Desired Thickness Research Articles

Temperature-dependent growth of topological insulator Bi2Se3 for nanoscale fabrication

Topological insulators and their characteristics are among the most highly studied areas in condensed matter physics. Bi2Se3 nanocrystals were synthesized via chemical vapor deposition at different temperatures on a silicon substrate with a gold catalyst. The effects of temperature on the obtained Bi2Se3 nanocrystals were systematically investigated. The size and length of Bi2Se3 nanocrystals change when the temperature increases from 500 °C to 600 °C. We found that the crystallization quality of the Bi2Se3 nanocrystals synthesized at 560 °C is optimal. At this temperature, we can get the desired thickness and length of the nanocrystals, which is quite suitable for nanoscale fabrication.

Fully Additive Fabrication of Electrically Anisotropic Multilayer Materials Based on Sequential Electrodeposition

MEMS-enabled multilayer composites, in which microfabrication is used to create micron-scale thickness layers within the volume of meso-scale thickness structures, can be exploited to create materials with highly anisotropic electromagnetic properties. Such materials have utility in both sensing and energy applications, including electrostatic and magnetic energy storage and conversion. A fabrication challenge in realizing these classes of materials lies in the size-scale disparity between the thickness of an individual layer and the desired thickness of the final anisotropic material. We demonstrate a fully additive sequential electrochemical deposition approach for such structures, which enables scalable composite volume while maintaining micron-scale individual layer thicknesses. Alternating metal and polymer layers, which exhibit very different electrical conductivities, are continuously electrodeposited in batch-scale. Individual layer thicknesses are controlled by deposition currents and times, while lateral extents are defined by lithographically defined molds. The fabrication process is illustrated using electrodeposited NiFe alloys and polypyrrole, and the anisotropy of electrical conductivity is assessed for potential use of these structures as magnetic cores for high frequency switching converters. Due to the relatively resistive polypyrrole layers, electrical anisotropy of lateral to vertical conductivity exceeding 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> was achieved. This approach offers a solution-based, microfabrication compatible, and manufacturable route to functional composite materials that exhibit high electrical anisotropies.

On pixel-exact rendering for high-order mesh and solution

With the increasing use of high-order methods and high-order meshes, scientific visualization software need to adapt themselves to reliably render the associated meshes and numerical solutions. In this paper, a novel approach, based on OpenGL 4 framework, enables a GPU-based rendering of high-order meshes as well as an almost pixel-exact rendering of high-order solutions. Several aspects of the OpenGL Shading Language and in particular the use of dedicated shaders (GPU programs) allows to answer this visualization challenge. Fragment shaders are used to compute the exact solution for each pixel, made possible by the transfer of degrees of freedom and shape functions to the GPU with textures. Tessellation shaders, combined with geometric error estimates, allow us to render high-order curved meshes by providing an adaptive subdivision of elements on the GPU directly. A convenient way to compute bounds for high-order solutions is described. The interest of using Bézier basis instead of Lagrange functions lies in the existence of fast and robust evaluation of polynomial functions with de Casteljau algorithm. A technique to plot highly nonlinear isolines and wire frames with a desired thickness is derived. It is based on a finite difference scheme performed on GPU. In comparison with standard techniques, we remove the use of any linear interpolation step and the need to generate a priori a fixed subdivided mesh. This reduces the memory footprint, improves the accuracy and the speed of the rendering. Finally, the method is illustrated with various 3D examples.

Fabrication of 128Te thin target for nuclear levels lifetime measurements

Measuring nuclear level lifetimes of pico-seconds and femto-seconds order is important for understanding typical nuclear shapes. To extract such short lifetimes, specially designed thin targets are needed. A thin isotopically enriched 128Te target of thickness ∼ 1.2 mg/cm2 on the thick backing foil of natural gold of thickness ∼ 9.8 mg/cm2 has been prepared for the Doppler shift attenuation method (DSAM) lifetime measurement. The target was made by vacuum deposition technique using the cryogenic pump based Ultra High Vacuum (UHV) chamber available at the Inter University Accelerator Centre (IUAC), New Delhi. In this activity, a specially designed indigenously developed graphite crucible with 1 mm opening was used to minimize material loss and to improve the deposition efficiency of the material. To get the desired thickness of the target, only 20 mg of isotopically enriched 128Te material was used. The quality check of the prepared foil was done by the Energy Dispersive X-ray fluorescence (EDXRF) technique.

