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Wideband Wide-Scanning Phased Array in Triangular Lattice with Electromagnetic Band-Gap Structures
摘要： A phased array in triangular lattice, with a large element spacing, wide band and wide scan angle, is investigated in this paper. The array is designed based on a connected backed-cavity antenna element. Scan blindness is observed for this triangular lattice array when the beam scans in the E plane due to large element spacing which provides a suitable propagation condition for the leaky surface waves in the array aperture. Therefore, compact electromagnetic band-gap (EBG) structures are loaded in the array element to suppress the leaky surface waves and then remove the E-plane scan blindness for the largest impedance bandwidth. The bandwidths close to the theoretical values are achieved as the beam is scanned in the E and H planes, for the given element spacing. The validity of design is verified by fabricating a 13×5 prototype, the measured results are in good agreements with the full-wave simulations.
关键词： scan blindness,phased arrays,wide scanning,Electromagnetic band-gap (EBG) structures,triangular lattice
更新于2025-09-19 17:15:36
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Tuning of opto-electrical properties of hematite thin films using Co2+ doping
摘要： Hematite thin films have attracted widespread interest in recent years because of their advanced electronic and optical properties. Optical and electronic properties of hematite thin films can be enhanced/tuned using doping or additive-based strategies. An application oriented sol–gel method is used for the synthesis of cobalt (Co) doped hematite sol with variation in Co concentration in the range of 0–10 wt%. Hematite phase is observed in undoped thin films annealed at 300 °C under 500 Oe magnetic field for 60 min. Strengthening of hematite phase is observed with increase in Co concentration up to a value of 8 wt%. Bond angle with +ive tilt (i.e. ~ 19.74°) was observed in refined structural parameters for thin films prepared with Co concentration in the range of 0–8 wt%. Higher Co concentration, i.e. 10 wt%, results in decrease in crystallinity of the films along with smaller +ive tilt in bond angle (i.e. ~ 8.82°). High transmission (~ 88%) is observed for thin film prepared using dopant concentration of 8 wt% in the visible and infrared regions. The energy band gap varies from 2.42 to 2.25 eV with variation in Co concentration from 0 to 10 wt%. Relatively smaller band gap values are correlated with defect induced states in the band gap. Spectroscopic ellipsometry is used for calculation of refractive index and high values are indication of high density of thin films. Relatively higher value of dielectric constant (~ 183, log f = 5.0) along with lower value of tangent loss is observed at Co concentration of 8 wt%. Higher grain boundary resistance (1.88 × 105 ?) was observed at 8 wt% Co concentration. Variation in d.c. conductivity with dopant concentration is studied in detail using Jonscher’s power law. The value of frequency exponent (n) lies in the range of 0.88–0.98 (< 1) with variation in dopant concentration signifying that motion of charge carriers involves translational motion along with sudden hopping process. It is important to mention here that combined tuning of optical and electrical properties are observed in the present study with no change in phase pure hematite crystallographic structure.
关键词： Hematite thin films,Optical properties,Sol-gel method,Electrical properties,Dielectric constant,Transmission,Band gap,Cobalt doping
更新于2025-09-19 17:15:36
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Effect of tungsten doping on structural and optical properties of rutile TiO2 and band gap narrowing
摘要： Pure and W doped nanocrystalline rutile TiO2 samples were synthesized using high energy ball milling process. Rietveld refinement results of X-ray diffraction data confirmed that pure sample exhibited rutile TiO2 phase whereas doped samples contained both rutile TiO2 and a secondary Ti0.54W0.46O2 phase. Different models of Williamson–Hall method were employed to evaluate crystallite size and strain in the samples. The crystallite size was found to decrease from 50 to 47 nm with increase in the dopant concentration. The pure TiO2 exhibited tensile microstrain which became compressive and increased upon doping. A blue shift in A1g Raman mode with doping of W also indicated the increase in the compressive strain. The HR-TEM images also confirmed the presence of higher strain in doped samples compared to un-doped sample. The observed decrease in band gap from 3 to 2.83 eV with dopant concentration, as calculated from UV–vis spectroscopy data, may be attributed to the increased strain. The decrease in the intensity of photoluminescence emission indicated the increase in number of defects and oxygen vacancies with increasing dopant concentration. This is further, supported by the rise in Urbach energy, a signature of increased number of defects in doped samples. This study shows that the dopant induced strain plays significant role in band gap narrowing.
