Half-maximum Increase Research Articles

Creation and Characterization of Nanoscale Ribbons on MoS2 by Atomic Force Microscope Nanolithography

The atomic force microscope (AFM) has been widely used for fabricating the nanoscale oxide ribbons on various materials surface. Herein, we first conducted local anodic oxidation (LAO) lithography on two-dimensional nanomaterial (2D), i.e. multilayer MoS2, using AFM. The correlation of patterning behavior on the MoS2 flakes between the lithography conditions was investigated. The height and full width half maximum (FWHM) increase linearly with increasing tip voltage, even at different tip speeds, which is consistent with the results obtained from the Cabrera-Mott oxidation theory. The size of the clear relation decreases linearly with increasing tip speed, indicating that longer tip writing patterns result in more oxidation. The formation mechanism of the patterned oxide lines is presented along with LAO reaction processes.The final LAO lithography products have been demonstrated to be MoO2 and MoO3 by micro-Raman spectroscopy. These results show that LAO lithography using AFM is an effective technique for nanofabrication of nanodevices.

Powder synthesis and luminescence of a novel yellow-emitting Ba5Si11Al7N25: Eu2+ phosphor discovered by a single-particle-diagnosis approach for warm w-LEDs

White LEDs combined by blue LED chip and yellow YAG: Ce phosphor are the mainstream of the lighting industry. However, due to the lack of red light component, it is difficult to meet the requirements of warm white lighting. The novel needle-like Ba5Si11Al7N25:Eu2+ particle discovered by the single-particle-diagnosis method shows a broad yellow emission band centered at ∼570 nm and a FWHM of 98 nm. Compared with YAG: Ce phosphor, the novel Ba5Si11Al7N25:Eu2+ phosphor exhibits longer emission wavelength, indicating potential application in warm white LEDs. In this work, the phase-pure powder of Ba5Si11Al7N25:Eu2+ is obtained in a non-stoichiometric ratio by the double-crucible method, and it shows similar luminescent properties as the single particle. Upon excitation with violet light (400 nm), the maximum emission wavelength of the as-prepared Ba5(1-x)Si11Al7N25: 5xEu2+ phosphors shift from 558 nm to 591 nm with Eu2+ ions concentration increasing, and the full width at half-maximum (FWHM) increase from 87 nm to 100 nm. The broad emission band is attributed to three luminescent centers corresponding to three different Ba2+ ions sites Ba5Si11Al7N25:Eu2+ phosphor, which is demonstrated by time-resolved emission spectra and the decomposition of the emission spectrum at 4 K. The Ba5Si11Al7N25:Eu2+ phosphor shows a small thermal quenching with a quenching temperature as high as 700 K. The as-prepared phosphor can absorb both of UV and blue light effectively and exhibits similar quantum efficiency under the excitation of 400 nm (58.5 %) and 450 nm (54.5 %). The fabricated white LED lamp emitted a warm white light with CIE coordinates of (0.3838, 0.3252) and CCT = 3412 K, implying the potential applications in warm w-LEDs.

Temperature-Dependent Photoluminescence of CdS/ZnS Core/Shell Quantum Dots for Temperature Sensors.

Exploring the temperature-dependent photoluminescence (PL) properties of quantum dots (QDs) is not only important for understanding the carrier recombination processes in QD-based devices but also critical for expanding their special applications at different temperatures. However, there is still no clear understanding of the optical properties of CdS/ZnS core/shell QDs as a function of temperature. Herein, the temperature-dependent PL spectra of CdS/ZnS core/shell QDs were studied in the temperature range of 77-297 K. It was found that the band-edge emission (BEE) intensity decreases continuously with increasing temperature, while the surface-state emission (SSE) intensity first increases and then decreases. For BEE intensity, in the low temperature range, a small activation energy (29.5 meV) in the nonradiative recombination process led to the decrease of PL intensity of CdS/ZnS core/shell QDs; and at high temperature the PL intensity attenuation was caused by the thermal escape process. On the other hand, the temperature-dependent variation trend of the SSE intensity was determined by the competition of the trapping process of the surface trap states and the effect of thermally activated non-radiative defects. As the temperature increased, the PL spectra showed a certain degree of redshift in the peak energies of both band-edge and surface states and the PL spectrum full width at half-maximum (FWHM) increases, which was mainly due to the coupling of exciton and acoustic phonon. Furthermore, the CIE chromaticity coordinates turned from (0.190, 0.102) to (0.302, 0.194), which changed dramatically with temperature. The results indicated that the CdS/ZnS core/shell QDs are expected to be applied in temperature sensors.

