Side-gated Graphene Research Articles

Bioelectronics for bitterness-based phytocompound detection using human bitter taste receptor nanodiscs

Various organisms produce several products to defend themselves from the environment and enemies. These natural products have pharmacological and biological activities and are used for therapeutic purposes, retaining bitter taste because of chemical defense mechanisms. Cnicin is a plant-derived bitter sesquiterpene lactone with pharmacological characteristics such as anti-bacterial, anti-myeloma, anti-cancer, anti-tumor, anti-oxidant, anti-inflammatory, allelopathic, and cytotoxic properties. Although many studies have focused on cnicin detection, they have limitations and novel cnicin-detecting strategies are required. In this study, we developed the bioelectronics for screening cnicin using its distinct taste. hTAS2R46 was produced using an Escherichia coli expression system and reconstituted into nanodiscs (NDs). The binding sites and energy between hTAS2R46 and cnicin were investigated using biosimulations. hTAS2R46–NDs were combined with a side-gated graphene micropatterned field-effect transistor (SGMFET) to construct hTAS2R46–NDs bioelectronics. The construction was examined by chemical and electrical characterization. The developed system exhibited unprecedented performance, 10 fM limit of detection, rapid response time (within 10 s), 0.1354 pM−1 equilibrium constant, and high selectivity. Furthermore, the system was stable as the sensing performance was maintained for 15 days. Therefore, the hTAS2R46-NDs bioelectronics can be utilized to screen cnicin from natural products and applied in the food and drug industries.

Quantum transport in graphene Hall bars: Effects of side gates

Quantum electron transport in side-gated graphene Hall bars is investigated in the presence of quantizing external magnetic fields. The asymmetric potential of four side-gates distorts the otherwise flat bands of the relativistic Landau levels, and creates new propagating states in the Landau spectrum (i.e. snake states). The existence of these new states leads to an interesting modification of the bend and Hall resistances, with new quantizing plateaus appearing in close proximity of the Landau levels. The electron guiding in this system can be understood by studying the current density profiles of the incoming and outgoing modes. From the fact that guided electrons fully transmit without any backscattering (similarly to edge states), we are able to analytically predict the values of the quantized resistances, and they match the resistance data we obtain with our numerical (tight-binding) method. These insights in the electron guiding will be useful in predicting the resistances for other side-gate configurations, and possibly in other system geometries, as long as there is no backscattering of the guided states.

Leakage and field emission in side-gate graphene field effect transistors

We fabricate planar graphene field-effect transistors with self-aligned side-gate at 100 nm from the 500 nm wide graphene conductive channel, using a single lithographic step. We demonstrate side-gating below 1 V with conductance modulation of 35% and transconductance up to 0.5 mS/mm at 10 mV drain bias. We measure the planar leakage along the SiO2/vacuum gate dielectric over a wide voltage range, reporting rapidly growing current above 15 V. We unveil the microscopic mechanisms driving the leakage, as Frenkel-Poole transport through SiO2 up to the activation of Fowler-Nordheim tunneling in vacuum, which becomes dominant at higher voltages. We report a field-emission current density as high as 1 μA/μm between graphene flakes. These findings are important for the miniaturization of atomically thin devices.

Visualisation of edge effects in side-gated graphene nanodevices.

Using local scanning electrical techniques we study edge effects in side-gated Hall bar nanodevices made of epitaxial graphene. We demonstrate that lithographically defined edges of the graphene channel exhibit hole conduction within the narrow band of ~60–125 nm width, whereas the bulk of the material is electron doped. The effect is the most pronounced when the influence of atmospheric contamination is minimal. We also show that the electronic properties at the edges can be precisely tuned from hole to electron conduction by using moderate strength electrical fields created by side-gates. However, the central part of the channel remains relatively unaffected by the side-gates and retains the bulk properties of graphene.

Side-gate graphene field-effect transistors with high transconductance

We have fabricated epitaxial side-gate graphene field-effect transistors (FETs) with high transconductance. A side-gate graphene FET with 55 × 60 nm2 active channel dimensions and a lateral gate-channel separation of 95 nm showing a high transconductance of 590 mS/mm is presented. An estimation of the electrostatic gate-channel capacitance of epitaxial side-gate graphene FETs shows that it is in the same order as the electrostatic gate capacitance of common top-gate graphene MOSFETs justifying the high transconductances of our devices. The results of the present paper demonstrate the potential of the side-gate architecture for graphene transistors.

Side Gate Graphene and AlGaN/GaN Unipolar Nanoelectronic Devices

Three-terminal junction devices were realized in graphene grown heteroepitaxially on semiinsulating silicon carbide as well as in AlGaN/GaN heterostructures grown by MOCVD on sapphire containing a two dimensional electron gas. These nanoelectronic devices were fabricated using electron beam lithography. In both types of heterostructures room temperature electrical measurements revealed a pronounced nonlinear electrical behavior of the fabricated nanoelectronic devices. The obtained voltage rectification at room temperature demonstrates the feasibility of func-tional three-terminal junctions in heterostructures consisting of types of high carrier mobility struc-tures than classical III-V semiconductor heterostructures.

The Aharonov–Bohm effect in a side-gated graphene ring

We investigate the magnetoresistance of a side-gated ring structure etched out of single-layer graphene. We observe Aharonov–Bohm oscillations with about 5% visibility. We are able to change the relative phases of the wave functions in the interfering paths and induce phase jumps of π in the Aharonov–Bohm oscillations by changing the voltage applied to the side gate or the back gate. The observed data can be interpreted within existing models for ‘dirty metals’.

Transport gap in side-gated graphene constrictions

We present measurements on side-gated graphene constrictions of different geometries. We characterize the transport gap by its width in back-gate voltage and compare this to an analysis based on Coulomb blockade measurements of localized states. We study the effect of an applied side-gate voltage on the transport gap and show that high side-gate voltages lift the suppression of the conductance. Finally we study the effect of an applied magnetic field and demonstrate the presence of edge states in the constriction.