Electrostatic force microscopy studies of nanoscale systems

Stephen Wayne Howell, Purdue University

Abstract

Electrostatic force microscopy has been used to study the electrostatic force on a nanometer length scale. The experimental techniques, implemented to measure electrostatic force, were based on established methods reported in the literature. These measurements were acquired using an electrostatic force microscope (EFM). The EFM consisted of a commercially available atomic force microscope (AFM) that was modified to measure the electrostatic interaction between an AFM tip and a sample substrate. In addition to modifying the commercial AFM, a homebuilt AFM/EFM was constructed at Purdue capable of making electrostatic measurements in an ultra high vacuum environment. After performing several experiments designed to test both the operation and the sensitivity of the EFM, extensive studies of several nanoscale systems were conducted. In particular, the EFM was used to measure the electrostatic potentials of a single nanometer-sized gold cluster and self-assembled arrays of encapsulated gold clusters. The surface potential of the array was found to be at a higher positive potential than the underlying gold substrate, indicating that the encapsulated clusters have a lower work function than bulk gold. In addition, the EFM was used to measure surface potential as a function of time for various LTG:GaAs substrates after the removal of the oxide layer. The behavior of the surface potential with respect to time was found to be dependent on the agent used for the oxide removal. Finally, the EFM was used to measure the surface potential of self-assembled monolayers chemisorb onto Au(111). The monolayers' surface potentials were found to depend on the molecular structure of the molecules forming the monolayer.

Degree

Ph.D.

Advisors

Reifenberger, Purdue University.

Subject Area

Molecules|Condensation

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