Modal analysis of silicon-on-insulator based rib waveguide using fully vectorial finite-difference mode solver

In order to interface optical integrated devices with external sources, an understanding of the modal characteristics of the optical waveguide is essential. The finite difference approach is utilized in this work to analyse a rib waveguide based on a silicon-on-insulator platform. A silicon device layer with thickness of 220 nm and a buried oxide with thickness of 2000 nm are considered. It is important to study the modal field distribution and parameters of the waveguide. The simulation results on the behaviour of modal parameters show that both effective refractive index and group index decrease with wavelength. The effective refractive index of the guided mode increases with rib width and slab thickness. It is also observed that energy is more confined in a deeply etched waveguide than in a shallow etched waveguide. Additionally, it is noted that the effective mode area and full-width half maximum increase with rib width and slab thickness.

Design of novel cyan phosphor Ca7NaLu(PO4)6:Eu2+ for full-visible-spectrum white LED: enhanced thermal stability and tuned emission by neighbor cation effect

Cyan phosphor is desirable to fill the cyan gap (480–520 nm) in white light-emitting diodes (wLEDs) to achieve full-visible-spectrum lighting. In this paper, a novel highly efficient cyan emitting Ca7NaLu(PO4)6:Eu2+ (CNLP:Eu2+) phosphor was synthesized, exhibiting broadband and bright emission ranging from 425 to 675 nm and an excitation band ranging from 250 to 450 nm. Notably, CNLP:0.09Eu2+ shows an excellent internal quantum efficiency of 90% and a high external quantum efficiency of 57.6%. In addition, a neighbor cation effect induced by replacing Ca with Sr was used to design a series of Ca7-ySryNaLu(PO4)6:Eu2+ (C7-ySyNLP:Eu2+y = 1, 4, 7) phosphors with a good thermal stability and tunable emission. The spectra of the C7-ySyNLP:Eu2+ phosphors undergo a red shift and the full width at half maximum increase from 78 to 100 nm with an increase of Sr content. Furthermore, a near-ultraviolet pumped wLED that fills the cyan gap was fabricated by composing CNLP:0.09Eu2+ with commercial phosphors, showing high color rendering index (Ra = 95). The excellent luminescent properties of as-prepared phosphors indicate they are promising for the production of high-color rendering index full-visible-spectrum wLEDs.

Investigation on the red shift of the charge transfer band in Eu3+ doped REMO3 (RE = Lu/Y/La; M = B/Al) phosphors

A series of Eu3+-doped REMO3 (RE = Lu/Y/La; M = B/Al) phosphors have been synthesized via a high-temperature solid-state method. With the increase of the cation radius from Lu3+ ion to Y3+ ion to La3+ ion in Eu3+-doped REMO3 matrices, the Eu-O charge transfer (CT) energy decreases and the full width at half maximum (FWHM) increases. With the change of cation in the borate radical and aluminate radical from B3+ ion (0.27 Å) to Al3+ ion (0.535 Å), the red-shift of the Eu-O CT band occurs, and their FWHMs increase. Our work provides a reference for Eu3+-doped other complex oxides.

