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Synthesis and optical studies of nanocrystalline Eu2+-doped and RE3+(Nd3+, Dy3+)-codoped Ba4Al14O25 materials for UV-LEDs
摘要： Green emitting Ba4Al14O25:Eu2+ and Ba4Al14O25:Eu2+,RE3+ (RE3+ = Nd3+, Dy3+) phosphors for ultraviolet light emitting diodes (UV-LEDs) were prepared via combustion technique at 600 °C. The as-prepared samples were reheated at 1150 (2 h) and 1350 °C (6 h) in a tube furnace under reducing condition (95 % dinitrogen and 5 % dihydrogen). The photoluminescence emission (PL) spectra were recorded to examine the effect of temperature and presence of co-dopants on the luminescence properties of materials. On excitation at 362 nm, PL spectra of these phosphors exhibited intense band at 480?520 nm due to spin-allowed 4f65d1→4f7 transition in Eu2+. The luminescence intensity and persistence behaviour of materials was improved in presence of Nd3+ and Dy3+ ions as codopants. The diffraction analysis confirmed the synthesis of lattice having orthorhombic structure with Pmma symmetry. The crystalline nature of samples was found to be increased at higher temperature. Transmission electron microscope (TEM) images exhibited that the prepared materials have nearly spherical shape in nano-range. The structure and chemical bonding of materials were supported by Fourier transform infrared (FTIR) spectra.
关键词： Nanocrystalline,Ba4Al14O25,Luminescence,TEM,UV-LEDs,Persistence
更新于2025-09-23 15:21:01
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Synthesis, DFT studies, fabrication, and optical characterization of the [ZnCMC] <sup>TF</sup> polymer (organic/inorganic) as an optoelectronic device
摘要： A novel carboxymethyl cellulose zinc thin film [ZnCMC]TF was fabricated using the sol–gel technique. Different characterization techniques such as Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet–visible spectroscopy (UV-Vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and the optical properties were used to study the properties of [ZnCMC]TF. The molecular structure, FTIR, and optical properties were optimized. The Raman spectrum of the [ZnCMC]TF complex shows several bands in the range of 72–556 cm?1 due to (nZn–O) stretching and (Zn–O) bending, which is an obvious distinction between the FTIR and Raman spectra of [ZnCMC]TF. The optimization was performed using density functional theory (DFT) by DMol3 and Cambridge Serial Total Energy Package (CASTEP) program. The chemical structure was confirmed by spectroscopic and structural properties for both CMC and [ZnCMC]TF; the XRD results showed the same crystal structure (Monoclinic 2). [ZnCMC]TF has a larger grain size than CMC and has a similar behavior in the optical gap energy. The optical constants increased with increasing photon energy, refractive index n, absorption index k, and optical conductivity. The SEM images provide very good evidence in favor of the reaction of zinc transition metal with CMC for the formation of the [ZnCMC]TF complex. The resulting [CMC] spherical thin film and the [ZnCMC]TF polymeric nanorods were examined by different techniques including TEM and EDX. The optical properties obtained from the simulated FTIR, XRD, and CASTEP are in good agreement with those obtained from the experimental studies on CMC and ZnCMC. Based on the optical findings, [ZnCMC]TF is a promising candidate in applications such as solar cells and optoelectronic devices.
关键词： TEM,DMol3,zinc thin film,carboxymethyl cellulose,UV-Vis,DFT,optoelectronic devices,XRD,EDX,CASTEP,sol–gel technique,SEM,FTIR,optical properties,Raman spectroscopy
更新于2025-09-23 15:21:01
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Evolution of Size and Optical Properties of Upconverting Nanoparticles during High Temperature Synthesis
摘要： We investigated the growth of β-phase NaYF4:Yb3+,Er3+ upconversion nanoparticles synthesized by the thermal decomposition method using a combination of in situ and offline analytical methods for determining the application-relevant optical properties, size, crystal phase, and chemical composition. This included in situ steady state luminescence in combination with offline time-resolved luminescence spectroscopy, as well as small-angle X-ray scattering (SAXS) transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and inductively coupled plasma optical emission spectrometry (ICP-OES). For assessing the suitability of our optical monitoring approach, the in situ collected spectroscopic data, that reveal the luminescence evolution during nanocrystal synthesis, were compared to measurements done after cooling of the reaction mixture of the as-synthesized particles. The excellent correlation of the in situ and time-resolved upconversion luminescence with the nanoparticle sizes determined during the course of the reaction provides important insights into the various stages of nanoparticle growth. This study highlights the capability of in situ luminescence monitoring to control the efficiency of UCNP synthesis, particularly the reaction times at elevated temperatures and the particle quality in terms of size, shape and crystall structure, as well as luminescence lifetime and upconversion quantum yield.
关键词： thermal decomposition,XRD,ICP-OES,TEM,in situ luminescence,SAXS,upconversion nanoparticles
更新于2025-09-23 15:21:01
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Direct in situ TEM visualization and insight of the facet-dependent sintering behaviours of gold on TiO?
