General Parametrization of Persisting Long-Range Nanoscale Phenomena in Force Measurements Emerging under Ambient Conditions

Abstract

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.

The power laws of nanoscale forces under ambient conditions

“…Provided these three conditions are met, the force can otherwise be arbitrary in the context of this work. We further note that all the data that we have acquired on mica, graphite, gold, aluminium, quartz, sapphire, platinum and a range of polymers 30 (data not shown) met the above conditions. The present work however employs data acquired on a graphite sample only.…”

“…In order to experimentally test the range of applicability of (3) we now proceed to parameterize the force profile in terms of the adhesion force F AD by considering F at a distance d such that F = bF AD . We note that by varying b from 0 to 1 any arbitrary (see restrictions above) force profile can be fully parameterized and quantified 30 as in Fig. 1b.…”

“…1b by employing the Sader-Jarvis-Katan algorithm. 14,15,30 In this algorithm, the raw amplitude A and phase f data comprise the input while the F versus d profiles comprise the output (see the ESI † for details). In order to test the predictions of ( 6…”

Integrated Nano- and Macroscale Investigation of Photoinduced Hydrophilicity in TiO2 Thin Films

“…The six cantilever oscillation amplitude ( A 1 ) versus distance ( Z c ) curves represent as-deposited (Figure a,d) and 350-TiO 2 (Figure b,e) and 500-TiO 2 (Figure c,f). In Figure d–f, it can be seen that the curves exhibit a negative slope at small Z c after UV exposure; it has previously been established that this feature indicates the presence of a nanoscale water layer on the sample surface , and thereby demonstrates the nanoscale hydrophilicity of the UV-treated surfaces.…”