Faculty Profiles - OHNO, Yutaka

Papers - OHNO, Yutaka

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Electrical properties of carbon nanotube FETs

Mizutani T., Nosho Y., Ohno Y.

Journal of Physics: Conference Series Vol. 109 ( 1 ) 2008.3

Language：Japanese Publisher：Journal of Physics: Conference Series

The electrical properties of carbon nanotube FETs (CNTFETs) have been studied in detail. The conduction type of the CNTFETs was dependent on the work function of the contact metal, which suggests that Fermi level pinning at the metal/nanotube interface does not happen. Based on the two-probe and four-probe resistance measurements, it was shown that the carrier transport at the contact is explained by the edge contact model even in the diffusive regime. The chemical doping using F4TCNQ was effective to reduce not only the channel resistance but also the contact resistance. It has also been shown that the surface potential measurement based on the electrostatic force detection in the scanning probe microscopy was effective in studying the behavior of the CNTFETs such as the transient behavior and the effect of the defects. Finally, in the CNTFETs fabricated using plasma-enhanced (PE) CVD-grown nanotubes, most of the drain current could be modulated by the gate voltage with little non-depletable drain current suggesting the preferential growth of the nanotubes with semiconducting behavior. © 2008 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/109/1/012002

Scopus

Potential profile measurement of carbon nanotube FETs based on the electrostatic force detection

Okigawa Yuki, Umesaka Takeo, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

NANO Vol. 3 ( 1 ) page： 51 - 54 2008.2

Potential profile measurement of carbon nanotube FETs based on the electrostatic force detection

Okigawa Y., Umesaka T., Ohno Y., Kishimoto S., Mizutani T.

Nano Vol. 3 ( 1 ) page： 51 - 54 2008.2

Language：Japanese Publisher：Nano

We have measured the potential distribution on carbon nanotube (CNT) field-effect transistors (FETs) using electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KFM). Clearer potential profiles were obtained by EFM than by KFM. When the CNT-FET is in the ON state, the EFM image shows uniform potential distribution along the CNT. In contrast, when the CNT-FET is in the OFF state, nonuniform potential image with dark spots are obtained. The dark spots can be attributed to the defects in the CNTs. © 2008 World Scientific Publishing Company.

DOI： 10.1142/S1793292008000812

Scopus

Electrical properties of carbon nanotube FETs

Mizutania T., Ohno Y., Kishimoto S.

ASDAM 2008, CONFERENCE PROCEEDINGS page： 1 - 8 2008

AlGaN/GaN MIS-HEMTs with HfO<inf>2</inf> gate insulator

Kawano A., Kishimoto S., Ohno Y., Maezawa K., Mizutani T., Ueno H., Ueda T., Tanaka T.

Physica Status Solidi (C) Current Topics in Solid State Physics Vol. 4 ( 7 ) page： 2700 - 2703 2007.12

Language：Japanese Publisher：Physica Status Solidi (C) Current Topics in Solid State Physics

AlGaN/GaN MIS-HEMTs using HfO2 gate insulator with a large dielectric constant have been fabricated. HfO2 gate insulator was deposited by pulsed laser deposition at room temperature. It has been demonstrated that the HfO2 gate insulator is effective in suppressing the gate leakage current keeping a large transconductance. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/pssc.200674769

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Enhanced 1520 nm photoluminescence from Er3+ ions in di-erbium-carbide metallofullerenes (Er2C2)@C-82 (isomers I, II, and III)

Ito Yasuhiro, Okazaki Toshiya, Okubo Shingo, Akachi Masahiro, Ohno Yutaka, Mizutani Takashi, Nakamura Tetsuya, Kitaura Ryo, Sugai Toshiki, Shinohara Hisanori

