Cover photograph:

Parametric Frequency Conversion and
Logic Operations Using Electromechanical Resonators
We realize a logic device in an electromechanical resonator. Two inputs, A and B, are applied to one
electrode as alternate voltage of different frequencies, fA and fB, respectively. The signals are transferred
to mechanical oscillations which are mixed and frequency converted to fC and fD. These two outputs are
obtained when both (for fC) or just one (for fD) of the inputs are active which corresponds to logicals (A and B)
and (A or B) respectively. Other examples of multiple logic operation are also shown. (Page 27)

A-plane AlN LED

Emission spectrum ofA-plane AlN LED

Radiation properties ofA-plane and C-plane LED

Emission Mechanism of AlN Deep-Ultraviolet Light-Emitting DiodeWe have developed an aluminum nitride (AlN) deep-ultraviolet light-emitting diode (LED) with awavelength of 210 nm, which is the shortest wavelength ever observed from any semiconductor.
Due to a unique valence band structure (negative crystal-field splitting energy), AlN has a strong
polarization property and therefore its emission intensity largely changes depending on the crystal
planes of its surface. Here, for improving the AlN LED’s emission efficiency, we propose an A-plane
LED structure, which shows strong surface emission compared with the conventional C-plane one.
(Page 16)Highly Integrative Artificial Cell Membrane Microarray
We develop a new technique for fabricating an artificial cell membrane microarray, which is an
important platform for biochip applications. Parallel 10-µm-wide lines, each filled with a membranewith a unique composition at 5-µm intervals are successfully fabricated. The red, green and blue
fluorescence correspond to the different membrane compositions. Our new method offers a finer
microarray that is more than 100 times more highly integrated, than those obtained with previously
reported methods. (Page 18)－Ⅰ－Ramsey fringes at different operating frequencies

Dephasing time obtained by spin-echo

Coherent Operation of a Gap-Tunable Flux Qubit
By replacing the smallest Josephson junction of the qubit with a DC-SQUID, we demonstrate thein situ coherent tunability of the gap of a superconducting flux qubit. In a conventional design, thetunneling energy of the flux-qubit is fixed in the fabrication process. However, in the new device, we
can control qubit tunneling energy in nano second while keeping the qubit at its degeneracy point(optimum flux bias) where the flux-noise is considered to be minimum. From Ramsey fringes andecho-measurement, the best dephasing time of T2=0.6 μs in this type of flux-qubit are obtained. This
improved device will accelerate research of quantum information processing via quantum bus andquantum memory. (Page 31)

PL spectra in a weak coupling regime(mode attraction).

PL color map in a strong coupling regime (disappearanceof Rabi splitting with anti-crossing dispersion).

Cavity Quantum Electrodynamics Using Single Quantum Dot
We fabricate a photonic crystal nanocavity with a single quantum dot (QD), and investigate theinteraction between a single exciton (X) and the cavity mode (C), namely the effect of cavity quantum
electrodynamics (cQED). In a weak X-C coupling regime, we observe an unusual mode attraction
between X and C. Moreover, we find that Rabi splitting disappears while anti-crossing dispersion is
maintained in a strong coupling regime. These are novel cQED effects that arise from the large exciton
dephasing of the solid-state two-level system. (Page 39)－Ⅱ－Message from the Director
We are extremely grateful for your interest andsupport with respect to our research activities.
The three research areas at NTT Basic ResearchLaboratories (NTT-BRL), namely Materials Science,
Physical Science, and Optical Science, are undertaking
work designed to create new values supporting NTT’s
future business and to promote advances in sciencethat will ultimately benefit all mankind.
A fundamental goal of these research activities is
to improve global competitiveness. Therefore, NTTBRL is collaborating with many universities andresearch institutes throughout the world as well aswith other NTT laboratories. NTT-BRL organizes
international conferences related to quantum physics
and nanotechnology and also holds a "Science Plaza"
to enhance public understanding of our activities andto ensure a frank exchange of opinions.
It gives us immense pleasure to fulfill our mission of being an open laboratory, and todisseminate our research output worldwide. Your continued support is greatly appreciated.
June, 2011

