Degree Of Intermixing Research Articles

Asymmetric polyelectrolyte multilayer membranes: Influence of bottom section polycation on layer growth and retention mechanisms

It has been previously demonstrated that asymmetric polyelectrolyte multilayer (PEM) membranes are highly promising for use in water treatment due to their ability to combine a high selectivity with a high permeability. This is achieved by first coating a more open (highly permeable) bottom PEM to fill the pores of the support membrane, and subsequently a more dense (highly selective) top PEM. However, fundamental understanding on the interaction between top and bottom PEM section and the effect of the bottom section on the resulting membrane properties is still lacking. In this study, symmetric membranes with different polycations are prepared and compared with asymmetric membranes which contain an additional poly (allylamine hydrochloride)/poly (acryl amide) (PAH/PAA) top section. PEM layer growth was first studied with optical reflectometry, demonstrating that the growth of the top PEM section is dependent on the previously deposited bottom PEM section. Membrane performance was assessed with cross-flow measurements, where permeability and molecular weight cutoff (MWCO) measurements showed distinct differences for the symmetric membranes. Although these properties converge upon coating of the top section, differences remain. This can be explained by a contribution of the bottom section to hydraulic resistance and by intermixing of the top and bottom section. The degree of intermixing is attributed to differences in mobility of the used polycations. Single salt retention measurements even show that changing the bottom section polycation allows for tuning of the salt retention mechanism of the resulting asymmetric membranes. Whereas membranes with PAH in the bottom section are dominated by dielectric exclusion, membranes with Poly (vinylbenzyltrimethylammonium chloride) (PVBTMAC) in the bottom section show a dominant Donnan exclusion. These observations were confirmed by varying both the salt concentration and the operational flux. Overall, our work demonstrates that asymmetric coating on different bottom PEM chemistries can be used as a promising tuning parameter in layer-by-layer coating. This allows for a more rational design of asymmetric PEM membranes, opening opportunities for tuning membranes towards specific applications.

Revisiting transport phenomena and their role in intermixing during dissimilar laser beam welding

A study was conducted in order to understand the intermixing during welding dissimilar steel materials in overlap condition. Based of a manganese steel, different combinations were investigated considering convective transport processes, local alloy constitution and mechanical properties, and the underlying metallurgical effects. The analysis reveal an uneven distribution of alloying elements where the ferritic and martensitic phases are largely suppressed. Micro hardness measurements show hard spots but leading to a ductile character of the weld metal. The investigation show the strong effects of the processing parameters on the degree of intermixing and the inhomogeneity of the weld metal.

Dzyaloshinskii-Moriya interaction at disordered interfaces from ab initio theory: Robustness against intermixing and tunability through dusting

The Dzyaloshinskii-Moriya interaction (DMI), which is essential for the stabilization of topologically non-trivial chiral magnetic textures such as skyrmions, is particularly strong in heterostructures of ultra-thin magnetic materials and heavy elements. We explore by density-functional theory calculations the possibility to modify the magnetic properties at Co/Pt interfaces with chemical disorder. In these systems, we find a particular robustness of the DMI against intermixing. Upon dusting the interface with a third element (all 4d transition metals and B, Cu, Au, and Bi), a strong reduction of the DMI is predicted. This opens up possibilities to tune the DMI through the degrees of intermixing and dusting.

Stock structure of Atlantic spadefish Chaetodipterus faber from Southwest Atlantic Ocean inferred from otolith elemental and shape signatures

