Grain rotation in thin films of gold

Morphology evolution of thermally annealed polycrystalline thin films

“…Such a torque promotes the reorientation of the grains via the generation of a shear stress σ s ∝ −∇ θ (γ gb /λ) ·T (with ∇ θ the surface gradient vector in the azimuthal direction) in order to reduce the GB energy γ gb (θ ) through the formation of pseudocoherent GBs. Thus-generated σ s is then accommodated/relaxed by means of two complementary mechanisms: Equation (2) puts together information provided by previous studies [27][28][29] in agreement with molecular dynamic and phase field simulations 21,22,30 that demonstrates the key role played by the grain reorientation in processes of coalescence and normal grain growth for polycrystalline systems and in particular for Au films. 21,29 In this context, the model assumes elastic deformations of pure torsion (involving shear strain gradients along the grain thickness; see a description of basic kinematics of torsion in Ref.…”

“…Thus-generated σ s is then accommodated/relaxed by means of two complementary mechanisms: Equation (2) puts together information provided by previous studies [27][28][29] in agreement with molecular dynamic and phase field simulations 21,22,30 that demonstrates the key role played by the grain reorientation in processes of coalescence and normal grain growth for polycrystalline systems and in particular for Au films. 21,29 In this context, the model assumes elastic deformations of pure torsion (involving shear strain gradients along the grain thickness; see a description of basic kinematics of torsion in Ref. 31) on the basis of considering a λ ⊥ -thick shallow layer of surface grains (as discussed above) with circular cross-sections, which are: (i) azimuthally coupled to each other [according to data in Fig.…”

“…Assuming then that J θ s decays as 1/λ β g with β = 1 (Refs. 12 and 13) for surface currents on grains larger than the diffusion length or β = 2 for perimeter currents along the grain boundary, 21 we get M gb ∝ 1/λ 2+β g ⇒ λ g ∝ t p with p ≈ 1/7-1/8 for GB migration, giving rise simultaneously to both surface grain growth and in-plane grain reorientation. Note that the thus-estimated range for the coarsening exponent is in excellent agreement with our results.…”

Detecting grain rotation at the nanoscale

“…It is known that dislocation glide on preferred slip systems gives rise to crystallographic texture whereas grain rotation or GB sliding alone randomizes the grain orientation distribution (6,28). It is found that grain rotation is driven by the change of GB energy (28). The angle between boundaries is a measure of the relative energies of the GBs.…”

“…The motion of dislocations results in plastic deformation and grain shape change to minimize the system energy and equilibrate the interactions among neighboring grains. Coarse grains need larger torque and energy for rotation and hence have a low rotation rate (28). In finer nanocrystals, much higher shear stress is needed for the nucleation of dislocations.…”