Dan Bizzotto

No abstract available.

Self-assembled monolayers (SAMs) are important structures commonly employed to functionalize metal surfaces. To optimize a metal-SAM construct, it is important to characterize the influence of the surface crystallography. In this thesis, a single crystal Au bead electrode was employed to investigate different types of SAMs, enabling studies on a variety of surfaces under identical conditions and avoiding laborious experimental replicates on a large number of crystal orientations.The application of a single crystal Au bead electrode was demonstrated by investigating the reductive desorption process for two types of SAM: the alkanethiolate SAM and the α-aminoisobutyric acid (Aib) peptide thiolate SAM. Using in situ fluorescence imaging, the influence of surface crystallography on reductive desorption was observed, reflected as a correlation between the density of broken bonds of a surface and the reductive desorption potential of a SAM deposited on the surface. Besides the surface crystallography, intermolecular interactions also had a significant impact on determining the desorption potential.Aib peptide thiolate SAMs on a Au(111) facet were further investigated. It was found that the low packing density Aib peptide thiolate SAMs exhibited a potential-modulated fluorescence response which was believed to be due to the orientational or structural change of the peptide molecules in response to the applied potential.The potential-driven reorientation effect of the DNA SAMs has been intensively explored due to its application in biosensing. Characterization of the DNA SAMs with in situ fluorescence methods suggested that surface crystallography exerts an influence not only on the formation of the DNA SAMs but also on the efficiency of the potential-driven response. Moreover, a spectroelectrochemical technique that couples electrochemistry, fluorescence microscopy and harmonic analysis was developed to explore the non-linearity of the fluorescence response to an applied AC potential. This technique could be potentially applied to detect changes in DNA hybridization state.The experimental results demonstrate the convenience and wide applicability of using a single crystal Au bead electrode to investigate SAMs. On the other hand, applying existing and developing new spectroelectrochemical techniques give insights into creating SAMs with desirable properties.

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Thin organic layers deposited on electrodes are ubiquitously proposed for a variety of surface-related applications. The quality of these layers is usually assessed by analytical methods that average the measured signal over a large area compared to the molecular scale. This work outlines the use of in-situ fluorescence microscopy as a characterization method by analyzing three examples of such layers.First, a heterogeneous Langmuir layer was physically adsorbed to a gold electrode via the Langmuir-Schaefer method and the effects of the substrate analyzed by comparing the adsorbed layer with the predecessor floating film. Through the use of a dimer-forming fluorophore, substrate mediated condensation was suggested.Second, the reductive desorption of self-assembled monolayers (SAMs) from microelectrodes was used to investigate the movement of the released thiolate molecules. Once in solution, these molecules were found to follow a buoyant movement, consequence of the high local concentration of H₂ resulting from the simultaneous reduction of water under the conditions employed.Finally, a DNA SAM system that has been previously suggested as a biosensing platform was investigated for heterogeneity. It was found that the substrate crystallography had a significant effect on the density and efficiency of potential driven change in conformation of the immobilized probes. Furthermore, a deconvolution method is proposed in order to correct for the effect of the electrode charging time constant on the measurements of the kinetics of the DNA conformation change.Overall, the performed experiments show that in-situ fluorescence microscopy is a useful technique to analyze distance dependent phenomena involving these deposited layers. Moreover, the coupling between electrochemistry and fluorescence allows not only to monitor but also to drive changes in the layers, creating systems capable of studying the dynamics of the deposited films.The inclusion of the proposed technique as a characterization tool during the development of systems based on ultrathin organic films could improve the understanding of the influence of the deposition conditions on the film quality, helping to attain the necessary robustness to make the proposed systems actually achieve their proposed applications. Supplementary video material is available at: http://hdl.handle.net/2429/51003

