We report on a comprehensive structural and nanoindentation study of nanolaminates of Al2O3 and ZnO synthesized by atomic layer deposition (ALD). By reducing the bilayer thickness from 50 nm to below 1 nm, the nanocrystal size could be controlled in the nanolaminate structure. The softer and more compliant response of the multilayers as compared to the single layers of Al2O3 and ZnO is attributed to the structural change from nanocrystalline to amorphous at smaller bilayer thicknesses. It is also shown that ALD is a unique technique for studying the inverse Hall-Petch softening mechanism (E. Voce and D. Tabor, J. Inst. Metals 79(12), 465 (1951)) related to grain size effects in nanomaterials.
The loading rate effect on the brittle-ductile transition temperatures of tungsten single crystals at the micro-scale was investigated by microcantilevers with a (100)[001] crack system. Specimens with a length to width to height of 15 µm / 4 µm / 6 µm were fabricated by focused ion beam milling. At low temperatures (-90 to -25 °C) the samples failed by brittle cleavage fracture, irrespective of the applied loading rate at a fracture toughness of 3.2 MPa•m 1/2 . With increasing temperatures up to 500 °C and depending on the applied loading rate, the fracture toughness increased and significant crack tip plasticity and dislocation-controlled microcleavage were observed by means of high resolution electron backscatter diffraction measurements performed after testing. With respect to macroscopic specimens, a shift of the brittle-ductile transition to lower temperatures and a significantly lower activation energy of the brittle-ductile transition of 0.36 eV were found. We explain this by the increase in flow stresses due to sample size effects.
Glass is recently envisioned as a stronger and more robust alternative to silicon in MEMS applications including high frequency resonators and switches. Identifying the dynamic mechanical properties of microscale glass is thus vital for understanding their ability to withstand shocks and vibrations in such demanding applications. But despite nearly half-a-century of research, the micromechanical properties of glass and amorphous materials in general, are
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