Thickness Of Homogeneous Layer Research Articles

Memory Seeds Enable High Structural Phase Purity in 2D Perovskite Films for High-Efficiency Devices.

2D perovskites are a class of halide perovskites offering a pathway for realizing efficient and durable optoelectronic devices. However, the broad chemical phase space and lack of understanding of film formation have led to quasi-2D perovskite films with polydispersity in perovskite layer thicknesses, which have hindered device performance and stability. Here, a simple and scalable approach is reported, termed as the "phase-selective method", to fabricate 2D perovskite thin films with homogenous layer thickness (phase purity). The phase-selective method involves the dissolution of single-crystalline powders with a homogeneous perovskite layer thickness in desired solvents to fabricate thin films. In situ characterizations reveal the presence of sub-micrometer-sized seeds in solution that preserve the memory of the dissolved single crystals and dictate the nucleation and growth of grains with an identical thickness of the perovskite layers in thin films. Photovoltaic devices with a p-i-n architecture are fabricated with such films, which yield an efficiency of 17.1% enabled by an open-circuit voltage of 1.20 V,while preserving 97.5% of their peak performance after 800 h under illumination without any external thermal management.

Influence of natural oxide layers at Ni/NiAl interfaces on Ni3Al phase formation

The influence of natural oxide layers at interfaces in diffusion couples is studied. Concentration distributions at (Ni)/NiAl interfaces and the formation of the Ni3Al phase at 650 °C are characterized using scanning electron microscopy (SEM) and aberration corrected scanning transmission electron microscopy (STEM) with Energy-Dispersive X-ray spectroscopy (EDX) with unprecedented spatial resolution. Employing the common practice of chemical etching with 10 vol% HCl does not remove the oxide layers irrevocably – they are detected at the Kirkendall plane after diffusion annealing of (Ni)/NiAl diffusion couples, if high resolution microscopy is employed. The oxide layer at the Kirkendall plane is of a thickness of ~5 nm, comparable to that of the combined natural oxide layers on the (Ni) and NiAl surfaces. The oxide acts as a diffusion barrier, retarding or locally suppressing growth of Ni3Al into the (Ni) phase. For comparison, oxide-free Kirkendall planes were obtained by subjecting the joining surfaces of (Ni) and NiAl to gentle grinding with low contact pressure in a glove-box in purified Ar atmosphere before assembling the diffusion couple. After diffusion annealing, the Ni3Al layers are distinctly thicker and of a more homogeneous layer thickness as compared to samples with residual oxides. It is shown that evaluating interdiffusion coefficients in oxide-free diffusion couples yields higher values as compared to the conventionally assembled counterparts.

A new route to fabricate multilayer steel with multiscale hierarchical structure

SUS304/A283-C multilayer steels are processed via vacuum hot rolling, which possesses homogeneous layer thickness, straight interface and strong interfacial bonding. The austenite in SUS304 stainless steel layers can transform into α’-martensite in the process of cold rolling deformation, causing the hard SUS304 layer and the soft A283-C layer deformation inconsistency, as a result of the decrease of fracture elongation and the formation of laminated/network hierarchical interface. Annealing could availably regulate the grain characteristics, and the diffusion behavior of alloying element, and could also eliminate dislocation plugging. The hard layer and soft layer present a dual-scale distribution, besides, the grains of every layer change from the nanoscale structure to ultrafine structure. Thus, the multiscale hierarchical structure can be obtained by cold rolling and succedent annealing. Superior tensile properties can be obtained at 650 °C with the ultimate strength of 748 MPa and fracture elongation of 25%. Besides, the excellent bending deformation capacity can be also obtained at 650 °C. Therefore, the multilayer steel with multiscale hierarchical structure containing laminated/network structure in micro scale, hierarchical grain structure in submicron scale is conducive to strengthening and toughening multilayer steels.