The Atlantic spadefish, Chaetodipterus faber, is an economically important species along the Southwest Atlantic Ocean, especially in the southeastern-south Brazil. Despite this, knowledge about stock structure is scarce and, at present, is no formal management strategy to ensure the long-term sustainability of the C. faber fishery in Brazil. In order to understand the stock structure of C. faber in the Southwest Atlantic, a total of 100 individuals ranging from 30 to 40 cm total length were collected from the five main fishery regions of Brazil [Espírito Santo (ES), Rio de Janeiro (RJ), São Paulo (SP), Paraná (PR), and Santa Catarina (SC)], between December 2015 and March 2016. The shape outline of each otolith was assessed using Elliptic Fourier descriptors (EFD). Multi-Elemental signatures (MES) of whole otoliths were obtained using inductively coupled plasma mass spectrometry. Data were analyzed through uni- and multivariate statistics. Canonical analysis of principal coordinates indicated that spatial differences were mainly driven by Sr/Ca ratios, Ba/Ca ratios and EFD 14. Combining data from both techniques (EFD and MES), the leave-one-out classification re-assigned individuals to their region of origin with an accuracy of 100% (ES), 85% (RJ), 80% (SP), 85% (PR), and 65% (SC). The hereby results indicate that the connectivity between the local population of C. faber in the ES region (20 °S) with the southern populations (>22 °S) is limited; moreover, data suggest the presence of spatially structured semi-discrete groups between 23 °S and 27 °S. Despite the possibility of intermixing C. faber populations in the Brazilian Southwest Atlantic coast, local populations should be regarded as different stocks for fisheries management purposes. However, at present, the degree of intermixing and the contribution that each local population receive from distant recruitment sources is unknown and demands further studies.

Investigation of Si/3C-SiC interface properties using classical molecular dynamics

Molecular dynamics simulations were carried out for different structural models of the Si/3C-SiC interface using the Tersoff SiC potential that can model both Si and SiC. We find that the bonding at the Si/3C-SiC interface has a strong effect on the crystallization of the Si phase and that a degree of intermixing is present between the two materials with some C atoms migrating from the 3C-SiC (hereinafter referred to as SiC) into the Si region. The degree of intermixing is likely to exhibit a strong dependence on the temperature and most likely also increases with time, which would lead to changes in the Si/SiC interface during the life of the Si/SiC composite. The inter-mixing also creates disorder and defects of threefold and fivefold bonded atoms in the vicinity of the interfaces. In particular, {111}12⟨110⟩ misfit dislocations were formed at all three types of interfaces [(100), (110), and (111)] in order to relieve the local stress due to lattice mismatch. Additionally, the Si(110)/SiC(110) and Si(111)/SiC(111) interfaces prepared at higher temperatures show the formation of the {111}16⟨112⟩ partial dislocation which arises due to intrinsic stacking faults. We find that the bonding at the crystalline(c) c-Si/SiC interface is weaker than that in bulk crystalline Si, whereas bonding at the amorphous(a)-Si/SiC interface is stronger than that in amorphous Si. Therefore, the rupture in the yield stress occurs at the vicinity of the Si/SiC interface and in the Si region for the a-Si/SiC systems, respectively. Finally, for both bulk and Si/SiC interface systems, a strong variation of the yield strength with temperature was observed.

Interface Intermixing in Type II InAs/GaInAsSb Quantum Wells Designed for Active Regions of Mid-Infrared-Emitting Interband Cascade Lasers.

The effect of interface intermixing in W-design GaSb/AlSb/InAs/Ga0.665In0.335AsxSb1 − x/InAs/AlSb/GaSb quantum wells (QWs) has been investigated by means of optical spectroscopy supported by structural data and by band structure calculations. The fundamental optical transition has been detected at room temperature through photoluminescence and photoreflectance measurements and appeared to be blueshifted with increasing As content of the GaInAsSb layer, in contrast to the energy-gap-driven shifts calculated for an ideally rectangular QW profile. The arsenic incorporation into the hole-confining layer affects the material and optical structure also altering the InAs/GaInAsSb interfaces and their degree of intermixing. Based on the analysis of cross-sectional transmission electron microscopy images and energy-dispersive X-ray spectroscopy, we could deduce the composition distribution across the QW layers and hence simulate more realistic confinement potential profiles. For such smoothed interfaces that indicate As-enhanced intermixing, the energy level calculations have been able to reproduce the experimentally obtained trend.