摘要： To prevent sintering of supported nanocatalysts is an important issue in nanocatalysis. A feasible way is to choose a suitable support. However, whether the metal-support interactions promote or prevent the sintering has not been fully identified due to the lack of confirmed evidences. Herein, we report on completely different sintering behaviours of Au nanoparticles on distinct anatase TiO2 surfaces by in situ TEM. The full in situ sintering processes of Au nanoparticles were visualized on TiO2 (101) surface, which coupled the Ostwald ripening and particle migration coalescence. In contrast, no sintering of Au on TiO2 anatase (001) surface was observed under the same conditions. This facet-dependent sintering mechanism is fully explained by the density function theory calculations. Our work not only offers the direct evidence of the important role of supports in the sintering process, but also provides insightful information for the design of sintering-resistant nanocatalysts.
关键词： in situ TEM,particle migration and coalescence (PMC),sintering,metal?support interaction (MSI),Au-TiO2,Ostwald ripening (OR)
更新于2025-09-23 15:21:01
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Inset-fed rectangular MICROSTRIP patch antenna bandwidth enhancement
摘要： Bandwidth enhancement of the traditional inset-fed rectangular microstrip patch antenna is numerically analyzed using degraded ground plane technique. Input impedance calculation based on the electromagnetic theory in traveling-wave in conjunction with field distribution in quasi-TEM mode approximation is carried out. Radiated electric field properties are performed using Ampere’s law of the magneto-static. Some antenna performances such as ?10 dB return loss bandwidth of 36.7%, beam-width of about 94(cid:1), and stable gain of 3.4 dB have been achieved.
关键词： degraded GND inset-patch,traditional inset-patch,return loss,quasi-TEM mode,radiation pattern
更新于2025-09-23 15:21:01
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Structural and Quantitative Investigation of Perovskite Pore Filling in Mesoporous Metal Oxides
摘要： In recent years, hybrid organic–inorganic perovskite light absorbers have attracted much attention in the field of solar cells due to their optoelectronic characteristics that enable high power conversion efficiencies. Perovskite-based solar cells’ efficiency has increased dramatically from 3.8% to more than 20% in just a few years, making them a promising low-cost alternative for photovoltaic applications. The deposition of perovskite into a mesoporous metal oxide is an influential factor affecting solar cell performance. Full coverage and pore filling into the porous metal oxide are important issues in the fabrication of highly-efficient mesoporous perovskite solar cells. In this work, we carry out a structural and quantitative investigation of CH3NH3PbI3 pore filling deposited via sequential two-step deposition into two different mesoporous metal oxides—TiO2 and Al2O3. We avoid using a hole conductor in the perovskite solar cells studied in this work to eliminate undesirable end results. Filling oxide pores with perovskite was characterized by Energy Dispersive X-ray Spectroscopy (EDS) in Transmission Electron Microscopy (TEM) on cross-sectional focused ion beam (FIB) lamellae. Complete pore filling of CH3NH3PbI3 perovskite into the metal oxide pores was observed down to X-depth, showing the presence of Pb and I inside the pores. The observations reported in this work are particularly important for mesoporous Al2O3 perovskite solar cells, as pore filling is essential for the operation of this solar cell structure. This work presents structural and quantitative proof of complete pore filling into mesoporous perovskite-based solar cells, substantiating their high power conversion efficiency.
关键词： STEM-TEM,mesoporous,perovskite,pore filling,XRD
更新于2025-09-23 15:21:01
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Formation of Gold Nanoparticles in a Free-Standing Ionic Liquid Triggered by Heat and Electron Irradiation
摘要： Ionic liquids (ILs) feature negligibly low vapor pressures and can thus be freely introduced into the high vacuum of a transmission electron microscope. With this extraordinary property, the ILs offer a powerful tool for in situ transmission electron microscopy (TEM) in window-free liquid media at very high resolution. In this work, we use the IL 1-butyl-3-methyl imidazolium chloride in order to study nucleation and growth of gold nanoparticles (NPs) in free-standing liquid droplets by scanning TEM (STEM). The results confirm that the used IL allows for generating Au NP in situ, triggered by electron irradiation and heat. Firstly, the isotropic growth of small, spherical Au NPs was initiated and monitored whereas different growth mechanisms were observed, i.e. growth by monomer attachment, growth through particle coalescence and possible Ostwald ripening events. After the initial growth phase, a second, anisotropic growth process was induced by a moderate temperature increase and continued electron irradiation. As a result, larger, faceted crystals such as tetrahedra, octahedra or decahedra were formed. As all these polymorphs are terminated by {111}-facets, the IL might not only act as liquid medium but in addition as a surfactant which preferentially attaches on the {100}-facets.
