Elliptical Microstructures Research Articles

Imaging of voltage-controlled switching of magnetization in highly magnetostrictive epitaxial Fe-Ga microstructures.

The magnetoelectric behavior of epitaxial Fe-Ga microstructures on top of a (001)-oriented PMN-PT piezoelectric substrate is imaged with magnetic X-ray microscopy. Additionally, the micron-scale strain distribution in PMN-PT is characterized by X-ray microdiffraction and examined with respect to the results of the Fe-Ga magnetoelectric switching. The magnetic reorientation of Fe-Ga is found to be strongly correlated with size, shape, and crystallographic orientation of the microstructures. In the case of square-shaped structures, size dictates the influence of the strain distribution on both the initialization of the ground state and on the magnetic reorientation during application of voltage. On the other hand, elliptical microstructures demonstrate completely different magnetic responses depending on the relative orientation of their long axis with respect to the crystallographic directions of the PMN-PT. This study demonstrates that engineering the behavior of highly magnetostrictive epitaxial microdevices is possible. It further elucidates that voltage-induced actuation can be largely tuned to achieve the desired type of magnetic switching ranging from vortex circulation reversal, domain wall motion, to a large rotation of magnetization. Because of the outstanding properties of the investigated material system, the reported findings are expected to be of great interest for the realization of next-generation energy-efficient magnetic memory and logic devices.

Directional light beams by design from electrically driven elliptical slit antennas.

We report on the low-energy, electrical generation of light beams in specific directions from planar elliptical microstructures. The emission direction of the beam is determined by the microstructure eccentricity. A very simple, broadband, optical antenna design is used, which consists of a single elliptical slit etched into a gold film. The light beam source is driven by an electrical nanosource of surface plasmon polaritons (SPP) that is located at one focus of the ellipse. In this study, SPPs are generated through inelastic electron tunneling between a gold surface and the tip of a scanning tunneling microscope.

Deepening subwavelength acoustic resonance via metamaterials with universal broadband elliptical microstructure

Slow sound is a frequently exploited phenomenon that metamaterials can induce in order to permit wave energy compression, redirection, imaging, sound absorption, and other special functionalities. Generally, however, such slow sound structures have a poor impedance match to air, particularly at low frequencies and consequently exhibit strong transmission only in narrow frequency ranges. This therefore strongly restricts their application in wave manipulation devices. In this work, we design a slow sound medium that halves the effective speed of sound in air over a wide range of low frequencies (hence our referral to the microstructure as “broadband”), whilst simultaneously maintaining a near impedance match to air. This is achieved with a rectangular array of acoustically rigid cylinders of elliptical cross section, a microstructure that is motivated by combining transformation acoustics with homogenization. Microstructural parameters are optimized in order to provide the required anisotropic material properties as well as near impedance matching. We then employ this microstructure in order to halve the size of a quarter-wavelength resonator (QWR) or equivalently to halve the resonant frequency of a QWR of a given size. This provides significant space savings in the context of low-frequency tonal noise attenuation in confined environments where the absorbing material is adjacent to the region in which sound propagates, such as in a duct. We employ the term “universal” since we envisage that this microstructure may be employed in a number of diverse applications involving sound manipulation.

Highly-sensitive capture of circulating tumor cells using micro-ellipse filters

Circulating tumor cells (CTCs) detection, enumeration and characterization with microfluidic chips has critical significance in cancer prognosis offering a non-invasive “liquid biopsy”. Based on physical differences of size and deformability, we explore micro-ellipse filters consisting of microfuidic slits in series gradually narrowed. Slender tunnels sensitively capture tumor cells with slim chance to escape. Tumor cells could reside at capture sites organized by arrays of micro-ellipse microposts enduring less stress. Circular elliptical microstructures produce smooth flow minimally reducing any damage. “Air Suction” could extremely shorten capture. Capture efficiency comes out to be a robust yield of 90% and percentage obeys Gaussian distribution at various stages. With rare number accurately enumerated, micro-Ellipse filters have been tested high efficiently capturing tumor cells in both whole and lysed blood. To clinically validate the device, the microfluidic chip was utilized to identify and capture CTCs from metastatic breast, colon and non-small-cell lung (NSCLC) cancer patients. CTCs were detected positive in all samples with 4 patients having more than 20 CTCs. Those sensitive results are consistent with theoretical expectation. Efficient micro-ellipse filters enable clinical enumeration of metastasis, on-chip anti-cancer drug responses and biological molecular analysis.

