Molecular Devices Formed by Direct Monolayer Attachment to Silicon
Curt A. Richter, Christina Hacker, Lee J. Richter, Eric M. Vogel
We present the results of studies of solution-based attachment of long-chain aliphatic molecules to hydrogen-terminated Si<111> surfaces formed to determine the electrical properties of hybrid silicon-molecular nanoelectronic devices. We have applied an improved solution-based method for the direct attachment of organic molecules to Si. In this method, ultraviolet radiation is used to assist the covalent attachment of alcohols to the hydrogen-terminated Si<111> surface to successfully form molecular monolayers. To determine the quality of these organic monolayers, they were physically and chemically characterized with infrared spectroscopy, spectroscopic ellipsometry, and contact angle measurements. The electrical properties of these organic films were probed by using current-voltage (IV) and capacitance voltage (CV) measurements obtained from a metal-organic-silicon test structure fabricated by post-monolayer metal deposition. Devices containing monolayers of differing chain length have been studied, and the expected decrease in accumulation capacitance with longer molecules (which form thicker films) was observed. The measured CV's are in agreement with traditional theory for a metal-insulator-semiconductor capacitor.