Variation Of Optical Properties Research Articles

Electrical, Optical & Structural characteristics of reduced graphene oxide: A comparative analysis using different reducing agents

The study of optical and electrical properties of functionalised materials of GO and rGO are crucial for their different applications in energy storage, optoelectronics and biosensing. The structural disorder occurring during the synthesis process largely affects the optical properties of the materials. In this work we have tried to study the variation in optical and electrical properties of rGO by varying the synthesis parameters. Different rGO samples prepared from the same precursor (graphite powder) by using various reducing agents are studied. It is observed that the physical conditions during the synthesis process affect the bandgap of the synthesised samples. This study is correlated with the elemental analysis, surface morphology and defect studies.

Impact of N-Doping on MoSe2 Monolayer for PH3, C2N2, and HN3 Gas Sensing: A DFT Study.

In this research, the different characteristics of MoSe2 and N-doped MoSe2 monolayers were studied using density functional theory calculations. The negative cohesive energy (-5.216 eV for MoSe2 and -5.333 eV for N-MoSe2) verified their energetical stability. The variation of structural, electronic, and optical properties of MoSe2 and N-MoSe2 via adsorption of PH3, C2N2, and HN3 gases are studied. The N-doping results in a stronger adsorbent-gas interaction, resulting in maximum adsorption energy of -0.036, -0.033, and -0.198 eV for the selected gases. The MoSe2 and N-MoSe2 monolayers showed a direct band gap of 1.48 eV and 1.09 eV, respectively. However, upon interaction with the gases, a notable shift in the band gap of both adsorbents is observed. N-MoSe2 showed semiconductor-to-conductor transition via C2N2 and HN3 adsorption. The sensitivity of MoSe2 for the selected gases has improved remarkably via N-doping. Also, HN3 gas can be easily detected by the N-MoSe2 monolayer due to the greater changes in work function (0.45 eV). The absorption coefficient of both adsorbents is over 105 cm-1 order in the UV region, which suffers a mild peak shifting due to gas adsorption. This study suggests that N-MoSe2 can be a potential candidate for selected gas sensing.

Investigations on Stubble-Burning Aerosols over a Rural Location Using Ground-Based, Model, and Spaceborne Data

Agriculture crop residue burning has become a major environmental problem facing the Indo-Gangetic plain, as well as contributing to global warming. This paper reports the results of a comprehensive study, examining the variations in aerosol optical, microphysical, and radiative properties that occur during biomass-burning events at Amity University Haryana (AUH), at a rural station in Gurugram (Latitude: 28.31° N, Longitude: 76.90° E, 285 m AMSL), employing ground-based observations of AERONET and Aethalometer, as well as satellite and model simulations during 7–16 November 2021. The smoke emissions during the burning events enhanced the aerosol optical depth (AOD) and increased the Angstrom exponent (AE), suggesting the dominance of fine-mode aerosols. A smoke event that affected the study region on 11 November 2021 is simulated using the regional NAAPS model to assess the role of smoke in regional aerosol loading that caused an atmospheric forcing of 230.4 W/m2. The higher values of BC (black carbon) and BB (biomass burning), and lower values of AAE (absorption Angstrom exponent) are also observed during the peak intensity of the smoke-event period. A notable layer of smoke has been observed, extending from the surface up to an altitude of approximately 3 km. In addition, the observations gathered from CALIPSO regarding the vertical profiles of aerosols show a qualitative agreement with the values obtained from AERONET observations. Further, the smoke plumes that arose due to transport of a wide-spread agricultural crop residue burning are observed nationwide, as shown by MODIS imagery, and HYSPLIT back trajectories. Thus, the present study highlights that the smoke aerosol emissions during crop residue burning occasions play a critical role in the local/regional aerosol microphysical and radiation properties, and hence in the climate variability.