Thermally activated inter-dots carriers' transfer in InAs QDs with InGaAs underlying layer: Origin and dependence on the post-growth intermixing

This paper reports on experimental and theoretical investigation of atyical temperature-dependent photoluminescence properties of InAs quantum dots in close proximity to InGaAs strain-relief underlying quantum well. The impact of a post-growth intermixing process on these properties has been studied. For the as-grown sample, the maximum of the emission band follows a sigmoidal function while the photoluminescence linewidth mimics a V-shape function as the temperature increases, from 11 to 300 K. These behaviors are attributed to thermally activated carrier transfer mechanisms within the inhomogenious distribution of quantum dots. These atypical behaviors are found to disappear progressively with the degree of intermixing and consequent narrowing of the dot size dispersion. The experimental results have been interpreted in the frame of the localized states ensemble model revealing that the large dots size distribution is the main origin of the observed anomalies. Furthermore, the calculations show that the quantum well continuum states act as a transit channel for the redistribution of thermally activated carriers.

Preparation of high quality layered-layered composite Li2MnO3–LiMO2 (M = Ni, Mn, Co) Li-ion cathodes by a ball milling–annealing process

Cathode powders based on the layered-layered composite Li2MnO3–LiMO2 (M=Mn, Co, Ni) have been prepared by a ball milling and annealing process. In principle, this easily scalable and simple process allows for the variation of the stoichiometry, degree of intermixing, and crystallite size by varying the ratio of Li2MnO3 and LiMO2 parent compounds, milling time, and annealing time and temperature. The resultant cathode powder composition of Li1.2Mn0.54Ni0.13Co0.13O2 (M=Mn, Co, Ni) has been shown to have the same crystallographic and electrochemical features as those prepared by conventional sol–gel or co-precipitation methods, with specific discharge capacity of about 250mAhg−1 between 4.7 and 2V. Improvements in specific discharge capacity were demonstrated by the addition of an AlPO4 coating on the cathode powder following the mill-anneal synthesis method. In addition to providing a new means to vary the properties of this cathode system in a more controlled fashion, this synthesis approach also can be used to examine the hypothesis of electrochemical stabilization of the Li2MnO3 by the substitutional LiMO2 structural unit.

Effect of metal oxide nanostructures on the explosive property of metastable intermolecular composite particles

The fineness of reactants, degree of intermixing and interfacial contact area between fuel and oxidizer comprising of metastable intermolecular composite (MIC) particles are important factors to determine their overall kinetics of burning process. Here, we demonstrate a viable method for enhancing the explosive property of MICs by tailoring the nanostructures of oxidizer located in close proximity to fuel nanoparticles. The measured pressurization rate for a specific sample of solid Al nanoparticle (fuel)-porous CuO nanowire (oxidizer) MICs exploded in a closed vessel was found to be increased by a factor of ~ 10 compared with that for solid Al nanoparticle-solid CuO nanoparticle MICs. In addition, with the assistance of intensive sonication energy, the fabricated porous oxidizer nanowires were disintegrated into oxidizer nanoparticles, which considerably reduced the pressurization rate when they were ignited with fuel nanoparticles. This suggests that the morphology of oxidizer nanostructures from solid nanoparticles (i.e. 0-D) to porous nanowires (i.e. 1-D) play a key role in significantly changing the interfacial contact area with fuel nanoparticles so that nascent oxygen can be produced effectively for promoting the explosive property of the fuel nanoparticles.

Local thermal-mechanical analysis of ultrathin interfacially mixed poly(ethylene oxide)/poly(acrylic acid) layer-by-layer electrolyte assemblies

Ion conductivities of layer-by-layer (LBL) assemblies of solid thin film polyelectrolyte systems involving poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) were found to be a strong function of the number of bilayer stacks, n, with conductivities approaching 10 − 7 S/cm for n < 10, compared to 10 − 9 S/cm for n ≥ 10 and 10 − 10 S/cm for bulk PEO. Increased ion conductivity for low LBL stack numbers ( n < 10) originated to part from an effective suppression of the PEO crystallization via PEO/PAA blending, which could be inferred from local glass transition temperature measurements involving shear modulation force microscopy. Another phenomenon responsible for high conductivity in thin films was found in the in-plane phase heterogeneity of PEO and PAA. Increased ion conductivity for larger LBL stacks ( n ≥ 10) were attributed to low concentration autoblending caused by PEO-PAA hydrogen bonding, and an average layer thickness of noticeably less than 100 nm. The effect of interfacial constraints was evident in the degree of intermixing, addressed by a thin film extended Fox blend analysis, in the glass and melting transitions of PEO and PAA pure film components. While the glass transition value of PAA decreased by 55% to 46 °C for an 8 nm film, the melting transition for PEO decreased by 15% to 64 °C caused by surface tension effects.

