Semitransparent Layer Research Articles

Synthesis of Fe:MgAl2O4 nanopowders by laser ablation

The features of production of Fe:MgAl2O4 nanopowders by evaporation of targets made from a simple oxide mixture (Fe2O3, MgO, Al2O3) by repetitively pulsed CO2 laser radiation with I = 1.8 MW/cm2 peak power density and Paver = 600 W average radiation power as well as by ytterbium fiber laser radiation (I = 0.4 MW/cm2 and Paver = 300 W) were studied. It was demonstrated that the nanopowder produced with the use of the CO2 laser has the specific surface of 56 m2/g and contains two crystalline phases, i.e. MgAl2O4 (98.2 wt%) and MgO (1.8 wt%), with Fe ions dissolved in them. At the average radiation power of 600 W, the output of the nanopowder was 16 g/h. For the nanopowder produced using the ytterbium fiber laser, a twofold increase of the specific surface (105 m2/g) was observed. This nanopowder contains four phases, i.e. MgAl2O4 (67.5 wt%), γ-Al2O3 (24.8 wt%), Fe3O4 (3.2 wt%) and MgO (4.5 wt%). In this case, the output of the nanopowder was 2.7 g/h due to high transparency of initial target and the formation of a “forest-like” array of 4–5-mm-high spikes covered with a semitransparent melt layer. Significant differences in the phase compositions of the nanopowders obtained using these lasers are associated with a higher rate of the laser plume cooling for the ytterbium fiber laser.

Theoretical Modeling of the Internal Power Flow and Absorption Loss of the Air Mode Based on the Proposed Poynting Vector Analysis in Top-emitting Organic Light-emitting Diodes

We propose the Poynting vector analysis of the air mode in a top-emitting organic light-emitting diode (OLED) by combining the transfer matrix method and dipole source term. The spatial profiles of the time-averaged optical power flow of the air mode are calculated inside and outside the multilayer structure of the OLED with respect to the thickness of the semi-transparent top cathode and capping layer (CPL). We elucidate how the micro-cavity effect controlled by the thickness variation of the semi-transparent top cathode or CPL affects the internal optical power and absorption loss inside the OLED multilayer and the external optical power coupled into the air. When the calculated absorption loss and external power obtained by the proposed Poynting vector and currently-used point dipole models are compared, two calculation results are identical, which demonstrates the validity of the two models.

Features of Light Transmission and Stark Effect in a Plasmonic Nanostructure Comprising Organic Semiconductor and Subwavelength Aluminum Grating

Specific features of light transmission and electroabsorption in a plasmonic nanostructure with organic semiconductor (zinc phthalocyanine, ZnPc) and subwavelength aluminum grating (AlGr) have been experimentally investigated. The glass–AlGr–ZnPc–Al nanostructure was prepared using layer-by-layer deposition. First, only a part of the structure has been analyzed to check the grating quality. After deposition of an organic semiconductor (ZnPc) layer on the grating, the transmission of TE and TM polarized light through AlGr and ZnPc layers upon excitation of plasmon resonances has been studied. Afterwards, a semitransparent aluminum layer has been deposited on the ZnPc layer (an additional electrode for measuring the electroabsorption effect). For TM polarized light, a multiple increase in the electroabsorption effect has been found (in comparison with a structure without subwavelength grating). This result can be explained by the Stark effect on exciton transitions and the presence of two cavities in the structure, which are related to the excitation of plasmonic states and the Fabry–Perot effect between aluminum electrodes. The presence of the cavities leads to a decrease in the group velocity of light and, accordingly, increases the density of exciton states, which are characterized by a large difference between polarizabilities in the excited and ground states.

Recent advances in high-performance semitransparent perovskite solar cells

Abstract Semitransparent perovskite photovoltaics have been developed to realize practical applications, such as windows in buildings/automobiles or the top cells of tandem devices. Among the functional layers constituting solar cell devices, fabricating efficient semitransparent light absorbers is one of the key issues for developing semitransparent devices. This short review describes the recent strategies for structuring semitransparent perovskite layers to achieve high performance in terms of both power conversion efficiency and transmittance.

