Anisotropic Deposition Research Articles

Efficient photocatalytic degradation of methylene blue via synergistic dual co-catalyst on SrTiO3@Al under visible light: Experimental and DFT study

BackgroundPhotocatalytic oxidation is a green method for water purification. However, the operation of traditional photocatalysts depends on exposure to UV radiation, which only forms a small portion of the spectrum comprising sunlight. The expansion of photocatalyst absorption to the visible range of light could greatly improve the efficiency and economic viability of the process. MethodsThe photocatalyst was prepared by first synthesising SrTiO3 nanoparticles by chemical precipitation followed by calcination. Then, SrTiO3 was doped with aluminium using a flux method with Al2O3 and SrCl2 at 1150 °C. Finally, the dual co-catalysts, Rh/Cr2O3 and CoOOH, were photodeposited onto SrTiO3@Al via sequential irradiation. Significant findingsThe Rh/Cr2O3/SrTiO3@Al/CoOOH nanocomposite degraded 87% of methylene blue (MB) (10 mg/L) under visible light in 1 h, a 3.3-fold improvement over pure SrTiO3 and 2.1-fold over a similar commercial composite. This enhancement is due to efficient charge separation resulting from Al doping and improved carrier transport as a result of the anisotropic deposition of the co-catalysts. Optimisation showed that 20 mg of photocatalyst in 50 mL of MB solution (5 mg/L) degraded 100% thereof within 45 min. DFT calculations showed uneven electron distribution in SrTiO3′s conduction band and structural changes with Al doping, further enhancing photocatalytic activity.

Anisotropic growth of Au-Ag heteronanostructures through plasmon-induced reduction.

Plasmonic heteronanostructures are promising building blocks for photofunctional materials and devices including photocatalysts, optical materials, and optoelectronic devices. In the present work, we fabricated Au-Ag bimetallic heteronanostructures based on site-selective and anisotropic Ag deposition and growth on Au nanocubes. Plasmonic Au nanocubes were adsorbed onto a glass plate, and the distal mode or proximal-distal mode of the nanocubes was selectively excited in the presence of Ag+ and citrate ions. Polycrystalline Ag was deposited around the top of the Au nanocubes by the distal mode excitation, and single crystalline Ag was grown laterally from the Au nanocubes by the proximal-distal mode excitation. The present method would be applied to the fabrication of various plasmonic nanostructures composed of two or more heterodomains.

(Invited) Whisker Growth during Adsorbate Suppressed Electrodeposition

Anisotropic electrochemical deposition and whisker growth is shown to be a consequence of operating a bistable active-passive critical system under galvanostatic control. Specifically, whisker growth is examined during galvanostatic Cu electrodeposition from an electrolyte containing suppressor additives. Disruption of the passivating polyether-halide bilayer triggered by metal deposition leads to positive feedback and highly localized deposition. On macroscale electrodes active-passive Turing patterns develop while on micrometer-sized electrodes the bifurcation is frustrated and proceeds as a single active zone reinforced by hemispherical transport fields. Extended electrodeposition leads to symmetry breaking and lateral propagation of a single whisker. An increasing fraction of the applied current supports expansion of the passive sidewall area and eventually results in termination of anisotropic deposition. The dynamic range between passive versus active growth determines the shape and extent of whisker formation. Similar critical behavior may account for reports of whisker growth in certain metal/metal ion battery systems.

