Optical Point Of View Research Articles

Unveiling the acetone sensing mechanism by [formula omitted] chemiresistors through a joint theory-experiment approach

The acetone sensing mechanism by WO3 was investigated through a combined experimental and theoretical approach. The γ−monoclinic WO3 powder was synthesized by a template-mediated sol-gel method and characterized on structural, surface, morphological and optical points of view. A thin film of WO3 was deposited on interdigitated Au electrodes by hot-spray method and tested at 300 ∘C (while applying a bias of 1.0 V) for acetone gas sensing, both in presence and absence of oxygen in the gas carrier. Interestingly, the absence of oxygen had no significant effect on the sensor response intensity but it dramatically increased the recovery times (from 120 s to 2700 s). In order to explain these experimental results, by means of ab initio density functional theory calculations, we modeled a defective γ−WO3 surface structure and simulated the adsorption of acetone and oxygen molecules on top of it. We unprecedentedly evidenced that, in presence of surface oxygen vacancies, both acetone adsorption and its oxidation reaction can occur. However, their contribution to the sensor response strictly depends on the inert/oxidative atmosphere present in the sensing chamber, which in turn strongly affects the surface oxygen population. Our findings can either be the guidelines for future studies aimed at delineating the possible reaction products or pave the way for the engineering of tailored nanomaterials having specific surface features and enhanced sensing properties.

Limiting mechanisms for photon recycling in thin‐film GaAs solar cells

AbstractPhoton recycling mechanisms in single junction thin‐film GaAs solar cells are evaluated in this study. Modelling supported by experimentally obtained results is used in order to correlate the reflectance of the cell's rear layers, the photon recycling probability, and the solar cell performance. Solar cells with different top and bottom metallization configurations are produced, and their performance is analyzed from the optical and electrical point of view. It is shown that the photon recycling probability increases with the rear mirror reflectance and solar cell thickness, which results in the increase of the devices open circuit voltage. However, the front grid coverage, usually disregarded in rear mirror focused studies, strongly reduces the photon recycling probability. Furthermore, perimeter and interface recombination hinder the internal radiative efficiency of the solar cells, preventing further increase of the devices' open circuit voltage as a result of improvements of the rear mirror reflectivity. In order to exploit the significant benefit of increased photon recycling probability to the solar cell performance, these limiting mechanisms need to be properly addressed.

Functionalization of eggshell membranes with CuO\u2013ZnO based p\u2013n junctions for visible light induced antibacterial activity against Escherichia coli

Biopolymers provide versatile platforms for designing naturally-derived wound care dressings through eco-friendly pathways. Eggshell membrane (ESM), a widely available, biocompatible biopolymer based structure features a unique 3D porous interwoven fibrous protein network. The ESM was functionalized with inorganic compounds (Ag, ZnO, CuO used either separately or combined) using a straightforward deposition technique namely radio frequency magnetron sputtering. The functionalized ESMs were characterized from morphological, structural, compositional, surface chemistry, optical, cytotoxicity and antibacterial point of view. It was emphasized that functionalization with a combination of metal oxides and exposure to visible light results in a highly efficient antibacterial activity against Escherichia coli when compared to the activity of individual metal oxide components. It is assumed that this is possible due to the fact that an axial p–n junction is created by joining the two metal oxides. This structure separates into components the charge carrier pairs promoted by visible light irradiation that further can influence the generation of reactive oxygen species which ultimately are responsible for the bactericide effect. This study proves that, by employing inexpensive and environmentally friendly materials (ESM and metal oxides) and fabrication techniques (radio frequency magnetron sputtering), affordable antibacterial materials can be developed for potential applications in chronic wound healing device area.