关键词： Strain,Peak profile analysis,Band gap narrowing,Rutile TiO2 nanoparticles,High energy ball milling
更新于2025-09-19 17:15:36
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Comparative studies on polarisability, and optical properties of BiZnBo–SLS and PbZnBo–SLS glass
摘要： Soda Lime Silica (SLS), mainly composed of SiO2, was utilised in this study as the source of SiO2 for fabrication of glass. A study of physical and optical properties was performed for the glass system of x [RmOn] (0.50?x) [ZnO] 0.20 [B2O3] 0.30 [SLS], where RmOn are Bi2O3 and PbO with x = 0.05, 0.10, 0.20, 0.30, 0.40, and 0.45 mol. The glass was prepared by melt-quenching method. Optical properties of the glass samples were obtained using UV–visible absorption measurements. The main objective of this study was to compare the structural, polarizability, and optical properties of these two series synthesized silica based glass. The structure of the glass system was determined by X-ray diffraction (XRD). The density and molar volume were found to increase as Bi2O3 and PbO concentration increased. The optical band gap, Eopt values for bismuth glasses were between 2.58 and 2.92 eV and varied from 2.42 to 2.92 eV for lead glasses. The highest concentration of Bi2O3 and PbO in glass system showed the smallest Eopt. Bi2O3 glass exhibit the significant value towards direct or indirect band gap in optoelectronic field compared to PbO glass. Refractive index of glass samples was measured by UV–visible spectrophotometer. The value lay between 2.42 and 2.52 for bismuth glass and 2.42 and 2.57 for lead glass and the value increased as bismuth ion (Bi3+) and lead ion (Pb2+) concentration increased. Metallisation criterion was investigated on the basis of refractive index and band gap. The metallisation criterion of the glass sample linearly decreased with increasing concentration of bismuth and lead ions as a result of increasing number of refractive indices and decreasing number of band gap energy. The positive value of metallisation criterion indicates that the glass materials are insulators or not metallic. In conclusion, the obtained results show that the addition of bismuth oxide in silica glass improved its structural and optical properties compared to lead glass.
关键词： UV–visible,Polarizability,Refractive index,Metallisation criterion,Energy band gap
更新于2025-09-19 17:15:36
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Syntheses, structures, optical properties, and electronic structures of Ba6Cu2GSn4S16 (G = Fe, Ni) and Sr6D2FeSn4S16 (D = Cu, Ag)
摘要： Ba6Cu2GSn4S16 (G = Fe, Ni), and Sr6D2FeSn4S16 (D = Cu, Ag) were synthesized in an A-B-P-Q (A = Sr, Ba; B = Cu, Ag, Li; P = Sn, Ge; Q = S, Se, Te) system, through the introduction of the Fe and Ni atoms. The four compounds were found to be isostructural. They crystallize in space group ??4?3?? (no. 220) of the three-dimensional cubic structure. The structure is composed of SnS4 and (Cu|G)S4 by sharing corners with Ba2+ cations distributed in the channels of the Ba6Cu2GSn4S16 (G = Fe, Ni). The structure is composed of SnS4 and (D|Fe)S4 by sharing corners with Sr2+ cations distributed in the channels of the Sr6D2FeSn4S16 (D = Cu, Ag). The UV-vis diffuse reflectance spectra showed the Ba6Cu2FeSn4S16, Ba6Cu2NiSn4S16, Sr6Cu2FeSn4S16, and Sr6Ag2FeSn4S16 energy band gaps to be 1.20 eV, 0.82 eV, 1.53 eV and 1.87 eV, respectively.
