Multiscale modeling, simulations, and experiments of coating growth on nanofibers. Part I. Sputtering

Abstract

This paper is Part I of an integrated experimental/modeling investigation of a procedure to coat nanofibers and core-clad nanostructures with thin-film materials using plasma-enhanced physical vapor deposition. In the experimental effort, electrospun polymer nanofibers are coated with aluminum under varying operating conditions to observe changes in the coating morphology. This procedure begins with the sputtering of the coating material from a target. This paper focuses on the sputtering process and transport of the sputtered material through the reactor. The interrelationships among the processing factors for the sputtering and transport are investigated from a detailed modeling approach that describes the salient physical and chemical phenomena. Solution strategies that couple continuum and atomistic models are used. At the continuum scale, the sheath region and the reactor dynamics near the target surface are described. At the atomic level, molecular-dynamics ͑MD͒ simulations are used to study the sputtering and deposition mechanisms. Ion kinetic energies and fluxes are passed from the continuum sheath model to the MD simulations. These simulations calculate sputtering and sticking probabilities that in turn are used to calculate parameters for the continuum reactor model. The reactor model determines the concentration field of the coating material.

Modeling and simulation of coating growth on nanofibers

“…We have developed a comprehensive model integrating across atomic to continuum length scales for simulating the sputtering, transport, and deposition of coating material onto a nanoscale substrate. [8][9][10][11] In this paper we conduct numerical simulations of the concentration field that couple with level set simulations of the evolution equation for the coating free surface. The model simulations predict that as the Damköhler number is increased the coating morphology changes from a wavy to a nodular to a needletype form as observed experimentally and shown in Figs.…”

“…[8][9][10][11]. In this model the transport of neutral species is separated into two components: ͑1͒ a one-dimensional reactor-scale model 8 and ͑2͒ a two-dimensional local nanofiber-scale model.…”

“…[8][9][10][11]. In this model the transport of neutral species is separated into two components: ͑1͒ a one-dimensional reactor-scale model 8 and ͑2͒ a two-dimensional local nanofiber-scale model. [9][10][11] These models are linked as follows: the reactor-scale model provides the far-field ͑half the distance away from an adjacent fiber͒ input of the neutral species concentration, C ‫ء‬ .…”

“…2,[5][6][7] This paper is a continuation of Refs. [8][9][10][11]. Those works presented a coordinated experimental and modeling program for the synthesis of core/clad and hollow nanowire structures.…”

“…The previous works [8][9][10][11] derived and solved the model both analytically and numerically under restrictive assumptions. In particular, Ref.…”