Contact model and evaluation of friction force molecular component

Abstract

According to the level of the measurement scale, the friction force changes its nature and is determined by different depend-encies. The paper views a procedure for determining a friction force molecular component based on the evaluation of specif-ic shearing resistance of molecular links un-der the elastic interaction of a silicon nitride cantilever needle having a steel sample, used for scanning a section of a sample surface in the nanometer range with an atomic force microscope (AFM) «FemtoScan» under low loads. A sensitive element (measuring device) of an atomic force microscope acts as a force sensor for measuring both: a normal load very roughly, and a change in the force, applied to the cantilever under known stiffness, including the value of the cantilever rod form alteration. It also changes the load on the sensitive element (to assess the mo-lecular component of the friction force, the route of the «smoothest» surface itself was chosen). The paper also provides an analytical assessment of the contact interaction parameters of a cantilever needle in a nano-scale, rep-resented as a spheri-cal indenter, with an elastic half-space as a surface under study, based on the Hertz theory. Analysis of the calculation and experiment data on measuring the resistance force of the indenter during scanning of the surface under study, showed good convergence of the results with a deviation of even values from the experimental data of no more than 7,5 %. Calculations using the established formulas showed that with an increase in the load on the contact at the nanoscale, the coefficient of friction decreases due to a faster growth of contact spots in the elastic state (provided that angularity of inequalities related to sub-roughness remains constant), which was also confirmed in the course of the experiment.