Determining the Threshold of Detection of a Minimal Specific Weight of Particles in the Study of Shock-Wave Dusting of Surfaces of Materials

Particles are discharged from surfaces of materials under a shock-wave load. Experimental results on determining the minimal values of a specific weight of particles with which their velocity can be detected using a heterodyne interferometer [photon Doppler velocimetry (PDV) method] are presented. An effect of multiple frequency shift of a Doppler signal in the case of laser radiation being reflected from surfaces of materials and a semitransparent layer of dust particles is described.

MORPHOLOGICAL MAPPING OF THE BOTTOM OF MESOLOGGI LAGOON WITH THE USE OF ASTRONAUT PHOTOGRAPHY AND GIS

Mesologi lagoon is a large and shallow environment with intense fish farming applications and the consequent enclosing of very large areas with fish fences and nets, which make field mapping almost impossible. Anthropogenic influence is eminent and a recent and updated morphological map was necessary. A mapping technique is presented based on the use of astronaut photography that is distributed freely by the Internet site of NASA. The digital photograph was geometrically corrected, visually, as semi transparent layer over a scanned map image by the use of PHOTOSHOP software. The areas of known depth were used to classify the depths of the lagoon with the PHOTOSHOP tool "replace color". An image therefore was produce with the depths classified as solid colors. This image was used as base map in MAPINFO, to produce a digital map in GIS environment, where all anthropogenic influence and depths (as depth ranges) are exist as separate layers and reveal the morphological background of the lagoon. The GIS map was used to calculate the water volume of the lagoon and the changes of the volume, as the sea level fluctuates with the tide. The depth-volume diagram was created and shows that during low water (-30cm) the volume is reduced by 43%, in contrast an increase of only 12% when sea level become 30cm higher. This is the result of the construction of peripheral embankments that restricts extension of the lagoon in high water. The implication of this situation is that the water renewal is restricted when sea level is kept high by a barometric low or an onshore wind, in contrast to very good renewal time when sea level is kept low by a barometric high.

Limiting Optical Diodes Enabled by the Phase Transition of Vanadium Dioxide

A limiting optical diode is an asymmetric nonlinear device that is bidirectionally transparent at low power, but becomes opaque when illuminated by sufficiently intense light incident from a particular direction. We explore the use of a phase-transition material, vanadium dioxide (VO2), as an active element of limiting optical diodes. The VO2 phase transition can be triggered by optical absorption, resulting in a change in refractive index orders of magnitude larger than what can be achieved with conventional nonlinearities. As a result, a limiting optical diode based on incident-direction-dependent absorption in a VO2 layer can be very thin, and can function at low powers without field enhancement, resulting in broadband operation. We demonstrate a simple thin-film limiting optical diode comprising a transparent substrate, a VO2 film, and a semi-transparent metallic layer. For sufficiently high incident intensity, our proof-of-concept device realizes broadband asymmetric transmission across the near infrared, and is approximately ten times thinner than the free-space wavelength.

Colored and semitransparent silver nanoparticle layers deposited by spin coating of silver nanoink

In this letter, we report on the fabrication and characterization of colored and semitransparent silver nanoparticle layers. A spin coating of silver nanoink is used to deposit silver nanoparticle layers onto substrates. The transmittance and color of the silver nanoparticle layers are significantly dependent on the spin speed and nanoink concentration, owing to variations in the size and distribution of the nanoparticles. Both color variation and efficiency improvement are achieved with the application of silver nanoparticles to semitransparent Si thin-film solar cells, which is associated with the excitation of the dipole or quadruple plasmon modes of the silver nanoparticles.

Numerical investigation of radiation transfer in packed bed of semitransparent coated spherical particles

A packed bed of multilayered spherical particles plays a very important role in several engineering applications, such as the thermal insulation material of polystyrene foam and solar absorber for thermal energy conversion. In this study, we investigate the transmission of diffused beam in a one-dimensional densely packed bed. Spherical particles with double-layer structure and same radius are distributed randomly in transparent host media. The semitransparent inner layer is coated with a semitransparent shell. The size parameter χ of these spheres is sufficiently large to simulate their interaction with radiation through a Monte Carlo ray-tracing technique based on the geometrical optics approximation. After verification of the code for radiative transfer in a single coated sphere, the effects of optical thickness, refractive index, thickness, and porosity on the transmission are examined in detail. Transmittance and reflectance are employed to describe the radiative properties of a packed bed filled with multilayered semitransparent spherical particles.

