Research Activities
in
NTT Basic Research Laboratories
Volume 17
Fiscal 2006

September 2007
NTT Basic Research Laboratories,
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From Science to Innovative Technology
We at NTT Basic Research Laboratories (BRL)
are extremely grateful for your interest and support
with respect to our research activities.
The missions of BRL are 1) to create newconcepts and guiding principles for network andinformation-processing technologies that will allow
us to overcome capacity and security related
limitations, and 2) to extend our knowledge of thescience and technology that will lead to medium andlong-term innovations. We believe that this willboth contribute to the success of NTT's business andpromote advances in science that will ultimately
benefit all mankind. To achieve these goals, wemust continuously deliver research output in atimely and well-directed manner. To this end, we
adopt a three-tier research theme classification withappropriate management strategies tailored for each:High-priority research: Work where speed is critically important and that is generally
pursued as strategic projects in collaboration with in-house or outside partners.



Exploratory research: Exploratory work that is likely to evolve into high-priority
research projects.

Innovative research: Work that goes beyond conventional technology to achieve
fundamental and innovative breakthroughs.

BRL's high-priority research themes are currently focused on quantum information
processing and nano-bio research. The former aims at clarifying the nature of electrons andphotons, which are the basis for the quantum mechanics of light and matter. The goal is todevelop practical applications such as quantum cryptography and quantum computing toovercome capacity and security limitations. By exploiting our expertise in quantum optics,
quantum solid-state physics, nano-fabrication, and other key technological areas, BRL has
achieved remarkable successes in unraveling the mysteries that lie behind a variety of systems
including quantum dots, superconducting devices, and cold atoms. Based on these achievements,
we are examining the practical viability of quantum cryptography and quantum computers incollaboration with many research institutes, both in Japan and overseas. The aim of ournano-bio research is to create a new area of science through the fusion of neuroscience,
biomolecular science, and nanotechnology. This should enable the realization of novel devices
that integrate molecular structures, proteins, and artificial nanostructures.
As an example of exploratory researches, one project is investigating quantized mechanicalmotion in nanometer scale structures together with their quantum electronic properties. BRL
researchers are also undertaking exploratory work on techniques that will allow us tomanipulate nanostructures at will. These techniques include a method for cutting carbon
nanotubes at desired points. Researchers working on spintronics are seeking better

understanding and control of electron spin states with a view to achieving revolutionary
developments.
Lastly, we are also pursuing highly innovative research that has the groundbreaking potential
to overturn conventional technologies in the near future. The great progress made on
wide-bandgap semiconductors, single-electron devices, photonic crystals, and carbon thin films
convinces us that they will ultimately displace existing technologies.
To conduct these research activities, BRL is collaborating with many universities andresearch institutes in Japan, US, Europe, and Asia as well as other NTT laboratories. BRL also
regularly organizes international symposia and conferences at NTT Atsugi R&D Center. In
February 2007, we hosted the International Conference on Nanoelectronics, Nanostructures andCarrier Interactions, which attracted the participation of more than 140 researchers from aroundthe world. It gives us immense pleasure to fulfill our mission of being an open laboratory in thisway, and to disseminate our research output throughout the world.
This report highlights the main achievements and research activities of NTT Basic ResearchLaboratories in 2006. We hope that it will help to promote awareness of the work undertaken at
NTT BRL, and enhance future collaboration.

Junji Yumoto
Director
NTT Basic Research Laboratories
3-1 Morinosato Wakamiya, Atsugi,
Kanagawa 243-0198, Japan
Phone: +81 46 240 3300
Fax

: +81 46 270 2358

Contents
page

Member List .............................................................................................................................................. 1
I. Research Topics◆Overview of Research in Laboratories ................................................................................................... 15◆Materials Science Laboratory................................................................................................................. 16♦ Aluminum Nitride Light-Emitting Diodes with the Shortest Wavelength♦ Diamond FET with Maximum Frequency of Oscillation of 120 GHz♦ High Breakdown Voltage with Low On-state Resistance of InGaN/GaN Vertical Conducting
Diodes♦ Ultraviolet Luminescence from Hexagonal BN Heteroepitaxial Layers♦ Single-walled Carbon Nanotube Synthesis Using Gold, Silver and Copper Nanoparticle Catalysts♦ Chemical States of Metal Catalysts in CVD Ambient for Single-walled Carbon Nanotube
Growth♦ Position Control of Nanowires Using Catalysts Islands Arranged at Surface Atomic Steps♦ Microchannel Device Using Self-Spreading Lipid Bilayer as Molecule Carrier♦ Self-assembly of Vesicle Nanoarrays on Si: A Potential Route to High-density Functional
Protein Arrays♦ Ion Conducting Polymer Microelectrodes for Interfacing with Neural Networks♦ Ion Sensing Assisted by Assembly of Gold Nanorods♦ Terahertz Spectroscopy of Biomolecules in Nanospace◆Physical Science Laboratory .................................................................................................................. 28♦ Gain-cell Dynamic Random-access Memory with Long Data Retention♦ Detection of Single Boron Acceptor in Silicon Nano-transostor♦ Electron Phase Sensing in a High Q Mechanical Resonator♦ Block Copolymer Lithography toward 16-nm-technology Nodes♦ Single-electron Counting Device♦ Density-of-states Imaging in Semiconductor Heterostructures♦ Quantum Transport in Silicon-On-Insulator Structures♦ Decoherence of a Superconducting Flux Qubit♦ Aharonov-Casher Effect by Spin-orbit Interaction♦ Detection of Domain Wall in a Permalloy Wire Using a Semiconductor and Ferromagnetic
Hybrid Structure♦ Controllable Coupling between Flux Qubit and Nanomechnical Resonator by
Magnetic Field◆Optical Science Laboratory .................................................................................................................... 39♦ 10 GHz Clock Quantum Cryptography Experiment♦ Differential-phase Quantum Key Distribution Experiment Using a Series of
Quantum Entangled Photon Pairs♦ Pair-wise Entanglement for Characterizing Quantum Phase Transition♦ Optical Properties of GaAs Quantum Dots Formed in (Al,Ga)As Nanowires♦ Quantum Dot Laser Using Photonic Crystal Nanocavity♦ Spatiotemporally Resolved Soft X-Ray Absorption Spectroscopy of a Femtosecond Laser
Ablation Plume♦ Time Resolved Measurement of Photonic Crystal Optical Nanocavity♦ Coupled Resonator Waveguide Formed by Ultrahigh-Q Si Photonic Crystal
Nano-resonators♦ Optical Micromachine by Ultrahigh-Q Nanocavities

II. Data◆ The 4th Advisory Board......................................................................................................................... 49◆ International Conference on Nanoelectronics, Nanostructures and Carrier Interactions .......................... 50◆ Award Winners’ List .............................................................................................................................. 51◆ In-house Award Winners’ List................................................................................................................ 53◆ List of Visitors’ Talks............................................................................................................................. 54◆ Research Activities of Basic Research Laboratories in 2006 ................................................................ 58◆ List of Invited Talks at International Conferences................................................................................. 60

Cover photograph:Long Time Photon Caging by Ultrahigh Q Photonic Crystal Optical Nanocavity
Light is fundamentally difficult to confine or stop in a small space. We succeeded to store photons for an
extremely long 1 ns in a very small space by using photonic crystal nanocavity. At the center of the image,a scanning electron microscope image of the ultrahigh Q photonic crystal optical nanocavity is shown, andthe electrical field of the trapped photons in a cavity is illustrated at the bottom left.

Member List
As of March 31, 2007(*/ left NTT BRL in the middle of the year)

NTT Basic Research Laboratories
Director,Dr. Junji YumotoResearch Planning Section

Executive Research Scientist,

Dr. Itaru Yokohama

Senior Research Scientist,

Dr. Hideki Gotoh

Senior Research Scientist,

Dr. Koji Muraki

Senior Research Scientist, Supervisor,

Dr. Yuichi Harada

NTT R&D Fellow

Prof. Yoshihisa Yamamoto(Stanford University, U.S.A)
Dr. Hideaki Takayanagi(Tokyo University of Science)

NTT Research Professor

Prof. Masahito Ue d a(Tokyo Institute of Technology)
Dr. Fujio Shimizu(The University of Electro-Communications)
Prof. Shintaro Nomura(University of Tsukuba)Prof. Kyo Inoue(Os aka Uni v er si t y )－1－Materials Science Laboratory

Executive Manager,

Dr. Keiichi Torimitsu
Dr. Hiroo Omi
Dr. Katsuhiro Ajito Dr. Yuko Ueno
Dr. Isao Tomita
Dr. Rakchanok, Rungsawang*Thin-Film Materials Research Group:
Dr. Toshiki Makimoto (Group Leader)
Dr. Makoto Kasu
Dr. Yasuyuki Kobayashi
Dr. Tetsuya Akasaka
Dr. Kazuhide Kumakura
Dr. Yoshitaka Taniyasu
Dr. Kenji Ueda
Dr. Alexandre Tallaire

Dr. Hisashi Sato*
Dr. Shin-ichi Karimoto
Dr. Atsushi Nishikawa

Low-Dimensional Nanomaterials Research Group:
Dr. Yoshihiro Kobayashi (Group Leader)
Dr. Fumihiko Maeda
Dr. Hiroki Hibino
Dr. Satoru Suzuki
Akio Tokura

Dr. Kawamura Tomoaki*
Dr. Ilya Sychukov

Molecular and Bio Science Research Group:
Dr. Keiichi Torimitsu (Group Leader)
Dr. Keisuke Ebata
Dr. Kazuaki Furukawa
Dr. Nahoko Kasai
Dr. Akiyoshi Shimada
Dr. Yoshiaki Kashimura
Touichiro Goto
Dr. Mimei Kobayashi*
Dr. Yoichi Shinozaki

Dr. Koji Sumitomo
Dr. Hiroshi Nakashima
Dr. Tobias Nyberg*
Dr. Jonas Rundqvist－2－

Physical Science Laboratory

Executive Manager,

Dr. Hiroshi Yamaguchi
Dr. Yoshiro Hirayama*
Dr. Yukinori Ono
Takeshi Karasawa

Nanodevices Research Group:
Dr. Akira Fujiwara (Group Leader)
Dr. Masashi Uematsu*
Dr. Hiroyuki Kageshima
Dr. Mohammed Khalafalla
Nanostructure Technology Research Group:
Dr. Hiroshi Yamaguchi (Group Leader)
Dr. Masao Nagase
Dr. Kenji Yamazaki
Junzo Hayashi
Dr. Hajime Okamoto
Dr. Koji Onomitsu
Quantum Solid State Physics Research Group:
Dr. Toshimasa Fujisawa (Group Leader)
Dr. Kiyoshi Kanisawa
Dr. Satoshi Sasaki
Dr. Toshiaki Hayashi
Dr. Takeshi Ohta
Dr. Kei Takashina
Dr. Vincent Renard*
Superconducting Quantum Physics Research Group:
Dr. Kouichi Semba (Group Leader)Dr. Hayato Nakano
Dr. Tetsuya Mukai
Dr. Shiro Saito
Dr. Kousuke Kakuyanagi
Dr. Alexander Kasper*
Spintronics Research Group:
Dr. Tatsushi Akazaki (Group Leader)
Dr. Yuichi Harada
Dr. Hiroyuki Tamura
Dr. Masumi Yamaguchi
Toshiyuki Kobayashi－3－

Dr. Katsuhiko Nishiguchi

Toru Yamaguchi
Dr. Imran Mahboob

Dr. Kyoichi Suzuki
Dr. Norio Kumada
Dr. Paula Giudici

Hirotaka Tanaka
Dr. Ying-Dan Wang

Dr. Yoshiaki Sekine
Dr. Hideomi HashibaOptical Science Laboratory

Executive Manager,

Dr. Yasuhiro Tokura
Dr. Atsushi Yokoo

Quantum Optical State Control Research Group:
Dr. Yasuhiro Tokura (Group Leader)
Dr. Kaoru Shimizu
Kazuhiro Igeta
Dr. Makoto Yamashita
Dr. Hiroyuki Shibata
Dr. Fumiaki Morikoshi
Dr. Toshimori Honjo
Daisuke Hashimoto
Dr. Jens Tobiska
Quantum Optical Physics Research Group:
Dr. Hidetoshi Nakano (Group Leader)
Dr. Tetsuomi Sogawa
Dr. Tadashi Nishikawa
Dr. Kouta Tateno
Dr. Takehiko Tawara
Dr. Atsushi Ishizawa
Dr. Haruki Sanada
Dr. Guoquiang Zhang
Photonic Nano-Structure Research Group:
Dr. Masaya Notomi (Group Leader)
Dr. Satoki Kawanishi
Dr.Eiichi Kuramochi
Dr. Akihiko Shinya
Dr. Masao Kato*
Dr. Heongkyu Ju*－4－

Masami Kumagai
Dr. Hiroki Takesue
Dr. Kiyoshi Tamaki

Hidehiko Kamada
Dr. Katsuya Oguri
Dr. Nicholas Cade*Dr. Hideaki Taniyama
Dr. Takasumi Tanabe

Distinguished Technical Member

Hiroshi Yamaguchi was born in Osaka on October 30, 1961. He received the B.E., M.S. in physics andPh.D. degrees in engineering from the Osaka University in 1984, 1986 and 1993, respectively. He joined
NTT Basic Research Laboratories in 1986. He was a visiting research fellow in Imperial College,
University of London, U.K. during 1995-1996. Since 1986 he has engaged in the study of compound
semiconductor surfaces prepared by molecular beam epitaxy mainly using electron diffraction and scanningtunneling microscopy. His current interests are mechanical and elastic properties of semiconductor low
dimensional structures. He is a research coordinator of NEDO international joint research project(Nano-elasticity) during 2001-2004 and a member of the Japan Society of Applied Physics and the PhysicalSociety of Japan. He was awarded the paper awards of the Japanese Society of Applied Physics in 1989 and2004. From 2006, he is a guest professor in Tohoku University.

Distinguished Technical Member

Toshimasa Fujisawa was born in Tokyo on May 23, 1963. He received the B.E., M.S. and Ph.D. degrees inelectrical engineering from Tokyo Institute of Technology in 1986, 1988 and 1991, respectively. He joined
NTT Basic Research Laboratories in 1991. He was a guest scientist in Delft University of Technology,
Delft, the Netherlands during 1997-1998. Since 2003, he is also a guest associate professor at Tokyo
Institute of Technology. Since 1991 he has engaged in the study of semiconductor fine structures fabricatedby focused-ion-beam technique and electron-beam lithography technique, transport characteristics ofsemiconductor quantum dot. His current interests are single-electron dynamics in quantum dots, and theirapplication to quantum information technologies. He received Sir Martin Wood Prize in 2003 and JSPS
(Japan Society for the Promotion of Science) Award in 2005. He is a member of the Japan Society ofApplied Physics, and the Physical Society of Japan.

－5－Distinguished Technical Member

Masaya Notomi was born in Kumamoto, Japan, on 16 February 1964. He received his B.E.,
M.E. and Dr. Eng. degrees in applied physics from University of Tokyo, Tokyo, Japan in 1986,
1988, and 1997, respectively. In 1988, he joined NTT Optoelectronics Laboratories. Since
then, his research interest has been to control the optical properties of materials and devices
by using artificial nanostructures, and engaged in research on semiconductor quantum
wires/dots and photonic crystal structures. He has been in NTT Basic Research Laboratories
since 1999, and is currently working on light-propagation control by use of various types ofphotonic crystals. From 1996-1997, he was with LinköpingUniversity in Sweden as a visiting
researcher. He is also a guest associate professor of Tokyo Institute of Technology (2003- ). He
received 2006/2007 IEEE/LEOS Distinguished Lecturer Award. He is an associate editor ofJapanese Journal of Applied Physics. He is a member of the Japan Society of Applied Physics,
the American Physical Society, and IEEE/LEOS.

Distinguished Technical Member

Makoto Kasu was born in Tokyo on May 30, 1961. He received the B.E., M.S. and Ph.D.
degrees in electrical engineering from Kyoto University in 1985, 1987 and 1990, respectively.
He joined NTT Basic Research Laboratories in 1990, and is currently a group leader ofThin-Film Materials Research Group. He was a guest scientist in University of Ulm, Germany
from 2002 to 2003. Since 1990 he has engaged in scanning tunneling microscope (STM)-based
nanostructure fabrication and widegap semiconductors. His current interests are aluminum
nitride (AlN) deep ultraviolet light-emitting diodes (LEDs) and diamond high-frequency
high-power transistors. He received Electronic Materials Symposium (EMS) award. He is amember of the Japan Society of Applied Physics, the Institute of Japan, and the JapaneseSociety of Surface Science. He is also an invited professor of University of Paris (XIII) and theleader of SCOPE project "Diamond RF Power Devices for Microwave, Millimeter-Wave Range
Power Amplifiers" of the Ministry of Internal Affairs and Communications, Japan.

－6－Advisory Board (2006 Fiscal Year)
Name

Title
Affiliation

Prof. Gerhard Abstreiter

Professor
Walter Schottky InstituteGermany

Prof. Boris L. Altshuler

Professor
Department of Physics
Columbia University, U.S.A.

Prof. Serge Haroche

Professor
Département de Physique
De l'Ecole Normale Supérieure

Prof. Mats Jonson

Professor
Department of Physics,
Göteborg University, Sweden

Prof. Anthony J. Leggett

Professor
Department of Physics
University of Illinois at Urbana-Champaign, U.S.A.

Prof. Johan E. Mooij

Professor
Kavli Institute of Nanoscience Delft
Delft University of Technology, The Netherlands

Prof. John F. Ryan

Professor
Clarendon Laboratory
University of Oxford, U.K.

