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Title:Nonlithographic manufacturing of 1-D silicon nanostructures with tunable surface morphology via thermal dewetting and metal-assisted chemical etching
Author(s):Azeredo, Bruno
Advisor(s):Ferreira, Placid M.
Department / Program:Mechanical Sci & Engineering
Discipline:Theoretical & Applied Mechans
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):silicon nanowires
metal-assisted chemical etching
thin-film annealing
high emissivity
Abstract:This thesis presents a non-lithographic approach to generate wafer-scale single crystal silicon nanowires (SiNWs) with controlled side-wall profile and surface morphology. The approach begins with silver (Ag) thin-film thermal dewetting, gold (Au) deposition and lift-off to generate a large-scale Au mesh on Si substrates. Followed by metal-assisted chemical etching (MacEtch), where the Au mesh serves as catalyst, arrays of smooth Si nanowires with tunable taper are produced. By using the Le Chatelier Principle, the rate of reduction relative to that of oxidation is increased by adding increasing amounts of ethanol to the etchant. Consequently, excess electron holes migrate and diffuse away from the catalyst-silicon interface and towards the wire surface, making the wire surface susceptible to lateral etching as well. The ratio between the vertical and lateral etch rates can be tuned to produce wires with taper angle up to 13 degrees. The mean diameter of so fabricated SiNWs can be controlled to range from 62 nm to 300 nm with standard deviations as small as 13.6 nm, and the areal coverage of the wire arrays can be up to 46%. Control of the mean wire diameter is achieved by controlling the pore diameter of the metallic mesh which is, in turn, controlled by adjusting the initial thin-film thickness and deposition rate. To control wire surface morphology, a post-fabrication roughening step is added to the approach. This step uses Au nanoparticles and slow-rate MacEtch to produce rms surface roughness up to 3.6 nm. Additionally, 1-D nanostructures with complex cross-section shapes – such as I-beams, tubes, multiwalled concentric tubes – are demonstrated by replacing the self-assembled thermally dewetted patterns in the manufacturing approach described above. Instead, silver patterns are created by Solid-State Superionic Stamping (S4), a non-lithographic and ambient method for patterning silver thin-films, and combined with the lift-off and MacEtch processes to produce such complex nanostructures. Sub-160 nm nanostructures were produced by this approach with high pattern fidelity over millimeter scale silicon substrates.
Issue Date:2014-05-30
Rights Information:Copyright 2014 Bruno Azeredo
Date Available in IDEALS:2014-05-30
Date Deposited:2014-05

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