Synthesis of Al and Cu wires embedded glass fiber reinforced polymer (AWGFRP and CWGFRP) composites and their mechanical characterization

Abstract In the recent years, researchers have been trying to add ceramic powders such as silica and alumina, carbon nano tubes and other metal wires in the GFRP laminates to find their influence on the laminate properties. In this work, Aluminium and copper wire embedded Glass Fibre Reinforced Polymer laminates (AWGFRP and CWGFRP) were prepared. In the synthesis, woven glass fibre mat of 80 g per square meter is used as reinforcement and epoxy polymer is used as matrix material. During synthesis, over the E glass woven mats aluminium and copper wires of 0.7 mm diameter were embedded and epoxy as matrix is applied by brush and these mats were arranged one over another to get the desired thickness of the laminate. These set-ups were allowed to cure at atmosphere pressure and temperature for 10 days to get the desired properties. Three laminates were prepared in the following manner. One laminate with aluminium wire embedment, the second one with copper wire embedment and the third laminate as plain GFRP laminate were prepared. The mechanical properties such as tensile strength, impact strength, hardness and compressive strength of Aluminium and Copper wire Glass Fibre Reinforced Polymer composites (AWGFRP and CWGFRP) were compared with plain Glass fibre Reinforced Polymer (GFRP) composites.

High‐Performance Phosphorene‐Based Transistors Using a Novel Exfoliation‐Free Direct Crystallization on Silicon Substrates

AbstractPhosphorene is one of the most promising elemental 2D materials. So far, mechanical exfoliation is the main route toward the formation of phosphorene sheets. Although field‐effect transistors are realized on phosphorene, their arrangement and size are dictated by the randomness of the exfoliation and transfer methods. Here, the evolution of highly crystalline and large‐area phosphorene sheets with a laser‐assisted phase transition from red phosphorus directly on silicon substrates in desired locations is reported. The original red phosphorus can be patterned prior to laser‐assisted crystallization to achieve the desired shape, location, and layer thickness (either mono or few). A 1064 nm laser is employed as the source to impart energy onto the red phosphorus layer and to achieve allotrope transformation. A combination of argon–oxygen (Ar:O2) and helium–hydrogen (He:H2) gases is exploited in a sequential manner to lead to phosphorene sheets. Various techniques are used to examine the physical properties of phosphorene sheets. Field‐effect transistors are made at different phases of crystallization and a high field‐effect mobility of 1450 cm2 V−1 s−1 and on/off ratio of 103 are achieved. Moreover, the optoelectrical characteristics of the phosphorene‐based phototransistors under different illumination powers and back‐gate voltages are investigated, showing superior performance.

Can Oblique Sliced Method Avoid Warping?

Warping is the most important problem of costal cartilage grafts used in secondary rhinoplasties. The aim of this study is to show that costal cartilage grafts prepared with oblique sliced method (OSM), can solve the warping problem and provides successful results in both functional and aesthetic appearance. There are 42 patients who had previous nose surgery and dissatisfied with their facial appearance included in the study to perform secondary rhinoplasty with costal cartilage graft OSM technique. The outcomes of the operations were performed objectively using facial measurements and subjectively using rhinoplasty outcomes evaluation (ROE) scale, before and 12 months after the operation. The mean of total ROE score was 8.171 ± 3.285 on the pre-operative period and it was increased to 19.11 ± 3.652 where the P value was found to be <0.0001. And the post-operative 12th month period all values of nasal dorsal angulation was lower then 1° and the mean of angulation degrees was 0.224° with the minimum value 0.000° and maximum value 0.801°. The study revealed the outcome of rhinoplasty which done by OSM was statically significant both subjective patient's satisfaction and objective facial measurements. The authors suggest using of OSM in secondary rhinoplasties because the graft can be easily prepared with the desired thickness and carved into different shape without risk of warping.

Planar Brownian motion and Gaussian multiplicative chaos

We construct the analogue of Gaussian multiplicative chaos measures for the local times of planar Brownian motion by exponentiating the square root of the local times of small circles. We also consider a flat measure supported on points whose local time is within a constant of the desired thickness level and show a simple relation between the two objects. Our results extend those of Bass, Burdzy and Khoshnevisan and in particular cover the entire $L^1$-phase or subcritical regime. These results allow us to obtain a nondegenerate limit for the appropriately rescaled size of thick points, thereby considerably refining estimates of Dembo, Peres, Rosen and Zeitouni.

