Several Millimeters In Length Research Articles

Surface-Guided Crystallization of Xanthine Derivatives for Optical Metamaterial Applications.

Numerous bio-organisms employ template-assisted crystallization of molecular solids to yield crystal morphologies with unique optical properties that are difficult to reproduce synthetically. Here, a facile procedure is presented to deposit bio-inspired birefringent crystals of xanthine derivatives on a template of single-crystal quartz. Crystalline sheets that are several millimeters in length, several hundred micrometers in width, and 300-600nm thick, are obtained. The crystal sheets are characterized with a well-defined orientation both in and out of the substrate plane, giving rise to high optical anisotropy in the plane parallel to the quartz surface, with a refractive index difference Δn ≈ 0.25 and a refractive index along the slow axis of n ≈ 1.7. It is further shown that patterning of the crystalline stripes with a tailored periodic grating leads to a thin organic polarization-dependent diffractive meta-surface, opening the door to the fabrication of various optical devices from a platform of small-molecule based organic dielectric crystals.

Temperature-Dependent Sheet Resistance and Surface Characterization of Thin Copper Films Bonded to FR4 Composite under Mechanical Vibrations

Electrical boards, also called printed circuit boards, constitute the basis of most electronic devices. These boards are mainly fabricated of thin copper films bonded to fiber epoxy laminates, such as FR4. Being the most important functional component of these devices, they sometimes undergo mechanical stresses such as shock and vibration during transport and operation that can induce electrical failure and malfunction; hence, studies addressing the effects of vibrations on their electrical properties have important applications. In this paper, small cantilever samples made of bare copper bonded to FR4 with three isolated rectangular zones were studied to analyze, for the first time, variations in electrical properties such as sheet resistance and resistivity before and after 200 k, 500 k, and 800 k vibration cycles at three different temperatures (25, 35, and 45 °C). A significant rise in resistance equivalent to 1657% of the initial value was observed from 0 to 800 k vibration cycles. These changes were accompanied by a 95% decrease in conductivity, from 4.1 × 107 to 2.3 × 106 S/m, whereas very little change in the electrical properties was observed due to temperature rise. Surface analysis by ESEM showed cracks ~1 µm in width and several millimeters in length with a crack density of ~8 cracks per mm after 800 k cycles. The surface composition (100% copper) was not altered even upon a high number of vibration cycles, and static drop contact angle measurements of 117–119 degrees indicated an increase in the hydrophobicity of the surface attributed to increased surface roughness and the accumulation of very small air bubbles on the cracks.

Direct laser writing of 3D metallic mid- and far-infrared wave components

Abstract A method for direct fabrication of 3D silver microstructures with high fabrication throughput on virtually any substrate is presented. The method is based on laser-induced photoreduction of silver ions to silver atoms, supported by nucleation, substrate functionalization and a multiple exposure fabrication process. The combination of the novel photosensitive suspension and the novel fabrication scheme enables effective fabrication speeds of up to 1 cm per second, with a minimum structure size of less than 1 μm, a resolution of more than 750 lines/mm and a resistivity of 3.0 · 10−8 Ωm. With this fabrication speed, it is now possible to produce conductive silver topographies several millimeters in length. Thus, with a single technology, one can fabricate photonic components with characteristic spectral features ranging from mid-to far-infrared.

Ultralong waveguide grating antenna enabled by evanescent field modulation.

Waveguide grating antenna (WGA) is a key component for an on-chip optical phased array. In order to form a beam with a small divergence angle, WGAs of several millimeters in length are highly desired. However, in high-index-contrast platforms such as silicon-on-insulator (SOI), such long WGAs typically require weakly modulated gratings with critical feature sizes below 10 nm. In this paper, we experimentally demonstrate a new, to the best of our knowledge, strategy to implement long WGAs. Instead of directly modulating a waveguide, we propose periodically modulating the evanescent field with subwavelength blocks. With this arrangement, weak grating strength can be achieved while maintaining a minimum feature size as large as 100 nm. For proof-of-concept, we experimentally demonstrate a 1-mm-long, single-etched WGA on a conventional 220 nm SOI platform, which achieves a far-field divergence angle of 0.095° and a wavelength scanning sensitivity of 0.168°/nm.