Photo2clipart

We present a method to create vector cliparts from photographs. Our approach aims at reproducing two key properties of cliparts: they should be easily editable, and they should represent image content in a clean, simplified way. We observe that vector artists satisfy both of these properties by modeling cliparts with linear color gradients, which have a small number of parameters and approximate well smooth color variations. In addition, skilled artists produce intricate yet editable artworks by stacking multiple gradients using opaque and semi-transparent layers. Motivated by these observations, our goal is to decompose a bitmap photograph into a stack of layers, each layer containing a vector path filled with a linear color gradient. We cast this problem as an optimization that jointly assigns each pixel to one or more layer and finds the gradient parameters of each layer that best reproduce the input. Since a trivial solution would consist in assigning each pixel to a different, opaque layer, we complement our objective with a simplicity term that favors decompositions made of few, semi-transparent layers. However, this formulation results in a complex combinatorial problem combining discrete unknowns (the pixel assignments) and continuous unknowns (the layer parameters). We propose a Monte Carlo Tree Search algorithm that efficiently explores this solution space by leveraging layering cues at image junctions. We demonstrate the effectiveness of our method by reverse-engineering existing cliparts and by creating original cliparts from studio photographs.

Sporadic E S Layers at High Latitudes During a Magnetic Storm of March 17, 2015 According to the Vertical and Oblique Ionospheric Sounding Data

We consider the behavior of the parameters of the ionospheric E s layers according to the vertical sounding at the Sodankyla observatory and oblique sounding at the Lovozero (Murmansk region)—Gor’kovskaya station (Leningrad region) path during a superstorm of March 17, 2015. Temporal and spatial behavior of these parameters is compared. It was found that the storm significantly distorted the normal course of variations of the sporadic E s layer characteristics. Specific behavior of the layers during a storm at points separated by about 300 km was detected. With the help of ray tracing calculations using the IRI model, oblique sounding ionograms were constructed for the radio path analyzed. Primary attention is given to the maximum usable frequency of the F 2 layer—MUF-F 2. Additionally, for the disturbed conditions where there is only a high-power E s layer on the experimental ionograms, the values of MUF-E s and the ratio K =MUF-E s/f o E s for various cutoff frequencies f o E s of the E s layer and its altitudes $$ {h}_{E_s} $$ are calculated within the framework of the well-known approximations. Calculations for the case of weak disturbance and semitransparent E s layers are carried out with the IRI model adapted to the current diagnostics parameters. It was found that the calculated and experimental values of MUF-F 2 are close to each other or coincide, while this cannot be said about MUF-E s. The calculated and experimental values of MUF-E s can be matched in the model of mirror reflection from a flat layer for intense layers and the model of the E layer for thick E s layers of low intensity.

Visible-Blind UV Photodetector Based on Single-Walled Carbon Nanotube Thin Film/ZnO Vertical Heterostructures.

Ultraviolet (UV) photodetectors based on heterojunctions of conventional (Ge, Si, and GaAs) and wide bandgap semiconductors have been recently demonstrated, but achieving high UV sensitivity and visible-blind photodetection still remains a challenge. Here, we utilized a semitransparent film of p-type semiconducting single-walled carbon nanotubes (SC-SWNTs) with an energy gap of 0.68 ± 0.07 eV in combination with a molecular beam epitaxy grown n-ZnO layer to build a vertical p-SC-SWNT/n-ZnO heterojunction-based UV photodetector. The resulting device shows a current rectification ratio of 103, a current photoresponsivity up to 400 A/W in the UV spectral range from 370 to 230 nm, and a low dark current. The detector is practically visible-blind with the UV-to-visible photoresponsivity ratio of 105 due to extremely short photocarrier lifetimes in the one-dimensional SWNTs because of strong electron-phonon interactions leading to exciton formation. In this vertical configuration, UV radiation penetrates the top semitransparent SC-SWNT layer with low losses (10-20%) and excites photocarriers within the n-ZnO layer in close proximity to the p-SC-SWNT/n-ZnO interface, where electron-hole pairs are efficiently separated by a high built-in electric field associated with the heterojunction.

