In Situ Characterization of Electrical and Optical Properties of Air-Sensitive Ultra-Thin Films and Thin-Film Interfaces

University Of Florida, Gainesville FL

Investigators

Abstract

The focus of this project is on the fabrication and in situ characterization of air sensitive ultra-thin films and thin-film interfaces. The capability to perform these investigations relies on a recently constructed Sample-Handling-In-VAcuum (SHIVA) chamber in which thin-film samples can be reliably connected/disconnected at the deposition station (where optical and transport measurements can be made) and then transferred, without exposure to air, to the bottom of a vacuum-compatible cryostat for low temperature (1.3K) and high field (7T) magnetotransport measurements. The rationale for this approach centers on observations that air sensitivity can be a primary impediment to unraveling intrinsic behavior in a variety of systems. The scope of work will be concentrated in four overlapping areas: percolation and the metal-insulating transition, metal/C60 bilayers and composites, magnetism in reduced dimensions, and the determination of screening lengths at metal-dielectric interfaces. Specific systems to be studied include Ag films near the percolation threshold (exhibits pure geometric behavior and a negative classical magnetoresistance), magnetic (Ni, Fe, Co, Gd) metal/C-60 bilayers and composites (exhibits charge transfer and anomalous positive magnetoresistance), thin disordered magnetic and magnetic semiconductor (e.g., Fe, GdxSi1-x) films, and tunnel junction capacitor structures with magnetic electrodes (exhibits magnetocapacitance due to dependence of screening length on magnetic field). We expect that the SHIVA system will greatly facilitate a comprehensive understanding of novel physical phenomena occurring in air sensitive systems. This research is carried out with students who will acquire training skills that will prepare them for future employment in the scientific/technological sector of our economy. As the thickness of a metallic film decreases, its electrical properties become increasingly sensitive to its interface with the underlying substrate and its interface with the ambient environment. For example, many freshly deposited thin films (e.g., Al, Fe) will rapidly oxidize when exposed to air and, if sufficiently thin, will in a short time become totally oxidized. To measure the intrinsic electrical properties of such air-sensitive thin films, it therefore becomes necessary to utilize specialized techniques in which air is prevented from reaching the sample in the period between its fabrication and electrical characterization. The capability to perform these investigations relies on a recently constructed Sample-Handling-In-VAcuum (SHIVA) chamber in which thin-film samples can be reliably connected/disconnected at the deposition station (where optical and transport measurements can be made) and then transferred, without exposure to air, to the bottom of a separate vacuum-compatible chamber for electrical measurements at low temperatures and high magnetic fields. Specific systems to be studied include metal films near the conduction threshold, magnetic metal/Carbon-60 bilayers and composites, thin disordered magnetic and magnetic semiconductor films, and tunnel junction capacitor structures with magnetic electrodes. We expect that the SHIVA vacuum deposition and characterization system will greatly facilitate a comprehensive understanding of novel physical phenomena occurring in air sensitive systems. Students will participate in this research. They will thereby acquire skills and training in preparation for employment in scientific/technological sectors of industry, academe, and government.