Pillar Length Research Articles

Pillared lanthanide metal organic frameworks with sinusoidal channels formed from bent mixed-donor phenanthroline based ligands of different length.

Five new lanthanide MOFs were prepared by solvothermal synthesis to investigate the effect of ligand and pillar length using the unsymmetrical mixed-donor ligands L1H (4'-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-[1,1'-biphenyl]-3-carboxylic acid) and L2H (3-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)benzoic acid)...

Photolithographic Structuring of Ordered Silicon Micropillar Electrodes for Lithium-Ion Batteries and Electrochemical Performance

Ordered and vertically oriented silicon (Si) micropillar structures, when optimally designed, can accommodate the lithiation-induced volumetric expansion that is limiting the implementation of Si as negative electrodes in Li-ion batteries. As there is not much work in this area, this study is focused on evaluating systematically the potential of Si micropillar electrodes prepared by photolithographic structuring of Si. The specific objective is to determine the effect of micropillar length and the free space around the pillars on the electrochemical performance of the electrode. The Si micropillar electrode with the pillar length of 14 μm showed a high specific capacity (2600 mAh/g) and a high areal capacity (3 mAh/cm2), which were stable for over 100 cycles. However, there was significant capacity degradation in 32 and 48 μm-long Si pillar electrodes due to cracking and electrode damage during cycling. In the 32 μm Si micropillar electrode, a small change in porosity from 69 to 86% caused a substantial increase in specific capacity from 1400 to 2000 mAh/g over 100 cycles, with the areal capacity decreasing from 3 to 2 mAh/cm2. The findings also show the directions for further work for the optimization of Si micropillar electrodes.

Decoupling Method for the Convective-Dominated Leaching Process of Ion-Adsorption-Type Rare-Earth Ores

Ion-adsorption-type rare-earth ores (IATREOs) that have experienced granite weathering have good permeability, and their leaching process involves the solute transport problem, which is dominated by convection. Because of the oscillation and dispersion errors of existing numerical methods for solving the convective-dominated solute transport equation, the results have low precision in the twin leaching process. In this paper, the convection–dispersion equation is decoupled into the dispersion equation, the convection equation, and the source-sink equation; the Crank–Nicolson and implicit difference methods are used to solve the dispersion equation and the source-sink equation, respectively. The solution of the convection equation is achieved on the basis of its physical interpretation. Therefore, a decoupling method for the convective-dominated solute transport equation is established. In comparison to the two examples with analytical solutions, the calculation errors of the method established in this paper are less than 2.00%, and it can solve the oscillation and dispersion problems. The rationality of the method is further demonstrated through the column leaching experiment of IATREOs. In comparison to the test results, the coefficients of determination of the breakthrough curves of rare-earth ions and ammonium ions calculated by the proposed method are all greater than 0.850, and the peak concentration error of rare-earth ions is less than 7.00%. This indicates that the proposed method can simulate the leaching process well. Furthermore, by combining the multiple/half method and the dichotomy method, an optimization method for determining the leaching agent amount was established to analyze the relationship between the leaching agent and the ratio of dispersion to pillar length. The results can provide a solution that can be used to mine IATREOs from experience to theory.

Modeling the effect of chirality on thermal transport in a pillared-graphene structure.

The anisotropic heat transport in graphene-CNT based materials provoked the development of three-dimensional pillared-graphene (PG) systems. In this study, we performed non-equilibrium molecular dynamics simulations to analyze PG thermal conductivity and thermal boundary conductance. For the first time, we have considered the influence of pillar chirality and the temperature effect on PG heat transport. We analyzed the influence of pillar chirality and pillar length on the in- and out-of-plane transport properties. For the temperature-dependent analysis, the chosen temperatures were in the range of 100 K to 500 K. To elucidate the mechanism underlying the heat transport, we investigated the phonon density of states (DOS) in the different regions of PG systems. The overlap factor was calculated to quantify the mismatch in the phonon DOS profiles. Across the pillar region, the overlap factor correlates directly with the thermal boundary conductance. When heat is transported in an out-of-plane direction, the zig-zag PG system performs better than the armchair PG system. The atomic arrangement at the graphene-CNT interface plays an inevitable role in limiting heat transport in PG systems. The calculated phonon energy in the zig-zag PG interface is higher than that in the armchair PG interface.

