Author ORCID Identifier

https://orcid.org/0000-0002-1369-270X

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Electrical and Computer Engineering

First Advisor

Dr. Todd Hastings

Abstract

Focused electron beam induced processing (FEBIP) is a nano-scale fabrication technique that allows the direct deposition of functional materials. However, it suffers from significant drawbacks, such as high cost, low speed, unavailable precursors for many materials and low purity of deposits. Liquid-phase focused electron beam induced processes (LP-FEBIP) are being investigated due to the potential benefits over the gas phase technique. In this method, deposition or etching occurs at the interface between a substrate and a bulk liquid. In this work, electron beam induced deposition of copper nanostructures from aqueous solutions of copper sulfate is demonstrated. The addition of sulfuric acid eliminates oxygen contamination from the deposit and produces a deposit with ~95 at. % copper. The addition of sodium dodecyl sulfate (SDS), Triton X-100, or polyethylene glycol (PEG) improves pattern resolution and controls deposit morphology but leads to slightly reduced purity. High resolution nested lines with a 100 nm pitch are obtained from CuSO4–H2SO4–SDS–H2O. Higher aspect ratios (~1:1) with reduced line edge roughness and unintended deposition are obtained from CuSO4–H2SO4–PEG–H2O. Evidence for radiation-chemical deposition mechanisms was observed, including deposition efficiency as high as 1.4 primary electrons/Cu atom.

Limiting regimes for EBID of copper from aqueous solutions containing surfactants is also studied. Findings show that deposition efficiency depends strongly on dwell time and moderately on refresh time. It is observed that remarkable deposition efficiency under all conditions (1-10 Cu atoms/primary electron) consistent with the radiation chemistry model of deposition. Certain metallic nanostructures, typically silver and gold, support localized surface plasmon resonances (LSPR) that confine electromagnetic fields at the nanoscale. EBID is appealing for the rapid-prototyping of such structures. Here we show that silver nanostructures deposited from liquid precursors on bulk substrates support LSPR. The effect of different surfactant types on the silver deposition process is elucidated. Moreover, the substrate effect is studied on reducing the size, and also extraneous deposition and darkfield spectroscopy are used to characterize the optical properties of the deposited silver structures. Here we show that silver nanostructures deposited from an aqueous solution of silver nitrate and Brij L4 are plasmonically active with resonances in the visible to near-IR spectral region. Support of localized surface plasmon resonances is an indication of the sufficiently high purity of the deposits from the AgNO3 and Brij L4 solution. To verify the measured data, we also simulated the silver deposits with a numerical approach using a finite difference time domain (FDTD) method.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.185

Funding Information

National Science Foundation under Grant No. CMMI-1538650; 2015-2019.

National Science Foundation Grant No.ECCS-1542164; 2015-2020.

National Science Foundation Grant No. CMMI-1125998; 2016-2017.

Available for download on Monday, May 17, 2021

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