Itaru Yokohama
Director
NTT Basic Research Laboratories－Ⅲ－

Contents
page◆Cover♦ Parametric Frequency Conversion and Logic Operations Using ElectromechanicalResonators◆Color Frontispiece .............................................................................................................Ⅰ♦ Emission Mechanism of AlN Deep-Ultraviolet Light-Emitting Diode♦ Highly Integrative Artificial Cell Membrane Microarray♦ Coherent Operation of a Gap-Tunable Flux Qubit♦ Cavity Quantum Electrodynamics Using Single Quantum Dot◆Message from the Director .................................................................................................Ⅲ◆NTT Basic Research Laboratories Organogram ................................................................. 1◆Member List ........................................................................................................................ 2
I. Research Topics◇ Overview of Research in Laboratories ............................................................................................... 13◇ Materials Science Laboratory ............................................................................................................ 14♦ Robust Superconductivity in Pr2CuO4 Prepared by MBE♦ Nucleus and Spiral Growth Mechanisms of GaN Studied by Selective-Area MOVPE♦ Emission Mechanism of AlN Deep-Ultraviolet Light-Emitting Diode♦ AlGaN/GaN HEMTs Epitaxially Grown on Single-Crystal Diamond♦ Highly Integrative Artificial Cell Membrane Microarray♦ Evaluation of Carrier Density in Doped Single-Wall Carbon Nanotubes♦ Transport Properties of Epitaxial Monolayer and Bilayer Graphene♦ Manipulation of Biomolecules on Solid Substrate Using Artificial Cell Membrane♦ AFM Observation of a Receptor Subunit Structure♦ Electrostatic Control of Artificial Cell Membrane Self-Spreading◇ Physical Science Laboratory ............................................................................................................... 24♦ Single-Electron Resonant Activation over an Oscillating Barrier♦ Theoretical Study of Magnetoelectric and Thermoelectric Properties of Graphene♦ Strong Stark Effect in Electroluminescence from Phosphorous-Doped SOI-MOSFETs♦ Parametric Frequency Conversion and Logic Operations Using Electromechanical Resonators♦ Carrier-Mediated Opto-Mechanical Coupling in GaAs Cantilevers♦ Voltage-Controlled Group Velocity of Edge Magnetoplasmon in the Quantum Hall Regime♦ Wide-Band Capacitance Measurement on a Semiconductor Double Quantum Dot

for Studying Tunneling Dynamics♦ Coherent Operation of a Gap-Tunable Flux Qubit♦ Generation of Non-Classical Microwave Photon States in an Inductor-Capacitor

Resonator Coupled to a Superconducting Flux Qubit♦ Quantum Zeno Effect with a Superconducting Qubit♦ Evaluation of Spin Polarization in p-In0.96Mn0.04As Using Andreev Reflection

Spectroscopy Including Inverse Proximity Effect♦ Photoluminescence Spectroscopy of the Low-Density Two-Dimensional Electron

System in Electric Fields◇ Optical Science Laboratory ................................................................................................................ 36♦ Single-Photon Detection Using Magnesium Diboride Superconducting

Nanowire at Telecommunication Wavelength♦ Tokyo QKD Network♦ Kondo Effects and Current Shot Noise in a Double Quantum Dot♦ Cavity Quantum Electrodynamics Using Single Quantum Dot♦ Nanowires Laterally Grown on GaAs Substrates in the Vapor-Liquid-Solid Mode
♦ Coherent Phonons in Metallic Single-Walled Carbon Nanotubes♦ High-Q One-Dimensional Photonic Crystal Nanocavity in a Silicon/SOI Platform♦ GPGPU Acceleration of the FDTD Calculation

II. Data◇ Science Plaza 2010.......................................................................................................................... 45◇ International Symposium on Nanoscale Transport and Technology (ISNTT2011)◇ The 6th Advisory Board (Fiscal 2010)◇ Award Winners’ List (Fiscal 2010)........................ 46............................................................................................ 47................................................................................................. 48◇ In-house Award Winners’ List (Fiscal 2010).................................................................................. 49◇ Numbers of Papers, Presentations and Patents (2010).................................................................... 50◇ List of Invited Talks at International Conferences (2010).............................................................. 52

NTT Basic Research Laboratories Organogram
As of March 31, 2011

Director

Itaru Yokohama, Dr.

Nano Bio Research
Executive Manager

Keiichi Torimitsu, Dr.

Research Planning Section
Executive Manager

Tetsuomi Sogawa, Dr.

Materials Science Laboratory
Executive Manager

Toshiki Makimoto, Dr.

Physical Science Laboratory
Executive Manager

Hiroshi Yamaguchi, Dr.