Mechanisms of Anisotropic Particle Deposition: Prolate Spheroid Layers on Mica

Anisotropic particle deposition was investigated using the streaming potential method complemented with the atomic force microscopy (AFM) determination of the absolute particle coverage. The polymer particles were synthesized using the stretching procedure with consecutive oxidation of surface hydroxyl groups and coupling of polyethyleneimine. The bulk particle physicochemical properties were characterized by scanning electron microscopy (SEM), dynamic light scattering, and laser Doppler velocimetry. The particles were positively charged in the pH range of 3–10, exhibiting a prolate spheroid shape with an axis ratio of five. Thorough AFM and in situ optical microscopy measurements yielded the adsorption kinetics of particles under the diffusion-controlled regime. The experimental data were adequately interpreted in terms of the random sequential adsorption model with the surface blocking function derived from the scaled particle theory. The root-mean-square (rms) parameter of the layers for a broad range of particle coverage was also determined and interpreted using the topographical model developed in this work. The experiments were complemented by the measurements of the streaming potential of particle layers under various ionic strengths and pHs. The ζ (zeta)-potential data acquired in this way enabled to determine the universal hydrodynamic function describing the dependence of the streaming potential on the particle coverage. The function was used to express the ζ-potential of surfaces covered by particles in terms of substrate rms. It was argued that the acquired results, in addition to being significanct to basic science, can be exploited as useful reference systems for quantitative interpretation of bioparticle deposition on abiotic surfaces.

QCM-D Investigations of Anisotropic Particle Deposition Kinetics: Evidences of the Hydrodynamic Slip Mechanisms.

Deposition kinetics of positively charged polymer microparticles, characterized by prolate spheroid shape, at silica and gold sensors was investigated using the quartz microbalance (QCM) technique. Reference measurements were also performed for positively charged polymer particles of spherical shape and the same mass as the spheroids. Primarily, the frequency and bandwidth shifts for various overtones were measured as a function of time. It is shown that the ratio of these signals is close to unity for all overtones. These results were converted to the dependence of the frequency shift on the particle coverage, directly determined by atomic force microscopy and theoretically interpreted in terms of the hydrodynamic model. A quantitative agreement with experiments was attained considering particle slip relative to the ambient oscillating flow. In contrast, the theoretical results pertinent to the rigid contact model proved inadequate. The particle deposition kinetics derived from the QCM method was compared with theoretical modeling performed according to the random sequential adsorption approach. This allowed to assess the feasibility of the QCM technique to furnish proper deposition kinetics for anisotropic particles. It is argued that the hydrodynamic slip effect should be considered in the interpretation of QCM kinetic results acquired for bioparticles, especially viruses.

Seed surface doping-mediated seeded growth of Au–Ag Janus nanoparticles with tunable sizes and multiple plasmonic absorption modes

Gold–silver Janus nanoparticles with tunable sizes are successfully prepared, where the anisotropic deposition is induced by seed surface doping.

Atomically Conformal Metal Laminations on Plasmonic Nanocrystals for Efficient Catalysis.

Despite the enormous application potential, methods for conformal few-atomic-layer deposition on colloidal nanocrystals (NCs) are scarce. Similar to the process of lamination, we introduce a "confine and shine" strategy to homogeneously modify the different surface curvatures of plasmonic NCs with ultrathin conformal layers of diverse catalytic noble metals. This self-limited epitaxial skinlike metal growth harvests the localized surface plasmon resonance to induce reduction chemistry directly on the NC surface, confined inside hollow silica. This strategy avoids any kinetic anisotropic metal deposition. Unlike the conventional thick, anisotropic, and dendritic shells, which show severe nonradiative damping, the skinlike metal lamination preserves the key plasmonic properties of the core NCs. Consequently, the plasmonic-catalytic hybrid nanoreactors can carry out a variety of organic reactions with impressive rates.

Direct writing of colloidal suspensions onto inclined surfaces: Optimizing dispense volume for homogeneous structures

HypothesisA process to fabricate structures on inclined substrates has the potential to yield novel applications for colloidal-based structures. However, for conventional techniques, besides the coffee ring effect (CRE), anisotropic particle deposition along the inclination direction (IE) is expected to occur. We hypothesize that both effects can be inhibited by reducing the dispense volume during printing by direct writing. ExperimentsWe combined an additive manufacturing technique, namely direct writing, with colloidal assembly (AMCA) for an automated and localized drop-cast of polystyrene and silica suspensions onto inclined surfaces. Herein, we investigated the influence of the substrate tilting angle and the dispense volume on the printing of colloids and the resulting structures’ morphology. FindingsThe results demonstrate that a reduction in the dispense volume hinders the CRE and IE for both particles’ systems, even though the evaporation mode is different. For polystyrene, the droplets evaporated solely in stick-mode, enabling a “surface capturing effect”, while for silica, droplets evaporated in mixed stick–slip mode and a “confinement effect” was observed, which improved uniformity of the deposition. These findings were used to generate a model of the critical droplet radius needed to print homogeneous colloidal-based structures onto inclined substrates.

