Scanning probe studies of thin films

The first part of this thesis deals with the phenomenon of thermoelectricity. It involves the improvement of the thermoelectric properties of silicon using innovative nanostructures. My contribution was to help fabricate these thermoelectric devices, and is the focus of this part of the thesis.

The second part and primary focus of this thesis is the analysis of thin films using scanning probe techniques. These surface techniques include atomic force microscopy, electric force microscopy, Kelvin probe force microscopy, and scanning tunneling microscopy. The thin films studied are graphene and molybdenum disulfide, two remarkable materials that display unique two-dimensional qualities. These materials are shown to be useful in studying the properties of adsorbates trapped between them and the substrate on which they rest. Moreover, these adsorbed species are seen to affect the structural and electronic properties of the thin films themselves. Scanning probe analyses are particularly useful in elucidating the properties of these materials, as surface effects play a significant role in determining their characteristics.

The final part of this thesis is concerned with the study of Akt in live cells using protein capture agents previously developed by my colleagues. The activation and degradation of Akt is investigated using various biological assays, including Western blots, in vitro kinase assays, and cell viability assays. Finally, the usefulness of synthetic capture agents in perturbing protein pathways and as delivery agents is assessed and analyzed.

Surface Activity and Bulk Defect Chemistry of Solid Oxide Fuel Cell Cathodes

In the first half of this thesis, a new robotic instrument called a scanning impedance probe is presented that can acquire electrochemical impedance spectra in automated fashion from hundreds of thin film microelectrodes with systematically varied properties. Results from this instrument are presented for three catalyst compositions that are commonly considered for use in state-of-the-art solid oxide fuel cell cathodes. For (La_0.8Sr_0.2)_0.95Mn_O3+δ (LSM), the impedance spectra are well fit by a through-the-film reaction pathway. Transport rates are extracted, and the surface activity towards oxygen reduction is found to be correlated with the number of exposed grain boundary sites, suggesting that grain boundaries are more surface-active than grains. For La_0.5Sr_0.5Co_O3-δ (LSC), the surface activity degrades ~50x initially and then stabilizes at a comparable activity to that of previously measured Ba_0.5Sr_0.5Co_0.8Fe_0.2O3-δ films. For Sr_0.06Nb_0.06Bi_1.87O₃ (SNB), an example of a doped bismuth oxide, the activity of the metal-SNB boundary is measured.

In the second half of this thesis, SrCo_0.9Nb_0.1O_3-δ is selected as a case study of perovskites containing Sr and Co, which are the most active oxygen reduction catalysts known. Several bulk properties are measured, and synchrotron data are presented that provide strong evidence of substantial cobalt-oxygen covalency at high temperatures. This covalent bonding may be the underlying source of the high surface activity.