Surface-enhanced Raman scattering of metal nanoparticle assembly in agarose and highly ordered metal nanorod arrays

• Main Author: Keating, Martin
• Published: University of Strathclyde 2015
• Subjects: 530
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665236

This thesis examines metal nanoparticle/agarose (MNPA) gel composites and highly ordered metal nanorod arrays, fabricated by guided nucleation during oblique angle deposition (OAD), as surface-enhanced Raman scattering (SERS) substrates. The effectiveness of MNPA has been effectively demonstrated previously using silver nanoparticles (AgNPs), but it is poorly understood how different NP growth conditions affect the SERS response. SERS intensity of gold and silver NPA is examined in detail as a function of salt and (by default) reducing solution concentration, and the effect of using different reductants is also investigated; reproducibility of selected gels is carefully explored. In addition, SERS of highly ordered Ag and copper (Cu) nanoarrays is examined in depth. Normally, OAD generates a random nanorod distribution on flat supports, where nucleation is a random process. This however hinders the control of geometrical parameters such as rod separation and diameter which directly affect the SERS response, an effect mitigated by introducing a guiding element to influence nucleation. Until recently, only semiordered SERS-active Ag nanorod arrays had been accomplished by OAD. These however depended on time-consuming and expensive electron beam lithography (EBL) to write a template to guide nucleation and the subsequent growth of nanorods. Importantly, lengthy fabrication times force a practical upper size limit on the substrate, meaning it is exceedingly small which drastically reduces its potential for sensing applications. It also severely restricts the number of substrates which can be produced in a given time. This thesis addresses these issues via the construction of highly ordered, SERS-active, large-area Ag and Cu nanorod arrays, using a cheap, large-scale, nanoimprinted polymer template to influence nucleation during the initial stages of OAD. Moreover, OAD is a high throughput method, as it permits the simultaneous fabrication of several substrates during a relatively short deposition cycle.