Mechanical & Materials Engineering, Department of


Date of this Version

Spring 5-2015


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Engineering (Materials Engineering), Under the Supervision of Professor Jeffrey E. Shield. Lincoln, Nebraska: May, 2015.

Copyright (c) 2015 Yuan Tian


The simulation, fabrication, and characterization of self-assembled ultrahigh density sub-10nm Co nanowire arrays are presented in this dissertation. The general phase separation nanowire growth simulation was operated based on a modified Ising model. The fabrication process can be summarized as the binary Co-X systems lateral phase separation during physical vapor deposition – the plasma layer deposition with a single alloy Co-X target. The “X” stands for Al or Si. The nanowire fabrication and diameter deduction was achieved by balancing the growth rate and surface diffusivity. For Co-Al binary system, the formed sub-10 nm Co nanowires are of face-centered cubic structure through high-resolution transmission electron microscopy. Plus, the total phase separation happened between Co and Al – Co is not detectable in the surrounding Al matrix via scanning transmission electron microscope elemental mapping. The formed Co nanowire array in Al matrix displays unusual magnetic anisotropy, which is originated from the ultrahigh packing density. For Co-Si binary system, the FCC Co nanowire average diameter is 5.38±0.04 nm with wire density 2×1016/m2. The matrix contains both Si and Co. The Co nanowire average diameters of both systems were calculated through in-plane X-ray diffraction, which are consistent with the TEM results within experimental error. XRD reveals that the axis is the nanowire growth direction. The average nanowire diameters of Co-Al system were also calculated through atomic force microscope adhesion images. The diameter vs. deposition rate plot is quantitatively consistent to the predicted theoretic relation.

Advisor: Jeffrey E. Shield