A study toward large-area low-defect nanosphere lithography

Surface-enhanced Raman spectroscopy (SERS) is a powerful label-free molecular characterization technique that detects ultra-low analyte concentrations. The critical requirement for the SERS enhancement effect is the presence of large magnitude electromagnetic fields existing between small-gap nanoparticle dimers. Considerable research effort is devoted to developing uniform and high enhancement response from SERS-based sensors. The achievement of this aim using uncomplicated and low-cost methods remains an active challenge nonetheless. Nanosphere lithography (NSL) leverages the benefits of a self-assembled nanosphere mask to deliver spontaneous high-density patterning of triangular nanoparticles. The use of a two-step shadow evaporation method with NSL masks creates programmable gap nanoparticle dimers. However, reliable control over the dimer gap requires further study of the mask properties. This thesis aims to combine the shadow evaporation method with large-area single-crystalline nanosphere masks to create sub-10 nm gap nanoparticle dimer arrays. A novel dynamic self-assembly process for large-area quasi-single crystals of polymeric spheres is detailed. The addition of propylene glycol to the colloidal solution and low-velocity air and low-frequency acoustic external energy input unlocks the reliable fabrication of high-quality masks. The short-range and long-range defect density characterization identifies sphere polydispersity and evaporation-induced line defects as the primary causes of defect generation. Solvent treatment of the colloidal crystal reduces mean defect density by a factor of 5x with complete elimination of evaporation-induced line defects. The long-range orientation of the colloidal crystal is preferentially realigned to a single orientation using a hexagonal hydrophobic template. Nanoparticle arrays made from the improved masks demonstrate enhancement factors of 8.95 × 10^(6) and uniformities below 12%.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Grewal, Sartaj S

Contributors dc:contributor

• Lyding, Joseph W
• Murphy, Catherine J
• Li, Xiuling
• Chen, Qian
• Fang, Kejie

• Engineering

Statement dc:rights

• Copyright 2021 Sartaj Grewal

Language dc:language

en, eng

Handle dc:identifier

http://hdl.handle.net/2142/113892

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F113892