Sharp Edge Profiles Research Articles

Fluid resonance in narrow gaps formed by three-box system with sharp and round edge profiles under irregular wave actions

Fluid resonance within narrow gaps in multiple-box systems with sharp and round edge profiles under irregular wave actions are investigated by using a viscous fluid flow solver based on OpenFOAM® package. In difference to the two-peak behavior under regular wave actions, the variation of free surface amplitudes in narrow gaps with incident spectral peak frequencies show the single-peak behavior, including the sharp and round edge profiles. Spectral analysis indicates that the wave spectrums of fluid oscillations in narrow gaps mainly around the first- and/or second-order resonant frequencies. The second-order fluid resonance is easier to be aroused for round edge profiles than that for sharp edge profiles. Furthermore, the statistical and histogram results indicate the significant periods are always around the resonant frequencies; while the corresponding standard deviations approach to cover the region between two resonant frequencies. The above results confirm that the wave responses in narrow gaps mainly oscillate with two resonant frequencies under irregular wave actions.

Electric discharge aided surface post-treatment of laser powder bed fused non-planar metallic components for enhanced form accuracy

Laser powder bed fusion (LPBF) of metals is an advanced technology gaining popularity in the manufacturing domain for producing near net shape products. The feasibility in batch production and design freedom highlights the promising scope of LPBF over conventional fabrication methods. However, loss of geometrical and dimensional accuracy is a critical challenge in LPBF due to solidification induced volumetric shrinkage and formation of surface irregularities. The aforementioned challenge gets aggravated whenever the fabricated components are non-planar. Studies on post-processing induced modification of dimensional and form accuracy of LPBF components is limited in literature. Moreover, the existing post-treatment operations using laser source, chemicals and mechanical forces exhibit limitations in ensuring desired geometrical accuracy in LPBF components. Therefore, the feasibility evaluation of integrating an alternate post-processing method with LPBF in improving geometrical accuracy become meaningful and worth exploring. Thus, the present study investigates the efficacy of a low energy thermo-electric post-processing method called wire electrical discharge polishing (WEDP) in ensuring geometrical form and dimensional accuracy of LPBF components. The study proposes a mathematical model which discloses the factors to be considered for dimension compensation in computer aided design (CAD) model. The results of the present study indicate that the proposed approach can impart notable reduction in form deviation leading to improved geometrical accuracy. The substantial error in terms of circularity over LPBF curved specimens were drastically reduced after WEDP process. Moreover, the cylindricity of curved specimens was improved by ~80 %. Despite the reduction in flatness error to ~7 μm, the irregularities pertaining to the edges were successfully removed from inclined LPBF surfaces resulting in sharp edged profile. The polishing speed was observed to be strongly dependent on the stair-stepping effect over vertically built LPBF surface. The discharge energy in WEDP played a vital role in influencing the circularity and surface integrity of the processed surface. Furthermore, the thermal impact of WEDP process leads to microstructural modification near the surface, whereas residual stress state after WEDP remains similar to LPBF condition. In a nutshell, the WEDP method looks promising in improving the geometrical and dimensional accuracy of LPBF components thereby enhancing the acceptability of parts in industrial applications.

Blades Optimization for Maximum Power Output of Vertical Axis Wind Turbine

Wind power is a significant and urging sustainable power source asset to petroleum derivatives. Wind machines, for example, H-Darrieus vertical pivot wind turbines (VAWTs) have increased much notoriety in research network throughout the most recent couple of decades because of their applications at destinations having moderately low wind speed. Be that as it may, it is noticed that such wind turbines have low effectiveness. The point of this examination is to plan rotor cutting edges which could create most extreme power yield and execution. Different plan factors, for instance, harmony length, pitch edge, rotor distance across, cutting edge length and pitch point are explored to upgrade the presentation of VAWT. Rotor cutting edges are manufactured using the NACA-0030 structure and tried in wind burrow office and contrast its outcomes and DSM 523 profile. Numerical simulations are performed to get best geometry and stream conduct for achieving greatest power. It is seen that for higher tip-speed-proportion (TSR), shorter harmony length and bigger distance across the rotor (i.e., lower robustness) yields higher effectiveness in NACA 0030. Nevertheless, for lower TSR, the more drawn out agreement length and slighter distance across rotor (i.e., higher strength) gives better implementation. The pitch point is - 2° for TSR = 3 and - 3° for TSR = 2.5. The most extreme power yield of the wind turbine is acquired for the sharp edge profile NACA 0030. Besides, instantaneous control coefficient, power coefficient (CP) is the greatest reason for azimuthal edge of 245° and least esteem for 180°.

Producing anomalous uniform periodic nanostructures on Cr thin films by femtosecond laser irradiation in vacuum.