Study of semi-transparent conductive layers for the realization of high quantum efficiency transmission mode CsI photocathodes for vacuum photodetectors

We worked on the R&D of an innovative photodetector, the Vacuum Silicon Photomultiplier Tube (VSiPMT). The VSiPMT is composed by a photocathode and a solid state amplification stage. A semi-transparent conductive layer is necessary to supply voltage and to obtain a highly efficient CsI photocathode. Since the literature is poor on this topic we performed a systematic and detailed study of a set of semi-transparent conductive layers, made by different material and thickness. A CsI photocathode was evaporated on each sample. The impact of the semi-transparent conductive layer on the quantum efficiency of the photocathode is discussed.

In-line interferometer for broadband near-field scanning optical spectroscopy.

We present and investigate a novel approach towards broad-bandwidth near-field scanning optical spectroscopy based on an in-line interferometer for homodyne mixing of the near field and a reference field. In scattering-type scanning near-field optical spectroscopy, the near-field signal is usually obscured by a large amount of unwanted background scattering from the probe shaft and the sample. Here we increase the light reflected from the sample by a semi-transparent gold layer and use it as a broad-bandwidth, phase-stable reference field to amplify the near-field signal in the visible and near-infrared spectral range. We experimentally demonstrate that this efficiently suppresses the unwanted background signal in monochromatic near-field measurements. For rapid acquisition of complete broad-bandwidth spectra we employ a monochromator and a fast line camera. Using this fast acquisition of spectra and the in-line interferometer we demonstrate the measurement of pure near-field spectra. The experimental observations are quantitatively explained by analytical expressions for the measured optical signals, based on Fourier decomposition of background and near field. The theoretical model and in-line interferometer together form an important step towards broad-bandwidth near-field scanning optical spectroscopy.

Highly Conductive Semitransparent Graphene Circuits Screen‐Printed from Water‐Based Graphene Oxide Ink

The use of graphene materials as conductive inks for flexible and transparent electronics is promising, but challenged by the need for stabilizers, specialized organic solvents, and/or high temperature annealing, severely limiting performance or compatibility with substrates and printing techniques. Here, the development of a scalable water‐based graphene oxide ink is reported that can be screen‐printed on flexible plastic substrates and subsequently reduced using a 1:1 mixture of trifluoroacetic acid and hydroiodic acid, thereby creating an electric circuit. The reduced prints exhibit low sheet resistance of 327 Ω sq−1 for thin semitransparent layers with 37% transmittance. This methodology with postprinting chemical reduction outperforms high temperature annealing, thereby eliminating the need for such a step, which is incompatible with flexible plastic substrates. The strategy relies on low cost, industrially compatible chemicals and can be scaled up for low cost manufacture of roll‐to‐roll printed electronics.

Black Phase-Changing Cathodes for High-Contrast Organic Light-Emitting Diodes

High-contrast organic light-emitting diodes (HC-OLEDs) with black phase-changing (PC) cathodes have been designed and fabricated. The black PC-cathode consists of a front thin semitransparent metal layer, an organic PC layer, and a rear thick reflective metal layer. To achieve a targeted high contrast over the full visible spectrum, several organic molecules and their binary and ternary compounds were researched to meet optical design requirement. By combining a design in the complex refractive index and in the thickness of the PC layer, it is demonstrated that the optical reflectance of the HC-OLED can be reduced from ∼80% to below that of the glass substrate (∼5%) by using a ternary organic compound as the PC layer. This black PC-cathode produces extremely high optical contrast, and yet it does not alter the current–voltage characteristics of the device.

Automatic online layer separation for vessel enhancement in X-ray angiograms for percutaneous coronary interventions.