Optical Science Laboratory
Executive Manager

Yasuhiro Tokura, Dr.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)1

Member List
As of March 31, 2011(*/ left the position in a year)

NTT Basic Research Laboratories
Director, Dr. Itaru Yokohama

Nano Bio Research

Executive Manager,

Dr. Keiichi Torimitsu

Research Planning Section

Executive Research Scientist,

Dr. Tetsuomi Sogawa

Senior Research Scientist,

Dr. Hiroki Takesue
Dr. Kazuhide Kumakura*

Senior Research Scientist,

Dr. Akihiko Shinya
Dr. Kazuaki Furukawa*

NTT Research Professor
Prof. Shintaro Nomura (University of Tsukuba) *Prof. Kyo Inoue (Osaka University) *2

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)Materials Science Laboratory

Executive Manager,
		

Dr. Toshiki Makimoto
Dr. Nahoko Kasai
Dr. Satoru Suzuki*

Thin-Film Materials Research Group:
Dr. Hideki Yamamoto (Group Leader)
Dr. Makoto Kasu*
Dr. Makoto Kasu
Dr. Yasuyuki Kobayashi
Dr. Hisashi SatoDr. Tetsuya Akasaka
Dr. Yoshitaka Taniyasu
Dr. Yoshiharu Krockenberger

Dr. Hideki Yamamoto*Dr. Kazuhide Kumakura
Dr. Kazuyuki Hirama

Low-Dimensional Nanomaterials Research Group:
Dr. Hiroki Hibino (Group Leader)
Dr. Fumihiko Maeda
Dr. Kazuaki Furukawa
Dr. Satoru Suzuki
Dr. Kenichi Kanzaki

Dr. Hiroo Omi
Shinichi Tanabe

Molecular and Bio Science Research Group:
Dr. Keiichi Torimitsu (Group Leader)
Dr. Koji Sumitomo
Dr. Nahoko Kasai*Dr. Hiroshi Nakashima
Dr. Yoshiaki Kashimura
Dr. Youichi Shinozaki*
Dr. Aya Tanaka

Dr. Akiyoshi Shimada
Touichiro Goto
Dr. Shogo Tsukada

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)3

Physical Science Laboratory

Executive Manager,

Dr. Hiroshi Yamaguchi
Toru Yamaguchi
Dr. Kenji Yamazaki*
Takeshi Karasawa

Nanodevices Research Group:
Dr. Akira Fujiwara (Group Leader)
Dr. Yukinori Ono
Dr. Hiroyuki Kageshima
Dr. Jin-ichiro Noborisaka
Dr. Gento Yamahata
Nanostructure Technology Research Group:
Dr. Hiroshi Yamaguchi (Group Leader)
Dr. Kenji Yamazaki
Toru Yamaguchi*
Dr. Hajime Okamoto
Daiki Hatanaka
Junzo Hayashi
Quantum Solid State Physics Research Group:
Dr. Koji Muraki (Group Leader)
Dr. Satoshi Sasaki
Dr. Kiyoshi Kanisawa
Dr. Takeshi Ohta
Dr. Toshiaki Hayashi
Dr. Ken-ichi Hitachi
Dr. Keiko Takase
Tadashi Saku
Superconducting Quantum Physics Research Group:
Dr. Kouichi Semba (Group Leader)Dr. Hayato Nakano
Dr. Shiro Saito
Hirotaka Tanaka
Dr. Kousuke Kakuyanagi
Dr. Xiaobo Zhu
Spintronics Research Group:
Dr. Tatsushi Akazaki (Group Leader)
Dr. Yuichi Harada
Dr. Hiroyuki Tamura
Dr. Hiroshi Irie
Dr. Yoshiaki Sekine
4Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Dr. Katsuhiko Nishiguchi
Dr. Gabriel Lansbergen

