Holon Institute of Technology, Faculty of Sciences,Seminar
Transition Metal Silicides and Oxides – High Density Data Storage and Memory Elements of the Future?
Prof. Ilan Goldfarb, Tel Aviv University
December 12, 2013 | 13:15 | Room 424/8
In the first part of the talk, I will survey our long going effort directed towards controlled growth of mesoscopically self-ordereded epitaxial Me-silicide (Me=Ti, Co, Fe, Ni) nanostructure arrays, and their resulting unusual physical properties, as exemplified by iron-silicide; α-FeSi_2 nanoislands were solid-phase epitaxially grown on vicinal stepped Si(111) surfaces, and analyzed as a function of Fe-coverage and annealing temperature by time-resolved scanning tunneling microscopy(STM), x-ray photoelectron spectroscopy(XPS), aberration-corrected high-resolution transmission electron microscopy (HRTEM), and superconducting quantum interference device (SQUID) magnetometry.
Well self-ordered arrays consisted of (2×2)-reconstructed silicide nanoislands decorating stepbunch edges of a vicinal Si(111), and showed considerable in-plane superparamagnetism (~1.9 µ_B / Fe atom at 4K), although the bulk crystal α-FeSi_2 phase lacks any sort ofmagnetism at all! Such anomalous magnetic behavior of the α-FeSi_2/Si(111) nanoislands may open new pathways to Si-based spintronic and high-density magnetic data storagedevices. Plausible explanations for this anomaly will be proposed and discussed.
In the second part, I will talk about our recent work on electronic structure of oxides in the context of memristor technology. Technologically, transition metal oxides are useful in a variety of applications, including electronics, optics, and gas sensing.
Scientifically, the physics of electron conduction in amorphous materials presents a formidablechallenge. In this work we characterize conduction mechanisms in thin amorphous films of three representative binary Me-O (Me=Ta, W, and Nb) systems as a function ofoxidation, photoemission with temperature-dependent transport measurements. Despite certain differences, these thin amorphous oxide films all display oxidation-induced Anderson localization, resulting in a transition from metallic to a hopping Fermi glass conduction, down to sub-percolation threshold.
The electron localization estimated from the band structure probed by photoemission is in good agreement with that from the transport measurements, and the two can be used to construct phase diagrams of conduction in the degree of oxidation-conductivity coordinates, which are instrumental in the design of resistive-switching and similar devices.