The Titano-Porphyrin doped pillared graphene as a novel “turn-off” fluorescent sensor for CO gas: Theoretical study

Abstract The aim of this study is to investigate and improvement of the CO gas sensing capacity of pure and Titano-Porphyrin doped pillared graphene (Ti-PIPG) using DFT calculations at B3LYP/6-31G (d) level of theory. To this end, a pillared graphene (PG) containing two parallel graphene sheets with four vertical (6,0) single walled carbon nanotubes as holders was selected. First, the effects of stretching and screwing distortions were studied on the stability, band gap and CO sensing capability of undopped PG. The results showed that the normal and distorted forms of PG could only be as a CO storage capacitor. Next, the graphene sheet of pillared graphene structure was doped using Titano-Porphyrin moiety to enhance the CO gas sensing capacity. The geometrical structures, binding energies, electronic and optical properties, ΔN, FOT, DOS, distribution of the HOMO-LUMO, NBO basis analysis and TDDFT absorption spectra were scrutinized to predict the adsorption properties and mechanism of Ti-PIPG-CO system. Based on the calculated E a d s B S S E and Eg, it is expected that the Ti-PIPG could be a promising candidate in gas sensor design for detection of CO. In optical point of view, the CO adsorption on Ti-PIPG quenched the fluorescence as due to a PET mechanism. Generally, this sensor is used to sense CO through changes in its both electrical and optical properties. The results showed that, doping could enhance the sensing capacity of pillared graphene in comparison to pure structure.

Snell’s law for the Schwarzschild black hole

The Wheeler equation, for electromagnetic disturbances in a gravitational field, was found by Fiziev to have exact solutions both above and below the event horizon, in the form of waves propagating both inwardly and outwardly. This observation can be interpreted and verified from the optical point of view, entirely on the basis of the Schwarzschild metric for length contraction and time dilation, in order to derive a differential version of Snell's law for the Schwarzschild black hole. It reveals interesting physics, including the correct amount of light deflection by the Sun, internal and external Oppenheimer-Snyder cones of the black hole, properties of its phonon sphere and the conclusion that light-rays are kept below the horizon by length contraction and time dilation rather than deflection.

Influence of applied external fields on the nonlinear optical properties of a semi-infinite asymmetric AlxGa1−xAs/GaAs quantum well

The asymmetric potential profiles are of great interest from the nonlinear optical properties point of view for semiconductor devices. The reason for this statement is because the existing theories on nonlinear optical properties obviously depends on the dipole matrix element for the involved transitions and an complete characterization for asymmetric potential profiles enables to the semiconductor device designers to have possible ranges of implementation and because the dipole matrix elements strongly depends on the asymmetry of the potential profile. Once the potential profile is well defined, with the desired range on operation, the external factors play also an important role on the optical properties tuning. In particular, in this paper we reported the absorption coefficient and the relative refractive index changes for semi-infinite inverse Gaussian-like profile for an AlxGa1−xAs/GaAs quantum well when is subjected to a z-directed electric field, to an in-plane x-directed magnetic field and finally to a non-resonant intense laser field effect, being the Al concentration the parameter that allows to shape the potential profile. In general, we conclude that the external factor are an efficient way to tune the optical properties that are in the range of the THz spectrum, at least for the intersubband transitions reported here.

Thunderbayite, TlAg3Au3Sb7S6, a new gold-bearing mineral from the Hemlo gold deposit, Marathon, Ontario, Canada

