Pillar Matrix Research Articles

Epitaxial pillar–matrix nanocomposite thin films of Bi–Ti–Fe–O and CoFe2O4 grown on SrTiO3 (110)

Controlling nanostructures and crystallographic orientations in epitaxial nanocomposite thin films are important for tuning their physical properties. Here, we present epitaxial nanocomposite thin films of (110) oriented CoFe2O4 (CFO) and (1110) oriented Bi5Ti3FeO15 (BTFO15) grown on SrTiO3 (110) substrates with a vertically aligned pillar–matrix type structure. The size and density of CFO pillars embedded in the BTFO matrix were controlled by the growth temperature and CFO concentration. Moreover, BTFO takes intergrowth phases with the general formula of Bi4Ti3O12 • nBiFeO3 (n = 1–∼1.5) depending on the growth temperature. Scanning probe analysis on the ferroelectric properties of BTFO15–CFO nanocomposite thin films suggested that the BTFO has a switchable out-of-plane polarization component originating from the tilted orientation of its a–b plane polarization. For high CFO pillar density, however, a non-negligible number of conductive paths which might be formed at the pillar–matrix interface are likely to prevent the polarization reversal.

Data reduction of friction factor, permeability and inertial coefficient for a compressible gas flow through a milli-regenerator

A regenerator of a Stirling machine alternately absorbs and releases heat from and to the working fluid which allows to recycle rejected heat during theoretical isochoric processes. This work focuses on a milli-regenerator fabricated with a multiple jet molding process. The regenerator is a porous medium filled with a dense pillar matrix. The pillars have a geometrical lens shape. Two metallic layers (chromium and copper) are deposited on the polymer pillars to increase heat transfer inside the regenerator. We performed experiments on different milli-regenerators corresponding to three porosities (ε = 0.80, 0.85 and 0.90) under nitrogen steady and oscillating compressible flows (oscillating Reynolds number in the range 0 < Reω < 60 and Reynolds number based on the hydraulic diameter ReDh,max<6000) for different temperature gradients (ΔT < 100°C). Temperature, velocity and pressure experimental measurements are performed with microthermocouples (type K with 7,6 µm diameter), hotwires and miniature pressure sensors, respectively. We identified a threeterm composite correlation equation for the friction factor based on a Darcy-Forchheimer flow model that best-fit the experimental data. In steady and oscillating flows permeabilities and inertial coefficients are of the same magnitude order. Inertial coefficients decrease when the porosities increase.

Participating in Paradox: An Integrative Framework

Drawing from Alan Watts’s philosophy of paradox, this essay aims to articulate an integrative framework of ontological paradox (i.e., that all aspects of existence feature distinct and integral dimensions). The metaphysical tenet of separation, which undergirds scientific materialism and denies humanity’s embedded place in the world, is merely one pattern of participating in such a paradox. What then are the different types of ways, beyond a materialistic ontology, in which individuals can relate to and participate in the ever-evolving whole of existence (and whole of themselves)? Spanning the fields of philosophy, science, psychology, religion, and mysticism, this integrative inquiry seeks to reconcile and synthesize a broad range of orientations to ontological paradox into a greater frame of reference. The result is the limb and pillar matrix. Providing an alienation-integration spectrum that applies to both internal/micro paradox (i.e., the relation of one’s self to oneself) and external/macro paradox (i.e., the relation of self to the cosmic whole), the limb and pillar matrix consists of five key questions or “pillars” and seven “limbs” or patterns of participating in paradox. The pillars of paradox relate to (a) the existence and (b) resolvability of ontological paradox, as well as (c) access, (d) progressive resolution, and (e) stabilization of resolution (i.e., full integration). The limbs of paradox establish seven multivalent participatory patterns: ignorance, denial, deferment, bypass, transcendence, resolution, and dissolution.

Ultrafast spontaneous driving of water droplets on monolayer graphene-covered gradient nanopillared surfaces

