There have been rapidly increasing demands for flexible lighting apparatus, and micrometer-scale light-emitting diodes (LEDs) are regarded as one of the promising lighting sources for deformable device applications. Herein, we demonstrate a method of creating a deformable LED, based on remote heteroepitaxy of GaN microrod (MR) p-n junction arrays on c-Al₂O₃ wafer across graphene. The use of graphene allows the transfer of MR LED arrays onto a copper plate, and spatially separate MR arrays offer ideal device geometry suitable for deformable LED in various shapes without serious device performance degradation. Moreover, remote heteroepitaxy also allows the wafer to be reused, allowing reproducible production of MR LEDs using a single substrate without noticeable device degradation. The remote heteroepitaxial relation is determined by high-resolution scanning transmission electron microscopy, and the density functional theory simulations clarify how the remote heteroepitaxy is made possible through graphene.

The production of holes by electron beam irradiation in hexagonal boron nitride is monitored over time using atomic resolution transmission electron microscopy.

The effects of hydrogen on the ground-state electronic and magnetic structures of ${\mathrm{AB}}_2$ (A=Zr; $B=\mathrm{V},$ Cr, Mn, Fe, Co, Ni) Laves phase compounds were investigated by first-principles local-density-functional calculations. We calculated the relative stability of atomic hydrogen at various interstitial tetrahedral sites formed by two A atoms and two B atoms $(2A2B$ site), one A atom and three B atoms $(1A3B$ site), and four B atoms $(4B$ site). We find that (i) for ${\mathrm{ZrV}}_2$ and ${\mathrm{ZrCr}}_2,$ hydrogen prefers the site with the largest interstitial hole size (i.e., $2A2B$ site); (ii) for ${\mathrm{ZrMn}}_2,$ ${\mathrm{ZrFe}}_2,$ and ${\mathrm{ZrCo}}_2,$ the hydrogen binding energies at the $1A3B$ site become comparable to or even lower than those at the $2A2B$ site once the antibonding states of B atoms become progressively occupied. In H-free ${\mathrm{ZrFe}}_2,$ we found a large magnetic moment $\left(0.5\mathrm{}{\mu }_{\mathrm{B}}\right)$ at the Zr site, which is coupled antiparallel to the moment at the Fe site $\left(1.9\mathrm{}{\mu }_{\mathrm{B}}\right).\mathrm{}$ The hydrogen absorption does not have a strong effect in suppressing the magnetic moments of atoms closest to the absorbed hydrogen but increases the magnetic moments of atoms not having hydrogen as the nearest neighbor. This increase in the moment is partly due to the H-induced lattice expansion.

We report on the syntheses of core-shell Fe_x@Pt (x = 0.4–1.2) nanoparticles (NPs) with Pt-shell thickness systematically controlled while the overall particle size is constant. The syntheses were achieved via one-pot ultrasound-assisted polyol synthesis (UPS) reactions. Fe_1.2@Pt showed a record-breaking high core-element content (55 at%) of core-shell NPs. Based on observations from a series of control experiments, we propose a mechanism of the NPs' formation that enables control of shell thickness in UPS reactions. Fe_x@Pt NPs showed drastic enhancements in mass and specific activity for oxygen reduction reaction (ORR) and significantly enhanced durability compared to commercial Pt NPs. Fe_x@Pt with a 1 (monolayer) ML Pt shell showed the highest activity. The ab initio density functional theory calculations on the binding energies of oxygen species on the surfaces of Fe_x@Pt NPs showed that the 1 ML case is most favourable for the ORR and in good agreement with the experimental results.