Pillar Shape Research Articles

Deep depth profiling using gas cluster secondary ion mass spectrometry: Micrometer topography development and effects on depth resolution.

Secondary ion mass spectrometry using the argon cluster primary ion beam enables molecular compositional depth profiling of organic thin films with minimal loss of chemical information or changes in sputter rate. However, for depth profiles of thicker organic films (> 10 μm of sputtered depth) we have observed the rapid formation of micron-scale topography in the shape of pillars that significantly affect both the linearity of the sputter yield and depth resolution. To minimize distortions in the 3D reconstruction of the sample due to this topography, a step-wise, staggered sample rotation was employed. By using polymer spheres embedded in an organic film, it was possible to measure the depth resolution at the film-sphere interface as a function of sputtered depth and observe when possible distortions in the 3D image occurred. In this way, it was possible to quantitatively measure the effect of micron-scale topography and sample rotation on the quality of the depth profile.

Effect of the functional group of polyethylene glycol on the characteristics of copper pillars obtained by electroplating

Five polyethylene glycol (PEG)-based compounds with varying terminal functional groups were investigated as suppressors to investigate the effect of different terminal functional groups on the ability of PEG-based suppressors to inhibit Cu pillar electroplating. The inhibition ability of the suppressors increased with increasing steric hindrance of the aromatic functional group and length of the alkyl group. PEG-based compounds bearing terminal functional groups with large steric hindrances significantly impeded the diffusion of electroplating accelerator, thus enhancing the inhibitory effect. When the molecular weight of PEG was less than 1000, possessing a terminal functional group had a greater effect on the inhibitory ability than increasing the molecular weight. The wetting ability of the electrolyte increased as the inhibitory ability of the suppressor increased. The significant steric effect of PEG p-(1,1,3,3-tetramethyl butyl)-phenyl ether was confirmed, which contributed to the convex shape of the Cu pillars and the growth of small-sized Cu grains. Conversely, the interaction between PEG and Cu electrode surface was weak. Thus, flat-top Cu pillars were obtained when PEG was used as the suppressor.

Numerical modeling of time-dependent spalling of rock pillars

Time-dependent deformation of brittle rock pillars is investigated using laboratory-scale pillar models using the grain-based time-to-failure model (GBM-TtoF). First, time-dependent deformations of rock pillars are analyzed and the results are compared qualitatively with field observations. Second, the influence of the boundary profile of pillar walls on time-dependent strength and deformation of rock pillars is investigated. Two factors, pillar shape and loading ratio, which influence the time-dependent strength and deformation of rock pillars, are studied by conducting a series of creep simulations using four pillar models with width to height ratios of W/H = 0.5, 1.0, 1.5 and 2.0. Finally, long-term strengths and deformation features of slender and squat pillars are analyzed. It is found that time-dependent strengths and deformation of rock pillars can be simulated using the GBM-TtoF creep model properly. Gradual spalling on the pillar walls can be captured using pillar models with rough boundary profiles. Creep deformations of slender and squat pillars could be quite different. Slender pillars are more likely to fail as time passes but squat pillars can tolerate more spalling on the walls without losing their stability. It is demonstrated that the GBM-TtoF creep model can simulate time-dependent strength and deformation of hard rock pillars well under creep loading conditions.

Evaluating the effects of pillar shape and gallium ion beam damage on the mechanical properties of single crystal aluminum nanopillars

In situ TEM nanopillar compression experiments are widely used to study the mechanical behavior of nanoscale materials. Often, the pillars are fabricated using gallium-focused ion beam (FIB) milling from a bulk sample. During the FIB process, the choice of the pillar shape and the energy of the Ga ions can significantly impact the mechanical performance of samples with electron-transparent dimensions. Here, we systematically explore the effects of various pillar fabrication parameters in a single crystal aluminum (Al) system with a well-controlled crystal orientation. A novel method is proposed to fabricate square pillars to minimize FIB artifacts such as tapering, high pillar base compliance, and preferential deformation at the pillar tip. These square pillars enable more uniform deformation and accurate measurement of the engineering strain. Lastly, we show an intriguing in situ TEM laser irradiation experiment, which has enabled direct visualization of the surface oxide layer in FIB-fabricated Al pillars.