Effects of intermixing on modulation p-doped quantum dot superluminescent light emitting diodes

Different capping of quantum dot (QD) materials is known to produce different degrees of intermixing during a post-growth thermal annealing process. We report a study of the effect of different degrees of intermixing on modulation beryllium doped quantum dot superluminescent light emitting diodes (QD-SLEDs). The intermixed QD-SLEDs show high device performance whilst achieving a large central emission wavelength shift of approximately 100nm compared to the as-grown device. The evolution of the emission spectra and power with drive current suggest a transition from QD-like to QW-like behavior with increasing degree of intermixing. A selective area intermixed QD-SLED is demonstrated, and with optimized differential intermixing, such structures should allow ultra-broadband sources to be realized.

Assessment feasibility of in-situ capping and contaminant mobility in NAPL-contaminated sediments

In-situ capping (ISC) has been successfully used in numerous sites to separate contaminants such as polycyclic aromatic hydrocarbons (PAHs) in the sediment from the overlying water. The effectiveness of ISC over extremely soft sediment contaminated with nonaqueous phase liquids (NAPLs), however, is less well understood. Such sediments exhibit low bearing capacity and may be subject to significant consolidation increasing the potential for NAPL and dissolved contaminant expression in water. A series of experiments were conducted on lagoon and surge pond sediments from a site in south Louisiana contaminated with varying degrees of NAPL to predict the ability to cap the sediments without sediment failure and with containment of the NAPL. The methodology employed may prove useful in other sediment capping projects. The results indicated that placement of a cap would result in intermixing in cap sediment interface, and penetration of NAPL and dissolved contaminants into the cap layer due to consolidation. Sediments with higher NAPL content (up to 30% NAPL) exhibited a greater degree of intermixing of sediment and cap materials and greater penetration of contaminants. High NAPL content sediments were also more likely to be resuspended by the act of capping leading to contamination of the cap layer. The study demonstrated that traditional sand capping technology is feasible to cap NAPL contaminated sediment but identified the nature and extent of problems to be expected when substantial NAPL is present.

Impurity-free disordering of InAs∕InP quantum dots

Impurity-free disordering (IFD) of the InAs quantum dots (QDs) capped with either an InP layer or an InGaAs∕InP bilayer is studied. The samples are coated with a SiO2 or TiO2 dielectric layer followed by rapid thermal annealing at 700, 750, 800, and 850°C for 30s. A large differential energy shift of 157meV is induced by SiO2 in the QDs capped with an InGaAs∕InP bilayer. Contrary to the reported results on the suppression of intermixing of GaAs based QDs by TiO2, the authors find that intermixing of InAs∕InP QDs is promoted by TiO2. X-ray photoelectron spectroscopy depth profiles show that both In and P outdiffuse to a TiO2 layer whereas Ga, In, and P outdiffuse to a SiO2 layer leading to different degrees of intermixing. The results indicate that a group V interstitial diffusion mechanism might be responsible for IFD of InAs∕InP QDs.

Understanding the inductively coupled argon plasma-enhanced quantum well intermixing

Recently, we have been developing an inductively coupled argon plasma-enhanced QWI technology for tuning the bandgap of InGaAs/InP QW laser structure. The application of ICP energy plays a strong role to the interdiffusion of point defects instead of the ion bombardment mechanism, resulting in high degree of intermixing. The effects of the plasma-induced defects, the factors that affect the QWI process and the general correlations of the plasma exposure effect to bandgap shift have been well understood with the analytical model. The theoretical results appear to be in good agreement with the experimental data of the intermixed samples. The model serves as a good simulation tool to explain the intermixing mechanism and further to optimize the intermixing process for the fabrication of the photonic integrated circuits.

