Layer Coverage Research Articles

Comparative study of water and ammonia rinsing processes of potassium fluoride-treated Cu(In,Ga)Se2 thin film solar cells

In this work, potassium fluoride (KF)-treated Cu(In,Ga)Se2 (CIGS) thin films were rinsed in ammonia and water solutions before buffer layer (CdS) deposition and the effects of rinsing on photovoltaic properties were investigated. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) measurements revealed that sodium atoms out-diffused at the surface region during KF deposition. Water and ammonia rinsing processes of KF-treated CIGS thin films reduced alkali metals from the surface. However, sodium at the Cu-depleted surface layer remained at a high concentration, suggesting the occupation of Cu vacancies with sodium atoms. On the other hand, ammonia rinsing removed the Cu-poor region from the surfaces of KF-treated CIGS thin films affecting the growth (or nucleation) of the CdS layer. The surface coverage of the CdS layer deposited on the ammonia-rinsed KF-treated CIGS thin film was inferior to than that of water-rinsed samples, resulting in the poor cell performance due to an increased interface recombination.

Two-dimensional percolation transition in two atomic layers of Fe on W(110): Direct measurement of a static percolation critical exponent in a two-dimensional Ising system

When the coverage of the second atomic layer of Fe in an Fe/W(110) ultrathin film reaches a critical value, the system moves suddenly from a frustrated magnetic state without long-range order to an in-plane ferromagnetic state with long-range order, and displays many features of a percolation transition. Measurements of the magnetic susceptibility as the films are grown at 255 K show power law scaling that is limited by noise at low deposition, and by the dynamics of the paramagnetic, frustrated state at high deposition. Because the measurements represent a system driven by a finite field oscillating at a finite frequency, it is demonstated that the threshold deposition for percolation is bounded by the depositions where the real and imaginary components of the susceptibility have maxima. Fitting for the critical exponent of the static susceptibility at these bounds gives a bounded value for $\gamma_p=2.39\pm0.04$, in agreement with theory.

Ternary oxide BaSnO3 nanoparticles as an efficient electron-transporting layer for planar perovskite solar cells

Organic-inorganic hybrid perovskites are a promising candidate for fabricating high-efficiency solar cells. In this work, well-dispersed ternary oxide BaSnO3 (BSO) nanoparticles with high crystallinity were successfully synthesized by a facile peroxide-precipitate route. And then BSO was first used as an efficient electron-transporting layer in planar perovskite solar cells. Influences of the coverage, roughness and thickness of planar BSO layer on the photovoltaic performance of the solar cells were systemically investigated. It is found that better coverage of BSO layer on the transparent oxide electrodes can significant reduce current leakage and suitable thickness of electron-transporting layer is favorable to reduce series resistance. Both of them contribute to the improved power conversion efficiency of cell devices. Additionally, the BSO-based device exhibits a comparable device performances to the TiO2 one, which can be ascribed to the efficient charge extraction as BSO/perovskite interfaces, the low charge transfer resistance and the suppressed carrier recombination. The optimized BSO-based planar perovskite solar cells exhibits power conversion efficiency of 10.96% with Jsc of 17.45 mA/cm2, Voc of 0.986 V and FF of 0.637. Thus, this work will pave the way for employing ternary oxide as electron-transporting material for high-performance perovskite solar cells.

Aspects of Habitat Use by Birds during Spring in Natural Forests and Non-Native Plantation Forests in the Lower Siret Meadow (Eastern Romania)

Abstract The Lower Siret Meadow forest habitats have been altered from natural structure because of commercial forestry operations, activities that are defining the forest management from previous decades. Afforestation programs aimed to test the introduction of exotic tree species in order to increase wood production and to reduce harvest time intervals. These commercial influences reflect in the decrease of natural forest areas, aspect that could influence the birds presence. Studies on the ecological impact of plantations on birds are scarce, and no studies were found regarding this aspect in the region. Using six different sample areas both in native and non-native tree plantations, we investigated how bird presence is influenced by the support capacity offered by both natural or non-native plantations and which vegetation variables are related to our results. We compared the data from the surveyed areas to relate birds presence and dependence on certain characteristics of the habitats. Our results pointed out that species diversity is higher in natural forests with local tree species and vegetation characteristics like forest canopy density, shrub coverage, and herbaceous layer.

