טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentTing Mao
SubjectThe Au-ZrO2 Interface: Energy and Morphology
DepartmentDepartment of Materials Science and Engineering
Supervisor Full Professor Kaplan Wayne D.
Full Thesis textFull thesis text - English Version


Abstract

Metal-ceramic interfaces have numerous applications in composite materials, thermal barrier coatings, solid oxide fuel cells, etc. As such, a fundamental understanding of metal-ceramic interface energetics and structure is important since they define the overall function of the system. In this work, thin films of gold were deposited on (111) oriented yttria stabilized zirconia (YSZ) substrates and annealed at high temperatures until the films “dewetted’’ and equilibrated.


Two sets of solid-state dewetting experiments in reducing atmosphere were conducted. Equilibrated interfaces from the two experiments were found to have Ca or Cr adsorption by scanning transmission electron microscopy (STEM) combined with energy dispersive spectroscopy (EDS). Interfaces with an excess of Cr were found to have a lower energy than interfaces with an excess of Ca. 150 equilibrated particles from both experiments were characterized by electron backscattered diffraction (EBSD) and were found to have a random in-plane orientation relationship, but with a strong out of plane preferred orientation, which is {111} Au || {111} YSZ. This was corroborated by X-ray θ-2θ characterization. It was also found that the strong preferred orientation exists before dewetting.


Liquid and solid-state dewetting experiments were also conducted in air, where liquid dewetting resulted in a more isotropic orientation of {111} Au|| {111} YSZ than for solid-state dewetting.


Although no pure Au-(111) YSZ interface was characterized, based on comparisons with other systems it can be assumed that Ca/Cr segregation reduces the anisotropy, resulting in a preferred orientation instead of a low-index orientation relationship (e.g. for Ni on (111) YSZ).  Liquid-state dewetting changed the pre-existing preferred orientation of {111} Au || {111} YSZ of the as-deposited film, resulting in a more isotropic preferred orientation compared to solid-state dewetting.  This may be due to the heterogeneous nucleation process occurring during the course of liquid-state dewetting.