Phase transition behavior and electrical properties of C/Sb2Te3 multilayer films on flexible polyimide substrates

Phase change memory has become one of the ideal choices for flexible electronic memory due to its advantages of fast operation speed, high durability and low power consumption. This paper is dedicated to the preparation of C/Sb2Te3 multilayer films on polyimide (PI) substrates for high-performance flexible phase change memory (FPCM). The findings indicate that C/Sb2Te3 multilayer films on PI substrates exhibit superior thermal stability (higher than that of Silicon substrates) and excellent mechanical bending properties (up to 1 × 104 bending cycles). The variations in optical properties, crystal structure, resistance drift and morphology were systematically investigated for the flat state, 5 × 103 bending cycles and 1×104 bending cycles. FPCM devices based on [C (2 nm)/Sb2Te3 (10 nm)]5 multilayer films have been fabricated, which are capable of reversible SET/RESET operation in the flat, bending state and 1 × 103 bending cycles. An electrothermal model of the FPCM device cell based on C/Sb2Te3 was constructed, and the simulation results confirmed its good thermal confinement capability (∼1278 K). This study demonstrates the potential of C/Sb2Te3 multilayer films based on PI substrates in FPCM.

Synthesis of Zinc Sulfide Luminescent Nanoparticles Using Zinc Metal Complexes of S-benzyl Dithiocarbonate via Microwave Irradiation Route

This paper reported highly luminous zinc sulfide (ZnS) nanoparticles grown by microwave-irradiated single molecular precursors. The precursor was obtained by Schiff bases of S-benzyl dithiocarbazate (SBDTC) ligand using 5-Bromo-4-hydroxy-3-methoxy-2-nitro Benzaldehyde; 4NNbiscyno diethylamino benzaldehyde and p-amino acetophenone. The nanoparticles obtained were characterized by X-ray diffraction studies for structural analysis, transmission electron micrographs (TEM) for morphological analysis, and UV-Vis spectra for optical analysis. X-ray diffractograms exhibit mixed structures analysis (wurtzite and cubic) for particles obtained using 5-Bromo-4-hydroxy-3-methoxy-2-nitro benzaldehyde and 4NNbiscyno diethylamino benzaldehyde. However, the particles obtained by p-amino acetophenone Schiff bases of SBDTC exhibit only wurtzite structure. Variation in optical properties is also observed with the precursors used. The excellent optical properties of ZnS nanoparticles signify the role of microwave irradiation in synthesis. The Photoluminescence (PL) study shows the luminescence in the visible region and the maximum intensity for ZnS particles obtained by zinc complex of p-amino acetophenone Schiff base of S-benzyl dithiocarbazate. The microwave-assisted process can be used for large-scale production of nanoparticles for emitting light in the visible region in various detecting and sensing applications.

Investigation on the overall performance of hydrogel-based thermochromic windows with various structures

Thermochromic (TC) windows have attracted extensive attention due to their potential for improving building performance through the variation of optical properties in response to temperature. However, past studies on TC windows at the building scale primarily focused on optimizing and evaluating the properties of TC materials, with little attention paid to the varying window structures frequently encountered in engineering applications. In this study, the building performance of hydrogel-based TC windows was investigated from the structural perspective. A comprehensive simulation framework was developed, integrating overall performance simulations of energy consumption and indoor comfort. Using a self-fabricated hydrogel TC glass and an office building as the case study, the impact of the optical properties of the substrate glass on single, double, vacuum, and ventilation TC windows was analyzed. The results indicated that the optimal extinction coefficients for the studied windows range from 55 to 105 m−1 for visible irradiation and from 155 to 255 m−1 for near-infrared irradiation. Subsequently, the overall performance improvements of these types of TC windows relative to corresponding static versions were calculated. It was found that the impacts of TC glass on these four windows varied significantly. The electricity usage was reduced by 33 ∼ 53 %, and the thermal comfort and visual comfort were enhanced by –22 ∼ 20 % and 72 ∼ 100 %, respectively. This study reveals in detail how the TC window structure affects various aspects of building performance, aiming to inspire and guide the consideration of window structure in the practical applications of TC glass.

