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stresses. Under indentation, however, the deformation conditions are dissimilar: much
higher stresses, highly localized strain in nano/micro-volume, resulting in the involving
of the phase transformation mechanism of deformation, besides the dislocation one.
Therefore the aim of this work was to investigate the behaviour of Si in these condi-
tions and to study the influence of long lasting holding under the load on the phase
transformation and deformation peculiarities of material.
Experimental details. The depth-sensing nanoindentation technique with Berko-
vich diamond pyramidal indenter was used to induce local deformation on n-type,
phosphorous-doped Si (100) wafer of a resistivity of 4.5 Ω×cm. The range of loads
included 50, 100 and 500 mN to study the influence of load value. For each of these
loads we applied 2 loading regimes, including standard short holding time (5 s) under
the maximum load (P max) and long holding time (900 s) under P max. The loading and
unloading time was maintained 50 s for all loads and holding time regimes used. For
each separate combination of load and loading regime 10 indentation tests were perfor-
med. The load versus penetration depth P(h) and penetration depth versus time h(t)
dependences were acquired for each indentation made.
For indentations with longer holding time the thermal drift estimation was made,
for which during unloading, at 10% of P max, a 30 s holding was applied to measure the
displacement of the indenter and the respective corrections to P(h) curves, including
the creep plateau, were done. The mean value of thermal drift rate was found to be
0.15 nm/s.
The phase transformation characterization of the indentation zone was carried out
by micro-Raman spectroscopy using Monovista confocal Raman spectrometer with
532 nm wavelength laser focused to a spot of about 2 mm radius. This type of laser is
able to detect about 0.8 mm into the depth of the material when focusing at the surface.
By using the focusing of the laser in some depth it became possible to investigate
deeper regions of the material underneath the imprint.
Results and discussions. Peculiarities of P(h) dependences. Fig. 1 shows the ty-
pical load-penetration P–h curves for 50 mN, 100 mN and 500 mN indentations made
at short (5 s) and long (900 s) holding time. A creep plateau can be seen on the P–h
curves for long holding time indentations, which is not typical for room temperature

Fig. 1. Load–penetration (P–h) curves
of indentations made at 50 mN (a),
100 mN (b) and 500 mN (c):
1 – short holding (50 s);
2 – long holding (900 s).
The unloading events:
3 – kink pop-out;
4 – pop-out; 5 – elbow.

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