Comment on "Thermodynamic Self-Limiting Growth of Heteroepitaxial Islands Induced by Nonlinear Elastic Effect".

Making use of incontrovertible scaling arguments, here we demonstrate that the main findings of the recent Nano Letter paper Hu et al. ( Hu , H. , Niu , X. , and Liu , F. Nano Lett. 2016 , 16 , 3919 ) are incorrect and unphysical, that is, there is no self-limiting island growth due to nonlinear elastic effects, as claimed by Hu et al. We also note that the key concept of the paper by Hu et. al., that is, the island height dependence of the elastic strain field has already been published 10 years ago by Zinovyev , V. A. , Vastola , G. , Montalenti , F. , and Miglio , L. Surf. Sci. 2006 , 600 , 4777 , offering a correct and elaborate treatment even in a more generic sense, including also nonlinear elasticity effects consistently.

Energy-tunable sources of entangled photons: a viable concept for solid-state-based quantum relays.

We propose a new method of generating triggered entangled photon pairs with wavelength on demand. The method uses a microstructured semiconductor-piezoelectric device capable of dynamically reshaping the electronic properties of self-assembled quantum dots (QDs) via anisotropic strain engineering. Theoretical models based on k·p theory in combination with finite-element calculations show that the energy of the polarization-entangled photons emitted by QDs can be tuned in a range larger than 100 meV without affecting the degree of entanglement of the quantum source. These results pave the way towards the deterministic implementation of QD entanglement resources in all-electrically-controlled solid-state-based quantum relays.

A phenomenological model for the collective landing of bird flocks.

A three-dimensional phenomenological model was developed to describe the collective landing of bird flocks. The employed individual based model included the landscape (as an external field) and a continuous internal variable G, to characterize the landing intent of the birds. The birds' interaction with the landscape was coupled adaptively to their landing intent. During the flight, a sharp crossover is observed in the dynamics of the landing intent, i.e. from the initial, non-landing state (small G) to the landing state (large G) that was terminated by the landing of the flock. In the model, the landing process appears to be a highly concerted, collective motion of the birds, in agreement with the field observations.

Atomistic and lattice model of a grain boundary defaceting phase transition.

Recent calculations have shown that grain boundary (GB) stress is too small to stabilize finite GB facets, suggesting that the existing theory of GB defaceting phase transitions is incomplete. We perform molecular dynamics calculations, which show a reversible phase transition at approximately 400 K with a concerted shuffle of two atoms at the facet junction as the elementary excitation. Based on this excitation we formulate an appropriate lattice model, perform Monte Carlo simulations, and establish an analytical relationship between the elementary excitation energy and the transition temperature.

Why do grain boundaries exhibit finite facet lengths?

Uniform finite facets are frequently observed at grain boundaries (GBs) and are usually attributed to equilibrium stabilization by GB stress. We report calculations for an aluminum twin GB using density functional theory, the embedded-atom method, and continuum elasticity theory. These methods show that GB stress is much too small to stabilize finite facets, suggesting that the usual explanation is incorrect.