Printed with permission of The Institute of Pure and Applied Physics (IPAP)

JAPANESE JOURNAL OF APPLIED PHYSICS [Part2]

Abstracts of Express Letters
Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1267-L1270
Part 2, No. 41, 10 September 2005
©2005 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1310-L1312
Part 2, No. 43, 10 October 2005
©2005 The Japan Society of Applied Physics

Current-Driven Magnetization Switching in
CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

Fast Ambipolar Carrier Transport and Easy
Homeotropic Alignment in a Metal-Free
Phthalocyanine Derivative

Jun Hayakawa1,2,*, Shoji Ikeda2, Young Min Lee2, Ryutaro Sasaki2,
Toshiyasu Meguro2, Fumihiro Matsukura2, Hiromasa Takahashi1,2and Hideo Ohno2

Hiroaki Iino, Yukiko Takayashiki, Jun-ichi Hanna* andRichard J. Bushby1,**(Received September 2, 2005; accepted September 13, 2005; published September 30, 2005)(Received September 16, 2005; accepted September 28, 2005; published October 14, 2005)

Current-driven magnetization switching in low-resistance Co40Fe40B20/
MgO/Co40Fe40B20 magnetic tunnel junctions (MTJs) is reported. The critical-current densities Jc required for current-driven switching in samples
annealed at 270 and 300°C are found to be as low as 7.8 × 105 and 8.8
× 105 A/cm2 with accompanying tunnel magnetoresistance (TMR) ratiosof 49 and 73%, respectively. Further annealing of the samples at 350°C
increases TMR ratio to 160%, while accompanying Jc increases to 2.5 ×
106 A/cm2. We attribute the low Jc to the high spin-polarization of tunnel
current and small MsV product of the CoFeB single free layer, where Ms isthe saturation magnetization and V the volume of the free layer.
[DOI : 10.1143/JJAP.44.L1267]
Keywords: current-driven magnetization switching, magnetic tunnel
junction, MgO barrier, CoFeB

We have investigated charge carrier transport in the various phasesof the metal-free phthalocyanine derivative, 1,4,8,11,15,18,22,25-octaoctylphthalocyanine (8H2Pc), by the time-of-flight method. The discotic
columnar phase of 8H2Pc easily self-organizes in columns perpendicular tothe substrate when cooled from the isotropic phase. We found that welldefined transits were observed, not only for positive carriers, but also for
negative carriers. For the columnar rectangular phase at 85°C the holeand electron mobilities were very high at 0.2 and 0.3 cm2/(V·s), respectively. These mobilities depend on neither electric field nor temperature.
This ambipolar carrier transport was easily observed even in an ambient
atmosphere. Interestingly, the mobility in the isotropic phase was ofthe order of 10–3 cm2/(V·s) and did not depend on temperature, whichsuggests that the electronic conduction is governed by charge carriertransport in that phase as well. [DOI : 10.1143/JJAP.44.L1310]
Keywords: ambipolar carrier transport, discotic liquid crystal,electronic transport, phthalocyanine derivative, electron
mobility, time-of-flight method

1 Advanced Research Laboratory, Hitachi, Ltd., 1-280 Higashi-Koigakubo, Kokubunji, Tokyo
185-8601, Japan
2 Laboratory for Nanoelectronics and Spintronics, Research Institute of ElectricalCommunication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan* E-mail address: j-hayaka@rd.hitachi.co.jp

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1293-L1294
Part 2, No. 42, 10 October 2005
©2005 The Japan Society of Applied Physics

Interferometric Computed Tomography
Measurement and Novel Expression Methodof Discharged Flow Field with Unsteady Shock
Waves

Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, Nagatuta, Midori-ku,
Yokohama 226-8503, Japan
1 Centre for Self-Organizing Molecular Systems and School of Chemistry, University of Leed,
Leeds, LS2 9JT, U.K.
* E-mail address: hanna@isl.titech.ac.jp** E-mail address: R.J.Bushby@leeds.ac.uk

Masanori Ota*, Toshihiro Koga and Kazuo Maeno1,**(Received August 31, 2005; accepted September 15, 2005; published October 7, 2005)

A three-dimensinal interferometric computed tomography (CT)measurement has been applied to the unsteady and high-speed flow
field including shock waves. The flow field is induced by shock waves
discharged from a pair of circular open ends in the shock tube experiment.
The incident shock Mach number is 2.0 and discharged Mach number atthe open ends is 2.3. The computational fluid dynamics (CFD) simulation is
also applied to this flow field. To implement the detailed discussion of theexperimental result along with the CFD result, we propose a novel visualization method named as `distribution combined schlieren image (DCSI)’.
[DOI : 10.1143/JJAP.44.L1293]
Keywords: computed tomography, shock wave, three-dimensional
measurement, unsteady flow
Graduate School of Science and Technology, Chiba University, 1-33 Yayoi, Inage-ku, Chiba
263-8522, Japan
1 Faculty of Engineering, Chiba University, 1-33 Yayoi, Inage-ku, Chiba 263-8522, Japan* E-mail address: ota@graduate.chiba-u.jp** E-mail address: maeno@tu.chiba-u.jp

JSAP International No.14 (July 2006)21

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1313-L1315
Part 2, No. 43, 10 October 2005
©2005 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1393-L1396
Part 2, No. 46, 10 November 2005
©2005 The Japan Society of Applied Physics

Super-Accurate Velocity Measurement for
Evaluating TiO2–SiO2 Ultra-Low-Expansion
Glass Using the Line-Focus-Beam UltrasonicMaterial Characterization System

Hall Effect of Quasi-Hole Gas in Organic
Single-Crystal Transistors

Yuji Ohashi, Mototaka Arakawa and Jun-ichi Kushibiki*(Received September 8, 2005; accepted September 28, 2005; published October 14, 2005)