Design and development of an active indirect solar dryer for cooking banana

Active indirect mode solar dryers were designed and constructed for drying of cooking banana in Umudike, Nigeria. The dryers were constructed with special focus on the air inlet, to examine if the air inlet area had effect on the performance of the dryers. The air inlet areas were considered in five levels and four shapes namely: square, rectangular, circular and triangular. A total of 52 dryers were required for the experiment, based on the combination of factors and levels of experiment using the Central Composite Rotatable Experimental Design adopted for the study. Fresh samples of cooking banana were obtained from a local market, peeled, cleaned and sliced to the desired thickness for the drying experiment. Open sun drying was used a control. Data was collected on a two hourly interval on each drying day between the month of January and March. The dryers were observed to reduce the moisture content of the products from 4.53 to 1.57 kg within 9 to 16 h of drying, while moisture was reduced from 68.97 to 12.00% (wet basis). The dryers were able to conserve almost 40% of the total drying time for the products when compared to open sun drying. The efficiency of the driers ranged from 13.85 to 31.84%. It was observed that the air inlet area of the dryer had significant effect on the efficiency of drying of the product.

Draining under gravity in steel galvanization.

The problem of the coating of steel has been considered in several Mathematics in Industry study groups. In this process, after passing through a bath of molten alloy, steel sheeting is drawn upward to allow draining under gravity and stripping using an air knife, leaving a coating of desirable thickness. Here we discuss some aspects of the problem and in particular the gravity draining component. The problem is a very nice introduction to industrial modelling for students, but is also relevant for manufacturing.

Reversible graphitization of SiC: A route towards high-quality graphene on a minimally step bunched substrate

We show that the thermal decomposition of SiC (0001) surface is reversible, if carried out in near-equilibrium conditions, with an external Si atomic beam applied to the substrate. Taking advantage of this observation we design a novel process, allowing for the growth of uniform, few-layers, ABC-stacked graphene. This process is composed of two phases; the first is a graphene film growth and the second is its reduction to the desired thickness. We find that, when using this scheme instead of the conventional ones the heavy step bunching on the substrate is avoided, and the step heights remain below 2.75 nm.Since the step bunching is one of the most important factors prohibiting the use of epitaxial graphene on SiC in certain application areas, such as analog electronics or sensing, our method has the potential to be applied in future wafer-scale graphene technologies and processes. Moreover, the results obtained in this work exemplify general near-equilibrium phenomena and therefore they may be also relevant for growth methods of other 2D materials.

Response of the temporal turbulent boundary layer to decaying free-stream turbulence

The turbulent boundary layer developing under a turbulence-laden free stream is numerically investigated using the temporal boundary layer framework. This study focuses on the interaction between the fully turbulent boundary layer and decaying free-stream turbulence. Previous experiments and simulations of this physical problem have considered a spatially evolving boundary layer beset by free-stream turbulence. The state of the boundary layer at any given downstream position in fact reflects the accumulated history of the co-evolution of boundary layer and free-stream turbulence. The central aim of the present work is to isolate the effect of local free-stream disturbances existing at the same time as the ‘downstream’ boundary layer. The temporal framework used here helps expose when and how disturbances directly above the boundary layer actively impart change upon it. The bulk of our simulations were completed by seeding the free stream above boundary layers that were ‘pre-grown’ to a desired thickness with homogeneous isotropic turbulence from a precursor simulation. Moreover, this strategy allowed us to test various combinations of the turbulence intensity and large-eddy length scale of the free-stream turbulence with respect to the corresponding scales of the boundary layer. The relative large-eddy turnover time scale between the free-stream turbulence and the boundary layer emerges as an important parameter in predicting if the free-stream turbulence and boundary layer interaction will be ‘strong’ or ‘weak’ before the free-stream turbulence eventually fades to a negligible level. If the large-eddy turnover time scale of the free-stream turbulence is much smaller than that of the boundary layer, the interaction will be ‘weak’, as the free-stream disturbances will markedly decay before the boundary layer is able be altered significantly as a result of the free-stream disturbances. For a ‘strong’ interaction, the injected free-stream turbulence causes increased spreading of the boundary layer away from the wall, permitting large incursions of free-stream fluid deep within it.