Prof. Klaus von Klitzing

Professor
Max-Planck-Institut für Festkörperforschung
Germany－7－

Invited / Guest Scientists(2006 Fiscal Year)

Name

Affiliation
PeriodDr. Akio Tsukada

Tokyo University of Agriculture and Technology, Japan
June 05 – March 07

Dr. Go Yusa

Japan Science and Technology Agency (JST), Japan
October 05 – September 08

Dr. Yasuyoshi Miyamoto(Interchange Researcher)

NHK Science & Technical Research Laboratories, Japan
December 05 – November 06

Prof. Yong-Hang Zhang

Arizona State University, U.S.A.
January 06 – July 06

Dr. Goo-Hwan JeongJapan Science and Technology Agency (JST), Japan
April 06 – July 06

Dr. Yusuke Furukawa

University of Tokyo, JapanMay 06 – October 06

Ken SatoTohoku University, Japan
June 06 – July 06

Assoc. Prof. Shinichi Warisawa

University of Tokyo, Japan
June 06 – March 07

Dr. Koji Onomitsu

Waseda University, Japan
July 06 – September 06

Dr. Michael Stopa

Harvard University, U.S.A.
August 06 – September 06

Dr. Kasper Grove-Rasmussen

University of Copenhagen, Denmark
August 06 – December 06

Dr. Yuan-Liang Zhong

Tokyo University of Science, Japan
September 06 – February 07－8－Dr. Yueh-Chin Lin

National Chiao Tung University, Taiwan
November 06 – February 07

Assoc. Prof. Takaaki Koga

Hokkaido University, Japan
November 06 – December 07

Akira Yamazaki

Meiji University, Japan
November 06 – March 08

Dr. Alexandre Kemp

Japan Science and Technology Agency (JST), Japan
December 06 – December 07

Prof. Michel Devoret

Yale University, U.S.A.
January 07 – February 07

Prof. Amnon Aharony

Ben Gurion University of the Negev, Israel
January 07 – April 07

Prof. Ora Entin-Wohlman

Ben Gurion University of the Negev, Israel
January 07 – April 07

Dr. Hongwu LiuJapan Science and Technology Agency (JST), Japan
February 07 – January 08－9－Trainees(2006 Fiscal Year)

Name

Affiliation
PeriodSimon Perraud

University of Paris 6 / CNRS, France
October 04 – September 07

Rebeca Alonso"Miguel Hernández "University of Elche, Spain
January 06 – August 06

Raphael de Gail

ENS (Ecole Normale Supérieure), France
February 06 – April 06

Jean-François Morizur

ENS (Ecole Normale Supérieure), France
February 06 – July 06

François Parmentier

ENS (Ecole Normale Supérieure), France
February 06 – July 06

Benjamin Gaillard

INSA (Institut National des Sciences Appliquées deToulouse), France
February 06 – September 06

Wan-Cheng Zhang

Chinese Academy of Sciences, China
February 06 – August 06

Shih-Chieh Huang

National Chiao Tung University, Taiwan R.O.C.
March 06 – September 06

Lars Tiemann

Max-Planck-Institut für Festkörperforschung, Germany
March 06 – June 06

Christoph Hufnagel

University of Heidelberg, Germany
June 06 – June 07

Tiffany Yeh

Rice University, U.S.A.
June 06 – August 06－10－

Arthur Goetschy

ESPCI (Ecole Supérieur de Physique et de Chimie
Industrielles), France
July 06 – December 06

Camille Janer

ESPCI (Ecole Supérieur de Physique et de Chimie
Industrielles), France
July 06 – December 06

Samir Etaki

Delft University of Technology, The Netherlands
September 06 – December 06

Michailas Romanovas

Vilnius Gediminas Technical University, Lithuania
January 07 – August 07

Joana Durao

Porto's University, Portugal
January 07 – August 07

Ari Siitonen

University of Kuopio, Finland
January 07 – August 07

Daan Sprunken

University of Twente, The Netherlands
January 07 – August 07

Sylvain Sergent

INSA (Institut National des Sciences Appliquées deRennes), France
January 07 – August 07

Florian Domengie

INSA (Institut National des Sciences Appliquées deToulouse), France
February 07 – September 07

Guillaume Vincent

INSA (Institut National des Sciences Appliquées deToulouse), France
February 07 – September 07－11－

Japanese Students(2006 Fiscal Year)

Name

Affiliation (Period)

Yuichi Igarashi

University of Tokyo, Japan (Apr. 06 – Mar. 07)

Daisuke Itoh

Tohoku University, Japan (June 06 – Mar. 07)

Kenzo Ibano

Keio University, Japan (Apr. 06 – Feb. 07)

Shoko Utsunomiya

University of Tokyo, Japan (Apr. 06－Mar. 07)

Taichi Urayama

Keio University, Japan (Nov. 06 – Mar. 07)

Akihiro Eguchi

Kyushu University, Japan (Sep. 06 – Nov. 07)

Masato Edamoto

University of Tokyo, Japan (June 06 – Mar. 07)

Kuniaki Endo

Tokyo University of Science, Japan (Apr. 06 – Sep. 06)

Akira Oiwa

University of Tokyo, Japan (Apr. 06 – Mar. 07)

Kenichi Ono

University of Tokyo, Japan (July 06 – Aug. 07)

Satoru Ohno

Keio University, Japan (Apr. 06 – Mar. 07)

Minoru Oda

University of Tokyo, Japan (Apr. 06－Mar. 07)

Junya Ono

University of Tsukuba, Japan (Apr. 06 – Mar. 07)

Seiichiro Kagei

Tokyo University of Science, Japan (May 06 – Sep. 06)

Ryo Kajiura

Tokyo Institute of Technology, Japan (Apr. 06 – Mar. 07)

Keiichi Katoh

University of Tokyo, Japan (June 06 – Mar. 07)

Takayuki Kaneko

Meiji University, Japan (Apr. 06 – Mar. 07)

Takehito Kamada

Tohoku University, Japan (May 06 – Mar. 07)

Sunggu Kang

University of Tsukuba, Japan (Apr. 06 – Mar. 07)

Yosuke Kitamura

University of Tokyo, Japan (Apr. 06－Mar. 07)

Kenichiro Kusudo

University of Tokyo, Japan (Aug. 06－Mar. 07)

Christo Buizert

University of Tokyo, Japan (Apr. 06－Mar. 07)

Marika Gunji

Keio University, Japan (Apr. 06 – Aug. 06)

Ryota Koizumi

Tokyo University of Science, Japan (Nov. 06 – Mar. 07)

Daiu Koh

University of Tokyo, Japan (June 06－Mar. 07)－12－

Tetsuo Kodera

University of Tokyo, Japan (Apr. 06 – Mar. 07)

Takashi Kobayashi

Tohoku University, Japan (June 06 – Mar. 07)

Yosuke Sasaki

Tokyo Institute of Technology, Japan (Apr. 06 – Mar. 07)

Jonathan Baugh

University of Tokyo, Japan (Oct. 06 – Mar. 07)

Go ShinkaiTokyo Institute of Technology, Japan (Apr. 06 – Mar. 07)

Akihiro Souma

University of Tokyo, Japan (Apr. 06 – Mar. 07)

Atsushi Sogabe

Shonan Institute of Technology, Japan (Apr. 06 – Mar. 07)

Hidenobu Takahashi

Toyohashi University of Technology，Japan (Jan. 07 – Feb. 07)

Hiroyuki Takamichi

Tohoku University, Japan (May 06 – Mar. 07)

Naohiro Takemoto

Toyohashi University of Technology, Japan (Jan. 07 – Feb. 07)

Masaya Tazawa

Tokyo University of Science, Japan (Apr. 06 – Mar. 07)

Ryosuke Tanaka

University of Tokyo, Japan (June 06 – Mar. 07)

Koujiro Tamaru

University of Tokyo, Japan (June 06 – Mar. 07)

Shun Chikamori

Tokyo Institute of Technology, Japan (Apr. 06 – Mar. 07)

Shouei Tsuruta

Tokyo University of Science, Japan (Apr. 06 – Mar. 07)

Eigo Totoki

University of Tokyo, Japan (Apr. 06 – Mar. 07)

Hiromasa Nakano

Tokyo University of Science, Japan (Apr. 06 – Mar. 07)

Tomohiro Nakamura

Shonan Institute of Technology, Japan (Apr. 06 – Mar. 07)

Yoshitaka Niida

Tohoku University, Japan (May 06 – Mar. 07)

Yuita Noguchi

Osaka University, Japan (Aug. 06 – Sep. 07)

Keiichiro Nonaka

University of Tokyo, Japan (June. 06 – Mar. 07)

Junichi Hashimoto

Yokohama National University, Japan (Apr. 06 – Mar. 07)

Takuro Hashimoto

Shibaura Institute of Technology, Japan (Oct. 06 – Mar. 07)

Junichiro Hayakawa

Tohoku University, Japan (May 06 – Mar. 07)

Kenichi Hidachi

University of Tokyo, Japan (Aug. 06 – Mar. 07)

Hirotaka Masuyama

Tokyo University of Science, Japan (Oct. 06 – Mar. 07)

Takao Yamaguchi

Tokai University, Japan (Apr. 06 – Mar. 07)

Mizuki Miyamoto

Shonan Institute of Technology, Japan (Apr. 06 – Mar. 07)－13－

Kunio Morita

Tokyo University of Science, Japan (Apr. 06 – Mar. 07)

Noriko Moritake

Nagaoka University of Technology, Japan (Oct. 06 – Feb. 07)

Shin Yabuuchi

Keio University, Japan (Apr. 06 – Mar. 07)

Michihisa Yamamoto

University of Tokyo, Japan (Apr. 06 – Mar. 07)

Takahito Watanabe

Tokyo Institute of Technology, Japan (Aug. 06 – Sep. 06)－14－

Ⅰ．Research Topics

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Overview of Research in Laboratories
Material Science Laboratory
Keiichi Torimitsu
The Materials Science Laboratory (MSL) aims at producing new functional materials anddesigning of advanced device based on novel materials and biological function. Controllingthe configuration and coupling of atoms and molecules is our approach to accomplish thesegoals. Bio-nano research is set as our principle research in this laboratory.
We have three research groups covering from semiconductor devices, such as GaN, toorganic materials, such as receptor proteins. The characteristic feature of MSL is the effective
sharing of the unique nanofabrication and measurement techniques of each group. This
enables fusion of research fields and techniques, which leads to innovative material research
for the IT society.
We set up European laboratory in U.K. for bio-nano research, our principal research, in lastyear and strengthen our research activities. We promote collaborations with internationalorganizations to develop a firm basis of basic science.
Physical Science Laboratory
Hiroshi Yamaguchi
We are studying solid-state quantum systems and devices, which will have revolutionary
impact on communication and information technologies in the 21st century. In particular, we
are making firm and steady progress in the pursuit for solid-state nanodevices, and related
physics and technology for future quantum information processing. We maintain an opendoor policy and engage in collaborations with many outside organizations to enhance ourbasic research into fundamental issues.
The five groups in our laboratory are working in the following areas: quantum coherent
control of semiconductor and superconductor systems, carrier interactions in semiconductor
hetero- and nanostructures, spintronics manipulating both electron and nuclear spins, precise
and dynamical control of single electrons, nanodevices operating at ultimately low power
consumption, atom traps/optics, and novel nanomechanics based on compound
semiconductors. These studies are supported by cutting-edge nanolithography techniques,
well-controlled nanofabrication processes, high-quality crystal growth, and theoretical studies
including first-principle calculations.
Optical Science Laboratory
Yasuhiro Tokura
This laboratory aims the development of core-technologies that will innovate on opticalcommunications and optical signal processing, and seeks fundamental scientific progresses.
The three groups in our laboratory are working for the quantum state control of light, thequantum state control of materials by light, the analysis of high speed phenomena using very
short pulse laser, the optical properties of nano-structure semiconductor like quantum dot, andvery small optical integrated circuit using two-dimensional photonic crystals.
In this year, we realized improvements of quantum cryptography and quantum entangled
photon pair generation, high-Q (10,000) compound semiconductor photonic crystal resonator,and measurements of photon decay time and pulse delay time in ultra-high Q-value
photonic crystal resonator.

－15－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Aluminum Nitride Light-Emitting Diodes with the Shortest Wavelength
Yoshitaka Taniyasu and Makoto Kasu
Materials Science Laboratory
Aluminum nitride (AlN) is a direct-bandgap semiconductor with a bandgap energy of 6eV, the largest among semiconductors, and is therefore promising for light-emitting devices
with the shortest wavelength for semiconductors. Recently, we have succeeded in p-type
and n-type doping of AlN and have fabricated a p-n homojunction AlN light-emitting diode(LED) [1].
The AlN layers were epitaxially grown on SiC (0001) substrate by metalorganic vapor
phase epitaxy (MOVPE). To improve the crystal quality of the AlN layers, we suppressed
the parasitic reaction of Al and N sources in the gas phase. P-type and n-type AlN layers
were obtained by Mg and Si doping during MOVPE growth, respectively [1, 2]. Figure 1
shows schematics of the AlN LED. In this LED structure, between the p-type and n-type
AlN layers, an undoped AlN emission layer was inserted to suppress Mg- and Si-impurityrelated emission from the p-type and n-type AlN layers. The p-type and n-type AlN/AlGaN
superlattices (SLs) were used to reduce the contact resistance of the electrodes.
Figure 2 shows the emission spectrum of the AlN LED. Deep-ultraviolet light emission
was observed at 210 nm, the shortest wavelength ever reported for any kind of
semiconductors. On the basis of optical reflection and cathodoluminescence measurementsof free-exciton transition in AlN, we assigned the light emission to a near-band-edge emission
from AlN.
Because light with a shorter wavelength has a higher energy, the AlN LEDs can beapplied to light sources for decomposing very stable, harmful chemical substances, such asdioxin and polychlorinated biphenyls (PCBs), which cause serious environmental problems
all over the world. We will increase the emission efficiency of the AlN LEDs to a practicallevel by further improving their crystal quality and doping efficiency.
[1] Y. Taniyasu, M. Kasu, and T. Makimoto, Nature 441 (2006) 325.
[2] Y. Taniyasu, M. Kasu, and T. Makimoto, Appl. Phys. Lett. 89 (2006) 182112.

Pad electrode

Emission Intensity (a.u.)

Semi-transparent
p-type electrodep-type AlN/AlGaN SLs

p-type AlN
n-typeelectrode

Undoped AlN
n-type AlN
n-type AlN/AlGaN SLs
AlN buffer

210 nm

RT
DC 40mA

200 210 220 230 240 250
Wavelength (nm)

SiC (0001) substrate

Fig. 2. Emission spectrum of AlN LED.

Fig. 1. Device structure of AlN LED.

－16－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Diamond FET with Maximum Frequency of Oscillation of 120 GHz
Kenji Ueda and Makoto Kasu
Materials Science Laboratory
Diamond is expected to be the most suitable material for high-power high-frequency
electronic devices because of its high electric breakdown field (>10 MV/cm), high carrier
mobility (4500 cm2/Vs for electrons, 3800 cm2/Vs for holes), and highest thermal
conductivity (22 W/cmK). Recently, using homoepitaxial single-crystal CVD diamond, we
achieved the maximum output-power density of 2.1 W/mm at 1 GHz [1], which is highenough for power amplifiers of the base stations in wireless communications systems.
However, the size of single-crystal CVD diamond is limited to 4 mm, which is the size ofcommercially available HPHT-synthesized diamond substrates. From the viewpoint ofsemiconductor-device processing, at least four-inch wafers are needed. One possible
solution to this problem is to use high-quality polycrystalline diamond, whose maximum sizeis 4 inches. Here, using a high-quality polycrystalline diamond film, we report significant
progress in fabricating FETs. The grain size of the polycrystalline film is ~100 µm, which iscomparable to our FET size. Thus, the effect of the grain boundary seems to be very small.
As shown in Fig. 1, the FETs were fabricated on the freestanding polycrystalline diamondgrown by CVD (size: 10 mm×10 mm×0.5 mm). The diamond surface was passivated withhydrogen (H-passivation) to form a quasi two-dimensional hole channel. The source anddrain Au ohmic contacts were formed on the H-terminated surface. Electron-beamlithography and self-alignment techniques enabled us to form 0.1-µm-long Al Schottky gatecontacts. The DC characteristics show drain current (IDS) of 550 mA/mm at gate source
voltage (VGS) of -3.5 V. The IDS is comparable to the maximum value of single-crystal CVD
diamond FETs. The DC transconductance (gm) stays high (~140 mS/mm) in a relatively
wide VGS range. The transition frequency (fT) and maximum frequency of oscillation (fmax)
were extracted from the frequency dependence of the short circuit current gain (|h21|2) and theunilateral power gain (U) as shown in Fig. 2. The maximum fmax is 120 GHz, and in adifferent bias condition, fT of 45 GHz was obtained. These fT and fmax values are the highest
among diamond FETs [2].
[1] M. Kasu, K. Ueda, H. Ye, Y. Yamauchi, et al., Electron. Lett. 41 (2005) 1249.
[2] K. Ueda, M. Kasu, Y. Yamauchi, et al., IEEE Electron Device Lett. 27 (2006) 570.

Fig. 1. Schematic cross-section of apolycrystalline diamond FET.

Fig. 2. RF gain plot of FET.

－17－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

High Breakdown Voltage with Low On-state Resistance of InGaN/GaN
Vertical Conducting Diodes
Atsushi Nishikawa, Kazuhide Kumakura, and Toshiki Makimoto
Materials Science Laboratory
Due to wide band gap and high critical electric field of GaN, GaN-based electronic
devices are promising for high-power and high-temperature operation. Although a lateral
conducting structure using a semi-insulating substrate such as sapphire is usually fabricatedfor GaN-based devices, a vertical conducting structure using a conductive substrate isadvantageous for lower-loss and higher current density. Therefore, GaN-based verticalconducting devices are expected to be preferable for high-power electronic device
applications. So far, the study on GaN-based vertical pn junction diode was insufficientbecause of a high-resistance p-GaN layer and a buffer layer to grow a GaN layer on a heterosubstrate. We have overcome these difficulties by using an InGaN layer for the p-type layer
and GaN substrate on which a GaN layer can be directly grown. The diode fabricated in thisstudy exhibits a high breakdown voltage with a low on-state resistance [1].
The samples were grown on n-GaN substrates, using metalorganic vapor phase epitaxy(MOVPE). The sample structure consists of a 1.8-µm or 3.6-µm-thick lightly doped n-GaNlayer and a 140-nm-thick p-InGaN layer. For comparison, the same diode structure with 1.8µm-thick n-GaN was grown on a conductive SiC substrate. Figure 1 shows reverse currentvoltage (I-V) characteristics. The leakage current of the diode on a GaN substrate is one orderof magnitude lower than that on a SiC substrate due to the better crystal quality of GaN grown
on a GaN substrate. Since a thick crack-free GaN layer can be grown on a GaN substrate, thebreakdown voltage increases with increasing n-GaN layer thickness. For the 3.6-µm-thick
GaN layer, the breakdown voltage (VB) reaches as high as 571 V. At the same time, we
obtained the low on-state resistance of 1.23 mΩcm2 because of absence of the buffer layer, as
shown in Fig. 2. The figure-of-merit, V2/Ron, is calculated to be 265 MW/cm2, which is thehighest value among those ever reported for GaN-based vertical conducting Schottky and pnjunction diodes.
[1] A. Nishikawa, K. Kumakura, and T. Makimoto, Appl. Phys. Lett. 89 (2006) 153509.

10

-2

10

3.6 µmon GaN

1.8 µmon GaN

Current density (A/cm2)

Current density (A/cm2)1000
01.8 µmon SiC-410571 V @ 10 mA/cm2
-6

10

-8

10

-800

-400

0

Reverse voltage (V)

3.6 µmon GaN800
1.8 µmon GaN600

1.8 µmon SiC

400
200
0

0

2

4

6

8

Forward voltage (V)Fig. 2. Forward I-V characteristics.

Fig. 1. Reverse I-V characteristics.

