We fabricated epitaxial thin films of hexagonal DyMnO 3 , which otherwise form in a bulk perovskite structure, via deposition on Pt(111)//Al 2 O 3 (0001) and YSZ (111) substrates: each of which has in-plane hexagonal symmetry. The polarization hysteresis loop demonstrated the existence of ferroelectricity in our hexagonal DyMnO 3 films at least below 70 K. The observed 2.2 µC/cm 2 remnant polarization at 25 K corresponded to a polarization enhancement by a factor of 10 compared to that of the bulk orthorhombic DyMnO 3 . Interestingly, this system showed an antiferroelectric-like feature in its hysteresis loop. Our hexagonal DyMnO 3 films showed an antiferromagnetic Néel temperature around 60 K and a spin reorientation transition around 40 K. We also found a clear hysteresis in the temperature dependence of the magnetization, which was measured after zero-field-cooling and field-cooling. This hysteresis may well have been of spin glass origin, which was likely to arise from the geometric frustration of antiferromagnetically-coupled Mn spins with an edge-sharing triangular lattice.

The authors investigated the magnetic and ferroelectric properties of hexagonally grown HoMnO3 thin films. The magnetic measurements revealed bulklike magnetic phase transitions with an additional spin-glass-like behavior feature below the Néel temperature. The ferroelectricity in the films was distinctly different from the suggested bulk behavior. Below 40K, the HoMnO3 films showed typical ferroelectric character: their remnant polarization and coercive field values at 20K were 3.7μC∕cm2 and 0.69MV∕cm. Above 40K, however, the films exhibited an unusual antiferroelectriclike behavior, with more pronounced features appearing at higher temperatures. These intriguing physical properties make HoMnO3 films a potential candidate material for numerous future applications.

A clear experimental explanation of the contribution of Mott and Peierls transitions to the insulator−metal transition (IMT) characteristics in vanadium dioxide (VO 2 ) is still lacking. Examining the crystal and electronic structures of epitaxial VO 2 films grown at various deposition temperatures, a Mott or a Peierls transition was observed. The VO 2 film deposited at 500 °C showed suppressed Peierls transition characteristics because of the large inplane compressive strain in the insulating phase. The VO 2 films deposited at 600 and 650 °C had a higher IMT temperature because of the relaxation of both the in-plane and out-of-plane strain, and there were abundant V 4+ states. Therefore, it was related to a collaborative Mott−Peierls transition. Finally, the VO 2 film deposited at 720 °C showed a suppressed Mott transition because of the abundance of V 3+ states in the insulating phase. Furthermore, an analysis of the electronic structure of the insulating and metallic phases using in situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy provide a complete band diagram to support the above explanation of the deposition-temperature-dependent IMT characteristics.

A simulation of the helicopter/ship dynamic interface has been developed and applied to simulate a UH-60A operating from an LHA class ship. Time accurate CFD solutions of the LHA airwake are interfaced with a flight dynamics simulation based on the GENHEL model. The flight dynamics model was updated to include improved inflow modeling and gust penetration effects of the ship airwake. A maneuver controller was used to simulate pilot control inputs for specified approach and departure trajectories. The CFD solutions show significant time varying flow effects in the airwake. Time histories of the aircraft angular rate and pilot control activity indicate that the time varying nature of the airwake has significant effect on aircraft response and pilot workload.

Theoretically, the edges of a MoS2 flake and S-vacancy within the lattice have nearly zero Gibbs free energy for hydrogen adsorption, which is essentially correlated to the exchange currents in hydrogen evolution reaction (HER). However, MoS2 possesses insufficient active sites (edges and S-vacancies) in pristine form. Interestingly, active sites can be effectively engineered within the continuous MoS2 sheets by treating it with plasma in a controlled manner. Here, we employed N2 plasma on a large-area continuous-monolayer MoS2 synthesized via metal–organic chemical vapor deposition to acquire maximum active sites that are indeed required for an efficient HER performance. The MoS2 samples with maximum active sites were acquired by optimizing the plasma exposure time. The newly induced edges and S-vacancies were directly verified by high-resolution transmission electron microscopy. The 20 min treated MoS2 sample showed maximum active sites and thereby maximum HER activity, onset overpotential of ∼−210 mV vs reversible hydrogen electrode (RHE), and Tafel slope of ∼89 mV/dec. Clearly, the above results show that this approach can be employed for improving the HER efficiency of large-scale MoS2-based electrocatalysts.

The authors investigated the role of oxygen partial pressure on the epitaxial growth of an artificial hexagonal GdMnO3 phase, which should exist in an orthorhombic structure in bulk. The hexagonal GdMnO3 film showed diverse, but obvious, magnetic phase transitions with highly enhanced ferromagnetic properties. Its remnant magnetization at 4.2K is higher than those of other hexagonal RMnO3 (R=Ho, Er, and Yb) compounds, and the Curie temperature increases by around 25K. The results demonstrate that the epitaxial stabilization technique is a promising method for fabricating an artificial material with enhanced magnetic properties.

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