Methods to Measure Material Viscoelastic Properties using Sharp, Flat and Buckling Tips inside ESEM

Methods to measure the viscoelastic property of time- dependent materials are proposed using sharp, flat and buckling tips inside Environmental Scanning Electron Microscope (ESEM). Single W303 yeast cells were employed in the study. All of the tips were used to indent into the material in nanoindentation tests. Three loading histories were used: (1) a ramp loading history, in which a sharp indenter was used; (2) a step loading history, in which a flat indenter was implemented; and (3) a fast unloading history, in which a buckling nanoneedle was applied. Analysis of the viscoelastic material response was performed for each of the loading history by choosing an appropriate theory between the correspondence principle and the functional equation. Results from each of the tests show good agreement, in which more strong conclusion can be obtained.