Frictional receding contact problem of a functionally graded layer resting on a homogeneous coated half-plane

This paper investigates the frictional receding contact problem between a functionally graded (FG) layer resting on a homogeneous coated half-plane when the system indented by a rigid cylindrical punch. The shear modulus of the upper graded layer is assumed to vary exponentially in the depth direction. Upon loading, the advancing contact and receding contact occur between the FG layer and rigid punch and between the FG layer and coating, respectively. Under the assumptions of sliding contact, the shear and normal contact stresses are related through Coulomb’s law of friction. The contact problem is converted analytically using Fourier integral transforms and the proper boundary conditions into a system of two singular integral equations. The unknowns of these integral equations consist of the contact stresses under the punch and between the FG layer and coating as well as the dimensions of the contact zones. The Gauss–Jacobi quadrature collocation method is then employed to transform the singular integral equations into a system of nonlinear equations which are solved using an appropriate iterative algorithm to compute the contact stresses and the dimensions of the contact areas. The main purpose of this paper is to examine the influence of several parameters on the upper and lower contact stresses, which include the material inhomogeneity parameter, friction coefficient, punch radius, applied load, thickness of homogeneous layer, shear modulus of homogeneous layer and shear modulus of homogeneous half-plane. One of the most important conclusions from this study is that the contact stresses and contact areas can be controlled with the addition of the homogeneous layer.

Chemical vapor deposition of poly-p-xylylene in narrow tubes

Depositing a film via chemical vapor deposition results in superior conformity compared with other deposition techniques, primarily due to the unique chemical interactions between the surface and the reactive compounds. This technique requires a readily accessible surface and so, if the transport of the reactive species is impeded, irrespective of whether this depletion is caused by diffusion or convective flow, a homogeneous layer thickness cannot be achieved. This is often the case when applying films to the interiors of tubes, especially tubes with a dead-end, such that the inevitable loss of film-building components leads to a drop in thickness along the deposition length. The present work examined the deposition of the organic polymer poly-p-xylylene, using a reactor with dimensions that were large compared with the mean free path and tubes in which this factor (the Knudsen number) becomes unity, such that the deposition can be approximately described with the continuum model. A so-called temperature seesaw was employed to mitigate variations in layer thickness by generating an opposing temperature gradient. It was found that, under a vacuum of several tens of mTorr, the polymer could be deposited on the interior wall of a tube with an aspect ratio of at least 100 with an accuracy of ±7.5 %. The true ceiling temperature for the N derivate of this polymer was also determined to be 70±2 °C.

Manufacture of dense CAU-10-H coatings for application in adsorption driven heat pumps: optimization and characterization

CAU-10-H displays a highly suitable step-wise water adsorption behaviour for application in adsorption driven heat pumps and chillers. For actual application, manufacturing of coatings of this material on thermally conductive surfaces is highly desired. Direct, single-step, crystallization of CAU-10-H on either metallic or anodized aluminium yields a significant amount of by-product(s) and an inhomogeneous substrate coverage. Although adequate pretreatment of the substrates before crystallization improves the quality of obtained coatings, significant improvements are achieved only when crystal nucleation and growth are separated. More specifically, application of a reactive seeding approach with anodized aluminium leads to full coverage of the substrate surface, high MOF loading and high purity of the crystalline phase, homogeneous layer thickness, narrow crystal size distribution, and good stability in repeated water adsorption–desorption cycles.

Preparation and characterization of nanometer‐thin freestanding polymer foils for laser‐ion acceleration

ABSTRACTWe report on the production and characterization of polymer‐based ultra‐thin (sub 10 nm) foils suited for experiments on laser‐ion acceleration in the regime of radiation pressure acceleration. Beside the remarkable mechanical stability compared with commonly used diamond‐like‐carbon foils, a very homogeneous layer thickness and a small surface roughness have been achieved. We describe the technical issues of the production process as well as detailed studies of the mechanical stability and surface roughness tests. The capability of producing uniform targets of large area is essential for advanced laser‐ion acceleration projects which are dealing with high repetition rate and extended measurement series, but might also be useful for other applications which require ultra‐thin and freestanding substrates of high quality. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1355–1360

Slot-Die Coating: A New Preparation Method for Direct Methanol Fuel Cells Catalyst Layers