We report on producing unprecedentedly uniform periodic structures on chromium thin films in vacuum conditions with irradiation of femtosecond laser pulses. In sharp contrast to the observations in air, the achieved surface structures of the ablated groove arrays are surprisingly found to have not only an extraordinarily uniform distribution but also a deep-subwavelength period of 360 nm. The measured both width and depth of the ablated periodic grooves are 150 and 120 nm, respectively, showing a large depth-to-width ratio and sharp-edge profiles. Remarkably, such well-organized nanostructures can be enabled to robustly extend into an infinitely long range via the sample scanning and even have a large-area production with a cylindrical lens. Raman spectral analyses reveal that the regular formation of such nanostructures benefits from avoiding the material oxidation and thermal disturbance of the air plasma on the sample surface.

Tailoring sidewall profiles of magnetic tunnel junctions fabricated with various etching conditions

Structural and compositional characteristics of MgO-based magnetic tunnel junctions were characterized using advanced transmission electron and focused-ion beam microscopies. These junctions were fabricated from two ferromagnetic layers separated by a dielectric one and have a switchable resistance that depends upon the relative magnetizations of those two ferromagnetic layers. Certain etching conditions were used to complete the fabrication process aiming to achieve sharp-edge profiles on either side of the pillars. Controlling the edge profiles of those fabricated pillars enables to avoid shortcuts that induce magnetoresistance effect. Not only structural properties of each layer in the MgO junction are characterized, but its compositional characteristics are also explored with electron energy loss spectroscopy, this aims to elucidate the role of elements existing in the given MgO structure. Results of this work are of technological interest since they provide a better understanding in the microstructural properties of the MgO-based magnetic tunnel junctions.

Localized deoxygenation of graphene oxide foil by ion microbeam writing

An efficient mask-less production of patterns in insulating foils of graphene-oxide was carried out under impact of 5 MeV alpha particle beams delivered by the Ion Micro Beam system at the Tandetron Laboratory of the Nuclear Physics Institute in Rez (Czech Republic). Graphene-oxide (GO) matrix has been exposed to controlled fluences with the aim of inducing deoxygenation and enhancement of the electrical conductivity in selected areas of the exposed samples. The reported designed patterns and their sharp edge profiles demonstrate the feasibility of the process.The compositional changes in the exposed areas of the GO were investigated by Rutherford backscattering spectrometry, elastic recoil detection analysis, scanning electron microscopy, and correlated with the electrical properties measured by a standard 2-point probe technique.

Development a projection ion beam instrument that uses a gas ion source for metal-contamination-free microsampling

The authors have developed a metal-contamination-free ion beam instrument with a duoplasmatron that serves as a gas ion source and a projection ion beam optical system that generates a shaped gas ion beam. The luminance of the duoplasmatron ion source is low. However, a projection ion beam optical system can increase the ion current with sharp beam edge profiles enough for microsampling fabrication. A metal-contamination-free shaped gas beam can be used to achieve clean inline sampling and wafer return strategy. The irradiation system of the instrument has three electrostatic lenses, an E × B mass separator, and a mechanism for bending the ion beam to prevent neutral particles from irradiating the samples. The instrument also has a gas flow system for ion beam assisted deposition and a needle transport system for microsampling. Experiments using a prototype implementation demonstrated that microsampling can be achieved by using shaped gas ion beams.

Micro-grooving into thick CVD diamond films via hollow-cathode oxygen plasma etching

Hollow-cathode oxygen plasma etching was proposed as a promising means to make micro-texturing into CVD diamond coatings. Oxygen ions and electrons were confined in the hollow-cathode to have higher ion and electron densities in the order of 1017 to 1018m−3 in the inside of hollow-cathode. Quantitative plasma diagnosis proved that direct reaction of oxygen atom or radicals with carbon in the diamond coating should drive the reactive ion etching (RIE) process. A diamond-coated WC (Co) disc specimen was employed to describe the RIE-behavior with aid of stainless steel mask with the line width of 100μm. Surface depth profile measurement as well as the Raman spectroscopy demonstrated that a micro-groove was precisely etched into the diamond film as a sharp-edged profile.

Formation of indium tin oxide film by wet process using laser sintering

Indium tin oxide (ITO) films were prepared via a very simple and low-cost preparation technique based on a wet process using a continuous wave (CW) laser and an indium tin (In–Sn) alloy nanoparticle ink. The formation of continuous transparent conductive films using a laser sintering method and micropatterning of the ITO films using a laser direct writing method were investigated. This process is simpler than the conventional two-step heat treatment method and other wet processes that use ITO nanoparticles as starting materials. In addition, the optical and electrical properties of the ITO films were improved. Notably, the conductivity and transmittance were remarkably influenced by the processing parameters, including the laser power and scan speed. Suitable processing conditions were thus investigated and optimized, and ITO micropatterns with accurate linear and sharp edge profiles were obtained by controlling the laser power and focusing conditions in the laser direct writing process.