Spontaneous driving of liquid droplets on textured substrate is of great importance in understanding some biological processes and designing numerous functional surfaces. However, the pinning force usually reduces the velocity and moving stability of liquid droplets in self-driving process. In this paper, a novel design of nanopillared surface with a gradient density of structural pillar matrix covered by a monolayer graphene is proposed to realize ultrafast self-driving of water droplets. Classical molecular dynamics results provide a deep insight into the enhanced spontaneous driving behaviors, and reveal the underlying mechanism of the decrease in pinning force by a monolayer graphene. The droplet can move spontaneously at a ultrahigh speed of 75.7 m/s (272.52 km/h) from sparsest to densest regions of pillars while a wettability gradient is created by the gradient distribution density of pillar matrix relying on the wetting transparency of monolayer graphene. In particular, the gradient short pillared texture triggers an opposite self-driving regularity in which the water droplet moves from densest to sparsest regions of pillars, intrinsically because the gradient short-pillared surface leads to a wetting transition from hydrophobic to hydrophilic since the monolayer graphene can be adsorbed into the sparsest short-pillared texture. Furthermore, the influence mechanism of the pillar shape and pillar matrix on the self-driving behaviors of the water nanodroplet is clarified. The findings will theoretically direct the design of graphene-covered functional surfaces for spontaneous driving of liquid droplets.

Timewalk correction for the Timepix3 chip obtained with real particle data

In this work we have developed a prototype gaseous pixel detector by combining a micromegas grid with a Timepix3 chip for the readout. The micromegas foil supported by a matrix of pillars about 50 $\mathrm{\mu m}$ high was manually placed on top the chip. By placing a cathode foil above the chip an ionization detector was created with a drift gap of 13.5 mm. The Timepix3 chip, thanks to the simultaneous measurement of the time-of-arrival (ToA) and charge via time-over-threshold (ToT) allows corrections to remaining timewalk effects, improving further the position resolution along the drift direction. We present the timewalk correction for Timepix3 chip obtained with real data from a particle beam and its impact on the tracking performance. The results obtained show an significant improvement on the position resolution for single-hits and tracks along the drift direction compared to previous experiments.

Materials News: Interfacial chemistry and atomic arrangement of ZrO2 − La2/3Sr1/3MnO3 pillar-matrix structures

We studied ZrO2 − La2/3Sr1/3MnO3 pillar–matrix thin films which were found to show anomalous magnetic and electron transport properties. With the application of an aberration-corrected transmission electron microscope, interfacial chemistry, and atomic-arrangement of the system, especially of the pillar–matrix interface were revealed at atomic resolution. Minor amounts of Zr were found to occupy Mn positions within the matrix. The Zr concentration reaches a minimum near the pillar–matrix interface accompanied by oxygen vacancies. La and Mn diffusion into the pillar was revealed at atomic resolution and a concomitant change of the Mn valence state was observed.

Epitaxial Bi5Ti3FeO15–CoFe2O4 Pillar–Matrix Multiferroic Nanostructures

Epitaxial self-assembled ferro(i)magnetic spinel (CoFe2O4 (CFO)) and ferroelectric bismuth layered perovskite (Bi5Ti3FeO15 (BTFO)) pillar-matrix nanostructures are demonstrated on (001) single-crystalline strontium titanate substrates. The CFO remains embedded in the BTFO matrix as vertical pillars (∼50 nm in diameter) up to a volume fraction of 50%. Piezoresponse force microscopy experiments evidence a weak out-of-plane and a strong in-plane ferroelectricity in the BTFO phase, despite previously reported paraelectricity along the c-axis in a pure BTFO film. Phenomenological Landau-Ginzburg-Devonshire-based thermodynamic computations show that the radial stress induced by the CFO nanopillars can influence these ferroelectric phases, thus signifying the importance of the nanopillars. The CFO pillars demonstrate robust ferromagnetic hysteresis loops with little degradation in the saturation magnetization (ca. 4 μB/f.u.). Thus BTFO-CFO nanocomposites show significant promise as a lead-free magnetoelectric materials system.

Route to production of suspended perforated membranes

The authors report a flexible approach to fabrication of suspended perforated membranes. Interferometric lithography is used to pattern photoresist to create an etch mask on a silicon substrate. Reactive ion etching results in the formation of a matrix of silicon pillars. The interstices of the pillar matrix are then filled with the membrane material. Subsequent removal of the silicon matrix and underlying substrate yields a suspended membrane with perforations where the pillar matrix protruded prior to removal. The method combines interferometric lithography and conventional lithography to provide both periodic and nonperiodic patterns in a seamless process flow. The use of a matrix of sacrificial pillars enables the formation of higher aspect ratio holes than standard liftoff or etched film approaches. Perforated membranes of a siloxane based silica, photocurable polymer, and evaporated Cr are presented, demonstrating the wide process latitude of this approach. Such suspended membranes have application in photonic, metamaterials, DNA translocation, and biological and chemical sensors.

