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Improved field emission from appropriately packed TiO2 nanorods: Designing the miniaturization
摘要： An improved electron field emission (FE) property from vertically aligned TiO2 nanorods (TNR) on conducting fluorine doped tin oxide coated glass substrate, prepared by hydrothermal technique, has been reported here. The TNRs having high aspect ratio with appropriate separation were prepared by optimizing the nucleation temperature. The TNR density has been optimized to cease the screening effect in closely packed nanorods. The well aligned rods have been designed so that the applied field is equally distributes on each rod to improve the electron emission. The morphology of the nanorod has been studied using scanning electron microscopy and observed FE current density-field response has been analysed within the frame work of Fowler-Nordheim modelling. Two orders of magnitude enhancement in the electric field has been observed for this kind of geometry giving improved turn on field and field enhancement factor of 0.2 V/m m and 37 thousands respectively.
关键词： Fowler-Nordheim modelling,Hydrothermal technique,Field emission,TiO2 nanorods,Field enhancement factor
更新于2025-09-09 09:28:46
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Sulfur doping of M/In <sub/>2</sub> O <sub/>3</sub> (M=Al,W) nanowires with room temperature near infra red emission
摘要： We have investigated the growth of Al doped In2O3 nanowires via the vapor-liquid-solid mechanism at 800?C using Au as a catalyst. We find that the Al is not incorporated into the cubic bixbyite crystal structure of In2O3 but nevertheless was detected in the form of Al2O3. The nanowires had metallic like conductivities and exhibited photoluminescence at 2.3 eV which shifted to 1.5 eV after exposure to H2S above 500?C due to the formation of β-In2S3 and deep donor to acceptor transitions with a lifetime of ≈ 1 μs. The near infra red emission was also observed in W/In2O3 but not in W/SnO2 core-shell nanowires after processing under H2S at 600?C, confirming it is related to β-In2S3. The nanowires remain one dimensional up to 900?C due to the shell which is interesting for the fabrication of high temperature nanowire sensors.
关键词： β-In2S3,M/In2O3 nanowires,Al doped In2O3,room temperature near infra red emission,Sulfur doping
更新于2025-09-09 09:28:46
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SALT long-slit spectroscopy of LBQS 2113-4538: variability of the Mg II and Fe II component
摘要： Context. The Mg II line is of extreme importance in intermediate redshift quasars since it allows us to measure the black hole mass in these sources and to use these sources as probes of the distribution of dark energy in the Universe, as a complementary tool to SN Ia. Aims. Reliable use of Mg II requires a good understanding of all the systematic effects involved in the measurement of the line properties, including the contamination by Fe II UV emission. Methods. We performed three spectroscopic observations of a quasar LBQS 2113-4538 (z = 0.956) with the SALT telescope, separated in time by several months and we analyze in detail the mean spectrum and the variability in the spectral shape. Results. We show that even in our good-quality spectra the Mg II doublet is well fit by a single Lorentzian shape. We tested several models of the Fe II pseudo-continuum and showed that one of them well represents all the data. The amplitudes of both components vary in time, but the shapes do not change significantly. The measured line width of LBQS 2113-4538 identifies this object as a class A quasar. The upper limit of 3% for the contribution of the narrow line region (NLR) to Mg II may suggest that the separation of the broad line region and NLR disappears in this class of objects.
关键词： quasars: individual: LBQS 2113-4538,quasars: emission lines,dark energy
更新于2025-09-09 09:28:46
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Simultaneous Dual-mode Emission and Tunable Multicolor in the Time Domain from Lanthanide-doped Core-shell Microcrystals
摘要： The dual-mode emission and multicolor outputs in the time domain from core-shell microcrystals are presented. The core-shell microcrystals, with NaYF4:Yb/Er as the core and NaYF4:Ce/Tb/Eu as the shell, were successfully fabricated by employing the hydrothermal method, which con?nes the activator ions into a separate region and minimizes the effect of surface quenching. The material is capable of both upconversion and downshifting emission, and their multicolor outputs in response to 980 nm near-infrared (NIR) excitation laser and 252 nm, and 395 nm ultraviolet (UV) excitation light have been investigated. Furthermore, the tunable color emissions by controlling the Tb3+-Eu3+ ratio in shells and the energy transfer of Ce3+→Tb3+→Eu3+ were discussed in details. In addition, color tuning of core-shell-structured microrods from green to red region in the time domain could be obtained by setting suitable delay time. Due to downshifting multicolor outputs (time-resolved and pump-wavelength-induced downshifting) coupled with the upconversion mode, the core-shell microrods can be potentially applied to displays and high-level security.
