טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKauffmann Yaron
SubjectCharacterization of Micro-Strains in Nano-Crystalline
Materials
DepartmentDepartment of Materials Science and Engineering
Supervisors Professor Rachman Chaim
Professor Wayne D. Kaplan


Abstract

Nano-crystalline (NC) materials attract considerable interest, since these materials contain a large volume fraction of grain boundaries, which lead to novel properties. Thus, thorough investigation of the atomistic structure and the accurate characterization of the microstructural parameters, such as grain size and internal strains, are of considerable interest from both scientific and technological viewpoints.


The main goal of this research is to quantitatively characterize different microstructural parameters in nano-crystalline materials, such as the presence and distribution of micro-strains in the nano-grains, and the influence of grain size on the micro-strains.


NC gold thin films were chosen as a model system. XRD and TEM of the specimens after different annealing treatments showed that the grain size and their morphology evolve during the annealing process. Grain growth, reorientation, and/or recrystallization of the grains results in a columnar microstructure and a reduction of internal micro-strains.


Molecular dynamics (MD) simulations were carried out to shed some light on the possible origin of the strain fields in the nano-grains, and to correlate between the various micro-strain results received from XRD and HRTEM. The origin of these micro-strains is probably the presence of a high density of grain boundary dislocations causing strain field gradients in the grain, which depend on the structure of the boundary.


The experimental and theoretical results from the present work predict strain fields in the nano-grains of a few percent in directions perpendicular to the GBs, and much lower strain fields (of a few tenths of percent) in the direction perpendicular to the thin film free surface.