－18－

10

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Ultraviolet Luminescence from Hexagonal BN Heteroepitaxial Layers
Yasuyuki Kobayashi, Tetsuya Akasaka, and Toshiki Makimoto
Materials Science Laboratory

Intensity (arb. units)RT
NH3=3s
3s
2s
1s

7

1.6

6.9

1.4

6.8

1.2

6.7
6.6
6.5

3

3.5

4 4.5 5 5.5 6 6.5
Energy(eV)Photonenergy(eV)Fig. 1. CL spectra at RT from h-BN thin films
grown by FME.

1

bulk
h-BN

0

1

2
3
4
NH3 supply time (s)0.85XRC FWHM (degree)

c-axis lattice constant (A)Hexagonal boron nitride (h-BN) is a promising material system for exciton-based quantum
information processing and for optical device applications in the ultraviolet spectral region.
For investigating the optical properties and fabricating optical devices with a p-n junction andquantum well structures, a high-quality h-BN layer on a suitable substrate is indispensable.
During the past few decades, BN thin films have been deposited by a number of methods.
However, there has been no report of ultraviolet luminescence at room temperature (RT) fromthese BN thin films.
Recently, we have achieved growth of single crystal h-BN (0001) heteroepitaxial layers
on Ni (111) substrate by flow-rate modulation epitaxy (FME) using triethylboron andammonia (NH3) [1]. Here, we report RT observation of near-band-gap (NBG) luminescenceat a wavelength of 227 nm in cathodoluminescence (CL) from the h-BN heteroepitaxial layers[2].
Figure 1 shows the CL spectra for h-BN layers grown under NH3 supply times of 1, 2, and3 s with NH3 flow rate of 700 sccm. A NBG ultraviolet emission peak centered at energy of
5.47 eV (227 nm) and one broad deep-level emission peak centered at around 3.85 eV (322nm) are clearly observed for h-BN layer grown under NH3 supply times of 3 s. To ourknowledge, this dominant NBG ultraviolet emission feature at RT has never reported for hBN films deposited on any substrates. The luminescence intensity at the NBG peak increases
monotonically with increasing NH3 supply time, indicating that h-BN grown by FME withlonger NH3 supply time is preferable for obtaining stronger NBG luminescence.
Figure 2 shows the NH3 supply time dependence of c-axis lattice constant and full widthat half maximum (FWHM) of (0002) h-BN X-ray rocking curve (XRC) for these three h-BN
samples. The c-axis lattice constant of all three is identical to that of bulk h-BN samples. The
FWHM of the (0002) h-BN XRC decreases from 1.5 to 0.7o with increasing NH3 supply timefrom 1 to 3 s. The FWHM of 0.7o is the narrowest value ever reported for a h-BN layer. The
lower h-BN growth rate and larger amount of NH3 with the longer NH3 supply time may
reduce the lattice defects in h-BN heteroepitaxial layers, resulting in the stronger NBG
ultraviolet emission from h-BN samples.
The present result is a vital step toward the ultimate goal of h-BN-based optical devices.
[1] Y. Kobayashi, et al., J. Cryst. Growth 298 (2007) 325.
[2] Y. Kobayashi, et al., Phys. Stat. Sol. (b) 244 (2007) 1789.

0.6

Fig. 2. The lattice constant and the FWHM of
XRC as a function of the NH3 supply time.
－19－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Single-walled Carbon Nanotube Synthesis Using Gold, Silver andCopper Nanoparticle Catalysts
Daisuke Takagi1 and Hiroki Hibino2
1
Tokyo University of Science, 2Materials Science Laboratory
We succeeded in synthesizing high-quality single-walled carbon nanotubes (SWCNTs)from gold-group elements (Cu, Ag and Au) by chemical vapor deposition (CVD) for the firsttime [1]. SWCNTs are a key material in nanotechnology and have been intensively studied as
the building blocks of nanoelectronics. Iron-group elements (Fe, Co, and Ni) have been used
as catalysts for SWCNT synthesis by CVD. However, the detailed role of metal catalyst for
the nucleation and growth of SWCNT is not fully understood yet. Our finding should shed
new light on the essential role of catalysts in SWCNT growth and should lead to highly
controlled SWCNT synthesis by using novel catalyst species.
CVD, in which carbon-containing precursor molecules like ethanol or methane reacts withmetal catalyst nanoparticles at elevated temperature, is the most common SWCNT synthesis
process being investigated toward practical applications. Iron-group elements and their alloys(Co-Mo, Fe-Co etc) have been mainly used as the catalyst materials for CVD growth. On theother hand, gold-group elements have been regarded as the most unlikely elements to produce
SWCNTs since it has been assumed that catalysts must have an affinity for carbon, e.g. highsolubility and compound formation. The results of our work (Fig.1) overrule this assumption
and indicate that SWCNTs can be formed from gold-group elements, which have extremely
low solubility of carbon in bulk phase. The traditional CVD growth mechanism is based on
the consideration of the affinity between carbon and catalyst species. In this study, wedemonstrated that gold-group elements act as highly efficient catalysts for CVD synthesis of
SWCNTs under the following three conditions: (1) Very small metal nanoparticles (3 nm orless in diameter). (2) For activation (Fig. 2), heat-treatment at high temperature (~900 ºC) in
air for cleaning of catalyst surfaces. (3) High growth temperature for thermal decompositionof carbon-containing precursor molecules. Moreover, this recipe is also effective for othervarious metals, such as platinum-group elements (Rh, Pd and Pt), and results in high-density
SWCNT yields by CVD. These results mean that the catalytic function for SWCNT synthesis
is not specific to the properties of iron-group elements, such as solubility of carbon andprecipitation of graphite. Therefore, the CVD growth mechanism from catalyst particles
should be reconsidered taking this fact into account. The availability of novel catalystmaterials will push the development of growth processes for
Without activation
precise control of SWCNT structures and their non-ferromagnetic
properties and catalytic activities for semiconductor nano-wiregrowth will lead to new applications of SWCNTs in industries.
[1] D. Takagi, et al., Nano Lett. 6 (2006) 2642.

With activation

Fig. 1. TEM images of SWCNTs grown from Au, Ag, and Cu catalyst
nanoparticles.

－20－

Fig. 2. Comparison of SWCNT
yield without and withactivation process.

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Chemical States of Metal Catalysts in CVD Ambient for Single-walled
Carbon Nanotube Growth
Fumihiko Maeda
Materials Science Laboratory
Single-walled carbon nanotubes (SWCNTs) are promising for the generation beyond
silicon-based microfabrication technology. However, the mixture of various characteristics,
such as metals and semiconductors with various band gaps, are obtained for CNTs. The
control of their characteristics is essential in order to achieve large-scale integration for CNTbased devices. Hence, we have been investigating the growth mechanism of CNTs with theaim of controlling their growth and obtaining the desired CNTs. Since catalytic nanoparticles
play an important role in growing CNTs, their chemical states are of great interest for thisinvestigation. Recently, we have succeeded in growing SWCNTs by CVD and performing
successive in--situ x-ray photoelectron spectroscopy measurements. As a result, we have beenable to elucidate the chemical state of catalytic nanoparticles after the growth [1, 2].
Figure 1 shows the core-level photoelectron spectra of Co, which is a catalyst for the CNT
growth. These spectra were captured before the growth process, at the heating stage, and after
CNT growth using ethanol. In the case of ex-situ deposition, which is the conventional growth
procedure, Co was oxidized by exposure to air, resulting in the formation of Co3O4. This
oxide turned to CoO during the heating process under ultra-high vacuum and, finally, metallic
Co was obtained after CNT growth. In the case of in-situ deposition, the new process without
air-exposure after metal deposition, Co remained metallic throughout the growth process.
These two results indicate that the metallic state is stable under the growth ambient. This isinconsistent with existing CNT growth models, which need the carburization of catalytic
nanoparticles. Meanwhile, the CNT yield for the in-situ deposition was higher than that for
the ex-situ deposition. From the analysis of core-level photoelectron intensity, we found thatthe amount of decomposed carbon on the surface for the in-situ deposition is larger than thatfor the ex-situ deposition. The situation after CNT growth in the former case is schematicallyillustrated in Fig. 2. The formation of thick graphitic films indicates that the uniform metallic
nanoparticles have a high ability for the decomposition and that a large amount of migrating
carbon remains without being included in the nanoparticles during CVD. We will further
investigate the reactions of CNT growth and clarify the growth mechanism.
[1] F. Maeda, et al., Jpn. J. Appl. Phy. 46 (2007) L148.
[2] F. Maeda, et al., Mater. Res. Soc. Symp. Proc. 96 (2007) 30963-Q05-04.

Fig. 1. Co 2p photoelectron spectra.

Fig. 2. Schematic representations after CNT growth.
－21－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Position Control of Nanowires Using Catalysts Islands Arranged at
Surface Atomic Steps
Hiroki Hibino1 and Kouta Tateno2
1
Materials Science Laboratory, 2Optical Science Laboratory
Semiconductor nanowires are attracting intense interest as building blocks of futurenanoscale electronic and optoelectronic devices. To pursue their application, we have to
produce nanowires with controlled size, structure, and position. This is critically related to thecontrol of the metal catalyst used in nanowire formation based on the vapor-liquid-solidmechanism. Gold is one of the most widely used metal catalysts, and we have already shownthat the size and position of Au-Si alloy islands can be controlled using atomic steps on
Si(111) as templates for island formation [1]. Here, we demonstrate that these islands act as
catalysts for the fabrication of vertical GaP nanowires aligned in one dimension [2].
Au-Si alloy islands arranged at atomic steps were obtained by depositing Au on Si(111) at
high (∼700°C) and then low (∼400°C) temperatures. Their size and density were controlled bymonitoring the island formation in-situ in real time using low-energy electron microscopy.
After the Au-Si alloy island formation, the samples were removed from UHV to air andintroduced into the metal organic vapor phase epitaxy reactor without any special treatments.
We found that there are three aspects to the growth of vertical GaP nanowires on Si(111): cosupply of trimethylgallium and PH3, two growths at different temperatures, and a low PH3
flow rate.
Figure 1 shows a scanning electron microscopy (SEM) image of vertical nanowires selfarranged in lines with the length of several micrometers. The one-dimensional alignment of
the wires proves that the Au-Si alloy islands arranged at the steps can be used as catalysts fornanowire formation. The SEM images also show that the wires have a fairly constant lengthand diameter. Figure 2 shows cross-sectional transmission electron microscopy (TEM)
images and energy-dispersive X-ray spectroscopy (EDS) mappings of a GaP nanowire. There
are no apparent defects passing through the nanowire/substrate interface, which is a promisingfeature for the integration of III-V semiconductor photonics into Si electronics.
Our approach to control the size and position of nanowires does not involve any "topdown" lithographic techniques; it is a pure "bottom-up" self-assembly method. Self-assembly
has potential advantages of low cost, large scale, high quality, and so on, but there still remainlots of problems to be solved, especially in the controllability of the size and position ofnanostructures. We hope that our approach will contribute to establishing self-assembled
nano-device fabrication methods.
[1] H. Hibino and Y. Watanabe, Surf. Sci. 588 (2005) L233.
[2] K. Tateno, H. Hibino, H. Gotoh, and H. Nakano, Appl. Phys. Lett. 89 (2006) 033114.

Fig. 1. An SEM image of GaP nanowires viewed
from the direction inclined 38° from thesurface normal. Inset: top view.

Fig. 2. A TEM image of a GaP nanowire. (b) EDS
mapping images of Si, Ga, and P at the
nanowire/substrate interface.
－22－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Microchannel Device Using Self-Spreading Lipid Bilayer as Molecule
Carrier
Kazuaki Furukawa
Materials Science Laboratory
Self-spreading is a lipid wetting process at a solid-liquid interface, where a single
supported lipid bilayer (SLB) is formed by a self-assembly process at the rim of a lipid spot
adhering to a hydrophilic surface. We examined the self-spreading on the patterned surface
and found that self-spreading occurs only on the hydrophilic surface of SiO2. This led us topropose a new type of microchannel device, which we call "lipid-flow chip" [1].
The device structure and principle of the device operation are shown schematically in Fig.
1. The device is equipped with microchannel part of 10 µm wide and 400 µm long, and has awell on each side, which has been fabricated by conventional photolithography and lift-off
process. A single self-spreading SLB grows only on hydrophilic surfaces after the SLB has
been introduced into the pattern. When two SLBs collide in the middle of the channel, they
form a unified SLB where molecular diffusion from one side to the other becomes dominant.
SLBs are used only for transporting the molecules of interest. Thus an SLB is regarded as, forinstance, a carrier gas for gas chromatography.
The device is beneficial for detecting an intermolecular interaction. As one example, we
demonstrate the observation of fluorescence resonance energy transfer (FRET) between adonor (CC2) and an acceptor (FITC). As shown in Fig. 2, two lipid bilayers containing eachdye-conjugated molecule was collided with each other in the microchannel. After the collision,
they form a unified lipid bilayer, and the dyes are mixed with each other by lateral diffusion.
The distribution of dye concentration is symmetrical to the point of the collision. A great
reduction in donor fluorescence is, however, observed in a mixed area of donor and acceptor.
This is because of the two relaxation processes, emission and FRET, exists in excited donor.
The great reduction of donor emission is attributed to the effective FRET. Our device is also
advantageous for quantitative analyses of FRET efficiency between a variety of dye pairs.
We plan to apply the technique to enzymes and proteins in order to study molecularinteractions such biomolecules have.
[1] K. Furukawa, et al., Lab Chip 6 (2006) 1001.

Photoresist
10µm

FITC →← CC2

Photomultiplier Output(arbitrary unit)

Photoresist
CC2 fluorescence

FITC
fluorescence

－23－

1

2 3

30

40

50

10

min

0
0

Fig. 1. Device structure and principle of the operation. L-αPC extracted from egg yolk is used for the carrying
medium of dye-conjugated lipid molecules.

time
0

10

20

Position/µm

60

70

80

Fig. 2. Time-lapse observation of FRET.
5% of CC2- and FITC-conjugatedlipid are mixed in L-α-PC.

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Self-assembly of Vesicle Nanoarrays on Si: A Potential Route toHigh-density Functional Protein Arrays
Chandra S. Ramanujan1, Koji Sumitomo2, Maurits R. R. de Planque1, Hiroki Hibino2,
Keiichi Torimitsu2, and John F. Ryan1
1
University of Oxford, 2Materials Science Laboratory
DNA arrays have played a critical role in developing our understanding of genomics.
However, whilst they can measure the expression levels of large numbers of genes
simultaneously, they cannot be used to further characterize the protein products of such genes
and their activity. An important objective of current research is to extend the use of array
technology to both directly study the function of the proteins to aid drug discovery. Whereas
DNA microarray technology is well-developed, the protein equivalent is still at the earlystages of development. Protein microarrays have been recognized as a valuable tool since
they require only a nanolitre-scale sample volume with a few picograms of the target protein
or drug.
We show that 100 nm unilamellar thiol-tagged vesicles bind discretely and specifically to
Au nanodots formed on a Si surface (See Fig.1). An array of such dots, consisting of 20 nm
Au-Si three-dimensional islands, is formed by self-assembly on terraces of small-anglemiscut Si(111) after Au deposition [1]. Consequently, both the formation of the nano-pattern
as well as the subsequent attachment of the vesicles are self-organized and occur without theneed for any ‘top-down’ lithographic processes. This approach has the potential to provide thebasis of a low-cost, high-density nanoarray for use in proteomics and drug discovery.
Today’s DNA microarray technology has the potential of screening up to 105 ~106 probes
in a 300 µl solution volume. In our nanodot arrays about 109 nanodots are covered by a 10 µl
droplet [2]. The next steps towards producing a protein chip will include reconstituting
proteins into the vesicles and determining a reliable way of labeling and reading the array,possibly using scanned probe techniques such as AFM or a combination of AFM andScanning Near-field Optical Microscopy (SNOM). The AFM-SNOM has a resolution of
about 100 nm. The gold-silicon combination provides an ideal substrate with a low
background for fluorescence detection techniques. One way of producing a protein nanoarray
would be to first scan and locate each nanodot, and then repeatedly expose to different
protein-vesicle solutions and re-scan, until the chip is fully loaded. The deposition of anumber of different protein-vesicles can be achieved by optimizing exposure time and vesicle
density. The interaction of these mapped vesicle-proteins with fluorescent-labeled antibodies
could be detected using the AFM-SNOM.
[1] H. Hibino and Y. Watanabe, Surf. Sci. 588 (2005) L233.
[2] C. S. Ramanujan, et al., App. Phys. Lett. 90 (2007) 033901.

Fig. 1. AFM image of nanodot rows with vesicles that are modified to specifically attach to the gold nanodots
formed by an earlier self-assembly process.

－24－Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Ion Conducting Polymer Microelectrodes
for Interfacing with Neural Networks
Tobias Nyberg, Akiyoshi Shimada, Nahoko Kasai, and Keiich Torimitsu
Materials Science Laboratory
We have examined the stimulation and recording properties of conjugated polymer
microelectrode arrays as interfaces with neural networks of dissociated cortical neurons.
The polymer electrodes were electrochemically polymerized from a blend of poly (3,4ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT-PSS) and ethylenedioxythiophene(EDOT) onto indium tin oxide (ITO) microelectrodes. Conducting polymers have beenutilized to increase the surface roughness and improve the performance of planar electrodes[1].
The stimulation properties were investigated as a means of supplying a neural networkwith information. The impedance of the polymer electrodes (circles) was markedly lower thanthat of the ITO electrodes (squares) for low and medium frequencies and the phase of thepolymer electrodes (solid line) was lower than that of the ITO electrodes (dashed line) for
medium frequency as shown in Fig. 1. The peak current was proportional to the applied
voltage pulses for polymer electrodes.
Dissociated cortical neurons from Wister rat embryos (embryonic day 18) were thenplated on the electrodes and cultivated to form neural networks. Spontaneous activity was
detected by both bare ITO and polymer electrode after 5 days in vitro and the bursting
frequency increased as the networks matured. The stimulation efficiency at low voltages wasevaluated and referenced to ITO electrodes. Polymer electrode stimulation evoked a muchgreater response from the network than stimulation from ITO electrodes as seen in Fig. 2.
Polymer electrodes could be used at low stimulating potentials for the efficient stimulation ofneuronal tissue for more than one month and interfacing could be maintained for several
months. These results show that conducting polymer electrodes have the biocompatibility
needed microelectrodes for interfacing with neural networks.
[1] T. Nyberg, et al., J. Neurosci. Methods. 160 (2007) 16.

Fig. 1. Bode plot of polymer and ITOelectrodes.

Fig. 2．Evoked response for polymer
and ITO stimulation.

