Spectroscopic Evidence of a Dimensionality-Induced Metal-to-Insulator Transition in the Ruddlesden-Popper LaNiO Series.

Perovskite-based heterostructures have recently gained remarkable interest, thanks to atomic-scale precision engineering. These systems are very susceptible to small variations of control parameters, such as two-dimensionality, strain, lattice polarizability, and doping. Focusing on the rare-earth nickelate diagram, LaNiO (LNO) catches the eye, being the only nickelate that does not undergo a metal-to-insulator transition (MIT).

Nature of the metal-insulator transition in few-unit-cell-thick LaNiO films.

The nature of the metal-insulator transition in thin films and superlattices of LaNiO only a few unit cells in thickness remains elusive despite tremendous effort. Quantum confinement and epitaxial strain have been evoked as the mechanisms, although other factors such as growth-induced disorder, cation non-stoichiometry, oxygen vacancies, and substrate-film interface quality may also affect the observable properties of ultrathin films. Here we report results obtained for near-ideal LaNiO films with different thicknesses and terminations grown by atomic layer-by-layer laser molecular beam epitaxy on LaAlO substrates.

Strain-Engineered Oxygen Vacancies in CaMnO Thin Films.

We demonstrate a novel pathway to control and stabilize oxygen vacancies in complex transition-metal oxide thin films. Using atomic layer-by-layer pulsed laser deposition (PLD) from two separate targets, we synthesize high-quality single-crystalline CaMnO films with systematically varying oxygen vacancy defect formation energies as controlled by coherent tensile strain. The systematic increase of the oxygen vacancy content in CaMnO as a function of applied in-plane strain is observed and confirmed experimentally using high-resolution soft X-ray absorption spectroscopy (XAS) in conjunction with bulk-sensitive hard X-ray photoemission spectroscopy (HAXPES).

Response surface optimization of mucilage aqueous extraction from flixweed (Descurainia sophia) seeds.

The effects of four factors of pH (4-8), temperature (50-95°C), weed-seed ratio (W/S, 15-45), and time (1-4 h) on the yield of mucilage extraction of Descurainia sophia seeds were investigated using response surface methodology-Box-Behnken design (RSM-BBD). Results showed that a second-order model for the studied response was adequately fitted with a coefficient of determination of 98.7% (p<0.

Modeling arbitrary layers of continuous-level defenses in facing with strategic attackers.

We propose a novel class of game-theoretic models for the optimal assignment of defensive resources in a game between a defender and an attacker. Compared to the other game-theoretic models in the literature of defense allocation problems, the novelty of our model is that we allow the defender to assign her continuous-level defensive resources to any subset (or arbitrary layers) of targets due to functional similarity or geographical proximity. We develop methods to solve for equilibrium, and illustrate our model using numerical examples.