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Preparation and optical properties of angle-dependent photonic crystals based on multi-layer films
摘要： The CreSiO2 photonic crystals, featured with two-dimensional structure and optical variation, was prepared by magnetron sputtering and electron beam lithography method. The finite difference time domain method (FDTD) is used to study the light-modulated characteristics of photonic crystals. Hue difference (⊿H) was used to evaluate the optical variations of photonic crystals, and bigger ⊿H indicates stronger angle dependency of color variation. Various parameters are analyzed for their impact upon ⊿H, including hole geometry (radium, r), hole gap (distance between the centers of two circles, d) and hole depth (h). The results matched the ones from simulation. Carbon quantum dots and up-conversion nanocrystals NaYF4 were inserted into the photonic crystals, and testing results of these doped crystals showed optical variation of fluorescence in the UV and IR region.
关键词： Finite difference time domain,Multi-layer films,Photonic crystal,Optical variability
更新于2025-09-23 15:23:52
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Optical investigation of radiation-induced color centers in lithium fluoride thin films for low-energy proton-beam detectors
摘要： In the last few years, the peculiar photoluminescence properties of radiation-induced color centers in lithium fluoride (LiF) films have been successfully used for advanced diagnostics of low-energy proton beams produced by the TOP-IMPLART linear accelerator for protontheraphy under development at ENEA C.R. Frascati. The two-dimensional spatial dose map of the transversal section of proton beams was fully reconstructed in a wide interval of doses. In this work the optical emission properties of LiF thin films, grown by thermal evaporation on glass and Si (100) substrates and subsequently irradiated by proton beams of nominal energy 3 MeV at doses higher than 105 Gy, were carefully investigated. Their structural and morphological analyses were performed by X-ray diffraction and atomic force microscopy. A careful comparison of the photoluminescence and photoluminescence-excitation spectra of F2 and F3+ electronic defects was performed. Substrate-enhanced photoluminescence intensity increase up to 100% was observed in colored LiF films grown on Si substrates with respect to glass ones. This behavior can be substantially ascribed to the reflective properties of the Si substrate at the emission wavelengths of F2 and F3+ CCs, although other complex effects due to the polycrystalline nature of the films cannot be excluded.
关键词： Photoluminescence,Lithium fluoride,Radiation detectors,Color centers,Thin films
更新于2025-09-23 15:23:52
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Understanding the oxygen barrier property of highly transparent poly(lactic acid)/benzoxazine composite film by analyzing the UV-shielding performance
摘要： This work reports a new composite film from poly(lactic acid) (PLA) and benzoxazine (BOZ). Introduction of BOZ to PLA simultaneously improves the ultraviolet (UV)-shielding and oxygen barrier properties, which show strong dependence on the content of BOZ. The PLA film demonstrates almost no UV-shielding capacity, but the PLA/BOZ composite film can reach UV-shielding capacity of 98.3% at 350 nm. The corresponding average oxygen permeability coefficient of the composite film is as low as 1.168 × 10^{-18} m^3 m m^{-2} s^{-1} Pa^{-1}, which is significantly lower than that of PLA (5.540 × 10^{-17} m^3 m m^{-2} s^{-1} Pa^{-1}). Meanwhile, the composite film retains visible transparency ≥90.0% at 550 nm. The relationship and its implication between the oxygen barrier performance and UV-shielding capacity are discussed, which propose new guidelines for the development of high barrier PLA film.
关键词： thermosets,films,blends,thermoplastics
更新于2025-09-23 15:23:52
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Determination of physical properties of graphene doped ZnO (ZnO:Gr) nanocomposite thin films deposited by a thermionic vacuum arc technique
摘要： This study is focused on the growth of graphene doped ZnO (ZnO:Gr) nanocomposite thin films by a thermionic vacuum arc (TVA) technique. ZnO:Gr nanocomposite thin films were deposited onto glass and silicon (Si) substrates. The influence of the dopant effect on structural, optical, morphological properties of the ZnO:Gr nanocomposite thin films were investigated by using various analysis techniques such as interferometer, UV-Visible spectrophotometer, X-ray diffraction (XRD), Raman spectrometer, Fourier Transform Infrared spectroscopy (FTIR), Photoluminescence (PL) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), and Atomic Force Microscopy (AFM). Thicknesses value of ZnO:Gr nanocomposite thin films for the deposited layers onto glass and Si substrates were measured as to be 50 nm and 20 nm, respectively. In XRD patterns, the reflections of the ZnO and carbon nanostructures were observed. Using UV–Vis spectrophotometer and optical interferometer, the refractive index, reflectance, transmittance, absorbance and optical band gap graphs of the ZnO:Gr nanocomposite thin films were determined. Optical band gap of the ZnO:Gr nanocomposite thin film that deposited on glass substrate was determined as to be 3.15 eV via optical method and the result is in good harmony with PL measurement. PL spectrum showed an ultraviolet (UV) emission peak at 397 nm (3.12 eV). From the Raman analysis of the ZnO:Gr nanocomposite thin films, ZnO, D and 2D peaks of the graphene were observed. FTIR spectroscopy was used to analyze the chemical composition of the samples. According to AFM and FESEM analysis, ZnO:Gr nanocomposite thin films are smooth, flat, granular, uniform and dense form. Due to the larger crystallite sizes ZnO:Gr nanocomposite thin film onto Si substrate has lower resistivity according to the ZnO:Gr nanocomposite thin film deposited onto glass substrate. As a result, ZnO:Gr nanocomposite thin films are promising material for potential applications as to be a transparent conducting oxide (TCO) material.
