Vertical Pillars Research Articles

Self-assembled growth and magnetic properties of a BiFeO3-MgFe2O4 nanocomposite prepared by pulsed laser deposition

The fabrication and magnetic properties are described for a nano-composite epitaxial thin film system consisting of perovskite phase BiFeO3 and spinel phase MgFe2O4 grown on a (001) SrTiO3 substrate by combinatorial pulsed laser deposition. The MgFe2O4 phase formed well-defined vertical pillars in a BiFeO3 matrix, and both phases were epitaxial with the substrate. The BiFeO3-MgFe2O4 composite films showed soft magnetic behavior and magnetically isotropic properties which is explained by the weak magnetoelastic effects in MgFe2O4.

Novel high-Q modes in thick 2D photonic crystal slabs

The periodic nature of photonic crystals (PCs) (Yablonovitch 1987 Phys. Rev. Lett. 58 2059–62; John 1987 Phys. Rev. Lett. 58 2486–9) has been extensively exploited for the past quarter of a century using photonic bandgap (PBG) effects to manipulate photons in engineered electromagnetic structures. Structures such as photonic crystal nanocavities are widely considered to be key in realizing future nanoscale optoelectronic devices. These cavities are capable of creating resonant modes with high-quality factor (Q) and small mode volume, in other words a large Purcell factor (Purcell 1946 Phys. Rev. 69 681), and have been widely researched in the two-dimensional photonic crystal slab (PCS) defect cavity configuration (Painter et al 1999 J. Opt. Soc. Am. B 16 275–85). Here, we demonstrate for the first time how three confinement mechanisms are thought to coincide to give rise to a high-Q resonance for a slab containing a modified L3 defect where the slab thickness is such that the guiding in the slab is no longer single moded (Tandaechanurat et al 2008 Opt. Express 16 448–55). This is in contrast to the conventional design approach, where the PCS thickness is chosen to be of the order of half a lattice constant to ensure that a PBG exists to confine cavity modes strongly within the slab (Painter et al 1999 J. Opt. Soc. Am. B 16 275–85; Johnson et al 1999 Phys. Rev. B 60 5751–8; Khankhoje et al 2010 Nanotechnology 21 065202). These newly identified high-Q modes can be important in terms of the fabrication of slabs and other devices such as vertical pillars since they allow high-Q factors in thicker and more fabrication tolerant geometries.

Picturing Generosity

In this study, we investigate the success of national campaigns for charitable causes in the Netherlands using historical data from archival sources, including newspapers, and the internet. We describe the 102 national campaigns held in the Netherlands between 1951 and 2011, focusing on uniquely Dutch contextual features such as a society organized along vertical pillars and highly formalized collaboration between international aid organizations. We then formulate and test hypotheses concerning possible explanations for the success of national campaigns as a specific type of fundraising campaign. We focus on the effect of campaigns organized for “innocent” victims, versus campaigns organized for victims of man-made disasters, the effect of media coverage on campaigns, campaign frequency, government contributions, and economic conditions. The results show that campaigns for victims of man-made disasters are less successful. Campaigns organized in periods of fewer competing campaigns and campaigns receiving government support are more successful.

주차보조를 위한 초음파 센서 기반의 주변차량의 주차상태 및 기둥 분류

This paper proposes a classification method of parallel, vertical parking states and pillars for parking assist system using ultrasonic sensors. Since, in general parking space detection module, the compressed amplitude of ultrasonic data are received, the analysis of them is difficult. To solve these problems, in preprocessing state, symmetric transform and noise removal are performed. In feature extraction process, four features, standard deviation of distance, reconstructed peak, standard deviation of reconstructed signal and sum of width, are proposed. Gaussian fitting model is used to reconstruct saturated peak signal and discriminability of each feature is measured. To find the best combination among these features, multi-class SVM and subset generator are used for more accurate and robust classification. The proposed method shows 92 % classification rate and proves the applicability to parking space detection modules.

Design principles for superamphiphobic surfaces

To predict the properties of superamphiphobic layers we analyzed the wetting of a square and a hexagonal array of vertical pillars composed of spheres (radius R) partially sintered together. Apparent contact angles above 150° are obtained by pinning of a non-polar liquid surface at the underside of the top sphere resulting in a Fakir or Cassie state. Analytical equations are derived for the impalement pressure in the limiting case A0 ≫ R2, where A0 is the area of the regular unit cell containing a single pillar. The case of close pillars is investigated numerically. By balancing forces at the rim of a drop, we calculate the apparent receding contact angle. To describe drag reduction of a flowing liquid we calculate the apparent slip length. When considering pressure-induced flow through cylindrical capillaries of radius rc, significant drag reduction occurs only for thin capillaries. The mechanical stability with respect to normal forces and shear is analyzed. Nanoscopic silica glass pillars would be able to sustain the normal and shear stresses caused by capillary and drag forces. For a high impalement pressure and good mechanical stability A0 should be small and R (respectively the neck diameter) should be large, whereas a large A0 and a small R imply low contact angle hysteresis and high slip length.