ACS NANO Vol. 1 ( 5 ) page： 456 - 462 2007.12

Language：Japanese Publisher：ACS Nano

Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C 82 cage such as Er2@C82 (isomers I, II, and III) and (Er2C2)@C82 (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er2@C82 (I, II, III) and (Er2C 2)@C82 (I, II, III) metallofullerenes are characterized by comparison with the UV-vis-NIR absorption spectra of (Y2C 2)@C82 (I, II, III), where molecular symmetries of the structures are determined to be Cs, C2v and C 3v, respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er3+ ions in Er 2@C82 (I, III) and (Er2C2)@C 82 (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C82 cage. In particular, the PL intensity of (Er2C2)@C 82 (III) has been the strongest among the isomers of Er 2@C82 and (Er2C2)@C82. Optical measurements indicate that the PL properties of Er2@C 82 (I, II, III) and (Er2C2)@C82 (I, II, III) correlate strongly with the absorbance at 1520 nm and the HOMO-LUMO energy gap of the C82 cage. © 2007 American Chemical Society.

DOI： 10.1021/nn700235z

Web of Science

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PubMed

Excitonic transition energies in single-walled carbon nanotubes: Dependence on environmental dielectric constant

Ohno Yutaka, Iwasaki Shinya, Murakami Yoichi, Kishimoto Shigeru, Maruyama Shigeo, Mizutani Takashi

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS Vol. 244 ( 11 ) page： 4002 - 4005 2007.11

Language：Japanese Publisher：Physica Status Solidi (B) Basic Research

The dependence of optical transition energies in single-walled carbon nanotubes (SWNTs) on environmental dielectric constant (εenv) have been investigated in the range of εenv from 1.0 to 37, by immersing SWNTs bridged overtrenches in various organic solvents by means of photoluminescence (PL) and the excitation spectroscopies. With increasing εenv, both E11 and E22 exhibited a redshift by several tens meV and a tendency to saturate at a εenv ∼ 5 without an indication of significant (n,m) dependence. The redshifts can be explained by dielectric screening of the repulsive electron-electron interaction. We have also investigated the time-resolved PL in air and in solvent, respectively, utilizing the excitation intensity correlation technique. When the sample was immersed in solvent, the correlation signal collapsed, and the decay time decrease as compared to in air. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/pssb.200776124

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The effects of chemical doping with F(4)TCNQ in carbon nanotube field-effect transistors studied by the transmission-line-model technique

Nosho Y., Ohno Y., Kishimoto S., Mizutani T.

NANOTECHNOLOGY Vol. 18 ( 41 ) 2007.10

Language：Japanese Publisher：Nanotechnology

We have studied the effects of p-type chemical doping with F 4TCNQ (tetrafluorotetracyano-p-quinodimethane) in carbon nanotube field-effect transistors (CNFETs). The transmission-line-model technique using multi-probe CNFETs has been employed to investigate the effects of chemical doping on the channel resistance and contact resistance. It has been found that chemical doping is effective in the reduction of the contact resistance as well as the channel resistance. The device performances of top-gate CNFETs such as transconductance, on-resistance, and on/off ratio were improved by the F 4TCNQ chemical doping on the access regions. © IOP Publishing Ltd.

DOI： 10.1088/0957-4484/18/41/415202

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Dependence of exciton transition energy of single-walled carbon nanotubes on surrounding dielectric materials

Miyauchi Y., Saito R., Sato K., Ohno Y., Iwasaki S., Mizutani T., Jiang J., Maruyama S.

CHEMICAL PHYSICS LETTERS Vol. 442 ( 4-6 ) page： 394 - 399 2007.7

Language：Japanese Publisher：Chemical Physics Letters

We theoretically investigate the environmental effect for optical transition energies of single-walled carbon nanotubes (SWNTs), by calculating the exciton transition energies of SWNTs. The static dielectric constants used in the exciton calculation can be expressed as a function of the dielectric constants of the surrounding material and that of the SWNT, in which the static and dynamic dielectric constants of the SWNT represent the screening effect of core electrons and the valence π electrons, respectively. The calculated results reproduce the environmental effect of the experimental transition energies for various surrounding materials and for various diameters of SWNTs. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2007.06.018

