Kinetic growth and epitaxy of Ag nanowires on Si (100)

Boquan Li, Waclaw Swiech and Jian-min Zuo

Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign

We have investigated the morphological evolution of Ag nanostructures on Si (100) using in-situ and ex-situ TEM and LEEM. We find that the shapes of the Ag are growth/annealing temperature-dependent. Ag clusters deposited at RT are round, defective and randomly orientated as determined by nano-beam electron diffraction. After annealing, the clusters transform into epitaxial pyramids with flat (100) top. We observed elongated islands coexisting with square islands when deposited at elevated temperature and annealed further. It appears that there is a small temperature window in which we observed long Ag nanowires. The nanowires are surrounded by a denuded zone, and are determined to grow along Si [110] or [1-10] direction. Detailed structural analysis indicates that the lattice mismatch, in the cube on cube epitaxy and forming the coincident-site lattice, is as small as 0.3%, which exclude strain energy dominates the wire growth. Initial results from LEEM suggest Si 2x1 reconstruction affect the wire growth. The wires length of ~ micron spans several 2x1 and 1x2 domains. Our experiments clearly indicate that the wire formation is a kinetics-controlled process.