On constriction and striation of a diffuse DBD in large gap filled with moderate pressure helium diluted by the air and easily ionized impurity

The experimental results on studying the plane-to-plane dielectric barrier discharge (DBD) excited in a very large volume (120 × 120 × 120 mm3) are presented. The DBD was powered by sinusoidal voltage with a frequency of 100 kHz. The plasma-forming gas is helium, which is slightly diluted by the air and trace impurity of an easily ionized gas. The total pressure of the working gas was varied within of 20–100 Torr. A moderate gas pressure allowed one the creation of non-typical DBD with a very long plasma column of 12 cm in length. Such a long gap DBD exhibits new features in its behavior compared to the well-known DBD in short gaps of several millimeters in length. Immediately after the discharge ignition, a long and uniform diffuse plasma column occurs that occupies the entire space of the inter-electrode bulk. However, this transversally homogeneous plasma mode is unstable. The ionization-thermal instability develops in the plasma owing to gas heating by the discharge. Therefore, the transversally uniform plasma breaks into several separate narrow current channels that move chaotically relative to each other. After a while, they eventually integrate into a single constricted plasma column located in the center part of the discharge volume. At the very beginning of its formation, the constricted plasma column is longitudinally uniform. But soon, it becomes streated. The strata are almost standing and their shape differs from that in a DC glow discharge at low pressure in a sealed tube. The revealed features in the slow spatial-temporal behavior of the long gap DBD are discussed with the involvement of mathematical analysis describing the small plasma disturbance development in the linear approximation.

A multi-view line scanning confocal microscope for fast imaging of extended samples

Confocal microscopy is a well-established standard for biological fluorescence imaging, capable of providing high contrast and axial sectioning through rejection of out of focus light. However, typical confocal techniques can suffer from slow imaging speeds, excessive bleaching, or small fields of view which make it challenging to image large areas at high resolution efficiently. Here we report on a custom-built line scanning confocal microscope with two opposing views that is capable of quickly imaging samples up to several millimeters in length at high resolution.

Synthesis of photoluminescent SiC-SiOx nanowires using coal tar pitch as carbon source

SiC-SiOx nanowires (NWs) with core-shell and chain-bead structures were synthesized via a catalyst-free chemical vapor deposition (CVD) route without Ar gas, using silicon and coal tar pitch powders as raw materials. The SiC-SiOx NWs with sharp tips formed by solid-vapor between Si (s) and CO (g) or C (s) and SiO (g), liquid-vapor between Si (l) and CO (g), and vapor-vapor between SiO (g) and CO (g) growth process along the [111] direction. The NWs were several millimeters in length, and the average diameters of the chains and beads were 40–90 nm and 325 nm, respectively. The obtained NWs had good blue-green photoluminescence property owing to the stacking faults and amorphous SiOx. This novel CVD route is simple, low cost and suitable for large-scale production.

X-Ray Phase Contrast Imaging of Liquid Film and Spray Development Inside an Aircraft Engine Swirler

Abstract Modern aircraft engines combine liquid fuel and air using an intricate flow device with many fuel and air flow passages. To date, the process by which the fuel atomizes within this swirler set has not been examined directly due to optical access limitations. In this work, high-speed X-ray phase-contrast imaging of a liquid spray inside a gas turbine engine swirler geometry is presented. Measurements were carried out at the 7-BM beamline of the Advanced Photon Source at Argonne National Laboratory using the high-energy broadband X-ray beam. The synchrotron X-ray source provides the necessary photon energy and flux to capture time-resolved fluid phenomena within the confines of the relevant geometry while liquid and air are flowing. Spray nozzle hardware and geometries were provided by the National Jet Fuels Combustion Program (NJFCP), allowing for characterization of the spray using a commercially relevant configuration. Modified swirlers were three-dimensional printed with acrylic to improve imaging access while maintaining influential internal features. Water was used as a surrogate fluid for these studies to demonstrate the visualization capabilities. The experiments were conducted at atmospheric exit pressure conditions with a pressure drop of 6% across the swirler. High-speed imaging of the pilot spray cone revealed sheet breakup several millimeters downstream of the orifice exit, upon interaction with the radial assist air flow. These droplets and ligaments were observed to impinge on the inner filming surface of the swirler and flow toward the exit while developing a tangential flow. Under these conditions, the liquid film grows up to several hundred microns in thickness on the filming surface, and subsequently forms ligaments up to several millimeters in length before breaking up. This work demonstrates the capability of X-ray diagnostics in visualizing liquid flows within solid geometries of technical relevance. Furthermore, the spatial quantification of filming flows and liquid interaction with the swirler air provides validation data for modeling of the multiphase flows and surface interactions within the swirler.