Multi-physics analysis of the galvanic corrosion of Mg-steel couple under the influence of time-dependent anisotropic deposition film

Abstract The anisotropic deposit film formed during the galvanic corrosion can impede the mass transfer of the involved species, thereby affecting the electro-chemical behavior and the evolution of galvanic corrosion. The limitations of experimental studies in the spatial-temporal scales restrict a deeper understanding of the corrosion mechanism, which can be complemented by numerical simulation. A multi-physics coupled model is proposed in this work to systematically investigate the temporal and spatial evolution of galvanic corrosion of the Mg-steel couple with the growing anisotropic deposition layer. By utilizing the multi-physics field coupled technique, various coupled physical-chemical processes underlying the corrosion behavior are built into the model, including chemical reactions, ionic mass transfer in the bulk solution and the deposition layer, interfacial reaction, deposition of corrosion products as well as the morphological transitions caused by metal dissolution and deposition. In particular, the anisotropic deposit film is considered to be a porous layer with a porosity varying in time and space as the corrosion evolves. The predicted corrosion morphology by this model is better than the previous models. The coupled relationship between the electrochemical behavior (e.g., electrode reaction kinetics, current density, surface potential) and the physical processes (e.g., ionic transport, geometric evolution of metal surface and film interface) is revealed. The results indicate that a porous deposition layer with a denser inner layer and a loose outer layer is generated, leading to more significant inhibition of mass transfer in the inner layer than the outer layer. The anisotropism of the deposition layer results in a non-uniform conductivity distribution and a discontinuous current density distribution in the electrolyte. The current density on the electrode surface is inhibited by the deposition layer and the variation in the cathode/anode area ratio during the corrosion process. The competition between the transport process and the electrochemical reaction determines the spatial-temporal evolution of the ion concentration.

An Investigation on the Settlement of Shallow Foundations Resting on Cross-Anisotropic Soil Deposits

Natural soil deposition process results in formation of anisotropic planes with different properties along different directions, and hence, such natural deposits possess inherent anisotropy. On the other hand, an estimate of the elastic settlement of surface foundations placed on such anisotropic deposits is very important. In this research, the effect of anisotropy (in fact, cross-anisotropy) on the elastic settlement of shallow foundations resting on anisotropic granular soils, often sands, has been investigated. The most important properties in this work, in addition to the geometry of the footing, are the soil modulus of elasticity, Poisson’s ratio and the ratio of these moduli along anisotropic planes in a cross-anisotropic medium. The governing equations of deformation in such media are first presented. Then, the elastic settlement of shallow foundations resting on such media has been estimated using the finite difference method, and then, some influence factors are presented. The factors are useful in estimating the elastic settlement of shallow foundations on cross-anisotropic soils, when the soil properties along two perpendicular directions are known. A series of design charts are provided in non-dimensional form so as to avail their practical use in a general form.

Assessment of apparent earth pressure for braced excavations in anisotropic clay

The evaluation of strut forces is critical to ensure the system stability of braced excavation in urban areas. The most common empirical approach to determine the forces in the struts is the empirical apparent pressure diagram (APD) method. Although the importance of soft clay anisotropy on the stability of excavation systems has been demonstrated by various researchers, there are only limited studies on the influence of anisotropy of soft clay on the forces in the struts. In this paper, extensive plane strain finite element studies have been carried out to analyze the strut forces and the apparent earth pressures for braced excavations in anisotropic clay deposits. The NGI-ADP soil constitutive model was adopted in the finite element analyses to assess the influence of various soil properties and wall stiffness properties on the strut forces. Based on the numerical results, modified design pressure envelopes which consider the anisotropic behavior of clays are proposed for flexible and stiff walls.

