Layers Of Different Thicknesses Research Articles

Selective hydrogenation of 1,3-butadiene in the presence of 1-butene under liquid phase conditions using structured catalysts

Different aluminium structured substrates (monoliths of 350 and 1100cpsi; foams of 10, 20 and 40ppi) have been loaded with NiPd/(CeO2-Al2O3) catalyst by washcoating. To improve the adherence between catalyst particles and metallic surface, aluminium substrates were previously anodized to produce a rough (cracked) surface. Catalytic layers of different thickness have been deposited onto aluminium substrates. The catalytic coatings were characterized measuring their textural properties, adhesion and morphology. These structured catalysts have been tested in the selective hydrogenation of 1,3-butadiene in presence of 1-butene under liquid-phase conditions. The effects of some design parameters over the catalytic performance were studied: catalyst loading (125, 250 or 500mg), geometry of the structured substrate (monoliths or foams), and porosity (cpsi or ppi). The catalytic results show that foams present better activity than the monoliths. This can be related to better mass and heat transfer in the case of foams. In addition, the catalytic coating thickness influence directly the reaction selectivity; thicker layers produce undesired products (BA and isomers) due to diffusion limitations. However, it seems that the mass transfer of reactants to the surface of the catalyst layer plays a major role than the diffusion of reactants inside the catalyst layer.

Thermal Rounding Kinetics and Demonstration of Steep and Flat Facets Succession in Selective Si-Based Epitaxy

Si1-xGex(SiGe) alloys are integrated in more and more complex structures, and their applications are numerous. Initially, epitaxy process was applied for SiGe channels in 32nm technologies and beyond [1]. In the 20nm technology generation, SiGe epitaxial growths are used for raised source/drain (RSD) in Fully Depleted Silicon-On-Insulator (FD-SOI) p-Metal Oxide Semiconductors (p-MOS). However, since the scaling of the transistors’ dimensions is reaching physical, material, and technological limitations [2], new challenges in Si-based technologies have to be defined. Up to now, one of the most promising studies overcoming major device issues such as parasitic capacitance [3], is the morphology’s control of SiGe epitaxial growths. This is the reason why the morphological behavior of epitaxial SiGe is of great interest for performance improvements. In SiGe epitaxies, surface morphology depends on different parameters such as deposited thickness, Ge content... But, one of the most important parameters for the morphological change is the thermal budget brought to the film during or after epitaxial growth. The consequence of a thermal budget on an epitaxial layer is the modification of the morphology to reduce the surface energy leading to thermal rounding. Finally, the transistors’ dimensions being very small, the morphology is even more affected and sensitive to any process conditions (temperature, pressure), and extensive studies on SiGe morphology are needed. For this work, patterned 300mm Si(001) bulk wafers are used as substrates. All the layers were selectively grown in a Rapid Thermal Chemical Vapor Deposition reactor using dichlorosilane, germane, and HCl chemistry at low pressure and relatively low temperature. The purge and unloading steps were adjusted to freeze the as-deposited morphology. This way, the observed morphology is the closest as possible to the one during the deposition. The first part consists of a quantitative study of the thermal rounding’s kinetics in Si1-xGex (x=0.25) epitaxies. To do so, as-deposited SiGe layers are annealed at different thermal budgets. Then, the morphology evolution during annealing is studied as a function of temperature and time. The results of post annealed SiGe epitaxies are reported in Fig.1. It is observed that an annealing temperature increase of 25°C (from 650°C to 725°C) considerably impacts the morphology which evolves progressively passing through different steps. First, the edges begin to round and retract. In this step, the as-grown facets and their corresponding overgrowths fade away completely. Then, the thermal rounding gives rise to a formation of rounded ridges all around the pattern. Finally, the corner ridges approach towards each other until they collapse to form a single large dome. The rounding kinetics is quantified by measuring the displaced volume of matter. In the final paper, an extensive study will be given in which the effect of H2pressure on the kinetics will be presented. It will be shown that the pressure has a real influence on the rounding effect due to an increase of the hydrogen coverage slowing the Si diffusion at the surface. In many MOS applications, the SiGe epitaxy has to be capped typically with a Si (or SiGe) layer to maintain good performances. In this second part, the morphology behavior of such caps is studied. Si and SiGe layers of different thicknesses, growth rates and Ge contents were grown on a rounded SiGe layer, prepared as explained in the first part. It is shown that both Si and SiGe behave differently. The SiGe cap decreases the surface undulation amplitudes more efficiently than Si. Indeed, in large patterns, the 16 nm thick SiGe cap surface is smoother (RRMS=3.57nm) than the surface of Si cap (RRMS=7.37nm) (see Fig.2). In small patterns, a regular faceted morphology is observed for thick SiGe cap which is not the case for Si cap, showing once again that SiGe cap is more efficient (Fig.3). On the other hand, for thin Si and SiGe caps, the top surface presents domes with a succession of flat and steep facets. Those facets are <113> facets for the steep ones, and <11h> with h being 9 or even more, for flat facets (Fig.4). To summarize, firstly, the thermal rounding has been quantified and shown to be very sensitive to moderate thermal budgets (e.g.700°C). Secondly, Si and SiGe caps deposited on such a rounded surface have been compared. It has been reported that thin caps present successive terraces rather than regular faceted morphology. Keywords: SiGe, Si, Epitaxy, Rounding, Capping. [1] Weber,O Symp. VLSI Techno Dig Tech Pap, 2004, p. 42. [2] Haron,N. IEEE, 2008; pp 98–103. [3] Cheng,K. Symp. VLSI Tech., 2009, pp 212-213. Figure 1

