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Estimation of interaction energy and contact stiffness in atomic-scale sliding on a model sodium chloride surface in ethanol
19.03.2018 09:30

Friction force microscopy (FFM) in aqueous environments has recently proven to be a very effective method for lattice-resolution imaging of crystal surfaces. Here we demonstrate the use of ethanol for similar measurements on water-soluble materials. Lattice resolved frictional stick-slip traces of a cleaved NaCl(100) surface submerged in ethanol are compared with previous obtained FFM results in ultrahigh vacuum (UHV). We use the Prandtl-Tomlinson framework to estimate the amplitude of the corrugation potential and the contact stiffness. The surface potential amplitude scales with the applied normal loads are in good agreement with data obtained for NaCl measured under UHV conditions, but demonstrates deviations from the ideal periodic potential given by the Prandtl-Tomlinson model. An additional finding is that the use of ethanol allows us to explore higher load ranges without detectable evidence of surface wear. The contact stiffness does not vary significantly with the normal load up to 38 nN, while above it a sudden increase by almost one order of magnitude was observed. Comparing this to previous results suggests that considerable atom rearrangements may occur in the contact region, although the (100) surface structure is preserved by ethanol-assisted diffusion of Na and Cl ions.

Publication:

Liron Agmon, Itai Shahar, Danny Yosufov, Carlos Pimentel, Carlos M. Pina, Enrico Gnecco, Ronen Berkovich: "Estimation of interaction energy and contact stiffness in atomic-scale sliding on a model sodium chloride surface in ethanol". Scientific Reports 8 (2018)


Lateral friction force maps

Lateral friction force maps of NaCl showing the atomic lattice structure the surface of NaCl(100) immersed in ethanol. (a) 10 × 10nm2 map measured with Setup I, under an external normal load FN  = 12.1nN and 2D FFT (inset). (b) 5 × 5nm2 map measured with Setup II, under an external normal load FN  = 11nN.

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