Design of sphere seeds for glancing angle deposition

Abstract

Glancing angle deposition (GLAD) is a specific type of physical vapor deposition that has the unique ability to generate three-dimensional nanofeatures in a process-efficient and low-cost manner. Our research group previously demonstrated how line seeds can be strategically implemented to create a variety of novel well-organized nanostructures. In this paper we explore the use of spherical seeds that self-assemble into hexagonally close packed patterns for GLAD seeding. This bottom-up approach is cost-effective and efficient for seeding, and no top-down nanofabrication technique is needed. Although seeding theories appropriate for GLAD nanofabrication are necessary, little theory has been proposed in the literature for three dimensional seeds, and yet most of the seeds used in GLAD are 3D surfaces. In this paper, we introduce a scheme for spherical GLAD seeding, and derive an analytical model for the diameter of nanopillars and percent coverage given process parameters of sphere diameter and incident angle. The model can be used to design sphere seeds, while the percent coverage is used to validate sphere designs as a function of the incident angle. Experimentally, the diameter of the nanopillars depends mostly on the incident angle, while changing the diameter of the spherical seeds has only a minor effect. The nanopillar diameter decreases as the incident angle increases. For example, nanopillars smaller than 100 nm can be grown from 200 nm spheres when the incident angle is at least 85°. Spherical seeds can be used for creating hexagonal periodic patterns of GLAD nanostructures, which have applications in optics and biology.