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 with various organosilanes to determine magnitude and dispersion information about single-molecule bond-rupture forces. X-ray photoelectron spectroscopy (XPS) and contact-angle measurements were used to study and quantify organosilane adsorption on the glass surface and on SiO₂-coated AFM tips. Hydrogen bond interactions between hydroxyl- and thiol-terminated groups on the tip and surface were detected and measured. Differentiation between the functionalities of the acetate- and thioacetate-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 determine the nature of the surface after an organic transformation has occurred to the functional groups present. They also represent a first step in detecting chemical reactions on a localized scale and in measuring the dispersion in the single-molecule bond-rupture force when it exists.