－25－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Ion Sensing Assisted by Assembly of Gold Nanorods
Hiroshi Nakashima and Kazuaki Furukawa
Materials Science Laboratory
Rod-like gold nanoparticles (gold nanorods: NRs) show their shape and size-dependent
optical properties whose origin is localized surface plasmon resonance (LSPR). The rodshaped geometry has an inherently high sensitivity to the local dielectric environment
including the adsorbates and the interparticle spacing of the NRs. Therefore, gold NRs havepromising applications as analytical probes in biotechnological systems.
Herein, we report the selective ion sensing of physiologically important cations such as Na+
and K+ using the LSPR absorption of gold NRs with thiol-modified crown ethers in response
to dispersed and aggregated gold NRs. The crown ethers attached themselves covalently to
the gold NR surface due to the high affinity of the thiol group to gold [1].
Figure.1 shows the absorption spectra of the gold NRs (length: 40 nm, diameter: 10 nm)
with 15-crown-5-SH on the addition of NaCl or KCl solution. The gold NRs exhibited two
plasmon absorption maxima around 680-700 and 520 nm, corresponding to a longitudinalmode along the long axis and a transverse mode perpendicular to the long axis, respectively.
When we increased the amount of added KCl solution, the longitudinal absorption intensity of
the NRs gradually decreased and the peak was blue-shifted. The spectral change was causedby the formation of NR aggregates. The recognition of K+ is proposed via a sandwich
complex of 2:1 between 15-crown-5 moiety and K+ (Fig. 2). This triggered the coupling of
the plasmon absorbance as a result of the NRs proximity to each other. In the presence of Na+,the absorption spectra profiles of gold NRs with 15-crown-5-SH remained largely unchanged.
The results originated from the fact that Na+ was recognized by simple 1:1 host-guest
interactions that correlated with the close fit of the cation to the crown cavity. Consequently,
the dispersed or aggregated states of the gold NR complex, which is dominated by the ion
sensing mechanism, result in further spectral changes.
The LSPR properties of gold NRs can be continuously tuned by adjusting their aspect ratio
from the ultraviolet to the infrared region, including the near-infrared region where tissuetransmissivity is at its highest. The functionalized gold NRs with various biomolecules will
provide nano detection platforms such as those used for diagnostic applications and biologicalimaging, and function as a colorimetric reporter via the highly sensitive LSPR properties.
[1] H. Nakashima, et al., Chem. Commun. (2007) 1080.

(a)Absorbance
吸光度

1µL
3µL
5µL
7µL
10µL
15µL
20µL
25µL
30µL

(b)

1µL
3µL
5µL
7µL
10µL
15µL
20µL
25µL
30µL

O

1:1 host-guest
1:1型でイオン捕捉
interaction

O

=

分散
dispersion
Na+

Na+
Na+

O

凝集
aggregation
+

K

Na+

Na
Na

+

Na+

K+

K+
K+

K+

Na+

Na+

K+

K+

K+

Na+

+

K+

Na+

Na+

Na+

K+
K+

K+

長軸方向
longitudinal
の吸収帯
mode

短軸方向
transverse
の吸収帯
mode

K+

Na+
400

O

SH

Na+

300

2:1 sandwich
2:1型のサンドイッチ
complexation
錯体形成により捕捉

O
O

500

600

700

波長 [nm][nm]Wavelength

800

900

300

400

500

600

700

800

900

100 nmWavelength
波長 [nm][nm]

Fig. 1. Absorption spectrum changes of gold NRs on
addition of (a) Na+ and (b) K+.
－26－

Fig. 2. Mechanism of ion recognition and SEM
image of assembled gold NRs.

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Terahertz Spectroscopy of Biomolecules in Nanospace
Katsuhiro Ajito1, Yuko Ueno1,2, Rakchanok Rungsawang1, and Isao Tomita1,3
1Materials Science Laboratory,
2
NTT Microsystem Integration Laboratories, 3NTT Photonics Laboratories
Terahertz (THz) wave region around 0.3 – 10 terahertz has attracted much attention inspectroscopy since it can reveal weak chemical bonds in molecules. We have recently
shown that THz time-domain spectroscopy (THz-TDS) using THz wave pulses exhibits
sufficient sensitivity to molecules to be used as a tool in analytical chemistry [1, 2].
Figure 1 shows angle-dependent THz-TD absorption spectra of cystein single crystal
measured by using linearly polarized THz wave. An ab initio frequency calculation of asingle amino acid molecule was used to predict the intramolecular vibrational modes. These
provide high absorption when molecules are probed with a THz electric field whosepolarization is parallel to the oscillating dipole directions [3].
Figure 2 shows THz-TD absorption spectra of two steric isomers, namely fumaric acid andmaleic acid molecules in nanosized pores of a mesoporus silicate and their crystals inpolyethylene pellets. The intermolecular modes observed with fumaric acid crystals areinactivated by incorporating the molecules in the nano-sized pores due to the separation of themolecules, whereas the intramolecular modes of maleic acid for the crystal and theincorporated samples are similar [4]. Incorporating target molecules in nano-sized spaces iseffective in reducing the concentration of the intermolecular hydrogen bonds of the sample,
and it is possible to distinguish intramolecular hydrogen-bonding vibrational modes fromintermolecular hydrogen-bonding vibrational modes.
We believe that THz spectroscopy will open a new filed in biological analysis in nanospace.
[1] K. Ajito, R. Rungsawang, I. Tomita, and Y. Ueno, Electrochemistry 74 (2006) 506.
[2] Y. Ueno, R. Rungsawang, I. Tomita, and K. Ajito, Anal. Chem. 78 (2006) 5424.
[3] R. Rungsawang, Y. Ueno, I. Tomita, and K. Ajito, J. Phys. Chem. B, 110 (2006) 21259 .
[4] Y. Ueno, R. Rungsawang, I. Tomita, and K. Ajito, Chem. Lett. 35 (2006) 1128.

COOH
HOOC
COOH
HOOC

COOH

HOOC
COOH
HOOC

O
HO
HO

O

O

O

HO

HO
O

HO

crystalFig. 1. Angle-dependent THz-TD
absorption spectra of cysteinsingle crystal at room
temperature. 0゜is definedwhen the c-axis of the crystal isparallel to the polarization of
the THz field.

OHOin poresFig. 2. THz-TD absorption spectra of fumaric acid and mareic acidmolecules (upper and lower) in nanosized pores of a mesoporus
silicate (solid lines) and their crystals in polyethylene pellets(dotted lines) at 77K.

－27－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Gain-cell Dynamic Random-access Memory with Long Data Retention
Katsuhiko Nishiguchi, Yukinori Ono, and Akira Fujiwara
Physical Science Laboratory
As the information technology market continues to expand in various fields, theperformance of data information processing circuits has been improved with an increase inmemory capacity. The capacity of dynamic random-access memory (DRAM), which storesinformation data as charges in a memory node (MN), has been increased by shrinking the
DRAM cell. However, further reduction in a MN capacitance would cause the stored signal to
be buried in noise. Therefore, cell miniaturization and a conservation of the MN capacitanceshould be achieved simultaneously. This requires complicated structures and new materials,
which leads to higher difficulties and costs in their fabrications.
One class of memory device that could allow further shrinking of the MN is a gain-cell
DRAM, in which a small signal originating from electrons stored in the MN is amplified by a
nearby transistor. However, good scalability of the MN in the gain-cell DRAM raises anotherproblem: a smaller MN means fewer electrons in the MN, which leads to shorter retention
time. The dominant origin of this short retention is a current leakage originating from a p-njunction formed in the MN. A consequence of this problem is that the data-refresh process,i.e., periodic data read-out and storage, would have to be performed more frequently than inordinary DRAMs, which would increase power consumption.
We thus fabricated a log-data-retention gain-cell DRAM without p-n junction. The device
is composed of two transistors, FET1 and FET2, which transfer and detect electrons,
respectively. Both were fabricated on an undoped silicon-on-insulator (SOI) wafer (Fig. 1)[1].
The upper gate (UG) is used to induce an inversion layer in the undoped FET1 channel. Whenthe lower gate (LG) turns FET1 off, an energy barrier under the LG electrically forms the MN
at the tip of the wire channel of FET1. By opening and closing FET1, the data ‘0’ and ‘1’ arerespectively represented by the presence and absence of electrons in the MN, which are
introduced from the electron reservoir (ER). Then, the stored data, i.e. electrons, are read out
as the change in current flowing through FET2, which is capacitively coupled to the MN.
Figure 2 shows that the fabricated device provides extremely long data retention (~104 s)even at 85 ºC. This is because the p-n junction formed at the boundary of the MN and FET1
in conventional DRAMs is replaced with the inversion layer formed by the UG, as shown in
the insets of Fig. 2. Additionally, fast data storage (~10 ns) and dynamic random accesscomparable to those of conventional DRAMs were also confirmed.
The demonstrated long data retention reduces the data-refresh cycles, thereby leading to
low power consumption. The fabrication process is highly compatible with MOSFET circuits
and is therefore promising for building gain-cell DRAMs embedded into logic circuits.

UG
LG MN
ER

poly-Si
FET2
FET1

FET1
Si

FET2
Si

100nm

Si
SiO2

Fig. 1. Structures of gain-cell DRAM.

FET2 current [nA][1] K. Nishiguchi, et al., IEEE Electron Device Lett. 28 (2007) 48.
94.8
94.4
94.0
93.6

ER
85°C

‘1’
MN
‘0’

100 102 104 Electrons
Time [s]Fig. 2. Data-retention characteristics.

－28－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Detection of Single Boron Acceptor in Silicon Nano-transostor
Yukinori Ono, Katsuhiko Nishiguchi, and Akira Fujiwara
Physical Science Laboratory
Highly scaled metal-oxide-semiconductor field-effect transistors suffer serious problems
from the fluctuation of the dopant-atom number, but in turn, offer a new concept of a device
in which the charge transport is regulated by means of only a few dopant atoms. It is therefore
important to obtain a deeper understanding of the effect of dopants on charge transport intransistors [1-3] and also to establish a technology for detecting and controlling the dopant
charges. Here, we report the detection of a single boron acceptor in a small transistor as a firststep towards the realization of single-dopant technology [4].
Nano transistors whose gate length and width are both 40 nm were fabricated on a siliconon-insulator substrate. The transistors comprise the channel lightly doped with boron, p-typesource/drain, and electrically formed leads inserted between the channel and the source/drain.
The insertion of the leads prevents the dopant diffusion from the source/drain and enables us
to investigate the conductance of the channel containing only a few dopant atoms. The
conductance was measured at 26 or 6 K as a function of the gate voltage using the substratevoltage (VBG) as a parameter. Figure 1 shows examples of the conductance characteristics fortransistors with the doping density of 2 x 1016 cm-3, corresponding to the mean boron numberin the channel of around one. The conductance modulation, indicated by the arrows, wasobserved in such lightly doped transistors but not in undoped ones. Figure 2 shows thedifferential conductance as functions of the gate and drain voltages, which demonstrates thatthe conductance modulation in Fig. 1 is due to the capture and emission of a single hole byand from a single boron acceptor.
The conductance level of the modulation peak was strongly dependent upon VBG and thedependence was different from one transistor to another (Fig. 1), which is because of therandom doping of boron atoms. This suggests that the VBG dependence conveys theinformation about the location (depth) of the boron and thus could lead to a way to count the
dopant-atom number and measure the location of individual dopant atoms in a transistor.
[1] Y. Ono, et al., Jpn. J. Appl. Phys. 44 (2005) 2588.
[2] Y. Ono, et al., Phys. Rev. B74 (2006) 235317.
[3] J.-F. Morizur, et al., Phys. Rev. Lett. 98 (2007) 166601.
[4] Y. Ono, et al., Appl. Phys. Lett. 90 (2007) 102106.
10-3Transistor A

Transistor B

VBG = -10 V

10-5

0.03

VBG = -8 V
Drain Voltage (V)Conductance (S)

10-4

0.04

-6

10

-7

10

10-8
10-9
10-10
10-11
-12

10

VBG
=8V

-1.6

-1.2

VBG =
10 V
-0.8

-0.4

Gate Votage (V)0.0 -1.2 -0.8 -0.4

Ｔｒａｎｓｉｓｔｏｒ Ａ

0.02
0.01
0.00
-0.01
-0.02
-0.03

0.0

0.4

Gate Voltage (V)Fig. 1. Conductance at 26 K of transistors whose mean boron
number in the channel is around one.

－29－

-0.04
-0.75 -0.70 -0.65 -0.60 -0.55 -0.50

Gate Voltage (V)Fig. 2. Differential conductancemeasured at 6 K.

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Electron Phase Sensing in a High Q Mechanical Resonator
Imran Mahboob and Hiroshi Yamaguchi
Physical Science Laboratory
Electromechanical systems are novel devices incorporating a high Q mechanical oscillator
within an electrical architecture. Due to their low energy dissipation characteristics, thesedevices offer unprecedented sensitivity for the detection of miniscule forces arising from forexample magnetic moments, electron and nuclear spins. Furthermore, the purity of themechanical mode enables fundamental energy dissipation processes to be studied for example
electron-electron and electron-phonon interactions in quantum electron transport in low
dimensional systems.
In this study, modulations in the phase of the electron wave function were used to detect
the miniscule displacements of the mechanical element [1]. A quasi-1D diffusive electron
system in an InAs quantum well was incorporated onto an AlGaSb nano-mechanicalsuspended beam and is shown in Fig.1(a). Additionally, a Au wire was also placed on thesuspended beam to enable the mechanical resonance to be actuated via the magnetomotive
method where an alternating current was passed in the Au channel in the presence of amagnetic field. An out of plane beam resonance frequency, f0 = 10.268 MHz and quality
factor, Q = 12500 was measured at 20 mK and is shown in Fig.1(b).
The beam oscillation was then detected by measuring the resistance change in the quasi1D electron system as a function of beam vibration frequency and magnetic field. The
resistance change at the beam resonance frequency (magnetopiezoresistance [MPR]) wasstrongly peaked. By varying the magnetic field, this resistance change at resonance could be
modulated. The MPR at mechanical resonance showed reproducible highly periodic
resistance oscillations which arise via strain induced electron phase modulation and is shownin Fig.1(c). The Fourier transform of the MPR [shown in Fig.1(d)] indicates that mechanicalactivation of the beam affects only a few electron trajectories and the electron interference in
only a single electron loop gives rise to the resistance oscillations observed in the MPR.
[1] I. Mahboob, et al., Appl. Phys. Lett. 89 (2006) 192106.

Fig. 1. An SEM image of the device (8 µm long and 1.5 µm wide) (a). The beam resonance measured by themagnetomotive method (b). The MPR, measured at mechanical resonance in the quasi-1D InAs system(c). The Fourier transform of the MPR (d).
－30－Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Block Copolymer Lithography toward 16-nm-technology Nodes
Toru Yamaguchi and Hiroshi Yamaguchi
Physical Science Laboratory
Block copolymer lithography (BCL) has attracted considerable attention as a combined
top-down/bottom-up approach to nanopatterning. It involves the use of microphase-separated
nanometer-sized domains of block copolymers as lithography templates. In recent times, thesignificance of BCL in the field of lithography is particularly increased due to the fact that
top-down lithography will soon be reaching its limit in the 22-nm regime, necessitating thedevelopment of innovative technologies. BCL has great potential for exceeding the resolution
limit of the state-of-art top-down lithography because its resolution is determined solely by
the molecular size of the block copolymer. The most important challenge in BCL is theachievement of a strict control on the alignment of various microphase-separated domains.
Among these domains, vertical lamellar domains composed of alternating stacked layers of
two dissimilar polymer chain blocks A and B (Fig. 1) have critical advantages as lithography
templates for nanodevice fabrication on account of their line shape, high aspect ratio, andwide flexibility in pattern configuration. However, the difficulty encountered in the formationof vertical lamellae was that the lamellar interface should be aligned in two directions,perpendicular to the substrate surface and parallel to the lithographically created features.
Here, we report our novel method of aligning lamellar domains by means ofgraphoepitaxy using a resist pattern as an alignment guide [1]. Graphoepitaxy is a techniquethat uses the surface topography of the substrate to direct the epitaxial growth of the block
copolymer film. The key to its success is the combination of the neutralization of a bottom
surface and the introduction of a hydrophilic guiding pattern; this makes it possible toindependently control the surface affinity of the substrate surface and the sidewall surface ofthe guiding pattern, which leads to the vertical orientation and lateral alignment of lamellar
domains, respectively (Fig. 1). We have successfully demonstrated that the lateral alignmentof the lamellar structure of a symmetric poly(styrene-b-methyl methacrylate) is achieved inconfined spaces of about 3La (La: laterally aligned lamellar period, La ~ 32 nm) betweenhydrogen silsesquioxane (HSQ) resist patterns on a neutral surface (Fig. 2). It is important toconsider that a lamellar structure with a period shorter than the pitch of the guide pattern
could be formed by this method. We believe that the combination of the artificial layout of theguide patterns and the best polymer materials could lead to a new type of high-resolution
lithographic technology in the 16-nm (1/2 La) regime.
[1] T. Yamaguchi and H. Yamaguchi, J. Photopolym. Sci. Technol. 19 (2006) 385.
Block copolymer

A

Single molecule

Guide pitch: 110 nm

B

HSQ guideLa
2 x molecular size

Neutralization layer
Fig. 1 Lateral alignment of lamellar domains.

200 nmFig. 2 AFM phase image of aligned domains.

－31－Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Single-electron Counting Device
Toshimasa Fujisawa
Physical Science Laboratory
Single-electron counting device (see a frontispiece) is promising for detecting individual
electron flow and analyzing an electrical current with various statistical analyses. Here, we
present some experiments as a single-electron ammeter for detecting an extremely faintcurrent and as a physical tool to investigate electron correlation in a transport [1].
We have developed a single-electron counting device, which measures the location of anelectron in two quantum dots by using a point contact electrometer (see the frontispiece). For
example, an average current can be obtained by counting the number of net electron flow in agiven period. We have demonstrated such current measurement on a single-electron transistor
as shown in Fig. (a). The obtained current shows Coulomb blockade oscillations as shown in
Fig. (b), where noise level of about 3 atto-ampere is three or four orders of magnitudes
smaller than that in a conventional ammeter.
In addition to the average current, various statistical analyses are also demonstrated.
Figure (c) shows a histogram of the interval between two consecutive forward electron
tunneling events (called forward recurrence time), where the reduction of the occurrence withzero interval suggests anti-bunching correlation. This appears from Coulomb interaction in
the single-electron transport through the counting device. Moreover, Fig. (d) represents ahistogram of the current measured in a short period Tavr (counting statistics), where higher
order noise of the current are extracted to characterize the distribution of the current. We
believe that various correlated transport can be examined with this technique.
[1] T. Fujisawa, et al., Science 312 (2006) 1634.

Fig. Experiments on single-electron counting. (a) A circuit diagram for measuring a current from a singleelectron transistor. (b) Coulomb blockade oscillations of the device. (c) Anti-bunching correlation in
the transport through the device. (d) Counting statistics of the current showing the second (S) and third(C) order noise.

