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Raman and fluorescence imaging on polyoxometalate composite agarose films
摘要： Composite agarose films were prepared with Eu(III) containing polyoxometalates, in particular the organic-inorganic hybrid [Eu(W5O18)2(pic)4]13- (Hpic = 3-hydroxypicolinic acid) and a Mo blue Eu(III) derivative. The latter compound shows interesting Eu(III) based photoluminescent properties, firstly described for a molybdenum blue compound. Imaging of the films optical properties and morphology was explored by Raman and fluorescence measurements in a confocal microscopy system, together with the AFM profile. Raman and fluorescence imaging were powerful tools for the characterization of the films, in particular concerning its chemical composition and homogeneity at the micrometric scale.
关键词： Fluorescence imaging,Agarose films,Polyoxometalates,Raman imaging,Europium
更新于2025-09-09 09:28:46
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Investigation of Single-Crystal Niobium for Microwave Kinetic Inductance Detectors
摘要： The Advanced Technology Centre (ATC) of National Astronomical Observatory of Japan is developing microwave kinetic inductance detectors (MKIDs) for large-array pixel cameras for millimeter and sub-millimeter astronomy. We investigated single-crystal Nb thin layers to form superconducting microresonators. We compared the performances of MKIDs based on crystalline Nb structure and those based on poly-crystalline Nb. We carried out the entire manufacture of the detectors in the ATC clean room. DC magnetron sputtering is used to grow single-crystal Nb films on r-plane sapphire substrates at an elevated temperature of 800 °C. The residual resistivity ratio (RRR) measured on these single-crystal Nb layers reached values ranging from 40 to 80. We made MKIDs with this crystalline Nb layer, and we measured internal quality factors of the detectors up to 106. The measurement of the noise power spectral density of these MKIDs gave a low value of ? 95 dBc/Hz from 100 Hz to 100 kHz. The internal quality factor Qi and the fractional resonance frequency change δf r/f r of MKIDs with respect to the temperature variation are usually following the extended Mattis–Bardeen equations. However, we noticed a deviation from the theoretical prediction for temperature lower than 1 K (in our case). This deviation has already been observed on Al MKIDs and explained by a theory taking into account the Kondo effect and the kinetic inductance contribution. We demonstrated that our measurements on single-crystal Nb MKIDs are also in agreement with the same theory.
关键词： Microwave kinetic inductance detector,Single-crystal niobium,Superconducting thin films
更新于2025-09-09 09:28:46
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Aliovalent Ho3+ ion doped BaZrO3 thin films; Structural, optical and photoluminescence properties
摘要： Ho doped BaZrO3 thin film phosphors with varying Ho content (1, 2, 3 and 4 at. %) were prepared via pulsed laser deposition technique. To understand the effect of doping on structural, morphological, optical and emission properties of thin films, X-ray Diffractrometer (XRD), Scanning Electron Microscopy (SEM), Spectroscopic Ellipsometry (SE) and Photoluminescence (PL) Spectroscopy have been used, respectively. Polycrystalline nature with single phase cubic crystalline structure of the films has been obtained. The optical band gap energy, as estimated by SE, has been found to increase with increase in the Ho content. The PL spectra of the synthesized phosphor exhibit green and yellow-orange as prominent emission bands in response to 328 nm as excitation wavelength.