关键词： FESEM,TVA,ZnO:Gr nanocomposite thin films,XRD,AFM
更新于2025-09-23 15:23:52
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Synthesis and characterization of optically transparent semi-aromatic polyimide films with low fluorine content
摘要： A series of novel semi-aromatic polyimides with low fluorine content were prepared from alicyclic dianhydrides, i.e. 1,2,4,5-cyclohexane-tetracarboxylic dianhydride (CHDA) and bicyclo[2.2.2]octa-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA), and three aromatic diamines containing ortho-substituted methyl and pendent phenyl groups, respectively. These polyimides exhibited excellent solubility even though their fluorine content lower than 10 wt.%. Chemical resistance to MEK and aqueous alkali of films was also satisfied for application as flexible substrates. The semi-aromatic polyimides showed outstanding heat resistance with Tg values up to 387 oC and good mechanical strength. These films had excellent optical transparency with cutoff wavelengths of 282-286 nm, transmittance >89% at 500 nm and yellowness indices <14.8. Especially, PIBF-3 and PIBF-6 were extremely transparent and very light color with thickness of 70 μm. Their improved optical transparency and elimination of coloration was mainly attributed to weakened electrophilicity of alicyclic dianhydrides, steric hindrance and distorted non-coplanar caused by ortho-substituted and bulky pendent groups.
关键词： Polyimide films,High transparency,Semi-aromatic.
更新于2025-09-23 15:23:52
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Spin Rectification dc Voltage Spectra via Sweeping Frequency
摘要： A new measurement method of a spin rectification dc voltage spectrum through fixing the magnetic field and sweeping the frequency has been proposed, which is compared to the common method to acquire a typical spectrum via sweeping an external magnetic field. Based on the shortened microstrip fixture, the measurements of rectified dc voltage as a function of frequency have been performed. From the analysis of results of the permalloy (Py) film with various thicknesses, the magnetic parameters are presented. This method can be used in samples with magnetic domains varied with respect to the external magnetic field, such as, stripe domain structures.
关键词： stripe domain structure,monolayer Py films,frequency-swept,spin rectification effect (SRE)
更新于2025-09-23 15:23:52
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Optical and photoconductive properties of indium sulfide fluoride thin films
摘要： This work reports on transparent semiconducting indium sulfide fluoride (ISF) thin-films exhibiting high sensitivity to ultraviolet radiation. The films were deposited on fused silica and silicon substrates using a radio-frequency plasma-enhanced reactive thermal evaporation system. The deposition was performed evaporating pure indium in SF6 plasma at a substrate temperature of 423 K. Rutherford backscattering measurements were used to determine the chemical composition of the films deposited on silicon substrates. The surface morphology was studied using scanning electron microscopy technique. The film characterization includes electrical, optical, and photoconductivity measurements. The synthesized compound is highly-resistive (~700 MΩ-cm at 300 K) and exhibits an evident semiconducting behavior. The activation energy of 0.88 eV is deduced from the temperature dependence of electrical resistivity. The indirect band energy gap of 2.8 eV is determined from transmittance spectra of the ISF films. The photoconductivity band is centered at 345 nm wavelength. The photoconductivity spectrum also shows the Urbach tail with a characteristic energy of 166 meV. ISF is a promising candidate for a buffer layer in chalcogenide-based solar cells.