－32－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Density-of-states Imaging in Semiconductor Heterostructures
Kyoichi Suzuki1, Kiyoshi Kanisawa1, Simon Perraud1,2, Camille Janer1,3,
Kei Takashina1, Toshimasa Fujisawa1, and Yoshiro Hirayama1,41
Physical Science Laboratory, 2CNRS, 3ESPCI, 4Tohoku University
As semiconductor devices develop and become highly integrated with ultra fine processes,
quantum mechanical effects in the devices dominate their characteristics. Local analysis of
the wavefunctions becomes important for realizing precise device performance. In addition,
new physical phenomena emerging from their nano-scale dimensions are expected. The
scanning tunneling spectroscopy (STS) method, which measures the tunneling current
characteristics using a scanning tunneling microscope (STM), allows us to investigate theelectron density of states (DOS) with nanometer resolution as a function of the energy,
corresponding to the squared wavefunctions. By scanning the probe, the spatial distributionof the DOS can be obtained.
By performing STS on cleaved semiconductor heterostructure surfaces (Fig. 1), we havesucceeded in imaging quantized subbands formed in a quantum well (Fig. 2) [1], interferenceof electron waves at an heterointerface (Fig.3) [2], and wavefunction coupling in a double
quantum well [3]. This method can be easily applied to more complicated heterostructures
allowing spatial wavefunction analysis in real devices.
[1] K. Suzuki, et al., Phys. Rev. Lett. 98 (2007) 136802.
[2] K. Suzuki, et al., Jpn. J. Appl. Phys. 46 (2007) 2618.
[3] K. Suzuki, et al., J. Cryst. Growth 301-302 (2007) 97.
<110>

1.0

GaSb

0.8

0.8

Energy (eV)

ϕ2

0.6
0.4
0.2

5
4
3
2

0.0

1

Low

ΦR
ΦI
GaSb

0.6
0.4
0.2
0.0

InAs

0.40000.39650.39300.38950.38600.38250.37900.37550.37200.36850.36500.36150.35800.35450.35100.34750.34400.34050.33700.33350.33000.32650.32300.31950.31600.31250.30900.30550.30200.29850.29500.29150.28800.28450.28100.27750.27400.27050.26700.26350.26000.25650.25300.24950.24600.24250.23900.23550.23200.22850.22500.22150.21800.21450.21100.20750.20400.20050.19700.19350.19000.18650.18300.17950.17600.17250.16900.16550.16200.15850.15500.15150.14800.14450.14100.13750.13400.13050.12700.12350.12000.11650.11300.10950.10600.10250.09900
0.09550
0.09200
0.08850
0.08500
0.08150
0.07800
0.07450
0.07100
0.06750
0.06400
0.06050
0.05700
0.05350
0.05000

Low

0
10
20
30
Position from heterointerface (nm)

0
5
10
15
20
Position perpendicular to heterointerface (nm)Fig. 2. DOS in an InAs/GaSb single quantum well.
Spatial standing wave patterns corresponding
to the confined subbands were observed.

InAs

Energy (eV)High

GaSb InAs GaSb

0.12000.11630.11250.10880.10500.10130.09750
0.09375
0.09000
0.086250.08250
0.07875
0.07500
0.07125
0.06750
0.063750.06000
0.05625
0.052500.04875
0.04500
0.04125
0.03750
0.03375
0.03000
0.02625
0.02250
0.01875
0.01500
0.01125
0.007500
0.003750
0

DOS
High

DOS

GaSb Barrier

InAs

GaSb
InAs
GaSb

Fig. 1. Cleaving is performed under ultra-highvacuum (UHV) (<2x10-10Torr) to obtain aclean flat surface. Then, the sample is loaded
into the STM setup cooled down to 4.8 K
without breaking UHV.

GaSb

Scanning

Fig. 3. DOS around an InAs/GaSb single
heterointerface. Interference patterns dueto the electrons incident on/reflected fromthe GaSb potential barrier were observed.

－33－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Quantum Transport in Silicon-On-Insulator Structures
Kei Takashina, Yukinori Ono, Akira Fujiwara, Yoshiro Hirayama*, and Toshimasa Fujisawa
Physical Science Laboratory
Besides being of immense technological importance, electrons in silicon offer a number of
unique possibilities for exploring new physical conditions and new phenomena. One of thesearises due to their bulk dispersion relation where there are six, energetically degenerate
conduction band valleys. In Si(100)-MOSFETs where electrons are two-dimensionallyconfined, this six-fold degeneracy is lifted, due to anisotropic effective mass, to leave only
two low lying valleys available for occupation. 2-D electrons in such structures consequently
have freedom as to how they occupy these degenerate valleys giving them a valley degree of
freedom on top of in-plane motion and spin.
In the present study, we have been able to show that valley-splitting, which lifts thisremaining two-fold valley degeneracy can be enlarged and controlled over an unprecedented
extent using SOI (Silicon-On-Insulator) MOSFETs [1] and that its effects can be observed
clearly by direct transport measurements even without magnetic field (Figures) [2]. The
results demonstrate considerable potential for exploring valley-related phenomena and new
device possibilities.
[1] K. Takashina, A. Fujiwara, S. Horiguchi, Y. Takahashi, and Y. Hirayama, Phys. Rev. B
69 (2004) 161304(R).
[2] K. Takashina, Y. Ono, A. Fujiwara, Y. Takahashi, and Y. Hirayama, Phys. Rev. Lett. 96(2006) 236801.
*Present address: Tohoku University

Fig. Two-terminal conductance at 4.2K as a function of front-gate voltage VFG at various values of back-gate
voltage VBG. The inset shows the experimental setup. A and B mark features associated with secondconfinement-subband occupation and valley splitting respectively. Right: 2nd derivative of the data showing
the evolution of the features. The white squares joined by lines mark self-consistently calculated positions of
the onset of second-confinement-subband occupation using nominal parameters of the device. (The feature
marked C is due to the onset of conduction.)－34－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Decoherence of a Superconducting Flux Qubit
Kosuke Kakuyanagi, Shiro Saito, Hayato Nakano, and Kouichi Semba
Physical Science Laboratory
In order to carry out quantum operations using qubits, we need to maintain quantum
coherence throughout all the quantum gate operations. However, coherence decreases overtime because of the interaction between qubits and their environment. This phenomenon iscalled decoherence, and we must clarify its origins if we are to extend the coherence time.
The superconducting flux qubit (Fig. 1) is a promising solid-based qubit that offers theadvantage of scalability. We attempt to measure the magnetic field dependence of the phaserelaxation time ( T2 ) and energy relaxation time ( T1 ) in order to clarify the decoherence of asuperconducting flux qubit [1]. Relaxation is generally caused by the energy fluctuation thatis generated from the interaction between qubits and their environment. Therefore, we canobtain information about the contribution of magnetic fluctuations to decoherence from fielddependence measurements of the relaxations.
Figure. 2 shows measurement results for the magnetic field dependence of T1 and T2
near the degeneracy point ( ∆Φ qb = 0 ). The magnetic field is plotted with flux quantum units( Φ 0 ). The T2 values increase as the external magnetic field approaches the degeneracy point.
At the degeneracy point, the T2 value reaches 250 ns. In contrast, the T1 values are uniform( T1 ~140 ns).
In general, T2 includes pure dephasing ( ΓΦ ) and T1 component contributions. The
relationship between T1 and T2 is described as 1 T2 = ΓΦ + 1 (2T1 ) . From the observed T1
and T2 values, the coherence time of a superconducting flux qubit at the degeneracy point ismainly suppressed by energy relaxation. Moreover, we can explain the behavior of themagnetic field dependence of pure dephasing in terms of the contribution of 1 / f type
frequency distributed magnetic fluctuations.
Energy relaxation is generated from high frequency fluctuations, whose frequency is thesame as the qubit energy. These results suggest that the coherence time of a superconducting
flux qubit improves when we suppress the high frequency noise. Next, we will attempt toimprove the coherence time of the superconducting flux qubit.

[1] K. Kakuyanagi, et al., Phys. Rev. Lett. 98 (2007) 047004.
300.0nSQUID

Readout
line

TT11
TT22

250.0n200.0nT22(s),(s), TT11(s)
(s)

3µm

Flux
qubit

150.0n100.0nBias line

Microwave line
50.0n
0.0

-4

-4.0x10

Fig. 1. Sample image of flux qubit.

-4-2.0x100.0∆Φqb (Φ0)-4

2.0x10Fig. 2. Field dependence of T1 and T2.

－35－

-4

4.0x10Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Aharonov-Casher Effect by Spin-orbit Interaction
Tobias Bergsten1,2, Toshiyuki Kobayashi1,2, Yoshiaki Sekine1,2, and Junsaku Nitta1,2,3
1
Physical Science Laboratory, 2CREST-JST, 3Tohoku University
The aim of spintronics is to manipulate spin of electrons in electronic circuits. This will
make it possible to design new kinds of electronic devices, e.g. the spin-FET proposed by
Datta and Das [1]. The common way to manipulate spin is by using magnetic field, because
the spin is related to magnetic properties. However, it is also possible to use an electric field
to influence the spin, utilizing spin-orbit interaction (SOI). The strength of the SOI in asemiconductor heterostructure can be engineered by careful design of the conductance andvalence bands, and it can also be controlled by an electrostatic gate on top of the device [2].
In the current study, we have controlled the interference of the electron waves due to spin
precession by gate voltage [3]. This is a demonstration of the Aharonov-Casher (AC) effect,
an interference of particles with magnetic moment interacting with an electric field.
The device used in this study was fabricated using InAlAs/InGaAs/InP quantum well,where the SOI strength is tunable by gate voltage by more than 3 peVm. To observe theinterference of electron waves traveling along a limited path, a ring array was etched out asshown in Fig. 1. The gate electrode is deposited on top of the rings using 50 nm-thick SiO2 as
a gate insulator.
The relative phase difference of partial electron waves, which propagate clockwise andcounterclockwise in a ring structure, was controlled by the gate voltage (AC effect) as well as
the magnetic field (Aharonov-Bohm and Al’tshuler-Aronov-Spivak effect) and measured as a
resistance oscillation (Fig. 2). Since the electron is a fermion particle (spin is 1/2), the spin
precession of one turn (2π) changes the quantum phase for π. Therefore, the resistanceoscillation period with respect to the gate voltage corresponds to the relative spin precession
angle of 4π between the two partial waves of an electron traveling opposite directions andcoming back to the original position. This shows that we have precise control of the spin
precession angle for over 12π. This spin control is essential for the spin-FET and it may also
prove important for future quantum computing devices based on spin qubits.
[1] S. Datta and B. Das, Appl. Phys. Lett. 56 (1990) 665.
[2] J. Nitta, T. Akazaki, H. Takayanagi, and T. Enoki, Phys. Rev. Lett. 76 (1997) 1335.
[3] T. Bergsten, T. Kobayashi, Y. Sekine, and J. Nitta, Phys. Rev. Lett. 97 (2006) 196803.

Fig. 1. SEM image of a ring array etched out ofan InAlAs/InGaAs/InP heterostructure.

Fig. 2. The resistance oscillation by AC effect(vertical direction) and AAS effect (horizontal
direction).

－36－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Detection of Domain Wall in a Permalloy Wire Usinga Semiconductor and Ferromagnetic Hybrid Structure
Yoshiaki Sekine1, Tatsushi Akazaki1, and Junsaku Nitta2,31
Physical Science Laboratory, 2Tohoku University, 3CREST-JST
Using the local Hall effect (LHE), we have succeeded in detecting a magnetic domain wall
(DW) trapped in a permalloy, NiFe, wire and in clearly distinguishing whether the DW
structure is a tail-to-tail or a head-to-head DW [1].
In the field of spintronics, devices utilizing DWs were proposed and many methods wereapplied to detect DWs. Among them, the LHE method using a semiconductor andferromagnetic hybrid structure has the advantage of large signal enough to investigate the DW
dynamics. An InGaAs two-dimensional electron gas (2DEG) that is 5 nm below the surface
was used for a Hall sensor that detects the stray field from the NiFe wire. A 60-nm-thickand 300-nm-wide NiFe wire consisting of a notch at the center, a taper end and a right-angle
end was deposited on the surface. These wire structures make it possible to trap a tail-to-tailor a head-to-head DW at the notch with changing the direction of the magnetic field, B.
Three Hall crosses were fabricated just below both ends and the center of the wire. Figures
1(a) and (b) show a scanning electron microscopy (SEM) image and a cross-sectional view ofthe sample, respectively. A tail-to-tail DW and a head-to-head DW are sketched in Fig. 1(c)and (d). With sweeping B parallel both to the wire and the 2DEG, the DW nucleates at theright-angle end, then the DW displaces to and pins at the notch. With changing B
furthermore, the DW depins from the notch, then the DW moves to and annihilates at theright-angle end. The B-dependence of the Hall resistivity, ρyx, on three Hall crosses isshown in Fig. 2. Here, ρyx1, 2, 3 are defined as ρyx on the right-angle end, notch, and taper
end, respectively. With increasing B, ρyx1 shows the sharp drop at 22 mT, whichcorresponds to the DW nucleation at the right-angle end. At 26 mT, rapid increase of ρyx3
represents the DW annihilation at the taper end. Between 22 and 26 mT, ρyx2 shows thepeak, which corresponds to the pinned tail-to-tail DW. With decreasing B, the sharpchanges in ρyx1 and 3 represent the DW nucleation and annhilation. Between -22 and -26
mT, the dip of ρyx2 corresponds to the pinned head-to-head DW. Note that the DW
nucleates at the right-angle end with sweeping B. The LHE method can make the distinction
between the tail-to-tail and head-to-head DWs. These results indicate the LHE method is
attractive for investigating the DW movement that is a key to DW devices.
[1] Y. Sekine, et al., AIP Conference Proceedings 893 (2007) 1291.
(a)

Taper

Ｂ

Right- (b)
Stray
angle
Field

Notch

(c)

NiFe
InGaAs(d)Fig. 1. (a) The SEM image of the sample. (b) The crosssectional view of the sample. The schematic view ofthe (c) tail-to-tail and (d) head-to-head DWs.

－37－

Fig. 2. The Hall resistivity, ρyx, vs themagnetic field, B. The peak anddip in ρyx2 correspond to the trapped
tail-to-tail and head-to-head DWs.

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Controllable Coupling between Flux Qubit and NanomechanicalResonator by Magnetic Field
Y.D Wang, Hajime Okamoto, Hiroshi Yamaguchi, and Kouichi Semba
Physical Science Laboratory
Flux qubit, also known as persistent current qubit, is micro-meter sized superconducting
loop interrupted by several (usually three) Josephson junctions. Flux qubit is one of the mostpromising candidates for physical realizations of quantum information processing. On theother hand, nanoelectromechanical systems (NEMS), whose scale is smaller size than microelectromechanical system (MEMS), are promising to improve abilities of measuring small
displacements and forces at a molecular scale. Meanwhile, nanomechanical resonator(NAMR) with sufficient high oscillation frequency at low temperature is supposed to behave
as quantized harmonic oscillator. Due to their comparative sizes and energy scales as well as
low dissipation, the coupling of NAMR and superconducting qubits has attracted a lot ofinterest to realize a novel solid-state cavity QED architecture. With this architecture, NAMR
can serve as a data bus for multi-qubits operations of flux qubits. Coupling mechanism
between flux qubit and NAMR also enables production and detection of quantum states of
NAMR. However, existing theoretical investigations only concentrated on the coupling of
NAMR with Josephson charge qubit while experimentally the coherence of flux qubit isundergoing rapid development.
We thus proposed an active mechanism to couple the mechanical motion mode of a
NAMR to the persistent current in the loop of superconducting Josephson junction (or phaseslip) flux qubit [1]. As shown in Fig.1, the coupling can be controlled in situ by an externalclassical magnetic field. According to our numerical estimation, the whole system forms a
new solid-state cavity QED architecture in "strong coupling limit". This architecture can beused to demonstrate quantum optics phenomena as well as coherently manipulate the qubit forquantum information processing. The coupling mechanism is applicable for more generalized
situations where the superconducting Josephson junction system is a multi-level system.
[1] F. Xue, Y. D. Wang, C. P. Sun, H. Okamoto, H. Yamaguchi, and K. Semba, New J. Phys.
9 (2007) 35.

F0

B0

Fig. 1. A mechanical beam (the gray bar) is incorporated in asuperconducting loop of a 3-Josephson-junction (eachJosephson junction is indicated by a cross) flux qubit. Undera magnetic field B0 along y direction, the persistent supercurrent in the qubit loop produces Lorentz force F0 on the
beam (NAMR) along z direction. Therefore, the z-direction
motion of the beam is coupled with the persistent current offlux qubit.

－38－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

10 GHz Clock Quantum Cryptography Experiment
Hiroki Takesue1，Eleni Diamanti2, Carsten Langrock2, Martin M. Fejer2, and Yoshihisa Yamamoto2
1
Optical Science Laboratory, 2Stanford University
For realizing practical quantum cryptography systems, increasing a key generation rate isimportant. Here we report a high-speed quantum cryptography experiment at a 10-GHz clock
frequency [1] using frequency up-conversion detectors (UCD) [2] with improved timing jitter.
We employed differential phase shift quantum key distribution protocol [3]. An actively
mode-locked laser output a 10-GHz clock pulse train whose wavelength and pulse width were1551 nm and 10 ps, respectively. The phase of each pulse was randomly modulated by 0 or π.
Then, the pulse train was attenuated so that the average photon number per pulse becomes 0.2,
and transmitted over optical fiber. The output pulses from the fiber were launched into a 1-bit
delayed interferometer, which was followed by two UCDs. In an UCD, a signal photon was
combined with a 1319-nm pump light and injected into a PPLN waveguide, in which thesignal photon was up-converted to a 700-nm photon. After suppressing noise photons with
optical filters, the up-converted photon was detected by a low-jitter Si APD. With those
detectors, we were able to receive high-speed photon trains with a high timing resolution.
Figure. 1 shows the histogram of detected signal when 3-ps pulses were input into an UCD.
Although the full width at half maximum of the timing jitter was as small as 30 ps, a large tailwas observed. We then adjusted the quantum efficiency, combined dark count rate, and time
window width at 0.3%. 750 cps, and 10 ps, and undertook quantum key distribution. The
sifted key rate at 100 km was 3.7 kbit/s. The obtained error rate as a function of fiber length isshown with squares in Fig. 2. The error rate was around 10%, which was due to the tailingcharacteristics of jitter. Interestingly, we did not observe significant variation in the error rate
when we used fibers with different lengths. This indicates that the use of short pulses andnarrow time window improved the ratio between signal and dark counts per time slot. Circles
in Fig. 2 show estimated error rate due to dark counts. A dark count-induced error rate wassuppressed to less then 1% even after 100 km transmission. Therefore, we can expect
significant improvement in the error rate by improving the UCD timing jitter characteristics.
[1] H. Takesue, et al., Opt. Express 14 (2006) 9522.
[2] C. Langrock, et al., Opt. Lett. 30 (2005) 1725.
[3] K. Inoue, E. Waks, and Y. Yamamoto, Phys. Rev. Lett. 89 (2002) 037902.

Fig.1. Detection signal histogram.

