Pillar Structure Research Articles

Synthesis, crystal structures and solvent dependent cis-trans conversion of 2-(4-hydroxylphenyl)-azopyrrole

Two 2-(4-hydroxylphenyl)-azopyrrole compounds, 1 (NH) and 2 (N-Me), have been synthesized and characterized by X-ray crystallography. The slight change of the substituent on pyrrole N atom can drastically tune the properties of azopyrrole. Compound 1 self-assembled into pillar structure through NH…O and OH…N hydrogen bonds, whereas, compound 2 self-assembled into double-strand helical structure through OH…N hydrogen bond and formed tube structure by crystal packing. The UV–Vis spectra studies revealed that the cis-trans conversion rate of compound 2 is solvent dependent, which is promoted by the protic solvent and polar solvent. The structure, stability and molecular orbital of different conformers of 1 and 2 were studied by DFT calculation.

Frictionless multiphasic interface for near-ideal aero-elastic pressure sensing.

Conventional pressure sensors rely on solid sensing elements. Instead, inspired by the air entrapment phenomenon on the surfaces of submerged lotus leaves, we designed a pressure sensor that uses the solid-liquid-liquid-gas multiphasic interfaces and the trapped elastic air layer to modulate capacitance changes with pressure at the interfaces. By creating an ultraslippery interface and structuring the electrodes at the nanoscale and microscale, we achieve near-friction-free contact line motion and thus near-ideal pressure-sensing performance. Using a closed-cell pillar array structure in synergy with the ultraslippery electrode surface, our sensor achieved outstanding linearity (R2 = 0.99944 ± 0.00015; nonlinearity, 1.49 ± 0.17%) while simultaneously possessing ultralow hysteresis (1.34 ± 0.20%) and very high sensitivity (79.1 ± 4.3 pF kPa-1). The sensor can operate under turbulent flow, in in vivo biological environments and during laparoscopic procedures. We anticipate that such a strategy will enable ultrasensitive and ultraprecise pressure monitoring in complex fluid environments with performance beyond the reach of the current state-of-the-art.

Terahertz phononic crystal in plasmonic nanocavity

Interaction between photons and phonons in cavity optomechanical systems provides a new toolbox for quantum information technologies. A GaAs/AlAs pillar multi-optical mode microcavity optomechanical structure can obtain phonons with ultra-high frequency (~THz). However, the optical field cannot be effectively restricted when the diameter of the GaAs/AlAs pillar microcavity decreases below the diffraction limit of light. Here, we design a system that combines Ag nanocavity with GaAs/AlAs phononic superlattices, where phonons with the frequency of 4.2 THz can be confined in a pillar with ~4 nm diameter. The Q c/V reaches 0.22 nm−3, which is ~80 times that of the photonic crystal (PhC) nanobeam and ~100 times that of the hybrid point-defect PhC bowtie plasmonic nanocavity, where Q c is optical quality factor and V is mode volume. The optomechanical single-photon coupling strength can reach 12 MHz, which is an order of magnitude larger than that of the PhC nanobeam. In addition, the mechanical zero-point fluctuation amplitude is 85 fm and the efficient mass is 0.27 zg, which is much smaller than the PhC nanobeam. The phononic superlattice-Ag nanocavity optomechanical devices hold great potential for applications in the field of integrated quantum optomechanics, quantum information, and terahertz-light transducer.

Investigation on anchor and base design for aluminum nitride flexural mode resonators

This paper investigates the impact of base and anchor on the quality factor (Q) of piezoelectric microelectromechanical system (MEMS) tuning fork resonators vibrating in in-plane flexural mode, and proposes a new strategy to improve Q significantly. Finite element method simulation and measured results reveal that base and anchor geometries have a significant impact on the thermoelastic damping (TED) which dominates the overall resonator quality factor. For the first time, we accurately extract Q value related to TED of piezoelectric tuning fork resonators by cryogenic temperature experiment, which is consistent with FEM simulation results. According to the analysis, a wider anchor or a longer base should promote overall Q by restraining the thermal conduction induced by TED. On the other hand, increase of width or length of anchor will force the out-of-plane flexural modes closer to the target mode, reducing the overall Q by multimode effect. With a wide anchor and a pillar structure under the base to suppress multimode effect, the resonator Q could be improved by 65% to more than 11 000 and impedance at series resonant frequency (f s) could be reduced by 78% to 6.5 kΩ. To our knowledge, the proposed resonator exhibits the highest f× Q and lowest motional impedance among the reported in-plane mode piezoelectric MEMS tuning fork resonators.

