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We fabricated 70 nm Al2O3 gated field effect transistors based on two-dimensional (2D) materials and characterized their optical and electrical properties. Studies show that the optical contrast of monolayer graphene on an Al2O3/Si substrate is superior to that on a traditional 300 nm SiO2/Si substrate (2.4 times). Significantly, the transconductance of monolayer graphene transistors on the Al2O3/Si substrate shows an approximately 10-fold increase, due to a smaller dielectric thickness and a higher dielectric constant. Furthermore, this substrate is also suitable for other 2D materials, such as WS2, and can enhance the transconductance remarkably by 61.3 times. These results demonstrate a new and ideal substrate for the fabrication of 2D materials-based electronic logic devices. [ABSTRACT FROM AUTHOR]

Plasmon was probed from graphene which was grown by chemical vapor deposition using terahertz time-domain spectroscopy at room temperature. Graphene was laid on a resonant cavity, and metal grating was then deposited on top of them. For the THz light polarized along the grid fingers, the optical conductivity of graphene changed from Drude response into strongly Lorentz behavior with a peak formed in the THz-region. These experimental results are highly consistent with the theoretical prediction of a single layer graphene. It confirms that the graphene plasmon frequency can be tuned by the length of grating. Moreover, the extinction in the transmission of single-layer graphene can also be increased beyond 60%. [ABSTRACT FROM AUTHOR]

The metal-oxide-graphene heterostructures have abundant physical connotations. As one of the most important physical properties, the electric transport property of the gold-chromium oxide-gra-phene heterostructure has been studied. The experimental measurement shows that the conductive mechanism is dominated by the space-charge-limited transport, a kind of bulk transport of an insulator with charge traps. Combining the theoretical analysis, some key parameters such as the carrier mobility and trap energy also are obtained. The study of the characteristics of the metal-oxide-graphene heterostructures is helpful to investigate the graphene-based electronic and photoelectric devices. [ABSTRACT FROM AUTHOR]

The metal/graphene contacts play a very important role in the performance of graphene-based devices. We report here a unique observation of current-induced doping in graphene transistors. The charge carrier type and the concentration in graphene can be manipulated by the current flowing through the graphene device, arising from the asymmetrical metal/graphene barriers between the source and drain electrodes and the accompanied current crowding effect. [ABSTRACT FROM AUTHOR]

Monolayer graphene has high symmetrical crystal structure and exhibits in-plane isotropic physical properties. However, twisted bilayer graphene (tBLG) is expected to differ physically, due to the broken symmetry introduced by the interlayer coupling between adjacent graphene layers. This symmetry breaking is usually accompanied by in-plane anisotropy in their electrical, optical and thermal properties. However, the existence of in-plane anisotropy in tBLG has remained evasive until now. Here, an unambiguous identification of the in-plane anisotropy in tBLG is established by angle-resolved polarized Raman spectroscopy. It was found that the double-resonant two-dimensional band is anisotropic. The degree of in-plane anisotropy is found to be dependent on the misorientation angles, which is two- and four-fold for tBLG with misorientation angles of 15° and 20°, respectively. This finding adds a new dimension to the properties of graphene, which opens a possibility to the development of graphene-based angle-resolved photonics and electronics. [ABSTRACT FROM AUTHOR]

We propose a terahertz half-wave plate composed of a periodic array of rectangular-shaped metal-dielectric-graphene (RMDG) sandwich structure on a dielectric substrate supported by a thick metallic film. The role of graphene sheet is to combine with the rectangular-shaped metal to provide tunable anisotropic hybrid magnetic plasmon resonance. The results reveal that about 90% of energy of the incident linearly polarized light at a certain frequency is converted to the perpendicular polarization direction after reflection from the wave plate. The high energy polarization conversion efficiency is attributable to the fact that the electric vector of the hybrid magnetic plasmon resonance in RMDG is mainly perpendicular to the graphene sheet and the absorption loss of graphene is suppressed. The half-wave plate we demonstrate here, consisting of nanostructured metal and non-structured graphene, utilizes mature metal nanostructure preparation process and avoids the graphene processing, which consequently facilitates the fabrication and promotes the application of half-wave plate. [ABSTRACT FROM AUTHOR]

