General parametrization of persisting long-range nanoscale phenomena in force measurements emerging under ambient conditions

Advances in quantification of nanoscale forces are mainly focused on repulsive forces, the sample's stiffness, and related parameters such as deformation. The reactivity and chemistry of the surface however depends on longer range forces that are prevalent in ambient conditions and control functional surfaces. Suitable models and appropriate parametrization of this range, however, are still emerging. Here, we define and employ metrics to parametrize long-range forces and experimental observables in dynamic atomic force microscopy and force measurements in a general way even when suitable physical models are lacking. We find that plateaus in the attractive part of the force that can be of more than 1 nm in range are a general characteristic of surfaces exposed to the ambient environment. These plateaus can be identified directly from force measurements or indirectly from computationally low-cost parameters that we define here. We further demonstrate that the defined metrics can be employed for rapid discrimination between sharp (less than 10 nm in radius) and blunt tips. Thus, our results exemplify the potential use of metrics to quantify phenomena that can lead to useful relationships without the restrictions of assumptions imposed by modeling the underlying physics.