Application of Static Disorder Approach to Friction Force Microscopy of Catalyst Nanoparticles to Estimate Corrugation Energy Amplitudes

Abstract

Friction force microscopy (FFM) of materials with well-defined crystalline surfaces is interpreted within the framework of the Prandtl–Tomlinson (PT) model. This model portrays the interaction with a surface through a deterministic periodic potential. While considering materials with polycrystalline or amorphous surfaces, the interpretation becomes more complex, since such surfaces may lack distinct lattice constant and/or corrugation energy amplitude. Here, we utilize an approach to describe the nanofriction measured on a catalyst with an irregular surface by describing the slip forces in terms of static disorder (SD) in the corrugation potential. We performed FFM measurements of the Fe–Al–O spinel catalyst powder, which is involved in reverse water–gas-shift reaction. The FFM measurements resulted in intermittent stick–slip pattern with large variance in the slip forces and their spatial distribution. We compare our results with a mean version of the PT model. The two models showed close proximity of the surface energy values and their trend with the applied normal load, where the SD model estimations were less scattered. The approach presented in this work may provide a useful tool to interpret the FFM measurements of materials with irregular surfaces.

Comparative Study of Dimensionality and Symmetry Breaking on Nanoscale Friction in the Prandtl–Tomlinson Model with Varying Effective Stiffness

“…The interaction potential between the tip apex and the sample is given as symmetric periodic function where U 0 F N is the amplitude of the corrugation potential at a given normal load F N , and a is the lattice periodicity. As previously mentioned, the applied normal load is related to the amplitude of the corrugation potential [35,36,41,57,64,65]. Following our previous work [57], we quantify this dependency by approximating a (single periodic) local minimum and its consecutive maximum in the interaction potential, which can be written in terms of a reduced bias field [14,66]:…”

“…During a scan, the tip bends and releases with respect to its position along the atomic-scale periodicity of the sample (for ordered surfaces), and produces a stick-slip pattern in the lateral force signal. Studies on nanoscale friction have shown that several properties influence this dynamics, such as contact area [4][5][6][7][8][9], sliding velocity [10][11][12][13][14][15][16], temperature [11,[17][18][19][20][21][22][23], anisotropy, symmetry and dimensionality [13,[24][25][26][27][28][29][30][31][32][33], and the applied normal load [4,5,23,26,[33][34][35][36][37][38][39][40][41][42][43].…”