Spectroelectrochemical investigation of passive layers formed on electrode surfaces

Corrosion, broadly defined as environmental damage to materials (usually metallic), is an important concern for maintaining infrastructure and for many manufacturing and transport processes. Corrosion is typically prevented or controlled by formation of a passivating layer that prevents diffusion of oxidative elements that might attack the base material, either by a passive oxide formed by sacrificial agents in the material or by use of organic inhibitors. Various electrochemical techniques are used to compare the relative efficacy of these passivation layers, including linear sweep voltammetry, which gives the breakdown potentials and corrosion currents, and AC impedance, from which film resistance and inhibition efficacy can be determined. Although voltammetry gives an idea of whether a film successfully passivates a metal surface, it gives little insight into the mechanism of inhibition and chemical interactions that take place between the film and metal surface. Shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) allows interrogation of the electrode-electrolyte interface where corrosion occurs. Benzotriazole (BTA) is the prototypical inhibitor used in both plating baths and for the chemical mechanical planarization in the microprocessor manufacturing. It forms a film that allows uniform removal of the electrodeposited copper to result in smooth surfaces. It has face dependent protection efficiency which has been studied by various surface sensitive techniques including scanning tunneling microscopy (STM), surface enhanced Raman spectroscopy (SERS), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and sum frequency generation (SFG). It is a good test for the viability of shell-isolated nanoparticle enhanced Raman (SHINERS) particles in investigating surface film formation on single crystal Cu. SHINERS did not reproduce the face dependent behavior found in STM and SFG experiments but did confirm difference between polycrystalline and single crystalline surfaces noted but not previously explained in literature. Rhodanine (RD) is common subunit in many pharmaceutical agents. It has been demonstrated to chelate metal ions, most notably Ag(I), and Cu (I) and Cu(II).It is has been studied as a corrosion inhibitor for Cu. In this dissertation, SERS was used to characterize the time dependent and potential dependent interactions of RD with Cu electrode surfaces to better elucidate the mechanism for inhibition. RD has greater corrosion inhibition than BTA at the same concentration, and this protection increases with time. The time dependent SERS spectra showed a marked decrease in intensity after 1 h which is attributed to formation of thick films opaque to the laser line. Atomic force microscopy (AFM) showed that films were 100 nm thick after 1-2 h incubation time. Levelers are used in electrodeposition of Cu to promote bottom up fill of features created on Si chips to connect devices. They work by passivating the surface thus promoting deposition within features rather outside. In the best case, leveler concentration is used to tune the plating potential. Previous work showed that pH 1 benzyldimethylhexadecyl ammonium chloride (BDAC) best served this function of tuning potential when compared to two other candidates, dodecyltrimethyl ammonium bromide (DTAB), and thonzonium bromide (ThonB). At pH 3, however, ThonB is best at tuning the plating potential with concentration. Using SHINERS we show that potential dependent behavior is observed for ThonB at low concentration whereas there is little to no corresponding behavior of DTAB or BDAC. BDAC strongly at both low and high concentrations whereas DTAB does not interact strongly with Cu surface at any of the three the concentrations used. Ni superalloys are typically used in aggressive environments (high temperatures and pressures, corrosive liquids such as those present for jet turbines, chemical processing plants, and in ductwork and heat exchangers for nuclear plants). They form a scale in high temperature oxidixing environment composed mostly of Cr and the other oxophilic elements in the alloy that protects the bulk alloy from oxidative damage. Investigating how long term heat treatment affects the electrochemical behavior and speciation has implications towards their use in nuclear reactor components. Heat treatment positively affected the corrosion resistance which corresponded with different product speciation, specifically with regards to the appearance of reduced Cr species