Finite element modelling of the compressive response of lattice structures manufactured using the selective laser melting technique

Previous work on lightweight energy-absorbing truss based structures has highlighted the potential of SLM-built lattices. Finite element models have been developed to predict the compressive response of lattice structures based on two simple architectures—a body-centred cubic structure (BCC) and a similar structure with vertical pillars (BCC-Z). Both 3D continuum and beam elements have been used to model the structures under quasi-static compressive loads. Key difficulties in modelling the lattice structures have been highlighted and possible solutions have been offered. The results from the FE models are compared to experimental data and have been shown to agree well. The collapse modes predicted by the FE models were also in agreement with the experimental observations. The stress distribution within the BCC unit cells at increasing levels of crush has been identified and shows the formation of plastic hinges in the struts near to the nodal regions. In the latter stages of this investigation, the unit cell geometry was modified in order to enhance the stiffness and yield stress under compressive loading conditions. Predictions made using both analytical and beam element FE models demonstrate that the stiffness and yield strength could be improved by varying the unit cell geometry. Further tests were carried out on modified lattice structures to verify the predictions.

High aspect ratio metal micro and nano pillars for minimal footprint MEMS suspension

Vertical nano and micro pillars perpendicularly rising from a substrate offer two lateral translatory–rotatory degrees of freedom. Electroforming allows their production as small footprint integrated suspension elements of micro to nano scale. This paper demonstrates the design of a novel inertial sensor concept with acceleration sensor and gyroscope function using only one inertial mass. Experimental results using UV Direct LIGA with AZ 125 nXT show the feasibility of a technology demonstrator with a copper micro pillar of 400 μm length and 40 μm diameter. Further work using x-ray Direct LIGA is scheduled for the production of the pillar with a length of 100 μm and a diameter of 3–6 μm. Fabrication concepts and pilot tests show promising possibilities for miniaturization towards nano scale pillars for minimal footprint suspension in MEMS.

Brood comb construction by the stingless bees Tetragonula hockingsi and Tetragonula carbonaria

Tetragonula hockingsi and T. carbonaria are two closely related species of Australian stingless bees. The primary species-specific character is the architecture of the brood comb. The brood comb of T. hockingsi is an open lattice comprising clumps of about ten cells that are connected by vertical pillars. In contrast, in T. carbonaria the brood comb is a compact spiral in which all brood cells (except on the margins) are connected by their walls to adjacent cells at the same height. We made detailed observations of the cell construction process in two colonies of each species. From these observations we formed a species-specific hypothesis about the algorithm followed by the bees during cell construction. The two algorithms allowed us to make predictions about the locations of new cells. Both T. hockingsi and T. carbonaria share a preference for constructing new brood cells in the clefts formed by two or three adjacent existing brood cells, but there are differences in detail for other components of the building process. The fundamental difference in the cell construction process of the two species is that for T. hockingsi, when a cluster of cells contains ten cells, the next cell added to the cluster is offset upwards by half a cell length, or, less often, a vertical pillar rather than a new cell is constructed. In T. carbonaria, cell construction is continuous at the comb margin so that there are no gaps between cells. Furthermore, it seems that T. hockingsi only makes use of local knowledge of the brood comb when deciding to place new brood cells, whereas T. carbonaria could make some building decisions based on knowledge of the total structure. We translated the species-specific algorithms into agent-based lattice swarm computer simulations of the cell construction process for the two species. These simulations produced representations of brood combs that are similar to those seen in vivo, suggesting that our biological rules are realistic.

Automation Highlights from the Literature

Automation Highlights from the Literature

Cost-Effective Silicon Vertical Diode Switch for Next-Generation Memory Devices

In this letter, a cost-effective vertical diode scheme for next-generation memory devices, including phase-change memories (PCMs), is realized. After the contact formation for diodes with only one mask layer, an amorphous silicon (a-Si) film was deposited within the contacts using SiH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ramp-up ambient in a conventional batch-type furnace in order to minimize the growth of native oxide. A deposition/etch-back/deposition scheme enabled us to achieve robust vertical diodes without any seams or interfacial oxide layer within the vertical diode pillars. Subsequent annealing at 600 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C provided solid-phase epitaxial alignment of the a-Si layer. An ideality factor revealed that the new scheme provided noticeable crystallinity of the silicon diodes. Moreover, the electrical characteristics of the diodes verified that the scheme was suitable for full operation of PCM devices.

