Investigation of microstructures of some layered thin films by electron microscopy

In this thesis, the microstructures of thermoelectric p type (Bi0,15Sb0,85)2Te3 and n type Bi2(Te0,9Se0,1)3 films grown on kapton substrates by sputtering at 168 oC and 200 oC respectively, W films grown on Si(100) substrates by LPCVD at 280 oC using different gas flows of H2+WF6+SiH4 reactions and InxGa1-xAs/GaAs(001) heterostructure grown by MBE at ~550 oC were investigated by electron microscopy. SEM images and EDX spectra showed that the surface morphologies of thermoelectric films exist in the form of big grains with small grains, rough surface and expected structure. The analyses of W/Si(100) films by SEM and EDX exhibited different surface morphologies and chemical structures due to the growth conditions (flow rate, delay and so?). It was seen from TEM images and SAD patterns that the thermoelectric films have poly crystalline structures with nano-sized and different orientations. It was also observed that the films have no second phase, precipitate and separation betwen the layers. Studies of lattice images for both of the samples were done by HRTEM. dhkl values of grains with different orientations were measured and some deformed areas were observed. The microstructures and interfaces of W/Si(100) films were examined using plan-view and cross-sectional TEM specimens. The films presented poly crystalline structures with randomly orientations. Oxide phase structure was found in one of the films with shorter initial growth time. It was confirmed using EDX that the second phase is WO3. The film with longer initial growth time presented a bit more rough interface structure, compared with the first one and many W incursions in the Si substrate. The microstructure of InxGa1-xAs/GaAs(001) heterostructure was investigated by TEM. Cross-sectional TEM specimens were prepared to examine the microstructures. It was seen that the epilayers associate with microcracks. More detailed examines showed that the cracks accompany with dislocations at the around and tip of them. These cracks and dislocations were imaged at the atomic scale by HRTEM. dhkl measurements were also evaluated.