关键词： band gap,optical properties,crystal structure,Chalcogenide
更新于2025-09-19 17:15:36
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Tailoring the Band Gap in the ZnS/ZnSe System: Solid Solutions by a Mechanically Induced Self-Sustaining Reaction
摘要： The complete ZnSxSe1?x solid solution was successfully obtained by the mechanochemical process denoted as a mechanically induced self-sustaining reaction. Excellent control of the chemical stoichiometry of the solid solution was possible by adjusting the atomic ratio of the starting Zn/S/Se elemental mixture subjected to milling. A mixture of both wurtzite-2H (hexagonal) and zinc blende (cubic) structures was always obtained, although for a similar milling time the proportion of the zinc blende structure increased with the Se content in the solid solution. However, wurtzite was the major phase for S-rich compositions when milling was stopped just after ignition. It was demonstrated that milling induces the wurtzite-to-zinc blende phase transition. The 8H hexagonal polytype was also observed in samples subjected to long milling times. Variation of the lattice parameters for both structures with the x value in the solid solution presented an excellent linearity, confirming the validity of Vegard’s law. However, variation of the band-gap energy (Eg) with x was not perfectly linear, and a small bowing parameter of 0.34 was obtained. It was possible to tune the Eg value between those of the end members of the solid solution in a continuous manner by adjusting the stoichiometry of the solid solution. The morphology and crystalline domain size can also be controlled by adjusting, in this case, the postignition milling time of the mechanochemical process.
关键词： band gap tuning,phase transformation,Vegard's law,ZnS/ZnSe solid solution,mechanically induced self-sustaining reaction,mechanochemical synthesis
更新于2025-09-19 17:15:36
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Fabrication of Pure Sb2S3 and Fe (2.5%): Sb2S3 Thin Films and Investigation Their Properties
摘要： Pure Sb2S3 and Fe (2.5%): Sb2S3 thin films were synthesized on Zn2SnO4 coated with FTO conductive glasses using chemical bath deposition (CBD) technique. The X-ray diffraction (XRD) patterns obtained show that both thin films have an orthorhombic structure. Although the crystal structure of the two thin films was the same, the crystalline size of Fe (2.5%): Sb2S3 thin film (51.15 nm) was found to be smaller than that of pure Sb2S3 (52.89 nm). The effect of Fe-doped metal on crystal size of Sb2S3 was observed with this result. Another important observation is that the energy band gap of Fe (2.5%): Sb2S3 thin film (2.00 eV) is larger than that of pure Sb2S3 (1.89 eV). The photovoltaic properties of the synthesized thin films were examined by applying both incident photon-to-current efficiency (IPCE) and current density (J)–voltage (V) measurements. The obtained IPCE(%) values at 600 nm for pure Sb2S3 and Fe (2.5%): Sb2S3 thin films are 30.29 and 49.06, respectively. Using the J–V curves, the calculated η (%) values for pure Sb2S3 and Fe (2.5%): Sb2S3 thin films are 3.95 and 5.44, respectively. Based on the data obtained from both measurements, it was observed that the Fe dopant significantly enhance the performance of the Sb2S3-based solar cell devices.
