron resonance (ESR) ion source. Raman and spectroscopic ellipsometry (SE) analysis were performed on TiO2 films prepared at different +N2 exposure times. The Raman measurements reveal the conservation of the anatase TiO2 crystalline structure after the ion beam exposure. From a detailed ellipsometric study, the thickness of layers, the dielectric function, the band gap and the Urbach energies were determined. The obtained results show an increase of the TiO2 band gap with the decrease of thickness of films during +N2 exposure time. The band gap energy was blue shifted from 20 meV to 140 meV as the exposure time was increased from 5 min to 20 min when the thickness was decreased from 30 nm to 21 nm. This increasing of band gap energy could be explained by the thickness effect. From the band tail, the Urbach energy was also affected by +N2 ion beam. These results are in good agreement with the observed broadending of the Raman band the OeTieO bending vibration mode, as the exposure time increases.
关键词： +N2 ion bombardment,TiO2,Urbach energy,Band gap energy,Raman,Ellipsometry
更新于2025-09-09 09:28:46
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Modulation of the electronic properties of two-dimensional MoTe2/WSe2 heterostructure by electrical field
摘要： The structure and electronic properties of two-dimensional MoTe2/WSe2 van der Waals heterostructure under external electric field have been investigated by first-principles calculation. The interlayer distance between MoTe2 and WSe2 is 3.613? and the binding energy per unit is ?0.183eV, which indicated that MoTe2 is bound to WSe2 via van der Waals interaction. The interlayer distance can be modified by external electric field and the band gap of MoTe2/WSe2 heterostructure continuously decreases with increasing external electric field, eventually a transition from semiconductor to metal is observed, particularly, the band alignment of the MoTe2/WSe2 heterostructure can be effectively tuned from intrinsic type-II to type-I. Applying external electric field along +z direction and ?z direction has different effects on the band gap due to the intrinsic spontaneous polarization in MoTe2/WSe2 heterostructure. Our study indicates that the external electric field can significantly tune the band offsets and modify the band alignment between MoTe2 and WSe2. The present study would be helpful for application of such transition-metal dichalcogenides heterostructures in nano- and optoelectronics.
关键词： band gap,MoTe2/WSe2 heterostructure,external electric field,Density of States
更新于2025-09-09 09:28:46
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Accurate Formula for the Macroscopic Polarization of Strongly Correlated Materials
摘要： The many-body Berry phase formula for macroscopic polarization is approximated by a sum of natural orbital geometric phases with fractional occupation numbers accounting for the dominant correlation effects. This formula accurately reproduces the exact polarization in the Rice?Mele?Hubbard model across the band insulator?Mott insulator transition. A similar formula based on a reduced Berry curvature accurately predicts the interaction-induced quenching of Thouless topological charge pumping.
关键词： natural orbital geometric phases,Rice?Mele?Hubbard model,Berry phase,macroscopic polarization,band insulator?Mott insulator transition,Thouless topological charge pumping
更新于2025-09-09 09:28:46
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Theoretical and Experimental Evidence of Modified Structure, Magnetism and Optical Properties in Ba and Mn Co-Substituted BiFeO <sub/>3</sub>
摘要： To improve the vacancy related defects associated with pure BiFeO3 (BFO) different Ba-Mn co-doped samples (Bi1-xBaxFeyMnyO3; x=0.1; y=0.0, 0.05, 0.1, 0.15) were prepared from sol-gel method. The influence of co-doping on structural, magnetic and optical properties of BiFeO3 has been studied in different experimental conditions. Particle size and magnetic properties were measured from SEM and VSM analysis respectively. Again band gap was calculated from UV analysis. The co-doped samples showed reduced particles size as well as better surface morphology. M-H loops suggest that the presence of Mn2+ increased ferromagnetic quantity at some levels. Still room temperature occurrence of ferromagnetism obtained from M-H loops of all samples showed weak ferromagnetic behaviour. In addition the incorporation of Ba2+ at Bi3+ site and Mn2+ at Fe3+ site decreased the band gap which was evidenced by increased optical property.
关键词： Surface morphology,Ferromagnetism,BFO,Multiferroics,Band gap
更新于2025-09-09 09:28:46
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Towards Weakly Pareto Optimal: An Improved Multi-Objective Based Band Selection Method for Hyperspectral Imagery
摘要： Band selection refers to finding the most representative channels from hyperspectral images. Usually, certain objective functions are designed and combined via regularization terms. Owing to the parameters independence and the optimal solutions, multi-objective based methods have presented promising performance. However, the characteristics of the hyperspectral band selection problem make its range to be discrete. In this case, recently proposed weighted Tchebycheff based multi-objective band selection methods could only reach the weakly Pareto optimal, which would result in non-unique solutions. In this paper, we improve the decomposition process of the multi-objective based band selection method via a boundary intersection approach. Compared with weighted Tchebycheff decomposition, the proposed method is able to change the shape of the contour lines between Pareto Front and the ideal point, and this approach is particularly suitable for discrete-range problems. The effectiveness of our improvement is demonstrated by comparison experiments.
关键词： band selection,Multi-objective optimization,hyperspectral imagery
更新于2025-09-09 09:28:46