Stability evaluation of room-and-pillar rock salt mines by using a flat jack technique - A case study

Room-and-pillar mining is commonly employed for the extraction of rock salt in underground mines. Pillar stress is a major concern in these mines as it is directly related to stability and mineral recovery. In this study a flat jack method was used to measure pillar stresses in three underground rock salt mines in Pakistan. The field work included determination of in-situ stress, in-situ elastic modulus, recording of field variables (pillar length and width, height and width of opening, opening width to height ratio, extraction ratio, and overburden height) and collection of salt block samples. The geomechanical properties of rock salt (uniaxial compressive strength, Young's modulus, Brazilian tensile strength, and density) were also determined to estimate overburden stress, pillar strength, and factor of safety (both estimated and actual). It was found that the measured pillar stresses are proportional to the overburden stress values, with their magnitude ranging from 6.05 MPa to 11.97 Mpa, and the pillars were found to be stable. Regression analysis was performed to develop statistical models for in-situ stress and in-situ elastic modulus. Finally a quick guideline chart was developed to determine the suitable length of pillar for a given span and required level of safety. Keywords: flat jack, room-and-pillar mining, in-situ stress, factor of safety, regression analysis.

Ultrawide attenuation bands in gradient metabeams with acoustic black hole pillars

In this letter, it is suggested to attach acoustic black holes (ABHs) on a base beam with gradient parameters for wave attenuation in ultrawide bands. Three types of metabeams have been designed and compared. Analysis of the complex dispersion curves obtained by the wave and Rayleigh–Ritz method indicates that modifying the pillar length may cause some failure bands, which can be circumvented by changing the lattice constant. The forced vibrations of finite beams are recovered using the nullspace method, which has confirmed the merits of the metabeam with gradient lattice constant. This paper enriched the application range of ABHs.

Multiscale finite element simulation of mechanical properties of pillared graphene sheet reinforced composites

This article presents a detailed study of the elastic properties of pillared graphene sheet (PGS) reinforced composites. Modeling of several different composite structures using the numerical simulation software ABAQUS. The effects of carbon nanotube pillar distance (PD), pillar length (PL), CNT inclination angle, the volume fraction of PGS and the number of carbon nanotubes per layer in the PGS on the elastic properties of the reinforced composites are analyzed. The simulation results show that as the volume fraction of PGS increases, the Young's modulus E and shear modulus G of the reinforced composites also increase accordingly. The results also illustrate that the Young's modulus E and shear modulus G of the composites decrease as the tilt angle of the CNTs become larger, but increase with the content of CNTs per layer in the PGS. In addition, the PD and PL of CNTs also influence the elastic properties of the composites.

THE DEVELOPMENT OF NEW CONSTRUCTION METHODS ABOUT SHAKE PREVENTION DUCT STRUCTURES

Experimental studies are carried out on the newly devised method of shake-proof ducts with earthquake resistance, and it is verified whether the method will satisfy the allowable values of the construction guidelines in Japan. Based on the results, the aim is to improve the workability of the new method. The jig was installed on two shake prevention duct structures, fixed, and loaded horizontally. The vertical load was approximately 1kN assuming an actual duct, and the horizontal load was 4.9kN according to the construction guidelines. The interlaminar deformation angle and deflection angle was measured to determine if the allowable values are met. The construction methods about shake prevention duct structures was to install two pillars and connect the duct ring to the pillar with a plate. Bolts ware used to connect the duct ring to the plate and the pillar to the plate. Nine different tests conducted with parameters such as pillar height and cross-sectional standard. For a pillar length of 1500 mm, the allowable value in the Japanese construction guidelines was met, but for a pillar length of 2000 mm or more, it was difficult to meet the allowable horizontal displacement. However, it was possible to meet the allowable value by increasing the pillar cross section, increasing the bolts connecting the pillar to the plate, and reinforcing the base of a pillars.

