ORCID Identifier(s)

0000-0003-0057-4242

Graduation Semester and Year

2017

Language

English

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

First Advisor

Yaowu Hao

Abstract

Continuous monitoring of certain environmental pollutants, biological species, chemical species, and explosives are of utmost importance in recent times. Surface-enhanced Raman scattering (SERS) provides most promising option as it is a highly sensitive technique which allows for ultrasensitive detection of molecules and provides excellent structural information. To obtain rich results through Surface-enhanced Raman scattering, proper design of enhancing substrate plays vital role. Contemporary SERS substrates don’t provide ease to detect liquid analytes for in-situ spectroscopy. Liquid media detection through SERS relies on highly statistical binding of analytes to SERS-sensitive hot spots. Moreover, it becomes extremely difficult to detect flowing liquid media in-situ with two-dimensional substrates as very small volume of Liquid contact with substrates. Single crystal Ag dendrite structures possess high surface area along with narrow gaps and sharp edges. Compared with other nanostructures, the hierarchical nanostructures-dendritic Ag, consisting of multi-level branches can significantly promote the SERS enhancement and serve as effective SERS substrates with high sensitivity and reproducibility. Such complex nanostructures may provide a large amount of “hot spots” at the end of branches or the junctions of adjacent Ag branches. In addition, the large surface area of Ag dendrites can enhance the interaction between analytes and sensing substrates. Ag dendrites can easily be produced, by use of one of the simplest galvanic reactions, the reaction of AgNO3 with Cu. We have developed novel yet simple Surface-enhanced Raman scattering- active substrate having three-dimensional array of Ag-dendrites grown within square geometry capillary tube of borosilicate glass via such galvanic replacement reaction with inserted copper wire. Systematic study of growth mechanism of Ag-dendrites was carried out and complex nature of seemingly “simple” galvanic replacement reaction has been proposed. The resultant Ag dendrites were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and X-ray diffraction. A time-dependent investigation on the growth mechanism of the Ag dendrites revealed that they develop through a particle-mediated growth process. The effect of the reactant concentrations on the morphology of the synthesized Ag dendrites was also studied. This study on Ag dendrite growth mechanisms are not only scientifically intriguing, but also technologically important. Novel Ag dendrite three-dimensional SERS substrate exhibits excellent sensitivity and a very good reproducibility. We have detected rhodamine 6G (R6G) with lowest concentration of 10-11 M in aqueous solution. These Ag dendrite nanostructured three-dimensional SERS substrates are proved as excellent in-situ liquid media Raman detection substrates due to availability of extensive hot spots. It has significant potential to be used as SERS substrates for fast and accurate detection of trace amount of organic contaminants in flowing liquid media.

Keywords

Surface-enhanced Raman scattering, Ultrasensitive detection, Ag dendrite three-dimensional SERS substrate, Galvanic replacement reaction, Particle mediated growth process.

Disciplines

Engineering | Materials Science and Engineering

Comments

Degree granted by The University of Texas at Arlington

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