MODELING OF DISPLACEMENT PROCESSES IN HETEROGENEOUS ANISOTROPIC GAS RESERVOIRS

Nowadays there are important problems of increasing efficiency of development and exploitation of gas deposits. There are problems associated with the growth of gas production in heterogeneous anisotropic reservoirs, increasing gas recovery, achieving economic efficiency and so on. In this situation, there are popular methods of computer modeling of gas productive reservoirs, because they allow getting information of the structure and characteristics of the gas reservoir, the distribution parameters of permeability and other important factors in it. They also allow evaluating and calculating uncertainty arising from the lack of information about the gas reservoir properties outside the well. Currently there are many methods of computer modeling, allowing solving various practical problems. From another hand there are some problems related to the accuracy and adequacy of simulation of heterogeneous anisotropic permeable collector systems in real conditions of gas deposits exploitation. On the base of combined finite-element-difference method for solving the nonstationary anisotropic piezoconductivity Lebenson problem, with calculating of heterogeneous distribution of permeable characteristics of the gas reservoir, we carried out modeling of filtration processes between production and injection wells. The results of computer modeling show that intensity of the filtration process between production and injection wells depends essentially on their location both in a shifting-isotropic and anisotropic gas reservoir. Therefore, for the effective using of poorly permeable shifting-isotropic gas-bearing reservoirs, it is necessary to place production and injection wells along the main anisotropy axes of the gas-bearing layers. At the placing production and injection well systems in low-permeable anisotropic reservoirs of a gas field, the most effective exchange between them will take place when the direction of increased permeability of the reservoirs coincides with the direction of the location of the wells. Obviously, the best conditions for gas production processes in any practical case can be achieved due to optimal selection of all anisotropic filtration parameters of the gas reservoir. One can use obtained results for practical geophysical works with a purpose optimizing of gas production activity in low-permeable heterogeneous anisotropic reservoirs. Presented method for more detailed investigation of low-permeable heterogeneous anisotropic gas-bearing deposits can be used.

Study of thin layered reservoirs with toroidal sources and receivers (on the example of the Priobskoe oil field)

On the example of the Priobskoye oil field of the West Siberian oil and gas province, we show the relevance of studying thin-layered oil-saturated reservoirs, as well as consider the corresponding world experience. The operating principle of a probe system with toroidal sources and receivers is described, after which we perform 2D finite-difference simulation and analysis of its signals in typical geoelectric reservoir models. The dependence of the signals on the resistivity anisotropy coefficient is demonstrated. In realistic geoelectric sections of the Priobskoye field, obtained by numerical inversion of BKZ field data, 2D finite-difference simulation for the system with toroids is conducted. It implies the fundamental possibility of investigating thin-layered electrically anisotropic deposits of the Priobskoye field by means of the system with toroidal sources and receivers.

Random sequential adsorption of partially ordered discorectangles onto a continuous plane.

A computer simulation was used to study the random sequential adsorption of identical discorectangles onto a continuous plane. The problem was analyzed for a wide range of discorectangle aspect ratios (ɛ∈[1;100]). We studied the anisotropic deposition, i.e., the orientations of the deposited particles were uniformly distributed within some interval such that the particles were preferentially aligned along a given direction. The kinetics of the changes in the packing fraction found at different values of such the alignment are discussed. Partial ordering of the discorectangles significantly affected the packing fraction at the jamming state, φ_{j}, and shifted the cusps in the φ_{j}(ɛ) dependencies. The structure of the jammed state was analyzed using the adsorption of disks of different diameters into the porous space between the deposited discorectangles. The analysis of the connectivity between the discorectangles was performed assuming a core-shell structure of particles.

