Water-Mediated Self-Assembly of 16-Mercaptohexadecanoic Acid on GaAs (001)

Abstract

Self-assembled monolayers (SAMs) of alkanethiols have been widely investigated to generate both specific functionality and increased chemical/photonic stability of III–V semiconductor surfaces. Because of the availability of the COOH terminal group, the 16-mercaptohexadecanoic acid (MHDA) has often been investigated to engineer interfaces involving proteins, nucleic acids, and other biomolecules. Typically, MHDA SAMs have been deposited by incubating semiconductor substrates in MHDA/ethanol solutions. We have investigated the role of water on the process of MHDA SAM formation on the GaAs (001) surface, and we report on the formation of increasing quality MHDA SAM in proportion of the concentration of water mixed with ethanol, up to 50%. The transmission Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and water contact angle measurements suggest that MHDA SAM obtained from the ethanol/water 1:1 solution represent a superior quality carboxylic acid-terminated SAM on GaAs (001) reported to date.