Fig. 2. Error rate as function of fiber length.
－39－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Differential-phase Quantum Key Distribution Experiment
Using a Series of Quantum Entangled Photon Pairs
Toshimori Honjo1, Hiroki Takesue1, and Kyo Inoue2
1
Optical Science Laboratory, 2Osaka University/NTT Research Professor
Quantum key distribution (QKD) has been studied as a way to realize unconditionallysecure communications. We had been intensively worked on differential-phase-shift QKD(DPS-QKD) experiment where randomly phase-modulated coherent pulse stream was used.
Recently, we made a step toward more sophisticated QKD experiment using entangled photon
pairs[1].
Figure 1 shows the experimental setup. A 1-GHz pulse stream amplified by an erbiumdoped fiber amplifier (EDFA) was launched into a 500-m DSF. The DSF was cooled withliquid nitrogen to suppress noise photons through the spontaneous Raman scattering process.
A series of time-correlated entangled photon pairs was generated in the DSF by the
spontaneous four-wave mixing process[2]. After suppressing residual pump, the photons were
input into an arrayed waveguide grating (AWG) that separated the signal and idler photons.
The signal and idler photons were sent to Alice and Bob, respectively. Alice and Bob
randomly imposed phase-modulation on the incoming pulses by 0 or π/2, and then launchedthem into 1-bit delay planar lightwave circuit (PLC) Mach-Zehnder interferometers. Setting
the phase difference between the two arms to 0 and focusing on a certain time slot, they canobtain the following correlation
ψf =

1
2 2

{(ei (θ a +θb ) + 1) A1 B1 − (ei (θ a +θb ) + 1) A2 B2 − i(ei (θ a +θ b ) − 1) A1 B2 − i(ei (θ a +θ b ) − 1) A2 B1 }where θ a and θ b represents the differential phases imposed by Alice and Bob, respectively,wn

represents the state that a photon goes to detector n placed at the output of each PLC

Mach-Zehnder interferometer at site w, with w=A(Alice)or B(Bob). After the photontransmission, Alice and Bob disclosed the photon detection time and the differential phase
imposed on corresponding pulses through a public channel. In cases that Alice and Bob
detected photons at an identical time slot, they created a key bit using the above correlations.
With this setup, we generated sifted keys with a quantum bit error rate of 8.3 % and asifted key generation rate of 0.3 bit /sec[3]. We revealed the feasibility of this QKD scheme,
and showed the first step toward sophisticated quantum communications.
[1] K. Inoue, Phys. Rev. A 71 (2005) 032301.
[2] H. Takesue and K. Inoue, Opt. Express 13 (2005) 7832.
[3] T. Honjo, H. Takesue, and K. Inoue, Opt. Lett. 32 (2007) 1165.
1GHz

Laser Intensity
diode modulator

Alice

Erbium doped Filters
fiber amplifier

Liquid nitrogen
Dispersion-shifted fiber(500m)

Mach-Zehnder Arrayedinterferometer waveguidegrating

A1

Fiber
Bragg
grating{0,π/2}

Avalanche
photo diodeinterferometer

Phase
modulator

Phase
modulator

A2

Avalanche
photo
diode
Mach-Zehnder{0,π/2}

Band pass filter

Fig. 1. Experimental setup.
－40－

Bob
B1
B2

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Pair-wise Entanglement for Characterizing Quantum Phase Transition
Kaoru Shimizu and Akira Kawaguchi*
Optical Science Laboratory
Quantum behaviors of a one-dimensional interacting spin system have attracted many
research interests because that offers some important theoretical models for condensed matterphysicist. Moreover, from the view of one-way quantum computation, study of the spin
system may provide a variable knowledge for designing its operation scheme. In particular, it
is most important for us to establish a physically-clear interpretation for the variety of the
behaviors that are regulated by quantum uncertainty depending on the different values ofspin-spin interaction coefficient J and external magnetic field h.
By adapting some knowledge of quantum entanglement to the one-dimensional spin
system, we here obtained an insight that the quantum behaviors of the system can becharacterized in a quantitative way by small numbers of parameters; amplitudes and phases offour different types of quantum correlation (four Bell-states) between neighboring two spins,
though the system is composed of many numbers of spins. We employed the one-dimensionalanti-ferromagnetic Ising spin model represented by the Hamiltonian: H=JΣSZiSZi+1+hxΣSZi
with the transverse magnetic field hx. Then we studied the behavior of pair-wise quantum
entanglement† with regarding the different values of h/J, where the system changes from therandom phase of SZj ( for a large hx value) to the ordered phase (anti-ferromagnetic phase for asmall hx value). From critical behaviors of the pair-wise entanglement observed around thephase transition point, we can conclude that the amplitudes and phases of different quantum
correlation provide a quantitative description of quantum spin fluctuation[1].
Our proposed method on the basis of the entanglement analysis is a useful tool forunderstanding the quantum behaviors of one or two dimensional spin systems.
[1] K. Shimizu and A. Kawaguchi, Phys. Lett. A 355 (2006) 176.
*

Present address: Toyota Macs. Co. Ltd.
Reduced density matrix ρ for the neighboring spins is decomposed into the separable part (1−Λ)ρs andthe inseparable part Λρe, (Fig.1) where ρe is decomposed into the four Bell states so (Fig.2) that (1−Λ) is
minimal. We employ concurrence C(ρ) as a quantitative measure of pair-wise entanglement.
†

Fig.1. h dependence of concurrence C(ρ)(h=0.5: phase transition point).

－41－

Fig.2. Decomposition of ρe into four Bellstates (spin correlation).

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Optical Properties of GaAs Quantum Dots Formed in (Al,Ga)As
Nanowires
Haruki Sanada, Hideki Gotoh, Kouta Tateno, Tetsuomi Sogawa, and Hidetoshi Nakano
Optical Science Laboratory
Semiconductor nanowires (NWs) have been extensively investigated as fascinating
candidates for nanoscale photonics and electronics applications. The vapor-liquid-solid (VLS)
method is a technique for fabricating freestanding NWs with a broad range of semiconductormaterials. The method not only produces one-dimensional structures, but also offers
additional flexibility as regards band structure engineering by employing a conventional
heterostructure technology. Here we report the results of an experimental photoluminescence(PL) measurement undertaken to clarify the optical properties of single GaAs quantum dots
(QDs) formed in (Al,Ga)As NWs grown by the VLS method [1].
We fabricated GaAs QDs in (Al,Ga)As NW by the following two steps: (1) VLS growthof the NWs that have GaAs/(Al,Ga)As heterojunctions; and (2) normal MOVPE for covering
the NWs with (Al,Ga)As cap layers, which suppress the non-radiative surface recombinationof photoexcited carriers [2]. Figure 1 shows a cross-sectional SEM image of the similar
structure composed of a GaAs/AlAs system instead of a GaAs/(Al,Ga)As system. The image
shows that several QDs have formed inside the NW.
In Fig. 2, we compare the PL spectra with different excitation powers (Pexc) to examine
the characteristics of the two peaks labeled by A and B. For Pexc < 100 W/cm2, the integrated
intensities of peak A and B have linear dependence with Pexc and Pexc2, respectively, which isa typical behavior of exciton and biexciton emissions. In addition, the biexciton peak (peak B)
energy exhibits a red shift and its linewidth broadens as Pexc increases. This might be acharacteristic of QDs in NW structures grown by the VLS method because similar features
have been reported in VLS-based InAs/GaAs and Ga(As,P)/GaP QDs systems. We also foundthat the PL depends on the optical polarization axis, indicating that the nanostructures have ahighly asymmetrical shape. Although a more explicit consideration of their structuralconfigurations is required to clarify the mechanism, our method is a promising way ofengineering the positions and optical properties of GaAs/(Al,Ga)As nanostructures.
[1] H. Sanada, H. Gotoh, K. Tateno, and H. Nakano, Jpn. J. Appl. Phys. 46 (2007) 2578.
[2] K. Tateno, H. Gotoh, and Y. Watanabe, Appl. Phys. Lett. 85 (2004) 1808.
B

PL Intensity (a.u.)

875

A

420
210
105
52.5
25.0
12.5
6.25
2
3.25 W/cm
1.66

1.67

1.68

Energy (eV)Fig. 1. Cross-sectional SEM image of dot-inwire structure composed of a GaAs/AlAs
system.

Fig. 2. Excitation power dependence of the PL
spectra measured at 4 K.
－42－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Quantum Dot Laser Using Photonic Crystal Nanocavity
Takehiko Tawara1, Hidehiko Kamada1, Yong-Hang Zhang2,
Takasumi Tanabe1, and Tetsuomi Sogawa1
1
Optical Science Laboratory, 2Arizona State University
Photonic crystal (PhC) is advantageous for constructing nanocavities with a high quality
factor (Q) and a wavelength-sized modal volume (Vm). A high Q/Vm nanocavity enhances
the spontaneous emission rate of an active medium inside the cavity, and this enables us to
produce optical devices with high efficiency and a low power consumption. Moreover, theuse of semiconductor quantum dots (QDs) as an active medium will lead to higher efficiency
owing to the suppression of phonon scattering and the surface recombination of carriers. SuchQD PhC nanocavities are promising for use as ultrasmall and internal laser sources forphotonic integrated circuits.
In general, QD PhC nanocavities have a III-V semiconductor heterostructure consisting of,for example, GaAs-based materials. However, in many cases the Q value was only several
thousand, and this is insufficient to achieve the nanocavity effect. Certain factors are assumed
to cause this problem; (i) the accuracy of the dry etching process is too low to obtain a high Q
cavity, and (ii) there is a large optical loss induced by the re-absorption effect caused by QDs
that are not coupled with the cavity mode.
To achieve high processing accuracy, we used EB lithographic resist as an etching mask
and optimized the etching conditions for each layer with a different composition [1]. We also
designed the PhC structure, including the materials composing it and the cavity mode
detuning to the QD inhomogeneous broadening, to suppress the re-absorption effect. A Q ofover 10,000 was achieved by making these improvements (Fig. 1) [2]. Moreover, a lasing
action with very high spontaneous emission coupling to the lasing mode (β) was observed asa result of the excitation power dependence of the PL intensity and carrier lifetime (Fig. 2) [3].
These results provide us with a guideline for the structural design and fabrication method,
and are important in terms of achieving highly efficient ultrasmall light sources.
[1] T. Tawara, et al., Jpn. J. Appl. Phys. Phys. 45 (2006) L917.
[2] T. Tawara, et al., IPRM2007, Matsue, Japan, May 2007.
[3] T. Tawara, et al., CLEO/QELS2007, Baltimore, USA, May 2007.

Fig. 1. Quantum dot emission via cavity mode.

Fig. 2. Lasing characteristics.

－43－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Spatiotemporally Resolved Soft X-Ray Absorption Spectroscopy of a
Femtosecond Laser Ablation Plume
Katsuya Oguri, Yasuaki Okano, Tadashi Nishikawa, and Hidetoshi Nakano
Optical Science Laboratory

Wavelength [nm]Time-resolved x-ray measurement techniques have attracted much attention as a result of
the recent progress on the ultrashort x-ray pulse generation technology based on laser-based
x-ray sources and synchrotron radiation sources. These techniques enable us to measure theultrafast dynamics of crystal structures, atomic distances, coordination numbers, andelectronic states in a highly nonequilibrium state, and they are expected to become a key
technique for the new interdisciplinary field linking conventional x-ray science and ultrafast
optical science, namely "ultrafast x-ray science" [1].
Ｗe developed a spatiotemporally resolved XAS system by improving our previous time
resolved XAS system [2]. Using the system, we measured the space and time evolution of aplume generated by the femtosecond-laser-ablation process, which is expected to become a
new laser-processing technique [3]. We demonstrated that the system is a powerful tool for
probing the complicated phenomenon that evolves temporally and spatially with the solid toliquid to gas phase transition, and the dissociation of chemical bonding [4].
The most noteworthy characteristic of our system is that it combines the short pulse
duration of femtosecond laser plasma soft x-rays and the high spatial resolution of the
Kirkpatrick-Baez microscope, thus considerably improving the temporal and spatial
resolution, and the soft x-ray flux on a sample. The soft x-ray microscope and atransmission grating simultaneously provide us with spectral information and onedimensional spatial information of an expanding laser ablation plume (Fig. 1). Figure 2
shows the temporal evolution of a spatially resolved absorbance spectrum for an Al ablation
plume induced by 100-fs laser irradiation with an intensity of 1.5×1014 W/cm2. This figure
clearly shows that the Al ablation plume expands from the Al tape surface toward the vacuumwith time. The most remarkable feature of the ablation plume is the significant shift of the
LII,III absorption edge towards a shorter
Ti:sapphire laser
systemwavelength compared with that of solid
Al. Since the wavelength of the LII,III
Variable delay
Beam splitter
absorption edge of the ablation plume
corresponds to the transition energy
from the 2p state to continuum states,
LaserAblation
the edge shift depends on each particle
produced Soft x-ray puls e
Micro channel
plume
plasmaplate
constituting the ablation plume. This
K-B
Ellipsoidal
Transmission
CCD
Al tape microsope
mirrorTa taperesult demonstrates that our system is a
grating
camerapowerful tool for measuring the
Fig. 1. Schematic illustration of the system.
dynamics of laser ablation plumes.
30+100 ps+ 1 ns-500 ps[1] Bressler and Chergui, Chem. Rev.
+ 500 ps
+5 ns
25
104 (2004) 1781.
20
2.0[2] Oguri, et al., Appl. Phys. Lett. 87
1.5
15(2005) 011503.
1.0
10
0.5
[3] Okano, et al., Rev. Sci. Instrum. 77
0.0
5(2006) 046105.
0
50
0
50
0
50
0
50
0
50
Position [µm][4] Okano, et al., Appl. Phys. Lett. 89
Fig. 2. Temporal evolution of spatially resolved absorbance(2006) 221502.
spectrum for Al ablation plume.

－44－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Time Resolved Measurement of Photonic Crystal Optical Nanocavity
Takasumi Tanabe, Eiichi Kuramochi, Akihiko Shinya,
Hideaki Taniyama, and Masaya Notomi
Optical Science Laboratory

Power (a.u.)

A high-Q photonic crystal (PhC) nanocavity is very effective for application to all-opticalswitches that can operate at an ultra-low energy [1], because it can realize a high photon
density at an extremely low input power. It is known that an ultra-high-Q can be achieved
with a PhC nanocavity by employing the local width modulation of line defects [2]. A
scanning electron microscope image of such a nanocavity is shown in Fig. 1 (a). Although it
is difficult to recognize, the width of the line defect is slightly modulated in the circled region.
As a result, a mode-gap cavity forms in this area. Indeed, the far-field pattern shows that thelight is localized when the wavelength of the input light is same as the resonance of the cavity[Fig.1(b)]. Figure 1(c) shows the transmittance spectrum measured using a wavelength
tunable laser. The transmittance width is an extremely small 1.3 pm, which corresponds to a
Q of 1.2 million. To achieve higher wavelength resolution, we applied a single side band
modulator to sweep the frequency of the laser light with an ultra-high accuracy. We obtained
the same Q value and confirmed the accuracy of the measurement [3].
In contrast, since an ultra-high Q cavity system has a long photon lifetime, the Q can bedirectly obtained in the time domain. In addition, time resolved measurement is a powerful
way to characterize the dynamic behavior of the cavity system. Therefore, we combined
ring-down measurement with time correlated single photon counting to obtain the opticalproperty of the PhC cavity in the time domain [4]. First, a rectangular pulse is employed as
the input, and it is suddenly turned off at 0 ns. Then the photons that where trapped in thecavity start to decay through the output waveguide. By observing the discharging signal
using time resolved measurement we obtained a photon lifetime of 1.01 ns [Fig. 2(a)]. The
accuracy and the reproducibility of time domain measurement were confirmed [5] and thephoton lifetime agrees perfectly with that obtained with spectral domain measurement.
Finally we studied the propagation of a pulse through the cavity system by using time
resolved measurement. We obtained a pulse delay of 1.45 ns for an input pulse with a widthof 1.9 ns [Fig. 2(b)]. This value corresponds to the record smallest group velocity of 5.8
km/s demonstrated in any dielectric slow-light material. The above result paves the way forthe application of the enhancement of light and matter interaction or the development of an
optical delay line with a small footprint.
[1] T. Tanabe, et al., Appl. Phys. Lett. 90 (2007) 031115.
τ = 1.01 ns[2] E. Kuramochi, et al., Appl. Phys. Lett. 88 (2006) 041112.
(a)[3] T. Tanabe, et al., Electron. Lett. 43 (2007) 187.
[4] T. Tanabe, et al., Nat. Photonics 1 (2007) 49.
[5] T. Tanabe, et al., Opt. Express 15 (2007) 7816.
Input WG(a)(b)
Transmittance (a.u.)(c)

Output WG

1.3 pm

0

1

2

3

(b)
signalref.

-3 -2 -1 0 1 2 3 4 5 6 71555.471555.48

Time (ns)Wavelength (nm)Fig. 1. (a) Scanning electron microscope image of a width-modulatedline defect PhC nanocavity. (b) Far field pattern of the resonant
light. (c) Transmittance spectrum.
－45－

Fig. 2. (a) Discharging waveform.
(b) Pulse response.

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Coupled Resonator Waveguides Formed by Ultrahigh-Q Si Photonic
Crystal Nano-resonators
Eiichi Kuramochi, Takasumi Tanabe, Hideaki Taniyama, and Masaya Notomi
Optical Science Laboratory
A periodic chain of optical resonators (coupled resonator optical waveguide: CROW) has
been expected as a promising candidate of a slow light media [1]. An ultrahigh intrinsic
quality factor (Q) of a resonator is required to achieve ultraslow group velocity (vg) and low
propagation loss simultaneously. Recently, we have demonstrated that such CROW isachievable on a Si photonic crystal (PC) platform besides an advantage of ultra-small
footprint (~3µm@single resonator.)
Figure 1(a) is a microscope image of a PC-CROW fabricated by electron beam lithography(the number of the resonator: N=3.) A locally width-modulated line-defect resonator [2]realized ultrahigh experimental Q (1.2×106)[3]. Sharp peaks which corresponded to CROW
modes were clearly observed in transmittance measurements (Fig. 1(b).) Figure 2 shows
dispersion of CROW modes when the interval of the resonator (LCC) was 7a (a: lattice
constant=420nm.) Surprisingly, the dispersion of the coupled resonator modes were fitted
well by almost equal theoretically derived cosine-function, which corresponded to very small
coupling coefficient κ (~7×10-4), when N was changed from 5 to 60. The passing of lightover 60 PC resonators was achieved for the first time which successfully demonstrated
advantage of ultrahigh-Q. The dispersion was controlled well by LCC (Fig. 3) and the lowest κ(3.3×10-4) corresponded to very slow vg (~5×10-3c; c: the speed of light in vacuum.)
This work is encouraging possibility of a PC-based CROW as a slow light media.
[1] A. Yariv, et al., Opt. Lett. 24 (1999) 711.
[2] E. Kuramochi, et al., Appl. Phys. Lett. 88 (2006) 041112.
[3] T. Tanabe, et al., Opt. Express. 15 (2007) 7826.
192.5

192.8

(a)

(b)
-40
-60

Ref.
N=15

Frequency (THz)

Frequency (THz)

Transmission (dB, a.u.)κ = 3.3x10-4

192.6

-80

1560

1561

1562

1563

Wavelength (nm)Fig. 1. (a) Microscope image of a PCCROW (N=3, LCC=9a.) The
white octagons show modified
holes which creates ultrahigh-Q
resonators (The parameter is
described in Ref. 3.) (b) Atransmission spectrum of a PCCROW (LCC=7a, N=15).

