Over the last years, progress in nanomaterials design and manufacturing has revolutionized technology and opened up prospects for many scientific researches. The investigations of material properties (optical, electronic, mechanical…) at small scales have revealed amazing behaviors, different from those currently observed in bulk samples. For instance, silicon, which is known to behave at room temperature as a brittle material, shows an unexpected ductile behavior when the sample size decreases below a few hundreds of nanometers [1]. The mechanisms leading to this phenomenon remain, however, poorly understood. In this context, this research project aims at investigating in more details the deformation behavior of silicon nanopillars by combining experimental techniques (SEM, FIB, HRTEM) and molecular dynamics simulations. In this work, various nanopillars with different orientations and diameters (from 100 nm to 1 µm), were patterned by Reactive-Ion Etching and FIB micromachining. These pillars were then compressed with a slow-strain-rate (10^-4 s^-1) at room temperature using a nanoindenter equipped with a flat punch and operated in displacement-control mode. Post mortem observations of deformed nanopillars performed by SEM and TEM reveal the activation of different slip systems. The comparison between experimental and simulated HRTEM images notably evidences the simultaneous propagation of partial and perfect dislocations in {111} planes. In addition, unexpected plastic events have also been observed in {113} planes. On the basis of the microscopic observations, various possible deformation mechanisms involved during the nano-compression of the pillars are proposed.

[1] F. Östlund et al., Brittle-to-Ductile Transition in Uniaxial Compression of Silicon Pillars at Room Temperature, Adv. Func. Mat., 19, p1(2009).

This work is performed within the framework of the ANR-funded research project « BrIttle-to-Ductile Transition in Silicon at Low dimensions » (ANR-12-BS04-0003-01, SIMI4 program).

Figures:

Figure 1 : SEM image (TLD mode) of a deformed nanopillar.

Figure 2 : Bright field TEM image of a deformed nanopillar observed in cross section.

Figure 3 : HRTEM image showing various plastic deformation events in different slip planes observed in a deformed nanopillar.

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EMC Abstracts - https://emc-proceedings.com/abstract/hrtem-study-of-structural-defects-and-related-deformation-mechanisms-induced-by-nanocompression-of-silicon/