THE DEVELOPMENT OF NEW CONSTRUCTION METHODS ABOUT SHAKE PREVENTION DUCT STRUCTURES

Experimental studies are carried out on the newly devised method of shake-proof ducts with earthquake resistance, and it is verified whether the method will satisfy the allowable values of the construction guidelines in Japan. Based on the results, the aim is to improve the workability of the new method. The jig was installed on two shake prevention duct structures, fixed, and loaded horizontally. The vertical load was approximately 1kN assuming an actual duct, and the horizontal load was 4.9kN according to the construction guidelines. The interlaminar deformation angle and deflection angle was measured to determine if the allowable values are met. The construction methods about shake prevention duct structures was to install two pillars and connect the duct ring to the pillar with a plate. Bolts ware used to connect the duct ring to the plate and the pillar to the plate. Nine different tests conducted with parameters such as pillar height and cross-sectional standard. For a pillar length of 1500 mm, the allowable value in the Japanese construction guidelines was met, but for a pillar length of 2000 mm or more, it was difficult to meet the allowable horizontal displacement. However, it was possible to meet the allowable value by increasing the pillar cross section, increasing the bolts connecting the pillar to the plate, and reinforcing the base of a pillars.

Stability of inner dump slope under coal pillar support: case study in an open-pit coal mine

The stability of an inner dump slope was investigated under the effect of coal pillar support considering the development position of dumping. Based on the instability mechanism and load distribution characteristics of the supporting coal pillar, the three-dimensional mechanical effects of the supporting coal pillar are characterized. Using the two-dimensional equivalent principle and the residual thrust method, the stability of the inner dump slope was analyzed under the effect of pillar support at different dump development positions. The quantitative effects of various factors on the inner dump slope stability were revealed, and the coal pillar shape parameters were optimized through numerical simulations. The results indicate that the slope stability coefficient is linearly related to the top width and height of the coal pillar, slope angle, and base inclination angle, and has an exponential relation with the coal pillar strike length and slope height increment. There are quadratic and absolute value relations with the coal pillar outer and the inner bottom angle, respectively. The top width of the coal pillar in the inner dump of Shengli East No.2 open-pit coal mine should be at a level of + 824 m, and the optimal top width and height are 15 and 36.7 m, respectively. The instability mechanism of the supporting and retaining coal pillar obtained by numerical simulations and the stability of the inner dump are in good agreement with the theoretical analysis. Our results provide a theoretical basis for the design, treatment, and safe implementation of similar open-pit mine slope engineering.

Electrochemical additive manufacturing of graded NiCoFeCu structures for electromagnetic applications

This study introduces the concept of compositionally-graded electrochemical additive manufacturing of advanced metal alloys. The feasibility was demonstrated using a NiCoFeCu system for electromagnetic applications. The effects of grading frequency and voltage on output geometry and elemental composition were studied. Application of constant signals throughout pillar build yielded varying width and elemental composition along the pillar length. Additional grading of voltage from low to high favoured wider pillars and enhanced copper content. Auxiliary plating effects were used to explain compositional deviations from conventional electroplating. Frequency response varied with voltage, suggesting its use as a secondary, fine-tuned parameter.