Development of high frequency piezocomposite with hexagonal pillars via cold ablation process

This paper reports on the fabrication of 1–3 piezocomposite with hexagonal pillars for high frequency ultrasonic transducer based on the cold ablation technique. The piezocomposite with hexagonal pillars was designed, simulated, and fabricated using an ultraviolet picosecond laser. It performs better than the piezocomposite with other pillar shapes like square. The edge length and height of the hexagonal PZT pillar were 10 μm and 36 μm, the width of the kerf was about 5 μm. The 1–3 piezocomposite with a resonance frequency of 51.2 MHz and a coupling coefficient of 0.69 was fabricated. The transducer with fabricated 1–3 piezocomposite was prototyped and characterized. Compared to the conventional dice-and-fill technique, the cola ablation process allows for the manufacturing of 1–3 piezocomposites with higher variability of pillar design and distribution as well as smaller structural size. It suggests that the cold ablation process proves to be suitable for the fabrication of high frequency composite and transducers.

Effect of pillared surfaces with different shape parameters on droplet wettability via Lattice Boltzmann method

In this study, to explore the influences of different pillar shape parameters on the wettability of a water droplet, a two-dimensional pseudopotential model at a large density ratio was established to predict the wettability of a pillared wall microstructure via lattice Boltzmann method. The improved force term and tunable surface tension term were implemented in the model. The formation of vortex was studied during droplet contacts the surface. The influences of different pillar heights, widths, and spacings on the wettability and wettability conversion of droplets were investigated. The results reveal that the vortexes will be generated during droplet contacts the surface. The pillars can hold up droplets, thereby greatly increasing the droplet contact angle. With the increase of the pillar height, the droplet gradually shifts from filling the convex gap to being held up by the air in the gap. The pillar width mainly determines contact angle. Moreover, the contact angle decreases with the increase of the pillar spacing. However, when the pillar spacing is large enough, the droplet can enter the gap closest to the droplet. As roughness increases, the water droplet is converted from Wenzel state to Cassie state.

Tailoring MOF-derived porous carbon nanorods confined red phosphorous for superior potassium-ion storage

Abstract The metal-organic framework Zn-MOF-74, which has abundant oxygen-containing groups and Zn elements as pore creators during pyrolysis, can be an ideal precursor for a porous carbon matrix in battery electrodes, but its irregular morphology at the micron size is unfavorable. Here we demonstrate the facile solvothermal synthesis of uniform Zn-MOF-74 hexagonal nano/microrods (ZRods) with an accurate diameter modulation from tens of nanometers to micron size through varying the H2O content in the mixed solvent. An inverted volcano relationship between the ZRod diameters and H2O contents is presented. CH3COO- is identified to be critical to the hexagonal pillar shape formation, while a competitive reaction of protons dissociated from H2O is responsible for the size modulation. After calcination, the obtained porous carbon nanorods enable a high loading capacity and perfect encapsulation of P while reserving free spaces to accommodate the volume change of P in the composite anode, resulting in outstanding potassium storage performance in terms of remarkable initial Coulombic efficiency (78.5%), top-ranking reversible capacity (up to 595.8 mAh g-1), superior rate capability (187.5 mAh g-1 at 5 A g-1), and robust long-term cycling stability (retaining 150.7 mAh g-1 at 2.5 A g-1 after 400 cycles). This morphology modulation of Zn-MOF-74 will promote the advanced applications of Zn-MOF-74 as well as its derived carbon materials, and potentially opens a general pathway for the oriented evolution of various carboxylate-based MOFs.

State and prospects for the development of thick-seam mining technology in the southern Kuzbass

The paper discusses the factors that limit the growth of coal production in Kuzbass. They were identified by the results of statistical analysis of the actual production indicators of working faces in eight thick coal seams. Technological solutions for the rational control of hard-to-break roof rocks, the shape and size of coal pillars, which ensure the stability of protected workings and isolation of the worked-out area from endogenous fires, are substantiated.

TiN nanopillar-enhanced laser desorption and ionization of various analytes.

