|M.Sc Student||Angelina Gabelev|
|Subject||Effect of Stress and Plastic Strain on Grain Growth in Thin|
|Department||Department of Materials Science and Engineering||Supervisors||Full Professor Rabkin Eugen|
|Dr. Sherman Dov|
|Full Thesis text|
Thin films are used in many technological applications such as computers, microelectronics, health care technologies, etc. The mechanical properties of thin films depend strongly on their microstructure. Therefore, in order to achieve optimal material properties, the process of grain growth must be well understood so that the required microstructure can be obtained and stabilized. In this study, the effect of plastic strain on grain growth in thin Al and Cu films was investigated. Stresses are almost always present in thin films on substrates. Often those stresses lead to plastic strain that can change the microstructure of the film. This research sheds a new light on the phenomenon of grain growth in thin films as well as on grain growth in nanocrystalline materials in general.
Al and Cu films were deposited in different conditions on kapton substrates and deformed at both room and elevated temperatures. The microstructure of these films was studied by various means of characterization techniques (focused ion beam microscopy, scanning electron microscopy, atomic force microscopy and X ray photoelectron microscopy) and compared with microstructure of the films annealed without deformation.
The main findings of this research are:
Tensile plastic deformation at 300 ˚C leads to enhanced grain growth in thin Al films. This grain growth process is fundamentally different from conventional dynamic recrystallization and grain growth in bulk samples. It was shown, for the first time, that a low plastic strain applied during heat treatment significantly accelerates the grain growth in thin films, and that this effect is thickness-depended.
Oxygen contaminations alter the microstructure of as deposited Al and Cu thin films and the kinetics of its evolution. Not only that oxygen pins grain boundaries, but it also alters the mechanism of grain growth from normal to anomalous in Cu, and entirely prevents it in Al.
Surface topography of Al and Cu films was investigated with the aid of AFM and SEM. After those results were compared with the results of microstructure characterization with FIB, it was found that as sputtered topography does not reflect the real microstructure of the films. The effect of films topography on grain growth is discussed.