First Advisor

Sung Yi

Date of Publication

Fall 12-12-2019

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Mechanical Engineering

Department

Mechanical Engineering

Language

English

Subjects

Nanowires -- Synthesis, Copper alloys

DOI

10.15760/etd.7259

Physical Description

1 online resource (ix, 72 pages)

Abstract

Flexible electronics are the promising technology for prospective application in foldable phones. Currently, indium tin oxide (ITO) has been widely used for electronic devices including flat-panel display. However, it is brittle and expensive. Metal nanowires are considered as alternative materials. Among various metal nanowires, copper nanowires are attractive because of its high electrical conductivity, better flexibility, and low cost compared with ITO. However, copper nanowires are very prone to oxidize, which causes subsequent degradation of electrical conductivity. Due to this oxidation issue, core-shell structure nanowires, which are formed silver shell having high conductivity and low resistivity on the surfaces of copper nanowires are considered to enhance oxidation resistance. The objective of the present study is to optimize the synthesis of copper nanowires to improve yields changing synthesis and increasing the dimensions of the nanowires. Copper nanowires are synthesized under various conditions, which are different concentrations of hydrazine (N2H4), ethylenediamine (EDA), sodium hydroxide (NaOH), and copper precursor, and synthesis temperatures. In addition, a new facile method using an eco-friendly organic compound A is developed to fabricate copper-silver core-shell structure (Cu-Ag) nanowires. The highest yield of copper nanowires is obtained with the length of 4 - 13 µm and the diameter of 250 - 550 nm with an amount of 15 µl of diluted N2H4. The excessive amount of diluted N2H4 leads to an unbalance in the process and causes formation of copper nanoparticles. The smooth surface of copper nanowires is observed at synthesis temperature of 70°C. This is because EDA is likely actively performed at 70°C to protect the surface of copper seeds to prevent the aggregation. The insufficient amount of EDA induces copper seeds, which aid not grow to copper nanowire, and the formation of tapered copper nanowires, while the excessive amount of EDA causes the irregular surface of copper nanowires. High-quality copper nanowires, which have the length of longer than 18 µm and the diameter of 25 - 45 nm, are obtained by controlling the concentration of NaOH from 14.7 M to 9 M. NaOH concentration below 9 M is required the increased amount of EDA to prevent forming copper seeds from being aggregated. When the concentration of copper precursor is increased, copper nanowires become shorter in length and thicker diameter and the aggregation of copper seeds is observed. Cu-Ag nanowires are fabricated successfully by a new facile method using eco-friendly organic compound A. The result shows the thickness of silver shell close to 12 nm. This study indicates various synthesis conditions for copper nanowires to find the optimum condition and shows a new facile method to eco-friendly fabricate Cu-Ag nanowires. In addition, this study provides high potential in extensive applications of these nanowires such as flexible and stretchable devices.

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Persistent Identifier

https://archives.pdx.edu/ds/psu/30919

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