The present paper reports on the use of TiN nanopillars as a robust analytical substrate for laser desorption/ionization mass spectrometry (LDI-MS). TiN nanopillars were fabricated on silicon wafers through the dynamic oblique deposition of titanium, followed by thermal treatment in an ammonia atmosphere. The TiN nanopillars were readily applicable to a simple "dried-droplet" method in the LDI-MS without surface modification or pre-treatment. A broad range of analytes were investigated, including a small drug molecule, a synthetic polymer, sugars, peptides, and proteins. Intact molecular signals were detected with low noise interference and no fragmentation. The developed TiN-nanopillar-based approach extends the applicable mass limit to 150 kDa (immunoglobulin G) and was able to detect trypsinogen (24 kDa) at levels as low as 50 fmol μL-1 with adequate shot-to-shot signal reproducibility. In addition, we carried out MS analysis on biomolecule-spiked human blood plasma and a mixture of standard samples to investigate the promise of the TiN nanopillars for clinical research. The experimental observations are validated using electromagnetic and heat-transfer simulations. The TiN nanopillars show a reduced reflection and exhibit surges in the TiN surface temperature upon irradiation with electromagnetic radiation. Localization of thermal energy at the tips of the TiN pillars is likely to be responsible for the superior LDI performance. Our results suggest that the development of nanostructured TiN substrates will contribute to the widespread implementation of nanostructured solid substrates for biomedical and clinical applications with simple processes.

Determining stability conditions for haulage drifts protected by coal pillars

The aim of this research is to study the stability of haulage drifts and the manifestations of rock pressure in them lengthwise the working area when protecting them with coal pillars. To assess the stability of workings, field experiments were conducted to study the manifestations of rock pressure in the haulage drifts of a steep coal seam. It has been registered that as the breakage face progresses, the displacement of roof rocks on the contour of the drift linearly increases with an increase in the length of the working area. The deformation properties of coal pillars were studied taking into consideration the extent of the convergence of the roof and soil. This paper reports a theoretical model that describes the destruction of the above-drift coal pillars when unloading the coal-bearing massif that hosts the workings. It has been determined that the equilibrium state of coal pillars is ensured when the specific deformation and stress potentials are equal before the occurrence of main cracks of destruction. As the relative deformation of coal pillars increases at compression, when this equality is broken, the specific energy intensity of destruction increases. It is noted that at a distance exceeding l>10 m behind the breakage face, the occurrence of the main cracks of destruction is followed by a stability loss in the coal pillars. As a result of external forces, the change in the volume and shape of the coal pillars causes the intensification of the process of convergence of lateral rocks on the contour of haulage drifts lengthwise the working area and leads, with a certain degree of probability, to a deterioration in the stability of workings. The results of this study could be used to justify the choice of technique to protect haulage drifts. This would allow the timely development of minefield reserves thereby improving the safety of operations. It is recommended that the technique of protecting haulage drifts by coal pillars should be abandoned

Classification of protective pillars toward higher safety and innovation in room-and-pillar coal mining

During room-and-pillar mining, protective pillars of coal are usually left standing. The protective pillars differ in shape, size, process properties and extractability ratios of coal. The authors propose a classification of the protective pillars with respect to their structure and shape in order to estimate and predict their properties. The extractability ratios of coal are calculated for the initial rib pillars and panels at different final shapes of protective pillars. The protective pillars are ranked with respects to the coal extractability ratios. Such systematization of pillars enables selecting the best engineering solutions and innovative improvement of room-and-pillar mining in specific geological conditions toward enhanced safety and efficiency of underground coal production. The article is prepared in the framework of the Competitiveness Enhancement Program of the Tomsk Polytechnic University.

Enhance the mixing performance of water and ethanol at micro level using geometrical modifications

The mixing performance characteristics of water and ethanol in split and recombine micromixer (SARM) are significantly improved using topological modifications. Therefore, in this paper, effect of topological modifications on the mixing performance of water and ethanol in SARM with different configurations is reported. Finite Element Method based COMSOL Multiphysics 5.0 software was utilized for numerical analysis. The laminar flow and transport with diluted species physics were used for investigation of SARM. The influence of constriction height, angle between inlets and different pillar shape on the performance characteristics viz. mixing index, pressure developed and performance index was investigated. Initially numerical methodology applied for analysis was validated with results available in literature. Further, same code was utilized for the parametric analysis. From the study, it is concluded that U-shape pillar SARM showed best performance characteristics as compared with other configurations.

