HREM characterization of nano-composite Au/SiO2 layers

Nano-composite layers of Au nano-crystallites embedded in amorphous silica matrix were obtained by a radio-frequency co-sputtering technique. Glass or single crystal silicon wafers were chosen as substrates. After deposition, the layers were heat treated at 900 degrees C for 60 min. Microstructure of the layers was investigated using a TECNAI G(2) FEG SuperTwin (200 kV) transmission electron microscope. Thin foils were cut using a focused ion beam Quanta 3D. The investigations confirmed that the applied process allowed obtaining nano-composite layers containing spherical Au crystallites of average size of approximately 3 nm embedded in an amorphous silica matrix. Some of the nano-crystallites were twinned. The layers were heat treated in subsequent step and rise of the crystallite average size up to 5.5 nm confirming activation of diffusion processes was seen. Presence of irregularly shaped Au crystallites in the latter layers indicates incomplete sintering due to short annealing time.