Experimental and Theoretical Analysis of Argon Plasma-Enhanced Quantum-Well Intermixing

Plasma-enhanced quantum-well intermixing (QWI) has been developed for tuning the bandgap of InGaAs-InP material using an inductively coupled plasma system. The application of inductively coupled plasma enhances the interdiffusion of point defects resulting in a higher degree of intermixing. Based on a semi-empirical model of QW interdiffusion, the bandgap blue-shift with respect to the plasma exposure time and inductively coupled plasma energy has been analyzed. The theoretical results appear to be in good agreement with the experimental data of the intermixed samples. The model serves as a good simulation tool to explain the intermixing mechanism and further to optimize the intermixing process for the fabrication of the photonic integrated circuits.

Wavelength shift enhancement in quantum-well intermixed distributed-feedback lasers

The maximum possible shift in emission wavelength of a quantum-well (QW) intermixed distributed-feedback (DFB) laser as a function of degree of intermixing is studied. In a recent experiment, the wavelength shift of a QW intermixed DFB laser is around 13% of the bandgap blue shift. Our study indicates that if a smaller grating period is used, the wavelength shift can be increased by four times to 50% of the bandgap blue shift, because it is not necessary to change the carrier density significantly in order to maintain a modal gain above lasing threshold. The maximum tuning range is found to be 20 nm, indicating that QW intermixing can be used to fabricate multiwavelength DFB laser arrays for wavelength-division-multiplexing communication systems.

Atomic Resolution Imaging of Thin Film Interfaces

Abstract In recent years there has been a high degree of interest in multilayer film (MLF) structures because of their applications as magnetoresistive sensors and as memory elements in magnetoresistive random access memory arrays. As each of the layers in a spin-valve-based MLF structure1 is only a few nanometers in thickness, the morphology of the layers is crucial in controlling the magnetic and transport properties of the devices. In general, the microstructural features that can influence the film properties include layer roughness, layer composition, interfacial chemical mixing, grain size, grain boundary morphology, and crystallographic orientation, with the most important microstructural parameter being the nature of the interfaces between adjacent layers. With so many internal interfaces, each of which can have a different morphology and degree of intermixing, it is extremely difficult to determine the nature of each individual interface unless a technique is used that can analyze them independently, and with high spatial resolution.

Magnetostriction of free layer in top-type and bottom-type spin-valve films

We investigated magnetostriction of a free layer in top-type and bottom-type spin valves. The magnetostriction of the free layer in the top-type spin valve increased as the thickness of free layer decreased, which can be attributed to the increase in the surface magnetic anisotropy. However, the magnetostriction of the free layer in the bottom-type spin valve exhibited no significant change with decreasing thickness of free layer, and was smaller than that of in the top-type spin valve. This difference may come from the degree of intermixing at the interface of the free layer. We confirmed by X-ray photoelectron spectroscopy that intermixing between the spacer and free layer, Cu and CoFeB respectively, can be quite different for the top-type and the bottom-type spin valves, and that the magnetostriction can be influenced by the degree of intermixing. The magnetostriction tends to be small value when intermixing is significant, as we found in the bottom-type spin valve.

Structure and magnetic properties of Co/V multilayers

Two series of Co/V multilayers were sputtered respectively with higher(series I) and lower(series II) deposition rates. X-ray diffraction patterns show that series II has better structural quality. The saturation magnetization ( M s) and uniaxial perpendicular anisotropy constant ( K u) oscillate simultaneously with vanadium thickness and no interlayer coupling was observed in series I, while spin-wave resonance and weak interlayer coupling were observed in series II. We attribute the difference to different degree of intermixing and alloy formation in the multilayers.

Metal Sources and the Bronzes From Igbo-Ukwu, Nigeria

This paper reports on a brief survey of some old copper and lead workings along the Benue Rift in SE Nigeria. Samples of lead and copper ores collected from these were analyzed to determine their lead isotope ratios for comparison with lead isotope ratios obtained from the bronzes excavated at Igbo- Ukwu. At many of these locations small-scale workings are still in operation. The lead isotope ratios of a small selection of the bronzes suggest that there were two distinct sources of copper and lead used in antiquity but with a high degree of intermixing. The major copper and lead source has lead isotope values similar to those obtained from the copper and lead ores from the Abakaliki area of the Rift. These results support arguments previously advanced that the metal used to make the bronzes was local, thereby confirming their indigenous design and technology.