Masaaki Fujimori
Hitachi
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Featured researches published by Masaaki Fujimori.
Applied Physics Letters | 2005
Sadaki Samitsu; Takeshi Shimomura; Kohzo Ito; Masaaki Fujimori; Seiji Heike; Tomihiro Hashizume
We have prepared conducting polymer nanowires of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) with diameters under 10 nm by a molecular combing method, and have measured the conductivity of the individual PEDOT nanowires on platinum nanoelectrodes using manipulation with an atomic force microscope (AFM). The temperature dependence of the conductance was explained well by a quasi-one-dimensional variable range hopping model. The conductivity of two single nanowires was determined to be 0.6 and 0.09S∕cm, which is of the same order as that of PEDOT/PSS films. After all the nanowires crossed over the nanoelectrodes were cut off with AFM manipulation, the current was drastically decreased down to the background level. These results directly indicate that the conductivity was derived from the PEDOT nanowires on the nanoelectrodes.
Japanese Journal of Applied Physics | 2007
Tadashi Arai; Naoya Sato; Kazuo Yamaguchi; Masahiro Kawasaki; Masaaki Fujimori; Takeo Shiba; Masahiko Ando; Kazuyoshi Torii
A new long-wavelength-photosensitive self-assembled-monolayer (SAM) was developed, and a process fabricating alignment-free printable electrodes for flexible organic thin-film transistors (OTFTs) with the SAM was proposed. The SAM was degraded and its wetability was changed from hydrophobic to hydrophilic by irradiating it with UV light (>350 nm). The irradiated areas of SAM became more hydrophilic with tetramethylammonium hydroxide (TMAH) solution, which is a commercially available photoresist developer. Using the SAM and a back substrate exposure technique with TMAH rinsing, we can induce the self-alignment of solution-processed source/drain electrodes with respect to a gate electrode. A 20-µm-gap pattern of PEDOT was successfully formed by spin-coating on a plastic substrate.
Journal of Applied Physics | 2003
Yasuhiko Terada; Byoung-Ki Choi; Seiji Heike; Masaaki Fujimori; Tomihiro Hashizume
Using scanning tunneling microscopy and spectroscopy, we tested a pulse-injection method for placing molecules onto hydrogen-terminated Si(100) surfaces. The target molecules were multiwalled carbon-nanotube and π-conjugated poly(3-hexylthiophene) molecules dispersed or dissolved into a hexane or chloroform solvent. The results suggest that pulse injection can be used for fixing a variety of molecules in organic solvents onto H-terminated Si(100) surfaces while keeping most of the surface intact.
Japanese Journal of Applied Physics | 2003
Yasuhiko Terada; Byoung-Ki Choi; Seiji Heike; Masaaki Fujimori; Tomihiro Hashizume
We have used a pulse-injection method to fix multi-walled carbon nanotubes (MWNTs) onto hydrogen-terminated Si(100) surfaces. Using scanning-tunneling-microscopy (STM), we first tested several kinds of solvents for organic molecules which were pulse-injected onto the H-terminated Si(100) surfaces. Most of the solvent molecules of hexane and chloroform were desorbed from the surfaces after annealing the substrates, which indicates that they are suitable for fixing molecules onto the surface. Then, we fixed MWNTs which were dispersed in hexane and pulse-injected onto the H-terminated surface. An isolated MWNT was observed by STM and was investigated by scanning tunneling spectroscopy (STS). The STS spectra revealed a metallic feature of the particular MWNT.
Journal of Applied Physics | 2004
J Hayakawa; Kenchi Ito; Masaaki Fujimori; Seiji Heike; Tomihiro Hashizume; J Steen; Jürgen Brugger; Hideo Ohno
An array of exchange biased spin-valve giant-magnetoresistance nanopillars was fabricated and the current I dependence of the resistance R was investigated using an electrically conducting atomic-force microscope (AFM) probe contact at room temperature. We observed current induced switching in a MnIr∕CoFe∕Cu∕CoFe∕NiFe nanopillar using the AFM probe contact. Current-driven switching using nanoprobe contact is a powerful method for developing nonvolatile and rewritable magnetic memory with high density.