A method of improving the measurement accuracy of leaky surface
acoustic wave (LSAW) velocity for TiO2-doped SiO2 ultra-low-expansion glass using the line-focus-beam ultrasonic material characterization(LFB-UMC) system was investigated theoretically and experimentally. The
frequency dependence of the interference waveform attenuation in a V(z)curve obtained for the glass was calculated by considering the propagation
attenuation of LSAWs. The theoretical results revealed that the waveform
attenuation depends primarily on acoustic energy loss due to the waterloading effect on the specimen surface, and that the waveform attenuation decreases with decreasing frequency. Significant improvement of themeasurement accuracy was successfully demonstrated by using an LFB
ultrasonic device with a larger curvature radius R of the cylindrical sapphire
acoustic lens, R =2.0 mm, yielding an improved value of ±0.0020%
obtained at 75MHz, as compared to ±0.0053% obtained at 225MHz witha cylindrical lens of R=1.0 mm. [DOI : 10.1143/JJAP.44.L1313]
Keywords: line-focus-beam ultrasonic material characterization
system, velocity measurement, leaky surface acoustic
wave, ultra-low-expansion glass, TiO2-doped SiO2 glass,
CTE evaluation, EUVL system
Department of Electrical Engineering, Tohoku University, Sendai 980-8579, Japan*
E-mail address: kushi@ecei.tohoku.ac.jp

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1344-L1347
Part 2, No. 44, 10 October 2005
©2005 The Japan Society of Applied Physics

Bipolar Room Temperature Ferromagnetic
Semiconductor LaMnOP
Eiji Motomitsu1,2, Masahiro Hirano2, Hiroshi Yanagi3, Toshio Kamiya2,3and Hideo Hosono1,2,3,*(Received September 29, 2005; accepted October 2, 2005; published October 21, 2005)

We have discovered a high-temperature ferromagnetic semiconductorin which carrier polarity can be changed by impurity doping. A layered
compound of lanthanum manganese oxy-phosphide LaMnOP, which isa ferromagnetic material with a Curie temperature of ~320 K, exhibits
bipolar conduction by the substitution of La3+ sites with Ca2+ (hole doping)or Zr4+ (electron doping). Ferromagnetic interaction between the Mn2+
ions is changed in opposite direction by the carrier doping of a different
charge polarity; the Curie temperature (Tc) is monotonically increased
to ~600 K by the hole doping, whereas the ferromagnetic interaction isremarkably reduced by the electron doping and 5% Zr4+-doped LaMnOP
becomes paramagnetic. This finding provides an opportunity to realize
bipolar magnetic transistors that can operate at room temperature.
[DOI : 10.1143/JJAP.44.L1344]
Keywords: magnetic semiconductor, bipolar semiconductor, room
temperature ferromagnet, magnetoresistance, layered
structure, manganese oxy-phosphide
1 Frontier Collaborative Research Center, Tokyo Institute of Technology, Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
2 ERATO-SORST, JST, in Frontier Collaborative Research Center, Tokyo Institute of Technology,
Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
3 Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan* Corresponding author. E-mail address: hosono@msl.titech.ac.jp

22

JSAP International No.14 (July 2006)

Jun Takeya1,2,3,*, Kazuhito Tsukagoshi2,4, Yoshinobu Aoyagi2,5,
Taishi Takenobu3,6 and Yoshihiro Iwasa3,6(Received October 17, 2005; accepted October 19, 2005; published November 4, 2005)

Hall effect is detected in organic field-effect transistors, using appropriately shaped rubrene (C42H28) single crystals. It turned out that inverse
Hall coefficient, having a positive sign, is close to the amount of electricfield induced charge upon the hole accumulation. The presence of thenormal Hall effect means that the electromagnetic character of the surface
charge is not of hopping carriers but resembles that of a two-dimensionalhole-gas system. [DOI : 10.1143/JJAP.44.L1393]
Keywords: organic field-effect transistor, OFET, Hall effect, rubrene,
single-crystal FET
1 Materials Science Research Laboratory, CRIEPI, Tokyo 201-8511, Japan
2 RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
3 Institute for Material Reasearch, Tohoku University, Sendai 980-8577, Japan
4 PRESTO, Japan Science and Technology Corporation, Kawaguchi, Saitama 333-0012, Japan
5 Tokyo Institute of Technology, Yokohama 336-8502, Japan
6 CREST, Japan Science and Technology Corporation, Kawaguchi, Saitama 333-0012, Japan* E-mail address: takeya@criepi.denken.or.jp

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1414-L1416
Part 2, No. 47, 10 November 2005
©2005 The Japan Society of Applied Physics

Flat Band Voltage Shifts in Pentacene Organic
Thin-Film Transistors
Sung-Jin Kim1,2, Myeong-Seob So3, Min Chul Suh2,* andHo-Kyoon Chung2(Received September 1, 2005; accepted October 25, 2005; published November 11, 2005)

We have identified the mechanism of capacitance–voltage (C –V )hysteresis behavior often observed in pentacene organic thin-film transistors (OTFTs). The C–V characteristics were measured for pentacene OTFTs
fabricated on glass substrates with MoW as gate/source/drain electrodeand tetraethoxysilane (TEOS) SiO2 as gate insulator. The measurements
were made at room temperature and elevated temperatures. From theroom temperature measurements, we found that the hysteresis behavior
was caused by hole injection into the gate insulator from the pentacene
semiconductor for large negative gate voltages, resulting in the negative
flat-band voltage shift. However electron injection was observed only atelevated temperatures. [DOI : 10.1143/JJAP.44.L1414]
Keywords: C–V hysteresis behavior, organic TFT
1 School of Electrical Engineering #32, Seoul National University, Kwanak P.O. Box 34, Seoul
151-742, Korea
2 Corporate R&D Center, Samsung SDI Co., Ltd., 428-5, Gongse-Ri, Kiheung-Eup, Yongin-City,
Gyeonggi-Do 449-902, Korea
3 IXYS Corporation, 3540 Bassett St., Santa Clara, CA 95054-2704, U.S.A.
* E-mail address: mcsuh@samsung.com

Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1426-L1429
Part 2, No. 48, 10 November 2005
©2005 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1466-L1468
Part 2, No. 49, 10 November 2005
©2005 The Japan Society of Applied Physics

Precipitation of Amorphous Ferromagnetic
Semiconductor Phase in Epitaxially Grown
Mn-Doped Ge Thin Films

