SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Nanopillar

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Highly efficient room-temperature ultraviolet (UV) luminescence is obtained in heterostructures consisting of 10-nm-thick ultrathin ZnO films grown on Si nanopillars fabricated using self-assembled silver nanoislands as a natural metal nanomask during a subsequent dry etching process. Atomic layer deposition was applied for depositing the ZnO films on the Si nanopillars under an ambient temperature of 200°C. Based on measurements of photoluminescence (PL), an intensive UV emission corresponding to free-exciton recombination (approximately 3.31 eV) was observed with a nearly complete suppression of the defect-associated, broad-range visible emission peak. As compared to the ZnO/Si substrate, the almost five-times-of-magnitude enhancement in the intensity of PL, which peaked around 3.31 eV in the present ultrathin ZnO/Si nanopillars, is presumably attributed to the high surface/volume ratio inherent to the Si nanopillars. This allowed considerably more amount of ZnO material to be grown on the template and led to markedly more efficient intrinsic emission.

Concepts: Ultraviolet, Titanium dioxide, Luminescence, Zinc oxide, Sunscreen, Surface-area-to-volume ratio, Intensive and extensive properties, Nanopillar

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The uniquely tilted nanopillar array favorably influence carrier and phonon transport properties. We present an innovative interfacial design concept and a novel tilt-structure of hierarchical Bi1.5Sb0.5Te3 nanopillar array comprising unique interfaces from nano-scaled open gaps to coherent grain boundaries, and tilted nanopillars assembled by high-quality nanowires with well oriented growth, utilizing a simple vacuum thermal evaporation technique. The unusual structure Bi1.5Sb0.5Te3 nanopillar array with a tilt angle of 45° exhibits a high thermoelectric performance ZT = 1.61 at room temperature. The relatively high ZT value in contrast to that of previously reported Bi1.5Sb0.5Te3 materials and the Bi1.5Sb0.5Te3 nanopillar array with a tilt angle of 60° or 90° evidently reveals the crucial role of the unique interface and tilt-structure in favorably influencing carrier and phonon transport properties, resulting in a significantly improved ZT value. This method opens a new approach to optimize nano-structure film materials.

Concepts: Structure, Materials science, Array, Object-oriented programming, Axial tilt, Nanopillar

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Tapered nanopillars with various cross sections, including cone-shaped, stepwise, and pencil-like structures (300 nm in diameter at the base of the pillars and 1.1 μm in height), are prepared from epoxy resin templated by nanoporous anodic aluminum oxide (AAO) membranes. The effect of pillar geometry on the shear adhesion behavior of these nanopillar arrays is investigated via sliding experiments in a nanoindentation system. In a previous study of arrays with the same geometry, it was shown that cone-shaped nanopillars exhibit the highest adhesion under normal loading while stepwise and pencil-like nanopillars exhibit lower normal adhesion strength due to significant deformation of the pillars that occurs with increasing indentation depth. Contrary to the previous studies, here, we show that pencil-like nanopillars exhibit the highest shear adhesion strength at all indentation depths among three types of nanopillar arrays and that the shear adhesion increases with greater indentation depth due to the higher bending stiffness and closer packing of the pencil-like nanopillar array. Finite element simulations are used to elucidate the deformation of the pillars during the sliding experiments and agree with the nanoindentation-based sliding measurements. The experiments and finite element simulations together demonstrate that the shape of the nanopillars plays a key role in shear adhesion and that the mechanism is quite different from that of adhesion under normal loading.

Concepts: Oxygen, Aluminium, Continuum mechanics, Tensile strength, Epoxy, Adhesive, Algebraic geometry, Nanopillar

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A facile rapid dehydration strategy (RD) is explored for quasi-topotactic transformation of FeOOH nanorods to robust Fe2O3 porous nanopillars, avoiding collapse, shrink, and coalescence, compared with a conventional treatment route. Additionally, the so-called RD process is capable of generating beneficial porous structure for PEC water oxidation. The obtained RD-Fe2O3 photoanode exhibits a photocurrent density as high as 2.0 mA cm-2 at 1.23 V vs. RHE, and a saturated photocurrent density of 3.5 mA cm-2 at 1.71 V vs. RHE without any co-catalysts, which is about 270% improved photocurrent density over Fe2O3 with conventional temperature-rising route (0.75 mA cm-2 at 1.23 V vs. RHE and 1.48 mA cm-2 at 1.71 V vs. RHE, respectively). The enhanced photocurrent on RD-Fe2O3 is attributed to a synergistic effect of following factors: (i) preservation of single crystalline nanopillar decreases charge carriers recombination; (ii) the formation of long nanopillars enhance light harvesting; (iii) porous structure shortens hole transport distance from bulk material to electrode/electrolyte interface.

