Silicon nanosprings fabricated by glancing angle deposition for ultra-compliant films and interfaces

Micro and nanostructures with well-defined shape and dimensions are the hallmark in the design of scalable nanomaterials, yet the properties and precise geometry of such nanoscale building blocks are largely unknown. This work sheds light into the microstructure, material properties and mechanical behavior of individual nanosprings fabricated by seeded Glancing Angle Deposition (GLAD), with the purpose of designing highly compliant interfaces with drastically reduced coupling between normal and shear deformation. The mechanical response in tension/compression and bending of individual amorphous Si (aSi) nanosprings with 4 or 10 coil turns and different seed spacings was obtained with the aid of MEMS devices: The normal and bending spring stiffness valueswere in the range of 7-215 N/m and 1-31 N/m, respectively, resulting in estimates for the normal and shear film stiffness in the range of 90-1000 MPa and 15-150MPa, respectively. The true geometry of GLADSi springs was determined via SEM tomography and was incorporated in modified analytical and finite element models which, in turn, were used to compute the material modulus of aSi nanostructures fabricated by GLAD. TEM studies revealed that GLAD Si nanosprings are comprised of tightly bundled fine fibrils which impart flaw tolerance and reduce the effective elastic modulus. (C) 2018 Elsevier Ltd. All rights reserved.