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The elastic and adhesive properties of nominally vertically aligned carbon nanotube (CNT) turfs have been measured using nanoindentation. The perceived stiffness of a CNT turf is dependent on the unloading rate, which decreases at slower unloading rates. Depth-controlled nanoindentation was used to examine adhesion effects. Adhesive loads between the turf and the probe tip increased as the time the tip is in contact with the turf increased. As these effects could be from either more tubes coming into contact with the tip due to relaxation and motion of CNTs relative to one another or each tube in contact increasing its adhesive behavior and sub-contact stiffness due to tube-tube interactions within the turf, electrical resistance measurements during nanoindentation were carried out. When the tip is held at a fixed nominal depth, the current remains constant while the contact load decreases, suggesting the number of tubes in contact with the tip stays constant with time while the relaxation mechanisms in the turf occur at positions lower than the contact surface. These observations, in conjunction with in situ TEM compression test of CNT arrays, are used to describe the relative effects the various length and time scales may have on the perceived properties measured during experiments, including elastic modulus and adhesion for gecko-like dry adhesives.

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The elastic modulus of a variety of porous low dielectric constant thin films with porosities in the range of 24-47% and thicknesses between 148 and 235 nm is calculated using the Oliver-Pharr method, an intrinsic thin film model based on the Li-Vlassak method, and finite element simulations in the elastic regime by taking the tip imperfections into account. It is shown that the substrate effects are significant even at shallow indentation depths and strongly depend on the nanoindenter geometry. Elastic modulus values extracted from the intrinsic thin film model and finite element simulations, although based on different approaches, are found to be very similar and independent of the nanoindenter geometry.