Coating Growth on Nanofibers: Multi-Scale Modeling, Simulations and Experiments
A. Buldum, C. Clemons, E.A. Evans, K.L. Kreider and G.W. Young
The University of Akron, US
Keywords: modeling, simulations, growth, nanowire, nanofiber
Theoretical and experimental investigations on nanoscale deposition technology are critical for nanoscale materials research and for future nanodevice applications. Moreover, because of the varied and coupled physical phenomena involved (mechanical, electromagnetic, chemical, thermal, etc.), the development of mathematical models requires interdisciplinary components from the mathematical and physical sciences, and must proceed hand-in-hand with a coordinated experimental effort. In order to study nanoscale growth mechanisms and provide mathematical tools and scientific understanding of these complex nanoscale systems, we combine experiments with multi-scale modeling and simulations of the coating of polymer nanofibers with conducting materials. Experimental efforts start with the electrospinning of polymer nanofibers. These fibers are coated with carbon, copper and aluminum films by using a plasma enhanced physical vapor deposition (PVD) and sputtering process. Further to create aluminum nanotubes, polymer fibers are coated with aluminum and then the polymer core is removed by pyrolysis or dissolution. In this way tubes with inner diameters of 20 nm or more are formed. To simulate the coating process, continuum models and atomic scale models are developed, linked, and solved in an iterative fashion. At the continuum scale governing equations and boundary conditions are developed to describe sputtering from the target material, transport of the sputtered material through the reactor chamber, and deposition of the material onto the polymer nanofibers. Asymptotic solution methodologies that take advantage of the disparity in length and time scales in the system are used in combination with numerical methods to solve the model equations. These equations contain parameters and functions that describe the sputtering and deposition rates. This information is passed to the continuum models from the atomic scale models. At the atomic scale molecular dynamics (MD) simulations are performed on sector-shaped regions (determined by the continuum models) of the nanofibers. Modified periodic boundary conditions and embedded atom type potential energy functions are used. Local atomic scale morphology of the coatings is determined, as well as valuable information concerning deposition and sputtering rates.
Nanotech 2004 Conference Technical Program Abstract