Manufacturing of catalyst layers is one of the key processing steps in making membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs). The catalyst ink, which usually contains catalysts, ionomers, solvents, and additives, is generally applied to the substrate by a wet-coating technique. Established coating techniques which are used for manufacturing catalyst layers for fuel cells are knife-coating, screen-printing, and spraying. Slot-die coating is also an established coating technique, but not currently used for making fuel cell electrodes. For each coating technique the properties of the catalyst layer will depend on the properties of the coating technique and the properties of the substrate. Also each coating technique requires the catalyst ink to be adjusted to its specific rheological requirements. In this study, slot-die coating is developed as a new method for the continuous manufacture of catalyst layers for direct methanol fuel cells. The rheological demands for a homogeneous layer thickness are studied with model inks and a suitable catalyst ink is prepared. With this ink, decal electrodes are fabricated and CCM-type MEAs are made. Fuel cell tests show that the performance of the slot-die coated electrodes is comparable to electrodes made by knife-coating.

Linewidth properties of double-layer surface-relief resonant Brewster filters with equal refractive index

In this paper, double-layer surface-relief resonant Brewster filters consisting of a homogenous layer and a grating with equal refractive index are obtained by adjusting the grating filling factor, and linewidth properties of these types of filters are investigated. It is shown etch depth error does not change the filter linewidth, but the grating filling factor and the substrate refractive index can significantly change the filter linewidth. Moreover, the coupling strength can be appreciately affected by the homogeneous layer thickness, and one can obtain different linewidths at the same operating wavelength by selecting different homogeneous layer thickness with other physical parameters maintained.

プラズマ溶射法による遮熱コーティングシステムのセラミックトップコート/金属ボンドコート界面のナノキャラクタリゼーション

Characterization at the ceramic top-coat/metallic bond-coat interfacial region was conducted for several kinds of the plasma sprayed thermal barrier coating (TBC) systems by means of a transmission electron microscope (TEM), an electron probe micro-analysis (EPMA) and so forth, in order to find out the optimum compositional and structural conditions of the coating components together with the optimum coating processing condition for designing the advanced TBC systems. Specimens with different coating features were prepared systematically by using different coating parameters such as the top-coat spraying conditions and reheat-treatment conditions. Especially, the reheat-treatment was applied to the TBC specimen with different temperature either in air or in inert argon (Ar) gas atmosphere. It was found that in the case of reheat-treatment in air the thermally grown oxide (TGO) was developed at the interface as multiple oxide layers; one is Al2O3 layer developed discontinuously at directly above the bond-coat and another is the mixed oxides layer consisting of the Al, Cr, Co, Ni oxide particles on the Al2O3 layer. Such a TGO layer was heterogeneous and imperfect layer with containing many kinds of defects. On the contrary, the TGO layer formed by the reheat-treatment in Ar was composed dominantly of the continuous and fairly purified Al2O3 layer with large grain size and homogeneous layer thickness. The growth mechanism and influencing factors for TGO were discussed in some detail on the basis of the nano-characterization and quantitative evaluation of TGO.

Nano-Characterization of Ceramic Top-Coat/Metallic Bond-Coat Interface for Thermal Barrier Coating Systems by Plasma Spraying

Characterization at the ceramic top-coat/metallic bond-coat interfacial region was conducted for several kinds of the plasma sprayed thermal barrier coating (TBC) systems by means of a transmission electron microscope (TEM), an electron probe micro-analysis (EPMA) and so forth, in order to find out the optimum compositional and structural conditions of the coating components together with the optimum coating processing condition for designing the advanced TBC systems. Specimens with different coating features were prepared systematically by using different coating parameters such as the top-coat spraying conditions and reheat-treatment conditions. Especially, the reheat-treatment was applied to the TBC specimen with different temperature either in air or in inert argon (Ar) gas atmosphere. It was found that in the case of reheat-treatment in air the thermally grown oxide (TGO) was developed at the interface as multiple oxide layers; one is Al2O3 layer developed discontinuously at directly above the bond-coat and another is the mixed oxides layer consisting of the Al, Cr, Co, Ni oxide particles on the Al2O3 layer. Such a TGO layer was heterogeneous and imperfect layer with containing many kinds of defects. On the contrary, the TGO layer formed by the reheat-treatment in Ar was composed dominantly of the continuous and fairly purified Al2O3 layer with large grain size and homogeneous layer thickness. The growth mechanism and influencing factors for TGO were discussed in some detail on the basis of the nano-characterization and quantitative evaluation of TGO.

