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Band gap engineered zinc oxide nanostructures <i>via</i> a sol–gel synthesis of solvent driven shape-controlled crystal growth
摘要： A reliable sol–gel approach, which combines the formation of ZnO nanocrystals and a solvent driven, low shape-controlled, crystal-growth process to form well-organized ZnO nanostructures at temperature is presented. The sol of ZnO nanocrystals showed shape-controlled crystal growth with respect to the solvent type, resulting in either nanorods, nanoparticles, or nanoslates. The solvothermal process, along with the solvent polarity facilitate the shape-controlled crystal growth process, augmenting the concept of a selective adhesion of solvents onto crystal facets and controlling the final shape of the nanostructures. The XRD traces and XPS spectra support the concept of selective adhesion of solvents onto crystal facets that leads to yield different ZnO morphologies. The shift in optical absorption maxima from 332 nm in initial precursor solution, to 347 nm for ZnO nanocrystals sol, and finally to 375 nm for ZnO nanorods, evidenced the gradual growth and ripening of nanocrystals to dimensional nanostructures. The engineered optical band gaps of ZnO nanostructures are found to be ranged from 3.10 eV to 3.37 eV with respect to the ZnO nanostructures formed in different solvent systems. The theoretical band gaps computed from the experimental XRD spectral traces lie within the range of the optical band gaps obtained from UV-visible spectra of ZnO nanostructures. The spin-casted thin film of ZnO nanorods prepared in DMF exhibits the electrical conductivity of 1.14 × 10?3 S cm?1, which is nearly one order of magnitude higher than the electrical conductivity of ZnO nanoparticles formed in hydroquinone and ZnO sols. The possibility of engineering the band gap and electrical properties of ZnO at nanoscale utilizing an aqueous-based wet chemical synthesis process presented here is simple, versatile, and environmentally friendly, and thus may applicable for making other types of band-gap engineered metal oxide nanostructures with shape-controlled morphologies and optoelectrical properties.
关键词： electrical conductivity,ZnO nanostructures,optical band gap,shape-controlled crystal growth,sol–gel synthesis
更新于2025-11-19 16:56:42
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Luminescent, optical, magnetic and metamaterial behavior of cerium complexes
摘要： The complexes of cerium with nitrogen, oxygen and sulfur donor ligands were prepared by conventional method. These newly synthesized complexes were characterized by FTIR, UV-Vis, DART Mass, TGA, PXRD, SEM and TEM techniques. The magnetic studies were carried out by the vibrating sample magnetometer. The optical constants were measured by absorption and reflection spectra as a function of wavelength. The concentration dependence of refractive index and absorption were observed by the experimental method, which reveals that these parameters are affected by change in concentration. The optical band gap obtained from Tauc-plot indicates its probability to be a good semiconductor. The luminescence behavior of these cerium complexes were observed by the absorption and emission spectra and the emission life time were calculated by their life time spectra.
关键词： Optical band gap,Luminescence,Refractive index,Magnetic studies
更新于2025-09-23 15:23:52
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Thin Films of Barium Strontium Titanate from the Viewpoint of Light-Based Applications
摘要： In this paper we report results from optical transmittance spectroscopy complemented with data on structure from XRD measurements to determine optical properties of a series of as-deposited and annealed (at 900 °C) BaSrTiO3 (BST) thin films deposited by RF magnetron sputtering. The members of the series differ by the substrate temperature and additional oxygen to accompany argon in the deposition chamber. The perovskite structure with weak preferred (110) orientation was detected for annealed BST thin films whilst the as-deposited films were amorphous. Dispersive optical properties – refractive indices, absorption coefficients and optical band gaps were determined from transmittance spectra. After annealing refractive indices increase to prove the densification of material accompanied by the thickness shrinkage. Optical band gaps calculated either by Tauc procedure or determined as iso-absorption levels are also found to be deposition dependent.
关键词： absorption coefficient,thin films,barium strontium titanate,refractive index,optical band gap
更新于2025-09-23 15:23:52
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Optical Band Gap, Local Work Function and Field Emission Properties of MBE Grown β-MoO3 Nanoribbons
摘要： Monoclinic molybdenum trioxide (β-MoO3) nanostructures (shaped like nanoribbons: NRs) were grown on Si(100), Si(5512) and fluorine-doped tin oxide (FTO) by molecular beam epitaxy (MBE) technique under ultra-high vacuum (UHV) conditions. The dependence of substrate conditions and the effective thickness of MoO3 films on the morphology of nanostructures and their structural aspects were reported. The electron microscopy measurements show that the length and the aspect ratio of nanostructures increased by, 260% without any significant change in the width for a change in effective thickness from 5 nm to 30 nm. NRs are grown along <011> for all the effective thickness of MoO3 films. Similarly, when we increased the film thickness from 5 nm to 30 nm, the optical band gap decreased from 3.38± 0.01eV to 3.17± 0.01eV and the local work function increased from 5.397 ± 0.025 eV to 5.757 ± 0.030 eV. Field emission turn-on field decreased from 3.58 V/μm for 10-μA/cm2 to 2.5 V/μm and field enhancement factor increased from 1.1×104 to 5.9×104 for effective thickness variation of 5 nm to 30 nm β-MoO3 structures. The β-MoO3 nanostructures found to be much better than the α-MoO3 nanostructures due to low work function, low turn on field and high field enhancement factor, and are expected to be useful applications.