Investigation of the Composition of the Si/SiO2 Interface in Oxide Precipitates and Oxide Layers on Silicon by STEM/EELS

We investigated thermal oxide layers of different thickness on (100) and (111) silicon substrates by STEM/EELS in order to determine the stoichiometry profiles and compared these with stoichiometry profiles of plate-like and octahedral oxide precipitates in silicon. The results of these investigations demonstrate that the stoichiometry of SiO2 (x=2) cannot be reached if the oxide layer thickness is lower than 10 nm for thermal oxides grown at 900 °C. The lower the thickness of the layer is the lower is the maximum x value. This is due to an interface layer of equal maximum slope for all oxide layers. The slope was obtained from fitting by sigmoid functions. Similar results were found for the oxide precipitates in silicon but the slope is somewhat lower.

Atomic Layer Deposition of Amorphous TiO2 on Carbon Nanotube Networks and Their Superior Li and Na Ion Storage Properties

Titanium dioxide is a promising anode material for lithium and sodium‐ion batteries (LIBs, SIBs). Current research of TiO2 is mainly focused on the crystalline phase (anatase or rutile) with a battery‐like diffusion mechanism. In the present work, it is aimed to demonstrate the advantages of amorphous titanium dioxide over crystalline ones for both Li and Na ion batteries. Amorphous TiO2 thin layers of different thicknesses are deposited on carbon nanotube (CNT) network/carbon fiber paper (CFP) substrates, forming the double‐walled TiO2@CNT nanotubes. For comparison, the as‐obtained amorphous TiO2@CNT/CFP samples are annealed to achieve anatase TiO2. It is shown that, as an anode of LIBs, the amorphous TiO2 shows better performance than the anatase one in terms of specific capacity, rate capacity, as well as cycling performance. The difference in the electrochemical property stems from their different charge‐storage mechanisms; different from the diffusion‐limited process in crystalline TiO2, the amorphous TiO2 stores charges via a fast surface‐controlled capacitive process similar to the orthorhombic Nb2O5. Moreover, the amorphous TiO2@CNT/CFP electrodes are also confirmed to be suitable for SIBs.