Mono-functionalized pillar[n]arenes: Syntheses, host–guest properties and applications

Pillar[n]arenes are a novel class of macrocyclic hosts reported by Ogoshi and co-workers in 2008. Because of their rigid pillar structures, interesting host–guest properties and ease of modifications, pillar[n]arenes have been developed rapidly in the field of functional materials and biomedicine. The modifications of pillar[n]arenes at different positions can give them varied characteristics. Functional groups can be introduced into one position of pillar[n]arenes without changing host–guest properties of pillar[n]arenes. A series of pillar[n]arene dimers, trimers, tetramers and metallacycles can be constructed by mono-functionalized pillar[n]arenes. In this review, two synthetic methods of mono-functionalized pillar[n]arenes are summarized and structures containing mono-functionalized pillar[n]arenes are described. Furthermore, the applications of mono-functionalized pillar[n]arenes in different fields (e.g., supramolecular polymers, sensors, molecular machines, catalysis, biological applications and light-harvesting systems) are also introduced. Hopefully, this article will be useful for researchers studying pillar[n]arenes, especially the mono-functionalized pillar[n]arenes.

Development of a particle packed bed model for homogeneity evaluation of liquid chromatography column

Particle packed columns used for liquid chromatography (LC) can suppress a column internal band broadening (hereinafter referred to as band broadening) by packing monodisperse particles homogenously. However, a quantitative evaluation for the effects of particle shape and packed state on band broadening needs to be more investigated. In this study, we fabricated a model of particle packed bed using microfluid LC columns that have pillar array structure prepared by microfabrication technology, evaluating how structural factors inside of a column affect its band broadening. At first, microfluid LC columns was prepared using Si-quartz glass (Si-Q column) for the optimization of LC measurement system. Through the evaluation, it showed 11.6 times higher pressure tolerance compared to that of PDMS-soda lime glass (PDMS-g column).Then, an optimized LC measurement system was constructed using a microfluidic LC column made of Si-Q column, and it was confirmed that the measurement error was small enough and the LC measurement could be performed with high repeatability.Additionally, the effect of a distribution of structural size on band broadening was evaluated. It was confirmed that wide distribution of the structural size provided large band broadening in actual measurements. Comparing two columns having different structural log-normal distributions of 0 and 0.22 showed approximately 1.8 times difference in both real LC measurement.Lastly, the relationship between packed state and band broadening was evaluated.As packed state, we employed void arrangement and structural arrangement in the columns.Different location arrangements of 50 and 100 µm pillar sizes afforded different band broadening. Well-homogenized array showed approximately two times worse band broadening compared to that of delocalized array. Based on these results, the developed packed bed of particles model was able to evaluate the relation between structural factors and band broadening.

A thiazolothiazole based Zn(II) metal−organic framework with multi-responsive fluorescent sensing toward Al3+ and oxoacid anions in an aqueous solution

Luminescent metal−organic frameworks(LMOFs) have been utilized to identify dangerous and toxic contaminants, biomarkers, and biological species. However, the luminescent properties in MOFs have been limited by the organic connectors. In this study, we present a Zn-MOF based on thiazolothiazole ligand, which exhibits fluorescent sensing properties through a mixed bipyridine-dicarboxylate strategy. {[Zn2(NDC)2(4bppyttz)]·1.5DMF} (MOF 1) (4bppyttz=2,5-bis(4-(pyridin-4-yl)phenyl)thiazolo[5,4-d]thiazole, H2NDC=naphthalene-2,6-dicarboxylic acid) featured a three-fold interpenetrated pillared layer structure in the crystal structure. The fluorescent detection of Al3+ can be served as the turn-on effect and oxoacid anions such as CrO42−, Cr2O72−, and MnO4− can be served as turn-off effects. Furthermore, luminescence sensing studies demonstrated that MOF 1 showed high selectivity and multi-responsiveness primarily for Al3+, CrO42−, MnO4−, and Cr2O72− in an aqueous medium, with detection limits of 2.9, 3.4, 3.0, and 2.2 μM, respectively. To explain the quenching and enhancing mechanisms, XRD, absorption spectra, IR spectra, and theoretical calculations were discussed. Additionally, MOF-coated test strips were utilized to detect these ions, exhibiting excellent agreement with fluorescence spectroscopy. This work may offer a promising foundation for future thiazolothiazole-based MOFs applications in the detection of numerous contaminants.

Carbon Nitride Pillared Vanadate Via Chemical Pre-Intercalation Towards High-Performance Aqueous Zinc-Ion Batteries.