A Limit Equilibrium Model of Tabular Mine Pillar Failure

An improved understanding of pillar strength and pillar failure mechanisms is required to optimize tabular mine layout designs. The paper describes the application of a limit equilibrium model for pillar failure analysis. It is shown that the model is capable of reproducing a hardening or softening response for uniformly compressed strip or square pillars. The stress–strain behavior depends on three non-dimensional parameters Q, M and β. Q represents the ratio of the limit failed uniaxial strength to the intact material strength, M is the ratio of the failed limit strength envelope slope to the intact strength envelope slope and β is proportional to the pillar width to height ratio. The model is implemented in a displacement discontinuity solution scheme using unstructured triangular elements to allow irregular plan-view pillar shapes and mining step increments to be represented. The seam-parallel confining stress distribution in the fracture zone is determined using a fast marching solution algorithm. A case study of an experimental pillar extraction site in a platinum mine is presented to illustrate the capability of the model to simulate the evolution of pillar failure as pillar extraction proceeds. Good qualitative agreement to observed failure trends are obtained but the detailed calibration of the model parameters remains a challenge. Further work is required to enhance the representation of pillar edge spalling processes.

Production of Bio-Polymer Structures by Soft Molding Method with Biomimetic Approach

Biomimetic is the name of the approach that seeks sustainable solutions to the problems, taking the perfect functioning of nature for millions of years. The interest shown in biomimetic surfaces, inspired by multi-scale structures found in many plants and animals, is increasing day by day. Especially the unique wettability properties of the lotus leaf and rose petal. In this study, inspired by the structures of lotus leaf and rose petal, using the soft casting method with dental bio-polymer materials, structures with pillar dimensions of micron (µm) and millimeter (mm) were produced. These structures are replicated from two commercial products with different pillar lengths and different pillar shapes, mushroom and conical needle tips. Surface topographies of the replicated final products were analyzed by optical and stereo microscopes. Contact angles were tested to examine the wettability properties of the surfaces. According to the microscope results obtained, the demolding process, which is the riskiest step of the replication process, was successfully passed thanks to soft casting. Contact angle analysis showed that different pillar lengths and different pillar shapes changed the wettability properties of the replicated final product. The replicated mushroom-shaped micron-scale pillar structures exhibited a rose-petal effect and hydrophobic properties (approximately 1000) with only a single-scale configuration, while conical needle-shaped pillars of millimeter (mm) scale did not show any specific wetabilitty property.

OPTIMIZATION OF PILLAR SHAPE USING THE LEIBENSON–ISHLINSKY STABILITY CRITERION

The author solves the problem connected with determination of shape of pillars which remain stable under any compression due to barrel distortion. The analysis of cylindrical structures uses the known Leibenson–Ishlinsky stability criterion. The boundary conditions of the problem and its solution are obtained: elasticity in the form of the critical load dependence on the height/radius ratio of pillars. The found asymptote to the curves is associated with the optimized shape of pillars.

Characterization of sintered Cu nanopaste for micro-bumping with Injection Molded Solder technology

Abstract We have previously developed a novel plating-free bumping process using Cu nanopaste and Injection Molded Solder (IMS) technology. In the present study, we investigated the further detail about the microstructural and mechanical properties of sintered Cu nanoparticles formed into a pillar shape. By analyzing cross-sections of Cu nanoparticle pillars sintered in various conditions, we clarified how the sintering conditions affect the microstructural features, including the size and numbers of Cu grains and voids inside sintered Cu nanoparticles. In addition, we conducted the shear testing for the obtained Cu pillars to evaluate relationships between the mechanical strength and the microstructural features. We found that the results of the shear testing were consistent with the microstructural features of the sintered Cu nanoparticles. Finally, we injected molten solder onto the Cu nanoparticle pillars to evaluate the overall feasibility of the developed process. It was confirmed that the molten solder injected by IMS process has good wettability against the sintered Cu nanoparticles, which resulted in the successful bump formation without solder missing. In addition, The IMC layer between the sintered Cu nanoparticles and injected solder was formed well. These results proved the quality of microbumps fabricated by the novel bumping process using Cu nanopaste and IMS.

