NIST helps develop new method to attach long-chain aliphatic molecules to silicon.

NIST scientists have developed an improved solution-based method for the direct attachment of long-chain aliphatic molecules to Si. In this method, ultraviolet radiation is used to assist the attachment of alcohols to the hydrogen-terminated Si(111) surface to successfully from molecular monolayers. To investigate 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 and capacitance-voltage (CV) measurements obtained from a metal-organic-silicon test structure fabricated by post-monolayer metal deposition. The effect of differing alkane chain length on the electrical properties was investigated, and the CVs are in agreement with traditional theory for a metal-insulator-semiconductor. Initial results of this research were presented at the 2003 meeting of the American Chemical Society.

Direct attachment of organic molecules to the silicon surface is of increasing importance for emerging molecular electronics applications as devices incorporating molecules chemically bonded to silicon are amenable to integration with existing Si processing techniques. In addition, the chemical bond between Si and organic molecules is stronger and, therefore, expected to be more stable than the metal-molecule bond typically used in the assembly of molecular electronic devices. However, forming this Si-molecule bond to create self-assembled monolayers can be difficult. Costly and time consuming ultra-high vacuum techniques are often used to attach molecules to Si.

CONTACT: Christina Hacker, [phone]; [e-mail].