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Transmembrane proteins and ion channels are a major target for new drug development.Incorporating them into sensors requires a method to produce stable, easilymodifiable solid-supported phospholipid bilayers. This thesis demonstrates amethod for using potential control on the electrode to mediate liposome adsorption,allowing them to interact with a previously deposited octadecanol layer throughpotential-created defects.Compression isotherms and electrochemical measurements were used to establishthe effect of the incorporation of a small amount of fluorescent dye on theoctadecanol layers. Using these fluorescently-labelled octadecanol layers, electrochemicalmeasurements both independently and coupled with in-situ fluorescencemeasurements were used to characterize the interaction of liposomes with theselayers under potential control. It was found that application of moderate potentials- more negative than the onset of defect formation but less than that required fordesorption of the layer - facilitated the effective incorporation of liposome materialinto the octadecanol bilayer. The length of time spent at the poration potential hadlittle effect on the degree of liposome interaction with the adsorbed layer. The incorporationwas seen as a change in the double-layer capacitance and the creationof small fluorescent structures in the layer after exposure to liposomes at the porationpotential. A shift in the characteristic desorption potential was also seen withliposome incorporation.Atomic force microscopy coupled in-situ with electrochemical control was alsoused to investigate the interaction of liposomes with the adsorbed octadecanol layer.The structure of the adsorbed layer was observed and with liposomes present insolution, the creation of three-dimensional structures similar in nature to those seenby fluorescence was noted. The incorporation of liposomes into the octadecanolwas shown to be easily controlled by application of an electrical potential, openinga path for a new method of producing supported lipid bilayers in-situ for biosensingapplications.

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Copper interconnects in advanced integrated circuits are manufactured by processes that include electrodeposition, chemical mechanical polishing and annealing. The as-deposited copper is nano-crystalline and undergoes a microstructure evolution at room temperature (self-annealing) or during an annealing step. During this process, significant changes in resistivity and grain size are observed. In this work, the microstructure evolution in 0.5-3 μm-thick electrodeposited copper thin films was studied. Resistivity measurements were used to quantify the role of deposition conditions on the microstructure evolution rate. In-situ electron backscatter diffraction (EBSD) was employed to observe self-annealing at the film surface. The resistivity-microstructure correlation during self-annealing was examined. A phenomenological model using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach was developed to describe recrystallization during isothermal and continuous annealing treatments. The microstructure evolution in copper-silver alloys and films produced by variable deposition rates was investigated. Phase-field model was applied to simulate self-annealing and the effect of deposition current density.The results show that the drop in resistivity during self-annealing is accompanied by significant changes of the microstructure at the film surface. Different criteria were developed to assess self-annealing rate from EBSD maps including grain size, image quality and local orientation spread. Adopting a grain size threshold, it was found that there is a reasonable correlation between resistivity and microstructure during self-annealing. The recrystallization in copper thin films appears to be thermally activated with an activation energy of 0.89-0.93 eV. Adopting the principle of additivity, it was found that the recrystallization rate during continuous annealing can be described by the JMAK model using the isothermal resistivity profiles. A method was proposed to accelerate recrystallization based on a capping layer deposition. No recrystallization was observed when silver was co-deposited with copper in the absence of chloride (even when annealed at 100 °C for 5 hours). Phase-field model was able to describe self-annealing and the effect of deposition current density. The results in this thesis are of significance to the microelectronic industry where recrystallization is a crucial step in the fabrication of copper interconnects for the high performance integrated circuits.

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No abstract available.

A novel UHV microcalorimeter has been used to study the interaction betweencalcium and three polymers: MEH-PPV, MEH-PPP and P3HT. All three polymersbehave differently in their reaction kinetics with calcium. On MEH-PPV we measure45 μJ/cm² of heat generated in excess of the heat of bulk metal growth, 120 μJ/cm²for MEH-PPP, and 100 μJ/cm² for P3HT. Comparison of the MEH-PPV and MEHPPPdata indicate that the initial reaction of calcium with MEH-PPV occurs at thevinylene group. We propose, based on hypothetical models, that calcium reacts withthe vinylene groups of MEH-PPV with a reaction heat of 360 kJ/mol and at aprojected surface density of 1.7 sites/nm², while it reacts with the phenylene groupsof MEH-PPP in a two-step process with reaction heats of 200 and 360 kJ/molrespectively, at a projected surface density of 3.5 sites/nm².Optical absorption experiments, using either a 1.85 eV diode laser or a xenon lampcoupled to a scanning monochromator, have also been performed using the samecalorimeter sensor. In the case of MEH-PPV, using the laser we find an opticalabsorption cross-section of 3E-¹⁷ cm² per incident calcium atom at low coverages.The change in absorptance at higher coverages correlates perfectly with thepopulation of reacted Ca atoms determined calorimetrically. The size of theabsorbance cross-section, and its position just within the band gap of the polymer, areconsistent with the reaction being one of polaron formation. Calcium does not appearto dope P3HT, while the photon energy range of 1.5 to 3.75 eV used in theseexperiments is likely too small for probing polaronic energy states in MEH-PPP.

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