AVS 52nd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM1-ThM

Paper EM1-ThM10
Charging and Discharging Nanoscale Domains in Thin Films of Arylamines Studied with Kelvin Probe Microscopy

Thursday, November 3, 2005, 11:20 am, Room 309

Session: Molecular Electronics
Presenter: G.J. Szulczewski, University of Alabama
Authors: J. Sun, University of Alabama
S.C. Blackstock, University of Alabama
G.J. Szulczewski, University of Alabama
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The work reported here was motivated to assess the feasibility of a non-volatile molecular memory based on charge storage in amorphous thin films. Toward that end, thin films of a series of redox-gradient arylamines were vapor deposited on oxidized p-type Si(100) wafers and subsequently charged in tapping mode with a voltage applied to a metal-coated AFM tip. The redox-gradient is designed to facilitate one-way electron transfer from the periphery of the molecule to its core. The concept is realized by synthesizing molecules with an easy to oxidize (i.e. ionize) moiety at the interior of molecule and surrounding it with harder to oxidize redox moieties.@footnote1@ In effect the gradient acts as a charge funnel toward the interior of the molecule. The extent of charging was measured with Kelvin probe microscopy (KPM). The charged domains have an apparent diameter of about 200 nm in the KPM image, which is larger than the real area due to the long-range interaction of the charge and the tip/cantilever. The charge half-life was proportional to the magnitude of the redox-gradient. For example, amines without a redox gradient discharged within 1 hour. In contrast, amines with a redox-gradient of ~0.8 eV could retain 50% of their initial charge after 10 hours. The charging is reversible. By applying a negative bias on the KPM tip the charged region could be neutralized. Although the charge is stable for many hours and can be neutralized, there is diffusion of charge in the films due to Coulombic repulsion. @FootnoteText@ @footnote1@ T. D. Shelby and S. C. Blackstock, "Preparation of a Redox-gradient Dendrimer. Polyamines Designed for One-Way Electron Transfer and Charge Capture" J. Am. Chem. Soc. 1998, 120, 12155.