Waveguiding characteristics of a metal-clad dielectric grating for terahertz applications

Dielectric gratings (DGs) have recently been introduced as a new platform for guiding dielectric-based geometrically-induced surface plasmons (SPs) called spoof SPs (SSPs). In this paper, we report on the modal analysis of a metal-clad DG waveguide and compare its performance with other counterparts including the dielectric image guide (IG) and the metal grating (MG) waveguide. The proposed DG waveguide is made up of a periodic array of high-resistivity silicon (HR-Si) pillars on a metal plate with a metal cladding at a proper distance above the structure. By modal analysis of 2D and 3D structures, we show that the presence of the metal cladding enhances the modal field confinement without sacrificing the bandwidth. In addition, modal characteristics of the structure at hand in the presence of a thin substrate are studied. It is found that the lateral field confinement and bending loss can be impaired in the presence of a substrate. We also study the shape of dielectric pillars and show that nearly the same performance can be achieved by cubic and cylindrical pillars. Finally, some waveguide devices such as a bend, a directional coupler, and a ring resonator are also implemented and studied to assess the applicability of the proposed metal-clad DG waveguide.

Geometrical Deposits on Microstructured Surfaces

Research into evaporating droplets on patterned surfaces has grown exponentially, since the capacity to control droplet morphology has proven to have significant technological utility in emerging areas of fundamental research and industrial applications. Here, we incorporate two interest domains — complex wetting patterns of droplets on structured surfaces and the ubiquitous coffee-ring phenomenon of nanofluids containing dispersed aluminium oxide particles. We lay out the surface design criteria by quantifying the effect of pillar density and shape on the wetting footprint of droplets, yielding complex polygon droplet geometries. Our work is not constrained to pure liquids only, as we delve into the shape selection of particle-laden droplets of different concentrations. We visualise the deposition patterns through microscopy on surfaces exhibiting different features and further establish the ordering of particles on microscale surface asperities. At a high nanofluid concentration, we observe intriguing self-assembly of particles into highly ordered intricate structures. The collective findings of this work have the potential to enhance many industrial technologies, particularly attractive for high performance optical and electrical devices.

Enhanced Capture of Aerosol Particles on Resonator-Based PM Mass Sensors Using Staggered Arrays of Micro-Pillars

This work presents the effect of addition of micro-pillars with different array configurations on the particle collection efficiency (CE) of resonators for gravimetric airborne particulate matter (PM) sensors. Inline and radially staggered arrays of micro-pillars with rectangular and circular cross sections were 3D-printed on a surface of fused silica glass using 2-photon stereolithography and the particle collection efficiency of these pillar-covered surfaces due to impaction was evaluated. The experimental results show that in some cases the CE is highly dependent on the angle of incidence and array configuration of the pillars. The CE of inline array of rectangular micro-pillars (60%) was similar to the CE of the bare surface with no pillar. However, the radially staggered arrangement of the same pillar size and geometry improved CE by 25% on average. The presented result shows the strong significance of the incident angle, array configuration, and pillar shape on particle capture behavior of the pillared-enhanced impaction surfaces. The results pave the way for highly sensitive real-time gravimetric PM mass sensors. [2020-0124].

Stability analysis of underground mine hard rock pillars via combination of finite difference methods, neural networks, and Monte Carlo simulation techniques

Pillar stability is always evaluated using the safety factor (SF), which is defined as the ratio of pillar strength to pillar stress. However, most researchers have estimated pillar stress using the pillar shape ratio (w/h), uniaxial compressive strength (UCS) of the intact rock mass, and pillar depth (H). In this study, the geological strength index (GSI) of hard rock pillars was considered as a new variable for predictive purposes. This index was developed by combining numerical simulation software (i.e., FLAC3D) and a backpropagation neural network (BPNN). A hard rock pillar stability analysis, based on three methods including deterministic method, sensitivity analysis, and Monte Carlo simulation (MCS), was performed. A new formula was proposed to estimate the SF values based on the predicted stress, considering the GSI variable in the deterministic method. The sensitivity analysis indicated that the variables impacting the SF from high to low are UCS, GSI, w/h, and H. In this study, pillar stability was analyzed mainly using the GSI and MCS techniques. The MCS results revealed that the GSI is also a major factor in pillar stability and has a greater effect on weak pillars than on strong ones. Furthermore, a pillar is more likely to be unstable when both the GSI and the UCS are decreased. This study provides several references and procedures for improving the design of stable pillars considering the GSI as an important factor.