A Palm-Size Ultraviolet Laser Using a
Combination of a Monolithic Wavelength
Converter and an Optical Fiber

Satoshi Sugahara1,2,*, Kok Leong Lee1, Shinsuke Yada1 andMasaaki Tanaka1,3Satoshi Hatano1,2, Satoshi Ito2, Masashi Yoshimura1, Yusuke Mori1 andTakatomo Sasaki1(Received October 26, 2005; accepted November 1, 2005; published November 18, 2005)(Received November 8, 2005; accepted November 11, 2005; published November 25, 2005)

We investigated the origin of ferromagnetism in epitaxially grown
Mn-doped Ge thin films. Using low-temperature molecular beam epitaxy,
Mn-doped Ge films were successfully grown without precipitation of ferromagnetic Ge–Mn intermetallic compounds, such as Mn5Ge3. Magnetic
circular dichroism measurements revealed that the epitaxially grown
Mn-doped Ge films exhibited clear ferromagnetic behavior, but the Zeeman
splitting observed at the critical points was not induced by the s,p–dexchange interactions. High-resolution transmission electron microscopy andenergy dispersive X-ray spectroscopy analyses show phase separation of
amorphous Ge1-xMnx clusters with high Mn content from a Mn-free monocrystalline Ge matrix. Since amorphous Ge1-xMnx was characterized as ahomogeneous ferromagnetic semiconductor, the precipitation of the amorphous Ge1-xMnx clusters is the origin of the ferromagnetic semiconductor
behavior of the epitaxially grown Mn-doped Ge films.
[DOI : 10.1143/JJAP.44.L1426]
Keywords: spintronics, ferromagnetic semiconductor, magnetism,
germanium, manganese, magnetic circular dichroism,molecular beam epitaxy

We have developed a monolithic wavelength converter which iscomposed of optically contacted KTiOPO4 and GdxY1-xCa4O(BO3)3. It
generates an ultraviolet (UV) light at 0.355 µm just by the incidence of anear-infrared laser at 1.064 µm. Moreover, the converter is attached tothe end of an optical fiber which is delivering a near-infrared light to fabricate an extremely compact UV laser. A palm-size UV laser generates an
output power of 120 mW at a repetition rate of 60 kHz.
[DOI : 10.1143/JJAP.44.L1466]
Keywords: ultraviolet laser, monolithic wavelength converter, opticalfiber, nonlinear optical crystal, harmonic generation,
polarization

1 Department of Electronic Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan
2 PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama
332-0012, Japan
3 SORST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan* Present address: Department of Frontier Informatics, The University of Tokyo, 5-1-5
Kashiwanoha, Kashiwa, Chiba 277-8561, Japan. E-mail address: sugahara@cryst.t.u-tokyo.ac.jp

Uniaxial Alignment of Alq3 by Laser-Assisted
Molecular Beam Epitaxy

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1430-L1432
Part 2, No. 48, 10 November 2005
©2005 The Japan Society of Applied Physics

Highly Stable a-Si:H Films Deposited byUsing Multi-Hollow Plasma Chemical Vapor
Deposition
Kazunori Koga*, Toshihisa Inoue, Kouki Bando, Shinya Iwashita,
Masaharu Shiratani and Yukio Watanabe**(Received October 27, 2005; accepted November 2, 2005; published November 18, 2005)

Hydrogenated amorphous silicon (a-Si:H) films of high stability against
light exposure have been deposited by using a newly developed multihollow plasma chemical vapor deposition (CVD) method. Films deposited in the upstream region in the multi-hollow plasma CVD reactor are
a-Si:H films without incorporating a-Si:H nano-particles (clusters), while
those in the downstream region are a-Si:H films with incorporating clusters. A-Si:H films without clusters have a low initial defect density of 5 ×
1015 cm–3 and keep the value even after 100 h exposure of intense lightintensity of 240 mW/cm2, whereas a-Si:H films with clusters show a significant increase in defect density from its initial value of 5 × 1015 cm–3 to 2 ×
1016 cm–3 after 100 h light exposure. These results indicate that suppression of clusters incorporated into films is the key to realizing highly stablea-Si:H films. [DOI : 10.1143/JJAP.44.L1430]
Keywords: hydrogenated amorphous silicon films, light-induced
degradation, Staebler–Wronski effects, plasma CVD,
clusters, defect density

1 Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871,
Japan
2 Neoark Corporation, 2062-21 Nakano-machi, Hachioji, Tokyo 192-0015, Japan

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1469-L1471
Part 2, No. 49, 10 November 2005
©2005 The Japan Society of Applied Physics

Hisashi Ichikawa1, Koichiro Saiki1,2, Tadamasa Suzuki1,
Tetsuya Hasegawa1 and Toshihiro Shimada1(Received October 25, 2005; accepted November 4, 2005; published November 25, 2005)

The surface morphology of tris(8-hydroxyquinoline)aluminum(III) (Alq3)
epitaxially grown on KCl(001) was drastically changed by a simultaneous
blue laser irradiation during vacuum deposition. Needle-shaped microcrystals were aligned to the polarization direction of the laser, parallel to theKCl[010] axis. The origin of alignment was discussed in comparison withthe growth of non-polar organic molecular films, in which anisotropic
heating played an important role. [DOI : 10.1143/JJAP.44.L1469]
Keywords: Alq3, alignment, laser-assisted molecular beam epitaxy,
polar molecules, quinacridone
1 Department of Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
2 Department of Complexity Science and Engineering, The University of Tokyo, Kashiwa, Chiba
277-8561, Japan

Department of Electoronics, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan* E-mail address: koga@ed.kyushu-u.ac.jp** Professor Emeritus of Kyushu University.