AbstractThunderbayite (IMA2020–042), ideally TlAg3Au3Sb7S6, is a new mineral from the Hemlo gold deposit, Marathon, Ontario, Canada. It occurs as very rare anhedral rims up to 70 μm across in contact with aurostibite and associated spatially with stibarsen, biagioniite and native gold in a calcite matrix. Thunderbayite is opaque with a metallic lustre and shows a black streak. In reflected light, thunderbayite is weakly bireflectant and faintly pleochroic from grey–blue to slightly greenish grey–blue. Under crossed polars, it is weakly anisotropic with bluish to light-blue rotation tints. Internal reflections are absent. Reflectance percentages for the four Commission on Ore Mineralogy wavelengths (Rmin, Rmax) are: 37.9, 38.4 (471.1 nm); 35.3, 36.0 (548.3 nm); 33.9, 34.4 (586.6 nm); and 32.0, 32.5 (652.3 nm), respectively. A mean of five electron-microprobe analyses gave Ag 14.91(16), Au 27.40(22), Tl 9.37(9), Sb 39.80(34) and S 8.61(7), for a total of 100.09 wt.%, corresponding, on the basis of a total of 20 atoms, to Tl1.00Ag3.01Au3.03Sb7.12S5.84. Thunderbayite is triclinic, space group P1, with a = 8.0882(5), b = 7.8492(5), c = 20.078(1) Å, α = 92.518(5), β = 93.739(5), γ = 90.028(6)°, V = 1270.73(9) Å3 and Z = 2. The five strongest powder-diffraction lines [d in Å (I/I0) (hkl)] are: 4.04 (100) (200); 3.92 (80) (020); 2.815 (50) (220/$\bar{2}$20); 2.566 (45) ($\bar{1}$17); and 2.727 (40) (0$\bar{1}$7). The crystal structure [R1 = 0.0220 for 5521 reflections with I > 2σ(I)] can be considered as a strongly deformed pyrite-type structure with several metal–metal bonds. Thunderbayite shows close similarities with criddleite, TlAg2Au3Sb10S10, from an optical, chemical and structural point of view. The new mineral is named for the Thunder Bay district, Ontario, in which the Hemlo gold deposit is located.

4D Microscopy: Unraveling Caenorhabditis elegans Embryonic Development Using Nomarski Microscopy.

4D microscopy is an invaluable tool for unraveling the embryonic developmental process in different animals. Over the last decades, Caenorhabditis elegans has emerged as one of the best models for studying development. From an optical point of view, its size and transparent body make this nematode an ideal specimen for DIC (Differential Interference Contrast or Nomarski) microscopy. This article illustrates a protocol for growing C. elegans nematodes, preparing and mounting their embryos, performing 4D microscopy and cell lineage tracing. The method is based on multifocal time-lapse records of Nomarski images and analysis with specific software. This technique reveals embryonic developmental dynamics at the cellular level. Any embryonic defect in mutants, such as problems in spindle orientation, cell migration, apoptosis or cell fate specification, can be efficiently detected and scored. Virtually every single cell of the embryo can be followed up to the moment the embryo begins to move. Tracing the complete cell lineage of a C. elegans embryo by 4D DIC microscopy is laborious, but the use of specific software greatly facilitates this task. In addition, this technique is easy to implement in the lab. 4D microscopy is a versatile tool and opens the possibility of performing an unparalleled analysis of embryonic development.

Optical Characterization of Homogeneous and Heterogeneous Intralipid-Based Samples

Different scattering processes take place when photons propagate inside turbid media. Many powerful experimental techniques exploiting these processes have been developed and applied over the years in a large variety of situations from fundamental and applied research to industrial applications. In the present paper, we intend to take advantage of Static Light Scattering (SLS), Dynamic Light Scattering (DLS), and Time-Resolved Transmittance (TRT) for investigating all the different scattering regimes by using scattering suspensions in a very large range of scatterer concentrations. The suspensions were prepared using Intralipid 20%, a material largely employed in studies of the optical properties of turbid media, with concentrations from 10−5% to 50%. By the analysis of the angular and temporal dependence of the scattered light, a more reliable description of the scattering process occurring in these samples can be obtained. TRT measurements allowed us to obtain information on the reduced scattering coefficient, an important parameter largely used in the description of the optical properties of turbid media. TRT was also employed for the detection of inclusions embedded in Intralipid suspensions, by using a properly designed data analysis. The present study allowed us to better elucidate the dependence of scattering properties of Intralipid suspensions in a very large concentration range and the occurrence of the different scattering processes involved in the propagation of light in turbid media for the first time to our knowledge. In so doing, the complementary contribution of SLS, DLS, and TRT in the characterization of turbid media from an optical and structural point of view is strongly evidenced.