关键词： gold,in situ,TEM,heat,nanoparticle growth,ionic liquid
更新于2025-09-23 15:21:01
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Effect of laser shock peening on mechanical and microstructural aspects of 6061-T6 aluminum alloy
摘要： Laser shock peening (LSP) of 6061-T6 aluminum alloy was performed and parametric effects post LSP on mechanical aspects and microstructural evolution are meticulously studied using various means of characterization techniques such as residual stress analysis, surface roughness, Vickers microhardness, tensile testing, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD). Work hardened layer of ~1500 μm depth is obtained with significant improvement in cross-sectional microhardness up to 33.04%. Beneficial compressive residual stress of maximum magnitude up to -273 MPa was induced in laser peened specimens concentrating its overall effect around the depth of 100 μm along the effective depth region. Second phase Mg5Si6 (β?) precipitates were observed post LSP while analyzing XRD profiles along with the peak broadening and peak shifting towards higher 2θ angle justifying the results obtained in microhardness profile. High angle grain boundaries (HAGBs) fraction was increased in LSPed specimens and its effect is noticed in residual stress profile. Mg5Si6 (β?) precipitates are attributed as contributing precipitates in improving the mechanical properties of LSPed specimens along with the dense dislocation density caused by severe plastic deformation during LSP. The collective contribution of strain hardening, second phase precipitates, peak broadening, dislocation density and increased fraction of HAGBs is observed in mechanical and microstructural aspects of LSPed specimens. The results are discussed in detailed and are strongly correlated with each other.
关键词： EBSD,Aluminum alloy,cosα method,TEM,XRD,Laser shock peening
更新于2025-09-23 15:19:57
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High performance UV photodetector based on MoS2 layers grown by pulsed laser deposition technique
摘要： Highly efficient ultraviolet (UV) photodetector based on MoS2 layers has been fabricated using pulsed laser deposition (PLD) technique. Systematic layer dependent photoresponse studies have been performed from single layer to 10 layers of MoS2 by varying the laser pulses to see the effect of the number of layers on the photoelectrical measurements. Raman and Photoluminescence studies have been carried out to ensure the growth of high-quality MoS2 layers. Layers of MoS2 grown at 100 pulses were found to exhibit the characteristic Raman phonon modes i.e. E1 2g and A1g at 383.8 cm-1 and 405.1 cm-1 respectively and Photoluminescence (PL) spectra show B exciton peak for MoS2 at around 625 nm suggesting the growth of high-quality MoS2 layers. Atomic force microscopy (AFM) thickness profiling and cross sectional-high resolution transmission electron microscopy (HRTEM) analysis gives the thickness of grown MoS2 to be 2.074 nm and 1.94 nm, respectively, confirming the growth of trilayers of MoS2. X-ray photoelectron spectroscopy (XPS) spectra of the grown trilayer sample show characteristic peaks corresponding to Molybdenum and Sulphur doublet (Mo4+ 3d5/2,3/2 and S 2p3/2,1/2) confirming the chemical state of pure MoS2 phase without the presence of any Molybdenum oxide state. Dynamic photoelectrical studies with Indium Tin Oxide (ITO) as contact electrode upon UV laser illumination show superior responsivity of 3×104 A/W at 24 μW optical power of the incident laser (λ=365 nm) and very high detectivity of 1.81×1014 Jones at a low applied bias of 2 V. The obtained results are highly encouraging for the realization of low power consumption and highly efficient UV photodetectors based on MoS2 layers.
关键词： Pulsed laser deposition technique (PLD),2D material,UV photodetector,ITO electrode,cross-sectional TEM,Raman,MoS2 layers,XPS,AFM
更新于2025-09-23 15:19:57
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[IEEE 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII) - Berlin, Germany (2019.6.23-2019.6.27)] 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII) - In-Situ Transmission Electron Microscopy Coupled with Resonant Microcantilever for Comprehensive Evaluating Sulfurization Performance of Zinc Oxide Nanowires
摘要： This paper reports a new technique with in-situ transmission electron microscopy (in-situ TEM) and resonant microcantilever to comprehensively evaluate sulfurization performance of ZnO nanowires. Herein, in-situ TEM is used to real-time observe the sulfurization process of ZnO nanowires under SO2-contained atmosphere. temperature-varying micro-gravimetric method, thermodynamic interaction between ZnO nanowires and SO2 molecules is quantitatively evaluated by resonant microcantilever. By exposing the ZnO nanowires sample to SO2-contained atmosphere, a thick shell layer of ZnSO3 can be formed onto the surface of ZnO nanowires and a novel core-shell nanowire structure of ZnO@ZnSO3 is obtained finally. According to our comprehensive evaluation results, the ZnO nanowires sample with 100 nm diameter exhibits high reactive to SO2 molecules and is suitable for SO2 capture and storage.
关键词： sulfurization process,ZnO nanowires,thermodynamic parameter extraction,In-situ TEM
更新于2025-09-23 15:19:57