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Separation of two-dimensional thin-film-materials into single layers had been considered very challenging both theoretically and experimentally until the mechanical exfoliation method was discovered. After the successful separation of single- and/or few-layer graphene, the possibility of wrinkle formation has been one of the main open topics because they were not readily observed in experiments. Here, we report experimental observations of different kinds of repetitive nanoscale deformations (ripples, wrinkles, and crumples) in folded single-layer graphene (SLG) on an SiO2 substrate. Using high-vacuum atomic force microscopy, we observed that SLG that was pre-transferred onto an SiO2 substrate was accidentally folded multiple times during the tip-scanning, resulting in the formation of bilayer and trilayer graphene (TLG). Through high-resolution tapping-mode scanning, we could observe the wrinkles, ripples, and crumples in TLG. Additionally, we observed a herringbone pattern that was attributed to an intermediate stage between the wrinkles and ripples; this intermediate state was labeled as wrinklon structure. In our analysis, to characterize the ripples, wrinkles, and crumples, we measured the spatial repetition and amplitude of each pattern using their average line profile and compared them.

In this work, we investigate polarization-dependent excitation of the propagating surface plasmon polariton (SPP) modes in gold nanowires (Au NWs) combined with gold nanoparticles (Au NPs). The light coupling from focused light to SPPs on Au NWs is investigated for different structural combinations of Au NWs with Au NPs, using full-wave finite-element numerical simulations. The results show that the excitation of SPPs changes remarkably on varying the orientation of the NP on NW or the polarization angle of the incident light. Metallic NWs combined with NPs can be applied to the polarization-resolved SPP coupling in various optical and optoelectronic devices including photonic circuits and optical sensors.

We propose a vertical metal-insulator-metal (MIM) plasmonic cavity that comprises top Ag and bottom InGaAsP microring structures on an Ag substrate. A full vectorial numerical simulation was used to characterize the fundamental optical properties of the transverse-magnetic-like plasmonic whispering-gallery-modes (WGMs) excited in a variety of MIM plasmonic cavities. In addition, we exploit the controllability of far-field radiations using the single MIM microring cavity and successfully demonstrate strong directional and localized vertical radiations from the plasmonic WGMs by introducing a number of nanoscale disks along the circumference of the cavity. Our plasmonic cavity can be applied as a component of nanoscale photonic integrated circuits as well as spatially localized out-of-plane optical sensors.

We report a theoretical investigation of light coupling between a semiconductor nanowire (NW) and a plasmonic waveguide. The light emitted from the NW is coupled to the waveguide and excites a symmetric plasmonic waveguide mode propagating along the top surface of the waveguide. Using numerical simulations, coupling efficiencies were calculated for various coupling structures consisting of tapered/non-tapered NWs and single-strip/double-strip gold waveguides. The highest coupling efficiency of >2.8% was obtained between a tapered NW and a double-strip plasmonic waveguide with a height of 200 nm. This study offers a new opportunity for the efficient integration of nanoscale light sources with plasmonic waveguides and enables further miniaturization of ultracompact photonic integrated circuits.