关键词： β-MoO3 nanostructures,Field emission and Kelvin probe force microscopy (KPFM),Optical band gap,Molecular beam epitaxy (MBE),Electron microscopy
更新于2025-09-23 15:22:29
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Effect of annealing on the physical properties of thermally evaporated In2S3 thin films
摘要： The structural, compositional, morphological and optical properties of In2S3 thin films, prepared by thermal evaporation technique and annealed in sulfur ambient at different temperatures have been investigated. The grazing incident X-ray diffraction patterns have indicated polycrystalline form and predominantly cubic structure of annealed In2S3 films. The scanning electron microscopy revealed textured surface with uniformly distributed grains and the grain size increased with increase of annealing temperature. The optical parameters of the films have been determined using conventional transmission and reflection spectra as well as from surface photovoltage measurements.
关键词： Surface photovoltage,Annealing,In2S3 thin films,Structure,Optical band gap
更新于2025-09-23 15:21:21
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Optical, electrical, structural and magnetic properties of BiSe thin films produced by CBD on different substrates for optoelectronics applications
摘要： BiSe thin films have been grown on substrates as PMMA, ITO, glass and Si wafer by using chemical bath deposition (CBD) method. Deposition temperature and time and pH are kept to be constant during the production of the thin films. The thickness of BiSe thin films, which are produced on ITO, glass, PMMA and Si wafer substrate are 513, 468, 1039 and 260 nm, respectively. According to GAXRD results, the films, which are grown on glass and PMMA substrate, have amorphous structure, but, the films, which are grown on ITO and Si wafer substrate, have peaks of Bi2Se3 crystal. Grain sizes, crystallization number per unit area and dislocation density for ITO and Si wafer substrate are calculated as 112.40 nm and 43.04 nm; 2.25×10?5 and 7.91×10?5 (1/nm2), respectively. The contact angles and critical surface tension of distilled water, ethylene glycol, formamide and diiodamethane liquids for thin films grown on glass, ITO, PMMA and Si wafers were obtained by the Zisman method. The % transmittance and % reflectance values of thin films grown on glass, ITO, PMMA are calculated as % T: 79.90, 92.76 and 67.37; % R: 6.18, 2.07 and 10.59, respectively. Eg values of thin films grown on glass, ITO, PMMA are calculated as Eg=1.92; 2.18; 1.60 eV. The extinction coefficients, refractive indexes and relative dielectric constants of thin films grown on glass, ITO, PMMA are calculated as k=0.007; 0.002 and 0.012; n=1.65; 1.34 and 1.96; ε1=0.271; 0.083 and 0.528 respectively. Sheet resistance, hall mobility, sheet carrier densities, bulk carrier densities and conductivity types for glass, ITO, PMMA and Si are 6.52×107, 6.65×101, 1.09×108 and 6.45×102 (Ω/cm2); 2.38, 1.21×10?1, 5.34 and 1.52 (cm2/V.s); 4.01×1010, 7.71×1017, 1.06×1010 and 6.34×1015 (cm?2); 4.58×1014, 1.50×1022, 1.02×1014 and 2.89×1020 (cm?3); p, n, p and p, respectively. In addition, I–V characteristics and changes of magnetoresistance values versus magnetic field of the thin films are obtained by Van der Pauw method and HEMS.
关键词： magnetoresistance,thin film deposition,optical band gap,carrier density,surface properties,crystal growth
更新于2025-09-23 15:21:21
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Observation of Optical Band-Gap Narrowing and Enhanced Magnetic Moment in Co-Doped Sol–Gel-Derived Anatase TiO <sub/>2</sub> Nanocrystals
摘要： The magnetic behavior of TiO2 and doped TiO2 nanocrystals has been a challenge due to the unambiguous nature of defects present in oxide semiconductors. Here, a simple, low-temperature sol?gel method is developed for the synthesis of low-dimensional and highly efficient stable anatase TiO2 nanocrystals. The X-ray powder diffraction pattern and Raman spectra confirm the formation of a single-phase anatase structure of TiO2. High-resolution transmission electron microscopy studies reveal the crystalline nature of the sol?gel-derived nanocrystals. The increase in lattice parameters together with the shifting and broadening of the most intense Eg(1) mode in micro-Raman spectra of Co-doped TiO2 nanocrystals indicate the incorporation of Co in TiO2. Shifting of the absorption edge to the visible region in UV?visible spectra indicates narrowing of the band gap due to Co incorporation in TiO2. X-ray photoelectron spectra confirm the presence of Co2+ and Co3+ in Co-doped TiO2 samples. Oxygen vacancy defects lead to the formation of bound magnetic polarons which induces a weak ferromagnetic behavior in air-annealed 3% Co-doped TiO2 at room temperature. It is observed that irrespective of the dopant ion, whether magnetic or nonmagnetic, the overlapping of bound magnetic polarons alone can induce ferromagnetism, while the magnetic impurities give rise to an enhanced paramagnetic moment for higher Co concentrations. A detailed understanding on the variation of these magnetic properties by estimating the concentration of bound magnetic polarons is presented, which is in corroboration with the photoluminescence studies. The observed band-gap narrowing in Co-doped TiO2 nanostructures and the mechanism underlying the magnetic interactions associated with the magnetic impurity concentration are advantageous from an applied perspective, especially in the field of spintronic and magneto-optic devices.
