Since the successful exfoliation of graphene, various methodologies have been developed to identify the number of layers of exfoliated graphene. The optical contrast, Raman G-peak intensity, and 2D-peak line-shape are currently widely used as the first level of inspection for graphene samples. Although the combination analysis of G- and 2D-peaks is powerful for exfoliated graphene samples, its use is limited in chemical vapor deposition (CVD)-grown graphene because CVD-grown graphene consists of various domains with randomly rotated crystallographic axes between layers, which makes the G- and 2D-peaks analysis difficult for use in number identification. We report herein that the Raman Si-peak intensity can be a universal measure for the number identification of multilayered graphene. We synthesized a few-layered graphene via the CVD method and performed Raman spectroscopy. Moreover, we measured the Si-peak intensities from various individual graphene domains and correlated them with the corresponding layer numbers. We then compared the normalized Si-peak intensity of the CVD-grown multilayer graphene with the exfoliated multilayer graphene as a reference and successfully identified the layer number of the CVD-grown graphene. We believe that this Si-peak analysis can be further applied to various 2-dimensional (2D) materials prepared by both exfoliation and chemical growth.

Si photonics has been receiving substantial attention as an integration platform in photonics and optoelectronic research, owing to the ability to manufacture low-cost, compact integrated circuits. However, realizing efficient and high-quality light sources remains a major challenge. Herein, we report an on-chip transferrable low-threshold single microdisk laser, which is fabricated by the microtransfer printing using a structured polymer. The optically transparent and adhesive microtip enables readily reproducible, damage-free, and precisely aligned targeted transfer of a single microdisk in the growth substrate onto a prefabricated Si-post on a silicon-on-insulator wafer. Spectroscopic measurements revealed that the microdisk laser with a small Si-post exhibits rich lasing actions with an estimated threshold of ∼96.8 μW. A controlled experiment revealed that laser devices with varied Si-post sizes exhibit no significant changes in optical properties until the size of the Si-post becomes comparable with that of the microdisk. These observations agreed with the results of systematic three-dimensional numerical simulations. We believe that our microtransfer printing technique can be used to transfer micro- and nanostructures onto targeted locations and realize complex microscale heterogeneous architectures in a compact integrated circuit.

On-demand NW light sources in a photonic integrated circuit (PIC) have faced several practical challenges. Here, we report on an all-graphene-contact, electrically pumped, on-demand transferrable NW source that is fabricated by implementing an all-graphene-contact approach in combination with a highly accurate microtransfer printing technique. A vertically p−i−n-doped top-down-fabricated semiconductor NW with optical gain structures is electrically pumped through the patterned multilayered graphene contacts. Electroluminescence (EL) spectroscopy results reveal that the electrically driven NW device exhibits strong EL emission between the contacts and displays waveguiding properties. Further, a single NW device is precisely integrated into an existing photonic waveguide to perform light coupling and waveguiding experiments. Three-dimensional numerical simulation results show a good agreement with experimental observations. We believe that our all-graphene-contact approach is readily applicable to various micro/nanostructures and devices, which facilitates stable electrical operation and thus extends their practical applicability in compact integrated circuits.

In this review, we introduce novel plasmonic and metamaterial devices based on one-dimensional subwavelength nanostructures with cylindrical symmetry. Individual single devices with semiconductor/metal core/shell or dielectric/metal core/multi-shell structures experience strong light–matter interaction and yield unique optical properties with a variety of functions, e.g., invisibility cloaking, super-scattering/super-absorption, enhanced luminescence and nonlinear optical activities, and deep subwavelength-scale optical waveguiding. We describe the rational design of core/shell cylindrical nanostructures and the proper choice of appropriate constituent materials, which allow the efficient manipulation of electromagnetic waves and help to overcome the limitations of conventional homogeneous nanostructures. The recent developments of bottom-up synthesis combined with the top-down fabrication technologies for the practical applications and the experimental realizations of 1D subwavelength core/shell nanostructure devices are briefly discussed.

In this study, we proposed morphology-modulated Si nanowires (NWs) with a hexagonal cross-section and numerically investigated their resonant optical absorption and scattering properties. The calculated absorption and scattering efficiency spectra of the NWs exhibited optical resonances that could be controlled by tuning the aspect ratio (AR) of the NW cross-sectional shapes. The spectra also revealed interesting spectral behaviors including resonant peak shifts in the absorption spectrum and asymmetric line shapes in the scattering spectrum. To achieve spatially confined and wavelength-selective light absorption, we periodically modulated the geometry of the diameter in a single NW by combining two different ARs; we call these "diameter-modulated NWs." We designed various diameter-modulated NWs with short and long pitch sizes, and we observed unique and interesting features in the optical resonance and corresponding light absorption spectra such as grating modes and three-dimensional cavity modes. The proposed diameter-modulated NWs can be promising building blocks for the nanoscale localized light absorption and detection in compact nanophotonic integrated circuits.