One-dimensional photonic crystals with highly Bi-substituted iron garnet defect in reflection polar geometry

It is represented the results of modelling of magnetooptical properties in reflection polar geometry of one-dimensional photonic crystal, in which highly Bi-substituted iron garnet defect of composition Bi1.0Y0.5Gd1.5Fe4.2Al0.8O12 / Bi2.8Y0.2Fe5Oi2 is located between the dielectric Bragg mirrors (SiO2 / TiO2)m (were m is number of layer pairs) and buffer SiO2 and gold top layers of different thicknesses is placed on structure. The modification of spectral line- shapes of microcavity and Tamm plasmon-polariton modes depending on m is found.

Influence of process parameters of ultrasonic shot peening on surface nanocrystallization and hardness of pure titanium

Ultrasonic shot peening (USP) is a mechanical surface treatment to rapidly realize surface nanocrystallization of metals. In this paper, the influence rules and mechanism of process parameters of USP on surface nanocrystallization and hardness of pure titanium were studied. Significant hardness increases of different degrees were observed, and nanocrystalline (NC) layers of different thicknesses and grain sizes were obtained on the surface of pure titanium after USP treatments with different process parameters, including peening duration, shot diameter, sonotrode amplitude, and peening distance. The influence rules of process parameters on the NC layers and surface hardness of peened pure titanium were analyzed with experimental results measured by Vickers microhardness meter, optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction pattern (XRD), and high-resolution transmission electron microscope (HRTEM). After the influence mechanism of process parameters was discussed, a relationship expression was identified between the surface hardness of pure titanium treated by USP and the process parameters with a correlation coefficient equal to 0.998.

Electropolishing Procedure Dedicated to In-Depth Stress Measurements with X-Ray Diffractometry

Abstract Electropolishing is the sole reliable method of removing the outer layer of the specimen without changing its stress state. This feature of the electropolishing procedure allows researchers to investigate the in-depth stress distribution. Developing of the method in a diffraction laboratory is crucial because there is no universal theory for the electropolishing procedure allowing the removal of the layers of different thickness. This is due to the multiplicity of different factors affecting the electropolishing results. A factor of vital importance from the point of view of indepth stress measurements is the thickness of the electropolishing layer. Hence the importance of the procedures for the electropolishing of a layer of a precisely defined thickness. This work deals with the problem of the selection of the parameters in the electropolishing process for two types of materials: stainless steel and aluminium alloy. The tests of mutual correlation of current intensity, voltage applied and time of the procedure and its results are presented in the paper.

Solvent-free silver-nanoparticle surface-assisted laser desorption/ionization imaging mass spectrometry of the Irganox 1010 coated on polystyrene

Imaging mass spectrometry (IMS) of the antioxidant Irganox 1010 coated on a polystyrene (PS) was conducted using solvent-free silver-nanoparticle surface-assisted laser desorption/ionization (Ag-NP SALDI). The lateral resolution and probing depth of Ag-NP SALDI-IMS, which are important factors in determining the surface sensitivity, were investigated. Direct Ag vapor deposition produced a 10-nm-thick homogenous layer of Ag-NPs on the Irganox 1010/PS thin film. Ag adduct ions of Irganox 1010 and PS repeating structures, and Ag cluster ions appeared in the mass spectrum, which showed that Ag-NPs on the sample surface enhanced the ionization efficiency by functioning as cationization agents. At the lateral resolution of this method (20μm), complementary grid patterns (55 lines per inch) of Irganox 1010 on the PS were observed. The probing depth was investigated with Irganox 1010 layers of different thicknesses, the detection of silver adduct ions of PS indicated Ag-NP SALDI could ionize the PS layer beyond the Irganox 1010 layer. The probing depth was 50–100nm for 10-nm-thick Ag-NP SALDI.

Asymmetric SPP waveguide without sacrificing the size of subwavelength waveguide

Subwavelength constraints and propagation distance contradiction in surface plasmon polariton (SPP) waveguide are currently the key issues. This study based on symmetric dielectric waveguide structures is designed for loaded glass SPPs to propagate optimization devices. The SPPs and Kretschmann model with similar structure are achieved without sacrificing the size of subwavelength waveguide and propagation distance of SPPs. FDTD analysis results show that improved waveguide structure of SPPs can significantly increase the propagation distance to 20-folds and improve the electric field strength. Comparative film layers of different thicknesses be seen as well. The film is the thinnest with best localization. The improved structure significantly increased the coupling effect of SPPs. This structure for SPPs in new photonic devices, broadband communications systems, small photon loops, and other aspects of integrated optoelectronic applications provide critical devices.

