NEW MECHANISMS FOR NANOINDENTATION DATA PROCESSING USING ATOMIC FORCE MICROSCOPY METHOD

Elastic modulus accuracy using atomic force microscopy  depends significantly on processing quality of the experimental data obtained during nanoindentation.  Multiply repeated calibration can lead to conservative value of the calibration factor.  Such artefact is caused by probe slipping on silicon plate surface which is harder than  surface of the investigated specimen and which is non-uniform  in height. Elastic modulus calculated by the Hertz model depends on penetration value  while processing the indentation data at small depth of the probe penetration into the specimen.  A value  being close to asymptotical one  which is obtained  at rather large object deformation is taken as a required modulus. Such deformation is not always possible in an experiment,  or  it is achieved with rather large (tens of percent) relative deformations that is beyond permissible region of the Hertz model application.

The purpose of this paper is to demonstrate several new opportunities for  nanoindentation data processing, as at the stage of obtaining or verifying a calibration factor of the atomic force microscope so while analyzing an investigated object penetration curve.  The paper considers two methodologies for determination of the calibration factor on the basis of the Hertz  and Johnson-Kendall-Roberts models and proposes new mechanisms for determination of  elastic modulus while using method of atomic force microscopy.  The possibility to calibrate atomic force microscope according to material with known mechanical properties has been shown in the paper. The paper substantiates the necessity and provides an algorithm  for correction of the measured probe penetration depth with due account of  adhesive forces while calculating the in the region of small specimen deformations. The proposed methods for determination of the calibration factor and  asymptotic value of the elastic modulus will be useful for obtaining  reproducible and more accurate results of atomic force microscopy for mechanical properties.

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