关键词： multicolor emission,dual-mode emission,emission spectra,time-resolved,NaYF4:Yb/Er@NaYF4:Ce/Tb/Eu microrods
更新于2025-09-04 15:30:14
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Characterization of time-resolved emission of N<sub>2</sub>(C) in an atmospheric pressure nanosecond pulsed air-plasma using streak spectroscopy
摘要： A new optical emission spectroscopy (OES) system using a streak camera (streak-OES) is developed to obtain highly time-resolved OES measurements of nanosecond-duration pulsed air-plasmas at atmospheric pressure. The newly developed system is used to measure the time evolution of the emission of N2(C), a critical species in the two-step mechanism of rapid heating characteristic of nanosecond pulsed discharges. Time resolution of less than 400 ps is achieved in the current system, a significant improvement over conventional OES measurements with ICCD cameras or photomultiplier tubes (PMTs). In addition, as long as the driving voltage pulse lies within the streak camera sweep window, the entire plasma emission spectrum for a single discharge is acquired. This capability is in contrast to prior studies where the time-dependent emission is obtained by plotting measurements at single steps from separate discharges. The effect of pulse repetition frequency (PRF) on the N2(C) decay is investigated by recording emission spectra for single discharges at 5-100 kHz. The streak images clearly show that the decay time of the N2(C-B,0-0) transition increases as the PRF is increased. The emission decay exhibits two distinct phases with significantly different decay rates, consistent with prior measurements. The 1/e lifetimes of the two decay regimes are found using exponential fits to the emission decay curves. In addition, joint statistics relating the decay times and energy deposited in the plasma were also obtained.
关键词： streak camera,N2(C) emission,atmospheric pressure,nanosecond pulsed discharges,optical emission spectroscopy
更新于2025-09-04 15:30:14
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Investigation of explosive electron emission sites on surface of polished cathodes in vacuum
摘要： The field enhancement effect of the surface microstructures of electrodes with two different surface treatments is evaluated, on the basis of observations made by a 3-D laser microscope. The maximum field enhancement factor of the micro-protrusions on the surface after turning or mirror polishing is about 1-5.8. The vacuum gap breakdown strength of the mirror polished electrodes is 1-1.4 times higher than that of the turned electrodes, because the surface grooves are removed. Experiments to test the breakdown strength of 2.5 cm vacuum gaps with the electrodes after the treatments were carried out and the experimental results were found to correspond to the analysis. The results also revealed that it is not enough to induce explosive electron emission and vacuum breakdown just by the field enhancement at the micro-protrusions and grooves. Moreover, the emission sites of mirror polished cathode made of titanium alloy and stainless steel after vacuum breakdown were observed by a scanning electron microscope and an energy dispersive spectrometer. The results show that the proportion of carbon atoms in the damaged area of the stainless steel cathode surface is as high as 40-70%, and most of the pits located at the grain boundaries, which suggests that grain boundaries have important effects on the electron emission and vacuum breakdown.
关键词： explosive electron emission,grain boundary,field-induced electron emission,vacuum breakdown
更新于2025-09-04 15:30:14
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Note: Plasma optical emission spectroscopy for water vapor quantification and detection during vacuum drying process
摘要： A methodology involving plasma optical emission spectroscopy driven by a direct current (dc) plasma source is developed to quantify water vapor concentration in a gaseous stream. The experimental setup consists of a dc driven low-pressure plasma cell in which the emission from the plasma discharge is measured by using an optical emission spectrometer. The emission from Hα at 656.2 nm—the first transition in the Balmer series, was found to be the most sensitive to the water vapor concentration in the gas stream. Consistent linear trends of the emission signals with respect to variation in concentration of water are observed for multiple combinations of operating parameters. This method has been applied to a vacuum drying process of a mock nuclear fuel assembly to quantify the concentration of water vapor during the drying process.