关键词： spintronic,magnetic moment,nanocrystals,optical band-gap narrowing,TiO2,magneto-optic devices,Co-doped,sol?gel
更新于2025-09-23 15:21:21
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Temperature Dependence of Phonon Modes, Optical Constants, and Optical Band Gap in Two-Dimensional ReS2 Films
摘要： Effects of temperature on the optical properties of the large area ReS2 films (ten layers), which is prepared by chemical vapor deposition on SiO2/Si substrates, have been investigated by Raman and reflectance spectra. The phonon frequencies of eighteen Raman modes redshift about 3 cm-1 with increasing the temperature from 140 K to 320 K. The optical constants (n and k) at a photon energy region of 0.46-6.52 eV are obtained, and the values blue-shift with increasing temperature. Four interband transitions (Ep1, Ep2, Ep3, and Ep4) are observed at 1.53 eV, 2.98 eV, 4.25 eV, and 5.37 eV at 303 K, and the values increase with increasing the temperature. The physical origins have been assigned to the different band-to-band direct electronic transitions. The optical band gap of the ReS2 films increases from 1.36 eV at 303 K to 1.38 eV at 383 K. Based on the first-principles calculation results, the band gap increases from 1.32 eV at a normal lattice constant to 1.40 eV at 1.1 times lattice constant. This is because the energy levels present the tendencies of degeneracy, which due to the coupling between Re 5d orbital and S 3p orbital is weaker and the energy level splitting is smaller with increasing temperature.
关键词： optical constants,ReS2 films,2D materials,phonon modes,optical band gap
更新于2025-09-23 15:21:01
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Band Edge Tuning of Two-Dimensional Ruddlesdena??Popper Perovskites by A Cation Size Revealed through Nanoplates
摘要： Current understanding of the effects of various A site cations on the photophysical properties of halide perovskites (APbI3) is limited by the compositional tunability. Here we report the synthesis and characterization of colloidal nanoplates of a series of 2D Ruddlesden-Popper (RP) perovskites (HA)2(A)Pb2I7 (HA = n-hexylammonium) with seven small and large A site cations to reveal the size effects of such A cations. Absorbance and photoluminescence (PL) measurements show a clear parabolic trend of the optical band gap vs. the A cation size, with methylammonium and formamidinium near the bottom. This band gap shifting is attributed to the changing chemical pressure inside of the A site cavity templating the Pb-I framework. PL quantum yield and time resolved PL measurements show the effect of A cation size on the PL efficiencies and carrier lifetimes. This fundamental investigation can inform the choices of A site cations that can be incorporated into halide perovskite materials for optoelectronic applications.
关键词： chemical pressure,photoluminescence,A site cations,2D Ruddlesden-Popper perovskites,optical band gap
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE International Conference on Electrical, Computer and Communication Technologies (ICECCT) - Coimbatore, India (2019.2.20-2019.2.22)] 2019 IEEE International Conference on Electrical, Computer and Communication Technologies (ICECCT) - Characterisation and performance evaluation of amorphous silicon nitride as passivation layer in thin film aSi:H solar cells
摘要： The fabrication and characterisation of amorphous silicon nitride layer is presented in this paper. The suitability of using it in photovoltaic application has been investigated. It is observed that the band gap of the nitride layers increases with increase in nitrogen content. The experimental results shows that amorphous silicon nitride alloy can be used as passivation layer in devices due to its high optical band gap. On the basis of experimental results, a thin ?lm aSi:H single junction solar cell having aSiNx as passivation layer has been proposed. Further, the behaviour of the proposed structure has been evaluated through simulation using SCAPS1D solar simulator. It is found out that the involvment of amorphous silicon nitride as passivation layer on the top part of the solar cell results in a conversion ef?ciency of 12.9 % and short circuit current density (Jsc) of 15.18 mA/cm2 which are signi?cant values as far as a single junction amorphous silicon thin ?lm solar cell has been considered. Furthermore, a comparison study on solar cell performance parameters of aSi:H solar cell with and without aSiNx passivation layer has been done.
关键词： composition pro?le,optical band gap,FTIR spectrum,passivation layer,PECVD,conversion ef?ciency
更新于2025-09-16 10:30:52