The Influence of the Molecular Structure of Cyanine Dye on the Component Composition of Molecular Layers

The formation of the component composition of symmetric cationic cyanine dyes on glass is studied. The absorption spectra of layers of three homologous series of dyes with end heterocyclic groups of different spatial and chemical compositions are measured, and the absorption spectra of monomer components and aggregates are separated. The component compositions of layers of different thicknesses are compared. It is shown that the widening of the absorption spectra of molecular layers against the spectra of ethanol solutions of these compounds is caused mainly by the formation of various monomer stereoisomers and molecular aggregates and their interaction with the substrate surface and the neighborhood. The number of isomer forms and their relative concentrations depend on the layer thickness, the electron donor ability and spatial structure of end groups, and the cation conjugation chain length. The influence of the anion manifests itself only in the concentration ratio of the formed monomers and a small shift of the maxima of their absorption bands. The increase in the number of monomer forms produced in the layer corresponds to the increase in the conjugation chain length. Spatial obstacles created by heterocyclic groups inhibit the formation of definite stereoisomers, which reduces the number of components of the layer.

Quantification of layered patterns with structural anisotropy: a comparison of biological and geological systems.

Large-scale patterns evident from satellite images of aeolian landforms on Earth and other planets; those of intermediate scale in marine and terrestrial sand ripples and sediment profiles; and small-scale patterns such as lamellae in the bones of vertebrates and annuli in fish scales are each represented by layers of different thicknesses and lengths. Layered patterns are important because they form a record of the state of internal and external factors that regulate pattern formation in these geological and biological systems. It is therefore potentially possible to recognize trends, periodicities, and events in the history of the formation of these systems among the incremental sequences. Though the structures and sizes of these 2-D patterns are typically scale-free, they are also characteristically anisotropic; that is, the number of layers and their absolute thicknesses vary significantly during formation. The aim of the present work is to quantify the structure of layered patterns and to reveal similarities and differences in the processing and interpretation of layered landforms and biological systems. To reach this goal we used N-partite graph and Boolean functions to quantify the structure of layers and plot charts for “layer thickness vs. layer number” and “layer area vs. layer number”. These charts serve as a source of information about events in the history of formation of layered systems. The concept of synchronization of layer formation across a 2-D plane is introduced to develop the procedure for plotting “layer thickness vs. layer number” and “layer area vs. layer number”, which takes into account the structural anisotropy of layered patterns and increase signal-to-noise ratio in charts. Examples include landforms on Mars and Earth and incremental layers in human and iguana bones.

Pressure and shear stress caused by raindrop impact at the soil surface: Scaling laws depending on the water depth

AbstractRaindrop impact is an important process in soil erosion. Through its pressure and shear stress, raindrop impact causes a significant detachment of the soil material, making this material available for transport by sheet flow. Thanks to the accurate Navier–Stokes equations solver Gerris, we simulate the impact of a single raindrop of diameter D, at terminal velocity, on water layers of different thickness h: , , D, 2D, in order to study pressures and shear stresses involved in raindrop erosion. These complex numerical simulations help in understanding precisely the dynamics of the raindrop impact, quantifying in particular the pressure and the shear stress fields. A detailed analysis of these fields is performed and self‐similar structures are identified for the pressure and the shear stress on the soil surface. The evolution of these self‐similar structures are investigated as the aspect ratio h/D varies. We find that the pressure and the shear stress have a specific dependence on the ratio between the drop diameter and the water layer thickness, and that the scaling laws recently proposed in fluid mechanics are also applicable to raindrops, paving the road to obtain effective models of soil erosion by raindrops. In particular, we obtain a scaling law formula for the dependence of the maximum shear stress on the soil on the water depth, a quantity that is crucial for quantifying erosion materials. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Optimal Shell Thickness of Metal@Insulator Nanoparticles for Net Enhancement of Photogenerated Polarons in P3HT Films.

