Investigation Of Parallel Planar Defects And Texture Transformation In Electron Beam Evaporated Silver Thin Films
Texture transformation is a known phenomenon which occurs in face-centered cubic metal thin films. This phenomenon entails a transition of film texture from (111) in as-deposited films to (100) in post-annealed films depending on film thickness; thinner films maintain the as-deposited (111) texture while thicker films transform to (100) texture after heat treatment. Texture transformation was previously theorized to result from minimization of surface and interface energies and strain energy; however, additional evidence contradicts this theory, suggesting that an alternative driving force for texture transformation exists. Nanotwin defects have been observed in numerous face-centered cubic metal thin films and may be a driving force for texture transformation; whether or not film nanotwin density is affected by changes in deposition parameters is not yet agreed upon. The influence of deposition rate on nanotwin density and texture transformation of silver thin films is investigated in this work. Silver thin films were synthesized at varied deposition rates using electron beam evaporation. Film samples were annealed to induce texture transformation using two setups; the first setup was used to analyze texture transformation of samples with different thicknesses deposited at different rates and the second setup was used to analyze texture transformation of samples with identical thickness deposited at different rates in situ over time. The texture of thin film samples was analyzed using x-ray diffraction. To identify and characterize nanotwins in our thin films cross-sections of film samples were studied using transmission electron microscopy. X-ray diffraction measurements indicated that the as-deposited silver thin films had strong (111) texture and that thicker films developed partial or transformed completely to (100) texture after heat treatment. Investigation of x-ray diffraction measurements of samples deposited at different rates revealed that changes in deposition rate influence texture transformation in thin film samples. Increasing deposition rate was found to increase texture transformation in film samples; samples of identical thickness deposited at faster rates were found to have a higher (100) texture post anneal than samples deposited at slower rates and from the in situ study samples of identical thickness deposited at faster rates were found to have transformed in less time than samples deposited at slower rates. Transmission electron microscopy results for as-deposited silver film samples showed that nanotwins were in our evaporated silver thin films parallel to the substrate. Investigation of samples deposited at different rates revealed that changes in deposition rate influence nanotwin spacing in film samples. Increasing deposition rate was found to decrease nanotwin spacing in silver thin film samples. Nanotwins are found to be a viable driving force for texture transformation in facecentered cubic metal thin films in this work. A model based on classical nucleation theory modified for formation of twinned and untwined nuclei from a vapor phase was assessed as a method for predicting nanotwin spacing in thin films. Results from applying this model were found to closely match experimental nanotwin spacing measurements in our silver thin films samples; however, the use of this model is still questionable.
Van Dover,Robert B.
Materials Science and Engineering
M.S., Materials Science and Engineering
Master of Science
dissertation or thesis