192.4
0.0

N=15 (κ =7.3x10-4)
N=60 (κ =6.7x10-4)0.5
k (π/L)

1.0

Fig. 2. Dispersion characteristicsof PC-CROWs (LCC=7a).

－46－

192.0

κ = 6.5x10-4
LCC=5a
LCC=7a191.5
0.0

LCC=9aκ = 1.6x10-3
0.2

0.4

0.6

k (π/L)0.8

1.0

Fig. 3. Dispersion characteristicsof PC-CROWs (N=10).

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Optical Micromachine by Ultrahigh-Q Nanocavities
Masaya Notomi and Hideaki Taniyama
Optical Science Laboratory
Recently, ultrahigh-Q and simultaneously ultra-small optical cavities have been realizedby photonic crystals [1]. In such ultrahigh-Q nanocavities, various light-matter interactions
are expected to be greatly enhanced. We have theoretically found that we can convert opticalenergies into mechanical energies extremely efficiently by employing specially-designed
photonic-crystal nanocavities [2]. Our result demonstrates that one can introduce mechanicaldisplacement by extremely weak light, and indicates possibilities towards ultra-efficient
optical micro-machines in future.
Figure 1 shows our sample structure, which is a point defect cavity of a double-layer
photonic crystal. It is practically the same as our ultrahigh-Q photonic-crystal cavity design
except an air slit is inserted in the center of the slab. This cavity is special because one canlargely change the resonant wavelength by slight change of the slab spacing (slit width)
without deteriorating cavity Q. Owing to this feature, an optical pulse captured in this cavity
can generate extraordinary large radiation force (~ 1 µN per 1 pJ), because this force isdetermined by the spatial derivative of the electromagnetic energy in the cavity. Furthermore,this large force can do a large mechanical work due to the long cavity photon lifetime.
Consequently, the optical energy of the optical pulse is converted to the mechanical energy
very efficiently. We calculated this efficiency assuming realistic parameters, as shown in Fig.
2. Generally, such opto-mechanical energy conversion is intrinsically very inefficient (~10-12)
because of the mass-less nature of light (except photon rockets having relativistic speed).
Figure 2 shows that the efficiency can reach up to 10%. Such extremely-high efficiency is
only possible for mechanical displacement incorporated to ultrahigh-Q and ultrasmall cavities.
When the optical energy is converted to mechanical, the frequency of light in the cavity islowered. In other words, one can realize wavelength conversion of light using the reverse
process. Our numerical calculation shows that large wavelength conversion (larger than 20%of the original wavelength) is indeed possible. Last year, we have reported that adiabatic
wavelength conversion is possibly by dynamically tuning the resonance frequency of a cavity[3]. In fact, the present opto-mechanical process is physically identical. That is, very efficient
optical micromachines are intrinsically very efficient opto-mechanical wavelength converters.
[1] E. Kuramochi, et al., Appl. Phys. Lett. 88 (2006) 041112.
[2] M. Notomi, et al., Phys. Rev. Lett. 97 (2006) 023903.
[3] M. Notomi, et al., Phys. Rev. A73 (2006) 051803(R). 0

Log[ ∆U/U]-2-4

Q=5x107

Q=3x10

6

-6
-8

5

Q=2x10

-10
-19

>10

12

reference-21-23
Fig. 1. Double-layer photonic crystal cavity.

0.01

0.1

1

U (pJ)

10

100

Fig. 2. Energy conversion efficiency.
－47－

Ⅱ．DataResearch Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

The 4th Advisory Board
The Advisory Board, an external committee whose role is to evaluate the work of NTT
Basic Research Laboratories (BRL), met from February 6 - 8, 2007. This was the fourth
meeting of the Advisory Board, which was first convened in 2001 to provide an objective
evaluation of our research plans and activities to enable us to employ strategic management ina timely manner. On this occasion, we were happy to welcome a new member.
Over the course of the three days the board made valuable suggestions and comments inrelation to our research and management activities. They commented that the research level isgenerally high on an international scale, and that it is important for us to maintain thistop-level research and transmit information about our research achievements to the world.
They also raised several issues related to human resources, the research budget and internaland external collaboration. We plan to make improvements based on these valuablesuggestions.
At this meeting we offered both young researchers and NTT executives an opportunity tocommunicate with the board members. This included a lunch party for young researchers at
which they were able to interact with the board members. For the NTT executives, weorganized a Japanese style dinner, which provided a good chance to discuss the future
management strategy of NTT BRL from an international perspective. The next board meeting
will held in eighteen months.
.

Board members
Affiliations
Prof. Abstreiter
Walter Shottky
Prof. Altshuler
Columbia Univ.
Prof. Haroche
Ecole Normale
Prof. Jonson
Chalmers UTProf. Leggett
Univ. Illinois
Prof. Mooij
Delft UT
Prof. Ryan
Univ. Oxford
Prof. von Klitzing Max-Planck-Inst.

Research fields
Low-dim. physics
Condensed matter
Quantum optics
Condensed matter
Quantum physics
Quantum computer
Nano-bio technology
Semiconductor physics－49－Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

International Conference on
Nanoelectronics, Nanostructures and Carrier Interactions
The international conference on nanoelectronics, nanostructures and carrier interactions(NNCI2007) was held from February 21 to 23, 2007, at the NTT Atsugi R&D Center incollaboration with Solution Oriented Research for Science and Technology (SORST)
sponsored by the Japan Science and Technology Agency (JST).
Ultra-small "nano-scale" structures and the behavior of carriers in these structures havebeen the focus of a lot of attention for many years. Recently, the field has been advanced
significantly through the introduction of additional degrees of freedom, such as electron andnuclear spin, magnetism, and mechanical motion. In addition, novel quantum mechanicalconcepts such as quantum computing and quantum cryptography are attracting a great deal ofinterest. With the aim of further advancing these studies, this conference aspired to gather
leading scientists and provide forum for discussing the most recent topics in nanoelectronics,
nanostructures, and carrier interactions. The conference was chaired by Dr. Toshimasa
Fujisawa and Dr. Hiroshi Yamaguchi of NTT Basic Research Laboratories, together with Prof.
Yoshiro Hirayama of Tohoku University.
On February 21, after the opening and welcoming remarks by Dr. Junji Yumoto, Directorof NTT Basic Research Laboratories, the technical session was opened with the plenary talk"Architecture for a Shor Factorization Engine Based on Semiconductor Spins" by Prof. E.
Yablonovitch from University of California, Los Angeles. There were 17 oral presentations on
coherent spin control, quantum information processing, 2-dimensional systems,
metal-insulator transition, and electron transport in quantum dots, and 20 poster presentations.
On the 22nd, the 15 oral presentations discussed nanowires and nanotubes, novel
heterostructures, spintronics, and novel spin materials, and 20 posters were presented. On the
23rd, there were 15 oral presentations on scanning probe spectroscopy and imaging, electron
correlation and interference, silicon nanoelectronics, and spin-related phenomena in
nanostructures. We believe that we provided a very nice opportunity for mutualcommunication within and among the related research fields.
The participants were totally 145 people. All participants well enjoyed the high-quality
presentations and discussions on nanoelectronics, nanostructures, and carrier interactions.

－50－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Award Winners’ List (Fiscal 2006)

Minister of MEXT
(Ministry of Education,
culture, sports, science,and technology) Young
Scientist Award
35th Annual
International
Symposium on
Multiple-Valued Logic(ISMVL-2005)
Outstanding Paper
Award

A. Fujiwara"Physics and device application ofnanostructures in thefield of semiconductors"

Apr. 18,
2006

K. Degawa
T. AokiT. Higuchi
H. Inokawa
Y. Takahashi"A Two-Bit-per-CellContent-Addressable Memory Using
Single-Electron Transistors"

May 19,2006

T. Tanabe"All-optical switching and 5-GHz
RZ (Return to Zero) optical pulse
train modulation using silicon
photonic crystal cavities"

May 31,2006

European Materials
Research Society(E-MRS) 2006 Spring
Meeting
Best Poster
Presentation

H. Omi"Strain and Thermal Stability ofThin Silicon Overlayers on andbetween SiO2"

June 2,
2006

IEED/LEOS
Distinguished Lecturer
Award

M. Notomi"All-Optical Control of Photonic
Crystals"

July 1,
2006

The Laser Society ofJapan
26th Annual Meeting
Best Paper Award－51－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

JJAP Award for theBest Original Paper

S. Horiguchi
A. Fujiwara
H. Inokawa
Y. Takahashi"Analysis of Back-Gate Voltage
Dependence of Threshold Voltageof Thin Silicon-on-Insulator
Metal-Oxide-Semiconductor
Field-Effect Transistor and Its
Application to Si Single-ElectronTransistor"

Aug. 29,2006

The Japan Society ofApplied Physics
Young Scientist Awardfor the Presentation of
Excellent Paper

T. Tanabe"Direct time domain measurement ofphoton lifetime for ultra-high-Q
photonic crystal optical nanocavities"

Mar. 27,
2007

－52－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

In-house Award Winners’ List (Fiscal 2006)

NTT R&D Award

K. Muraki
N. Kumada"Techniques for precise control of
nuclear spins using semiconductor
nanostructures"Feb.15,2007

NTT R&D Award

Y. Taniyasu
M. KasuT. Makimoto"AlN deep-ultraviolet light-emitting
diode with 210-nm wavelength"

Feb.15,
2007

Award forAchievements by
Director of Basic
Research
Laboratories

Y. Taniyasu
M. KasuT. Makimoto"Development of technologies for AlN
crystal growth, doping, andlight-emitting device"Mar.22,
2007

Award forAchievements by
Director of Basic
Research
Laboratories

K. Nishiguchi
Y. OnoA. Fujiwara
H. Inokawa"Room-temperature operation of
single-electron transfer and detection
using Si transistors"

Mar.22,
2007

T. Fujisawa"Bidirectional counting of single
electrons" Science Vol. 312, 1634
(2006).

Mar.22,
2007

Award for
Excellent Papers by
Director of Basic
Research
Laboratories

A. Nishikawa
K. Kumakura"High critical electric field of AlGaN
p-i-n vertical conducting diodes on
n-SiC substrate" Appl. Phys. Lett. Vol.
88, 173508 (2006).

Mar.22,
2007

Award for
Excellent Papers by
Director of Basic
Research
Laboratories

H. Takesue
T. Honjo"Differential phase shift quantum key
distribution experiment over 105km
fibre" New J. Phys. Vol. 7, 232 (2005).

Mar.22,
2007

Y. Harada"The contribution to the newcollaboration researches scheme in
U.K. "

Mar.22,
2007

Award for
Excellent Papers by
Director of Basic
Research
Laboratories

Special Award by
Director of Basic
Research
Laboratories－53－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

List of Visitors’ Talks (Fiscal 2006)

l. Materials Science
Date

Speaker

Affiliation"Topic"May 29Dr. Michael Jetter

May 29Mr. Sarad Bahadur Thapa

June 6

Dr. Eric Mueller

July 7

Dr. Goo-Hwan Jeong

Sep. 7

Prof. Wolfgang Stolz

Sep. 15

Prof. Erhard Kohn

Oct. 6

Mr. Toshiaki Kato

Oct. 6

Mr. Ken Okada

Oct. 26

Prof. Etienne BustarretFeb. 1

Dr. Taisuke Ohta

University of Stuttgart, Germany"Quantum dots for single photon applications"
University of Ulm, Germany"Structural and spectroscopic properties of AlN
layers grown by MOVPE"
Coherent Inc.
"Continuous-Wave THz Transceivers & CW
Coherent High-Dynamic-Range THz Imaging"
CREST Honma Project"Diameter control and functionalization ofcarbon nanotubes"
Philipps-University, Germany"Novel dilute nitride III/V-semiconductor laser
system for the integration to Si-microelectronics"
University of Ulm, Germany"Diamond electronics will it be able to competewith III-Nitrides? "Tohoku University"Vertically aligned growth of single walledcarbon nanotubes by plasma-enhanced CVD and
its plasma effects"
Tohoku University"Functionalization of single walled carbon
nanotubes by DNA"CNRS-LEPES, France"Superconducting B-doped diamond and relatedmaterials: recent progress"
E. O. Lawrence Berkeley National Laboratory,
U.S.A.
"Controlling the Electronic Structure ofGraphene Layers"－54－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

lI. Physical Science
Date

Speaker

Affiliation"Topic"May 16

Prof. Kiyofumi Muro

July 12

Dr. Koji Usami

Aug. 1

Dr. Sebastian HofferberthAug. 11

Dr. Jens Hefort

Aug. 29

Mr. Tomohiro Tanaka

Sep. 5

Prof. Mikio Eto

Sep. 11

Dr. Kasper
Grove-Rasmussen

Chiba University"High-sensitive and high-resolution spectroscopyof spin quasi-phase and spin dynamics insemiconductor nanostructure at low temperatureand in high magnetic field"
Tokyo Institute of Technology"On Quantumness of Collective Spin Excitation"
University of Heidelberg"Radio-frequency dressed state potentials forneutral atoms"
Paul Drude Institute, Germany"Expitaxial Heusler alloys on GaAs substrates"
University of Tokyo"Phase Information from Two–Terminal
Conductance of Quantum Dot Systems"
Keio University"Spin injection through semiconductor quantum
point contact"
Niels Bohr Institute, Denmark

Sep. 12

Sep. 14

Oct. 20

Oct. 26

Nov. 6"Electronic transport in Carbon Nanotubes withnormal and superconducting leads"
Prof. Klaus Ploog
Paul Drude Institute, Germany"Ferromagnetic Semiconductors for Spin
Injection"
Prof. Yukio Tanaka
Nagoya University"Odd-frequency pairing state in superconducting
junctions"
Mr. Toshiyuki Ihara
University of Tokyo"Photoluminescence and photoluminescence
excitation spectra of one-dimensional electron
systems in T-shaped quantum wires"
Dr. Romain Danneau
University of New South Wales, Australia"Spin related phenomena in ballistic holequantum wires"
Prof. Alec Maassen van den Riken
Brink

－55－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Jan. 22

Prof. Yasser Omar

Jan. 29

Prof. Michel H. Devoret

Jan. 30

Prof. Michel H. Devoret

Jan. 31

Prof. Michel H. Devoret

Feb. 1

Prof. Michel H. Devoret

Feb. 9Prof. Hans Mooij

Feb. 16

Dr. Fei Xue

March 15

Prof. Lev B. Ioffe

March 15

Dr. Lara Faoro"Four-qubit superconducting quantum circuit"
Technical University of Lisbon, Portugal"Generation of Entanglement in Quantum Wire
and Application to Single-ElectronTransmittivity"
Yale University, U.S.A.
"Quantum-mechanical electrical circuits"
Yale University, U.S.A.
"Measurement of Dynamical Casimir Effect"
Yale University, U.S.A.
"Quantum Voting"
Yale University, U.S.A.
"QND fraction of JBA readout"
Delft University of Technology, Netherlands"Quantum Information Processing Using
Superconducting Circuit"
Riken"Liquid-State NMR Based Quantum Computing& Cavity Quantum Electrodynamics in
Solid-State System"
The State University of New Jersey, U.S.A.
"Microscopic origin of low frequency noises in
Josephson qubits"
The State University of New Jersey, U.S.A.
"The challenge of error correction in quantum
computation"lII. Optical Science
Date

Speaker

Affiliation"Topic"Apr. 11

Dr. Kouichi Ichimura

July 3

Prof. See Leang Chin

Aug. 21

Dr. Michael Stopa

Toshiba Corporation"EIT in a solid system and its application toquantum information Processing"
Laval University, Canada"Some new applications using femtosecond laser
filamentation in air"Harvard University, U.S.A.
"Magnetic field control of exchange and noise
immunity in double quantum dots"－56－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Oct. 23

Dr. Sergei Studenikin

Nov. 27

Prof. Norbert Lutkenhaus

Dec. 4

Prof. Daniel Gottesman

Dec. 6

Dr. Sae Woo Nam

Dec. 22

Dr. Hiroaki Terashima

Jan. 9Prof. Shun-Lien Chuang

March 2

Prof. Ora Entin-Wohlman

March 13

Prof. Robert M. Westervelt

National Research Council of Canada, Canada"Role of magnetoplasmons in microwave
induced resistance oscillations andzero-resistance states"
University of Waterloo, Canada"Security key rates, upper bounds and limitationsin quantum key distribution"
Perimeter Institute for Theoretical Physics,
Canada"The threshold for fault-tolerant quantum
computation"
National Institute of Standards and Technology,
U.S.A.
"Superconducting detectors for quantum
information applications"Tokyo Institute of Technology"Relativistic Effects on the
Einstein-Podolsky-Rosen Correlation"
University of Illinois, U.S.A.
"Slow Light in Quantum Dots and Quantum
Wells"Ben Gurion University, Israel"The magnetic structure of lanthanum titanate"
Harvard University, U.S.A.
"Imaging Electrons in Nanoscale Devices"－57－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Research Activities of Basic Research Laboratories in 2006
The numbers of research papers, presentations at the international conferences and applied
patents amounted to 169, 254, and 52 in Basic Research Laboratories as a whole. All numbers
according their research areas are as follows.