Wet ball milling of niobium by using ethanol, determination of the crystallite size and microstructures

This study investigates the effect of using ethanol as the process control agent during the wet ball milling of niobium (Nb). Dried nanocrystal Nb powders, of high purity, with particle sizes, ranging from 8.5 to 14.3 nm, were synthesized by ball milling. Commercial Nb powder of particle sizes of − 44 µm was employed by using the planetary ball mill equipped with stainless still vials with still balls in ethanol. A ball-to-powder mass ratio of 10:1 was used at a rotation speed of 400 rpm, an interval of 15 min with an interval break of 5 s, and a milling time of 10 h. The powder was dried in vacutec at a temperature of 100 °C, using a speed of 15 rpm in the vacuum of 250 mbar at a time of approximately 653 min. The crystal phase of the dried powders was analyzed using X-ray diffraction (XRD) with CuKɑ radiation, and by modification of the Scherrer equation, a single crystallite size of 11.85 nm was obtained. The morphology of the particles was observed using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). The XRD results show that the pure crystal sizes in nanometre (nm), which decreases as the 2θ and the full width at half maximum (FWHM) increases.

Temperature dependence of optical centers in 200 keV electron irradiated β-Ga2O3

In this work, the optical centers of β-Ga2O3 irradiated with 200 keV electrons were studied by photoluminescence (PL) spectroscopy. The oxygen vacancy-related center at 690 nm were enhanced after irradiation together with a new zero phonon line (ZPL) at 697 nm. The temperature dependence of these optical centers were carefully detailed and discussed. As the increase of measurement temperature, the ZPLs showed red-shift, intensity quenching and full width at half maximum (FWHM) increase. These data were fitted by the corresponding physical formula. Results showed compared with the 690 nm emission, the 697 nm emission had a similar intensity distribution, a weaker lattice relaxation strength, a weaker lattice vibration, and a lower thermal softness. These results indicated that the 697 nm emission was probably associated with the oxygen interstitials.

Microstructure, optical, and photoluminescence properties of β-Ga2O3 films prepared by pulsed laser deposition under different oxygen partial pressures* *Project supported by the Guizhou Provincial Science and Technology Planning Project, China (Grant No. 2018-5781), the National Natural Science Foundation of China (Grant No. 51762010), the Guizhou Provincial Science and Technology Foundation, China (Grant Nos. 2020-1Y021 and 2020-1Y271), and the Guizhou Provincial

The β-Ga2O3 films are prepared on polished Al2O3 (0001) substrates by pulsed laser deposition at different oxygen partial pressures. The influence of oxygen partial pressure on crystal structure, surface morphology, thickness, optical properties, and photoluminescence properties are studied by x-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), spectrophotometer, and spectrofluorometer. The results of x-ray diffraction and atomic force microscope indicate that with the decrease of oxygen pressure, the full width at half maximum (FWHM) and grain size increase. With the increase of oxygen pressure, the thickness of the films first increases and then decreases. The room-temperature UV-visible (UV-Vis) absorption spectra show that the bandgap of the β-Ga2O3 film increases from 4.76 eV to 4.91 eV as oxygen pressure decreasing. Room temperature photoluminescence spectra reveal that the emission band can be divided into four Gaussian bands centered at about 310 nm (∼ 4.0 eV), 360 nm (∼ 3.44 eV), 445 nm (∼ 2.79 eV), and 467 nm (∼ 2.66 eV), respectively. In addition, the total photoluminescence intensity decreases with oxygen pressure increasing, and it is found that the two UV bands are related to self-trapped holes (STHs) at O1 sites and between two O2-s sites, respectively, and the two blue bands originate from at Ga1 tetrahedral sites. The photoluminescence mechanism of the films is also discussed. These results will lay a foundation for investigating the Ga2O3 film-based electronic devices.

Temperature-dependent photoluminescence of H2TPP and ZnTPP thin films on Si substrates

Temperature-dependent photoluminescence (PL) properties of tetraphenyl porphyrin (H2TPP) and Zinc-tetraphenyl porphyrin (ZnTPP) thin films on the silicon substrates has been investigated. The photoluminescence (PL) properties are observed within the temperature range of 163–543 °K. The 405 nm diode laser beam is used to excite the molecule during the photoluminescence measurement. The integrated PL intensity exhibits abnormal behaviour, the intensity decreases with temperature in the temperature range of 163-273 °K, and then followed by the increase in the further temperature range of 273-543 °K. This anomaly reflects the competition between the radiative recombination process and the non-radiative recombination processes, i.e. carrier capture, thermalization, and carrier relaxation processes. The peak energy of 0-0 and 0-1 transitions show a red-shift with temperature, while their full width at half maximum increases.