A Study on Optimization of Planar Gate Type Metal-Oxide-Semiconductor Field-Effect-Transistors Multi Epitaxial Process in Super-Junction Structure

Power metal-oxide-semiconductor field-effect-transistors (MOSFET) is a high voltage control device that requires high reliability and efficiency and is used to improve efficiency in areas such as renewable energy generators, electric vehicles, power supply unit, converters and motor control. Electrical characteristics of the MOSFET include a Threshold voltage which is a voltage for operating the device, an On-resistance which is a device resistance in an on-state, and a breakdown voltage which means a device withstand voltage. A Super-Junction structure is proposed to design the device with a high breakdown voltage and a low on-resistance. A multi-epitaxial Super-Junction MOSFET forms a Pillar layers by injecting continuously P-type impurity at edge on stacked N-Pillar layer. By forming the Pillar region which is higher doping concentration than N-drift, the on resistance can be reduced. In the forward blocking mode, the depletion layer of the Pillar region is extended to both vertical and horizontal sides, for a high breakdown voltage can be obtained. By using a T-CAD tool which is a process simulator, electrical characteristics of 1,200 V class super-junction MOSFET are analyzed along process variables (pillar lateral length, pillar concentration). When the breakdown voltage of the super junction MOSFET and the Planar MOSFET are equal, On-resistance (based on 10 A) has a gain of approximately 20% by a difference of 0.189 ohm×cm. It is believed that this can contribute to the development of super junction MOSFET with improved reliability and electrical characteristics.

Determining the critical blasting load of cracked strip bauxite pillars

Cracked pillars have limited capabilities for the bearing of dynamic and static loads, consequently threatening the stability of entire goafs. In the current study, we establish a structural mechanical model for cracked strip pillars and determine a mathematical formula for the total energy based on an underground bauxite mine in Shanxi, China. Furthermore, the instability criterion is employed to derive an analytical method for the estimation of the critical blasting load qcr for cracked strip bauxite pillars. The relationship between qcr and pillar height (H), pillar width (b), pillar length (L), and the crack loosen zone width (d) is quantitatively evaluated. Results demonstrate that when L and d are constant, qcr decreases as H increases. Moreover, qcr is observed to increase with b for constant H and d, with a continuous reduction in curvature fluctuations. Although qcr increases with L for fixed H and b, the increase amplitude is small, indicating the limited influence of L. For constant L and b, qcr decreases as d increases, and when the value of d exceeds that of the inflection point, the rate of change is steeper. The proposed analytical method is validated using numerical results and a case study. Our work provides theoretical support for the safe production of bauxite mining.

Analytical Design and Experimental Verification of Lateral Superjunction Based on Global Region Normalization Method

The global region normalization (GRN) method is proposed to optimize the lateral superjunction (SJ), in this article. The GRN features normalizations in the global doping range of the SJ from zero to the maximum doping concentration N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> that was theoretically determined by the pillar width W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SJ</sub> . Then the optimization covers all the possible design points of the SJ. For the SJ with given W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SJ</sub> and pillar length L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SJ</sub> , the specific ON-resistance R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on,sp</sub> and breakdown voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> are normalized in the global region of the doping concentration N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SJ</sub> . With the GRN method, the global normalization function f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">η</sub> is deduced to reflect the quantitative variation trend of R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on,sp</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> and a design formula of the optimized N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SJ</sub> is presented. Furthermore, lateral SJ devices were fabricated according to the formula. The measured R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on,sp</sub> values of the SJ devices are reduced by almost 35% when compared with the theoretical limit of the triple RESURF device in a voltage range of 100-400 V. The experiments also reveal that the measured net R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on,sp</sub> of the SJ region approaches the R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on.sp</sub> ∝ V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.03</sup> relationship.