Nanotechnology | 2004
Masaaki Fujimori; Seiji Heike; Yasuhiko Terada; Tomihiro Hashizume
Four-probe fine electrodes were fabricated on a Si(100)-2 × 1-H surface using conventional lithographic and scanning-probe nano-fabrication techniques followed by standard cleaning and hydrogenation processes of the surface. It was confirmed by scanning tunnelling microscopy that a Si(100)-2 × 1-H surface is formed in the area except for the fine electrodes. Tunnelling spectroscopy of the electrode surface and electrical conduction measurements of nanoscale wires were performed for evaluating the fabricated electrodes. The results showed that the fabricated fine electrodes are capable of measuring the electrical properties of nanoscale surface objects.
Japanese Journal of Applied Physics | 2006
Yasuhiko Terada; Hidemi Shigekawa; Yuji Suwa; Seiji Heike; Masaaki Fujimori; Tomihiro Hashizume
Electronic structures of individual conducting polymers, poly(3-hexylthiophene)s (P3HTs), fixed on a hydrogen-terminated Si(100) surface have been examined by scanning tunneling microscopy/spectroscopy and first-principles calculations within the density-functional approach. The calculations reveal that the electronic structure of the polymer is only weakly influenced by the substrate, which ensures that the fixed polymers maintain a conduction property similar to that of isolated polymers. The current–voltage curves for the substrate-molecule-tip junction show rectification characteristics, indicating the carrier doping in the fixed polymers.
Journal of Applied Physics | 2005
Jun Hayakawa; Hideki Takahashi; Kenchi Ito; Masaaki Fujimori; Seiji Heike; Tomihiro Hashizume; Masahiko Ichimura; Shoji Ikeda; Hideo Ohno
We have investigated the current-driven magnetization reversal of exchange-biased spin-valve giant magnetoresistive nanopillars with a magnetically pinned ferromagnetic layer. Current-driven magnetization reversal of a ferromagnetic layer with a smaller MV (M: magnetization, V: volume) value is found to take place even when the layer is pinned by the exchange bias induced by an antiferromagnet. The critical current density Jc of the spin-valve nanopillar with a MnIr layer adjacent to the current-driven free layer is of the same order as that of a Co/Cu/Co nanopillar (∼107A∕cm2).
Journal of the Physical Society of Japan | 2006
Aoi Inomata; Takeshi Shimomura; Seiji Heike; Masaaki Fujimori; Tomihiro Hashizume; Kohzo Ito
We measured the electrical current-voltage characteristics of λDNA in vacuum using fine electrodes with a gap of about 200 nm. It was found that the electrical resistance of λDNA molecules between the fine electrodes had a large variation: from 7.8 MΩ to values larger than 1 TΩ. This was consistent with the controversial results given in previous reports. The temperature dependence of conductivity was explained well by the Arrhenius equation. In addition, the conductivity of a single molecule of double-stranded λDNA was measured by a “one-by-one” cutting method using atomic force microscopy (AFM). The conductivity was determined to be 3×10 1 S/cm, which is about the same order as that of semiconductors.
Journal of Applied Physics | 2005
Yasuhiko Terada; Kazushi Miki; Masaaki Fujimori; Seiji Heike; Yuji Suwa; Tomihiro Hashizume
We measured current–voltage (I–V) characteristics of individual conducting polymers, poly(3-hexylthiophene)s (P3HTs), fixed on hydrogen-terminated Si(100) using scanning tunneling microscopy (STM)∕spectroscopy. The I–V curves reveal rectification characteristics that are attributed to the shift of the energy level of the valence-band maximum of P3HT under bias. The current suppression at positive substrate bias results from the effect of differential charging of the polymer between the opposite bias polarities, indicating the possibility for doping of polymer nanowires by using a STM tip as a gate electrode.