Effects of Catechin on Activity of Angiotensin-Converting Enzyme and Generation of Reactive Oxygen Species in Rat Aorta.

Activity of angiotensin-converting enzyme (ACE) and intensity of ROS generation in the aorta were studied in male Wistar rats intraperitoneally injected with a mixture of (+) and (-) stereoisomers of catechin. ACE activity in aortal segments was evaluated by hydrolysis of hippuryl-histidine-leucine; ROS generation was measured by oxidation of dichlorodihydrofluorescein. The dynamics of ACE activity and intensity of ROS generation in the aorta after catechin administration and their dependence on the catechin dose were studied. The effects of dihydroquercetin and fucoidin on the studied parameters were analyzed. Catechin increased ACE activity; the maximum increase was achieved in 3 h after administration. Catechin dose producing a half-maximum increase in ACE activity was 0.04 μg/kg. The effects of catechin on ACE activity was attenuated by dihydroquercetin and completely abolished by fucoidin. Catechin did not enhance ROS production in the aorta, and in a dose of 0.1 μg/kg even inhibited this process. It is hypothesized that isomers of catechin produce opposite effects on ROS generation in the aorta.

Temperature dependence of nitrogen-vacancy optical center in diamond

Diamond, a wide band gap semiconductor material, has been attracting interest in several fields from electrics and optics to biomedicine and quantum computing due to its outstanding properties. These properties of diamond are related to its unique lattice and optically active defect centers. In this paper, the dependence of nitrogen-vacancy (NV) center on measurement temperature is studied by using the low-temperature photoluminescence (PL) spectroscopy in a temperature range of 80–200 K. The results show that with the increase of the measurement temperature, the zero phonon lines of NV defects are red-shifted, its intensity decreases and its full width at half maximum increases. These results are attributed to the synergetic process of the lattice expansion and quadratic electron-phonon coupling. The NV<sup>—</sup> and NV<sup>0</sup> centers have similar values in the quenching activation energy and the thermal softening coefficient, resulting from their similar structures. The small differences may be associated with the electron-phonon coupling. The broadening mechanism of the NV centers is carefully distinguished by <inline-formula><tex-math id="Z-20200615115616-1">\begin{document}$T^3,\; T^5,\; T^7$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20200395_Z-20200615115616-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20200395_Z-20200615115616-1.png"/></alternatives></inline-formula> Voigt function fitting with the relation. These results show that the full width at half maximum of the Gaussian component of NV<sup>—</sup> and NV<sup>0</sup> centers are randomly distributed near 0.1 meV and 2.1 meV, respectively, while the full width at half maximum of the Lorentz component of NV<sup>—</sup> and NV<sup>0</sup> centers increase with measurement temperature increasing. The full width at half maximum of Lorentz of NV<sup>—</sup> and NV<sup>0</sup> centers conform to the <inline-formula><tex-math id="Z-20200615115631-1">\begin{document}$ T^3 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20200395_Z-20200615115631-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20200395_Z-20200615115631-1.png"/></alternatives></inline-formula> relationship. It can be proved that under the action of the fluctuating field, the zero phonon lines of the NV defects exhibit an obvious homogeneous widening mechanism.

Spectral changes associated with transmission of OLED emission through human skin

A recent and emerging application of organic light emitting diodes (OLEDs) is in wearable technologies as they are flexible, stretchable and have uniform illumination over a large area. In such applications, transmission of OLED emission through skin is an important part and therefore, understanding spectral changes associated with transmission of OLED emission through human skin is crucial. Here, we report results on transmission of OLED emission through human skin samples for yellow and red emitting OLEDs. We found that the intensity of transmitted light varies depending on the site from where the skin samples are taken. Additionally, we show that the amount of transmitted light reduces by ~ 35–40% when edge emissions from the OLEDs are blocked by a mask exposing only the light emitting area of the OLED. Further, the emission/electroluminescence spectra of the OLEDs widen significantly upon passing through skin and the full width at half maximum increases by >20 nm and >15 nm for yellow and red OLEDs, respectively. For comparison, emission profile and intensities of transmitted light for yellow and red inorganic LEDs are also presented. Our results are highly relevant for the rapidly expanding area of non-invasive wearable technologies that use organic optoelectronic devices for sensing.