Dry-Stamping-Transferred PC71BM Charge Transport Layer via an Interface-Controlled Polyurethane Acrylate Mold Film for Efficient Planar-Type Perovskite Solar Cells

The study of interlayers is important to enhance the performance of inverted perovskite solar cells (PSCs) because interlayers in PSCs align energy levels and improve charge transport. However, previous research into applying interlayers for PSCs has focused only on wet-coated methods, such as spin coating, to form the interlayer. Here, we fabricated planar-type PSCs deposited with a 6,6-phenyl-C71 butyric acid methyl ester (PC71BM) layer onto a CH3NH3PbI3 (MAPbI3) layer by stamping transfer through a relatively dry process condition. We demonstrated the effects of a stamping-transferred PC71BM layer using polyurethane acrylate (PUA), the surface energy of which was modified by 2-hydroxyethyl methacrylate (HEMA) to increase the transfer reproducibility. In PSCs with a stamping-transferred PC71BM layer, we observed an enhanced JSC and a comparable power conversion efficiency (PCE), which were caused by an enhanced coverage of the electron transport layer onto the MAPbI3 layer with preserved crystallinity, which occurs owing to improved electron mobility and exciton dissociation. The optimized device PCE through the dry-transferred PC71BM exhibited a JSC, fill factor, and PCE of 21.65 mA/cm2, 76.0%, and 15.46%, respectively. Moreover, morphological analysis and electrical measurements confirmed the improved durability of dry-stamping-transferred PSCs.

Numerical analysis of the effect of structural and operational parameters on electric and concentration fields of a lithium electrolysis cell

A fully integrated mass transfer and electrochemical model of a lithium production cell solved using a finite element method is presented. The coupled effect of momentum and mass transfer, kinetics, and electric fields is taken all into account. The turbulent flow resulting from the bubbles generated at the anode is solved based on a k- $$\epsilon$$ model. The ohmic overpotential and hyperpolarization due to the bubbles are considered through a resistive layer and bubble coverage at the surface of the anode. Furthermore, the effects of the anode–cathode distance (ACD) and current density on the electric and concentration fields of the cell are simulated. The results of the transient simulation reveal that the diaphragm separates the cell in two regions with different flow fields: a first region between the anode and the diaphragm and a second zone between the diaphragm and the cathode. The flow of bubbles generated at the anode has an important impact only in the first region, where the most important gradients are found. The concentration of ions is uniform in the second region. As expected, the current density plays an important role in the electrokinetic of the cell. The change in the geometry of the cell, studied by varying the ACD or by removing the diaphragm, has an important impact on the cell potential and on the concentration of electroactive species near the electrodes. The cell voltage is reduced by as much as 40% when the diaphragm is removed.

Electrical Properties of the Multilayered Graphene in Terms of Carrier Density and Mobility