Pollen-inspired synthesis of porous and hollow NiO elliptical microstructures assembled from nanosheets for high-performance electrochemical energy storage

Numerous efforts have recently been focused on designing and synthesizing efficient nanostructures electrode materials for high-efficiency energy storage. Herein, hierarchical porous and hollow NiO elliptical microstructures constructed from nanosheets are synthesized by utilizing the renewable, cost-effective and widespread native rape pollen grains as template. Benefiting from the unique morphology, pollen-templated NiO shows outstanding electrochemical performances as electrode of supercapacitor, such as high specific capacitance (198.7mAhg−1 at 1A·g−1), excellent rate capability (89.2mAhg−1 at 30A·g−1) and long cycling life. Besides, asymmetric supercapacitor device was assembled by using pollen-templated NiO and activated carbon, which deliver excellent cycling stability (103.3% retention after 10,000 cycles) as well as high energy/power density (a high energy density of 66.4Whkg−1 and power density of 22.2kWkg−1). Moreover, the low-cost pollen template-based strategy is found to be a versatile method to prepare other porous and hollow elliptical microstructure of transition-metal oxides.

Analysis of Nanoscale Microstructures in Asphalts of Different Aging States

Asphalt surface features revealed in the tapping-mode atomic force microscope (AFM) have been extensively studied. Most of the existing studies focus on the so-called bee-shaped surface feature, believed to be made of paraffin wax crystals. In the research reported in this paper, five asphalts of widely different aging states and asphaltenes obtained from two of these asphalts were examined by using an AFM in tapping mode. Two types of surface features were identified in all the specimens, as follows: (1) disk-shaped feature rising from the specimen surface, and (2) elliptical (and sometimes irregular) feature slightly recessed from the surface. In addition, a Strategic Highway Research Program (SHRP) asphalt (AAD) was used to study the morphology of asphaltenes in wax-free asphalt. The analysis of the topography and phase images of the microstructures revealed by AFM suggests that the disk-shaped and elliptical microstructures may contain asphaltenes. The morphology of asphaltenes from the asphalt extracted from a 36-year-old pavement appears to match the hypothetical so-called island molecular structure.

Newly observed effects of water on the microstructures of bitumen surface

Bitumen films with a thickness of 350–400μm were prepared on glass microscope slides and studied using atomic force microscopy (AFM) in tapping mode. Upon heating and cooling, elliptical microstructures appeared on the bitumen film surface as expected for bitumen containing wax. These microstructures had different sizes and orientations, and depending on the bitumen type either covered the whole surface of the bitumen film or not. In cases where the surface was not completely covered, both the periphase (elliptical microstructure), considered here to be a wax crystallite, and the perpetua phase (matrix around the periphase) were observed. Typically, at the center of the crystallite, the so-called “bee” microstructure was found, consisting of observed hills and valleys. The bitumen films were submerged in water at ∼23°C, under different experimental conditions, and experienced deformations as a response to forces exerted due to the presence of water. As a result, new topographic features were observed on the bitumen film surfaces, e.g. the microstructures were strongly affected. The valleys of the “bee” microstructure as well as the interfaces between the periphase and the perpetua phase contained material with different mechanical properties from the surrounding surface. The increase in the exposure time to water or larger deformation resulted in the spreading of the material which filled the valleys on the original surface. It is proposed that tension, bending and pressure as a result of water exposure, resulted in cracking of the weakest points of the surface structure. After cracking the material situated underneath the cracked surface seeped up through the cracks, for instance due to upward and downward pressures exerted on the film. From these results, it was concluded that the valleys of the “bee” microstructure and the interfaces between the periphase and the perpetua phase were the weakest points on the bitumen surface microstructure and, therefore, were the first to crack. Furthermore, the appearance of nano-bumps on the surface of the wax crystallites was detected, but neither on the perpetua phase nor on the “new” material which seeped through the possible cracks. This observation suggests that the chemical and mechanical nature of the wax crystallites is different from that of the perpetua phase and of the “new” material which filled the valleys.

Boosted UV emission at 349 nm from mesoporous ZnS

Relatively oxygen-free mesoporous cubic ZnS particles were synthesised via a facile solvo-hydrothermal route using a water–acetonitrile combination. Boosted UV emission at 349 nm is observed from the ZnS prepared by the solvo-hydrothermal route. The increased intensity of this UV emission is attributed to activation of whispering gallery modes of almost elliptical microstructures made of porous nanostructures.