Electron tomography analysis of 3D order and interfacial structure in nano-precipitates

Abstract: Structural characterization is essential to understand the formation mechanisms of the nanostructures in thin absorber layers in third generation solar cells and amyloid protein aggregates. Since to the dimension of the precipitated structures is in nanometer scale, electron tomography technique in transmission electron microscopy (TEM) has been applied as a major tool to analyze the 3D order and distribution of precipitates using the electron tomography technique. Silicon rich silicon carbide (SRSC) films were deposited by plasma enhanced chemical vapor deposition (PECVD) technique and annealed in the nitrogen atmosphere for 1 hour at 1100 °C. The spectrum-imaging (SI) technique in Energy filtered TEM (EFTEM) imaging mode was used to develop electron tomography. From the reconstructed sub-volumes, the complex, three dimensional interfacial nanostructure between the precipitated NPs and their parental matrix was observed and explained in terms of thermodynamic concepts. Additionally, the feasibility of raw data 4D electron tomography has been demonstrated using the EFTEM SI dataset.The aggregation process of the human islet amyloid polypeptide (hIAPP) has a great impact on human health. In this thesis, a model system has been taken to study the ultrastructure of the hIAPP aggregates that are present in the fat body tissue surrounding the brain of Drosophila melanogaster. Electron tomography technique on TEM revealed clear crystalline structures in 3D. For the first time, the presence of a 5-fold twinned structure in biology was discovered. An intriguing finding is the filament like interconnection of hIAPP protein granules observed predominantly along the nearest neighbor directions. This suggests the existence of the directional binding forces between two nearest protein granules in addition to dipole-dipole interactions.