Quick Design of a Superjunction Considering Charge Imbalance Due to Process Variations

The breakdown voltage, ${V}_{{\text {BR}}}$ , of a superjunction whose pillar parameters, namely doping, length, and width, are optimized to yield the least specific ON-resistance, ${R}_{{\text {ONSP}}}$ , for the specified ${V}_{{\text {BR}}}$ , falls drastically for even small charge imbalances. Hence, a structure fabricated with these target parameter values often has a ${V} _{{\text {BR}}}$ much lower than specified due to the charge imbalance caused by random process variations. We give an analytical solution for alternate target parameter values which yield the specified ${V}_{{\text {BR}}}$ in spite of process variations, with minimum sacrifice in ${R} _{{\text {ONSP}}}$ . The solution is obtained by the method of Lagrange multipliers and a simple equation for the breakdown field versus charge imbalance. It is validated by TCAD simulation. It can either be approximated to a closed-form or can yield the target parameter values accurately with just a few iterations. Apart from eliminating the tedious iterations of prior design methods, our solution provides two new insights: when compared with an optimum balanced device, a device optimized considering typical charge imbalance has significantly lower pillar doping but almost the same pillar length and width; the breakdown field of a balanced device is a power law function of the pillar length alone. Although illustrated for 4H-SiC structures with ${V}_{{\text {BR,target}}}$ of 1–10 kV, our solution should work for any semiconductor after material specific changes.

From Geometry to Activity: A Quantitative Analysis of WO3/Si Micropillar Arrays for Photoelectrochemical Water Splitting

AbstractThe photoelectrochemical (PEC) activity of microstructured electrodes remains low despite the highly enlarged surface area and enhanced light harvesting. To obtain a deeper understanding of the effect of 3D geometry on the PEC performance, well‐defined WO3/n‐Si and WO3/pn‐Si micropillar arrays are fabricated and subjected to a quantitative analysis of the relationship between the geometry of the micropillars (length, pitch) and their PEC activity. For WO3/n‐Si micropillars, it is found that the photocurrent increases for WO3/n‐Si pillars, but not in proportion to the increase in surface area that results from increased pillar length or reduced pillar pitch. Optical simulations show that a reduced pillar pitch results in areas of low light intensity due to a shadowing effect. For WO3/pn‐Si micropillar photoelectrodes, the p–n junction enhances the photocurrent density up to a factor of 4 at low applied bias potential (0.8 V vs RHE) compared to the WO3/n‐Si. However, the enhancement in photocurrent density increases first and then decreases with reduced pillar pitch, which scales with the photovoltage generated by the p–n junction. This is related to an increased dead layer of the p–n junction Si surface, which results in a decreased photovoltage even though the total surface area increases.

Synergistic Effect of 3D Current Collectors and ALD Surface Modification for High Coulombic Efficiency Lithium Metal Anodes

Improving the performance of Li metal anodes is a critical bottleneck to enable next‐generation battery systems beyond Li‐ion. However, stability issues originating from undesirable electrode/electrolyte interactions and Li dendrite formation have impaired long‐term cycling of Li metal anodes. In this work, we have developed a bottom‐up fabrication process of vertically aligned and highly uniform Cu pillar arrays on a Cu foil via templated electrodeposition for use as a 3D current collector.[1] By rationally controlling geometric parameters of the 3D current collector architecture, including pillar diameter, spacing, and length, we have demonstrated the morphology of Li plating/stripping upon cycling can be controlled and optimal cycling performance can be achieved. In addition, we showed that deposition of an ultrathin layer of ZnO by atomic layer deposition on the current collector surface can facilitate the initial Li nucleation, which dictates the morphology and reversibility of subsequent cycling. This core–shell pillar architecture allows for the effects of geometry and surface chemistry to be decoupled and individually controlled to optimize the electrode performance in a synergistic manner. Using this model platform, we have demonstrated Li metal anodes with Coulombic efficiency up to 99.5% at 0.5 mA/cm2 and 99.4% at 1 mA/cm2, which are among the highest reported values to date. The results gained from this work can thus provide a pathway toward high‐efficiency and long‐cycle life Li metal batteries with reduced excess Li loading. [1] K.-H. Chen, A.J. Sanchez, E. Kazyak, A.L. Davis, N.P. Dasgupta, Adv. Energy Mater. 9, 1802534 (2019).