Concepts: Water, Hydrogen, Nanomaterials, Bulk density, Nanorod, Failure assessment, Nanopillar, Bulk cargo

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A new strategy to elaborate (1-3) type multiferroic nanocomposites with controlled dimensions and vertical alignment is presented. The process involves a supported nanoporous alumina layer as a template for growth of free-standing and vertically aligned CoFe2 nanopillars using a room temperature pulsed electrodeposition process. Ba0.70Sr0.30TiO3-CoFe2O4 multiferroic nanocomposites were grown through direct deposition of Ba0.7Sr0.3TiO3 films by radio-frequency sputtering on the top surface of the pillar structure, with in-situ simultaneous oxidation of CoFe2 nanopillars. The vertically aligned multiferroic nanocomposites were characterized using various techniques for their structural and physical properties. The large interfacial area between the ferrimagnetic and ferroelectric phases leads to a magnetoelectric voltage coefficient as large as ~320 mV cm-1 Oe-1 at room temperature, reaching the highest values reported so far for vertically architectured nanocomposite systems. This simple method has great potential for large-scale synthesis of many other hybrid vertically aligned multiferroic heterostructures.

Concepts: Condensed matter physics, Temperature, Nanomaterials, Materials science, Nanocomposite, Physical property, Nanopillar, The Pillar

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This work presents arrays of heterogeneous nanopillars stacked with Si bodies and SiO2 heads for biomedical applications. Novel crossed and overlapped spacer techniques are proposed to fabricate the nanopillar arrays in controllable dimensions. For the nanopillars in the arrays, the minimum spacing, body diameter and head tip-radius reach 100 nm, 23 nm and 11 nm, respectively. The maximum height is 1.2 μm. In addition, because of hydrophilic/hydrophobic selectivity between the SiO2 heads and Si bodies, localized nanoliter water-droplet condensing, fluorescein solution extraction and protein capturing are observed on the SiO2 pillar heads. These experiments demonstrate the great potential of heterogeneous nanopillars in biomedical applications.

Concepts: Space, Length, Maxima and minima, Body, Head, Nanopillar

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Bent Cu-Al-Ni nanopillars (diameters 90-750 nm) show a shape memory effect, SME, for diameters D > 300 nm. The SME and the associated twinning are located in a small deformed section of the nanopillar. Thick nanopillars (D > 300 nm) transform to austenite under heating, including the deformed region. Thin nanopillars (D < 130 nm) do not twin but generate highly disordered sequences of stacking faults in the deformed region. No SME occurs and heating converts only the undeformed regions into austenite. The defect-rich, deformed region remains in the martensite phase even after prolonged heating in the stability field of austenite. A complex mixture of twins and stacking faults was found for diameters 130 nm < D < 300 nm. The size effect of the SME in Cu-Al-Ni nanopillars consists of an approximately linear reduction of the SME between 300 and 130 nm when the SME completely vanishes for smaller diameters.

Concepts: Effect size, Twin, Austenite, Target Field, Region, Martensite, Shape memory alloy, Nanopillar

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Tapered nanopillar structures of different cross-sectional geometries including cone-, pencil-like, and stepwise are prepared from anodized aluminum oxide templates. The shape effect on the adhesion strength is investigated in experiments and simulation. Cone-shaped nanopillars are highly bendable under load and can recover after unloading, thus, warranting high adhesion strength, 34 N cm(-2) . Pencil-like and stepwise nano-pillars are, however, easily fractured and not recoverable under the same conditions.

Concepts: Oxygen, Aluminium, Electrolysis, Passivation, Anodizing, Nanopillar

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N. A. Kotov, S. J. Lee, and co-workers demonstrate on page 6119 that large-scale nanopillar arrays are produced in a single-step replication process and are transferable onto everyday materials. Ink-jet layer-by-layer assembly (LBL) creates overt and covert images on the nanopillars. The hidden images are revealed by light breath. Durable and scalable nanopillar arrays with LBL layers create new possibilities for combating counterfeiting of many goods, and other applications.

Concepts: Nanorod, Nanopillar, The Hidden

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Si/N-doped TiO2 core/shell nanopillar arrays with a nanoporous structure are fabricated through a simple protein-mediated TiO2 deposition process. The Si nanopillar arrays are used as templates and alternatively immersed in aqueous solutions of catalytic molecules (protamine, PA) and the titania precursor (titanium(iv) bis(ammonium lactato)dihydroxide, Ti-BALDH) for the layer by layer mineralization of a PA/TiO2 coating. After a subsequent calcination, a N-doped TiO2 layer is formed, and its thickness could be controlled by varying the cycles of deposition. Moreover, the nanoporous structure of the Si nanopillars strongly affects the formation of the TiO2 layer. The obtained Si/TiO2 nanocomposites show significantly improved solar absorption compared with commercially purchased TiO2 nanoparticles.

Concepts: Ultraviolet, Concentration, Chemistry, Nanomaterials, Solar cell, Solutions, Aqueous solution, Nanopillar