Kenzo Maehashi

Electric-field-induced band gap of bilayer graphene in ionic liquid

Ionic liquid-gated graphene field-effect-transistors (G-FETs) were fabricated to generate a band gap in bilayer graphene. The transfer characteristics of the G-FETs revealed that the transconductance when using the ionic-liquid gate was significantly higher than that when using the back gate, because an electrical double layer formed in the ionic liquid with 200-fold the capacitance of a 300-nm-thick SiO2 layer. The results indicate that the ionic-liquid-gate structure enables application of an effective electric field. Moreover, an increase in the resistance of the bilayer graphene was clearly observed as the magnitude of the electric-field intensity was increased, owing to the creation of the band gap. From measurements of electrical characteristics as a function of temperature, a band gap of 235u2009meV was created in bilayer graphene at an ionic-liquid-gate voltage of −3.0u2009V.

Direct graphene synthesis on a Si/SiO2 substrate by a simple annealing process

We report the direct synthesis of graphene on Si/SiO2 substrates by a simple annealing process. An amorphous carbon layer and a Ni/Au layer were deposited on a Si/SiO2 substrate, and then the sample was annealed under an H2/Ar atmosphere. The Au layer suppressed the formation of Ni islands and graphene was synthesized at the interface between the metal and SiO2 layers. The graphene had an effective mobility similar to that of graphene synthesized by chemical vapor deposition. The technique does not require reactive carbon source gasses and transfer processes, which makes it a practical method of graphene synthesis.

Position-Controlled Direct Graphene Synthesis on Silicon Oxide Surfaces Using Laser Irradiation

We have demonstrated a simple method of directly synthesizing graphene on dielectric surfaces using laser irradiation without a carbon source gas. The position of the graphene synthesis was precisely controlled. Moreover, channels were formed during graphene synthesis by scanning the laser beam across the substrate. The resulting device showed typical ambipolar transport behavior, which indicates that the channel consisted of graphene and that the device acted as a field-effect transistor (FET). Our laser irradiation technique does not require transfer processes and carbon source gases, and is a promising method for graphene synthesis and fabricating graphene FETs.

Detection Kondo effect in graphene quantum dots

Graphene is suitable material for keeping electron spin states and expected for spintronics devices because of weak spin-orbit interaction and weak nuclear spin interaction. From this reason spin-correlation phenomena are investigated in graphene. Kondo effect is forming spin singlet state between electrons in leads and a dot and one of the spin correlation effects in quantum dots. Here, we will report Kondo effect in a graphene quantum dot. We fabricated graphene quantum dots by electron-beam lithography and reactive-ion etching from chemical-vapor-deposition graphene. We measured graphene quantum dots at T ~ 20 mK by a dilution refrigerator. We observed zero-bias anomaly at Coulomb blockade in graphene quantum dots. As magnetic field increases, the zero-bias conductance was suppressed. These results indicate Kondo effect. We evaluated Kondo temperature ~ 4 K from the width of zero-bias conductance.

Glycan-functionalized graphene-FETs toward selective detection of human-infectious avian influenza virus

There are global concerns about threat of pandemic caused by the human-infectious avian influenza virus. To prevent the oncoming pandemic, it is crucial to analyze the viral affinity to human-type or avian-type sialoglycans with high sensitivity at high speed. Graphene-FET (G-FET) realizes such high-sensitive electrical detection of the targets, owing to graphenes high carrier mobility. In the present study, G-FET was functionalized using sialoglycans and employed for the selective detection of lectins from Sambucus sieboldiana and Maackia amurensis as alternatives of the human and avian influenza viruses. Glycan-functionalized G-FET selectively monitored the sialoglycan-specific binding reactions at subnanomolar sensitivity.

An application of graphene field effect transistor to enzymatic assay

Summary form only given. Graphene-FETs have a large potential for sensing biomolecules, due to graphenes high carrier mobility and high responsivity to charged biomolecules. Debye screening is one of the major limitations in graphene-FET biosensing, since many biomolecules are larger than the Debye length in physiological conditions. This limitation is overcome when the biomolecules are detected using their small reaction products. In this study, the authors demonstrated ammonia detection by graphene-FETs in aqueous solution, and carried out urease detection by the detection of ammonia products from urease. This novel scheme is expected to enhance applicability of graphene-FET biosensing. Also, the urease detection will contribute to infection diagnosis of Helicobacter pylori.

Direct graphene synthesis on polymer films and its application to flexible devices

In this study, the authors have carried out graphene synthesis by laser annealing for polymer-based graphene devices. Raman spectroscopy and electronic measurement showed graphene was synthesized on the polymer films without additional preparation of carbon sources. Graphene FETs and graphene strain sensors were successfully fabricated with this simple method, and they showed the strong potential of our method for application to flexible graphene devices.

Laser-Irradiated Direct Synthesis of Graphene and Device Application

We have demonstrated a simple method of synthesizing graphene directly on dielectric surfaces using laser irradiation. Moreover, channels of graphene FETs were formed at the same time as the graphene synthesis by scanning the laser beam. As compared with conventional graphene-FET fabrication processes, this shows quite simple and useful method.