Ternary Boron Carbon Nitride nanosheets with improved and controllable linear and nonlinear optical response for efficient photocatalytic performance

This work reports the systematic variation of linear and nonlinear optical (NLO) properties of ternary boron carbon nitride (BCN) nanosheets with varying carbon concentrations. These nanosheets are synthesized by the thermal substitutional method to modulate the band-gap of BCN nanosheets by varying the hBN and graphene domain ratios which is confirmed through UV–Vis absorption spectroscopy. The third-order optical nonlinearity of nanosheets was explored through the Z-scan technique. With increases in both carbon content and laser power, samples' NLO properties have shifted from saturable absorption to reverse saturable absorption. The enhanced nonlinearity with carbon concentration in BCN samples was responsible for higher photoinduced charge separation time. In UV–Vis driven photoreduction of organic pollutants, BCN nanosheets with a decreased bandgap and an increased charge separation time show higher catalytic efficiency. Therefore, based on the combined effect of many processes, the results revealed that the BCN nanosheets displayed greater potential for photoinduced reduction.

In-situ monitoring of tungsten oxides reduction during deuterium plasma exposure by spectroscopic ellipsometry

In this work, we investigate the optical properties variation of thermally grown W oxides during the exposure to low energy deuterium (D) plasma. In-situ ellipsometry in the 400–1000 nm range was coupled to ex-situ diagnostics, such as X-ray photoelectron spectroscopy (XPS) and focused ion beam coupled to scanning electron microscopy (FIB-SEM), to probe the evolution of chemical and morphological properties of the W oxides. First, a 70 nm thick WO3 layer was exposed to D plasma at a surface temperature of 650 K. An important reduction of the oxide layer was observed by FIB-SEM, and in-situ ellipsometry showed the evolution of the optical constants n and k of the oxide towards the ones of pure W metal. Secondly, a 300 nm thick WO3 layer was exposed to D plasma at a surface temperature below 373 K. In order to follow the oxide evolution step by step, we alternated in-situ ellipsometry and XPS surface characterization. A quite similar evolution of the optical constants was observed, in particular an increase of the extinction coefficient k in the near infrared, which was linked to a progressive reduction of the oxidation level at the surface, as seen by XPS. Interestingly, the reduction of the oxide at 373 K was below the resolution of the FIB-SEM. This observation indicates that ellipsometry in the 400–1000 nm range is able to follow in-situ the reduction of WO3 oxides by D plasma with high surface sensitivity.

Design of photonic crystals for nanokelvin-resolution thermometry

High-resolution thermometry is key for the development of calorimeters, bolometers, and high-stability light sources, as well as for probing dissipation and transport in microelectronics and quantum devices. Achieving nanokelvin-level temperature resolution at room temperature requires using large optical cavities, which are unsuitable for microscale integration. Here we computationally design a one-dimensional photonic crystal Band Edge Thermometer that achieves significant temperature sensitivity by combining: (i) the abrupt variation in optical properties of a direct bandgap semiconductor at the band edge, and (ii) a large quality factor in a resonant photonic structure. Two devices are designed which are constructed from GaAs/AlAs and GaN/AlN multilayer structures. The optimal sensor design features an extremely large thermoreflectance coefficient of 60.6 K−1 and a thermal time constant of 1.1 µs, with a sensor thickness of only 6.7 µm. The projected thermometry noise floor is 84 nK.Hz-½ for the GaAs/AlAs sensor and 35 nK.Hz-½ for the GaN/AlN sensor. The designed sensor architecture is expected to enable a broad range of applications in microcalorimetry and bolometry where a high temperature resolution combined with microscale sensor footprint is required.

Near-infrared luminescence shift in Ni2+-doped double perovskite phosphors

For applications such as near-infrared (NIR) spectroscopy requiring energy-efficient and compact broadband NIR light sources, a variety of Ni2+-doped phosphors emitting in the 1100–2000 nm range has been developed. However, the commercialization of Ni2+-doped NIR phosphors has not yet been achieved, and material exploration is ongoing. To gain insight into the luminescence properties of Ni2+, including emission wavelength and efficiency influenced by compositional and structural variations, Ni2+-doped double-perovskite AELaMgTaO6:Ni2+ (AE = Ba, Sr, or Ca) ceramic samples were synthesized, and their optical properties were examined. Because the energy of the Ni2+ 3d-3d transition is sensitive to structural variations in the local environment around the Ni2+ ions, we investigated the variation in optical properties by indirect ligand field engineering of NiO6 octahedra following the substitution of alkaline earth ions AE2+. The prepared AELaMgTaO6:Ni2+ samples were Ba-Sr or Ba-Ca complete solid solution systems with cubic-to-monoclinic phase transitions. The broad NIR luminescence band at ∼1350–1700 nm was blue-shifted by ∼100 nm, accompanied by Sr2+ or Ca2+ substitution. The local symmetry of the NiO6 octahedra was reduced from Oh to Ci owing to the phase transition, resulting in an enhancement of the NIR luminescence intensity and an increase in the quenching temperature. This study demonstrated that Ni2+ phosphors with the desired optical properties for NIR spectroscopy applications can be designed by controlling the composition ratio of the host compounds and the resultant variation in the local environment of the solid solution compounds.

