Modeling Evaporation Driven Self-Assembly Systems for Magnetic Storage Arrays
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0961-O16-05
Modeling Evaporation Driven Self-Assembly Systems for Magnetic Storage Arrays John J. Dyreby, Greg F. Nellis, and Kevin T. Turner Computational Mechanics Center, University of Wisconsin-Madison, 1513 University Ave, Madison, WI, 53706
ABSTRACT A modeling methodology based on computational fluid dynamics has been developed that is appropriate for the global regime of lithographically directed, evaporation driven selfassembly. The modeling technique has been experimentally verified through comparison with the well-known benchmark case of evaporation driven self-assembly associated with the evaporation of a colloidal, self-pinned droplet. The predicted evolution of the particle distribution during evaporation is compared to optical experimental measurements of the particle distribution within an evaporating droplet containing fluorescing nanoparticles.
INTRODUCTION Lithographically directed, evaporation driven self-assembly (EDSA) is a promising nanofabrication process that combines the control of a top-down lithographic process with the highly parallel nature of bottom-up self-assembly. The EDSA process is based on precisely altering the topography of a substrate using lithographic-based patterning processes prior to covering the substrate with a solution containing nanoparticles that is allowed to evaporate. As the solution evaporates, the contact line that delineates the solution from the surrounding air at the substrate surface will travel across the substrate and selectively pin and de-pin at the edges of the lithographic features. When the contact line pins, it causes a flow of fluid to develop toward the pinning site. This flow carries the particles that are suspended in the fluid to the pinned edge, causing a local build-up in concentration near these lithographically defined features. Under the right conditions, the particles will self-assemble and be deposited in the features [1]. If it is used in conjunction with an appropriate patterning process in order to define the locations where the particles will be deposited, EDSA may allow very small scale magnetic materials to be uniformly, rapidly, and precisely deposited. Even in the absence of patterns, the governing physics of the process can be used to make large scale ordered arrays that are ideal for magnetic storage [2]. As such, EDSA represents a potentially promising new technique for the fabrication of magnetic storage systems. The EDSA process has been successfully demonstrated experimentally using gold nanoparticles [1, 2]. However, it is a relatively new nanofabrication technique and the majority of the research in this area has focused on the final results rather than the underlying physics that govern the particle transport processes [1-4]. The EDSA process can be approximately divided into two regimes: a global regime and a local regime. The global regime is characterized by the bulk transport of particles and fluid
toward the lithographically defined features and is driven by evaporation from the free surface of the fluid. The par
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