Theoretical analysis of lens array for uniform irradiation on target in multimode fiber lasers

We propose and demonstrate a scheme to smooth and shape the on-target patterns in multimode fiber lasers, which includes expanding-collimating system and lens array (LA). A smooth pattern with flat-top and sharp-edge profiles can be obtained with the irradiation nonuniformity decreasing significantly. We analyze the effects of the parameters such as defocus distance, the tilt angles, the number of the incident fiber lasers, and the diffraction-weakened LA on the uniformity irradiation of target by numerical simulations.

The visibility of IQHE at sharp edges: experimental proposals based on interactions and edge electrostatics

The influence of the incompressible strips on the integer quantized Hall effect (IQHE) is investigated, considering a cleaved-edge overgrown (CEO) sample as an experimentally realizable sharp edge system. We propose a set of experiments to clarify the distinction between the large-sample limit when bulk disorder defines the IQHE plateau width and the small-sample limit smaller than the disorder correlation length, when self-consistent edge electrostatics define the IQHE plateau width. The large-sample or bulk quantized Hall (QH) regime is described by the usual localization picture, whereas the small-sample or edge regime is discussed within the compressible/incompressible strips picture, known as the screening theory of QH edges. Utilizing the unusually sharp edge profiles of the CEO samples, a Hall bar design is proposed to manipulate the edge potential profile from smooth to extremely sharp. By making use of a side-gate perpendicular to the two-dimensional electron system, it is shown that the plateau widths can be changed or even eliminated altogether. Hence, the visibility of IQHE is strongly influenced when adjusting the edge potential profile and/or changing the dc current direction under high currents in the nonlinear transport regime. As a second investigation, we consider two different types of ohmic contacts, namely highly transmitting (ideal) and highly reflecting (non-ideal) contacts. We show that if the injection contacts are non-ideal, but still ohmic, it is possible to measure directly the non-quantized transport taking place at the bulk of the CEO samples. The results of the experiments we propose will clarify the influence of the edge potential profile and the quality of the contacts, under QH conditions.

Femtosecond laser induced micropatterning of graphene film

Micropatterning of CVD synthesized large area graphene film is demonstrated with femtosecond laser cutting process. Homogenous microribbon or other patterned structure can be fabricated without using any resist or other material containing the graphene surface within a very short duration. Once the suitable laser beam doses are determined, sharp edge profile and clean etching are obtained. Scanning electron microscopic study shows that the patterned microribbon is having 5 μm width and mm in length. The width of the patterned microribbon can be controlled with control of laser energy and preprogramming of laser ablation process. Raman study at the edge of the microribbon shows increase in D peak and appearance of D + G mode, signifying edge defects. The defect can be explained from the breaking of sp 2 carbon hybridization with oxidation due to laser etching. The Raman study shows no amorphous carbon formation with laser cutting of the graphene film. The presented process shows a simple way to make patterned microribbon on large area graphene sheet which can be extremely necessary for microelectronics fabrication.

Effect of femtosecond laser pulse duration on thin-foil accelerated protons

The influence of pulse duration on proton acceleration using sub-ps (300–30 fs), ultra-intense ( 3.6 × 10 18 W / cm 2 to 3.6 × 10 19 W / cm 2 ), constant energy (0.14 J) laser pulses is studied using 2D simulations. The entire pulse duration is modelled, so that during the rising edge of the pulse a preplasma can naturally expand from the target front and rear sides into vacuum, altering, respectively, laser absorption and electrostatic field generation. In this paper, we study this effect for two target profiles—sharp-edge profile and smooth density gradient at the front side—and we point out the existence of a weak optimum pulse duration for proton acceleration. For the different pulse durations we considered, we first show that the maximum proton energy variations are similar to those of the rear side electrostatic field amplitude. The energy variations, however, are smaller than expected from the field variations, and we explain this effect by considerations on the characteristic proton acceleration time.

Measuring aortic diameter with different MR techniques: Comparison of three‐dimensional (3D) navigated steady‐state free‐precession (SSFP), 3D contrast‐enhanced magnetic resonance angiography (CE‐MRA), 2D T2 black blood, and 2D cine SSFP

