Atomically-thin two-dimensional (2D) materials including graphene and transition metal dichalcogenide (TMD) atomic layers (e.g. Molybdenum disulfide, MoS2) are attractive materials for optoelectronic and plasmonic applications and devices due to their exceptional flexural strength led by atomic thickness, broadband optical absorption, and high carrier mobility. Here, we show that crumple nanostructuring of 2D materials allows the enhancement of the outstanding material properties and furthermore enables new, multi-functionalities in mechanical, optoelectronic and plasmonic properties of atomically-thin 2D materials. Crumple nanostructuring of atomically thin materials, graphene and MoS2 atomic layers are used to achieve flexible/stretchable, strain-tunable photodetector devices and plasmonic metamaterials with mechanical reconfigurability. Crumpling of graphene enhances optical absorption by more than an order of magnitude (~12.5 times), enabling enhancement of photoresponsivity by 370% to flat graphene photodetectors and ultrahigh stretchability up to 200%. Furthermore, we present a novel approach to achieve mechanically reconfigurable, strong plasmonic resonances based on crumple-nanostructured graphene. Mechanical reconfiguration of crumple nanostructured graphene allows wide-range tunability of plasmonic resonances from mid- to near-infrared wavelengths. The mechanical reconfigurability can be combined with conventional electrostatic tuning. Our approach of crumple nanostructuring has potential to be applicable for other various 2D materials to achieve strain engineering and mechanical tunability of materials properties. The new functionalities in mechanical, optoelectronic, plasmonic properties created by crumple nanostructuring have potential for emerging flexible electronics and optoelectronics as well as for biosensing technologies and applications.
All-optical operation holds promise as the future of computing technology, and key components will include miniaturized waveguides (WGs) and optical switches that control narrow bandwidths. Nanowires (NWs) offer an ideal platform for nanoscale WGs, but their utility has been limited by the lack of comprehensive coupling scheme and of band selectivity. Here, we introduce a NW geometric superlattice (GSL) that allows controlled, narrow-band guiding in Si NWs through direct coupling of a Mie resonance with a bound guided state (BGS). Periodic diameter modulation in a GSL creates a Mie-BGS coupled-excitation that manifests as a scattering dark state with a pronounced scattering dip in the Mie resonance envelope. The frequency of the coupled mode, tunable from the visible to near-infrared, is determined by the pitch of the GSL and exhibits a Fourier-transform limited bandwidth. Using a combined GSL-WG system, we demonstrate spectrally-selective guiding and optical switching at telecommunication wavelengths, highlighting the potential to use NW GSLs for the design of on-chip optical components.
Anti-reflection(AR), a well-known technique of reducing unwanted reflections by applying an impedance matching layer, works for a specific wavelength and require the coating layer to be a quarter wavelength thick. A broadband operation of AR, however, is not fully understood except for the trial and error method. Here, we present a systematic analytic method of AR without the restriction of wavelength or thickness, i.e. achieving a perfect AR. Specifically, we find analytic permittivity and permeability profiles that remove any given impedance mismatch at the interface between two different dielectrics in a frequency independent way. Ultra-thin AR coating is also shown to be possible and confirmed experimentally with the l/25-wavelength thick AR coating layer made of metamaterials. We apply the concept of ultrathin double layer AR to the transparent conducting electrode, which we demonstrate by fabricating a low reflective dielectric/metal-layered electrode that provides significant electrical conductivity and light transparency.
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