关键词： optical properties,thin films,rare earth,perovskite
更新于2025-09-09 09:28:46
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Degradation study of malachite green on chitosan films containing heterojunctions of melon/TiO2 absorbing visible-light in solid-gas interfaces
摘要： Urea modified TiO2 nanoparticles were synthesized at different TiO2: urea ratios (10, 30 and 60 (%wt) named UTiO2-10, 30 and 60) by sol-gel method and annealing at 400 °C during 1h. Characterization revealed the presence of TiO2 nanoparticles with visible light absorption (between 400 and 500 nm) probably due by the formation of thermolysis urea byproducts such as melon, which may induce a TiO2/melon heterojunction. Then, modified nanoparticles were immobilized on chitosan films by adding 30% (70QS/30UTiO2) and 50% 50QS/50UTiO2) of UTiO2 nanoparticles. Functionalized films were characterized by SEM-EDS, DRS and AFM. Photo-induced degradation of malachite green stains was evaluated on these films under different wavelengths. Upon UV-A+visible light irradiation, films showed good activity even slightly better than those containing Evonik P-25 (70QS/30P-25). Upon visible light between 450 and 800 nm, films evidenced a satisfactory performance but slower than under UV-A+visible light irradiation whereas the photobleaching activity of 70QS/30P-25 was very poor. When visible light irradiation with wavelengths higher than 590 nm was used, a slight photobleaching was also observed. DRS spectra taken at different irradiation times showed that dye underwent N-demethylated oxidative reactions either upon UV-Visible or visible light irradiation. ATR-FTIR measurements revealed the generation of benzophenones after 6 h of irradiation probably suggesting the formation of singlet oxygen under visible light. 70QS/30UTiO2-10 films showed a good photo-bleaching activity after 18 h of continuous UV-A+visible light irradiation.
关键词： urea,Visible-light responsive TiO2,chitosan films,melon/TiO2 heterojunction
更新于2025-09-09 09:28:46
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Photoluminescent properties in perylene PVD films: Influence of molecular aggregates and supramolecular arrangement
摘要： Organic thin films are at the forefront of basic studies and applications in the field of physics, chemistry, biochemistry and materials science. For example, the intrinsic supramolecular arrangement, or simply the formation of aggregates may alter the optical and electrical properties, which would impact the potential applications of the material. Here, an attempt is made to correlate the molecular structures of two perylene derivatives, bis butylimido perylene (BuPTCD) and bis phenethylimido perylene (PhPTCD), with their film formation, in particular, the supramolecular arrangement and the photoluminescent properties. Emission spectra show that the PhPTCD has a radiative efficiency (RE) higher than that for BuPTCD when both are in solutions (monomers). Complementary, regarding PVD films, UV-Vis absorption measurements reveal that PhPTCD forms, predominantly, J aggregates, which are responsible for perylene derivative emission. However, BuPTCD PVD films are found to provide higher RE than PhPTCD PVD film. This apparent controversy could be explained considering other features such as crystallinity and molecular organization. The PVD film of BuPTCD is crystalline while PhPTCD PVD film is amorphous; BuPTCD has an edge-on while PhPTCD has a face-on molecular organization in PVD films.
关键词： perylene derivatives,PVD thin films,aggregates,photoluminescent properties,supramolecular arrangement
更新于2025-09-09 09:28:46
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Dislocation-induced thermal transport anisotropy in single-crystal group-III nitride films
摘要： Dislocations, one-dimensional lattice imperfections, are common to technologically important materials such as III–V semiconductors, and adversely affect heat dissipation in, for example, nitride-based high-power electronic devices. For decades, conventional nonlinear elasticity models have predicted that this thermal resistance is only appreciable when the heat flux is perpendicular to the dislocations. However, this dislocation-induced anisotropic thermal transport has yet to be seen experimentally. Using time-domain thermoreflectance, we measure strong thermal transport anisotropy governed by highly oriented threading dislocation arrays throughout micrometre-thick, single-crystal indium nitride films. We find that the cross-plane thermal conductivity is almost tenfold higher than the in-plane thermal conductivity at 80?K when the dislocation density is ~3?×?1010?cm?2. This large anisotropy is not predicted by conventional models. With enhanced understanding of dislocation–phonon interactions, our results may allow the tailoring of anisotropic thermal transport with line defects, and could facilitate methods for directed heat dissipation in the thermal management of diverse device applications.