Due to the graphene superior electrical mechanical and optical properties, graphene is particularly advantageous for flexible transparent conductive electrode applications. However, its sheet resistance still higher than indium tin oxide has been a critical problem. Increasing of graphene layers is well known and basic method for sheet resistance reduction. But, this enhancement was not fully explained in terms of carrier density and mobility which are the elements of the sheet resistance. Because of the graphene electrical property is strongly influenced by surface condition, each graphene layer in the multilayer might be has different electrical property. Therefore, simple measuring the sheet resistance gives insufficient information about the origin of sheet resistance decreasing. By understanding the number of layer and surface condition effect on carrier density and mobility, we can get the potential pathway to reduce the sheet resistance. So, separated measurement of electrical property is required. In this work, enhancement of electrical properties with increasing the number of graphene layer is systemically investigated by Hall measurement which can divide sheet resistance into the carrier mobility and density. In order to get multilayer graphene with the different interface condition, two different layer stacking methods were introduced. Single layer graphenes were synthesized by chemical vapor deposition and stacked the graphene with and without benzimidazole which strongly p-dopes the graphene. 1 to 4 layers of graphene were stacked and analyzed. The sheet resistance of inter-layer undoped and doped graphene are reduced from ~700 to ~220 Ω/sq and ~280 to ~80 Ω/sq, respectively. Both sheet resistances are inversely proportional to the number of layers. However, carrier mobility and density show clearly different characteristics. Regardless of the number of graphene layers, carrier density of inter-layer undoped graphene is maintained in the range of ~8 x 1012 /cm2, but it is linearly increased from ~1.8 x 1013 to ~6.2 x 1013 /cm2 when inter-layer was chemically doped. The carrier mobility of inter-layer doped graphene remained same in 1200 cm2/Vs but, that of undoped graphene is increased from 1000 to 3000 cm2/Vs. Because the major carrier generation of undoped graphene occurred only on the top of the layer, it has constant carrier density regardless of the number of graphene layer. Compare to the top layer, the layers inside undoped graphene have a much smaller carrier density it leads less charge carrier interaction and high carrier mobility. On the other hands, inter-layer doped graphene has uniform carrier density in inside each layer. So, it result the uniform carrier mobility and linearly increasing carrier density depending on the number of graphene layers. In addition, by stacking the various coverage of graphene which are the 16, 38, 84 and 100 % onto the full coverage monolayer graphene, we checked the partial coverage additional layer effect even without the second layer conducting path. The sheet resistance is gradually decreases from ~700 to ~350 Ω/sq by increasing the second layer coverage. The carrier density show uniform value of ~8 x 1012 /cm2 in all coverage, but mobility linearly increases from 1040 to 2288 cm2/Vs. Increased mobility leads the sheet resistance decreases. We find out that the origin of sheet resistance reduction in the multilayer graphene is different depending on the surface condition. This demonstration would be very useful for the use of graphene as a flexible transparent conductive electrode, and in other electrical applications.

Numerical Analysis of the Effect of Diaphragm Length, Position and Porosity on the Electric Field and Mass Transport inside a Lithium Electrolysis Cell

Lithium is commercially produced by the electrolysis of lithium chloride. This process is expensive due to the high energy consumption of the electrolysis process. A noticeable part of the energy lost in this electrochemical cell is caused by back reactions, essentially between chlorine bubbles produced at the anode and liquid lithium produced at the cathode. The diaphragm has two opposite effects on the cell energy consumption: it increases the current efficiency through its preventive effect on back reactions; however, it increases the energy consumption of the cell by introducing extra ohmic overpotential. Furthermore, in a lithium electrolysis cell, the diaphragm characteristics significantly influence the mass transfer, electric and velocity fields. A 2D axisymmetric electrochemical model of a lithium production cell is solved using a finite element method and used to minimize the cell energy consumption by optimizing the diaphragm characteristics and its position in the cell. The model is considering the coupled effect of momentum, electric, kinetic and mass transfer phenomena. The diaphragm separates the cell in two regions: 1- a turbulent region, between the anode and the diaphragm, and 2- a laminar region between the diaphragm and the cathode. The k-ε model is used to solve the turbulent flow resulting from bubbles generation at the anode. The bubbles cause an ohmic overpotential and hyperpolarization, considered through the resistive layer and bubble coverage at the surface of the anode. Furthermore, the effects of the diaphragm length, position and porosity on the electric field are simulated. In fact, the diaphragm position and length influence the current distribution at the surface of electrodes and the velocity distribution in the cell all of which influence ohmic and kinetic overpotentials. The experimental cell, simulated as a base case on which the model has been validated, contains a dense alumina diaphragm. The results show that up to 40% energy is saved when running a lithium electrolysis cell with a smaller porous diaphragm located as far as possible from the anode. Moreover, the diaphragm deteriorates the current density distribution along the electrodes with a detrimental effect to the integrity of the electrodes. The maximum current density, found at the bottom corner of anode, is higher when the diaphragm is longer and when it is closer to the anode. Finally, but not least, the results of this research are not only useful for improving the design of lithium production cells. They also could be extended and applied to the study of other molten salts electrochemical cells equipped with diaphragm.

