ORCID Identifier(s)

0000-0001-7224-1872

Graduation Semester and Year

2016

Language

English

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

First Advisor

Jin Seong Koh

Abstract

Nanopillars exhibit novel electrical and optical properties which could not be obtained from bulk materials. Many of their practical applications would require controlled placement of nanopillars at exact locations. However, precise placement and large scale fabrication of nanopillars have been challenging with conventional fabrication techniques. This thesis investigates a new approach to fabricate nanopillars at exact locations on a large scale. In this approach, fabrication of nanopillars is accomplished by first placing nanoparticles (NP) at exact locations and then performing anisotropic dry etching using these NPs as hard masks, resulting in formation of nanopillars on exact substrate positions. Precise placement of nanoparticles was carried out by forming an electrostatic guiding template that forces nanoparticles onto site specific locations on the substrate. The electrostatic guiding template was made of a gold layer on SiO2 substrate in which 100nm circular holes are made with underlying SiO2 substrate exposed. The gold substrate surface and exposed SiO2 surface were functionalized with self-assembled monolayers of 16-mercaptohexadecanoic acid (MHA) and 3-aminopropyltriethoxysilane (APTES), producing negatively and positively charged surfaces, respectively. DNA-functionalized Au nanoparticles (negatively charged due to DNA) were used for the nanoparticle hard masks. Guiding of the DNA-functionalized Au nanoparticles to a specific location was conducted by using the electrostatic funneling technique, where the SAMs-functionalized template guided the Au nanoparticles onto center positions of the circular holes. Placement of exactly one single Au nanoparticle at the center of the circular SiO2 exposed area was achieved using self-limiting electrostatic gating, which was controlled by varying ionic and pH concentration of the solution during attachment. Subsequently, with the precise placement of Au nanoparticles, a selective removal of Au deposited layer was carried out, leaving the single Au nanoparticles at specified positions on the SiO2 substrate. Then, using AuNP as a hard mask SiO2 layer was anisotropically etched to form SiO2 nanopillars. Using these SiO2 pillars as etch masks, Si substrate was subsequently etched anisotropically. With the above process, the resultant nanopillars had the lengths of 100 nm and diameter of 30 nm at desired locations. These controlled placements of nanopillars could be potentially used in electrical/ optical devices and chemical/biological sensors.

Keywords

Synthesis and processing, Reactive ion etching, Self-assembly

Disciplines

Engineering | Materials Science and Engineering

Comments

Degree granted by The University of Texas at Arlington

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