Vliyaniye sluchayev tsveteniya kokkolitoforid na bioopticheskiye kharakteristiki vod Chernogo morya po dannym nablyudeniy v 2012 i 2017 godakh

This paper presents and discusses the results of optical and biological measurements performed during the coccolithophore blooms. This study uses data of measurements from a stationary oceanographic platform (near the Southern coast of Crimea, 44°23' N, 33°59' E) in July 2012 (7–16 July) and in May 2017 (24–31 May), and data obtained during the R/V “Professor Vodyanitsky” expedition to the northern part of the Black Sea in June 2017 (14–30 June). Observation periods coincided with intensive blooms of coccolithophore. The measurements of the Secchi disk depth, light beam attenuation coefficient and reflectance coefficient, as well as biological determinations of the coccolithophore cells number in water samples, are considered and analyzed. In addition to field data, satellite information on the sea reflectance and backscattering are used. The beam attenuation coefficient, reflectance coefficient, backscattering coefficient and coccolithophore concentrations were increased as compared with no bloom period. The Secchi disk depth was abnormally low. The number of coccolithophore cells, according to biological data, varied from 150 thousand cells/L to 1.7 million cells/L and averaged 0.6 ± 0.4 million cells/L. According to these data, the estimated concentration of shed coccoliths was (1.46 ± 0.42) 1011 m-3 . The average coccolith concentrations calculated from satellite data were (1.29 ± 0.23) 1011 m-3 in July 2012, (1.32 ± 0.12) 1011 m-3 in May 2017, and (2.37 ± 0.69) 1011 m-3 in June 2017. During blooms, high variability was observed not only in optical properties, but also in biological properties, and the relationship between their spatial distribution was weak. From the optical point of view, the indicator of bloom is the number of coccoliths, not cells, which can lead to an incorrect description of the biological situation.

First principles characterization of defect-free and vacancy-defected monolayer PtSe2 gas sensors

In this paper, we investigate the gas sensing properties of pristine and vacancy-defected monolayer PtSe2 in the presence of NH3, NO2, NO, O2, and CO gas molecules. The current-voltage (I–V) characteristics as well as dielectric functions are calculated before and after gas adsorption using a non-equilibrium Green’s function (NEGF) formalism. The first-principles calculations reveal that the bandgap of PtSe2 decreases in the presence of NO, NO2, and O2 which lowers required bias voltages to drive the current, while presence of NH3 and CO gas molecules has no considerable effect on the bandgap and I–V characteristic of the sensor. Furthermore, adsorption of NO and NO2 on PtSe2 monolayer leads to the negative differential resistance in corresponding I–V characteristic. Adsorption of O2 on the sensor, especially on the pristine monolayer, increases the conductivity of sensor. From the optical properties point of view, NO2 and NO gas molecules induce new peaks at different energies in the optical absorption spectrum of the pristine and defective sensors, while O2 only modulates the absorption spectrum of the defect-free structure. At the presence of CO, the main energy peak of the spectrum shifts, whereas the presence of NH3 does not modulate the optical absorption spectrum considerably.

The effect of the polymeric matrix on the emission properties of YAG-based phosphors

In the present paper we have studied the possibility to obtain nanocomposites by embedding yttrium aluminum garnet doped with Ce3+ and Gd3+ (YAG:Ce,Gd) phosphor in different polymer matrices, polydimethylsiloxane (PDMS), poly(methyl methacrylate) (PMMA) and epoxy resin (RE), for deposition on blue chips with the applicable purpose of generating white light. In order to obtain the nanocomposites, the ex-situ method which is based on the formation of a homogeneous mixture between phosphor and the polymeric matrix was chosen. YAG:Ce,Gd phosphor is previously dispersed in a suitable solvent for increasing the degree of compatibility with the polymer matrix. The device obtained to demonstrate the possibility of using the composites in white light emission, consists of a printed circuit containing pads on which 12 blue chips can be mounted. After welding the chips and connecting them using gold wire, YAG:Ce,Gd-based nanocomposites were injected and a thermal treatment was performed for cross-linking the composite at temperatures below 120 °C. The maximum temperature is imposed by the functionality parameters of a blue chip. The developed materials were analyzed from a morphological, structural and optical point of view using FTIR spectrometry, X-ray diffraction, AFM microscopy and photoluminescence spectrometry as characterization techniques. The quality of the light emitted was studied from the photometric point of view, finding an improvement of the CRI parameter compared to a commercial white LED. The chromaticity coordinates were studied and a "warm white" light was found for the RE-YAG:Ce,Gd and "cold white" composite for the PDMS-YAG:Ce,Gd and PMMA-YAG:Ce,Gd composites.

