Bending flexibility, kinking, and buckling characterization of ZnO nanorods/nanowires grown on different substrates by high and low temperature methods

Abstract

Nanomechanical tests of bending flexibility, kinking, and buckling failure characterization of vertically aligned single crystal ZnO nanorods/nanowires were performed quantitatively by nanoindentation technique. These nanostructures were grown by the vapor liquid solid (VLS) method, a relatively high temperature approach, and the aqueous chemical growth (ACG) method, a relatively low temperature approach on different substrates, including SiC and Si. The first critical load at the inflection point found for the ZnO nanorods/nanowires grown by ACG method was 105 μN on the SiC substrates and 114 μN on the Si substrates. The corresponding buckling energies calculated from the force-displacement curves were 3.15×10−12 and 2.337×10−12 J, respectively. Similarly, for the samples grown by the VLS method, the first critical load at the inflection point and the corresponding buckling energies were calculated from the force-displacement curves as 198 μN and 7.03×10−12 J on the SiC substrates, and 19 μN and 1.805×10−13 J on the Si substrates. Moreover, the critical buckling stress, strain, and strain energy were also calculated for all samples. The strain energy for all samples was much less than the corresponding buckling energy. This shows that our as-grown samples are elastic and flexible. The elasticity measurement was performed for all the samples before reaching the first critical and kinking inflection point, and we subsequently observed the bending flexibility, kinking, and buckling phenomena on the same nanorods/nanowires. We observed that the loading and unloading behaviors during the bending test of the as-grown samples were highly symmetrical, and also that the highest point on the bending curves and the first inflection and critical point were very close. ZnO nanorods/nanowires grown on SiC by the ACG method, and those grown by the VLS method on Si substrates, show a linear relation and high modulus of elasticity for the force and displacement up to the first inflection and critical point. The results also show that the elasticity of the ZnO single crystal is approximately linear up to the first inflection point, is independent of the growth method and is strongly dependent on the verticality on the surface of the substrates. In addition, the results show that after the first buckling point, the nanorods/nanowires have plasticity, and become more flexible to produce multiple kinks.