Full coverage of perovskite layer onto ZnO nanorods via a modified sequential two-step deposition method for efficiency enhancement in perovskite solar cells

Full coverage of perovskite layer onto ZnO nanorod substrates with less pinholes is crucial for achieving high-efficiency perovskite solar cells. In this work, a two-step sequential deposition method is modified to achieve an appropriate property of perovskite (MAPbI3) film. Surface treatment of perovskite layer and its precursor have been systematically performed and their morphologies have been investigated. By pre-wetting of lead iodide (PbI2) and letting it dry before reacting with methylammonium iodide (MAI) provide better coverage of perovskite film onto ZnO nanorod substrate than one without any treatment. An additional MAI deposition followed with toluene drop-casting technique on the perovskite film is also found to increase the coverage and enhance the transformation of PbI2 to MAPbI3. These lead to longer charge carrier lifetime, resulting in an enhanced power conversion efficiency (PCE) from 1.21% to 3.05%. The modified method could been applied to a complex ZnO nanorods/TiO2 nanoparticles substrate. The enhancement in PCE to 3.41% is observed. These imply that our introduced method provides a simple way to obtain the full coverage and better transformation to MAPbI3 phase for enhancement in performances of perovskite solar cells.

Potassium-ion doped Cu(In,Ga)Se2 thin films solar cells: Phase formation, microstructures, and photovoltaic characteristics

A doping process of potassium-ion was adopted as an alternative to the toxic KCN etching used for the removal of Cu2-xSe compounds. The effects of potassium-ion doping on the phase formation and photovoltaic characteristics of the solution-coated Cu(In,Ga)Se2 films was investigated. As the incorporation of potassium ions was increased from 0 mol% to 1.0 mol%, the coexistent Cu2-xSe compounds were gradually reduced and the monophasic Cu(In,Ga)Se2 films were obtained. The potassium-ion doped Cu(In,Ga)Se2 films with dense and smooth morphology improved the coverage of CdS buffer layer and suppressed the additional shunt paths. Hence, the conversion efficiency of the solar cells fabricated without KCN treatment was significantly improved from 4.70%to 11.02%. Additionally, the diode factor (A) and the saturated current (J0) were reduced due to the suppression of carrier recombination and leakage current. Further increasing the content of potassium ions to 5.0 mol%, the oversupplied potassium ions reduced the grain size and induced the carrier recombination in the obtained films, thereby resulting in the deterioration of the cell performance. This investigation demonstrates that the incorporation of potassium ions into Cu(In,Ga)Se2 films with appropriated amounts can effectively diminish the formation of Cu2-xSe compounds, thereby improving the photovoltaic performance of the fabricated Cu(In,Ga)Se2 solar cells.

Using LDM to Achieve Seamless Local Service Insertion and Local Program Coverage in SFN Environment

Layered division multiplexing (LDM) is a spectrum efficient non-orthogonal multiplexing technology that has been adopted in the Advanced Television Systems Committee (ATSC) 3.0 Physical Layer Standard as a baseline technology. This paper studies a two-layer LDM with one layer used for providing a global service through a single frequency network (SFN), and the other for providing local coverage/services, such as location targeted advertising or local content insertion. The pilot boosting effect on SNR and co-channel interference is also analyzed. The LDM upper layer can be used to deliver time-division multiplexed mobile-HD and 4k-UHD services. The LDM lower layer with a negative SNR threshold can reliably provide seamless local coverage/service from each SFN transmitter without coverage gaps among adjacent SFN transmitter service areas. No directional receiving antenna is required for the local service reception and receivers simply tune into the stronger signal. In such LDM systems, while the upper layer is operating in a traditional SFN mode, the lower layer operates in a special form of distributed MIMO or gap-filler mode to provide targeted local coverage. For implementing the two-layer system introduced in this paper, only ATSC 3.0 baseline technologies are used, i.e., there is no need to modify the ATSC 3.0 standard. Given the upper and lower layers’ data rate requirements and the SNR thresholds, the lower layer power, with respect to the upper layer (injection level), can be optimized to maximize upper and lower layer performance and coverage. Since the advertisement time of the local service is typically less than 20% of the program time, nonreal time could be used to play-back the local content at five times the transmission bit rate for better (audio/video) service quality.