Embedding metal nanoparticles in the active layer of organic solar cells has been explored as a route for improving charge carrier generation, with localized field enhancement as a proposed mechanism. However, embedded metal nanoparticles can also act as charge recombination sites. To suppress such recombination, the metal nanoparticles are commonly coated with a thin insulating shell. At the same time, this insulating shell limits the extent that the localized enhanced electric field influences charge generation in the organic medium. It is presumed that there is an optimal thickness which maximizes field enhancement effects while suppressing recombination. Atomic Layer Deposition (ALD) was used to deposit Al2O3 layers of different thicknesses onto silver nanoparticles (Ag NPs), in a thin film of P3HT. Photoinduced absorption (PIA) spectroscopy was used to study the dependence of the photogenerated P3HT(+) polaron population on the Al2O3 thickness. The optimal thickness was found to be 3-5 nm. This knowledge can be further applied in the design of metal nanoparticle-enhanced solar cells.

New Formulation of the Mulilayer Iterative Method: Application to Coplanar Lines with Thick Conductor

The skin effect is an electromagnetic phenomenon that makes the current flows only on the surface of the conductors at high frequency. This article is based on the phenomenon to model a structure made in coplanar technology. In reality, these types of structures integrated metal layers of different thickness of copper (9 μm, 18 μm, 35 μm, 70 μm). The neglect of this parameter introduces errors, sometimes significant, in the numerical calculations. This is why an iterative method (FWCIP) based on the wave concept was restated. Validation of results was carried out by comparison with those calculated by Ansoft HFSS software and Agilent ADS Technology. They show a good matching.

Optimization of a guided-mode resonance filter by varying the thickness of the buffer layer

In this Letter, we demonstrate that by adjusting the thickness of the buffer layer, the optical responses of a guided-mode resonance filter (GMRF) can be improved for sensor applications. The GMRF is fabricated using a replica molding with a plastic substrate and a UV-curable polymer. SiO2 buffer layers of different thicknesses are deposited before the waveguide-layer deposition. The sensitivity of the GMRFs decreases slightly with increasing SiO2 layer thickness. By contrast, the full width at half-maximum reduces substantially with increasing SiO2 layer thickness, resulting in the improvement of the overall figure of merit.

Duplex surface treatment of steels by nitriding and chromizing

Duplex surface treatment, that is, chromizing and plasma nitriding (PN) of steels have attracted interest from industrial sectors because of its attractive properties and ability to apply on different types of steels. This paper aims to investigate duplex treatment on different types of steels at different treatment conditions. The improvements of the treated surfaces in terms of morphology and thickness, composition, surface hardness and roughness, as well as wear and friction of the engineered layer have been analysed. It was found that several layers of different thickness are formed due to duplex treatment which depends on the specimen’s carbon content and treatment temperature. Mainly carbides and nitrides of chromium and iron are formed, where the amount and composition of them are controlled by duplex treatment process parameters. These compounds enhance the hardness and wear resistance of the treated surface. The CrxN phase is the main contributor towards high microhardness of duplex-treated layers. In addition to high hardness, it also provides excellent wear resistance properties. The PN process reduces the coefficient of friction of chromized steels due to the lower friction coefficient of chromium nitride. However, the surface roughness of the treated surface increases due to the intrinsic properties of formed phases.