关键词： Hα emission,direct current plasma source,plasma optical emission spectroscopy,vacuum drying process,water vapor quantification
更新于2025-09-04 15:30:14
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Modeling clustered activity increase in amyloid-beta positron emission tomographic images with statistical descriptors
摘要： Background: Amyloid-beta (Aβ) imaging with positron emission tomography (PET) holds promise for detecting the presence of Aβ plaques in the cortical gray matter. Many image analyses focus on regional average measurements of tracer activity distribution; however, considerable additional information is available in the images. Metrics that describe the statistical properties of images, such as the two-point correlation function (S2), have found wide applications in astronomy and materials science. S2 provides a detailed characterization of spatial patterns in images typically referred to as clustering or flocculence. The objective of this study was to translate the two-point correlation method into Aβ-PET of the human brain using 11C-Pittsburgh compound B (11C-PiB) to characterize longitudinal changes in the tracer distribution that may reflect changes in Aβ plaque accumulation. Methods: We modified the conventional S2 metric, which is primarily used for binary images and formulated a weighted two-point correlation function (wS2) to describe nonbinary, real-valued PET images with a single statistical function. Using serial 11C-PiB scans, we calculated wS2 functions from two-dimensional PET images of different cortical regions as well as three-dimensional data from the whole brain. The area under the wS2 functions was calculated and compared with the mean/median of the standardized uptake value ratio (SUVR). For three-dimensional data, we compared the area under the wS2 curves with the subjects’ cerebrospinal fluid measures. Results: Overall, the longitudinal changes in wS2 correlated with the increase in mean SUVR but showed lower variance. The whole brain results showed a higher inverse correlation between the cerebrospinal Aβ and wS2 than between the cerebrospinal Aβ and SUVR mean/median. We did not observe any confounding of wS2 by region size or injected dose. Conclusion: The wS2 detects subtle changes and provides additional information about the binding characteristics of radiotracers and Aβ accumulation that are difficult to verify with mean SUVR alone.
关键词： positron emission tomography,statistical descriptors,two-point correlation function,amyloid-beta plaques,11C-Pittsburgh compound B
更新于2025-09-04 15:30:14
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Novel blue light emitting poly(arylene ether)s under the influence of guest concentrations in host-guest systems: Synthesis, electrochemical and photophysical properties
摘要： A series of novel blue (poly-arylene ether)s polymers based on the anthracene derivatives as the guest material, and the hole transfer carbazole dervatives as the host material have been successfully synthesized by nucleophilic polycondensation. The obtained polymers exhibited high glass transition temperatures (Tg) ranging from 180 to 255 °C and decomposition temperatures (Td) ranging from 358 to 477 °C. Number average molecular weight (Mn) ranged from 3.12 × 104 to 7.20 × 104, and polydispersity indices (PDI) ranged from 1.25 to 2.10. Cyclic voltammetry investigation inform that these polymers possess LUMO energy levels ranging from ?2.29 to ?2.46 eV. In case of thin films state, all the polymers emit blue luminance with the emission maximum peaks ranging from 442 to 448 nm. The electroluminescent devices based on the these polymers with a configuration of ITO/PEDOT:PSS/polymer/TmPyPB/LiF/Al emitted blue light with CIE chromaticity coordinates of (0.15, 0.10).
关键词： Polymer Light Emitting Diodes,Ether Linkage,Blue Light Emission,Anthracene,Carbazole
更新于2025-09-04 15:30:14
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The OH<sup>*</sup>(3&ndash;1) layer emission altitude cannot be determined unambiguously from temperature comparison with lidars
摘要： I investigate the nightly mean emission height and width of the OH?(3–1) layer by comparing nightly mean temperatures measured by the ground–based spectrometer GRIPS9 and the Nalidar at ALOMAR. The dataset contains 42 coincident measurements between November 2010 and February 2014, when GRIPS9 was in operation at the ALOMAR observatory (69.3?N, 16.0?E) in northern Norway. To closely resemble the mean temperature measured by GRIPS9, I weighted each nightly mean temperature profile measured by the lidar using Gaussian distributions with 40 different centre altitudes and 40 different full widths at half maximum. In principle, one can thus determine the altitude and width of the OH?(3–1) layer by finding the minimum temperature difference between the two instruments. On most nights, several combinations of centre altitude and width yield a temperature difference of ±2 K. The generally assumed altitude of 87 km and width of 8 km is never an unambiguous, good solution for any of the measurements. Even for a fixed width of ～8.4 km, one can sometimes find several centre altitudes that yield equally good temperature agreement. Weighted temperatures measured by lidar are not suitable to determine unambiguously the emission height and width of an OH? layer. If the OH?(3–1) rotational temperature is used as a proxy for the temperature at an altitude of 87 km with a width of 8.4 km, this proxy is representative to within ±16 K.
关键词： emission altitude,OH?(3–1) layer,Nalidar,ALOMAR,lidar,GRIPS9,temperature comparison
更新于2025-09-04 15:30:14