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Evidence of edge conduction at nanotube/metal contact in carbon nanotube devices

Nosho Yosuke, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS Vol. 46 ( 17-19 ) page： L474 - L476 2007.5

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 2: Letters

We have investigated the current flow path between the nanotube and the contact electrode in carbon nanotube devices using multiprobe devices. The contact and channel resistances have been evaluated by two methods; transmission-line-model technique and four-probe measurement. By comparing the results, we have found that channel resistance evaluated by the four-probe measurement includes contact resistance. This indicates that the widely used four-probe measurement is not applicable to nanotube devices for the evaluation of channel resistance excluding contact resistance. This finding also implies that electron transport between the nanotube and the contact metal occurs at the edge of the contact electrode. ©2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.L474

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Surface potential measurement of carbon nanotube field-effect transistors using Kelvin probe force microscopy

Umesaka Takeo, Ohnaka Hirofumi, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 46 ( 4B ) page： 2496 - 2500 2007.4

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

The surface potential of carbon nanotube field-effect transistors (CNT-FETs) was measured using Kelvin probe force microscopy (KFM). A clear potential image of the CNT channel with a diameter of 1.1 nm was obtained by measurement in air. The measured potential image was dependent on the sequence of the gate bias, and showed transient behavior with a time constant of several tens of minutes. These behaviors were consistent with the drain current transient and the hysteresis of the current-voltage characteristic of the CNT-FETs. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.2496

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(解説)カーボンナノチューブの光電子機能デバイス応用

大野雄高

マテリアルステージ 7 page： 33 2007

(解説)カーボンナノチューブトランジスタにおける電極界面の特性 Reviewed

大野雄高

表面科学 28 page： 40 2007

Fabrication process of carbon nanotube FETs using ALD passivation for biosensors

Nakashima Y., Ohno Y., Kishimoto S., Okochi M., Honda H., Mizutani T.

MICROPROCESSES AND NANOTECHNOLOGY 2007, DIGEST OF PAPERS page： 488 - + 2007

Interfacial Property of Metal/Nanotube Contacts in Carbon Nanotube Transistors

OHNO Yutaka, NOSHO Yosuke, MIZUTANI Takashi

Hyomen Kagaku Vol. 28 ( 1 ) page： 40 - 45 2007

Language：Japanese Publisher：The Surface Science Society of Japan

It is important to understand the interfacial properties of the nanotube/metal contacts because, in the case of carbon nanotube field-effect transistors (NT-FETs), the FET action is dominated by the Schottky barrier formed at the interface of the source contact. In this study, we have studied the interfacial properties from the electrical characterization of NT-FETs. First, the conduction pass in the vicinity of the contact electrodes has been investigated using a multi-terminal device. Then, the relation between conduction property of NT-FETs and work function of the contact metals has been investigated. The interfacial band structure has been discussed in terms of the temperature dependence of the drain current.

DOI： 10.1380/jsssj.28.40

CiNii Research

Relation between conduction property and work function of contact metal in carbon nanotube field-effect transistors

Nosho Y., Ohno Y., Kishimoto S., Mizutani T.

NANOTECHNOLOGY Vol. 17 ( 14 ) page： 3412 - 3415 2006.7

Language：Japanese Publisher：Nanotechnology

We have investigated the relation between the conduction property and the work function of the contact metal in carbon nanotube field-effect transistors (NTFETs). The conduction type and the drain current are dependent on the work function. In contrast to NTFETs with Ti and Pd contact electrodes, which showed p-type conduction behaviour, devices with Mg contact electrodes showed ambipolar characteristics and most of the devices with Ca contact electrodes showed n-type conduction behaviour. This indicates that the barrier height of the metal/nanotube contact is dependent on the work function of the contact metal, which suggests that the Fermi-level pinning is weak at the interface, in contrast to conventional semiconductors such as Si and GaAs. We have also demonstrated nonlinear rectification current-voltage characteristics in a nanotube quasi-pn diode with no impurity doping, in which different contact metals with different work functions are used for the anode and the cathode. © 2006 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/17/14/011

