Study on single-bond interaction between amino-terminated organosilane self-assembled monolayers by atomic force microscopy

Chemically modified atomic force microscope (AFM) tips and modified silicon wafers with self-assembled monolayers (SAMs) were produced using 3-aminopr opyltriethoxysilane (APTES) molecules. Prior to modification, the silicon w afers were thoroughly cleaned by improved RCA method, producing hydrophilic and smooth surfaces. The bare and modified silicon substrates were charact erized by contact angle measurement, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). In this paper, a statistical analysis m ethod, which makes use of the properties of the Poisson distribution, was a pplied to investigate the interaction between the tips and silicon surfaces covered with SAM terminating in amino groups. The single-bond force betwee n a single amino group pair in water was obtained from the total adhesion f orces measured by AFM and was found to be 200.0 +/- 43.6 pN. This value was assigned to the result of mainly hydrogen bond interaction between a singl e NH2-NH2 pair. Comparisons between our results and those measured by means of Johnson-Kendall-Roberts (JKR) theory and other methods were also made. (C) 2000 Elsevier Science B.V. All rights reserved.