Microfluidic fabrication of stable collagen microgels with aligned microstructure using flow-driven co-deposition and ionic gelation

The controlled biofabrication of stable, aligned collagen hydrogels within microfluidic devices is critically important to the design of more physiologically accurate, longer-cultured on-chip models of tissue and organs. To address this goal, collagen-alginate microgels were formed in a microfluidic channel by calcium crosslinking of a flowing collagen-alginate solution through a cross-channel chitosan membrane spanning a pore allowing ion diffusion but not convection. The gels formed within seconds as isolated islands in a single channel, and their growth was self-limiting. Total gel thickness was controlled by altering the concentration of calcium and collagen-alginate flow rate to reach an equilibrium of calcium diffusion and solution convection at the gel boundary, for a desired thickness of 30–200 μm. Additionally, less calcium and higher flow produced greater compression of the gel, with regions farther from the pore compressing more. An aligned, stable collagen network was demonstrated by collagen birefringence, circumferential texture orientation, and little change in gel dimensions with de-chelation of calcium from alginate by prolonged flow of EDTA in the channel. Resultant gels were most stable and only slightly asymmetric when formed from solutions containing 8 mg ml−1 collagen. Diffusion of 4 kDa and 70 kDa fluorescently-labeled dextran indicated size-dependent diffusion across the gel, and accessibility of the construct to appropriately-sized bioactive molecules. This work demonstrates the physicochemical parameter control of collagen gel formation in microfluidic devices, with utility toward on-chip models of dense extracellular matrix invasion, cancer growth and drug delivery to cells within dense extracellular matrix bodies.

A Novel Method for Electrospinning Nanofibrous 3-D Structures

The fast and precise fabrication of three-dimensional (3-D) structures made of nanofibers is an important development trend in the electrospinning technique. This paper describes a new and facile method of electrospinning to fabricate nanofibrous 3-D structures. The nanofibrous 3-D structures can be engineered to have the desired layer thicknesses, where the fiber spacing, density (i.e., fiber volume/unit volume), as well as shape of the structure may be controlled. While innumerable structural variations are possible with this method, this paper discusses, as proof-of-concept, a few cases that illustrate how 3-D nanofiber webs can be made for filtration application. Computerized automation of the method will make it possible to build almost any 3-D web structure suitable for a myriad of applications including ultra-light-weight insulation and scaffolds for hydrogel preparation and tissue.

Toward High Solar Cell Efficiency with Low Material Usage: 15% Efficiency with 14 μm Polycrystalline Silicon on Glass

Liquid‐phase‐crystallized silicon (LPC‐Si) is a bottom‐up approach to creating solar cells with the potential to avoid material loss and energy usage in wafer slicing techniques. A desired thickness of silicon (5–40 μm) is crystallized with a line‐shaped energy source, which is a laser, herein. The first part reports the efforts to optimize amorphous silicon contact layers for better surface passivation. The second part covers laser firing on the electron contact. It enables a controllable trade‐off between charge collection and fill factor (FF) by creating a low resistance contact, while preserving a‐Si:H (i) passivation in other areas. Short‐circuit current density (JSC) is observed to be up to 33:1 mA cm−2, surpassing all previously reported values for this technology. Open‐circuit voltage (VOC) of up to 658 mV also exceeded every previous value published at a low bulk doping concentration (1 × 1016 cm−3). Laser firing reduced JSC by 0:6 mA cm−2 on average but improved the FF by 22.5% absolute on average, without any significant effect on VOC. Collectively, these efforts have helped in achieving a new in‐house record efficiency for LPC‐Si of 15.1% and show a potential to reach 16% efficiency in the near future with optimization of series resistance.

Facile and Reliable Thickness Identification of Atomically Thin Dichalcogenide Semiconductors Using Hyperspectral Microscopy.

Although large-scale synthesis of layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) has been made possible, mechanical exfoliation of layered van der Waals crystal is still indispensable as every new material research starts with exfoliated flakes. However, it is often a tedious task to find the flakes with desired thickness and sizes. We propose a method to determine the thickness of few-layer flakes and facilitate the fast searching of flakes with a specific thickness. By using hyperspectral wild field microscopy to acquire differential reflectance and transmittance spectra, we demonstrate unambiguous recognition of typical TMDCs and their thicknesses based on their excitonic resonance features in a single step. Distinct from Raman spectroscopy or atomic force microscopy, our method is non-destructive to the sample. By knowing the contrast between different layers, we developed an algorithm to automatically search for flakes of desired thickness in situ. We extended this method to measure tin dichalcogenides, such as SnS2 and SnSe2, which are indirect bandgap semiconductors regardless of the thickness. We observed distinct spectroscopic behaviors as compared with typical TMDCs. Layer-dependent excitonic features were manifested. Our method is ideal for automatic non-destructive optical inspection in mass production in the semiconductor industry.

