AVS 52nd International Symposium
    Nanometer-Scale Science and Technology Monday Sessions
       Session NS1-MoM

Paper NS1-MoM8
Low Temperature Melting of Tungsten and Ruthenium Nanorod Arrays

Monday, October 31, 2005, 10:40 am, Room 204

Session: Nanometer Scale Structures
Presenter: T. Karabacak, Rensselaer Polytechnic Institute
Authors: T. Karabacak, Rensselaer Polytechnic Institute
D.-X. Ye, Rensselaer Polytechnic Institute
P.-I. Wang, Rensselaer Polytechnic Institute
G.-C. Wang, Rensselaer Polytechnic Institute
T.-M. Lu, Rensselaer Polytechnic Institute
Correspondent: Click to Email
We observed that tungsten and ruthenium nanorod arrays melted at ~30% and ~40% of their bulk melting points (W at 3410 °C and Ru at 2334 °C), respectively. These findings reveal the most dramatic reduction in the melting temperature of nanostructures ever reported in literature. The W and Ru nanorods were grown by an oblique angle sputter deposition technique through a physical self-assembly mechanism due to the shadowing effect. The W nanorods have an average width of ~75 nm and an average length of ~500 nm and the Ru nanorods have an average width of ~75 nm and an average length of ~370 nm. These nanorods were isolated from each other with gaps ~20 nm. The nanorods were vacuum-annealed at various temperatures in the range of 700-1000 °C for 30 minutes at each annealing temperature. The melting process was investigated through the analysis of scanning electron microscopy (SEM) images and X-ray diffraction (XRD) spectra. W and Ru nanorods started to coalesce and formed continuous films at temperatures ~1000 °C and ~950 °C, respectively. In addition, the melting was associated with recrystallization as observed from XRD spectra. After melting, W rods transformed from metastable cubic @beta@(200) phase to bcc @alpha@(110) and Ru rods changed their texture from hcp(100) to a mixture of (002) and (101) crystal orientations. The low temperature melting of the nanorods is explained to be mainly due to their small size and increased surface/volume ratio, which results in the "premelting". The premelting is believed to be further enhanced by the presence of interstitials (due to the atomic peening of energetic Ar, W, or Ru particles of tens of eV) or impurity (O in the case of @beta@-W rods) atoms in the lattice structure of the rods accompanied during sputter deposition.