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An efficient electro-optic transition control is reported in all-fiber graphene devices over a broad spectral range from visible to near-infrared. The ion liquid–based gating device fabricated onto a side-polished fiber with high numerical aperture significantly enhances the light-matter interaction with graphene, resulting in strong and nonresonant electro-optic absorption of up to 25.5 dB in the wavelength ranging from 532 to 1950 nm. A comprehensive analysis of the optical and electrical properties of the device fabricated with monolayer and bilayer graphene revealed that the number of graphene layers significantly impacts on the performance of the device, including modulation depth and driving voltage. Wavelength-dependent optical response is also measured, which clearly characterizes the electronic bandgap dispersion of graphene. The device exhibited more efficient electro-optic modulation in the longer wavelength region, where the maximum light modulation efficiency of 286.3%/V is achieved at a wavelength of 1950 nm.

Twisted bilayer graphene (tBLG) has received substantial attention in various research fields due to its unconventional physical properties originating from Moiré superlattices. The electronic band structure in tBLG modified by interlayer interactions enables the emergence of low-energy van Hove singularities in the density of states, allowing the observation of intriguing features such as increased optical conductivity and photocurrent at visible or near-infrared wavelengths. Here, we show that the third-order optical nonlinearity can be considerably modified depending on the stacking angle in tBLG. The third-harmonic generation (THG) efficiency is found to significantly increase when the energy gap at the van Hove singularity matches the three-photon resonance of incident light. Further study on electrically tuneable optical nonlinearity reveals that the gate-controlled THG enhancement varies with the twist angle in tBLG, resulting in a THG enhanced up to 60 times compared to neutral monolayer graphene. Our results prove that the twist angle opens up a new way to control and increase the optical nonlinearity of tBLG, suggesting rotation-induced tuneable nonlinear optics in stacked two-dimensional material systems., Nonlinear optics: When graphene ‘does the twist’ Modifying the angle between the two layers of twisted bilayer graphene can considerably improve how photons interact with it to generate higher-energy photons. Dong-Il Yeom of Ajou University and colleagues in Korea shined laser light onto twisted bilayer graphene stacked at various angles, and measured the outcoming optical signals. Twisted bilayer graphene is made by stacking two monolayer graphenes at an angle. The interlayer interaction in this material leads to intriguing properties. The scientists found that changing the angle could enhance a nonlinear optical property, called third-harmonic generation, by 60 times compared to monolayer graphene. The team then conducted Raman measurements and modeling calculations to understand how this process occurs. They say their findings could pave the way towards novel designs for enhancing optical nonlinearity in two-dimensional stacked materials.

Electrical characteristics of ion gels prepared by loading different amounts of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) in Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) are investigated and compared with those of ion liquid, [EMIM][TFSI] for possible application as a gate stack for flexible electronic devices. Capacitance and impedance as a function of frequency are measured, which can be well accounted for by a simple circuit model identifying the local device components. The operation of a flexible field effect transistor based on graphene and the ion gel as a top gate stack is also demonstrated.

Graphene has emerged as a promising 2-dimensional (2D) material composed of a monolayer of carbon atoms, which is expected to be utilized for nano- and optoelectronic device applications. In order to fabricate high speed graphene transistors with low power consumption, the growth of insulating thin films with high dielectric constant (high-k) on graphene is essential. Atomic layer deposition (ALD) is one of the best deposition techniques to grow functional thin films, however, it is extremely challenging to grow high-k thin films on graphene by ALD because of the lack of surface functional groups (such as hydroxyl groups) on graphene. Here, we demonstrate that the graphene surface is fully covered by Al2O3 thin films (10–30 nm), with significantly reduced leakage current (decreased by a factor of ∼107), through simple surface treatment of the graphene in the ALD chamber prior to the deposition of the Al2O3 layer by ALD to provide surface nucleation sites on the graphene, without breaking vacuum and changi...

We demonstrate an electrically tunable polarizer for terahertz (THz) frequency electromagnetic waves formed from a hybrid graphene-metal metasurface. Broadband (>3 THz) polarization-dependent modulation of THz transmission is demonstrated as a function of the graphene conductivity for various wire grid geometries, each tuned by gating using an overlaid ion gel. We show a strong enhancement of modulation (up to ∼17 times) compared to graphene wire grids in the frequency range of 0.2–2.5 THz upon introduction of the metallic elements. Theoretical calculations, considering both plasmonic coupling and Drude absorption, are in good agreement with our experimental findings.