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Takaaki Manaka,Kei Yoshizaki,Mitsumasa Iwamoto 한국물리학회 2006 Current Applied Physics Vol.6 No.5
Polar orientation of Alq3 (Tris(8-quinolinolato)aluminum) evaporated lms on metal electrode was investigated by Kelvin probemethod and optical second harmonic generation (SHG) measurement. For as-deposited lms under the dark condition, a largepotential formed across the lms was conrmed and it decreased drastically by light irradiation with a wavelength of 400 nm. Froma viewpoint of the interfacial electrostatic phenomena, there are two contributions to the surface potential, i.e. space charge eectcharges contribute mainly to the surface potential after irradiation. According to the SHG measurement, decrease of the signal fromAlq3 lms was observed after light irradiation. It is also found that using the fundamental light with a wavelength of 900 nm, SHintensity decreases steeply during the SH measurement in the absence of 400 nm irradiation possibly due to the two-photonexcitation.
Spin Dynamics of Triangular Spin Tubes
Hirotaka Manaka,Yoko Miura 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We performed temperature (T) dependence experiments on the AC magnetic susceptibility ofequilateral and non-equilateral triangular spin tubes CsCrF4 and α-KCrF4, respectively. In α-KCrF4, the linear (X00 ) and the nonlinear (X02 ) magnetic susceptibilities show sharp peaks at 4.0 K,which corresponds to an antiferromagnetic phase transition. On the other hand, in CsCrF4, broadand positive X00 (T) peaks appear above f = 31 Hz at T '4 K, but no anomaly of X00 (T) occurs atf = 31 Hz. Furthermore, the X02 (T) curve at f = 977 Hz shows a broad and negative peak at T 3K.We suspect that there is a gradual change in spin dynamics below T '4 K from the paramagneticstate at a high temperature to a slowly-fluctuating spin state without typical antiferromagnetic longrangeorder as one-dimensionality along the spin tubes coexists with geometrical spin frustration inthe equilateral triangular planes.
임은주,Takaaki Manaka,,Yuki Ohshima,Mitsumasa Iwamoto 한국전기전자재료학회 2008 Transactions on Electrical and Electronic Material Vol.9 No.4
Using pentacene field effect transistors (FETs) with Au source and drain electrodes, electron injection from the Au electrodes into the pentacene was investigated. The capacitance-voltage (C-V) and optical second harmonic generation (SHG) measurements were employed. Electron injection from the Au electrodes was suggested by the hysteresis behavior with the C-V characteristics and slowly decaying SHG signal under DC biasing. A mechanism of hole-injection assisted by trapped electrons is proposed. To confirm electron injection process, light-emitting behavior under the application of AC applied voltage was observed.
Mitsumasa Iwamoto,Takaaki Manaka,Kei Yoshiz 한국물리학회 2005 Current Applied Physics Vol.5 No.4
Carrier injection, carrier separation, and carrier transport in the films are key processes in organic devices. Therefore, the understanding of interfacial electrostatic phenomena is of crucial importance. From the view point of dielectric physics, we have been studying the surface polarization phenomena. Using Maxwell displacement current (MDC) measurement, optical second harmonic generation (SHG) measurement, and Kelvin-probe surface potential measurement, surface polarization phenomena at the interfaces have been elucidated experimentally and theoretically. This paper describes how the surface polarization phenomena can be clarified by these measurements. Finally, our experiment on evaporated Alq3 film is shown.
Mitsumasa Iwamoto,Takaaki Manaka,Eunju Lim,Ryousuke Tamura 한국물리학회 2007 Current Applied Physics Vol.7 No.4
gate insulator is due to the MaxwellWagner eect. The FET characteristics are derived based on a model in which carriers injected fromelectrodes are accumulated at the interface, and they are then conveyed along the channel by the force of electric eld formed betweensource and drain electrodes. Optical second harmonic generation from the channel is dependent on the o- and on-states of the FETchannel, and suggesting that carriers injected from source electrode make a signicant contribution to the space charge eld formation.
Eunju Lim,Takaaki Manaka,Ryosuke Tamura,Mitsumasa Iwamoto 한국물리학회 2007 Current Applied Physics Vol.7 No.4
eect transistor (OFET) devices. In our previous studies, we showed the evidence of carrier injection from source electrode by means ofoptical second harmonic generation (SHG) measurement and capacitancevoltage (CV) measurements, and explained the FET char-acteristics using a MaxwellWagner model. In this paper, to further clarify the behavior of the carrier transport and hole injection fromsource electrode, we focused on the hysteresis behavior observed in the currentvoltage (IV) andCV characteristics of pentacene FETs.CV measurements, we could show that the origin of the hysteresis behavior iscaused by holes, which are injected and subsequently trapped in FET channel.
Mitsumasa Iwamoto,Takaaki Manaka,,Cheng-Quan Li 한국물리학회 2005 Current Applied Physics Vol.5 No.2
At the metal.organic film nano-interface, surface polarization phenomena are observed, due to the displacement of excess charges from metal to the films as well as alignment of polar dipoles. Surface potential method has been employed to examine these surface polarization phenomena, and the distribution of space charges and distribution of electronic density of states have been determined. However, for further understanding of the nanometric interface phenomena, it is very helpful to develop an experimental method that can detect electrical and optical phenomena induced by the space charge formation. In this paper, it is shown that optical second harmonic generation measurement is effective through our experiment on phthalocyanine films deposited on Al and Au electrodes.
Lim, Eun-Ju,Manaka, Takaaki,Tamura, Ryosuke,Ohshima, Yuki,Iwamoto, Mitsumasa The Korean Institute of Electrical and Electronic 2008 Transactions on Electrical and Electronic Material Vol.9 No.4
Using pentacene field effect transistors (FETs) with Au source and drain electrodes, electron injection from the Au electrodes into the pentacene was investigated. The capacitance-voltage (C-V) and optical second harmonic generation (SHG) measurements were employed. Electron injection from the Au electrodes was suggested by the hysteresis behavior with the C-V characteristics and slowly decaying SHG signal under DC biasing, A mechanism of hole-injection assisted by trapped electrons is proposed. To confirm electron injection process, light-emitting behavior under the application of AC applied voltage was observed.
Triangular Spin Tubes with Bond Randomness
Yoko Miura,Hirotaka Manaka 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
We performed X-ray diffraction, magnetic susceptibility, and magnetization experiments on nonequilateraltriangular spin tubes composed of α-KCr1−xFexF4 (x = 00.13), which consisted ofone-dimensional Heisenberg antiferromagnets coexisting with geometrically-frustrated spin systemswith bond randomness. The variation of lattice parameters with x may indicate that the Fe3+ions constitute the low-spin state (S = 1/2). As a result of analyses of the frustration factor andthe spin-flop transition field, we found that the effect of geometrical spin frustration was enhancedand that the magnetic anisotropy was weakened as x was increased. Because these results areremarkably similar to the previous results for α-KCr1−xAlxF4, the effect of the chemical impuritysubstitutions, whether they are magnetic or nonmagnetic ions, on α-KCrF4 is clearly understood.