Predictive and Core-Network Efficient RRC Signalling for Active State Handover in RANs With Control/Data Separation

Frequent handovers (HOs) in dense small cell deployment scenarios could lead to a dramatic increase in signaling overhead. This suggests a paradigm shift toward a signaling conscious cellular architecture with intelligent mobility management. In this direction, a futuristic radio access network with a logical separation between control and data planes has been proposed in research community. It aims to overcome limitations of the conventional architecture by providing high data rate services under the umbrella of a coverage layer in a dual connection mode. This approach enables signaling efficient HO procedures since the control plane remains unchanged when the users move within the footprint of the same umbrella. Considering this configuration, we propose a core-network efficient radio resource control signaling scheme for active state HO and develop an analytical framework to evaluate its signaling load as a function of network density, user mobility, and session characteristics. In addition, we propose an intelligent HO prediction scheme with advance resource preparation in order to minimize the HO signaling latency. Numerical and simulation results show promising gains in terms of reduction in HO latency and signaling load as compared with conventional approaches.

Filter paper derived nanofibrous silica–carbon composite as anodic material with enhanced lithium storage performance

A filter-paper-derived nanofibrous silica–carbon composite composed of thin silica layer conformally coated on carbon nanofibers is synthesized by employing natural cellulose substance (ordinary laboratory filter paper) as both scaffold and carbon source. When the nanocomposite is employed as an anode material for lithium-ion batteries, it displays improved lithium-ion storage performance compared with the bare silica and carbon counter materials, due to the unique three-dimensional porous network structures of the carbon fiber scaffold and the thin silica layer. For the silica–carbon nanocomposite with 31.2wt% of silica content and the silica layer with a thickness of ca. 60nm, it delivers a stable discharge capacity of ca. 400mAhg−1 after 200 discharge/charge cycles at a current density of 100mAg−1. Moreover, improved electrochemical performances are achieved by coverage of an additional carbon layer or deposition of silver nanoparticles onto the silica–carbon nanofibers, which exhibits specific capacities of 488.7 and 477.5mAhg−1 after 100 discharge/charge cycles, respectively. The current synthetic method provides a facile and low-cost strategy for the large-scale production of nanofibrous silica–carbon based composites as anodic materials for lithium-ion batteries.

β-cyclodextrin as a Partial Replacement of Phosphorus Flame Retardant for Poly(Lactic Acid)/Poly(Methyl Methacrylate): A More Environmental Friendly Flame-Retarded Blends

ABSTRACTβ-Cyclodextrin was used together with isopropylated triaryl phosphate ester flame retardant to improve the flame resistance of poly(lactic acid)/poly(methyl methacrylate). Poly(lactic acid)/poly(methyl methacrylate)/flame-retardant blend (with and without β-cyclodextrin) was evaluated using limiting oxygen index, Underwriters Laboratories-94 vertical burning test, scanning electron microscopy, and thermogravimetric analysis (in O2 and N2). The addition of β-cyclodextrin was able to reduce the amount of flame retardant required for poly(lactic acid)/poly(methyl methacrylate) blends to achieve self-extinguishing properties. The poly(lactic acid)/poly(methyl methacrylate)20/flame-retardant/β-cyclodextrin blends achieved Underwriters Laboratories-94, V-0, and limiting oxygen index value of 29.3%. A compact and wide coverage of char layer was formed on the burning surface of poly(lactic acid)/poly(methyl methacrylate)20/flame-retardant/β-cyclodextrin blends.