Halogen Vacancies Enable Ligand‐Assisted Self‐Assembly of Perovskite Quantum Dots into Nanowires

AbstractInterest has been growing in defects of halide perovskites in view of their intimate connection with key material optoelectronic properties. In perovskite quantum dots (PQDs), the influence of defects is even more apparent than in their bulk counterparts. By combining experiment and theory, we report herein a halide‐vacancy‐driven, ligand‐directed self‐assembly process of CsPbBr3 PQDs. With the assistance of oleic acid and didodecyldimethylammonium sulfide, surface‐Br‐vacancy‐rich CsPbBr3 PQDs self‐assemble into nanowires (NWs) that are 20–60 nm in width and several millimeters in length. The NWs exhibit a sharp photoluminescence profile (≈18 nm full‐width at‐half‐maximum) that peaks at 525 nm. Our findings provide insight into the defect‐correlated dynamics of PQDs and defect‐assisted fabrication of perovskite materials and devices.

Halogen Vacancies Enable Ligand-Assisted Self-Assembly of Perovskite Quantum Dots into Nanowires.

Interest has been growing in defects of halide perovskites in view of their intimate connection with key material optoelectronic properties. In perovskite quantum dots (PQDs), the influence of defects is even more apparent than in their bulk counterparts. By combining experiment and theory, we report herein a halide-vacancy-driven, ligand-directed self-assembly process of CsPbBr3 PQDs. With the assistance of oleic acid and didodecyldimethylammonium sulfide, surface-Br-vacancy-rich CsPbBr3 PQDs self-assemble into nanowires (NWs) that are 20-60 nm in width and several millimeters in length. The NWs exhibit a sharp photoluminescence profile (≈18 nm full-width at-half-maximum) that peaks at 525 nm. Our findings provide insight into the defect-correlated dynamics of PQDs and defect-assisted fabrication of perovskite materials and devices.

Damage mechanisms in elastomeric foam composites: Multiscale X-ray computed tomography and finite element analyses

To understand the mechanisms of damage initiation and propagation in glass microballoon (GMB)/silicone elastomer matrix syntactic foam composites, multiscale X-ray computed tomography images obtained during in situ compression were analyzed using quantitative image processing and digital volume correlation (DVC) techniques. High-resolution tomograms revealed that both the initiation and propagation of GMB collapse depended on the local clustering of GMBs, leading to the formation of pseudo-crush bands in the composite. This resulted in prominent bands of axial strain variation that grew to several millimeters in length as revealed by DVC. A new mechanism based on stress redistribution around collapsed GMBs is proposed to explain the damage propagation, which is supported by finite element analysis and successfully captures the effects of cluster orientation on the observed damage.

The Generation of Warm Dense Matter Using a Magnetic Anvil Cell

Warm dense matter is present at the heart of gas giants and large exo-planets. Yet, its most basic properties are unknown and limit our understanding of planetary formation and evolution. In this state, where pressure climbs above 1 Mbar, matter is strongly coupled and quantum degenerate. This combination invalidates most theories capable of predicting the equation of state, the viscosity or heat conductivity of the material. When such properties are missing, understanding planetary evolution becomes an arduous endeavor. Henceforth, research in this field is actively growing, using high power laser or heavy ion beams to produce samples dense enough to overcome the 1 Mbar limit. These samples are not actively confined and tend to expand rapidly, precluding the existence of any thermodynamically stable equilibrium. However, a mega-ampere-class pulsed-power generator can produce confined matter in the Mbar range, providing two conditions are being met. First, the sample needs to be compressed cylindrically, to maximize magnetic pressure (compared to slab compression). Second, a damper must be used to preclude the formation of a corona around the sample. This corona robs the main sample from valuable current and limits the homogeneity of the compression. According to numerical simulations, the setup proposed here, and called a magnetic anvil cell, can reach pressure on the order of 1 Mbar using a mega-ampere pulsed power driver. These samples span several millimeters in length. Unlike diamond anvil cell, which pressure is limited below 1 Mbar due to materials strength, the magnetic anvil cell has virtually no pressure limit. Further, the current heats the sample to several eV, a temperature well beyond diamond anvil cell capabilities.

