Localized Programmable Gas Phase Electrodeposition and Its Applications in Functional Nanomaterials and Devices

Abstract

This thesis focuses on development and application of a gas phase nanomaterial integration concept. We developed and demonstrated a novel gas phase electrodeposition method to control material flux transported and deposited at desired points on a patterned biased substrate based on the Coulomb force. The thesis is divided into two sections: (A) a corona based analyte charging method and an electrodynamic nanolens based analyte concentration concept to effectively transport airborne analytes to sensing points to improve the response time of existing gas sensor designs, and (B) a gas phase electrodeposition process to grow free-standing point-to-point electrical nanowire connections spanning a distance of up to 10 µm. Section A introduces a new general approach which uses a corona based charging method in combination with an electrodynamic lens based collection concept to transport particles to precise points on a surface. We discovered that the transport is faster than diffusion based transport commonly used. The faster transport and speed was then applied to the field of nanosensors of airborne particles. Specifically, we were able to reduce the response time of existing airborne sensor designs by several orders of magnitude. The process, referred to as “corona/lens-based-collection”, enables us to transport nanomaterials and airborne analytes from a space that is centimeters away to specific sensing points on a surface with a minimal spot size approaching 100 nm. We find that the collection rate is several orders of magnitudes higher than the case where the corona/lens-based-collection is turned off and collection is driven by diffusion only. The collection scheme is integrated on an existing SERS based sensor that is sensitive to the adsorption of small molecules. We compare the results with and without corona/lens-based-collection and find that SERS signal is enhanced by three orders of magnitudes as a result of increased collection efficiency. In terms of response time, the process is able to detect analytes at 9 ppm (parts per million) within 1 second. As a comparison, 1 hour is required to approach the same signal intensity in the case where diffusion-only-transport is used. Section B presents a gas phase electrodeposition process to grow free-standing point-to-point electrical nanowire connections spanning a distance of up to 10 µm. The gas phase electrodeposition process uses a patterned resist with openings to a conductor to guide the deposition of charged nanoparticles. Nanowire growth occurs at charge dissipating contacts which are accessible due to the openings in the resist. The formation of interconnects between contacts or bridges across a trench is possible through nearest neighbor interaction. The growing nanowires are composed of metallic nanoparticles. We discovered that a reduction of the primary nanoparticles size to the 1-5 nm range is required to achieve electrical conductive and mechanically stable bondwires. The annealing temperature has been reduced to 250°C due to the small particle size. The diameter of the nanowires depends on the growth duration and the size of the openings. The adjustable range is 50 nm-1 µm. Mechanically stable bondwires have a typical diameter of 250 nm. A 5 µm long interconnects with a radius of 250 nm had a resistance of 85 Ω.