Interface treatment using amorphous-carbon and its applications

Breakthrough process technologies have been introduced that can increase the chemical sensitivity of an interface at which reactions occur without significantly altering the physico-chemical properties of the material. Such an interfacial treatment method is based on amorphous-carbon as a base so that fluids can be deposited, and the desired thickness and quality of the deposition can be ensured irrespective of the interface state of the material. In addition, side effects such as diffusion and decreasing strength at the interface can be avoided. This is simpler than existing vacuum-based deposition technology and it has an unmatched industrial advantage in terms of economics, speed, accuracy, reliability, accessibility, and convenience. In particular, this amorphous-carbon interface treatment technology has been demonstrated to improve gas-sensing characteristics of NO2 at room temperature.

Rational Synthesis of a Hierarchical Supramolecular Porous Material Created via Self-Assembly of Metal-Organic Framework Nanosheets.

Hierarchically porous materials with high stability and tailorable pore characters have potential for mass transfer applications, including bulky molecule capture and separation, heterogeneous catalysis, and drug delivery. The scope of functionalities can be notably broadened by employing metal-organic framework (MOF) sheets with tunable thickness as giant molecular building blocks for self-assembly into hierarchical supramolecular porous coordination materials. However, synthesizing MOF sheets with controllable bulkiness has proved challenging for scientists. We present a rational yet unprecedented bottom-up strategy to prepare a novel two-dimensional MOF sheet [Zn(BPDI)(Py)2] (BPDI = N,N'-bis(glycinyl)pyromellitic diimide; Py = pyridine) with unusual and highly desired tunable thickness. These sheets self-organize into a unique three-dimensional supramolecular coordination material (NEU-1) with tailorable porosity. To assess its technological relevance, NEU-1c is tested as a support of amine sorbent for CO2 capture. Multichannel porous NEU-1c solves the conventional trade-off suffered by supported amine carbon dioxide adsorbents between increasing amine content and decreasing access to amine sites. Our synthesis process opens the door to novel MOF nanosheets and unique hierarchical supramolecular porous materials with tailorable porosity.

656 Inter- and Intra-user Reliability of Skin Graft Thickness as a Function of Instrument

Abstract Introduction The most popular powered dermatomes (both electric and pneumatic) have a linear blade which oscillates at high speeds. Though the thickness of skin graft being elevated can be controlled by the depth-adjustment dial on the side of the instrument, factors, such as applied pressure, angle between the instrument and the surface, and curvature of the harvest site, can cause deviations from the target depth. As a result, the same depth setting can result in significantly different thicknesses of excised tissue among operators. A newer, powered dermatome has been developed which pneumatically rotates a circular blade at a fixed angle to the surface of the skin and does not require additional downward pressure. The goal of this study was to assess inter- and intra-user uniformity of graft thickness using conventional and newly designed dermatomes and assess the accuracy of the excised thickness. Methods Split thickness skin grafts were collected from the dorsum of Yorkshire pigs using a conventional dermatome and a newly designed test dermatome. Three different users collected three 2-inch wide by 4-inch long strips of skin using both instruments. Skin thickness at the center and edges of each strip were measured using a digital micrometer. Additionally, grafts were laser scanned to create a map of thickness for the entire piece of tissue. Reliability of the harvest was assessed using inter- and intra-class correlation coefficient. Results Both instruments were set to collect grafts 0.012” thick. Grafts harvested using the conventional dermatome ranged from 0.020–0.038” thick while grafts harvested with the test instrument ranged from 0.008–0.016” thick. On average, the conventional dermatome harvested grafts that were 2.16-fold thicker than the instrument setting while the test instrument collected grafts 0.91-fold the target thickness. Intra-user reliability was similar between instruments with greater reliability observed when users has substantial prior experience. Additionally, inter-user reliability was significantly increased with the test instrument. Conclusions Many factors control the uniformity and overall thickness of a skin graft including applied pressure and angle of attack, and how much tension is applied to the elevated graft. Using a conventional dermatome, variability in thickness was observed with greater average measured thickness versus depth setting. Grafts harvested using the newly designed instrument were on average closer to the desired thickness and more reproducible among users. Applicability of Research to Practice New instruments for skin harvesting may enhance uniformity of skin grafts.

Electrospinning Live Cells Using Gelatin and Pullulan.

Electrospinning is a scaffold production method that utilizes electric force to draw a polymer solution into nanometer-sized fibers. By optimizing the polymer and electrospinning parameters, a scaffold is created with the desired thickness, alignment, and pore size. Traditionally, cells and biological constitutes are implanted into the matrix of the three-dimensional scaffold following electrospinning. Our design simultaneously introduces cells into the scaffold during the electrospinning process at 8 kV. In this study, we achieved 90% viability of adipose tissue-derived stem cells through electrospinning.