JSAP International No.14 (July 2006)

23

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1503-L1505
Part 2, No. 50, 10 December 2005
©2005 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1509-L1511
Part 2, No. 50, 10 December 2005
©2005 The Japan Society of Applied Physics

Heteroepitaxial Growth of Rutile TiO2 on
GaN(0001) by Pulsed Laser Deposition

Fabrication of Nanoparticle Composite Porous
Films Having Ultralow Dielectric Constant

Taro Hitosugi1,2,*, Yasushi Hirose2, Junpei Kasai2, Yutaka Furubayashi2,
Makoto Ohtani2, Kiyomi Nakajima3, Toyohiro Chikyow3,
Toshihiro Shimada1,2 and Tetsuya Hasegawa1,2

Shota Nunomura*, Kazunori Koga, Masaharu Shiratani**,
Yukio Watanabe, Yoshinori Morisada1, Nobuo Matsuki1 andShingo Ikeda1(Received October 22, 2005; accepted November 15, 2005; published December 2, 2005)

Rutile TiO2(100) thin films have been grown on GaN(0001) surfaces
by using the pulsed laser deposition method. Reflection high-energy
electron diffraction (RHEED) measurements during the deposition clearly
revealed the layer-by-layer growth of TiO2 at a substrate temperature of
400°C under an oxygen pressure of 1 × 10–5 Torr. X-ray diffraction andatomic force microscopy confirmed that the obtained films have high crystallinity with atomically flat surfaces. Pole figure measurements revealed
the epitaxial relationship between TiO2 and GaN, namely that the in-plane–
TiO2〈010〉 axis aligns parallel to the GaN〈1010〉.
[DOI : 10.1143/JJAP.44.L1503]
Keywords: pulsed laser deposition, PLD, TiO2, GaN, epitaxial, thinfilm, gallium nitride, heteroepitaxial
1 Department of Chemistry, University of Tokyo, Tokyo 113-0033, Japan
2 Kanagawa Academy of Science and Technology (KAST), Kawasaki 213-0012, Japan
3 National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan* E-mail address: hitosugi@chem.s.u-tokyo.ac.jp

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1506-L1508
Part 2, No. 50, 10 December 2005
©2005 The Japan Society of Applied Physics

BGaN Micro-Islands as Novel Buffers for GaN
Hetero-Epitaxy*

Tetsuya Akasaka and Toshiki Makimoto(Received November 2, 2005; accepted November 11, 2005; published December 2, 2005)

BxGa1-xN (x~ 0.02) micro-islands provide novel buffers for growing
GaN films and AlGaN/GaN heterostructures on sapphire substrates.
These films and heterostructures show low threading dislocation density(TDD), low residual carrier concentration, and high two-dimensional
electron gas (2DEG) mobility: Non-doped GaN films had the TDD of 2
× 108 cm–2 and the residual electron concentration of 9.4 × 109 cm–3 at
433 K. AlGaN/GaN heterostructures exhibited 2DEG Hall mobility of 1720
and 13100 cm2 V–1 s–1 at 300 and 77 K, respectively. An almost constantsheet electron density (2.9–4.2 × 1012 cm–2) was obtained in the wide
temperature range from 500 to 77 K, indicating the absence of parallel
conduction in the GaN buffer layers. [DOI : 10.1143/JJAP.44.L1506]
Keywords: epitaxy, GaN, sapphire, BGaN, boron, dislocation, semiinsulating, AlGaN/GaN heterostructure, two-dimensional
electron gas, memory effect
NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi,
Kanagawa 243-0198, Japan* E-mail address: akasaka@nttbrl.jp

24

JSAP International No.14 (July 2006)(Received November 2, 2005; accepted November 15, 2005; published December 2, 2005)

Nanoparticle composite porous films having a dielectric constant of
ε r =1.7–3.5 have been deposited using plasma chemical vapor deposition. Nanoparticles as nano-building blocks and radicals as adhesives are
generated in plasmas, and nanoparticles are deposited together with radicals on substrates to form porous films. Nano-sized pores are dispersedin the films and their dielectric constants are controlled by the concentrations of pores, i.e., their porosities. The method is applicable to depositing
nanoparticle composite porous films for other applications.
[DOI : 10.1143/JJAP.44.L1509]
Keywords: plasma CVD, low-k, nanoparticles, LSI, ILD, porous film,
dielectric constant
Department of Electronics, Graduate School of Information Science and Electrical Engineering,
Kyushu University, Fukuoka 812-8581, Japan
1 ASM Japan K.K., Nagayama, Tama, Tokyo 206-0025, Japan* Present address: Research Center for Photovoltaics, National Institute of Advanced Industrial
Science and Technology, Tsukuba, Ibaraki 305-8568, Japan.
** E-mail address: siratani@ed.kyushu-u.ac.jp

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1550-L1552
Part 2, No. 51, 10 December 2005
©2005 The Japan Society of Applied Physics

Nano-Domain Engineering in LiNbO3 by
Focused Ion Beam
Xijun Li1,*, Kazuya Terabe1, Hideki Hatano1,2 and Kenji Kitamura1(Received November 2, 2005; accepted November 18, 2005; published December 9, 2005)

Domain tailored ferroelectric crystals are fascinating functional materials. This needs a simple and highly productive domain engineering
method at the micro- and nano-scales. In this letter, penetrating dot
domain of top and bottom diameters of 360 and 310 nm, respectively, in
100-µm-thick stoichiometric LiNbO3 by focused ion beam domain engineering has been demonstrated. Surface structures of the same size canbe fabricated by combining this focused ion beam domain engineeringwith HF-selective etching. [DOI : 10.1143/JJAP.44.L1550]
Keywords: domain engineering, focused ion beam, LiNbO3
1 National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
2 Corporate Research & Development Laboratories, Pioneer, 6-1-1 Fujimi, Tsurugashima,
Saitama 305-2288, Japan* E-mail address: Xijun.LI@nims.go.jp

Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1553-L1555
Part 2, No. 51, 10 December 2005
©2005 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L1-L3
Part 2, No. 1, 25 January 2006
©2006 The Japan Society of Applied Physics

Nanoholes Formed by Au Particles Digging
into GaAs and InP Substrates by Reverse
Vapor–Liquid–Solid Mechanism

Floating Nanodot Gate Memory Devices Basedon Biomineralized Inorganic Nanodot Array as
a Storage Node