Papers Published in International Journals(Jan. - Dec. 2006)
Materials Science
Physical Science
Optical Science
0

10

20

30

40

50

60

70

120

140

25

30

Number of Papers

Presentations at International Conferences(Jan. - Dec. 2006)
Materials Science
Physical Science
Optical Science
0

20

40

60

80

100

Number of Presentations

Applied Patents (Jan. - Dec. 2006)
Materials Science
Physical Science
Optical Science
0

5

10

15

20

Number of Applied Patents
Dom es tic－58－

International

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

The numbers of research papers published in the major journals are shown below.
General Science Journals
Journal titles
ScienceNature(IF2006)*(30.927)(29.273)

numbers
3
1

Specialized Science Journals
Journal titles(IF2006)*
Applied Physics Letter
4.127
Japanese Journal of Applied Physics
1.096
Physical Review B
3.185
Physica E
0.946
Physical Review Letters
7.489
Journal of Applied Physics
2.498
Optics Express
3.764
Physical Review A
2.997
Chemical Physics Letters
2.438
Diamond and Related Materials
1.988
Physica B
0.796
IEEE Electron Device Letters
2.825
Physica C
0.948
Nano Letters
9.847
Reports on Progress in Physics
8.893*IF2006: Impact Factor 2006 （Journal Citation Reports, 2006）

numbers
21
18
11
10
9
9
7
7
4
4
4
3
3
1
1

The average IF2006 for all research papers from NTT Basic Research Laboratories is 3.26.
The numbers of presentations in the major conferences are shown below.
Conference titles

numbers

28th International Conference on Physics of Semiconductors (ICPS28)
2006 International Conference on Soliid State Devices and Materials (SSDM2006)
International Symposium on Mesoscopic Superconductivity and Spintronics 2006 (MS+S2006)
Conference on Lasers and Electro-Optics Quantum Electronics and Laser Science Conference /Quantum Electronics and Laser Science Conference (CLEO/QELS)
7th International Conference on the Science and Application of Nanotubes (NT06)
Frontiers in Nanoscale Science and Technology (FNST2006)
14th International Conference on Molecular Beam Epitaxy (MBE2006)
International Workshop on Nitride Semiconductors (IWN2006)
International Conference on Nanoscience and Technology (ICN+T2006)
12th Conference on Laser Optics (LO2006)
2006 Materials Research Society Fall Meeting (MRS 2006 Fall)
IEEE Lasers and Electro-Optics Society 19th Annual Meeting (LEOS2006)
1st Canada－Japan SRO-COAST Symposium on Ultrafast Intense Laser Science
19th International Symposium on Superconductivity (ISS2006)
VIth Recontre de Vietnam, Nanophysics: from Fundamentals to Applications
International Symposium on Ultrafast Intense Laser Science (ISUILS5)International Symposium on Compound Semiconductors (ISCS2006)
International Conference on Raman Spectroscopy (ICORS2006)
American Chemical Society, 232nd National Meeting and Exposition (ACS)2006 International Workshop on Dielectric Thin Films for Future ULSI Devices-Science & Technology(IWDTF2006)
2006 IEEE Silicon Nanoelectronics Workshop (SNW2006)

－59－

21
21
19
9
8
8
7
7
6
6
5
5
4
4
3
3
3
3
3
3
3

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

List of Invited Talks at International Conferences (2006)
I. Materials Science Laboratory(1)

H. Omi, "Step Pattern Formation during Molecular Beam Epitaxy", Symposium on
Surface Physics 2006, Shizukuishi, Japan (Jan. 2006).

(2)

H. Hibino and M. Uwaha, "Instability of Steps During Ga Deposition on Si(111) ",Symposium on Surface Physics 2006, Shizukuishi, Japan (Jan. 2006).

(3)

H. Miyashita, I. Fujimoto, K. Hamada, K. Mikoshiba, and K. Torimitsu, "A High-Speed
AFM Observation of Inositol 1,4,5-Trisphosphate Receptor Reconstituted into a Lipid
Bilayer.", VIII. Annual Linz Winter Workshop, Linz, Austria (Feb. 2006).

(4)

K. Ajito, "Laser-trapping Raman Spectroscopy of Neurotransmitters in Single Nerve
Terminals", The 6th France-Japan Workshop on Nanomaterials, Sapporo, Japan (Mar.
2006).

(5)

M. Kasu, "Diamond RF Power Transistors: Present Status and Prospects", Materials
Congress 2006, London, U.K. (Apr. 2006).

(6)

Y. Taniyasu, M. Kasu, and T. Makimoto, "Formation Mechanism of Threading
Dislocations in AlN during MOVPE Growth", 13th International Conference on Metal
Organic Vapor Phase Epitaxy (ICMOVPE-XIII), Miyazaki, Japan (May 2006).

(7)

K. Torimitsu, "NanoBioscience –Analysis of Neural Functions with Bio-Molecules–",
7th International Conference "Materials in Clinical Applications" of the Forum on New
Materials, Sicily, Italy (Jun. 2006).

(8)

K. Ajito, R. Rungsawang, I. Tomita, and Y. Ueno, "Near-Infrared Raman and Terahertz
Spectroscopy and Biological Molecule Imaging", 20th International Conference on
Raman Spectroscopy (ICORS), Yokohama, Japan (Sep. 2006).

(9)

M. Kasu, K. Ueda, Y. Yamauchi, A. Tallaire, and T. Makimoto "Diamond-Based RF
Power Transistors: Fundamentals and Applications", The 17th European Conference on
Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide(Diamond 2006), Estoril, Portugal (Sep. 2006).

(10) K. Torimitsu, "Neurons and Receptor Proteins for Nano-Bio Interface", The
Nano-Bio-Cogno Convergence Seminar 2006: Valorization in Medicine and Healthcare(SOC-45), Leuven, Belgium (Sep. 2006).

－60－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)(11) H. Omi, "Step Instabilities on Vicinal Si(111) during Molecular Beam Epitaxy", 1st
non-virtual meeting "Instabilities at Surfaces", Burgas, Bulgaria (Sep.-Oct. 2006).
(12) Y. Taniyasu, M. Kasu, and T. Makimoto, "AlN deep-UV LEDs with a Wavelength of
210 nm", 6th Akasaki Research Center Symposium, Nagoya, Japan (Oct. 2006).
(13) K. Torimitsu, "Role of Magnesium in Neural Process", 11th International Magnesium
Symposium, Ise-Shima, Japan (Oct. 2006).
(14) M. Kasu, K. Ueda, A. Tallaire, Y. Yamauchi, and T. Makimoto, "Diamond Transistors
for RF Power Applications", Kobe University Frontier Technology Forum –Nano- andPhotonics-Technology in Innovation–, Kobe, Japan (Nov. 2006).

II. Physical Science Laboratory(1)

T. Mukai, "Quantum Computation with Atoms: Practical Schemes and Problems",
Post-COE Workshop on Cold Atoms: Fermion and Optical Lattice, Kyoto, Japan (Feb.
2006).

(2)

H. Takayanagi, S. Sasaki, S. Kang, S. Miyashita, T. Maruyama, H. Tamura, T. Akazaki,
and Y. Hirayama, "Manipulation and Control of Spins in III-V Semiconductors by Gated
Structures", 2006 RCIQE International Seminar, Sapporo, Japan (Feb. 2006).

(3)

Y. Ono, A. Fujiwara, K. Nishiguchi, Y. Takahashi, and H. Inokawa, "Single-ElectronTransfer in Silicon: Towards Single-Dopant Electronics", 3rd International Workshop on
Ubiquitous Knowledge Network Environment, Sapporo, Japan (Feb.-Mar. 2006).

(4)

K. Semba, "Coherent Control of a Flux-Qubit Coupled to a Quantum LC-Resonator",
UNI Erlangen Winter Seminar on Superconductivity, Finkenberg, Austria (Mar. 2006).

(5)

T. Fujisawa, "Counting Statistics of Single-Electron Transport through a Double
Quantum Dot", Capri Spring School on Transport in Nanostructures, Capri, Italy (Apr.
2006).

(6)

Y. Ono, K. Nishiguchi, K. Takashina, H. Inokawa, S. Horiguchi, and Y. Takahashi,"Impurity Conduction and its Control in SOI MOSFETs; Towards Silicon Single-Dopant
Electronics", 2006 IEEE Silicon Nanoelectronics Workshop (SNW2006), Honolulu,
Hawaii, U.S.A. (Jun. 2006).

(7)

T. Fujisawa, "Counting Statistics of Single Electron Transport through a Double
Quantum Dot", IEEE Nanotechnology Materials and Devices Conference－61－Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)(IEEE-NMDC2006), Daejeon, Korea (Jun. 2006).
(8)

Y. Hirayama, "Single-Electron Manipulation and Detection in a Quantum Dot System",International Conference for Quantum Structure Science (ICQS-2006), Beijing, China(Jun. 2006).

(9)

K. Semba, J. Johansson, S. Saito, T. Meno, H. Tanaka, H. Nakano, M. Ueda, and H.
Takayanagi, "Vacuum Rabi Oscillations Observed in a Flux Qubit LC-Oscillator System",
Macroscopic Quantum Coherence and Computing (MQC2), Napoli, Italy (Jun. 2006).

(10) M. Uematsu, "Oxygen Self-Diffusion in Silicon Dioxide: Effect of the Si/SiO2
Interface", 2nd International Conference on Diffusion in Solid and Liquids (DSL2006),
Aveiro, Portugal (Jul. 2006).
(11) G. Yusa, K. Muraki, N. Kumada, K. Takashina, K. Hashimoto, and Y. Hirayama,"Nuclear Spin Control by a Point Contact", 28th International Conference on Physics of
Semiconductors (ICPS28), Vienna, Austria (Jul. 2006).
(12) K. Suzuki, K. Kanisawa, S. Perraud, M. Ueki, K. Takashina, and Y. Hirayama,"Observation of Subband Standing Waves in Superlattices by Low-Temperature Scanning
Tunneling Spectroscopy", 28th International Conference on Physics of Semiconductors(ICPS28), Vienna, Austria (Jul. 2006).
(13) H. Takayanagi, S. Saito, J. Johansson, H. Tanaka, H. Nakano, M. Ueda, and K. Semba,"Flux Qubit Coupled to an LC-Resonator", Materials and Mechanisms ofSuperconductivity High Temperature Superconductors VIII (M2S-HTSC-VIII), Dresden,
Germany (Jul. 2006).
(14) K. Muraki, "Interaction of Electron and Nuclear Spins in Quantum Wells", 17th
International Conference on High Magnetic Fields in Semiconductor Physics (HMF-17),
Wuerzburg, Germany (Jul.-Aug. 2006).
(15) Y. Hirayama, "High Precision Control of Nuclear Spins in Semiconductor
Nanostructures", 13rd International Conference on Superlattice, Nanostructures andNanodevices (ICSNN-2006), Istanbul, Turkey (Jul.-Aug. 2006).
(16) T. Fujisawa, "Counting Statistics of Single Electron Transport through a Double
Quantum Dot", VIth Recontre de Vietnam, Nanophysics: from Fundamentals to
Applications, Hanoi, Vietnam (Aug. 2006).
(17) Y. Hirayama, S. Sasaki, and T. Fujisawa, "Non-Local Charge and Spin Interactions in
Semiconductor Quantum Dot Systems", International Workshop "Tera- andNano-Devices: Physics and Modeling", Aizu-wakamatsu, Japan (Aug. 2006).
－62－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)(18) G. Yusa, K. Muraki, N. Kumada, K. Takashina, K. Hashimoto, and Y. Hirayama,"Controlled Multiple Quantum Coherences of Nuclear Spins", 4th International
Conference on Physics and Application of Spin-Related Phenomena in Semiconductors(PASPS-IV), Sendai, Japan (Aug. 2006).
(19) K. Semba, J. Johansson, S. Saito, T. Meno, H. Tanaka, H. Nakano, M. Ueda, and H.
Takayanagi, "Vaccum Rabi Oscillations Observed in a Flux Qubit LC-Oscillator System",
VIth Recontre de Vietnam, Nanophysics: from Fundamentals to Applications, Hanoi,
Vietnam (Aug. 2006).
(20) H. Nakano, "Some theoretical aspects in Superconducting Flux-qubit systems", VIthRecontre de Vietnam, Nanophysics: from Fundamentals to Applications, Hanoi, Vietnam(Aug. 2006).
(21) H. Takayanagi, T. Akazaki, S. Yanagi, and H. Munekata, "Transport Properties of
Ferromagnetic Semiconductors with Superconducting Electrodes", International
Workshop on Mesoscopic Superconductivity and Magnetism (MesoSuperMag 2006),
Chicago, U.S.A. (Aug.-Sep. 2006).
(22) K. Muraki, "Spin/Charge Fluctuations in Quantum Hall Bilayers -Nuclear Spin
Relaxation and Coulomb Drag", Interactions, Excitations and Broken Symmetries in
Quantum Hall Systems (QHSyst-06), Dresden, Germany (Oct. 2006).
(23) K. Semba, "Josephson Junction Qubits", 2006 US-Japan Workshop on Quantum
Information Science, Hawaii, U.S.A. (Oct. 2006).
(24) K. Semba, "Superconducting Flux Qubit Coupled to an LC-Oscillator", 19thInternational Symposium on Superconductivity (ISS2006), Nagoya, Japan (Oct.-Nov.
2006).
(25) H. Takayanagi, Y.-L. Zhong, and T. Akazaki, "Noise and Conductance Fluctuation due
to Andreev Reflection", 19th International Symposium on Superconductivity (ISS2006),
Nagoya, Japan (Oct.-Nov. 2006).

III. Optical Science Laboratory(1)

Y. Tokura, "Coherent Single Electron Spin Control in a Slanting Zeeman Field", A
workshop on Imaging at the Nanoscale, Quantum Information Processing, Nanophotonics,
Nanoelectronics: Frontiers in Nanoscale Science and Technology (FNST), San Francisco,
U.S.A. (Jan. 2006).

－63－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)(2)

Y. Tokura, "Electron Spin Manipulation in Quantum Dot Systems", International
Workshop on Electron Spin Resonance and Related Phenomena in Low Dimensional
Structures, Sanremo, Italy (Mar. 2006).

(3)

Y. Tokura, "Interaction and Interference Effect in the Electron Current through Laterally
Coupled Quantum Dots", International Seminar and Workshop on Non-equilibrium
Dynamics in Interacting Systems, Dresden, Germany (Apr. 2006).

(4)

Y. Tokura, "Coherent Transport through Coupled Quantum Dots", MTI & CNM
International Argonne Fall Workshop on Nanophysics VI, Nanoscale Superconductivity
and Magnetism, Argonne, France (Nov. 2006).

(5)

M. Notomi, "Photonic Crystal Waveguides and Resonators", ePIXnet Winter School,
Pontresina, Switzerland (Mar. 2006).

(6)

M. Notomi, "Light Control by Photonic Crystals", ePIXnet Winter School, Pontresina,
Switzerland (Mar. 2006).

(7)

M. Notomi, E. Kuramochi, T. Tanabe, A. Shinya, and H. Taniyama, "All-OpticalControl of Photonic Crystal Nanocavities", 2006 Optical Society of America Integrated
Photonics Research and Applications Topical Meeting/ Nanophotonics Topical Meeting(OSA IPRA/NANO), Uncasville, U.S.A. (Apr. 2006).

(8)

M. Notomi, T. Tanabe, E. Kuramochi, A. Shinya, H. Taniyama, and S. Mitsugi,"Dynamic Control of Light by Photonic-Crystal Resonator-Waveguide-Coupled System",
Conference on Lasers and Electro-Optics/ Quantum Electronics and Laser Science
Conference (CLEO/QELS'06), Long Beach, U.S.A. (May, 2006).

(9)

H. Nakano, K. Oguri, Y. Okano, and T. Nishikawa, "Picosecond Time-Resolved XAFS
Measurements Using Femtosecond Laser-Produced Plasma X-Rays as a Probe," XIIInternational Conference on Laser Optics (LO’06), St. Petersburg, Russia (Jun. 2006).

(10) M. Notomi, E. Kuramochi, T. Tanabe, A. Shinya, and H. Taniyama, "All-OpticalControl of Photonic Crystal Nanocavities", Journée Nationale Cristaux Photoniques,
Marcoussis, France (Jun. 2006).
(11) H. Nakano, K. Oguri, Y. Okano, and T. Nishikawa, "Time-Resolved XAFS
Measurements Using Femtosecond Laser-Produced Plasma X-Rays", 1st Canada-Japan
SRO-COAST Symposium on Ultrafast Intense Laser Science, Tokyo, Japan (Jul. 2006).
(12) M. Notomi, E. Kuramochi, T. Tanabe, A. Shinya, and H. Taniyama, "All-OpticalControl of Photonic Crystal Nanocavities", 11th OptoElectronics and Communications－64－

Research Activities in NTT Basic Research Laboratories Vol. 17 (September 2007)

Conference (OECC2006), Kaohsiung, Taiwan R.O.C. (Jul. 2006).
(13) M. Notomi, E. Kuramochi, T. Tanabe, A. Shinya, and H. Taniyama, "All-OpticalControl Of Ultrasmall High-Q Photonic Crystal Nanocavities", Asia-Pacific OpticalCommunications Conference 2006 (APOC2006), Gwangju, Korea (Sep. 2006).
(14) S. Kawanishi, "High-Speed Optical Transmission Technology Using All-Optical Signal
Processing", Asia-Pacific Optical Communications Conference 2006 (APOC2006),
Gwangju, Korea (Sep. 2006).
(15) M. Notomi, E. Kuramochi, T. Tanabe, A. Shinya, and H. Taniyama, "All-Optical
Switching and Dynamic Control of Light by Photonic Crystal Nanocavities", 2006
International Conference on Solid State Devices and Materials (SSDM2006), Yokohama,Japan (Sep. 2006).
(16) K. Yamada, T. Tsuchizawa, T. Watanabe, H. Fukuda, H. Shinojima, T. Tanabe, and S.-I.
Itabashi, "All-Optical Signal Processing Using Nonlinear Effects in Silicon Photonic Wire
Waveguides", The 19th Annual Meeting of the IEEE Lasers and Electro-Optics Society,(LEOS2006), Montreal, Canada (Oct.-Nov. 2006).
(17) H. Nakano, K. Oguri, Y. Okano, and T. Nishikawa, "Femtosecond Laser-Induced
Melting and Ablation Processes Observed by Picosecond-Time-Resolved XAFS Using
Femtosecond Laser-Produced Plasma Soft X-Ray Pulses", 5th International Symposium
on Ultrafast Intense Laser Science (ISUILS5), Lijiang, China (Nov. 2006).
(18) K. Oguri, Y. Okano, T. Nishikawa, and H. Nakano, "Ejection of Liquid Aluminum
Nanoparticles
inFemtosecond-Laser-Ablation
Plume
Observedby
Spatiotemporally-Resolved XAFS", 5th International Symposium on Ultrafast Intense
Laser Science (ISUILS5), Lijiang, China (Nov. 2006).
(19) M. Notomi, "All-Optical Control of Photonic Crystals", Photonic Crystal Meeting ofIEEE Lasers and Electro-Optics Society (LEOS) Scottish Chapter, St. Andrews, U.K.
(Nov. 2006).
(20) A. Yokoo and H. Namatsu, "Nanoelectrode Lithography", 2006 Materials ResearchSociety Fall Meeting (MRS 2006 Fall), Boston, U.S.A. (Nov.-Dec. 2006).
(21) M. Notomi, "All-Optical Control of Light in Photonic Crystals", 2006 Symposium of
the IEEE Lasers and Electro-Optics Society (LEOS) Benelux Chapter, Eindhoven, The
Netherlands (Dec. 2006).

－65－

Editorial Committee
Hiroo Omi
Hiroyuki Kageshima
Hideaki Taniyama
Tetsuya Akasaka
Toshiaki Hayashi
NTT Basic Research Laboratories
3-1 Morinosato Wakamiya, Atsugi,
Kanagawa 243-0198, Japan
URL: http://www.brl.ntt.co.jp