  The fracture strength of ZnO nanowires vertically grown on sapphire
substrates was measured in tensile and bending experiments. Nanowires with
diameters between 60 and 310 nm and a typical length of 2 um were manipulated
with an atomic force microscopy tip mounted on a nanomanipulator inside a
scanning electron microscope. The fracture strain of (7.7 +- 0.8)% measured in
the bending test was found close to the theoretical limit of 10% and revealed a
strength about twice as high as in the tensile test. From the tensile
experiments the Young's modulus could be measured to be within 30% of that of
bulk ZnO, contrary to the lower values found in literature.