Curvature-driven capillary migration and assembly of rod-like particles.

Capillarity can be used to direct anisotropic colloidal particles to precise locations and to orient them by using interface curvature as an applied field. We show this in experiments in which the shape of the interface is molded by pinning to vertical pillars of different cross-sections. These interfaces present well-defined curvature fields that orient and steer particles along complex trajectories. Trajectories and orientations are predicted by a theoretical model in which capillary forces and torques are related to Gaussian curvature gradients and angular deviations from principal directions of curvature. Interface curvature diverges near sharp boundaries, similar to an electric field near a pointed conductor. We exploit this feature to induce migration and assembly at preferred locations, and to create complex structures. We also report a repulsive interaction, in which microparticles move away from planar bounding walls along curvature gradient contours. These phenomena should be widely useful in the directed assembly of micro- and nanoparticles with potential application in the fabrication of materials with tunable mechanical or electronic properties, in emulsion production, and in encapsulation.

Large Area Fabrication of Leaning Silicon Nanopillars for Surface Enhanced Raman Spectroscopy

Using a simple two step fabrication process substrates with a large and uniform Raman enhancement, based on flexible free standing nanopillars can be manufactured over large areas using readily available silicon processing equipment.

The quasi-static and blast response of steel lattice structures

Lattice structures based on two simple architectures have been manufactured from 316L stainless steel using the selective laser melting process. The compressive properties of structures based on a body-centered cubic (BCC) and a similar structure with vertical pillars (BCC-Z) were initially investigated at quasi-static rates of strain. Blast tests were subsequently performed on the lattice structures as well as on lattice sandwich structures with CFRP skins. When subjected to quasi-static compression loading, the BCC structure exhibited a progressive mode of failure, whereas the BCC-Z lattice deformed in a buckling-dominated mode of collapse. The blast response of the lattice cubes exhibited a linear dependency on the applied impulse up to the threshold for material densification. Relationships between the blast resistance and both the yield stress and energy absorption characteristics of the lattices have been established and an examination of the failed samples indicated that the collapse modes were similar in both the quasi-static and blast-loaded samples. Finally, the failure modes observed in the blast-loaded sandwich panels were investigated and found to be similar to those observed in the lattice blocks.

Novel MEMS Dipole/Monopole Antenna for Wireless Systems Operating at 77 GHz

In this paper, we present a novel MEMS antenna designed for operation at 77GHz. The antenna consists of two right-angle metal arms which are supported by two vertical silicon walls. These walls are fabricated using bulk micromachining through Deep Reactive Ion Etching (DRIE) process. The two right-angle arms are fed via a microstrip ring coupler which has two input ports. A new process ∞ow is introduced in this paper, which allows the realization of the proposed antenna on a single silicon wafer. The antenna is analyzed and optimized thoroughly using Ansoft/HFSS. The results show that based on the selection of port of excitation, the proposed antenna can radiate either dipole or monopole patterns. In the dipole (monopole) mode, the antenna has impedance bandwidth of 4.3% (4.2%), gain of 8.9dBi (5.5dBi), radiation e-ciency of 94% (95%). Micromachining technology is very attractive for integrated antennas as it ofiers e-cient packaging, high radiation e-ciency, wide impedance bandwidth, and less mutual coupling between antenna elements. These advantages are more di-cult to be achieved using the conventional planar technol- ogy especially at high frequencies. Research carried out on MEMS antennas can be classifled into two main categories. The flrst category features a ∞at antenna, such as patch, realized on a thin membrane surrounded by air. The membrane can be fabricated via either bulk (1) or surface (2) micromachining technology. This results in reducing the efiective dielectric constant of the medium around the antenna and consequently increases the bandwidth and radiation e-ciency. The second category features a 3D antenna, such as horn or waveguide, realized by etching grooves in a number of silicon wafers via bulk micromachining (3). The walls of these grooves are covered with metal. Each groove represents part of the desired 3D structure. The wafers are bonded together to form the complete 3D antenna. In this paper, a novel MEMS antenna design is presented. The proposed antenna is 3D in shape and it can be fabricated on a single silicon wafer without any need for wafer bonding or hybrid integration. The proposed antenna is capable of operating as either dipole or monopole based on the selection of the port of excitation. 2. ANTENNA STRUCTURE AND FABRICATION TECHNOLOGY The proposed MEMS antenna is shown in Fig. 1. It has two vertical silicon walls that can be fabricated using bulk micromachining through 0.675mm thick high resistivity silicon wafer with dielectric constant of 11.9 and conductivity of 0.05S/m. The width, length, and depth of each wall are 70m, 953m, and 475m, respectively. The last two dimensions correspond to ‚g=2 and ‚g=4 at the operating frequency of 77GHz. The thickness of the remaining silicon substrate is 200m. Two horizontal metal arms are covering the top surfaces of the walls. Two vertical pillars with square cross section of 55m £ 55m are drilled through the entire wafer. The inner surfaces of these pillars are covered with vertical metal arms, as shown in Fig. 1. It can be seen in this flgure that there are gaps between the vertical and horizontal arms. The top surface of the substrate is covered with slotted ground metal plane, through which the silicon walls are going up. This plane serves as a re∞ector that increases the directivity of the antenna. Moreover, it isolates between the antenna and the bulk silicon substrate, which reduces the surface wave losses and increases the radiation e-ciency. All metallic parts of this structure are made of copper with thickness of 3m. From the bottom side of the substrate, the vertical arms are connected to the two output ports of a ring coupler made of microstrip lines. Two feeding microstrip lines are connected to the input ports of the ring coupler. The width of each line is 200m which corresponds to 50› at 77GHz. The ring is made of a microstrip line whose width and characteristic impedance are 88m