Epitaxial thin-film growth ofC60onVSe2studied with scanning tunneling microscopy and x-ray diffraction

The growth of ${\mathrm{C}}_{60}$ films on layered 1T-${\mathrm{VSe}}_{2}$ has been investigated by combined scanning tunneling microscopy (STM) and x-ray diffraction. The STM results are discussed in the framework of the diffusion limited aggregation (DLA) model. Particularly, the crossover from fractal to uniform growth as a function of the aggregated particle concentration is studied and discussed in the context of DLA. The averaged vertical structure is determined by Bragg diffraction and x-ray reflectivity and is explained in conjunction with the STM results. The epitaxial growth in the (111) direction is confirmed and a homogeneous layer thickness is found. Interfacial roughness and the averaged dispersion of the film are derived from the data.

High rate PECVD of a-Si alloys on large areas

The deposition of a-Si alloys on large areas was investigated in the frequency region from 3 to 30 MHz. With increasing frequency an increasing deposition rate (5–30 μm h −1) and a decreasing powder formation result. An upscaling from small areas (100 cm 2–1000 cm 2) to larger areas (2500 cm 2 for the parallel plate and 5000 cm 2 for the coaxial reactor) was realized. With a homogeneous r.f. voltage we obtained a homogeneous r.f. power dissipation and a homogeneous layer thickness (±5%). An additional stabilization for the discharge over the length was obtained by use of a permanent magnetic field. We have calculated the deposition rate as a function of r.f. power, pressure, gas flow rate, frequency, magnetic field, discharge length and gas temperature on the basis of a semiquantitative plasma chemistry model.

On chemically vapour‐deposited Si/Ge growth in a multi‐wafer deposition process at atmospheric pressure

AbstractIn multi‐wafer deposition of Si/Ge thin films from silane, germane mixtures at low‐temperature epitaxy conditions not only the depletion of the silicon source but also of the germanium source along the reactor tube axis has to be counteracted in order to get homogeneous layer thickness as well as composition. Carrier gas throughput must be minimized to have a sufficient effective chemical reaction rate at low temperature. Thus it cannot be used to flatten layer growth along the susceptor. Yet the addition of a chemically reactive gas, as for instance hydrogen chloride, is suitable to ensure a nearly constant content of the layer forming source gases along the reactor tube. On the other hand hydrogen chloride may infiltrate additional contaminants leading for instance to high oxygen concentration in the deposited layer. However, oxygen soluted or precipitated changes particular features of Si/Ge behaviour for instance during the thin film growth, the following technological stress of the wafer, or the running electronic structures of microelectronic devices.

Short‐term variability in the bottom boundary layer of the deep Ocean

A series of 130 CTD profiles of temperature and salinity were measured in and above the benthic homogeneous layer at a location on the Blake‐Bahama Outer Rise (28°00′N, 71°30′W). Four sets of measurements were made over a 3‐day period. In order to observe the short‐term behavior of the boundary layer, individual profiles in each set were separated in time by about 4 min or in distance by about 30 m. Layer thickness changes of up to 20 m were observed in less than an hour. The fact that the variations in homogeneous layer thickness and the shape of the overlying temperature gradient are coherent and progressive suggests internal waves as a source of short‐term thickness variability. At the site where the greatest short‐term variability was observed, this interpretation is supported by the calculated Brunt‐Väisälä period (2.3 hours) and the lack of correlation between the thickness and temperature of the homogeneous layer. At another site, however, increasing layer thickness was accompanied by rising temperature within the layer, a feature indicating that mixing in of the overlying water may also produce thickness changes.