Comprehensive understanding of the focal property of lobster-eye optics.

Lobster-eye optics is a promising option to establish an all-sky monitor in the X-ray spectrum. With the development of micromachining technology, the performance of lobster-eye optics is gradually improving and has become more practical. In this paper, from an optical design point of view, the mathematical models of the square-channel lobster-eye lens and the meridional lobster-eye lens have been established based on prism analysis, and the focusing property differences of the two lenses are analyzed. There are several key conclusions: the square-channel lobster lens has no paraxial ideal focal point; the meridional lobster eye lens has better energy concentration for focusing and a weaker capacity for energy collection than the square-channel lobster eye lens in the high-energy X-ray spectrum; and the stray light arms of the square lobster-eye lens appear earlier than those of the meridional lobster-eye lens when the photon energy decreases. These conclusions can help improve the design of a lobster-eye lens for space detection and exploration.

Freeform Mirror Design for Novel Laser Warning Receivers and Laser Angle of Incidence Sensors.

In this paper, we present a novel configuration of an optical angle-of-incidence (AOI) sensor based on the application of a freeform mirror. The main challenge in designing this mirror was to provide a strictly linear transformation between AOI and the spatial position of the spot created on the linear detector array. Another two goals of this paper were to minimize stray light issues (improve the dynamic range) and create an intermediate focus and lateral shift in the detector position with respect to the plane of incidence. From an optical point of view, the designed mirror can thus be understood as the composition of three components: a high-numerical-aperture (NA) fully achromatic f-theta lens in one cross-section and a perfectly focusing lens, combined with a deviating prism in the second (orthogonal) cross-section. In comparison to the standard “shade” methods, the proposed approach allows a constant angular resolution to be maintained over the entire field of view. The mirror was designed on the basis of fundamental geometrical rules by numerically solving differential problems using an innovative scheme based on the minimization of the specific merit function. The proposed method was practically applied to design a freeform mirror for a 90°/120° field-of-view sensor, showing a satisfactory performance.

Preparation and characterization of stable fluorescent As4S4/ZnS/Fe3O4 nanosuspension capped by Poloxamer 407 and folic acid

Novel drug delivery systems containing advanced materials are currently the focus of many scientists, particularly in the field of medicine. Nowadays, these materials can play an important role when the authors talk about human health and especially the need to develop personalized treatment. In this work, multiparticulate As4S4/ZnS/Fe3O4 nanocomposite based on components possessing promising therapeutic, photoluminescent, and magnetic functionality was prepared by the milling. Subsequently, it was covered with the bio-compatible polymer Poloxamer 407 and/or folic acid for the functionalization of inorganic material. The samples were studied from the structural (X-ray powder diffraction analysis), magnetic, and optical (UV–Vis and photoluminescence spectroscopies) point of view. Particle size distribution and zeta potential measurements were performed to determine long-term stability of these nanosuspensions. Fourier transform infrared spectroscopy was used to identify bonding between organic and inorganic entities. Prominent optical fluorescence properties were found in a sample containing folic acid.

Some Considerations on the Composite Structure of the Human Eye

AbstractThe construction of the human eyeball has characteristics of the composite structure considering the optically transparent media (cornea, crystalline) that participate in the formation of images on the surface of the retina. Both the cornea and the crystalline are formed by thin cellular layers that behave like structures composed of elastic curved plates. The first part of the article presents the theoretical aspects that are the basis of the biomechanical approach of this ensemble. In the second part, the aspects of the modeling of the optical behavior of the eyeball and elasticity of the lens are presented. The final part of the article presents the conclusions regarding the behavior of the composite structure of the ocular globe from a biomechanical and optical point of view.

