Anisotropic deformation of thin films comprised of helical nanosprings

We investigate the mechanical anisotropy of thin films that consist of tantalum oxide (Ta2O5) helical nanosprings fabricated by dynamic oblique deposition. Not only the vertical but also the lateral stiffness of thin films is evaluated using specimens in which nanosprings are sandwiched between solid Ta2O5 layers. Lateral or vertical force is applied to the upper solid layer by a diamond tip built into an AFM. In particular, the lateral stiffness of a nanospring has never been reported before. Apparent shear and Young’s moduli, G′ and E′, of the thin films are 2–3 orders smaller than those of solid Ta2O5 film. Ratio E′/G′ of the two different nanosprings is 3.4 and 6.2, and about 2.5 for the solid film. The thin films show strong characteristic anisotropy that the solid one could hardly attain. The stiffness and its anisotropy strongly depend on nanospring shape.