AVS 52nd International Symposium
    Thin Films Wednesday Sessions
       Session TF-WeM

Paper TF-WeM9
Ultra-Hard Al-Si Nanocomposites Synthesized by High-rate Co-evaporation

Wednesday, November 2, 2005, 11:00 am, Room 306

Session: Mechanical and Tribological Properties of Thin Films
Presenter: D. Mitlin, University of Alberta, Canada
Authors: D. Mitlin, University of Alberta, Canada
C. Ophus, University of Alberta, Canada
V. Radmilovic, Lawrence Berkeley National Laboratory
T.J. Richardson, Lawrence Berkeley National Laboratory
U. Dahmen, Lawrence Berkeley National Laboratory
Correspondent: Click to Email
We used high rate co-evaporation to synthesize Al-Si nanocomposite films in the composition range of Al-1at%Si to Al-23at.%Si. Pure Al films were also synthesized using identical deposition conditions, and were used as a baseline. The Al-Si structures have a hardness as high as 4GPa (Al-23at.%Si), and display noticeable plasticity under nanoindentation (Al-12at.%Si). We used transmission electron microscopy (TEM) to analyze Al-12at.%Si and pure Al samples. The pure Al film had the expected grain size of upwards of one micrometer. The Al-Si film consists of a dense distribution of spherical nanoscale (10-30 nm) Si particles separating irregularly-shaped Al grains, many of which are also nanoscale (50-200 nm). This microstructural refinement is due to the Si particles disrupting the columnar growth of the Al grains by promoting re-nucleation. Additionally the particles also pin the Al grains which coarsen during deposition. X-ray diffraction results indicate that there is a marked decrease in the Al lattice parameter with increasing Si content. This effect is weaker after the samples have been stored at room temperature for six months. The structures' electrical resistivity remains near the level of pure Al for compositions up to 6.5at.%Si, but significantly increases at higher Si compositions. This work is the first step towards yielding Al-Si nanomaterials specifically optimized for integration into structural components of MEMS.