We evaluated and demonstrated strong vertical-coupling characteristics of vertical directional couplers based on long-range surface plasmon polaritons (LRSPPs) at 1.55μm wavelength. Fundamental even and odd modes supported by LRSPP metal-stripe waveguides compete more strongly on vertical coupling structures than on lateral coupling structures, possibly leading to less power consumption for switching and to compactness in device length and width. LRSPP-based vertically coupled routing of signals can also be a powerful means of developing three-dimensional photonic integrated circuits and optical printed circuit boards.

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The proximity effect of physical quantities like catalysis and wettability is a very interesting and fundamental topic to be studied. However, studies on the catalyst proximity-induced hydrogenation of h-BN are limited. In this study, we report the proximity effect of a Pt substrate on the hydrogenation of h-BN. We analyzed the degree of hydrogenation of monolayer h-BN (1L h-BN) on various Pt single-crystal surfaces via hydrogen plasma treatment; the degree of hydrogenation follows the order Pt(110) < Pt(111) < Pt(100). It was revealed that the catalytic activity of the Pt substrate inducing hydrogenation is related to the difference in the adsorption energy of hydrogen owing to the Pt surface orientation. The corrugated texture of h-BN was formed by the arrangement of h-BN on the Pt surface, referred to as the h-BN nanomesh. The h-BN nanomesh on the Pt surface consists of two regions: the “pores” are regions close to the substrate and the “wires” are loosely bound to the substrate. Finally, our experimental and density functional theory calculation results indicated that hydrogenation proceeded on the top side of the h-BN layer in the pore regions and is affected by Pt crystal surfaces. The same tendency was also observed during the conversion of h-BN to graphene on three different Pt crystals, indicating that the conversion process is related to the proximity effect to the Pt substrate.

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