Micromixing crowded biological agents by folding slugs through pillars

Abstract The natural state of the interior of a living cell is extremely dense with numerous molecules packed into a tiny amount of space. Such a physiological environment is known as “crowded” and can exert profound effects on the thermodynamic and kinetic properties of the molecules. In general most biochemical experiments involve low molecular concentrations and in the process, underestimate many reaction rates. This paper reports work on a microfluidic system fabricated using polydimethylsiloxane, and relied on chaotic advection to rapidly mix crowded biological solutions that have been isolated in droplets (slugs). By forcing the slugs through a pillar matrix, the slugs were compelled to stretch and fold repeatedly, creating unsteady fluid flows that rapidly mixed the slug contents in tens of milliseconds at Reynolds number in the order of 10−3. Both straight and serpentine channels containing pillars were used for mixing the slug contents. Our results suggested that the pillars generated a significant amount of interfacial stresses on the slugs and in the process induced rapid mixing. This makes the system suitable for the study of reaction kinetics, which requires reactants to be mixed faster than the actual reaction time itself.

Pressure drop of laminar gas flows in a microchannel containing various pillar matrices

The pressure drop of gas flows in a microchannel filled with a dense pillar matrix was investigated with specific attention to a pillar shape. Pillars of height 250 µm and aspect ratio of about 10 were etched in silicon using an optimized Bosch deep reactive ion etching process. The pressure drop head-loss coefficient due to compression and expansion of gas at the inlet and outlet of the pillar matrix was estimated to be about 1.4 for an opening ratio of 10. A comparison of friction factor correlations for circular pillar cross-sections agreed rather well with the correlations proposed for the macroscale. Experimentally determined friction factor correlations for several pillar cross-sections for Reynolds numbers in the range of 50–500 are presented. Among the various pillar cross-sections considered, sine-shaped pillars have the lowest friction factor. These pillar structures with low pressure drop but a rather large wetted area can be used quite effectively as regenerative materials enabling the development of microcryocoolers.

717 ピラー型ナノ構造配列を利用した電気泳動DNA分離における駆動電圧とピラー形状の影響(S07-3 マイクロ・ナノバイオメカニクス(3),S07 マイクロ・ナノバイオメカニクス)

We have demonstrated effective biomolecule separation methods based on size exclusion chromatography (SEC) type separation using nanostructured channels constituted with a flat pillar matrix and a convex pilar matrix. The performances of biomolecule separations were compared between different applied voltages and between the flat and convex pillar matrices. In the SEC type separation using the flat pillar matrix, the narrow lanes were designed for the passages for smaller molecules to detour. The specific feature of the convex fence matrix is that the lane width is changed at the halfway of the lane length. It was found from the result of the separation of λ-Hin d III digest (125-23130bp) that the separation resolution of the long DNA was highest for the lowest voltage of 20V. In contrast, the result of the separation of φX 174-Hae III digest (72-1353bp) showed that the separation resolution of the short DNA was highest for the highest voltage of 100V. In addition, it is interesting to note that the convex fence matrix enabled us to separate the peaks of 4, 6 and 9kbp fragments from the peak of 23kbp, while those peaks overlapped each other for the flat fence matrix.

Fabrication of phosphor micro-grids using proton beam lithography

A new nuclear microscopy technique called ion photon emission microscopy or IPEM was recently invented. IPEM allows analysis involving single ions, such as ion beam induced charge (IBIC) or single event upset (SEU) imaging using a slightly modified optical microscope. The spatial resolution of IPEM is currently limited to more than 10μm by the scattering and reflection of ion-induced photons, i.e. light blooming or spreading, in the ionoluminescent phosphor layer. We are developing a “Microscopic Gridded Phosphor” (also called Black Matrix) where the phosphor nanocrystals are confined within the gaps of a micrometer scale opaque grid, which limits the amount of detrimental light blooming. MeV-energy proton beam lithography is ideally suited to lithographically form masks for the grid because of high aspect ratio, pattern density and sub-micron resolution of this technique. In brief, the fabrication of the grids was made in the following manner: (1) a MeV proton beam focused to 1.5–2μm directly fabricated a matrix of pillars in a 15μm thick SU-8 lithographic resist; (2) 7:1 aspect ratio pillars were then formed by developing the proton exposed area; (3) Ni (Au) was electrochemically deposited onto Cu-coated Si from a sulfamate bath (or buffered CN bath); (4) the SU-8 pillars were removed by chemical etching; finally (5) the metal micro-grid was freed from its substrate by etching the underlying Cu layer. Our proposed metal micro-grids promise an order-of-magnitude improvement in the resolution of IPEM.