Are the Structures of Twist Grain Boundaries in Silicon Ordered at 0 K?

Abstract

Contrary to previous simulation results on the existence of amorphous intergranular films at high-angle twist grain boundaries (GBs) in elemental solids such as silicon, recent experimental results imply structural order in some high-angle boundaries. With a novel protocol for simulating twist GBs, which allows the number of atoms at the boundary to vary, we have found new low-energy ordered structures. We give a detailed exposition of the results for the simplest boundary. The validity of our results is confirmed by first-principles calculations.

Structure, shear resistance and interaction with point defects of interfaces in Cu–Nb nanocomposites synthesized by severe plastic deformation

“…To find the ground state interface configuration, vacancies and interstitials must be iteratively added until no negative formation energy sites remain. Using this approach or related ones, the ground states of some interfaces have been shown to have local densities and compositions markedly different from the neighboring crystals [8,37,45,46]. In the interface studied here, however, no negative vacancy or interstitial formation energy sites were found.…”

“…No such delocalization occurs in Cu-NbSPD: vacancies and interstitials absorbed at misfit dislocations in this interface remain compact, just like conventional point defects in crystalline solids. Second, similar to certain grain boundaries in semiconductors [45,46] and ceramics [60], Cu-NbMSP contains constitutional vacancies. Such vacancies are thermodynamically stable even at zero temperature because they are an intrinsic feature of the ground state interface configuration.…”

Non-coherent Cu grain boundaries driven by continuous vacancy loading

“…Similar algorithms have been used to reduce GB and heterophase interface energies by removing or adding atoms [30,43]. Indeed, our algorithm provides an effective way of finding low-energy GB structures, which approximate the thermal equilibrium state of well-relaxed boundaries at low temperature.…”

“…Using a method for grand-canonical simulated quenching (GCSQ), Phillpot and Rickman found that GB energies may be reduced by removing atoms [28,29]. Similarly, Von Alfthan and Sutton [30] showed that finding the lowest energy states of general GBs in Si often requires removing or adding atoms. Bai et al studied loading of radiation-induced interstitials into Cu GBs and assessed its effect on recombination reactions with vacancies [31,32].…”

“…Although our algorithm does not correspond directly to any real, physical process, it may be viewed as analogous to vacancies diffusing from a crystal into the GB at a rate sufficiently low that each vacancy reaches its lowest energy location within the GB before the next vacancy arrives. Similar algorithms have been used to find low energy states of GBs and heterophase interfaces by removing or adding atoms [30,43].…”