关键词： dislocations,time-domain thermoreflectance,thermal transport,anisotropy,group-III nitride films
更新于2025-09-09 09:28:46
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Composite GaN-C-Ga (‘GaCN’) Layers with Tuneable Refractive Index
摘要： This article describes novel composite thin films consisting of GaN, C and Ga (referred to as ‘GaCN’, as an analogue to BCN and other carbonitrides) as a prospective material for future optical applications. This is due to their tuneable refractive index that depends on the carbon content. The composites are prepared by introducing alternating pulses of trimethylgallium (TMG) and ammonia (NH3) on silicon substrates to mimic an atomic layer deposition process. Since the GaCN material is hardly reported to the best of our knowledge, a comprehensive characterization is performed to investigate into its chemical nature, primarily to determine whether or not it exists as a single-phase material. It is revealed that GaCN is a composite, consisting of phase-segregated, nano-scale clusters of wurtzitic GaN polycrystals, in addition to inclusions of carbon, nitrogen and gallium, which are chemically bonded into several forms, but not belonging to the GaN crystals itself. By varying the deposition temperature between 400 and 600 oC, and the NH3 partial pressure between 0.7×10-3 and 7.25 mbar, layers with a wide compositional range of Ga, C and N are prepared.
关键词： composite thin films,atomic layer deposition,optical applications,GaCN,tuneable refractive index
更新于2025-09-09 09:28:46
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Direct probing of cross-plane thermal properties of ALD Al <sub/>2</sub> O <sub/>3</sub> /ZnO superlattice films with improved figure of merit and their cross-plane thermoelectric generating performance
摘要： There is a recent interest in semiconducting superlattice films because their low dimensionality can increase the thermal power and phonon scattering at the interface in superlattice films. However, experimental studies in all cross-plane thermoelectric (TE) properties, including thermal conductivity, Seebeck coefficient, and electrical conductivity, has not been performed from these semiconducting superlattice films, because of substantial difficulties in the direct measurement of the Seebeck coefficient and electrical conductivity. Unlike the conventional measurement method, we present technique using a structure of sandwiched superlattice films between two embedded heaters as heating source, and electrodes with two Cu plates, which directly enables the investigation of the Seebeck coefficient and electrical conductivity across the Al2O3/ZnO superlattice films, prepared by atomic layer deposition (ALD) method. Used in combination with the promising cross-plane four-point-probe 3-ω method, our measurements and analysis demonstrate all cross-plane TE properties of Al2O3/ZnO superlattice films in the temperature range from 80 to 500 K. Our experimental methodology and the obtaining results represent a significant advancement in the understating of phonon and electrical transports in nanostructured materials, especially in semiconducting superlattice films in various temperature ranges.
关键词： Thermal conductivity,Cross-plane thermoelectric properties,Seebeck coefficient,Phonon transport,Superlattice films,3-omega measurement,Phonon scattering
更新于2025-09-09 09:28:46
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Controllable magnetization and resistivity jumps of manganite thin films on BaTiO <sub/>3</sub> substrate
摘要： Manganites thin films grown on ferroelectric BaTiO3 (BTO) exhibit dramatic jumps for both magnetization and resistivity upon cooling in accordance with the temperature-dependent structural transitions of the BTO substrate. Both upward and downward jumps have been reported at the same temperature point where BTO undergoes a structural transition from monoclinic to rhombohedral. Using La5/8Ca3/8MnO3/BaTiO3 as protype system, we solve the puzzle by showing that the direction of the jumps can be controlled by applying an electric field during post growth cooling which determines the orientation of the c-axis of the BTO substrate at room temperature. This offers a convenient way to control the magnetic and transport behavior of manganites films using electric field.
关键词： manganite thin films,resistivity jumps,electric field control,magnetization,BaTiO3 substrate
更新于2025-09-09 09:28:46
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Discrimination of molecular thin films by surface-sensitive time-resolved optical spectroscopy
摘要： An optical discrimination technique, tailored to nanometric-sized, low optical absorbance molecular complexes adhering to thin metal films, is proposed and demonstrated. It is based on a time-resolved evanescent-wave detection scheme in conjunction with hierarchical cluster analysis and principal value decomposition. The present approach aims to differentiate among molecular films based on statistical methods, without using previous detailed knowledge of the physical mechanisms responsible for the detected signal. The technique is open to integration in lab-on-a-chip architectures and nanoscopy platforms for applications ranging from medical screening to material diagnostics.
关键词： time-resolved optical spectroscopy,principal value decomposition,optical discrimination technique,hierarchical cluster analysis,molecular thin films
更新于2025-09-09 09:28:46