Kouta Tateno*, Hideki Gotoh and Hidetoshi Nakano

Atsushi Miura1, Takio Hikono1, Takashi Matsumura1, Hiroshi Yano1,
Tomoaki Hatayama1, Yukiharu Uraoka1, Takashi Fuyuki1,*, Shigeo Yoshii2
and Ichiro Yamashita1,2,3(Received November 10, 2005; accepted November 18, 2005; published December 9, 2005)

Under a CBr4 gas supply, Au nanoparticles dig into GaAs and InP
substrates to form nanoholes through the reverse vapor–liquid–solidmechanism. The nanohole formation tends to proceed in the [111]B direction. For GaAs, straight holes sometimes appear in the [011] and [211]B
directions. This is due to the stable {111}B facets, which block the etching.
For InP, many straight holes are seen in the [111]B direction. For bothmaterials, direct etching of the surface also occurs. It is therefore necessary to find the optimum etching conditions for high selectivity to fabricate nanoholes. [DOI : 10.1143/JJAP.44.L1553]
Keywords: nanohole, GaAs, InP, CBr4, etching, scanning electron
microscope
NTT Basic Research Laboratories, NTT Corporation, Atsugi, Kanagawa 243-0198, Japan* E-mail address: ktateno@will.brl.ntt.co.jp

Jpn. J. Appl. Phys. Vol. 44 (2005) pp. L1570-L1572
Part 2, No. 52, 10 December 2005
©2005 The Japan Society of Applied Physics

Ammonothermal Growth of GaN on
an over-1-inch Seed Crystal
1,*

2

1,2

1

Tadao Hashimoto , Kenji Fujito , Makoto Saito , James S. Speck andShuji Nakamura1(Received November 22, 2005; accepted November 30, 2005; published December 16, 2005)

GaN was grown on a 3 × 4 cm2 oval-shaped GaN seed crystal by theammonothermal method. About 15-µm-thick GaN films were uniformly
grown on each side of the seed. The Ga-polar surface was filled with pits
whereas the N-polar surface was featureless. The photoluminescence (PL)characterization also indicated qualitatively uniform optical properties oneach side of the crystal. The PL emission from the Ga-face was dominatedby the yellow luminescence whereas that from the N-face showed dominant band-edge emission. These preliminary characterization indicatedqualitatively uniform growth of GaN on an over-1’’ seed and demonstrated the scalability of the ammonothermal method.
[DOI : 10.1143/JJAP.44.L1570]
Keywords: bulk GaN, ammonothermal growth, seeded growth,supercritical ammonia
1 Materials Department and ERATO/JST UCSB group, University of California, Santa Barbara,
CA 93106-5050, U.S.A.
2 Mitsubishi Chemical Corporation, Ushiku, Ibaraki 300-1295, Japan* E-mail address: tadao@engineering.ucsb.edu(Received November 23, 2005; accepted December 6, 2005; published online December 28, 2005)

The memory effect in floating nanodot gate field-effect-transistor(FET) was investigated by fabricating biomineralized inorganic nanodot
embedded metal–oxide–semiconductor (MOS) devices. Artificially biomineralized cobalt (Co) oxide cores accommodated in ferritins were utilized
as a charge storage node of floating gate memory. Two dimensional arrayof Co oxide core accommodated ferritin were, after selective protein
elimination, buried into the stacked dielectric layers of MOS capacitors
and MOSFETs. Fabricated MOS capacitors and MOSFETs presented a clear
hysteresis in capacitance–voltage (C–V) characteristics and drain current–
gate voltage (ID–VG) characteristics, respectively. The observed hysteresis in
C–V and ID–VG are attributed to the electron and hole confinement within
the embedded ferritin cores. These results clearly support the biologicallysynthesized cores work as charge storage nodes. This work proved thefeasibility of the biological path for fabrication of electronic device components. [DOI : 10.1143/JJAP.45.L1]
Keywords: ferritin, biomineralized nanodot, floating gate memory,
MOS device, memory effect
1 Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5
Takayama, Ikoma, Nara 630-0192, Japan
2 Advanced Technology Research Laboratories, Matsushita Electric Industrial Co., Ltd., 3-4
Hikaridai, Seika, Kyoto 619-0237, Japan
3 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology
Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan* E-mail address: fuyuki@ms.naist.jp

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L105-L107
Part 2, No. 4, 25 February 2006
©2006 The Japan Society of Applied Physics

Improvement of Critical Current Density
Uniformity for Interface-Modified Josephson
Junctions in Single Flux Quantum Circuits
Hironori Wakana*, Seiji Adachi, Yoshinobu Tarutani, Koji Tsubone,
Kohei Nakayama and Keiichi Tanabe(Received December 12, 2005; accepted December 26, 2005; published online January 20, 2006)

We have investigated the distribution of critical current density (Jc) forinterface-modified ramp-edge Josephson junctions in high-Tc single flux
quantum (SFQ) circuits. The 1σ spread of Jc in a toggle flip-flop test circuitwith a conventional layout is 26.7% and much larger than typical values
obtained for junction series-arrays. It is found that the large spread comesfrom the substantial dependence of J c on the size of base electrodes,
which seems associated with a difference in their surface temperatureduring deposition of a counter electrode and the formation mechanism ofinterface-modified junctions. By employing separated base electrodes withsimilar size in a circuit layout, the Jc spread was drastically reduced to 8.4%,
which is almost the same as typical values for junction arrays.
[DOI : 10.1143/JJAP.45.L105]
Keywords: SFQ circuit, high temperature superconductor, rampedge junction
Superconductivity Research Laboratory ISTEC, 10-13, Shinonome 1-chome, Koto-ku, Tokyo
135-0062, Japan* E-mail address: wakana@istec.or.jp

JSAP International No.14 (July 2006)25

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L128-L131
Part 2, No. 5, 25 February 2006
©2006 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L187-L189
Part 2, No. 7, 25 February 2006
©2006 The Japan Society of Applied Physics

Annealing and Aging Effect in
0.95 Pb(Zr0.52Ti0.48)O3–0.05 NiFe1.9Mn0.1O4
Particulate Magnetoelectric Composites