关键词： Thin-films,Indium sulfide fluoride,Optical properties,Photoconductivity,Photovoltaics,Amorphous semiconductors
更新于2025-09-23 15:23:52
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Effect of Na doping on structural and optical properties in Cu2ZnSnS4 thin films synthesized by thermal evaporation method
摘要： Quaternary chalcogenide Cu2ZnSnS4 (CZTS) compound, a potential material for application as absorber layer in thin film solar cells, is synthesized by direct melting of the constituent elements taken in stoichiometry compositions. Alkali element Na was incorporated into CZTS thin films synthesized by thermal evaporation method, in order to further improve the structural and optical properties. X-Ray diffraction (XRD), Raman spectroscopy, Energy dispersive spectrometry and optical spectrophotometry were used to characterise the phase purity and optical properties. It showed that the diffusion of Na ions is uniform in the films after annealing. XRD analysis showed that CZTS films possess polycrystalline structure with [221] preferred orientation. Na ions incorporation in CZTS thin films could improve the cristallinity, the graine size and the absorption coefficient. For CZTS: Na 5%, optical results revealed higher absorption coefficient (>105 cm-1) and direct optical band gap of 1.56 eV with p-type conductivity.
关键词： Semiconductors,Sodium doping,Structural properties,Optical properties,Copper zinc tin sulfide,Thin films,Thermal evaporation
更新于2025-09-23 15:23:52
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Composite up-conversion luminescent films containing a nanocellulose and SrF2:Ho particles
摘要： The synthesis of up-conversion luminescent composite films based on a nanocellulose matrix containing Sr1-xHoxF2+x particles was proposed. The combination of sulfuric acid hydrolysis and ultrasonication allowed us to synthesize a series of stable nanocellulose dispersions from various raw materials (powdered sulphate bleached wood pulp, Blue Ribbon filter paper, and microcrystalline cellulose Avicel). The size distribution of cellulose nanoparticles in the aqueous dispersions was determined. Cellulose nanocrystals (CNC) and/or cellulose nanofibrils (CNF) dispersions were used to fabricate thin films by solution casting followed by solvent evaporation under ambient conditions. The size and shape of cellulose nanoparticles, surface morphology, crystallinity index of nanocellulose, polymerization degree, and optical properties were studied. By mixing aqueous dispersions of CNC with up-conversion Sr1-xHoxF2+x particles, homogeneous suspensions were obtained. Finally, a solution casting technique was used to prepare CNC/Sr1-xHoxF2+x and CNC/CNF/Sr1-xHoxF2+x nanocomposite films. CNC/CNF dispersions were utilized for the production of flexible, durable, transparent composite films. The synthesized nanocomposites demonstrated intense red luminescence upon Ho3+ excitation by 1912 nm laser radiation. The obtained up-conversion luminescent composite films can be considered as a promising material for photonics, in particular for near-IR laser labeling and radiation visualization, luminescent sensorics.
关键词： Nanocomposites,Up-conversion luminescent films,Cellulose nanofibrils,Cellulose nanocrystals,SrF2:Ho3+
更新于2025-09-23 15:23:52
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Nanomechanical, Mechanical Responses and Characterization of Piezoelectric Nanoparticle-Modified Electrospun PVDF Nanofibrous Films
摘要： Limitless implementations of nanofibrous membrane show the importance of understanding the nanomechanical responses for water purification and piezoelectric nanogenerator applications. Here, the polyvinylidene fluoride (PVDF) electrospun nanofibrous films doped by 0.01, 0.05 and 0.1 wt% of ZnO nanoparticles were prepared in the method of electrospinning. Characterizations of PVDF nanocomposite fibrous films were inspected using field emission scanning electron microscope, thermogravimetric analysis, water contact angle, uniaxial tensile test and nanoindentation technique. The influence of minimal concentration of piezoelectric nanoparticles on the morphological, water contact angle, dynamic water contact angle, piezoelectric, thermal and mechanical stabilities of nanocomposite fibrous films was examined. The nanoscale mechanical properties of the PVDF/ZnO nanofibrous films were performed by nanoindentation technique at different spots of nanofibrous mat to examine the elastic–plastic behavior of membranes. The eventual ZnO nanoparticle-modified nanofibrous membranes have been shown nano-level fibers, considerable hydrophilicity and preferable thermal, mechanical and piezoelectric properties. The doping of polymer by 0.1 wt% of ZnO nanoparticles exposed significant enhancement of thermal, mechanical and nanomechanical responses of the melting temperature 2% (170–173 °C), tensile strength 20% (2.418 MPa), elastic modulus 18% (2.418 GPa) and hardness 60% (235 MPa) and piezoelectric coefficient 13.42 pC/N of the nanofibrous films. These understandings of nanoscale properties are highly promising in the development of sensor and actuators, biomedical, energy harvesting and water filtration devices.
关键词： Thin films,Nanomechanical responses,Nanofibers,PVDF,Piezoelectric nanoparticles,Electrospinning
更新于2025-09-23 15:23:52