Investigation of the temperature dependence of water adsorption on silica-based stationary phases in hydrophilic interaction liquid chromatography

In the present work, the adsorption of water was investigated in aqueous normal-phase liquid chromatography on Cogent Silica C and Cogent Phenyl hydride stationary phases at different temperatures by frontal analysis – using coulometric Karl Fischer titration – to compare the temperature dependence of adsorption of water from aqueous acetonitrile.The Cogent Silica-C and Cogent Phenyl Hydride columns have a silicon hydride surface (silica hydride) with less than 2% free silanol group; therefore, they do not have a strong association with water. The adsorption behavior of water on the mentioned stationary phases was modeled by Langmuir isotherm. The preferentially adsorbed water was expressed in terms of a hypothetical monomolecular water layer equivalent in the inner pores. The uptake of water slightly depends on the temperature.The adsorbed water may fill four to eight percent of the pore volume over the studied temperature range, which approximately corresponds to the equivalent of 0.24–0.68 water layer coverage of the adsorbent surface. The phenyl hydride stationary phase shows decreased water uptake in comparison to the Silica C stationary phase.

Time-resolved monitoring of biofouling development on a flat sheet membrane using optical coherence tomography

Biofouling on a membrane leads to significant performance decrease in filtration processes. In this study, an optical coherence tomography (OCT) was used to perform a time-resolved analysis of dynamic biofouling development on a submerged membrane under continuous operation. A real-time change in the biofouling morphology was calculated through the image analysis of OCT scans. Three videos were generated through the acquisition of serial static images. This is the first study that displays the dynamic biofouling formation process as a video. The acquisition of OCT cross-sectional scans of the biofouling allowed to evaluate the time-lapsed evolution for three different time periods (early stage, double layers and long-term). Firstly, at the early filtration stage, membrane coverage and average biofouling layer thickness were found to be linearly correlated with the permeate flux pattern. Secondly, after 3 d of operation, an anomalous morphology was observed, constituted by a double-layered biofouling structure: denser on the bottom and looser on the top. In a long-term operation, the biofouling structure underwent a dynamic evolution over time, resulting in a multi-layered structure. The biofouling formation information was closely associated with filtration performance (i.e. flux) indicating the suitability of OCT as real-time and in-situ biofouling monitoring technique.

Amorphous Molybdenum Sulfide Deposited Graphene Liquid Crystalline Fiber for Hydrogen Evolution Reaction Catalysis

Amorphous Molybdenum Sulfide Deposited Graphene Liquid Crystalline Fiber for Hydrogen Evolution Reaction Catalysis

Diffused back surface field formation in combination with two-step H2 annealing for improvement of silicon nanowire-based solar cell efficiency

Silicon nanowire (SiNW)-based solar cell fabrication was developed using a combination of diffused back surface field (BSF) formation and two-step H2 annealing for greater efficiency enhancement. Two different n-SiNW structures synthesized by metal-catalyzed electroless etching and nanoimprinting followed by Bosch process were used as substrates to fabricate single-junction solar cells with chemical vapor deposition grown p-Si shell layer. Without BSF formation, shell layer coverage of nanoimprinted SiNW solar cells fabricated using two-step H2 annealing was optimized and the H2 annealing effect on the shell layer crystallinity was investigated using transmission electron microscopy. Then, the effects of combined H2 annealing process for BSF formation together with shell layer treatment were observed under various annealing times. Enhancement of ∼1.5% absolute efficiency of both SiNW-based solar cells was achieved. Reduction of carrier recombination by BSF layer accompanied with the reduction of the defect density on n-SiNW surfaces and inside p-Si layer could be accomplished.

Effect of temperature on the growth ofa-axis ZnO films: a reactive force field-based molecular dynamics study

Abstract

Characterization of Thin Diamond-Like Carbon Layer Coverage by Trace Metal Leaching Test

A trace metal leaching test was applied to investigate coverage of a diamond-like carbon layer. Three trace metals – cobalt, nickel and iron – were measured. The change of seed and diamond-like carbon thicknesses influenced the trace metal concentration detected due to the passivation of the substrate via pinholes. Artificial pinholes were applied for a diamond-like carbon pinhole study, and it was found that the diameter, shape and total surface area of the holes affected the trace metals detected. The surface morphology and thickness were examined using scanning electron microscope and transmission electron microscope. The passivation was analyzed using electron energy loss spectroscopy.