MEASUREMENTS OF SINGLE-MOLECULE BOND RUPTURE FORCES BETWEEN SELF-ASSEMBLED MONOLAYERS OF ORGANOSILANES WITH THE ATOMIC-FORCE MICROSCOPE

Atomic force microscopy (AFM) tips and glass surfaces were modified wi th various organosilanes to determine magnitude and dispersion informa tion about single-molecule bond-rupture forces. X-ray photoelectron sp ectroscopy (XPS) and contact-angle measurements were used to study and quantify organosilane adsorption on the glass surface and on SiO2-coa ted AFM tips. Hydrogen bond interactions between hydroxyl- and thiol-t erminated groups on the tip and surface were detected and measured. Di fferentiation between the functionalities of the acetate- and thioacet ate-terminated silanes and their reduced forms produced by on-surface reduction (the alcohol and thiol, respectively) was also accomplished. The experiments demonstrate the complementary information that can be obtained from AFM and XPS and illustrate how they can be used to dete rmine the nature of the surface after an organic transformation has oc curred to the functional groups present. They also represent a first s tep in detecting chemical reactions on a localized scale and in measur ing the dispersion in the single-molecule bond-rupture force when it e xists.