In situTEM study of grain growth in nanocrystalline copper thin films

Abstract

Nanocrystalline metals demonstrate a range of fascinating properties, including high levels of mechanical strength. However, as these materials are exposed to high temperatures, it is critical to determine the grain size evolution, as this process can drastically change the mechanical properties. In this work, nanocrystalline sputtered Cu thin films with 43 +/- 2 nm grain size were produced by dc-magnetron sputtering. Specimens were subsequently annealed in situ in a transmission electron microscope at 100, 300 and 500 degrees C. Not only was grain growth more evident at 500 degrees C but also the fraction of twins found. An analysis of grain growth kinetics revealed a time exponent of 3 and activation energy of 35 kJ mol(-1). This value is explained by the high energy stored in the form of dislocation, grain boundaries and twin boundaries existing in nanocrystalline copper, as well as the high probability for atoms to move across grains in nanocrystalline materials.

Solute stabilization of nanocrystalline tungsten against abnormal grain growth

“…12,13 A classic example of this phenomenon is found in nanocrystalline Ni where grain size increased by 20Â at only 30% of its melting point. 14 Similar behavior has been observed across a range of single-component nanocrystalline metals such as cobalt, 15 iron, 16 copper, 17 and silver 18 where microstructural evolution often prescribes to curvature-driven grain growth with the grain boundary velocity, m, proportional to the local mean curvature of the boundary, j:…”

“…(1) and demonstrated that an enhanced grain boundary mobility is accompanied by a reduced activation energy for grain growth. 13,17,20 However, the onset of microstructural evolution in a range of nanocrystalline metals often transpires through an abnormal growth process, which has been observed in copper, 21,22 nickel, 21,23 iron, 24 palladium, 13 and cobalt 15 as well as a number of binary nanocrystalline alloys. [25][26][27] As the average grain size increases from the nanocrystalline to the ultrafine grain regime, abnormal grain growth widely succumbs to curvature-driven mechanisms, 28 thus underscoring the importance of stabilizing the nanostructure collectively against the initial and late stages of grain growth in nanocrystalline metals.…”

Grain growth rate for coupled grain boundary migration and grain rotation in nanocrystalline materials

“…Equation (10) can once more integrated to obtain A 3/2 = Bt, thus indicating that R ∼ t 1/3 . This growth rate is observed in a large number of NC materials [23] and shows how grain rotation in NC materials contributes to slowing their overall growth rate compared to coarse-grained materials. The above models are useful for describing the GB motion in a bicrystal and to obtain a mean field understanding of growth in a polycrystal.…”

“…For purely rotation driven growth arising from coalescence of neighbouring grains after rotation, Moldovan et al [22] reported an exponent n = 4 for boundary diffusion controlled processes. Experiments performed on NC materials reported growth exponents closer to n = 3 [23]. Thus, NC materials have proven to be unexpectedly more stable than polycrystalline materials.…”

Chemical Vapor Deposition of Copper: Use of a Molecular Inhibitor to Afford Uniform Nanoislands or Smooth Films

“…4,6 Rigorous control of copper growth can be difficult: the surface energy of copper is high and the atomic diffusion rate is significant, so that dewetting often occurs during growth or subsequent annealing. [7][8][9][10][11][12] Thin films of copper can be deposited by a wide variety of techniques including wet chemical growth, physical vapor deposition, chemical vapor deposition (CVD) and atomic layer deposition (ALD). To deposit copper conformally in substrate architectures such as trenches and vias that have re-entrant or high aspect ratio features, ALD and CVD are preferred techniques because of the ability of the precursor molecules to diffuse throughout the structure.…”