Ferroelectricity Down to at Least 2 nm in
Multiferroic BiFeO3 Epitaxial Thin Films*

Rashed Adnan Islam and Shashank Priya

H. Béa, S. Fusil, K. Bouzehouane, M. Bibes1, M. Sirena, G. Herranz,
E. Jacquet, J.-P. Contour and A. Barthélémy*(Received November 27, 2005; accepted December 27, 2005; published online January 27, 2006)(Received December 24, 2005; accepted January 25, 2006; published online February 10, 2006)

The results in this letter show the possibility of realizing a high magnetoelectric (ME) coefficient material by synthesizing the particulate composites of ferroelectric and ferromagnetic components using the annealing
and aging treatment. The ME composites were fabricated using a combination of conventional mixed oxide sintering and thermal treatment. The
thermal treatment constituted of annealing at temperature closer to calcination temperature (~800°C) followed by aging at lower temperatures(300–400°C). Microstructure of the fabricated samples was analyzed
using the X-ray mapping in scanning electron microscopy (SEM) and it was
found that NiFe1.9Mn0.1O4 (NFM) is distributed inside the Pb(Zr0.52Ti0.48)O3(PZT) grains on the length scales of 100 nm. The magnitude of piezoelectric constant (d33) and the dielectric constant exhibited significant variation
with aging time and temperature. It was found that the magnitude of ME
coefficient for PZT–5NFM sample increased from 37 to 56 mV/cm·Oe afterthermal treatment, an enhancement of ~50%.
[DOI : 10.1143/JJAP.45.L128]
Keywords: piezoelectric, magnetoelectric, ferroelectric, ferromagnetic, PZT, nickel ferrite

We report here on the preservation of ferroelectricity down to 2 nm
in BiFeO3 ultrathin films. The electric polarization can be switched reversibly and is stable over several days. Our findings bring insight on thefundamental problem of ferroelectricity at low thickness and confirm thepotential of BiFeO3 as a lead-free ferroelectric and multiferroic material fornanoscale devices. [DOI : 10.1143/JJAP.45.L187]
Keywords: BiFeO3, multiferroic, ferroelectric, critical thickness,piezoelectric force microscope

Material Science and Engineering, University of Texas at Arlington, Arlington, TX 76019, U.S.A.
* E-mail address: spriya@uta.edu

Billel Kalache1, Pere Roca i Cabarrocas1 andAnna Fontcuberta i Morral1,2,*

Unité Mixte de Physique CNRS-Thales, Route Départementale 128, 91767 Palaiseau, France
1 Institut d’Electronique Fondamentale, Université Paris-Sud, 91405 Orsay, France* E-mail address: agnes.barthelemy@thalesgroup.com

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L190-L193
Part 2, No. 7, 10 February 2006
©2006 The Japan Society of Applied Physics

Observation of Incubation Times in
the Nucleation of Silicon Nanowires Obtainedby the Vapor–Liquid–Solid Method(Received January 12, 2006; accepted January 25, 2006; published online February 10, 2006)

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L132-L134
Part 2, No. 5, 25 February 2006
©2006 The Japan Society of Applied Physics

Self-Consistent Modeling of Feature Profile
Evolution in Plasma Etching and Deposition
Takashi Shimada*, Takashi Yagisawa and Toshiaki Makabe**(Received December 28, 2005; accepted December 31, 2005; published online January 27, 2006)

We investigate the relationship between local wall charging andthe feature profile in a SiO2 trench pattern, by considering the transport of electrons, positive ions, and neutral radicals from the two-dimensional sheath structure in a two frequency-capacitively coupled plasma
in CF4(5%)/Ar. Emphasis is given on the influence of both charging andneutral radical accumulation inside the SiO2 trench during plasma etching.
Feature profiles of the SiO2 trench are estimated by the Level Set method
under conditions with/without charging and neutral deposition.
[DOI : 10.1143/JJAP.45.L132]
Keywords: SiO2 etching, feature profile evolution, plasma process,surface charging, competitive process
Department of Electronics and Electrical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku,
Yokohama 223-8522, Japan* E-mail address: shimada@mkbe.elec.keio.ac.jp** E-mail address: makabe@mkbe.elec.keio.ac.jp

26

JSAP International No.14 (July 2006)

We report the observation of a characteristic incubation time in thegrowth of silicon nanowires using the vapor–liquid–solid growth mechanism. This incubation time manifests itself during the growth process as acharacteristic time delay in the range of several seconds to minutes, prior
to which no nanowires are formed. The observation is in excellent agreement with a theoretical model based on the diffusion of silicon throughthe catalyst, which predicts the presence of an incubation time, as determined by diffusion of the growth constituent through the solid catalyst.
Furthermore the theoretical dependence of the incubation time on theactivation energy is derived, and validated experimentally for the first timeby measuring the incubation times of silicon nanowires obtained by chemical vapor deposition for both gold and copper as a catalyst. The experimentally observed incubation times are in excellent agreement with thetheoretically predicted incubation times. The reported incubation times
are a universal feature of vapor–liquid–solid growth and can be applied
to any other metal/semiconductor system for the synthesis of nanowires
and provide a novel route to determine the phase space for nanowiresynthesis. [DOI : 10.1143/JJAP.45.L190]
Keywords: nanowire, silicon, growth mechanism, VLS
1 LPICM, Ecole Polytechnique, 91128 Palaiseau Cedex, France
2 Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, 85748
Garching, Germany* E-mail address: annafm@wsi.uni-muenchen.deAbstracts of Express Letters

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L217-L219
Part 2, No. 8, 25 March 2006
©2006 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L282-L284
Part 2, No. 10, 25 March 2006
©2006 The Japan Society of Applied Physics

Control of Measurement Environments forHigh-Efficiency Organic Photovoltaic Cells

Ideal Liquid Crystal Display Mode Using
Achiral Banana-Shaped Liquid Crystals

Tetsuya Taima*, Susumu Toyoshima, Kohjiro Hara, Kazuhiro Saito andKiyoshi Yase1

Yoshio Shimbo, Yoichi Takanishi, Ken Ishikawa, Ewa Gorecka1, Damian
Pociecha1, Jozef Mieczkowski1, Kinga Gomola1 and Hideo Takezoe*(Received December 15, 2005; accepted January 19, 2006; published online February 17, 2006)(Received February 3, 2006; accepted February 15, 2006; published online March 3, 2006)

