A method for determining the local mechanical properties using nanoindentation in oscillating mode
A new method of processing of data obtained using atomic force microscopy (AFM) in the oscillating nanoindentation mode is proposed. The model of the AFM probe on elastic beam (cantilever) interaction with a sample is developed. In addition to the static load, applied on a base of the cantilever, a force modulation, according to a harmonic law, is set. This approach makes possible to take into account not only the force of the probe-material interaction but also the phase shift of the cantilever oscillations with respect to a given harmonic signal on the cantilever base as well as the amplitudes ratio of these oscillations. This information allows the presence of the viscosity in the material evaluating. The advantage of the oscillatory regime over quasistatic indentation was shown. It consists in the possibility to exclude the influence of irreversible processes (plastic, brittle fracture in the material) on the result of the experiment and to reveal the presence of the time dependent behavior. It is shown that the model contains a small amount of constants; methods for their determination are proposed. The calculations, performed using the developed model, made it possible to make a number of recommendations on choosing the cantilever stiffness to obtain the most informative experimental results. This approach seems perspective in studying materials with a high degree of stiffness inhomogeneity, including the determination of the local properties of filled nanocomposites near filler particles.