Formation of Surface-Wrinkled Metal Nanosheets via Thermally Assisted Nanotransfer Printing

Nanopatterning methods for pattern formation of high-resolution nanostructures are essential for the fabrication of various electronic devices, including wearable displays, high-performance semiconductor devices, and smart biosensor systems. Among advanced nanopatterning methods, nanotransfer printing (nTP) has attracted considerable attention due to its process simplicity, low cost, and great pattern resolution. However, to diversify the pattern geometries for wide device applications, more effective and useful nTP based patterning methods must be developed. Here, we introduce a facile and practical nanofabrication method to obtain various three-dimensional (3D) ultra-thin metallic films via thermally assisted nTP (T-nTP). We show how to generate surface-wrinkled 3D nanostructures, such as angular line, concave-valley, and convex-hill structures. We also demonstrate the principle for effectively forming 3D nanosheets by T-nTP, using Si master molds with a low aspect ratio (A/R ≤ 1). In addition, we explain how to obtain a 3D wavy structure when using a mold with high A/R (≥ 3), based on the isotropic deposition process. We also produced a highly ordered 3D Au nanosheet on flexible PET over a large area (> 15 µm). We expect that this T-nTP approach using various Si mold shapes will be applied for the useful fabrication of various metal/oxide nanostructured devices with high surface area.

Nanoscale Elastoplastic Wrinkling of Ultrathin Molecular Films

Ultrathin molecular films deposited on a substrate are ubiquitously used in electronics, photonics, and additive manufacturing methods. The nanoscale surface instability of these systems under uniaxial compression is investigated here by molecular dynamics simulations. We focus on deviations from the homogeneous macroscopic behavior due to the discrete, disordered nature of the deformed system, which might have critical importance for applications. The instability, which develops in the elastoplastic regime above a finite critical strain, leads to the growth of unidimensional wrinkling up to strains as large as 0.5. We highlight both the dominant wavelength and the amplitude of the wavy structure. The wavelength is found to scale geometrically with the film length, λ∝L, up to a compressive strain of ε≃0.4 at least, depending on the film length. The onset and growth of the wrinkling under small compression are quite well described by an extended version of the familiar square-root law in the strain ε observed in macroscopic systems. Under large compression (ε≳0.25), we find that the wrinkling amplitude increases while leaving the cross section nearly constant, offering a novel interpretation of the instability with a large amplitude. The contour length of the film topography is not constant under compression, which is in disagreement with the simple accordion model. These findings might be highly relevant for the design of novel and effective wrinkling and buckling patterns and architectures in flexible platforms for electronics and photonics.

Improvement of a Tunable Stiffness Organ-Grasping Device by Design of a Wavy-Shaped Beam Structure

Tunable stiffness mechanisms can increase the noninvasiveness and stability of organ manipulation in laparoscopic liver resection. We have developed an organ-grasping device using beam-shaped tunable stiffness mechanism. Increasing the change ratio of stiffness will improve the performance of the device by offering high flexibility when adhering to the liver surface and high rigidity during the manipulation of the liver; however, optimal design of the beam has not been investigated. In this study, we investigate the wavy structure shape of the device that enhances the change in the ratio of stiffness. To increase the stiffness in a high-stiffness state, we used principal stress lines in the device to design the edge curve of the wavy shape material in the beams. We also investigated the arrangement of the wavy shape to decrease the stiffness in a low-stiffness state. Simulation using finite element method showed that the change ratio of stiffness was improved up to 13.0 by the new wavy shape arranged with the uniformly thick bottom of the waves.

Effect of High Velocity Deformation on Strength of ArmoredComposite Materials

This paper considers the problem of determining the strength of carbon fiber reinforced plastic with straight and curved fibers under high-speed loading. High-speed tests of unidirectional CFRP specimens with rectilinear and wavy structure have been carried out. The influence of the structure and high-speed loading on the ultimate strength and ultimate deformation of the material is investigated. For the first time, a detailed study of the effect of fiber curvature on the properties of CFRP under high-speed deformation has been carried out. As a result of dynamic tests, it was shown that the ultimate strength in unidirectional laying is higher than in wavy laying. The effect of increasing the ultimate deformations of specimens with bent fibers was established, which was noted earlier for the case of tensile tests.

The Microstructure and Mechanical Properties of TA1-Low Alloy Steel Composite Plate Manufactured by Explosive Welding

A TA1 (Ti alloy)/low alloy steel (LAS) composite plate was manufactured by explosive welding. The effects of the bonding interface microstructure on the mechanical properties and fracture behavior of the composite plate were investigated. The results show that the interface has a wavy structure with intermetallic compounds (IMCs) enclosed by a steel matrix. The metallurgical bonding interface was achieved by local diffusion, with a several micrometer-thick diffusion layer. Two kinds of microcracks were formed in the IMC region and the diffusion interface. Microcracks in the IMC region propagate with difficulty due to the impediment of the IMC/steel interface. The microcracks initiated at the interface need to propagate into the fine-grain steel matrix before crack connection and delamination. The shear strength of the TA1/LAS composite plate was over 350 MPa. The composite plate could be bent up to the equipment limit (135 degrees). Excellent mechanical properties were obtained since the crack propagation was hindered by the refined or elongated steel grains induced during explosive welding.

An Experimental Analysis of Microchannel Heat Sink using Novel Geometry with Nano Fluid and Water

Oblique fins with sectional cuts are used in place of continuous straight fins to better mix the fluid because of secondary flow in tilted cut oblique channels. The other factor is the re initialization of thermal as well as hydrodynamic boundary layer at the noted line of each fin which decline the density of boundary layer. These breakages of continuous fins resulted in secondary flow generation which enhances the heat transfer rate with reasonable pressure drop. Wavy channel novel geometry is also studied which utilises the length wise blend due to curvy geometry. For laminar region, the amount of convective heat transfer is a function of span wise fluidic mixing. Dean vortices which are cajoled due to centrifugal fluctuation increases the heat transfer capabilities. By clubbing the benefits of both novel geometries i.e. Dean vortices with secondary channel mixing a further better novel geometry branched wavy structure is developed whose fluid movement and heat transfer behaviors were examined numerically. Secondary branches are combined in an alter manner at 45^0 at the trough of the wavy channel to provide cross channel mixing. All the 3 geometries are studied at different range of Reynolds number which ranges from 240 to 600. An increase in heat transfer coefficient as compared to oblique and wavy channel was observed after the addition of secondary branches with decrease in pressure drop penalty. For simulating different geometries in ANSYS 2 methods are implemented which resulted in discrete phase modelling being the better method. The temperature, pressure, velocity contours from simulations were obtained to explain different behaviours.