关键词： Doping,Photovoltaic,Thin film,Particle size,Energy band gap,Synthesis
更新于2025-09-19 17:15:36
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Carbonaceous Biomass-Titania composites with Ti–O–C Bonding Bridge for Efficient Photocatalytic Reduction of Cr(VI) Under Narrow Visible Light
摘要： The aim of this study was to develop carbonaceous materials hybridized with anatase TiO2 composed of Activated Carbon-TiO2 (AC-TiO2), Olive Pits-TiO2 (OP-TiO2) and Wood Shaving-TiO2 (WS-TiO2) by ultrasonic-assisted sol-gel process for the photocatalytic Cr(VI) reduction under UV and narrow visible light. The morphology, crystal structure, surface chemistry and optical properties of the as-prepared and bare-TiO2 were investigated by SEM-EDS, XRD, FTIR, BET, UV-DRS, XPS and photo-current measurements. Unlike bare-TiO2, these composite photocatalysts exhibited an enhanced absorption in visible-light. The band gap energies were found to be 3.20 eV, 2.89 eV, 2.81 eV and 2.95 eV for bare-TiO2, AC-TiO2, OP-TiO2 and WS-TiO2, respectively. On the other hand, as-prepared photocatalysts showed significantly improved photocatalytic Cr(VI) reduction performances under UV and visible light illumination compared to bare-TiO2. A total reduction of 10 ppm of Cr(VI) was obtained after 30 min, 50 min and 130 min under visible light (>420) for AC-TiO2, OP-TiO2 and WS-TiO2, respectively at pH: 3 and in the presence of 10 ppm tartaric acid as hole scavenger, while no reduction was detected for bare-TiO2 under visible light (>420). The efficient photocatalytic reduction of Cr(VI) under visible light by AC-TiO2, OP-TiO2 and WS-TiO2 was mainly due to (i): the narrow band gap of TiO2 nanoparticle deposited in carbonaceous materials, (ii): self-photo-sensitizer role of carbonaceous materials via Ti–O–C bonds and (iii): the electron transfer from TiO2 to carbonaceous materials.
关键词： Cr(VI) Reduction,Environmental remediation.,Visible Light,Photocatalysis,Carbonaceous Biomass-TiO2,Band-gap Narrowing
更新于2025-09-19 17:15:36
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Optical resonance near the edge of a photonic band gap (PBG): turning the effects of a PBG on/off using a resonant driving field
摘要： We studied the effects of a coherent monochromatic resonant laser field driving the transition of a two-level atom embedded in a photonic band gap (PBG) material on the emission dynamics of the atom. When the transition frequency of the atom lies outside a PBG and sufficiently far from the band edge that the emission dynamics of the atom is not normally affected by the gap, the dynamic stark splitting of the upper level of the atom into two dressed states by a sufficiently strong resonant driving field can bring the lower dressed state close enough to the band edge or even inside the gap so as to be affected by the gap, providing a switchable means of extending the novel effects of atom–photon interaction near the edge of a PBG for atomic transitions outside the gap and far from the band edge. The net effect is as if a sufficiently strong resonant field driving a transition of an atom embedded in a PBG actively shifts the PBG close enough to the transition so that the gap affects the emission dynamics associated with the transition.
关键词： Photonic band gap,dynamic Stark splitting,optical resonance
更新于2025-09-19 17:15:36
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Photo and thermal induced Bi2Se3 formation from Bi/GeSe2 hetero junction layer for topological insulator
摘要： In the present paper, we report the evolution of Bi2Se3 topological phase from the Bi diffusion into GeSe2 layer in the Bi/GeSe2 hetero junction film with light and thermal energy. The photo and thermal induced changes in the structural and optical properties of thermally evaporated Bi/GeSe2 bilayer film has been studied by various characterization techniques. The amorphous to crystalline phase transition and the formation of Bi2Se3 topological phase was confirmed from the X-ray diffraction analysis. The deposition as well as diffusion of Bi into GeSe2 layer changed the optical constants like transmitivity, absorption power, optical band gap, Urbach energy, Tauc parameter as studied from UV–Vis–NIR spectroscopy. The transmission power decreased after thermal annealing and laser irradiation where the reverse effect was found in case of absorption coefficient. The optical band gap decreased after diffusion which can be explained on the basis of density of defect states with an increase in disorder. Scanning electron microscopy investigations showed that the surface morphology was influenced by the diffusion phenomena. The Raman analysis also confirms the Bi2Se3 phase evolution with appropriate vibrational peaks. The modifications in optical parameters with thermal and light induced diffusion can be used in various optical applications using such metal/chalcogenides heterojunction layers.
关键词： Amorphous materials,Optical properties,Bi2Se3 phase,Chalcogenides,Thin films,Band gap
更新于2025-09-19 17:15:36