Two-dimensional noble metal nanostructures: Facile fabrication, optical and electrochemical characterization, and sensing applications

This thesis reports a successful exploration and the development of a method for the facile fabrication of two-dimensional noble metal nanostructures that are suitable for applications as the substrates in chemo- and biosensing based on surface-enhanced Raman scattering (SERS) and electrocatalysis.;Chapter 1 is a concise overview of the relevant work by others in the fabrication of two-dimensional noble metal nanostructures, as well as their applications in SERS and electrocatalysis. Special attention was paid to highlight the limitations and disadvantages of these reported works, with the aim to better define the objectives of this thesis which was outlined at the end of this chapter.;Chapter 2 describes the method explored in this thesis for the facile fabrication of two-dimensional noble metal nanostructures. The method combines atomic sputtering technique with a nanostructured substrate, which serves as the template for the formation of two-dimensional metal nanostructures in dry deposition. The key step in the method is the fabrication of template with desired nanostructures. The conditions for metal film fabrication on two types of templates were systematically examined on their morphology, surface wettability and crystalline structures.;Chapter 3 focuses on the detailed study of two-dimensional polygonal networks of gold nanoparticles by both electrochemical and SERS techniques. The electrochemical behavior of the standard redox pairs, Fe(CN)6 3-/4- and Ru(NH3)62+/3+, on the as-fabricated Au film was studied. The redox behavior of Cytochrome-c on the bare and chemically-modified Au surface was studied. The electrooxidation and reduction of NO on both Au thin film and Au nanoparticles polygonal networks were investigated. The SERS technique was employed to study the molecules physi-adsorbed and chemo-adsorbed on the Au surface and under non-resonance and resonance conditions, respectively. Very stable and reproducible enhancement factor of ∼106 was obtained under the non-resonance condition.;Chapter 4 reports a systematic study of two types of two-dimensional silver nanostructures by SERS technique. The main findings in this chapter are (i) the stable and reproducible enhancement factor on Ag films fabricated on both anodic aluminum oxide and AnodiscRTM porous alumina membrane can reach as high as ∼107 under non-resonance condition; (ii) the SERS spectra of the adsorbed MBA molecules can serve as the sensitive and quantitative probe for the local pH. Three types of pH-sensitive Raman-codes are analyzed; and (iii) the as-fabricated Ag-nanostructure displays a photo-induced autoreduction of the adsorbed ferric Cytochrome-c.;Chapter 5 summarizes the electrochemical and optical study of the as-fabricated two-dimensional polygonal networks of Pd and Pt nanoparticles in comparison with the metal films prepared on the flat substrate. Special attention was paid to examine the electrocatalytic activities of the nanostructured film toward the reduction and oxidation of nitric oxide. Using self-assembled monolayer of BT as the surface-probing molecule, a surface enhancement factor of ca. ∼10 5 in the SERS spectra from both Pd and Pt under non-resonance condition was estimated. This is hitherto the highest EF observed from non-coinage metals.;Last but not the least, the main advantages and the limitations of our method are summarized with a brief perspective on the future directions.