Growth of Polystyrene Pillars in Electric Field.

Surface patterning on polymer films, which is a self-assembly process under the action of external and/or internal impetus, has a variety of applications, including drug delivery and flexible electronics. In this work, we study the growth of polystyrene pillars in the electric field for different combinations of annealing temperature, film thickness, and electrode separation (electric field intensity). There are five stages for the growth of the polystyrene pillars for all the configurations used in this work, including a nucleation stage, a linear growth stage, an acceleration stage in the pillar length prior to the contact between the top surface of a pillar and the upper electrode, a radial growth stage after the contact, and a stationary stage without further growth of the pillar. In the linear growth stage, there exist linear relationships between the pillar length and the annealing time and between the square of the pillar diameter and the annealing time. The activation energies for the rate processes controlling the radial growth and the length growth in the linear growth stage are 30.2 and 25.3 kJ/mol, respectively. There are two rate processes controlling the radial growth of the pillars: one is the field-induced flow of polymer through the polymer film to the roots of pillars and the other is the coalescence of pillars. The activation energy for the coalescence is 16.5 kJ/mol. The results obtained in this work offer a practical route to control the geometrical dimensions of polymer pillars through the processing parameters.

Synergistic Effect of 3D Current Collectors and ALD Surface Modification for High Coulombic Efficiency Lithium Metal Anodes

AbstractImproving the performance of Li metal anodes is a critical bottleneck to enable next‐generation battery systems beyond Li‐ion. However, stability issues originating from undesirable electrode/electrolyte interactions and Li dendrite formation have impaired long‐term cycling of Li metal anodes. Herein, a bottom‐up fabrication process is demonstrated for a current collector for Li metal electrodeposition and dissolution composed of highly uniform vertically aligned Cu pillars. By rationally controlling geometric parameters of the 3D current collector architecture, including pillar diameter, spacing, and length, the morphology of Li plating/stripping upon cycling can be controlled and optimal cycling performance can be achieved. In addition, it is demonstrated that deposition of an ultrathin layer of ZnO by atomic layer deposition on the current collector surface can facilitate the initial Li nucleation, which dictates the morphology and reversibility of subsequent cycling. This core–shell pillar architecture allows for the effects of geometry and surface chemistry to be decoupled and individually controlled to optimize the electrode performance in a synergistic manner. Using this platform, Li metal anodes are demonstrated with Coulombic efficiency up to 99.5%, providing a pathway toward high‐efficiency and long‐cycle life Li metal batteries with reduced excess Li loading.

Optimized single-crystal diamond scanning probes for high sensitivity magnetometry

The negatively-charged nitrogen-vacancy center (NV) in diamond forms a versatile system for quantum sensing applications. Combining the advantageous properties of this atomic-sized defect with scanning probe techniques such as atomic force microscopy (AFM) enables nanoscale imaging of e.g. magnetic fields. To form a scanning probe device, we place single NVs shallowly (i.e. < 20 nm) below the top facet of a diamond nanopillar, which is located on a thin diamond platform of typically below 1 μm thickness. This device can be attached to an AFM head, forming an excellent scanning probe tip. Furthermore, it simultaneously influences the collectible photoluminescence (PL) rate of the NV located inside. Especially sensing protocols using continuous optically-detected magnetic resonance benefit from an enhanced collectible PL rate, improving the achievable sensitivity. This work presents a comprehensive set of simulations to quantify the influence of the device geometry on the collectible PL rate for individual NVs. Besides geometric parameters (e.g. pillar length, diameter and platform thickness), we also focus on fabrication uncertainties such as the exact position of the NV or the taper geometry of the pillar introduced by imperfect etching. As a last step, we use these individual results to optimize our current device geometry, yielding a realistic gain in collectible PL rate by a factor of 13 compared to bulk diamond and 1.8 compared to our unoptimized devices.