Giant magnetoresistance of CoFe/Cu superlattices with the (Ni80Fe20)60Cr40 buffer layer

Magnetron sputtering was used to prepare substrate//(Ni80Fe20)60Cr40/[Co90Fe10/Cu] n /Cr superlattices containing permalloy–chromium buffer layer of different thicknesses. To achieve a maximum magnetoresistance of the superlattices, the thickness of their layers has been optimized. The use of the (Ni80Fe20)60Cr40 buffer layer was found to result in the formation a more perfect crystal structure of subsequent layers of the superlattice compared to that of superlattices with the Cr and Co90Fe10 buffer layers. The superlattice with the optimum thickness of the (Ni80Fe20)60Cr40 buffer layer and thin copper layers, the thickness of which is t Cu = 9.5 A, demonstrates the giant magnetoresistance effect equal to 54% at room temperature.

Optically switchable multi-stopband of non-quarter-wavelength dielectric multilayer using azobenzene polymer liquid crystal

Non-quarter-wave stacked dielectric multilayers including azobenzene polymer liquid crystal layers are investigated in this study. The azobenzene polymer liquid crystal has a photoinduced reversible refractive index based on photoisomerization. By using the reversible refractive-index change, the reflectance of a stopband can be controlled. In this system, the azobenzene molecules change their conformation when they are irradiated with ultraviolet (UV) or visible light. In general, stacking many layers of different thicknesses can produce broadband or multicolor reflections for a dielectric multilayer. However, in a multilayer having thick azobenzene layers, UV or visible light used for controlling photoisomerization hardly reaches the bottom part of the multilayer because the light is mainly absorbed at its top surface. To solve this problem, the dependence on the thickness ratio of the multilayer is investigated and a non-quarter-wave stacked multilayer having RGB reflections is experimentally demonstrated using thin azobenzene layers.

Influence of Al2O3 layer insertion on the electrical properties of Ga-In-Zn-O thin-film transistors

To investigate the influence of ionic/covalent interface of Al2O3/SiO2 gate insulator on the electrical properties of thin-film transistors (TFTs) with ionic Ga-In-Zn-O (GIZO) semiconducting channel layers, Al2O3 layers of different thickness were introduced between SiO2 and GIZO using plasma-enhanced atomic layer deposition. The GIZO layers were obtained by DC magnetron sputtering using a GIZO target (Ga:In:Zn = 1:1:1 mol. %). The GIZO TFTs with an Al2O3/SiO2 gate insulator exhibited positive threshold voltage (Vth) shift (about 1.1 V), Vth hysteresis suppression (0.23 V), and electron mobility degradation (about 13%) compared with those of a GIZO TFT with SiO2 gate insulator by the influence of ionic/ionic and ionic/covalent interface at Al2O3/GIZO and Al2O3/SiO2, respectively. To clarify the origin of the positive Vth shift, the authors estimated the shifts of flatband voltage (0.4 V) due to the dipole and the fixed charge (−1.1 × 1011/cm2) at Al2O3/SiO2 interface, from capacitance–voltage data for Pt/Al2O3/SiO2/p-Si capacitors. Based on these experimental data, the authors found that the positive Vth shift (1.1 V) could be divided into three components: the dipole (−0.4 V) and fixed charge (0.15 V) at the SiO2/Al2O3 interface, and the fixed charge (1.35 V) at the Al2O3/GIZO interface. Finally, it is noted that heterointerface of SiO2/Al2O3/GIZO stacks is important not only to recognize mechanism of Vth shift but also to design future TFTs with high-k dielectrics and low operating voltage.

Water flux in Pressure Retarded Osmosis

The transport of water through a semipermeable membrane in Pressure Retarded Osmosis (PRO) has been considered. The water flux is believed to consist of two components. The water flux from feed to draw solution is due to the difference in the water concentrations of feed and draw solutions. This flux is controlled by diffusion in accordance with Fick's Law. Second flux from draw to feed solution is caused by pressure applied to the draw solution. The total flux is proportional to the difference between the osmotic pressure and that applied to the draw solution. The membrane is assumed to be a set of several homogeneous layers of different thickness and with various diffusion coefficients. Each homogeneous layer can be characterized by diffusion resistance. The diffusion resistance of the membrane (r) is the sum of the diffusion resistance of individual layers. The water permeability coefficient (A) depends on the membrane diffusion resistance A=1/(RTr).