Fig. 3: AFM-based indentation on Pt-BMG.
From: Atomic-scale homogeneous plastic flow beyond near-theoretical yield stress in a metallic glass
a Force F vs penetration depth h curves measured with five different maximum loads (180–1180 nN) using a diamond tip referred to in the text as tip #1. Despite carrying out the indents at different locations on the sample surface, all curves overlap perfectly within the accuracy of the measurement, indicating both that local changes in mechanical properties are negligible as well as that reproducibility of the measurement is high. From fitting the part of the curves before the easily visible kink with Eq. (1) (dashed blue curve), a tip radius of ≈4.1 nm is obtained. b, c AFM indents carried out following the same protocol as in a, but with different tips and on different locations. All curves exhibit the same overall behavior as in a, thereby confirming the validity of the approach. From fitting the data again with Eq. (1), the radius for tip #2 of b was determined as R ≈ 4.5 nm and the one for tip #3 in c as R ≈ 6.1 nm. d–f Mean contact pressure Pm vs penetration depth h curves. Curves in d–f were derived from the data shown in a–c using Eq. (2). AFM images acquired before and after performing indentation experiments. g Topography of the pristine Pt-BMG surface on sample #2. The stepped surface structure imposed onto the BMG sample by the STO single crystal mold is clearly visible15. h Same location as in g, but after AFM indentation tests using diamond tip #2 have been carried out. The locations of individual indents are highlighted by dashed circles and labeled with the peak load reached during the experiment. Although no pile up is visible for a 280 nN peak load, higher peak loads clearly lead to larger pile ups around the indent.