To fabricate a high-performance of organic photovoltaic (PV) cells, notonly short-circuit photocurrent density (Isc), but also fill factor (FF) shouldbe improved. Here, we improved FF by controlling the measurement environment. Because of the prevention of electron trapping by oxygen in theorganic semiconducting layer, FF in vacuum environment increased 40%
compared with that in air under 80 mW/cm2 irradiation of air mass 1.5
global solar conditions at room temperature. Finally, we obtained a power
conversion efficiency of 3.6% by controlling the measurement environment and the optimization of the organic PV cell structure, where FF was
markedly improved up to 0.61. [DOI : 10.1143/JJAP.45.L217]
Keywords: organic thin-film solar cell, organic semiconductor,
photovoltaic, fill factor, ZnPc, C60

We have demonstrated a totally new liquid crystal display (LCD) modeusing a smectic A-like phase of banana-shaped molecules. An in-planeelectric field was applied to homeotropically aligned cells, resulting in fastpolarization reorientation and the associated birefringence. The reported
LCD mode has all the advantages of the existing LCD modes, such asvertical alignment (VA), in-plane switching (IPS), ferroelectric LC (FLC) or
antiferroelectric LC (AFLC) and V-shaped switching (VS) modes; namely,
fast response of the order of 100 µs, high contrast ratio (3000:1), wideviewing angle, continuous gray level, and small threshold voltage. These
performances originate from the cooperative motion of bent moleculeswith quasi-long-range order of dipoles based on a two-dimensional
Langevin process. [DOI : 10.1143/JJAP.45.L282]
Keywords: liquid crystal display, response time, contrast ratio,
viewing angle, Langevin process, ferroelectric switching,
SHG

Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology(AIST), AIST Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
1 Photonics Research Institute, National Institute of Advanced Industrial Science and Technology(AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan* Corresponding author. E-mail address: tetsuya-taima@aist.go.jp

Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama,
Meguro-ku, Tokyo 152-8552, Japan
1 Chemistry Department, Warsaw University, Al. Zwirki i Wigury 101, 02-089 Warsaw, Poland* E-mail address: htakezoe@o.cc.titech.ac.jp

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L279-L281
Part 2, No. 10, 25 March 2006
©2006 The Japan Society of Applied Physics

Fabrication of a Vertical-Channel Double-Gate
Metal–Oxide–Semiconductor Field-EffectTransistor Using a Neutral Beam Etching
Kazuhiko Endo, Shuichi Noda1, Meishoku Masahara, Tomohiro Kubota1,
Takuya Ozaki1, Seiji Samukawa1, Yongxun Liu, Kenichi Ishii,
Yuki Ishikawa, Etsuro Sugimata, Takashi Matsukawa,
Hidenori Takashima, Hiromi Yamauchi and Eiichi Suzuki(Received February 2, 2006; accepted February 11, 2006; published online March 3, 2006)

A vertical ultrathin-channel (UTC) formation process using a
low-energy neutral beam etching (NBE) for a double-gate (DG) metal–
oxide–semiconductor field-effect transistor (MOSFET) is proposed for the
first time. The NBE can perfectly eliminate the charge build-up and photon
radiation damages from the plasma. By utilizing the NBE, fin-type vertical
MOSFETs with damage-less smooth sidewalls were successfully fabricated.
The fabricated FinFETs realized higher electron mobility than that using a
conventional reactive ion etching. The improved mobility is well explainedby the atomically-flat surface utilizing by the NBE.
[DOI : 10.1143/JJAP.45.L279]
Keywords: double-gate MOSFET, neutral beam, etching, damageless, mobility
National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono,
Tsukuba, Ibaraki 305-8568, Japan
1 Institute of Fluid Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8557,
Japan

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L307-L309
Part 2, No. 11, 25 March 2006
©2006 The Japan Society of Applied Physics

Avalanche Characteristics of the Te-Doped
Amorphous Se Photoconductive Target for aComplementary Metal–Oxide–Semiconductor
Image Sensor
Wug-Dong Park and Kenkichi Tanioka1(Received February 20, 2006; accepted February 22, 2006; published online March 10, 2006)

We investigated the avalanche characteristics of the amorphous Se(a-Se) high-gain avalanche rushing amorphous photoconductor (HARP)
photoconductive target for a complementary metal–oxide–semiconductor(CMOS) image sensor. To improve the quantum efficiency of the a-Se
photoconductive target, thin a-Se layer was doped with Te. Te concentration of the Te-doped a-Se layer within the 0.4-µm-thick a-Se HARP film
was 15 wt.%. In the avalanche multiplication phenomena of the a-Se
HARP target, the photocurrent is affected by the ionization of the a-Se
atom due to hole accelerated at a high electric field. The avalanche multiplication factor and hole ionization rate of the Te-doped a-Se HARP target
exponentially increased with increasing target voltage. Also the spectral
response of the Te-doped a-Se HARP photoconductive target for a CMOS
image sensor was dependent on the target voltage.
[DOI : 10.1143/JJAP.45.L307]
Keywords: photoconductive layer, photoconductive target,
photocurrent, a-Se, avalanche multiplication factor, holeionization rate, spectral response, quantum efficiency
School of Electronic Engineering, Dongyang University, 1 Kyochon-Dong, Punggi-Up, Youngju,
Kyungbuk 750-711, Korea
1 Advanced Broadcasting Devices Research Division, NHK Science and Technical ResearchLaboratories, 1-10-11 Kinuta, Setagaya-ku, Tokyo 157-8510, Japan

JSAP International No.14 (July 2006)

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Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L310-L312
Part 2, No. 11, 25 March 2006
©2006 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L384-L386
Part 2, No. 14, 25 April 2006
©2006 The Japan Society of Applied Physics