Percutaneous coronary intervention is a minimally invasive procedure that is usually performed under image guidance using X-ray angiograms in which coronary arteries are opacified with contrast agent. In X-ray images, 3D objects are projected on a 2D plane, generating semi-transparent layers that overlap each other. The overlapping of structures makes robust automatic information processing of the X-ray images, such as vessel extraction which is highly relevant to support smart image guidance, challenging. In this paper, we propose an automatic online layer separation approach that robustly separates interventional X-ray angiograms into three layers: a breathing layer, a quasi-static layer and a vessel layer that contains information of coronary arteries and medical instruments. The method uses morphological closing and an online robust PCA algorithm to separate the three layers. The proposed layer separation method ran fast and was demonstrated to significantly improve the vessel visibility in clinical X-ray images and showed better performance than other related online or prospective approaches. The potential of the proposed approach was demonstrated by enhancing contrast of vessels in X-ray images with low vessel contrast, which would facilitate the use of reduced amount of contrast agent to prevent contrast-induced side effects.

Ultrasonically spray coated silver layers from designed precursor inks for flexible electronics

Integration of electronic circuit components onto flexible materials such as plastic foils, paper and textiles is a key challenge for the development of future smart applications. Therefore, conductive metal features need to be deposited on temperature sensitive substrates in a fast and straightforward way. The feasibility of these emerging (nano-) electronic technologies depends on the availability of well-designed deposition techniques and on novel functional metal inks. As ultrasonic spray coating (USSC) is one of the most promising techniques to meet the above requirements, innovative metal organic decomposition (MOD) inks are designed to deposit silver features on plastic foils. Various amine ligands were screened and their influence on the ink stability and the characteristics of the resulting metal depositions were evaluated to determine the optimal formulation. Eventually, silver layers with excellent performance in terms of conductivity (15% bulk silver conductivity), stability, morphology and adhesion could be obtained, while operating in a very low temperature window of 70 °C–120 °C. Moreover, the optimal deposition conditions were determined via an in-depth analysis of the ultrasonically sprayed silver layers. Applying these tailored MOD inks, the USSC technique enabled smooth, semi-transparent silver layers with a tunable thickness on large areas without time-consuming additional sintering steps after deposition. Therefore, this novel combination of nanoparticle-free Ag-inks and the USSC process holds promise for high throughput deposition of highly conductive silver features on heat sensitive substrates and even 3D objects.

Multi-layer topography measurement using a new hybrid single-shot technique: Chromatic Confocal Coherence Tomography (CCCT).

Often measurement tasks occur, where specimens consist of multiple layers or topography shall be examined through contaminations. Especially for unknown layer materials, it is important to measure the layer's refractive index to compensate for the errors induced on the measurement of underlying surfaces. Chromatic Confocal Coherence Tomography is proposed as a new hybrid single-shot scheme for a simultaneous measurement of thickness and refractive index of semitransparent layers, combining chromatic confocal and interferometric information. As a proof of concept, first measurements are presented along with a short discussion about their uncertainties, where minimal layer thickness and resolution are dominated by the confocal part of the signal, that is mainly influenced by the chosen microscope objective.

Optical and microstructural properties of decorative Al/Ti/TiO2 interference coatings

This paper presents a study of the optical properties and the microstructure of interference Al/Ti/TiO2 systems obtained by gas injection magnetron sputtering (GIMS). The samples are examined by means of spectroscopic ellipsometry, atomic force microscopy and spectrophotometry combined with colorimetric measurements. The optical constants of the Al, Ti and TiO2 layers are determined and carefully studied. The thickness of dielectric films varies from 23nm to 49nm and directly determines the color of a sample from orange to blue, respectively. The thickness of Ti films ranges from 0nm to 125nm which corresponds to both the semitransparent and opaque titanium layers. The colors of the Al/TiO2 interference systems are not highly saturated because of the high reflectance of aluminum in the visible spectral range. The introduction of a Ti film between Al and TiO2 reduced the effective amount of reflected light. Moreover, the thickness of the titanium layer is associated with the color saturation of the Al/Ti/TiO2 multilayered systems.