Dual-controlled switchable broadband terahertz absorber based on a graphene-vanadium dioxide metamaterial

We propose a dual-controlled switchable broadband terahertz (THz) metamaterial absorber based on a hybrid of vanadium dioxide (VO2) and graphene that demonstrates strong polarization-independent characteristics and works well at a wide range of incidence angles. The peak absorptance of the proposed absorber can be tuned from 26 to 99.2% by changing the Fermi energy of the graphene; the absorptance can be dynamically tuned from 9 to 99.2% by adjusting the conductivity of the vanadium dioxide because of its unique insulator-to-metal transition characteristic. Using these two independent controls in tandem, we found that the state of the proposed absorber can be switched from absorption (>96%) to reflection (>73.5%), and the transmittance can be tuned from 0% to 65% while maintaining broad bandwidth (1.05-1.6 THz), resulting in a better-performing switchable broadband terahertz absorber. Furthermore, we have provided a discussion of the interference theory in which the physical mechanism of the absorption is explained from an optical point of view. The absorber achieves dual-controlled absorptance switching via two independently controllable pathways, offering a new method for switching and modulation of broadband THz radiation.

Spectrum Measurement of Variable Irradiance Controlled LED-Based Solar Simulator

Efficiency of photovoltaic devices are based on testing all equipment and systems used to produce devices in a healthy way, from electrical and optical points of view. Considering that photovoltaic devices which enable the generation of electric energy from solar energy as a renewable energy source are widely used solar simulators should be utilized to provide actual daylight spectrum distributions. The most considerable component of solar simulators in photovoltaic device research is the light sources they use. Due to their advantages over conventional light sources, such as compactness, low power consumption, and low cost, research and studies on solar simulators use LEDs took place as an their illumination source. In this study, it is aimed to produce a low-cost Class A solar simulator with using six different type power LEDs, as specified in the IEC 60904-9 and ASTM E927-05 standards. At the end of the study with 24 power LEDs with six different wavelengths, the spectral match which is one of the three performance criteria of the solar simulator was obtained as Class A.

On the Physical Properties PEDOT:PSS Thin Films

A complete characterization from optical, morphological, electrical, photo-electrical and thermo-electrical point of view was done for PEDOT:PSS thin films and DMSO and EG sensitized PEDOT:PSS films. The studies on the electrical conductivity and electrical photoconductivity allowed the calculation of different relaxation times. The relaxation time of the electrical conductivity is of order of femtosecond and is multiplied by a factor 10 when PEDOT: PSS thin films were deposited on surfaces sensitized with DMSO and EG. Besides, the photoconduction excitation and relaxation times are of order of seconds. An increase in the relaxation photoconduction time by 2 was observed for films deposited on surfaces sensitized with DMSO and by 1.2 for films deposited on surfaces sensitized with EG. The time response of electrical conductivity after exposure to light adds supplementary knowledge for the understanding of the inertial processes, or hysteresis behavior of organic or perovskite solar cells involving PEDOT:PSS films. The electrical conductivity increases with the temperature and the use of DMSO and EG as surfactants lead to higher values of electrical conductivity and Seebeck coefficient. A better stability of the electrical conductivity with the temperature increase, was noticed for films deposited on surfaces sensitized with DMSO.

Hybrid organic-inorganic thin films based on zinc phthalocyanine and zinc oxide deposited by MAPLE

Hybrid organic-inorganic thin films based on zinc phthalocyanine (ZnPc) and ZnO nanoparticles were deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE). Synthesized by a simple wet chemical precipitation method, the ZnO nanoparticles were featured by a hexagonal wurtzite structure, a band-gap value of ~3.3 eV and emission bands typical for this semiconductor. The hybrid films containing ZnPc and various amounts of ZnO nanoparticles were evaluated from morphological, compositional, structural, optical and electrical point of view. No chemical decomposition of the organic compound was observed in the FTIR spectra of the deposited layers. The transmittance and photoluminescence spectra recorded on hybrid films disclose the optical signature of both organic (ZnPc) and inorganic (ZnO) components. The electrical measurements carried out under illumination emphasized the importance of the quantity of the inorganic component on the performance parameters of the structures prepared with the hybrid films. Our study provides new insight in the MAPLE deposition of the organic-inorganic hybrid films with potential applications in the photovoltaic cells area.