Асимптотическая стадия роста автокаталитических III-V нитевидных нанокристаллов методом молекулярно-пучковой эпитаксии

A new analytic theory is developed for asymptotic stage of self-catalyzed growth of III-V nanowires (NWs) by molecular beam epitaxy (MBE), where NWs collect all group III atoms deposited from vapor. The shadowing NW length is derived which corresponds for the full shadowing of the substrate surface in MBE. The NW length and radius are derived depending on the effective deposition thickness and MBE growth parameters. It is shown that the NW length increases, and their length decreases with decreasing the array pitch and increasing the V/III flux ratio.

Tachyonic preheating in plateau inflation

Plateau inflation is an experimentally consistent framework in which the scale of inflation can be kept relatively low. Close to the edge of the plateau, scalar perturbations are subject to a strong tachyonic instability. Tachyonic preheating is realized when, after inflation, the oscillating inflaton repeatedly re-enters the plateau. We develop the analytic theory of this process and expand the linear approach by including backreaction between the coherent background and growing perturbations. For a family of plateau models, the analytic predictions are confronted with numerical estimates. Our analysis shows that the inflaton fragments in a fraction of an e-fold in all examples supporting tachyonic preheating, generalizing the results of previous similar studies. In these scenarios, the scalar-to-tensor ratio is tiny, r < 10-7.

Analytic theory for current-voltage characteristic of a nanowire radial p-i-n diode

In this article, process of current flow in a nanowire radial p-i-n diode has been considered in detail. It has been shown that cylindrical geometry of the structure gives rise to specific asymmetry of the concentration distribution for current carriers injected to the i-layer, which is opposite to asymmetry that is due to inequality of carriers’ mobilities. This specific asymmetry rises with bringing the i-layer nearer to the nanowire center. Together with that, decrease of the current density in a “long” p-i-n diode and its increase in a “short” p-i-n diode take place (at given forward voltage). And variation of radial thickness of the i-layer demonstrates maximums in the current density at the thickness close to the bipolar diffusion length.

High energy barriers for edge dislocation motion in body-centered cubic high entropy alloys

Recent theory proposes that edge dislocations in random body-centered cubic (BCC) high entropy alloys have high barriers for motion, conveying high strengths up to high temperatures. Here, the energy barriers for edge motion are computed for two model alloys, NbTaV and MoNbTaW as represented by interatomic potentials, using the Nudged Elastic Band method and compared to theoretical predictions. The average magnitude of the barriers and the average spacing of the barriers along the glide direction agree well with the analytical theory, with no adjustable parameters. The evolution of the barriers versus applied stress is modeled, and the mean strength is in reasonable agreement with the predicted zero-temperature strength. These findings validate the analytic theory. A reduced analytic model based on solute misfit volumes is then applied to Hf-Mo-Nb-Ta-Ti-Zr and Mo-Nb-Ta-Ti-V-W alloys, rationalizing the observed significant strength increases at room temperature and 1000 ∘C upon addition of solutes with large misfit into a base alloy. The analytic theory for edge motion is thus a powerful validated tool for guiding alloy selection.