The Where of Mineral Names: Skorpionite, Skorpion Mine, Lüderitz District, Karas Region, Namibia

Skorpionite, Ca3Zn2(PO4)2CO3(OH)2·H2O, forms acicular, vitreous, colorless monoclinic crystals a few millimeters long and seldom more than several millimeters in length (fig. 1). These are elongate...

Electrospun magnetic cobalt–carbon nanofiber composites with axis-sheath structure for efficient peroxymonosulfate activation

Cobalt–carbon nanofiber composites (Co-CNFs) were synthesized by electrospinning and subsequent carbonization and their performance for peroxymonosulfate (PMS) activation was evaluated. Co-CNFs have a large aspect ratio (150 nm in diameter and several millimeters in length) to avoid aggregation and large specific surface area (1304 m2/g) to provide more reaction sites for enhancing catalytic activities. Zero valence cobalt was proved to be the main cobalt species of axis or core of the fiber, which might account for its excellent magnetic response, and Co3O4 was the main cobalt species of sheath or coat according to XRD and XPS results. The Co-CNFs exhibited higher catalytic performances than Co3O4 or CNFs for PMS activation and dyes were completely removed in a short time in the Co-CNFs/PMS system. The Co-CNFs derived from cobalt acetate demonstrated the highest catalytic performance and their Co leaking was similar to that of catalysts derived from other cobalt salts. The degradation efficiency increased with the carbonization temperature, cobalt loading, degradation temperature, PMS and catalyst dosage. The dye degradation processes followed pseudo-first-order kinetics. The activation energy of Co-CNFs/PMS/orange G system was derived as 29.8 kJ/mol by the Arrhenius equation. The Co-CNFs exhibited high catalytic performances and excellent stability for five repetitive usage. The possible orange G degradation pathway was proposed based on intermediate detection.

Growth of preexisting abnormal grains in molybdenum under static and dynamic conditions

This investigation compares the growth rates of preexisting abnormal grains under both static and dynamic conditions. Abnormal grains several millimeters in length were produced in two commercial-purity molybdenum (Mo) materials by tensile straining at temperatures from 1923 to 2073K (1650–1800°C). This process is termed dynamic abnormal grain growth (DAGG) because it produces abnormal grains during concurrent plastic straining. DAGG creates abnormal grains at much lower temperatures than does static abnormal grain growth (SAGG). Abnormal grains created through DAGG were characterized with their surrounding microstructures and were then subjected to annealing treatments. Only one-third of the preexisting abnormal grains subsequently grew by SAGG. Among these, SAGG occurred only in those specimens that required the largest strains to initiate DAGG when creating the abnormal grain(s). The rates of boundary migration observed for SAGG were approximately two orders of magnitude slower than those for DAGG. When DAGG in one specimen was interrupted by extended static annealing, it did not recur when straining resumed. The dislocation substructure developed during hot deformation, which includes subgrains typical of five-power creep, is critically important to both DAGG and SAGG of preexisting abnormal grains under the conditions examined.

Fatigue propagation of short and long cracks in gaseous hydrogen environment in 3.5NiCrMoV steel

Abstract Turbo generators for nuclear plants are mostly equipped with hydrogen cooling systems. Current practice of characterizing the growth of fatigue cracks on the basis of fracture mechanics primarily relies on fatigue tests for long cracks which are typically of several millimeters in length. However, in view of extended life for the plants, the damage tolerance evaluation of such fatigue-critical engineering components requires understanding of the propagation of cracks of significantly smaller dimensions. Then the near threshold of short cracks is investigated and compared to the behavior of long crack by experiments under 4 bar hydrogen atmosphere. The short crack fatigue propagation in hydrogen atmosphere is shown similar to that in air, growing faster than the long crack and at ΔK ranging below the long crack threshold; this effect is related to a reduced crack closure shielding. The propagation behavior of long crack under hydrogen atmosphere is shown similar to that obtained in air in the low rate range, i.e. when the maximum of the stress intensity factor K max is lower than a critical level of about 16 MPa m 1/ 2 with higher crack growth rate than in high vacuum. This environment effect is related to the presence of residual water vapor in both gases. For higher K max , much faster growth rates under hydrogen atmosphere in comparison to air and vacuum are observed and related to hydrogen assisted intergranular propagation combining fatigue and sustained loading damage. The results are discussed on the basis of micrographic observations supporting the involved mechanisms.

