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indentation of hard materials. But in the case of Si this can be possible due to the phase
transformation during loading of the initial diamond cubic structure (Si-I) into the b-Sn
structure (Si-II), which being a metallic, more plastic phase is expected to be extruded
more easily underneath the indenter toward the surface allowing further penetration of
the indenter. This is consistent with the results obtained by Rabier et al. [11] demon-
strating an exceptional ductility of b-Sn metallic phase at room temperature during
silicon deformation under a pressure of 15 GPa.
The P–h curves for short holding are characterized by the formation of typical
“pop-out” and “elbow + pop-out” events in the case of 50 and 100 mN load applied
(Fig. 1a, b, curves 1). With the increase of holding time the tendency to the formation
of a so-called “kink pop-out” was observed (Fig. 1a, b), more often displayed for
100 mN indentations (8 cases from 10) and more rarely for 50 mN indentations (2
cases from 10); in the rest of the cases the “pop-out” effect is maintained. The 500 mN
indentations exhibit the “kink pop-out” for both short and long holding time (Fig. 1c).

Fig. 2. Magnified fragments of curves from Fig. 1 containing the unloading events
of indentations made under short holding (a–c) and long holding (d–f) at P max equal
to 50 mN (a, d), 100 mN (b, e) and 500 mN (c, f): 1 – pop-out; 2 – kink pop-out; 3 – elbow.

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