Vanadium based compounds are promising cathode materials for aqueous zinc (Zn)-ion batteries (AZIBs) due to their high specific capacity. However, the narrow interlayer spacing, low intrinsic conductivity and the vanadium dissolution still restrict their further application. Herein, we present an oxygen-deficient vanadate pillared by carbon nitride (C3 N4 ) as the cathode for AZIBs through a facile self-engaged hydrothermal strategy. Of note, C3 N4 nanosheets can act as both the nitrogen source and pre-intercalation species to transform the orthorhombic V2 O5 into layered NH4 V4 O10 with expanded interlayer spacing. Owing to the pillared structure and abundant oxygen vacancies, both the Zn2+ ion (de)intercalation kinetics and the ionic conductivity in the NH4 V4 O10 cathode are promoted. As a result, the NH4 V4 O10 cathode delivers exceptional Zn-ion storage ability with a high specific capacity of about 370 mAh g-1 at 0.5 A g-1 , a high-rate capability of 194.7 mAh g-1 at 20 A g-1 and a stable cycling performance of 10 000 cycles.

Carbon Nitride Pillared Vanadate Via Chemical Pre‐Intercalation Towards High‐Performance Aqueous Zinc‐Ion Batteries

AbstractVanadium based compounds are promising cathode materials for aqueous zinc (Zn)‐ion batteries (AZIBs) due to their high specific capacity. However, the narrow interlayer spacing, low intrinsic conductivity and the vanadium dissolution still restrict their further application. Herein, we present an oxygen‐deficient vanadate pillared by carbon nitride (C3N4) as the cathode for AZIBs through a facile self‐engaged hydrothermal strategy. Of note, C3N4 nanosheets can act as both the nitrogen source and pre‐intercalation species to transform the orthorhombic V2O5 into layered NH4V4O10 with expanded interlayer spacing. Owing to the pillared structure and abundant oxygen vacancies, both the Zn2+ ion (de)intercalation kinetics and the ionic conductivity in the NH4V4O10 cathode are promoted. As a result, the NH4V4O10 cathode delivers exceptional Zn‐ion storage ability with a high specific capacity of about 370 mAh g−1 at 0.5 A g−1, a high‐rate capability of 194.7 mAh g−1 at 20 A g−1 and a stable cycling performance of 10 000 cycles.

Suppressed physical aging in PMMA‐titanium oxide nanocomposites by controlling alignment of nanoparticles

AbstractThis study investigates the physical aging process of PMMA‐TiO2 nanocomposites with different particle alignments. By using an external electric field to control the alignment of TiO2 particles, a uniform distribution of TiO2 particles in PMMA is transformed into a micrometer‐level pillar structure. The physical aging process is measured using differential scanning calorimetry, and the particle alignment is confirmed by microscopy. Comparison of the aging behavior of different samples shows that the addition of randomly distributed TiO2 nanoparticles accelerates the aging rate of the material. However, when the nanoparticles are realigned into a pillar structure, the aging rate significantly decreases. Moreover, in our experimental time scale, a dual‐relaxation mechanism of aging is observed in the PMMA/TiO2 nanocomposites. This work highlights the importance of particle alignment and structure on the aging behavior of polymer nanocomposites, which could have implications for designing materials with improved stability in applications that require slow aging.

An Evaluation of Bath Life Effects on Photoresist Removal for Wafer Level Packaging

With the emergence of 3D integration and wafer level packaging, the pillar bumping process has become a critical processing step. As the process has matured, significant efforts have been made for optimization in terms of both production and cost. This is especially true for photoresist stripping, since thick photoresists are needed to pattern high aspect ratios and must be removed in subsequent steps to expose underlying metal films. In this study, the removal of a thick negative tone photoresist with solder pillar plated wafers were investigated using a dimethyl sulfoxide blend with a quaternary ammonium hydroxide. Emphasis was placed on exploring the feasibility of an extended bath life beyond 7 days. Coupon level beaker tests were used to provide insight into the swelling and dissolution mechanisms with fresh and aged chemistry. Additionally, several chemistries were compared to examine the effect of the quaternary ammonium hydroxide. Based on these findings, chemical aging studies were performed on 300 mm wafers using a highly customizable single wafer processing tool that combined soaking and a high-pressure spray processing to potentially prolong the bath age even further. In addition to stripping efficiency at extended bath life, the compatibly with pillar structures and seed layers is investigated. Results from the study highlight potential methods to extend bath life while maintaining photoresist stripping efficiency.