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Chirality-dependent environmental effects in photoluminescence of single-walled carbon nanotubes

Ohno Yutaka, Iwasaki Shinya, Murakami Yoichi, Kishimoto Shigeru, Maruyama Shigeo, Mizutani Takashi

PHYSICAL REVIEW B Vol. 73 ( 23 ) 2006.6

Language：Japanese Publisher：Physical Review B - Condensed Matter and Materials Physics

The optical transition energies, E11 and E22, of single-walled carbon nanotubes (SWNTs) suspended in air have been investigated for 20 species by photoluminescence and excitation spectroscopies. We have studied the environmental effects in photoluminescence by comparing our results with those for the SWNTs wrapped by sodium-dodecyl-sulfate (SDS), as reported by Weisman and Bachilo [Nano Lett. 3, 1235 (2003)]. The energy differences between air-suspended and SDS-wrapped SWNTs, Δ Eii = E ii air - E ii SDS, depends on the chiral vector (n,m), specifically on the chiral angle and type of SWNT (type I or type II). The Δ E11 and Δ E22 mostly blueshifted, with the exception of the Δ E22 of some type II SWNTs (that have a small chiral angle), which redshifted. With an increase in the chiral angle, the Δ E11 increased in type I SWNTs and decreased in type II SWNTs. In contrast, the Δ E22 demonstrated opposite dependence on the chiral angle. The differences in Δ E11 and Δ E22 between type I and type II disappeared in the SWNTs with chiral angles close to 30° (near armchair). The (n,m) dependence of the environmental effect on the transition energies can be explained by the difference in the effective mass, which contributes to the energy of Coulomb interactions between carriers. © 2006 The American Physical Society.

DOI： 10.1103/PhysRevB.73.235427

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Fabrication of carbon nanotube field effect transistors using plasma-enhanced chemical vapor deposition grown nanotubes

Ohnaka Hirofumi, Kojima Yoshihiro, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 45 ( 6B ) page： 5485 - 5489 2006.6

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

Single-walled carbon nanotubes are grown using grid-inserted plasma-enhanced chemical vapor deposition (PECVD). The field effect transistor operation was confirmed using the PECVD grown carbon nanotubes (CNTs). The preferential growth of the semiconducting nanotubes was confirmed in the grid-inserted PECVD by measuring current-voltage (1-V) characteristics of the devices. Based on the measurement of the electrical breakdown of the metallic CNTs, the probability of growing the semiconducting nanotubes has been estimated to be more than 90%. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.5485

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Fabrication of antigen sensors using carbon nanotube field effect transistors

Tani Kentaro, Ito Hiroshi, Ohno Yutaka, Kishimoto Shigeru, Okochi Mina, Honda Hiroyuki, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 45 ( 6B ) page： 5481 - 5484 2006.6

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

Antigen sensors using carbon nanotube field effect transistors (CNT-FETs) were fabricated. In order to avoid the problem of exposing source and drain electrodes directly to the phosphate buffered saline (PBS) solution, source and drain electrodes were covered with evaporated SiO film. The immobilization of antibodies on the device surface was confirmed by the observation of fluorescence. Drain current in the sensor device was decreased by the antibody-antigen binding, which suggests a potential use of CNT-FETs as antigen sensors. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.5481

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Suppression of hysteresis in carbon nanotube field-effect transistors: Effect of contamination induced by device fabrication process

Shimauchi Hideki, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 45 ( 6B ) page： 5501 - 5503 2006.6

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

We have statistically studied the suppression of hysteresis in carbon nanotube field-effect transistors. The effect of the device fabrication process on the hysteresis has been investigated. The results show that contamination induced by the fabrication process impedes the suppression of hysteresis in device passivation. To remove the contamination, we have introduced a cleaning process as a treatment before passivation. The effectiveness of passivation with polymethylmetacrylate has been improved by the cleaning process using H 2SO4/H2O2 solution. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.5501

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Papers - OHNO, Yutaka