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Dive into the research topics where Norifumi Kajimoto is active.

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Featured researches published by Norifumi Kajimoto.


Journal of Applied Physics | 2006

Decay process of a large surface potential of Alq3 films by heating

Norifumi Kajimoto; Takaaki Manaka; Mitsumasa Iwamoto

In order to clarify the decaying process of a large surface potential of as-deposited Alq3 films on a metal electrode by heating and photoexposure, Kelvin probe method and optical second harmonic generation (SHG) measurement were employed. The change of surface potential during heating was not in accordance with the change of SH intensity at a temperature lower than 100°C. For heating at less than 100°C and photoexposure, x-ray diffractions showed no change. We discussed these results from a viewpoint of the disordering of orientational polar structure of Alq3 molecules and the injection of electrons from metal electrodes. Then the following model was suggested. The potential decay process of Alq3 films on aluminum (Al) electrodes by heating was found to be due to electron injection from Al electrode into Alq3 films, which does not accompany the structural change of Alq3 films in the region of temperature lower than 100°C, though the crystallization of Alq3 evaporated film was suggested at a temperature h...


Japanese Journal of Applied Physics | 2006

Surface morphology and electrical transport properties of polydiacetylene-based organic field-effect transistors

Gang Zou; Eunju Lim; Ryosuke Tamura; Norifumi Kajimoto; Takaaki Manaka; Mitsumasa Iwamoto

Bottom-contact polymerized 10,12-tricosadiynoic acid (PTDA) field-effect transistors (FETs) were fabricated successfully by the Langmuir–Blodgett (LB) method. The surface morphology of PTDA LB films deposited on a FET substrate was imaged by atomic force microscopy (AFM). The current–voltage (I–V) characteristics of the bottom-contact PTDA FETs were measured in detail. The equation of the FET characteristics was derived with consideration of the carrier transport mechanism of holes conveyed along the channel, and the effective mobility was evaluated. To clarify the carrier injection and succeeding carrier accumulation and carrier transport from a source electrode to a drain electrode across PTDA, a Maxwell–Wagner model was employed to analyze the I–V characteristics of the bottom-contact PTDA FETs. Finally, to further clarify the carrier injection, we measured the capacitance–frequency (C–F) characteristics of the bottom-contact PTDA FETs and the surface potential formed across PTDA LB films on a Au electrode.


Japanese Journal of Applied Physics | 2007

Cooperative Molecular Field Effect on the Surface Potential of Tris(8-quinolinato)aluminum Films

Norifumi Kajimoto; Takaaki Manaka; Mitsumasa Iwamoto

The effect of a large surface potential across tris(8-quinolinato)aluminum (Alq3) films on the work function, based on the cooperative molecular model, and accounting for the electrostatic energy stored in the organic films, has been investigated. It is shown that the orientational ordering of polar molecules directly affects the carrier injection into as-deposited Alq3 film on the metal surface. The experimental results on the relationship between the work function of metals and the surface potential of Alq3 organic film both on Au and Al electrodes have also been analyzed.


Japanese Journal of Applied Physics | 2008

Orientational Reordering of Liquid Crystalline Monolayers by Cooperative Molecular Field Effect

Dai Taguchi; Norifumi Kajimoto; Takaaki Manaka; Mitsumasa Iwamoto

The polar orientational order of the liquid crystal, 4-n-pentyl-4′-cyanobiphenyl (5CB), molecularlayers evaporated onto Al and Ag electrodes was studied by optical second-harmonic generation measurement in terms of the first-order orientational order parameter, S1= (0 : thermodynamic average). It was found that S1 for 5CBs on Al electrode is larger than that on Ag. This experimental result supports our analysis that the orientational reordering of 5CB molecules undergoes due to holes injected from electrodes by the cooperative molecular field effect is true in actual 5CB layers. Finally, we concluded that carrier injection at the interface gives effect on the orientational order at the interface, and vice versa.


Japanese Journal of Applied Physics | 2005

Enhancement of Surface Potential Buildup and Decay of Tris(8-quinolinato)aluminum Film Deposited on Ultraviolet/Ozone-Treated Gold Electrodes

Norifumi Kajimoto; Muhamad Rasat Muhamad; Saadah Abdul Rahman; Takaaki Manaka; Mitsumasa Iwamoto

The enhancement of the surface potential of tris(8-quinolinato)aluminum (Alq3) film deposited on ultraviolet (UV)/ozone-treated gold electrodes was confirmed by surface potential measurement, and the ordering of molecular dipoles was suggested. The enhanced surface potential of the order of 10 V decayed rapidly by photoirradiation, due to molecular dipole disordering, but a surface potential of 100–400 mV remained. Interestingly, this remaining surface potential of Alq3 on the UV/ozone-treated gold electrode was always smaller than that of Alq3 film on an untreated gold electrode. It was concluded that the UV/ozone treatment is effective in decreasing the density of surface states at the Alq3-metal interface as well as for the enhancement of molecular dipole ordering.


Chemical Physics Letters | 2006

Electrostatic energies stored in dipolar films and analysis of decaying process of a large surface potential of Alq3 films

Norifumi Kajimoto; Takaaki Manaka; Mitsumasa Iwamoto


Journal of Chemical Physics | 2007

Cooperative molecular field effect and induced orientational ordering effect in polar liquid crystalline films on metals.

Dai Taguchi; Norifumi Kajimoto; Takaaki Manaka; Mitsumasa Iwamoto


The Japan Society of Applied Physics | 2007

Orientational Re-ordering of Polar Organic Monolayers by Cooperative Molecular Field Effect

Dai Taguchi; Norifumi Kajimoto; Takaaki Manaka; Mitsumasa Iwamoto


電気学会研究会資料. DEI, 誘電・絶縁材料研究会 | 2006

Decay process of a large surface potential across as-deposited Alq_3 films : Analysis from view point of electrostatic energies stored in dipolar layer

Norifumi Kajimoto; Takaaki Manaka; Mitsumasa Iwamoto


The Japan Society of Applied Physics | 2006

Decay process of a large surface potential of as-deposited Alq3 films

Norifumi Kajimoto; Takaaki Manaka; Mitsumasa Iwamoto

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Mitsumasa Iwamoto

Tokyo Institute of Technology

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Takaaki Manaka

Tokyo Institute of Technology

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Dai Taguchi

Tokyo Institute of Technology

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Ryosuke Tamura

Tokyo Institute of Technology

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Gang Zou

University of Science and Technology of China

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