Van der Waals Epitaxy of Horizontally Orientated Bismuth Iodide/Silicon Heterostructure for Nonvolatile Resistive‐Switching Memory with Multistate Data Storage

AbstractThe film quality of insulators significantly affects performance of resistive random‐access memories (RRAMs), particularly in current leakage and degradation. In this study, a facile and practical method is employed to achieve the van der Waals epitaxy of bismuth iodide (BiI3) on silicon by using a self‐assembled monolayer of octadecyltrichlorosilane (OTS) as a buffer layer. The BiI3layer is compact and has high crystallinity, a pinhole‐free, and compact surface; every BiI3crystal is horizontally aligned with OTS–Si substrate. The RRAMs with the Si++/OTS/BiI3/Au structure exhibit excellent resistive switching properties with a very high on/off ratio of 109, long‐term stability for data retention, high endurance in write–erase cycles, and multistate information storage capacity. The crystal orientation, anisotropic carrier transport, morphology, deposition rate, and roughness considerably influence the resistive switching results. These are thoroughly investigated by analyzing the current–voltage characteristics at various temperatures, scanning electron microscope, atomic force microscope, X‐ray photoemission spectroscopy, and X‐ray diffraction patterns. It is proposed that the resistive switching mechanisms is caused by the iodine ion migration, which changes the valence charge of bismuth. This leaves a partially formed conductive metallic bismuth filament in the BiI3layer under the electrical field that enables multistate data storage.

Anisotropic Copper Electrodeposition on Microelectrodes

Copper electrodeposition is critical to electronics manufacturing, ranging across lengthscales from nanometer damascene plating to 100s of micrometers for through-silicon-vias in 3D interconnect packaging and even millimeter-scale in printed circuit board manufacturing. Essential to this process is formation of void-free copper structures in high aspect ratio cavities, which is achieved with various additives that enable superconformal or bottom-up electrodeposition. When the additive package consists of only a suppressor (polyether) and chloride, the superconformal phenomenon is driven by S-shaped negative-differential resistance (S-NDR), which promotes spatial bifurcation of the electrode surface into active and passive depositing regions. All S-NDR systems involve kinetic suppression, polyether-chloride adsorption in this case, and kinetic activation, potential-driven disruption of the polyether-chloride adlayer. The term S-NDR is derived from the s-shape the i-V curve expresses when cyclic voltammetry (CV) is post-experimentally corrected for ohmic resistance, resulting in a system that expresses a multiplicity of reaction rates (current) for a given driving force (potential).Electroanalytical measurements using microelectrodes (UMEs) offer an avenue for exploring S-NDR systems without significant iR-drop in solution. In other reaction systems, the reduced electrode dimension of UMEs has shown the ability to frustrate active-passive bifurcation, resulting in a homogeneously reacting electrode surface. Nonetheless, potential-controlled measurements such as cyclic voltammetry restrict S-NDR behavior from fully expressing itself, as the potential is the control parameter throughout the experiment. Current-controlled techniques, however, allow the thermodynamic state (i.e., potential) to dynamically shift as the polyether-chloride suppressing layer is formed and disrupted. In this work, current-controlled measurements in the form of linear galvanodynamic sweeps (GDS) are utilized to explore S-NDR behavior and electrode bifurcation during copper electrodeposition. GDS and CV measurements on UMEs are compared across a range of additive concentrations and polyether types. Influence of the operating mode on pattern formation is evaluated by in-situ optical microscopy on UMEs ranging from 10 μm to 25 μm in diameter. Spatial bifurcation during GDS measurements is further exploited to grow anisotropic copper deposits.

Percolation in irreversible deposition on a triangular lattice: effects of anisotropy

The percolation properties in anisotropic irreversible deposition of extended objects are studied by Monte Carlo simulations on a triangular lattice. Depositing objects of various shapes and sizes are made by directed self-avoiding walks on the lattice. Anisotropy is introduced by imposing unequal probabilities for placing the objects along different directions of the lattice. The degree of the anisotropy is characterized by the order parameter p determining the probability for deposition in the chosen (horizontal) direction. For each of the other two directions adsorption occurs with probability . It is found that the percolation threshold increases with the degree of anisotropy, having the maximum values for fully oriented objects. Percolation properties of the elongated shapes, such as k-mers, are more affected by the presence of anisotropy than the compact ones.Percolation in anisotropic deposition was also studied for a lattice with point-like defects. For elongated shapes a slight decrease of the percolation threshold with the impurity concentration d can be observed. However, for these shapes, significantly increases with the degree of anisotropy. In the case when depositing objects are triangles, results are qualitatively different. The percolation threshold decreases with d, but is not affected by the presence of anisotropy.