Photo- thermo-induce changes in As2S3- and As2S3: Au-nanoparticles filled porous glass composite: Optics and the molecular structure simulation of the responsible chalcogenide transformations

In this study we continue a more detailed investigation of the photoinduced effect in nanoporous glass impregnated with As2S3 NPs and Au NPs and its influence on the material's optical properties. The goal of this research is establishing the quantum chemical peculiarities of these processes taking into account the impact of gold nanoparticles on the photoinduced structural transformations of As-S component using Raman spectroscopy and theoretically investigating the molecular structure of arsenic sulfide As-S through ab initio quantum chemical calculations. These support the possibility of further variations in optical properties of such composite materials and photo-thermo driven elements made on their basis.

Laser-induced ultrasound in multiple thin layers-An analytical solution.

Laser-induced ultrasound is based on the thermo-elastic conversion of absorbed short light pulses to pressure pulses. In the work presented here, laser-induced ultrasound in a planar structure of interconnected layers with variations in optical, thermal, and mechanical properties is studied. Layered structures can be used for generating wideband ultrasonic pulses specific to a chosen application. An analytical time-domain solution is derived for the resulting pressure transmitted from the layered structure. The solution is derived for an arbitrary number of layers with an arbitrary optical absorption profile. Free space Green's functions with image sources are used to derive the solution. A solution employing the Beer-Lambert law is also proposed. The simplification with reflections only at the boundaries is in agreement with previous published results. The spectral properties of the generated pulse are derived, where the effects of optical absorption coefficients and layer thicknesses are shown. The analytical solution is compared to one-dimensional (1D) simulations and a three-dimensional (3D) simulation, realised as a two-dimensional (2D) axially symmetric case, using the matlab toolbox k-Wave. The 3D simulation on-axis pressure agrees well with the 1D analytical solution when the diameter of the laser beam is larger by approximately 1 order of magnitude than the thickness of the planar layered structure.

Cathodoluminescence emission and electron energy loss absorption from a 2D transition metal dichalcogenide in van der Waals heterostructures

Nanoscale variations of optical properties in transition metal dichalcogenide (TMD) monolayers can be explored with cathodoluminescence (CL) and electron energy loss spectroscopy (EELS) using electron microscopes. To increase the CL emission intensity from TMD monolayers, the MoSe2 flakes are encapsulated in hexagonal boron nitride (hBN), creating van der Waals (VdW) heterostructures. Until now, the studies have been exclusively focused on scanning transmission electron microscopy (STEM-CL) or scanning electron microscopy (SEM-CL), separately. Here, we present results, using both techniques on the same sample, thereby exploring a large acceleration voltage range. We correlate the CL measurements with STEM-EELS measurements acquired with different energy dispersions, to access both the low-loss region at ultra-high spectral resolution, and the core-loss region. This provides information about the weight of the various absorption phenomena including the direct TMD absorption, the hBN interband transitions, the hBN bulk plasmon, and the core losses of the atoms present in the heterostructure. The S(T)EM-CL measurements from the TMD monolayer only show emission from the A exciton. Combining the STEM-EELS and S(T)EM-CL measurements, we can reconstruct different decay pathways leading to the A exciton CL emission. The comparison with SEM-CL shows that this is also a good technique for TMD heterostructure characterization, where the reduced demands on sample preparation are appealing. To demonstrate the capabilities of SEM-CL imaging, we also measured on a SiO2/Si substrate, quintessential in the sample preparation of two-dimensional materials, which is electron-opaque and can only be measured in SEM-CL. The CL-emitting defects of SiO2 make this substrate challenging to use, but we demonstrate that this background can be suppressed by using lower electron energy.

