Role of integrated lateral stress in surface deformation of He-implanted surfaces

Abstract

The first measurements of integrated lateral stress S have been obtained for He implantations to fluences where surface deformation occurs. Implants into Mo, Nb, and Al were carried out at room temperature. The low‐fluence results provide values for the induced volume expansion per implanted He atom. The high‐fluence results demonstrate that blistering, as observed in Mo and Nb, is directly related to relief of S. However, flaking, as observed in Al, does not result in appreciable relief of S. The saturation value of integrated lateral stress, S_max, is proportional to yield stress for the three materials and is independent of the He projected range. A model to describe the blistering phenomenon is developed based on the standard elastic stability equation for a plate subjected to in‐plane forces. This elastic instability model uses only measurable material parameters and does not depend explicitly on the behavior of He in the material. The model explains the τ∝d^2/3 relation observed for blister diameter d and thickness τ, and predicts the d‐vs‐τ relation for Nb, Ti, V, Pd, 4301 SS, and Be to within 40% of the values measured by other workers over 3 orders of magnitude variation in d. Comparison of the model with the present Mo and Nb results, where S_max is measured directly, gives agreement to better than 10% with no adjustable parameter.