The Mechanical Properties of Sandwich Structures Based on Metal Lattice Architectures

A range of metallic lattice structures were manufactured using the selective laser melting (SLM) rapid prototyping technique. The lattices were based assemblies of repeating unit-cells with their strands oriented at 0°, ±45°, and 90° to the vertical when viewed from the front. Mechanical tests on the strands and the lattice blocks showed that these systems exhibit a high level of reproducibility in terms of their basic mechanical properties. An examination of the compression failure mechanisms showed that the [±45°] and [±45°, 90°] lattices failed in bending and stretching modes of failure, whereas the [0°, ±45°] lattices failed as a result of buckling of the vertical pillars. Sandwich structures were manufactured by binding woven carbon-fiber reinforced plastic to the lattice structures. Subsequent three-point bend tests on these structures identified the principal failure mechanisms under flexural loading conditions. Here, cell crushing, hinge rotation, and gross plastic deformation in the strands were observed directly under the point of loading. Low-velocity impact tests were conducted on the sandwich beams and a simple energy-balance model was used to understand how energy is absorbed by the sandwich structures. The model suggests that the majority of the incident energy of the projectile was absorbed in indentation effects, predominantly in the core material, directly under the steel indenter.

Health workers' views on quality of prevention of mother-to-child transmission and postnatal care for HIV-infected women and their children

BackgroundPrevention of mother-to-child transmission has been considered as not a simple intervention but a comprehensive set of interventions requiring capable health workers. Viet Nam's extensive health care system reaches the village level, but still HIV-infected mothers and children have received inadequate health care services for prevention of mother-to-child transmission. We report here the health workers' perceptions on factors that lead to their failure to give good quality prevention of mother-to-child transmission services.MethodsSemistructured interviews with 53 health workers and unstructured observations in nine health facilities in Hanoi were conducted. Selection of respondents was based on their function, position and experience in the development or implementation of prevention of mother-to-child transmission policies/programmes.ResultsFactors that lead to health workers' failure to give good quality services for prevention of mother-to-child transmission include their own fear of HIV infection; lack of knowledge on HIV and counselling skills; or high workloads and lack of staff; unavailability of HIV testing at commune level; shortage of antiretroviral drugs; and lack of operational guidelines. A negative attitude during counselling and provision of care, treating in a separate area and avoidance of providing service at all were seen by health workers as the result of fear of being infected, as well as distrust towards almost all HIV-infected patients because of the prevailing association with antisocial behaviours. Additionally, the fragmentation of the health care system into specialized vertical pillars, including a vertical programme for HIV/AIDS, is a major obstacle to providing a continuum of care.ConclusionMany hospital staff were not being able to provide good care or were even unwilling to provide appropriate care for HIV-positive pregnant women The study suggests that the quality of prevention of mother-to-child transmission service could be enhanced by improving communication and other skills of health workers, providing them with greater support and enhancing their motivation. Reduction of workload would also be important. Development of a practical strategy is needed to strengthen and adapt the referral system to meet the needs of patients.

