Abstract

This dissertation consists of spectroscopic and microscopic studies of two electrochemical systems; (1) interactions between self-assembled monolayers on gold surfaces in alkaline media and between gold surfaces in acidic media, and (2) saccharin adsorption on nickel and copper electrodes.

First, a reversible desorption/adsorption of ethanethiol (ET) and 1-hexadecanethiol (HDT) self-assembled monolayers (SAMs) on gold substrate is addressed with AFM force measurements. For a HDT-modified tip/substrate, the overall changes of force curve is well corresponding to its voltammetric features. The adhesion interaction between HDT-modified tip/substrate shows large adhesion that agrees with the JKR theory, while the adhesion is reduced to ¼ of its origin value after HDT on the substrate is removed.

The interaction between potential-controlled gold surfaces in acidic media is also addressed. Only the hydroxide-adsorbed tip interacts with AuOH of gold surface at the high positive potential region, and the increase of adhesion force is attributed to specific bonding between the tip and the substrate. In addition, the adhesion force starts to increase well before the onset of oxidation shown in the voltammetry. It is also found that the specific adsorption of anions of electrolytes can affect both approach and adhesion measurements.

Second, the adsorption of saccharin on roughened nickel electrode is presented with cyclic voltammetry and surface-enhanced Raman spectroscopy, as well as complementary DFT calculations. CV measurements reveal a strong influence of both chloride concentration and pH of electrolyte on the nickel surface and the inhibitory effect on the nickel oxidation by saccharin addition. SERS measurements provide evidence for strong interaction between the Ni surface and saccharin additives and dependence on the electrode potential. The overall behavior observed in SERS is explained based on the normal Raman spectra of saccharinate anion and its nickel-saccharinate complexes.

In addition, the adsorption of saccharin on a copper electrode was studied with electrochemical methods, surface-enhanced Raman spectroscopy, and in-situ STM measurements. The results of electrochemical studies of the interaction of sodium saccharinate and chloride as additives on the copper electrode and their synergic effects are described.