Magnetic field sensor based on a magnetic-fluid-infiltrated photonic crystal L4 nanocavity and broadband W1 waveguide

Based on numerical simulations, we propose a new type of magnetic sensor based on a two-dimensional (2D) photonic-crystal nanocavity infiltrated by a magnetic fluid and a broadband W1 waveguide. The defect length and the diameter of the holes surrounding the L4 nanocavity are optimized, yielding a structure with a quality factor of 8655.8. Magnetic fluids with different magnetic nanoparticle volume fraction concentrations and various refractive indices are infiltrated into special holes. Magnetic field sensing is realized based on the change in the refractive index of the magnetic fluid with the external magnetic field strength, resulting in a shift of the resonant wavelength. The magnetic field sensitivity and full-width at half-maximum increase with the number of infiltrated air holes. A refractive index sensitivity of 146.97 nm/refractive index unit (RIU) is obtained for the structure with 12 infiltrated air holes, with an optimum figure of merit indicating the good performance of this magnetic field sensor structure. These distinguished features and the excellent tunable refractive index property of the magnetic fluid make the designed device suitable for application in magnetic field sensing.

Fraunhofer Lines in the Center-to-Limb Transition over the Solar Disk

Two-dimensional spectra of the Sun (from the center to the limb of the disk) in wavelength ranges of λ = 532.0–532.8 and 539.1–539.9 nm were registered with the ATsU-5 telescope (the Russian abbreviation ATsU corresponds to the Astronomical Coelostat Mounting) of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine (MAO NASU) after replacing the regular main mirror by a short-focus one (with a focal length of 1 m). An advantage of the applied method is that the spectrum is registered simultaneously for different heliocentric positions on the solar disk. The observational data were reduced for the influence of light scattered in the spectrograph, the atmospheric-stray light, the spectrograph instrumental profile, and some aberrations. The center-to-limb ratios of the spectra are compared to the data available in the literature. The data on variations in the profiles of eleven spectral lines in transition from the center to the limb of the solar disk were obtained. The revealed nonmonotonicity of these changes is explained by inhomogeneities in physical conditions on the surface of the Sun. In general, the depths of the studied Fe I lines demonstrate the decreasing tendency in the strength of lines when passing toward the limb. For most lines, the full widths at half maximum increase toward the disk edge. The equivalent widths show differently directed variations. The parameters of the line Mn I λ 539.4 nm behave in a different way: all three analyzed parameters grow toward the disk edge; however, at the extreme limb, the depth and the equivalent width also start to decrease. The limb-effect of lines was measured; it exhibits the highest value when the core positions in weak lines are compared. For strong lines, the limb-effect is strongest while comparing the middle parts of the line bisectors.

The influence of Co content on the luminescence properties of Co-doped ZnO nanoparticles

Co-doped ZnO nanoparticles have been synthesized by co-precipitation technique. Photoluminescence spectra change in the range from 350 nm to 600 nm and remain unchanged at about 690 nm with the Co content increase. The UV emission is assigned to exciton emission. The density of band-edge states increases with Co content. The blue emission could be ascribed to the recombination of electrons in Co[Formula: see text] ions and holes in the valence band, whose relative intensity and full-width at half-maximum (FWHM) increase with the increase of cobalt concentration. The red emission results from the intra-d-shell emission at Co, which is independent of Co content. The relative density and energy-level position of green emission centers are also influenced by Co content.