Electroplated Aluminum Pillars for Ultrasonic Flip Chip Bonding

Flip chip bonding is a widely used method in 3D integration. In this study, the use of electroplated Aluminum as pillar structure for ultrasonic flip chip bonding is demonstrated for the first time. Al pillars were deposited from a chloroaluminate ionic liquid on a 6 inch silicon wafer. The influences of ultrasonic bonding parameters (bonding time, ultrasonic power and bonding force) were investigated at room temperature. Al pillar bonding was performed successfully in less than 1 s. High bonding forces are recommended as more pillars get mechanical contact to the substrate, thus, ultrasonic energy can be transferred to the interface causing bonding.

How to build a pillar: A proof of Thomassen's conjecture

Carsten Thomassen in 1989 conjectured that if a graph has minimum degree much more than the number of atoms in the universe (δ(G)≥101010), then it contains a pillar, which is a graph that consists of two vertex-disjoint cycles of the same length, s say, along with s vertex-disjoint paths of the same length3 which connect matching vertices in order around the cycles. Despite the simplicity of the structure of pillars and various developments of powerful embedding methods for paths and cycles in the past three decades, this innocent looking conjecture has seen no progress to date. In this paper, we give a proof of this conjecture by building a pillar (algorithmically) in sublinear expanders.

Simple and Ingenious Manner To Build Li-Rich Layered Materials with Surface Layered/Spinel Heterostructures and Li Deficiencies

The voltage and capacity attenuation is one of the main bottlenecks limiting the commercialization of Li-rich layered materials, the introduction of a spinel structure and Li deficiencies into materials may mitigate or suppress these shortcoming. The Li-rich layered materials with surface layered/spinel heterostructures and Li deficiencies (LR-S) are prepared by a simple and ingenious manner; that is, the 10 wt % precursors are added to uptake the volatilize of Li ions, which produced from the Li-rich material (LR-0) in a high-temperature post-treatment process. The generation of the spinel structure and Li deficiencies in the LR-S sample are confirmed by the inductively coupled plasma mass spectrometry, X-ray diffraction, Raman spectra, and high-resolution transmission electron microscopy characterizations. The LR-S sample displayed excellent electrochemical performances; that is, the capacity retentions is 88.92% at 1 C after 200 cycles, and the voltage drop for each cycle is 1.91 mV, respectively. The reason is mainly attributed to the spinel structure serving as a pillar structure and the Li deficiencies modulating the oxidation products of the oxygen ion in the removal/uptake process.

Fractal model-based crystal pillar structure simulation and mechanism analysis of impurity migration process in layer melt crystallization

Layer melt crystallization (LMC) is regarded as a green purification technique and is widespread in the separation of isomers. Based on the highly efficient separation, this work combined the experiments and models to explore the crystal pillar structure and impurity migration. Firstly, we established the crystallization process kinetic model to reveal the crystal growth rules and pointed out the correlations of growth rate and supercooling degree. Then the fractal porous model was used to analyze the crystal pillar structure, where the fractal characteristics tended to the Euclidean geometric features with porosity increase in both crystallization and sweating processes. Next, we simulated the melt seepage rate through the pore channel, where the modeling results showed high consistency with the experiments. Finally, the effects of pore structure, kinetics, and sweating intensity on the separation and impurity migration in both crystallization and sweating processes were revealed, to guide the technical design.

Boiling heat transfer on two-tier hierarchical structured surface

In this paper, pool boiling on two-tier hierarchical structured surface is investigated with three-dimensional LB method. Two-tier pillar structures with different scales are designed, termed as primary and secondary pillar, respectively. On the hierarchical surface with upward-orientation secondary pillars, the bubble departure is promoted. And, the heat transfer can be improved by increasing the primary pillar spacing and enhancing surface wettability. Increasing the height of secondary pillar is favorable for enhancing capillary wicking, but can also bring greater flow resistance. On the hierarchical surface with lateral-orientation secondary pillars, the heat transfer is limited by the large flow resistance. With the enlargement of primary pillar spacing, the impact brought by flow resistance is moderated, and the heat flux can be enhanced. Finally, the boiling performance regarding the effect of wall temperature is concerned, where the structured surface with upward-orientation secondary pillars show the better boiling performance than other structured surfaces.

Spreading, Breakup, and Rebound Behaviors of Compound Droplets Impacting on Microstructured Substrates.