Fabrication of large arrays of high-aspect-ratio single-crystal silicon columns with isolatedvertically aligned multi-walled carbon nanotube tips

This paper describes the fabrication of large arrays(106 unitsin 1 cm2)of 100 µm tall, single-crystal silicon columns with submicron tip cross-sections. The columns areformed using thin film deposition and growth, reactive ion etching, and deep reactive ionetching. The columns can be either slightly tapered or have pencil-like morphology withnanoscaled tip diameter (41 nm). Conformal thin film coating was used to substantially anduniformly modify the porous structure and, thus, vary by orders of magnitude the fluidpermeability of the structure. Gaps between the vertical pillars were varied between9 µm and 50 nm. Isolated45 nm diameter, 5 µm tall plasma enhanced chemical vapour deposited multi-walled carbon nanotubes (MWNTs)were grown on the top surface of the columns using a 7 nm thick evaporated Nifilm as catalyst. Field emission characterization of the resulting structure wasconducted and it is in agreement with scanning electron micrographs of the MWNTs.

Shadow modulated two-dimensional heterostructures using vertical pillars

A vertical pillar shadow epitaxy technique is introduced for fabricating coplanar striped or cross-hatched GaAs∕AlAs two-dimensional heterostructures, where the pattern area of each individual layer can be varied in situ. An array of vertical pillars is mounted adjacent to the substrate wafer to block epitaxial molecular flux, with shadow position determined by the azimuthal substrate angle, and feature resolution set by source diameter. Complex planar heterostructures can be achieved in a single epitaxial growth, such as the checkerboard of superlattices with varying period number demonstrated here. Superlattice layers are characterized via scanning electron microscope, and thicknesses closely match an umbra/penumbra model.

Numerical Simulations of Lightning Surge Responses in a Seismic Isolated Building by FDTD and EMTP

Current distribution and overvoltages in a structure of a seismic isolated building struck by lightning are analyzed by a Finite-Difference Time-Domain (FDTD) method and by the Electromagnetic Transients Program (EMTP). The simulated results by the FDTD method show that the voltage at the first floor, which is an important factor of a design of building installation, shows a damped oscillatory wave. The transient overvoltage is caused by the multiple reflections within the structures and the resonance between a stray capacitance of the structure and an equivalent inductance of the bonding wire, which electrically shunts a rubber insulator installed for dumping earthquake tremor. The investigation shows that the transient response can be expressed by a lumped-parameter equivalent circuit. Two numerical models for circuit analysis method are proposed in this paper. A multiphase model reproduces a distribution of currents flowing through vertical pillars by mutual couplings between the pillars. A single phase model is obtained by a simplification of the multiphase model and gives the voltage at the first floor. The calculation time is remarkably reduced compared to that by the FDTD method. The accuracy of the models is discussed in comparison with the results obtained by the FDTD method.

Investigation on Seasonal Water Area Change in Lake Sakata Based on POLSAR Image Analysis

This paper examines seasonal change of the true water area of Lake Sakata by using Polarimetric Synthetic Aperture Radar area of Lake Sakata by using Polarimetric Synthetic Aperture Radar (POLSAR) image analysis. The true water area includes not only the body of water but also the water area under emerged-plants and/or floating-leave plants in the lake. Statistical POLSAR image analysis is carried out for both X- and L-band data, based on the three-component scattering power decomposition method, where the decomposed components are surface scattering, double-bounce scattering and volume scattering components. From the results of the image analysis for the L-band POLSAR data acquired by Pi-SAR system, it is found that strong double-bounce scattering can be observed at the vicinity of the boundary region between water area and the surrounding emerged-plants area in early and middle summer. This phenomenon is an important factor for environmental monitoring. To verify the generating mechanism of the double-bounce scattering, the Finite-Difference Time-Domain (FDTD) polarimetric scattering analysis is also executed for a simplified boundary model, which simulates the local boundary region around the lake and consists of lots of vertical thin dielectric pillars on a perfect electric conductor (PEC) plate or on a PEC and dielectric hybrid plate. Taking into account the polarimetric feature of the double-bounce scattering obtained by both the FDTD and POLSAR image analyses, one can distinguish the actual water area from the bush of the emerged-plants around the lake, even when the water area is concealed by emerged-plants and/or floating-leave plants. Consequently, it is found that by using the proposed approach, one can estimate the true water area seasonal change for the lake and the surrounding wetland.