Pop-in effect in Ge- and Si-coated single-crystalline Si

In nanoindentation tests the pop-in effect is a sudden increase in penetration depth without an increase in load, caused by some special effect because of the smaller specific volume of the high-pressure phase in Si. It has been investigated in Si samples covered with 20, 50, 100 and 150 nm thick layers of amorphous Si or Ge in single and multiple load events. The impressions caused by the indentation were imaged by atomic force microscopy. The characteristics of the load curves and the shape of the indented impressions are correlated. Our experiments provide a consistent evaluation of the Young's modulus and hardness of the samples and consistent data on the exact shape of the indent impressions. The dependence of the variation of the magnitude and spatial distribution of the relaxed volume on the composition and thickness of the sputtered layer is discussed.