The model of the influence of the electron refluxing on the electron transport andKαemission

AbstractIn our previous research (Zhaoet al., 2016), we focus on the transport processes from hot electrons toKαX-ray emission in a copper foil and nanobrush target when the electron refluxing effect is not taken into account. In this work, considering the refluxing effect, the transport of hot electrons in a solid target is studied by adding the electric fields both at the front and rear surfaces of the target with Monte Carlo code Geant4. Simulation results show that the electron refluxing has an important influence onKαphoton yield and the size ofKαradiation source.Kαyield from the 10-μm-thick target with the electron refluxing effect is 2.7–3.7 times more than that without the refluxing for the electron temperatures from 0.4 to 1.4 MeV. The laser-to-Kαphoton energy conversion efficiency${\rm \eta} _{L \to K_{\rm \alpha}} $with the refluxing effect is always higher than that without the refluxing, and both of them decrease gradually with laser strengthIλ2. Considering the electron refluxing effect or not, the variations ofKαyield with the target thicknessdare very different. A critical thickness of the targetdc(~30 μm) is achieved to confirm whether the refluxing effect is valid for the target. For the target with the thicknessdless thandc, the refluxing effect can enhanceKαyield with several times, while for the target with the thicknessdlarger thandc, the refluxing effect is not so effective. The full-width at half-maximum increases from 23 to 56 µm after including the refluxing effect by the electron beam with the radius of 10 µm and the temperature of 400 keV.

Optimization of post-deposition annealing in Cu2ZnSnS4 thin film solar cells and its impact on device performance

In this work we present an optimization of the post-deposition annealing, in Cu2ZnSnS4 (CZTS) thin film solar cells, applied at different stages of the solar cell preparation, namely, bare CZTS absorber, CZTS/CdS heterojunction and CZTS/CdS/i-ZnO/ITO complete solar cell. We performed current-density measurements, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman scattering, photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) studies to enlighten the mechanisms by which solar cells performance improvement comes about. As a result, we concluded that the optimum post-deposition annealing for CZTS is at 300°C for 15min and at atmospheric pressure. The highest efficiency gain was obtained when the absorber layer composition is close to the ideal one and when a single annealing step is performed on complete solar cells, where, we obtained efficiency improvements from below 1% to over 6.6%. Despite the observed improvement in device performance for annealing at intermediate stages it is, however, less pronounced than for full cell annealing. In this process we demonstrate very substantial cell performance improvements. XRD results show a shift of all Bragg peaks to lower diffraction angle values, after post-deposition annealing. Also, the intensity of the peaks decreases and their full width at half maximum increases. PL measurements show that, post-deposition annealing, leads to a clear reduction of the non-radiative recombination channels and that the electronic structure is dominated by fluctuating potentials. XPS measurements reveal an interdiffusion of Cu, Zn and possibly Cd across the interface between buffer and CZTS absorber layers as the source of the significant observed cell performance enhancement.

A Photonic Crystal Magnetic Field Sensor Using a Shoulder-Coupled Resonant Cavity Infiltrated with Magnetic Fluid.

A kind of photonic crystal magnetic field sensor is proposed and investigated numerically. The shoulder-coupled resonant cavity is introduced in the photonic crystal, which is infiltrated with magnetic fluid. Through monitoring the shift of resonant wavelength, the magnetic field sensing is realized. According to the designed infiltration schemes, both the magnetic field sensitivity and full width at half maximum increase with the number of infiltrated air holes. The figure of merit of the structure is defined to evaluate the sensing performance comprehensively. The best structure corresponding to the optimal infiltration scheme with eight air holes infiltrated with magnetic fluid is obtained.

Fabrication of Laser Detectors using Ge wafer Doped with Sb

Germanium antimony (Ge:Sb) thin films have been fabricated by thermal evaporation system deposition at atmospheric pressure between (5.8x10-6 to 7.5x10-6) mbar. The (Ge:Sb) thin films then exposure to Nd:YAG laser with 1064μm wavelength at different energy densities (100,200) mj/cm2. XRD analysis show that Germanium antimony thin films are polycrystalline and the full width at half maximum (FWHM) increase as laser energy densities increases. Photocurrent and quantum efficiency of the detector increases as the laser energy densities increases.