- Dr. Xuyang [Rhett] Zhou, The University of Alabama, Tuscaloosa
Thin films are found in a variety of technically important applications ranging from optical coatings to integrated circuit technologies. When these films are deposited, the residual stresses can be sufficient to cause a film to delaminate, with buckling or microcracking causing failure of the film in the intended application. Understanding and manipulating the stress-generation mechanisms in these films is of vital importance. In this research, the use of solute segregation to the grain boundaries is discussed as a means to regulate the nanogranular grain size to control the stress state of the film. Using Fe(Cr) as a case study, the preferential solute specificity to the grain boundaries is revealed through the use of cross-correlative precession electron diffraction with atom probe tomography. These results are then used to verify and validate a hybrid molecular dynamics/Monte Carlo computational model for solute segregation, with specific attention to how grain boundary inclination angle regulates solute concentration. Through the use of grain size control in these films, these two nominally high-tensile-stress-state elemental films, in the alloy state, had the tensile stress reduced. Further studies as a function of high chromium content and in situ deposition temperature revealed both the formation of the high-temperature sigma phase, as well as spinodal decomposition within the film.