To compare nongated three-dimensional (3D) contrast-enhanced magnetic resonance angiography (CE-MRA) with 3D-navigated cardiac-gated steady-state free-precession bright blood (3D-nav SSFP) and noncontrast 2D techniques for ascending aorta dimension measurements. Twenty-five clinical exams were reviewed to evaluate the ascending aorta at 1.5T using: breathhold cine bright blood (SSFP), cardiac-triggered T2 black blood (T2 BB), axial 3D-nav SSFP, and nongated 3D CE-MRA. Three radiologists independently measured aortic size at three specified locations for each sequence. Means, SDs, interobserver correlation, and vessel edge sharpness were statistically evaluated. Measurements were greatest for 3D-nav SSFP and 3D CE-MRA and smallest for T2 BB. There was no significant difference between 3D-nav SSFP and 3D CE-MRA (P = 0.43-0.86), but significance was observed comparing T2 BB to all sequences. Interobserver agreement was uniformly >0.9, with T2 BB best, followed closely by 3D-nav SSFP and 2D cine SSFP, and 3D CE-MRA being the worst. Edge sharpness was significantly poorer for 3D CE-MRA compared to the other sequences (P < 0.001). If diameter measurements are the main clinical concern, 3D-nav SSFP appears to be the best choice, as it has a sharp edge profile, is easy to acquire and postprocess, and shows very good interobserver correlation.

Precision material modification and patterning with He ions

The authors report on the use of a helium ion microscope as a potential technique for precise nanopatterning. Combined with an automated pattern generation system, they demonstrate controlled etching and patterning of materials, giving precise command over the geometery of the modified nanostructure. After the determination of suitable doses, sharp edge profiles and clean etching of areas in materials were observed. In this article they present examples of patterning on SiO2 and graphene, which is particularly relevant. This technique could be an avenue for precise material modification for future graphene based device fabrication. The technique has the potential to revolutionize the way that very thin, one-atomic layer materials are modified in a controlled and predictable way.

Precision cutting and patterning of graphene with helium ions

We report nanoscale patterning of graphene using a helium ion microscope configured forlithography. Helium ion lithography is a direct-write lithography process, comparableto conventional focused ion beam patterning, with no resist or other materialcontacting the sample surface. In the present application, graphene samples onSi/SiO2 substrates are cut using helium ions, with computer controlled alignment,patterning, and exposure. Once suitable beam doses are determined, sharp edgeprofiles and clean etching are obtained, with little evident damage or doping to thesample. This technique provides fast lithography compatible with graphene, with∼15 nm feature sizes.

Influence of subpicosecond laser pulse duration on proton acceleration

The influence of pulse duration on proton acceleration using subpicosecond (30–300 fs), ultraintense (from 3.6×1018 to 3.6×1019 W/cm2), constant energy (0.14 J) laser pulses is studied using two-dimensional simulations. The entire pulse duration is modeled so that during the rising edge of the pulse a preplasma can naturally expand from the target front and rear surfaces into vacuum, altering respectively laser absorption and electrostatic field generation. In this paper, we study this effect for two target profiles (sharp-edge profile and smooth density gradient at the front side) and we point out the existence of a weak optimum pulse duration for proton acceleration. For the different pulse durations we consider, we first show that the maximum proton energy variations are similar to those of the rear side electrostatic field amplitude. The energy variations, however, are smaller than expected from the field variations, and we explain this effect by characteristic proton acceleration time.

Beam smoothing by lens array with spectral dispersion

A scheme of combining technology of lens array (LA) and smoothing by spectral dispersion (SSD) is introduced to improve the irradiation uniformity in laser fusion based on the earlier works on LA. The feasibility of the scheme is also analyzed by numerical simulation. It shows that a focal pattern with flat-top and sharp-edge profile could be obtained, and the irradiation nonuniformity can fall down from 14% with only LA to 3% with both SSD and LA. And this smoothing scheme is depended less on the incidence comparing to other smoothing methods. The preliminary experiment has demonstrated its effectiveness.

Photon Emission at Step Edges of Single Crystalline Gold Surfaces Investigated by Scanning Tunnelling Microscopy

Light emission in scanning tunnelling microscopy arising from Au tips scanning Au(111) surfaces with multiple defects is mapped simultaneously with topography. The remarkably good correspondence between features in the topography and the photon maps masks marked differences in the details of the correlation between the topographic and photonic signal profiles across different types of features. The variation of photon signal with topography is qualitatively explained in terms of the influence of changes in the geometry of the tip–sample nanocavity on the support and scattering of localised surface plasmon modes that are responsible for the light emission. In particular, evidence from optical spectroscopy shows the existence of a higher energy mode when a sharp step edge profiles the tip; this mode is not present in planar facet areas of the same sample.

Magnetic Force Microscopy Study of Track Edge Magnetization structures Recorded on Perpendicular Recording Media

Track edge magnetization structures for a single-layered perpendicular media recorded with ring-type head are observed by magnetic force microscopy (MFM). Quantitative analysis of the microscopic magnetization structure is carried out through spectrum analyses of the MFM images. Magnetization structures with sharp track edge profile are formed by using a trimmed symmetrical pole tip shap write head. Several peaks in the Fourier-transformed spectra are considered to reflect the presence of magnetization irregularities. Medium noise measured at the recorded track edge is about 2.6dB larger than that measured from the DC-erased area.