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Preparation and characterization of materials for tunneling and ballistic nanojunctions

Rajesh Rajasekaran, University of Nebraska - Lincoln

Abstract

Ferromagnetic thin-film structures separated by ultrathin dielectrics on the order of few nanometers can be used to generate spin-polarized currents by spin-dependent tunneling across the dielectric barrier. In this thesis, the formation of ultrathin, pinhole free, silicon oxide layers using a wet chemical deposition technique is described. The procedure involves the repetitive execution of a set of reactions, each cycle nominally leading to the formation of a monolayer of SiO2. Unlike the conventional sputtering and chemical vapor deposition methods used, this procedure can be performed at room temperature, an advantage that may be a boon when dealing with temperature sensitive magnetic materials as the electrodes encompassing the dielectric. I was able to create multilayered structures that exhibit exchange bias characteristics that should ultimately enable us to manipulate the magnetic moment of ferromagnetic components on either side of the dielectric barrier. Besides the fundamental knowledge gained, this research could ultimately lead to highly sensitive magnetic sensors or switches. ^ The self assembly of two functionalized biphenyl molecules on gold and cobalt surfaces was studied using x-ray photoemission studies. The nature of self assembly, orientation, preferential bonding and electronic structure of the molecules were studied. The results obtained, together with theoretical predictions, indicate that both molecules are promising prospects for insulating barriers in magnetic tunnel junction devices. ^ Bismuth, having a large carrier mean free path, is expected to exhibit ballistic transport property when confined to few hundreds of nanometers and large magnetoresistance value. Highly crystalline bismuth was grown by electrochemical deposition between nickel electrodes patterned by focused ion beam milling or electron beam lithography. The gap between the nickel electrodes was a few tens of nanometers. If connected together by a thin bismuth point contact, such a ferromagnet-bismuthferromagnet junction could give magnetoresistance values on par with GMR devices.^

Subject Area

Chemistry, Analytical

Recommended Citation

Rajasekaran, Rajesh, "Preparation and characterization of materials for tunneling and ballistic nanojunctions" (2008). ETD collection for University of Nebraska - Lincoln. AAI3338831.
http://digitalcommons.unl.edu/dissertations/AAI3338831

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