High-Speed Resistive Switching of TiO2/TiN
Nano-Crystalline Thin Film

Polarity Determination of InN by Atomic
Hydrogen Irradiation

Masayuki Fujimoto*, Hiroshi Koyama, Yasunari Hosoi1, Kazuya Ishihara1
and Shinji Kobayashi1

Yuya Hayakawa, Daisuke Muto, Hiroyuki Naoi1, Akira Suzuki2,
Tsutomu Araki and Yasushi Nanishi(Received February 8, 2006; accepted February 20, 2006; published online March 10, 2006)(Received February 28, 2006; accepted March 10, 2006; published online March 31, 2006)

High-speed resistive switching was observed in a TiO2/TiN nanocrystalline thin film sandwiched between platinum electrodes. A low
resistance state was achieved by applying a single negative 2.0-V amplitude 20-ns wide electric pulse, while a high resistance state was achieved
by applying a single positive 2.2-V amplitude 30-ns wide electric pulse.
So-called forming process, heating bit material by current flow to form
conductive filament path before the resistive switching operation was
not required. There was an approximately 40,000% increase in resistivechange that was repeatedly obtained in the system.
[DOI : 10.1143/JJAP.45.L310]
Keywords: resistive switching, TiN, TiO2, nano-crystalline, platinum
electrode, thin film

We have succeeded in determining the polarity of InN by atomic
hydrogen (H*) irradiation for the first time. The surface of N- and In-polar
InN films was exposed to H* at nominal temperatures between 200 and
500°C for 30 to 90 min. After H* irradiation, indium (In) droplets appearedon the surface of N-polar InN, whereas they did not appear on In-polar
InN. As the sample temperature was raised, the size of the In droplets on
N-polar InN became bigger; furthermore the thickness of the remaining
InN layers decreased. On the contrary, the thickness of In-polar InN layers
remained unchanged. The mechanisms for these polarity-dependent
surface behaviors are discussed. We propose H* irradiation as one of thepromising methods for the polarity determination of InN.
[DOI : 10.1143/JJAP.45.L384]
Keywords: InN, polarity, atomic hydrogen irradiation

Graduate School of Electronic Science and Technology, Shizuoka University, 3-5-1 Jyouhoku,
Hamamatsu, Shizuoka 432-8561, Japan
1 Advanced Technology Development Laboratories, Sharp Corporation, 2613-1 Ichinomoto-cho,
Tenri, Nara 632-8567, Japan* E-mail address: fujimoto@cjr.shizuoka.ac.jp

Department of Photonics, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577,
Japan
1 Center for Promotion of the COE Program, Ritsumeikan University, 1-1-1 Noji-Higashi,
Kusatsu, Shiga 525-8577, Japan
2 Research Organization of Science and Engineering, Ritsumeikan University, 1-1-1 Noji-Higashi,
Kusatsu, Shiga 525-8577, Japan

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L313-L315
Part 2, No. 11, 25 March 2006
©2006 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L387-L389
Part 2, No. 14, 25 April 2006
©2006 The Japan Society of Applied Physics

Organic Field-Effect Transistors Based on
Oligo-p-Phenylenevinylene Derivatives

Enhancement of Magneto-Optical Properties
of Anatase Co:TiO2 Co-Doped with Nb

Takeshi Yasuda*, Masatoshi Saito1, Hiroaki Nakamura1 and Tetsuo Tsutsui

Go Kinoda1, Taro Hitosugi1,2,*, Yukio Yamamoto1, Yutaka Furubayashi1,
Kazuhisa Inaba1,3, Yasushi Hirose1, Toshihiro Shimada1,2 andTetsuya Hasegawa1,2(Received February 17, 2006; accepted February 22, 2006; published online March 10, 2006)

Organic field-effect transistors (OFETs) have been fabricated using
thermally vacuum-evaporated films of two oligo-p-phenylenevinylenes,
1,4-bis(4-methylstyryl)benzene (4MSB), and 1,4-bis(2-methylstyryl)benzene(2MSB). From the electrical characteristics of the OFETs, a field-effectmobility of the 4MSB films was calculated to be 0.13 cm2 V–1 s–1, while
the mobility of the 2MSB films was 1.0 × 10–4 cm2 V–1 s–1. The mobility of
4MSB is comparable to that of widely studied organic semiconductors,
such as oligothiophenes and pentacene. From atomic force microscopy
and X-ray diffraction, densely-packed submicron-size grains with a highdegree of molecular order were observed in a vacuum-sublimed 4MSB
film. [DOI : 10.1143/JJAP.45.L313]
Keywords: organic field-effect transistor, oligo-p-phenylenevinylene,
mobility, organic semiconductor, oligomer
Department of Applied Science for Electronics and Materials, Graduate School of Engineering
Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
1 Central Research Laboratories, Idemitsu Kosan Co., Ltd., Sodegaura, Chiba 299-0293, Japan* Corresponding author. E-mail address: yasuda@asem.kyushu-u.ac.jp(Received February 24, 2006; accepted March 10, 2006; published online March 31, 2006)

We have fabricated Ti0.95-xNbxCo0.05O2 thin films by the pulsed laser
deposition technique. Carrier density was found to be almost identicalto the Nb concentration up to x=0.06, indicating that doped Nb atoms
generate carriers with >80% efficiency. In this doping range, magnetooptical properties were significantly enhanced by Nb-doping. The remanent Faraday rotation at a wavelength of 405 nm was as high as 5.6 ×
103 deg/cm, which is approximately one order of magnitude higher thanthat of a film free of Nb-doping. The present results support the hypothesis that conduction electrons play an essential role in the ferromagnetismof Co-doped TiO2. [DOI : 10.1143/JJAP.45.L387]
Keywords: TiO2, ferromagnetism, diluted magnetic semiconductor,
DMS, epitaxial, thin film, Co-doping, pulsed laser deposition, PLD
1 Kanagawa Academy of Science and Technology (KAST), Kawasaki 213-0012, Japan
2 Department of Chemistry, University of Tokyo, Tokyo 113-0033, Japan
3 Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503,
Japan* E-mail address: hitosugi@chem.s.u-tokyo.ac.jp

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JSAP International No.14 (July 2006)