Inhomogeneous intrinsic stress in sputtering-deposited platinum films and its effect on the formation of helical structures

Abstract

Recently, we reported an approach to form helical nanostructures, namely nanocoils, through the spontaneous bending deformation of fiber-shaped Pt films. In that study, the inhomogeneous intrinsic stress developed during Pt sputtering was proposed to be the origin of the driving force for deformation. Unfortunately, the existence of inhomogeneous intrinsic stress in the Pt films was not verified experimentally. Moreover, the intrinsic stress, which affects the bending deformation and determines the shape of the nanocoils, was not quantitatively measured. Thus, the current study investigates the intrinsic stress in Pt films deposited by two magnetron sputtering systems by measuring the film forces; moreover, it discusses the effect of stress inhomogeneity on the formation of Pt nanocoils. An inhomogeneous intrinsic stress distribution along the thickness direction was confirmed, and the tensile and compressive stresses were found to reach hundreds of megapascals. The Pt films deposited by the two sputtering systems exhibited completely different stress distributions. Regardless of this, the Pt film with inhomogeneous intrinsic stress eventually led to the formation of Pt nanocoils, whereas that with a uniform stress did not. It was therefore verified that inhomogeneous intrinsic stress was the origin of the driving force for the formation of a helical structure. Finally, it was found that the bending radius could be estimated by measuring the intrinsic stress. The results of this study will provide a perspective on the application of intrinsic stress to helical-structure manufacturing.