Functional oxides with strongly correlated electron systems, such as vanadium dioxide, manganite, and so on, show a metal-insulator transition and an insulator-metal transition (MIT and IMT) with a change in conductivity of several orders of magnitude. Since the discovery of phase separation during transition processes, many researchers have been trying to capture a nanoscale electronic domain and investigate its exotic properties. To understand the exotic properties of the nanoscale electronic domain, we studied the MIT and IMT properties for the VO2 electronic domains confined into a 20 nm length scale. The confined domains in VO2 exhibited an intrinsic first-order MIT and IMT with an unusually steep single-step change in the temperature dependent resistivity (R-T) curve. The investigation of the temperature-sweep-rate dependent MIT and IMT properties revealed the statistical transition behavior among the domains. These results are the first demonstration approaching the transition dynamics: the competition between the phase-transition kinetics and experimental temperature-sweep-rate in a nano scale. We proposed a statistical transition model to describe the correlation between the domain behavior and the observable R-T curve, which connect the progression of the MIT and IMT from the macroscopic to microscopic viewpoints.

Unlike normal hydrogen doping in a H2 gas atmosphere assisted by precious metal catalysts at high temperatures, the cost-effective hydrogenation of rare-earth nickelate (RNiO3) thin films in acid solution with abundant protons supplies a tunable protonation-induced phase transition via the internal mechanism of electron–proton synergistic co-doping under ambient conditions. Here, we report the first ever large-area hydrogenation of a millimeter-scale NdNiO3 film by metal–acid treatment, which leads to marked changes in optical and electrical transport properties corresponding to the hydrogen-induced electronic phase transition. We found that reflectance and conductance modulations are governed by the concentration of protons in NNO, which is controlled by the crystal facet orientation, which in turn affects the proton doping speed. The effect of the crystal orientation on the speed of protonation may be due to anisotropic hydrogen diffusion owing to the existence of an energetically favored channel along the [001] direction in the NdNiO3 film. Our work provides a green route for the development of electronic devices based on nickelates with hydrogenation.

The control of three-dimensional (3D) geometrical shapes is one of important approaches that contribute the development of new functionalities in material science. We produced 3D Si pyramids with atomically flat and reconstructed {111} facet surfaces supporting atomically resolved material growth in 3D space for the first time. The complex 4-fold clean 7×7 and 2×2-Fe low-energy electron diffraction (LEED) patterns reflecting the pyramidal geometry showed the realization of atomically reconstructed facet surfaces on the 3D patterned Si. Cross-sectional transmission electron microscopy (TEM) revealed the epitaxial heterointerfaces between Fe nanofilm and Si facet surfaces. The LEED and TEM results indicate the applicability of the Si pyramid as a supporting substrate for arbitrarily oriented 3D functional structures. The pyramidal Fe nanofilm displayed magnetic properties depending on the geometric shape, owing to the facet surfaces and the sharp facet edges. The unique anisotropic magnetization behavior of the 3D pyramid shape indicates that the epitaxial growth of an arbitrary geometry by virtue of the atomically ordered substrate surfaces in 3D space can contribute to the modification of the functionality.

The present study uses the SPH and DEM coupling to investigate influence of the hBN particles on friction of the elastic coarse-grained micronscale iron. Lubrication by the hBN particles significantly improves the friction performance of iron in various simulation behaviors. Size of the particles, the background (air/water) containing the particles and its temperature result in reduction of the friction coefficient. The surface mending, the protective film and the energy dissipation are the main mechanisms related to the friction reduction. Additionally, it is worthy to note that the static friction and the kinetic friction can be obviously observed by this elastic coarse-graining.