Nanoimprinting of Metals by Highly-Grafted Nanotube Arrays
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Nanoimprinting of Metals by Highly-Grafted Nanotube Arrays Lili Li1,2, Zhenhai Xia1 and Yanqing Yang2 Department of Mechanical Engineering, The University of Akron, Akron OH44326, USA School of Materials, Northwestern Polytechnic University, Xi’an, China ABSTRACT Molecular dynamics (MD) simulations are reported for buckling and interfacial friction of single- and double-walled carbon nanotubes (CNT) with interwall sp3 bonds imprinted on copper substrates. A small perturbation of mechanical vibration is applied to the systems in the nanoimprinting. The imprinting capabilities of double-walled CNTs are much better than singlewalled CNTs. While the single-walled CNT is insensitive to the vibration, the indentation force and buckling of double-walled CNTs with interwall sp3 bonding is dependent on the amplitude of the perturbation, providing a way to controlling the interfacial friction. There is an optimal amplitude, at which the buckling and friction force of the CNTs are minimized in nanoimprinting. INTRODUCTION Nanoimprinting is a simple technique that can generate nanometer patterns over a large area. It provides not only high resolution but is also cheap and creates high throughput nanopatterns. In nanoimprinting, the nanopatterns are formed by pressing a master mould onto the surface of a substrate. Although nanoimprinting was originally developed to imprint on soft polymer direct nanoimprinting on hard materials, such as metal, has recently been proved feasible using diamond or SiC moulds [1–3]. Carbon nanotubes (CNT) are attractive as nanoimprinting molds owing to their unique properties such as high strength and high stiffness [4-5]. Using the CNT arrays of high grafting density as a nanoimprint stamp can transfer the high-density patterns into metal thin films. Directly transferring the high-density nanopatterns into thin metal or other films is of interest in the applications such as nanofiltration, and nanoscale device fabrication. Furthermore, carbon materials are excellent solid lubricants for dry machining, and carbon nanotubes may be self-lubricating in nanoimprinting. To achieve successful pattern transfers, it is required to understand the deformation behavior of metal films as well as effects of adhesion and friction and to investigate effects of pattern aspect ratios. Detailed theoretical analysis will be greatly helpful to materials and process design and can also provide insights into the understanding of various phenomena in this procedure. Analytical results using finite element method (FEM) have been performed to study the polymer deformation [6-8], which provided valuable insights into the material deformation behavior and the proper estimations of deformed pattern shapes. However, FEM does have limits regarding the analysis of nanoscale systems. When the system of consideration becomes smaller than several tens of nanometers, continuum mechanics will fail to predict the system behavior because material properties changes drastically at nanoscale, compared with those in macroscal
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