Temperature-induced evolution of subsurface nanocavities in argon-implanted copper

Abstract

The evolution of argon-filled nanocavities in a copper crystal under annealing is studied experimentally and theoretically. The subsurface argon-filled nanocavities are formed after a short annealing at a temperature ∼1000 K by coalescence of subsurface defects initially created by argon implantation. The further prolonged annealing at a temperature above 1075 K leads to decomposition of the nanocavities and diffusion of implanted argon out of the sample. According to a simple analysis, the mechanism of the nanocavity formation is governed not only by the migration of simplest defects, such as vacancies and argon and copper interstitials, but also to a large extent, by diffusion and interaction of the complexes of these simplest defects. The experimental studies with x-ray photoelectron spectroscopy and scanning tunneling microscopy and spectroscopy provide valuable data sets of the density of nanocavities and their size and depth distribution. Based on the experimental results, a theoretical model is developed. The calculation with the model proves that the growth of the nanocavities is mainly determined by the temperature-induced migration of vacancy-argon complexes. By combining the experimental data with the simulation results, the migration energy of these kinds of complexes is estimated ∼2.55-2.75 eV. Moreover, the calculation with our model provides the estimate of the dissociation energy of a multiple complex, consisting of two vacancies and two argon atoms, as 1.10-1.18 eV. These parameters, reported in this article, play a key role in the description of the kinetics of the growth and decomposition of nanocavities.

Direct epitaxial growth of subsurface Co nanoclusters

“…A more or less three-dimensional (3D) symmetric shape would be expected for an isotropic 3D growth as in the case of Ar nanoclusters formed deep below the Cu(001) [39,40] and Cu(110) [41][42][43] surfaces. However, a simple analysis reveals that this is not the case.…”

Nano-donuts on metal surfaces

“…Thus, by varying U T , the topography related features such as donuts can be distinguished from the interference features. In case of Ar bubbles in Cu(0 0 1) [26], STM images showed pits that did not differ substantially between 0.3 and 1 V bias voltage. But large variation in the interference feature is reported for STM images between 1.1 and 0.27 V in an earlier work (see Fig.…”

Copper thin films by ion beam assisted deposition: Strong texture, superior thermal stability and enhanced hardness

“…Due to their limited solubility in Cu, Ar atoms are mainly trapped at vacancies. The vacancy-Ar clusters are characterized by a high binding energy (>2.87 eV) and a high migration energy (>2.55 eV), indicating that they are very stable and immobile even at high temperatures [29]. By considering all these situations, it is reasonable to assume that the main surviving defects in the as-deposited IBAD-Cu films are interstitial clusters, vacancy clusters and vacancy-Ar clusters.…”

“…The remaining are continuously incorporated into immobile vacancy-Ar clusters and finally give rise to Ar-filled voids. Due to the strong binding energy of Ar atoms to vacancies, those voids are very stable even close to 800°C [29]. Since the formation energy and diffusion barrier for vacancies in GBs are much lower than those in the bulk [27,28], mobile vacancies have higher tendency to diffuse to GBs.…”

“…For example, nanometer-sized voids have been found to form in irradiated fcc [23,24], bcc [25] and hcp [26] metals. Due to their low formation energy at GBs [27,28], voids form preferentially along GBs [24] and they are very stable even at very high temperatures [29]. These voids could act as pinning centers, similar to secondary phase particles, for GB migration and stabilize the microstructure.…”