Artificial neural networks trained on simulated multispectral data for real-time imaging of skin microcirculatory blood oxygen saturation.

Imaging blood oxygen saturation ( ) in the skin can be of clinical value when studying ischemic tissue. Emerging multispectral snapshot cameras enable real-time imaging but are limited by slow analysis when using inverse Monte Carlo (MC), the gold standard for analyzing multispectral data. Using artificial neural networks (ANNs) facilitates a significantly faster analysis but requires a large amount of high-quality training data from a wide range of tissue types for a precise estimation of . We aim to develop a framework for training ANNs that estimates in real time from multispectral data with a precision comparable to inverse MC. ANNs are trained using synthetic data from a model that includes MC simulations of light propagation in tissue and hardware characteristics. The model includes physiologically relevant variations in optical properties, unique sensor characteristics, variations in illumination spectrum, and detector noise. This approach enables a rapid way of generating high-quality training data that covers different tissue types and skin pigmentation. The ANN implementation analyzes an image in 0.11s, which is at least 10,000 times faster than inverse MC. The hardware modeling is significantly improved by an in-house calibration of the sensor spectral response. An in-vivo example shows that inverse MC and ANN give almost identical values with a mean absolute deviation of 1.3%-units. ANN can replace inverse MC and enable real-time imaging of microcirculatory in the skin if detailed and precise modeling of both tissue and hardware is used when generating training data.

Evaluation of Nocturnal Aerosol Optical Depth Determining From a Lunar Photometry in Lanzhou of Northwest China

AbstractA Cimel Sun‐sky‐lunar photometer (CE318‐T) is designed to perform daytime and nighttime photometric measurements and calculate diurnal cycle of aerosol optical depth (AOD). Nevertheless, the determination of nocturnal AOD from CE318‐T requires a precise knowledge of extraterrestrial lunar irradiance, which significantly changes with moon's phase angle (MPA) and lunar libration in a single night. This study evaluated the 1‐year nocturnal AODs at Lanzhou by using three different methods, which were validated by collocated measurements of DIAL Lidar (as a reference) and Cimel software (as a proxy). The results indicated that three independent approaches could implement a similar performance to compute nocturnal AOD near full moon phase (i.e., MPA = 0°) under moderate aerosol loading. The spectral AOD values at nighttime calculated by ROLO Lunar Langley (Robotic Lunar Observatory model) and Sun‐moon Gain Factor (SMGF) methods are significantly underestimated under low moon's illumination or high MPA (MPA < −47° or MPA > 47°) and distinctly dependent on MPA. The RIMO correction factor (RCF) (ROLO Implementation for Moon photometry Observation correction factor) method could compensate the underestimated extraterrestrial lunar irradiances of ROLO model for about 6.76%–9.78%, and thus greatly improve the calculation accuracy of nighttime AOD. The day/night coherence transition test has demonstrated that we would obtain a good diurnal variation of AODs at Lanzhou after RCF correction. The overall averages of nocturnal AOD440nm differences between Cimel software and ROLO model and SMGF method are 0.064 ± 0.024 and 0.052 ± 0.022, respectively, while the corresponding difference of RCF is less than 0.021 ± 0.014 for all wavelengths, falling within uncertainty range of AERONET AOD products (∼±0.02). The diurnal variations of AODs determined from RCF method agree well with synchronous results of DIAL Lidar, with total mean AOD532nm differences of 0.038 ± 0.024 and 0.023 ± 0.017 in daytime and nighttime, respectively. The spectral AODs computed from RCF method are well consistent with Cimel software, although there are some discrepancies under low AOD cases (AOD440nm < 0.30), and the overall average of AOD440nm differences are less than −0.0053 ± 0.002 and −0.0185 ± 0.013 in daytime and nighttime, respectively. Our results confirmed that the CE318‐T photometer can be reasonably calculated nighttime AOD and Ångström exponent (AE440–870nm) at urban Lanzhou by using three independent methods, although the former two need to be greatly improved under low moon's illumination. The RCF method was proved to reliably calculate nocturnal AOD from moonlight irradiance, which didn't rely on MPA. A more accurate lunar irradiance model needs to be developed to improve the underestimation of current ROLO model. Long‐term climatological information of nocturnal AOD is crucial for comprehensively characterizing the diurnal variations of aerosol optical properties and atmospheric boundary layer structure during the winter at typical northern city of China, which deserves to be further investigated in the future.

