The University of Oklahoma (OU) recently acquired a Zeiss Neon, a dual beam SEM/FIB Cross beam machine. This thesis focuses on its utilization via two independent projects, one involving the characterization of solar-cells semicon- ductor materials while the other focuses on the FIB to provide information about a preserved megaspore.

Part I: Solar-Cells

Third generation photovoltaics (PVs) seek to increase the efficiency of PVs and reduce their cost. One candidate to this third generation involves the use of quantum dot (QD) structures to create an intermediate band-gap. This de- vice can overcome the Shockley-Queisser efficiency limit (about 30%) by better utilizing the solar spectrum. However, the current results are far from the the- oretical limit, partly because of the material quality of the QDs structure. This project involves high-density self-assembled InAs/GaAs 1−x Sb x QDs grown by molecular beam epitaxy at the University of Oklahoma (OU). Ultimately, size, shape, density, composition, and crystalline quality of the QDs as well as sim- ilar details for the matrix layers play an important role in the PV efficiency. Hence, the characterization of these properties is important. Characterizing multiple layers of QDs will ultimately require cross-sectional transmission microscopy; however, along the way, atomic force microscopy (AFM) and field- emission scanning electron microscopy (FE-SEM) will more easily yield details about the uncapped top QD layer. For example AFM accurately determines QD density, and quantitatively describes QD shape. On the other hand, AFM is sensitive to tip/probe-shape artifacts. Cross-sectional FE-SEM can clear up some of these artifacts and indicate crystalline quality; cross-sectional FE-SEM was found as a means of giving better lateral resolution than our typical AFM results. Ultimately, cross-sectional images from a transmission electron micro- scope (TEM), would provide the best information, however pitfalls and machine breakage delayed us in our work; while SEM/FIB in situ TEM preparation is now possible, it could not be operated

Part II: Megaspores

Optical and electron microscopy are critical tools for studying preserved and fos- silized organisms. Due to its early development and refinement, light microscopy has dominated the study of organic-walled fossils. Taxonomic identification and discrimination is almost exclusively based on features visible under transmitted light. However electron microscopy, and in particular TEM, has been applied to investigations of the ultrastructure of the walls and ornament that are beyond the resolution of light microscopy. Hypotheses for the assembly of the walls have been formulated based on these data. Recently new techniques, such as FIB, SEM, and synchrotron radiation tomography, have expanded the boundaries of imaging fossils. This thesis part focuses on investigating Arcelites Hexapartitus species megaspore, using an SEM with FIB to obtain three dimensional infor- mation about their inner exine channels. Channels were readily imaged through the inner exine using a number of cross-beam geometries. The channels seem to be simply connected running through the inner part of the exine layers, however, the channels/pores are found to stop before exiting this inner exine layer at both its inner and outer surfaces. Additionally, it was found that they are not continuous this inner exine layer. Investigations concerning the material obstructing the channels have begun. So far, there is no evidence of a foreign material present. It appears that the pores simply end before exiting the layers and have occasional nano sized regions of sporopollenin, the megaspore wall material, blocking the channels.