Date on Master's Thesis/Doctoral Dissertation

8-2006

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Electrical and Computer Engineering

Committee Chair

Cohn, Robert W.

Author's Keywords

Self-assembly; Gallium; Thin films; Metallic thin films

Subject

Thin films

Abstract

Liquid gallium (Ga) spontaneously alloys with thin films of metals such as Ag, Au, Pt Al, and Cu at near or even below room temperature resulting in rapid self-assembly of nanostructures. In this dissertation, studies of the formation of these nanostructures are reported together with application of the processes towards device fabrication. Ag 2 Ga needles, CoGa 3 rods, and Ga 6 Pt plates self-assemble at room temperature at the interface of Ga and thin films of Ag Co, and Pt. The Ag 2 Ga needles orient nearly vertical to the interface which suggests that an individual needle can be directed to grow in a desired direction by drawing a silver-coated surface from the Ga droplet. Needles from 25 nm to microns in diameter and up to 33 microns long were grown by this method. Needle-tipped cantilevers have been used to perform atomic force microscopy (AFM) and voltage lithography. Mechanical properties of the Ag 2 Ga needles are measured during bending, buckling, yielding, and AC electric excitation of vibrational modes. The rates of reactive spreading of Ga through thin films of Au and Ag from room temperature to 200°C are measured. A model of the reduction in spreading rate of Au-Ga over time describes the reduction in area for inter granular flow as the Ga 2 Au crystallites precipitates and grow together. Ga spreading on Au microelectrodes is used to perform time-resolved measurement of changes in the contact resistance of multiwall carbon nanotubes. Networks of Au-Ga nanowires form when a liquid Ga drop spreads and reacts on 10- to 100- nm-thick Au thin film at temperatures between 310°C and 400°C. Au suspended nanowires were fabricated by etching these networks in HCl followed by anisotropic etching of the Si substrate. Suspended nanowires as long as 6 Ìm and as narrow as 35 nm diameters have been produced. Superporous Au and Pt thin films with feature size as small as 5 nm are formed after HCI etching of metal thin films that have been reacted with gallium. Superporous Pt formed on a set of microelectrodes was evaluated for electrochemical sensing. These electrodes showed a 6 fold improvement in its limit of detection for H 2 O 2 over the nonporous Pt electrodes.

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