Contribution of individual phonon to the band gap renormalization in semiconductors

Understanding the origin of temperature-dependent bandgap in semiconductors is essential for their applications in photovoltaics, optoelectronic and space applications. In this regard the electron–phonon coupling is known to play a crucial role in the temperature dependence of the bandgap of semiconductors. Several models have also been proposed in this regard which are also found experimentally compatible; however, these models need to account for more information about the contribution of individual modes in band gap renormalization. The present report is an analytical attempt to do so by utilizing the Bose–Einstein oscillator model, thereby discussing a method for finding the individual renormalization term contributed by respective phonon modes to the overall bandgap. This study contributes to the fundamental understanding of the temperature variation of optical properties of semiconductors that correlates with the role of electron–phonon interaction.

P‐109: Investigation of Low Residual Stress Anti Reflection Coating with High Hardness for Display Applications

Anti reflection coating with high hardness on the OLED display surface was studied to improve the wear resistance and visibility of OLED. However, the high residual stress inside the multilayer thin film configuration of anti reflection coating has been a problem and the improvement is necessary. In this study, the residual stress and optical properties variation on various deposition conditions on the thin film were investigated. In addition, we suggested new coating structure using nanocomposites to overcome the residual stress of films.

Probing the variations of synthesis, antimicrobial activity, and optical properties of new lanthanide and transition metal complexes of salicylaldehyde‐dipropylenetriamine ligand

Probing the variations of synthesis, antimicrobial activity, and optical properties of new lanthanide and transition metal complexes of salicylaldehyde‐dipropylenetriamine ligand

Developing a Portable Autofluorescence Detection System and Its Application in Biological Samples.

Advanced glycation end-products (AGEs) are complex compounds closely associated with several chronic diseases, especially diabetes mellitus (DM). Current methods for detecting AGEs are not suitable for screening large populations, or for long-term monitoring. This paper introduces a portable autofluorescence detection system that measures the concentration of AGEs in the skin based on the fluorescence characteristics of AGEs in biological tissues. The system employs a 395 nm laser LED to excite the fluorescence of AGEs, and uses a photodetector to capture the fluorescence intensity. A model correlating fluorescence intensity with AGEs concentration facilitates the detection of AGEs levels. To account for the variation in optical properties of different individuals' skin, the system includes a 520 nm light source for calibration. The system features a compact design, measuring only 60 mm × 50 mm × 20 mm, and is equipped with a miniature STM32 module for control and a battery for extended operation, making it easy for subjects to wear. To validate the system's effectiveness, it was tested on 14 volunteers to examine the correlation between AGEs and glycated hemoglobin, revealing a correlation coefficient of 0.49. Additionally, long-term monitoring of AGEs' fluorescence and blood sugar levels showed a correlation trend exceeding 0.95, indicating that AGEs reflect changes in blood sugar levels to some extent. Further, by constructing a multivariate predictive model, the study also found that AGEs levels are correlated with age, BMI, gender, and a physical activity index, providing new insights for predicting AGEs content and blood sugar levels. This research supports the early diagnosis and treatment of chronic diseases such as diabetes, and offers a potentially useful tool for future clinical applications.

Moiré superlattices arising from growth induced by screw dislocations in layered materials

Abstract Moiré superlattices (MSLs) are modulated structures produced from homogeneous or heterogeneous two-dimensional layers stacked with a twist angle and/or lattice mismatch. Enriching the methods for fabricating MSL and realizing the unique emergent properties are key challenges on its investigation. Here we recommend that the spiral dislocation driven growth is another optional method for the preparation of high quality MSL samples. The spiral structure stabilizes the constant out-of-plane lattice distance, causing the variations in electronic and optical properties. Taking SnS2 MSL as an example, we find prominent properties including large band gap reduction (~0.4 eV) and enhanced optical activity. First-principles calculations reveal that these unusual properties can be ascribed to the locally enhanced interlayer interaction associated with the Moiré potential modulation. We believe that the spiral dislocation driven growth would be a powerful method to expand the MSL family and broaden their scope of application.