In this study, we numerically investigate the dynamic behaviors of micron-scale compound droplets impacting onto superhydrophobic surfaces patterned by micropillar arrays using a three-dimensional free-energy-based lattice Boltzmann method. We address how the interplay between physical parameters (i.e., Weber number) and geometric parameters (i.e., pillar density and spacing and the droplet core-shell size ratio) affects the spreading, breakup, and rebound behaviors of compound droplets, which remains unknown and unquantified. We identify three flow regimes in which the interfacial morphology between the core and shell evolves and breaks up in distinct ways: namely, hole nucleation at the substrate, rupture of the film at the apex of the shell, and toroidal formation of the core droplet before its detachment from the pillars. We demonstrate that the transition between the three regimes and the maximum spreading factor of compound droplets can be changed by varying the core-shell size ratio, the pillar density, and the Weber number. The non-wetting behavior of the pillar structures eventually forms a new suspended pure droplet or a new suspended compound droplet, which can be characterized by the core-shell size ratio, pillar density, and Weber number.

Droplet evaporation on pillar structured surface: A 3D lattice Boltzmann numerical study

In this paper, a three-dimensional symmetric lattice Boltzmann (LB) model is built up to investigate evaporation of a sessile droplet on pillar structured surfaces. Parametric effects on droplet evaporation, including pillar structure size, roughness, temperature and wettability, are studied comprehensively, with emphasis on the variations of contact angle, contact radius and velocity of triple-phase contact line (TPCL) as well as heat and mass fluxes during evaporation. Pillar structures are found to induce the droplet to split into spherical cap part and liquid film part, resulting in an evaporation mode different from that on a plain surface. The extent of pinning-depinning is strongly associated with structures when TPCL retracts between pillars. Increasing surface temperature can accelerate evaporation by breaking the constant contact angle (CCA) mode, and increasing surface roughness accelerates evaporation by decreasing the duration of CCA mode. The majority of heat and mass transfer takes place around TPCL. High wettability can facilitate the evaporation of spherical cap due to the meniscus at liquid–vapor interface in the vicinity of pillar top surface. The substrate heat flux directly affected by structure size is higher in the region where pillars are distributed, and the solid–liquid interfacial heat flux varies with the specific interface location within droplet. The total mass flux primarily depends on the TPCL length determined by the droplet evaporation mode. When the droplet evaporates by partial penetration in the Cassie state, the amount of evaporation at liquid–vapor interface between pillars is greater than that above pillars. This paper provides more details and insights for a deep understanding of droplet evaporation on pillar structured surfaces.

Effect of Micropillar Array Morphology on Liquid Propagation Coefficient Enhancement.

Roughness on hydrophilic surfaces allows for fast propagation of liquids. In this paper, the hypothesis is tested which theorizes that pillar array structures with nonuniform pillar height levels can enhance wicking rates. In this work, within a unit cell, nonuniform micropillars were arranged with one pillar at constant height, while other shorter pillars were varied in height to study these nonuniform effects. Subsequently, a new microfabrication technique was developed to fabricate a nonuniform pillar array surface. Capillary rising-rate experiments were conducted with water, decane, and ethylene glycol as working liquids to determine the behavior of propagation coefficients that were dependent on pillar morphology. It is found that a nonuniform pillar height structure leads to a separation of layers in the liquid spreading process and the propagation coefficient increases with declining micropillar height for all liquids tested. This indicated a significant enhancement of wicking rates compared to uniform pillar arrays. A theoretical model was subsequently developed to explain and predict the enhancement effect by considering capillary force and viscous resistance of nonuniform pillar structures. The insights and implications from this model thus advance our understanding of the physics of the wicking process and can inform the design of pillar structures with an enhanced wicking propagation coefficient.

Nanoscale Structure–Property Relations in Self-Regulated Polymer-Grafted Nanoparticle Composite Structures

Using a model system of poly(methyl methacrylate)-grafted silica nanoparticles (PMMA-NP) and poly(styrene-ran-acrylonitrile) (SAN), we generate unique polymer nanocomposite (PNC) morphologies by balancing the degree of surface enrichment, phase separation, and wetting within the films. Depending on the annealing temperature and time, thin films undergo different stages of phase evolution, resulting in homogeneously dispersed systems at low temperatures, enriched PMMA-NP layers at the PNC interfaces at intermediate temperatures, and three-dimensional bicontinuous structures of PMMA-NP pillars sandwiched between two PMMA-NP wetting layers at high temperatures. Using a combination of atomic force microscopy (AFM), AFM nanoindentation, contact angle goniometry, and optical microscopy, we show that these self-regulated structures lead to nanocomposites with increased elastic modulus, hardness, and thermal stability compared to analogous PMMA/SAN blends. These studies demonstrate the ability to reliably control the size and spatial correlations of both the surface-enriched and phase-separated nanocomposite microstructures, which have attractive technological applications where properties such as wettability, toughness, and wear resistance are important. In addition, these morphologies lend themselves to substantially broader applications, including: (1) structural color applications, (2) tuning optical adsorption, and (3) barrier coatings.