Self-assembly of nanotubes and ordered mesostructures using weak interactions

Two simple organic compounds, 5-nitroisophthalic acid (npa) and 4,4′-bipyridine (bpy), were used as building blocks for supramolecular self-assembly by hydrothermal synthesis. SEM, TEM, and XRD were used to analyse the multi-step assembly process in which npa and bpy assembled into nanotubes (or nanobelts) of about 30–100 nm in diameter and several millimetres in length and microtubes (or microbelts). The tubes then further assembled to form complex ordered structures, such as pom-pom-shaped and flower-like mesostructures.

Dragon kings of the deep sea: marine particles deviate markedly from the common number-size spectrum.

Particles are the major vector for the transfer of carbon from the upper ocean to the deep sea. However, little is known about their abundance, composition and role at depths greater than 2000 m. We present the first number-size spectrum of bathy- and abyssopelagic particles to a depth of 5500 m based on surveys performed with a custom-made holographic microscope. The particle spectrum was unusual in that particles of several millimetres in length were almost 100 times more abundant than expected from the number spectrum of smaller particles, thereby meeting the definition of “dragon kings.” Marine snow particles overwhelmingly contributed to the total particle volume (95–98%). Approximately 1/3 of the particles in the dragon-king size domain contained large amounts of transparent exopolymers with little ballast, which likely either make them neutrally buoyant or cause them to sink slowly. Dragon-king particles thus provide large volumes of unique microenvironments that may help to explain discrepancies in deep-sea biogeochemical budgets.

Growth of threaded AlN whiskers by a physical vapor transport method

Threaded aluminum nitride (AlN) whiskers are grown by a physical vapor transport method in a radio-frequency induction heating furnace. The resultant whiskers are characterized by X-ray diffraction, Raman scattering, scanning electron microscopy, transmission electron microscopy and photoluminescence. The analysis shows that the whiskers are single-crystalline, wurtzite AlN. The threaded AlN whiskers are 0.5 μm∼100 μm in diameter and several millimeters in length in the fiber direction, and have lots of tiny sawteeth on the surface. The morphology of this threaded AlN whisker is beneficial for bonding when the whisker is used in composite. The growth of the whiskers is dominated by the vapor—solid (VS) mechanism, and the particular morphology might result from an oscillating condition produced in the radio-frequency induction heating furnace.

Axonal fasciculation and the role of polysialic acid‐neural cell adhesion molecule in rat cortical neurons

Axonal fasciculation is a mechanism deployed by growing axons to reach their targets during development of the nervous system. Published data have suggested the involvement of neuronal cell adhesion molecules (NCAM) in axonal fasciculation. We have characterized the formation of axonal fascicles in serum-free, primary cultures of cortical neurons from embryonic rat brains. Unlike the published data, axonal fascicles in our system have a unique morphology: they are waveform, are rarely thicker than 20 μm, and can reach up to several millimeters in length. We observed an age and time dependence in the formation of fascicles. They formed only in cultures from embryonic day 15-17 brain and only between 4 days in vitro (DIV) and 11 DIV. Electron microscopy showed that the fascicles consisted of mostly axonal processes. Immunocytochemical staining confirmed that the fascicles were positive for the 66-kDa neurofilament protein, NF66, but they contained few, if any, microtubule-associated protein-2-positive or glial fibrillary acidic protein-positive processes. Polysialic acids appeared to be critical in the formation of fascicles. Neuraminidase treatment prevented the formation of fascicles when added before 5 DIV. Addition of a specific inhibitor blocked the effect of neuraminidase. The cortical neurons in our model shared several important features with axon fasciculation in vivo and may provide a unique system for studying the molecular mechanisms involved in the formation of axonal tracts in the brain.