Design and development of a low-cost open-source 3D printer and its single response optimization using polylactic acid (PLA) material

Fused deposition modelling fabricates a 3D model from CAD data using a heated tip to extrude thermoplastic material onto a surface layer-by-layer. At present, there are number of commercial 3D printers available. Owing to the high cost, material restrictions and difficulty to study process parameters of commercial 3D printers, an open source 3D printer is designed and developed taking into consideration the cost analysis as well. Design of experiments (DOE) is used with an orthogonal array using three process parameters layer thickness, orientation Infill Orientation and temperature of extruder, to get tensile strength of the specimen. A standard specimen of ASTM D638 made up of PLA material is selected for analysis in 27 experiments where tensile testing is performed to calculate the tensile strength of each specimen. A probability distribution curve is drawn to ascertain the validity of the experiments where the results fall close to the mean value. Using the ANOVA approach and regression model a full quadratic equation is obtained and a graph is obtained which corroborates with the fact that although anisotropic deposition of material results in disparity of tensile strength, but the values fall within permissible limits. The results highlight that in case of PLA material as the layer thickness decreases, the tensile strength tends to increase. It is also to be noted that although layer thickness and orientation angle have been analysed extensively as process parameters compared to temperature the later within the selected range has shown certain inclination towards a typical value. The future scope is to analyse various other process parameters like raster width, raster angle, object orientation, feed rate, infill density, space filling, etc. to give a comprehensible outlook to the study of the process parameters in open source 3D printers using other polymers.

Seismic bearing capacity of shallow foundations rested on anisotropic deposits

ABSTRACT This paper investigated the effect of the anisotropy of the internal friction angle on the seismic bearing capacity factor of shallow foundations placed over a frictional soil deposit with the adoption of pseudo-static and pseudo-dynamic seismic loading approaches. The simplified Coulomb failure mechanism was assumed, and the method of analysis was limit equilibrium formulation. The results of the two approaches showed that the seismic bearing capacity factor decreases with increase in the degree of anisotropy and seismic accelerations. However, the pseudo-dynamic seismic loading approach was shown to return higher bearing capacity predictions for the footings rested over the anisotropic soil deposits in comparison to the pseudo-static approach. For the both approaches, the bearing capacity of the overlying shallow footing is lost after a certain base excitation. The results of this study were presented in charts and tabular forms and were compared well with findings of other researchers.

An estimate of the bearing capacity of shallow foundations on anisotropic soil by limit equilibrium and soft computing technique

ABSTRACTThe limit equilibrium method with a multi-block failure mechanism has been utilised to study and estimate the bearing capacity of shallow foundations on anisotropic deposits. The multi-block mechanisms of Hill and Prandtl types were adapted to consider the effect of the footing–soil interface roughness. Both mechanisms composed of passive and active wedges and multiple transitional blocks between them. As an anisotropic medium, the soil shear strength parameters were considered to entail a linear relationship with the bedding plane orientation. The dependency of the soil shear strength parameters to the depositional characteristics renders the problem to be highly nonlinear and hence, an iterative procedure was adopted to achieve a converged and optimal bearing capacity estimation. The optimisation was made by the Genetic Algorithm (GA) in an iterative process. Bearing capacity of isotropic soils was also calculated as a benchmark solution and then, extended to anisotropic soils. Some correction factors for three bearing capacity terms have been presented which cover a wide range of the anisotropy ratio. In general, the shear strength anisotropy proved to decrease the bearing capacity of a shallow foundation. The results were compared with some experimental and numerical results.