We show numerically and theoretically that coherent perfect absorption can be achieved in suspended monolayer graphene with ultra-broad bandwidth from visible to near-infrared range under oblique incidence. The absorption can be tuned from 0% to 100% by controlling the relative phase of the coherent incident light, showing great capacity in absorption modulation. We also studied tunable coherent absorption of graphene placed in high refractive index media with a gap (symmetrically based graphene), finding that graphene keeps high absorption (over 90%) with near-infrared light, and the maximum absorption wavelength is determined by the thickness of the gap. The broadband and high tunable absorption in graphene in the visible and near-infrared light will provide an efficient way to manipulate the interaction between light and graphene and serve applications in optical modulators, transducers, sensors and coherent detectors. Moreover, this absorption enhancement theory also applies to other 2D materials including black phosphorus, MoS2 and so on. [ABSTRACT FROM AUTHOR]

Tunable terahertz plasmon in a graphene-based device with a grating serving as a top gate is studied. Transmission spectra exhibit a distinct peak in the terahertz region when the terahertz electric field is perpendicular to the grating fingers. Our results show that the extinction in the transmission of single-layer graphene shields beyond 80%. Electronic results further show that the graphene plasmon can be weakly adjusted by tuning the gate voltage. Theoretical calculation also implies that the plasmon frequency of graphene can fall into the terahertz region of 1–2 THz by improving the sustaining ability and capacitance of the top gate. [ABSTRACT FROM AUTHOR]

We have numerically demonstrated that electrically tuneable directional coupling and switching can be realized based on the multimode interference effect in dielectric-loaded graphene plasmon waveguides (DLGPWs) of our own design. The total field profile resulting from a superposition of all guided modes in the multimode dielectric-loaded graphene plasmon waveguide is electrically controllable because the propagation properties of the first three guided modes supported by the DLGPW can be effectively manipulated by electrostatic doping of graphene. The functional size of the device is only several micrometres, which is much smaller than the working wavelength. Such electrically controlled multifunctional devices may find potential applications in high-density integrated active plasmonic circuits. [ABSTRACT FROM AUTHOR]

We demonstrate a tunable terahertz half-wave plate composed of a periodic array of graphene nanodisk dimers supported on a dielectric spacer backed by a planar gold layer. The polarization conversion phenomena are attributed to the hybridization effect caused by coupling interactions between plasmonic resonances in the graphene nanodisk dimers. By varying the distance between graphene nanodisks, the polarization conversion performance can be controlled. Further, the polarization conversion can be dynamically tuned at different frequencies via electrostatic doping of graphene. Other novel phenomena and applications could be developed from coupled graphene structures in the future. [ABSTRACT FROM AUTHOR]

We demonstrate numerically that a tunable absorber with absorption of 99.94% in the far infrared range can be obtained using a nonstructured graphene. The mechanism originates from a nonstructured graphene film supported on a periodical dielectric array that can show Fermi level modulation periodically and produce plasmonic resonances in the far infrared range. The nonstructured graphene can avoid the unexpected edge effects and does not influence the unique properties of graphene, which will be helpful in practice to achieve the unity absorption and facilitate the development of many related applications. [ABSTRACT FROM AUTHOR]

We investigate numerically the electromagnetically induced transparency-like behavior in all-dielectric planar photonic metamaterials. The proposed metamaterial consists of a periodical array of silicon metamolecules. Each metamolecule comprises a radiative resonator and a subradiant resonator that couple to each other through near field interactions. Resonances with extremely high quality factors of up to several thousands are predicted, and a group refractive index of more than 200 can be realized at the transparency window. This provides an effective platform for slow light, enhanced nonlinearity and sensing applications and presents opportunities for developing new types of active lasing and optomechanical metamaterials. [ABSTRACT FROM AUTHOR]

First-principles calculations are performed to investigate the transport properties of zigzag α-graphyne nanoribbbns (ZαGNRs). It is found that asymmetric ZαGNRs behave as conductors with linear current-voltage relationships, whereas symmetric ZαGNRs have very small currents under finite bias voltages, similar to those of zigzag graphene nanoribbons. The symmetry-dependent transport properties arise from different coupling rules between the π and π" subbands around the Fermi level, which are dependent on the wave-function symmetry of the two subbands. Based on the coupling rules, we further demonstrate the bipolar spin-filtering effect in the symmetric ZαGNRs. It is shown that nearly 100% spin-polarized current can be produced and modulated by the direction of bias voltage and/or magnetization configuration of the electrodes. Moreover, the magnetoresistance effect with the order larger than 500000% is also predicted. Our calculations suggest ZαGNRs as a promising candidate material for spintronics. [ABSTRACT FROM AUTHOR]