Dr. Koji Onomitsu
Dr. Imran Mahboob

Dr. Kyoichi Suzuki
Dr. Norio Kumada
Dr. Gerardo Gamez*

Dr. Shin-ichi Karimoto
Dr. Alexandre Kemp

Dr. Masumi YamaguchiOptical Science Laboratory

Executive Manager,

Dr. Yasuhiro Tokura
Dr. Takehiko Tawara
Dr. Satoshi Sasaki*

Quantum Optical State Control Research Group:
Dr. Yasuhiro Tokura (Group Leader)
Dr. Kaoru Shimizu
Kazuhiro Igeta
Dr. Makoto Yamashita
Dr. Hiroyuki Shibata
Dr. Tetsuya Mukai
Dr. Toshimori Honjo
Dr. Kiyoshi Tamaki
Daisuke Hashimoto
Dr. Nobuyuki Matsuda
Dr. William John Munro
Dr. Toshihiro Kubo
Quantum Optical Physics Research Group:
Dr. Tetsuomi Sogawa (Group Leader)Dr. Hidetoshi Nakano
Dr. Tadashi Nishikawa
Hidehiko Kamada
Dr. Kouta Tateno
Dr. Katsuya Oguri
Dr. Atsushi Ishizawa
Dr. Guoquiang Zhang
Dr. Keiko Kato
Photonic Nano-Structure Research Group:
Dr. Masaya Notomi (Group Leader)
Dr. Atsushi Yokoo
Dr. Eiichi Kuramochi
Dr. Hideaki Taniyama
Dr. Hisashi Sumikura
Dr. Young-Geun Roh*
Dr. Jimyung Kim

Dr. Masami Kumagai
Dr. Hiroki Takesue*
Dr. Fumiaki Morikoshi
Dr. Koji Azuma
Dr. Kensuke Inaba

Dr. Hideki Gotoh
Dr. Takehiko Tawara*
Dr. Haruki Sanada

Dr. Akihiko Shinya*
Dr. Kengo Nozaki
Dr. Danang Birowosuto

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

5

Senior Distinguished Researcher
Masaya Notomi was born in Kumamoto, Japan, on 16 February 1964. Hereceived his B.E., M.E., and Ph. D. degrees in applied physics from Universityof 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 quantum wires/dots and photonic crystal structures.
He has been in NTT Basic Research Laboratories since 1999, and a group leaderof Photonic Nanostructure Research Group since 2004. He is also entitled as
Senior Distinguished Scientist of NTT. From 1996-1997, he was with Linköping
University in Sweden as a visiting researcher. He was a guest associate professorof Department of Applied Electronics in Tokyo Institute of Technology (20032009), and is currently a guest professor of Department of Physics in Tokyo
Institute of Technology. He received IEEE/LEOS Distinguished Lecturer Awardin 2006, JSPS (Japan Society for the Promotion of Science) prize in 2009, Japan
Academy Medal in 2009, and The Commendation for Science and Technology
by the Minister of Education, Culture, Sports, Science and Technology (Prize for
Science and Technology, Research Category) in 2010. He is serving as a memberof National University Corporation Evaluation Committee in the Japanese
government. He is also a member of the Japan Society of Applied Physics, APS,
IEEE, and OSA.

6

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Distinguished Researchers
Akira Fujiwara was born in Tokyo, Japan on March 9, 1967. He received his B.S.,
M.S., and Ph.D. degrees in applied physics from The University of Tokyo, Japan
in 1989, 1991, and 1994, respectively. In 1994, he joined NTT LSI Laboratories
and moved to NTT Basic Research Laboratories in 1996. Since 1994, he has
been engaged in research on silicon nanostructures and their application to
single-electron devices. He was a guest researcher at the National Institute ofStandards and Technology (NIST), Gaithersburg, MD, USA during 2003-2004.
He received the SSDM Young Researcher Award in 1998, SSDM Paper Award in
1999, and Japanese Journal of Applied Physics (JJAP) Paper Awards in 2003 and2006. He was awarded the Young Scientist Award from the Minister of MEXT
(Ministry of Education, Culture, Sports, Science, and Technology) in 2006. He isa member of the Japan Society of Applied Physics and the IEEE.

Koji Muraki was born in Tokyo, Japan in 1965. He received his B.S., M.S.,
and Ph.D. degrees in applied physics from The University of Tokyo, Japan, in
1989, 1991, and 1994, respectively. In 1994, he joined NTT Basic ResearchLaboratories, Kanagawa, Japan. Since then, he has been engaged in the growthof high-mobility heterostructures and the study of highly correlated electronic
states realized in such structures. He was a guest researcher at Max-Planck
Institute, Stuttgart, Germany during 2001-2002. He is a member of the PhysicalSociety of Japan and Japan Society of Applied Physics.

Hiroshi Yamaguchi was born in Osaka on October 30, 1961. He received the B.E.,
M.S. in physics and Ph.D. degrees in engineering from the Osaka University in
1984, 1986 and 1993, respectively. He joined NTT Basic Research Laboratories
in 1986 and has engaged in the study of compound semiconductor surfaces using
electron diffraction and scanning tunneling microscopy. His current interests
are micro/nanomechanical devices using semiconductor heterostructures. He
was a visiting research fellow in Imperial College, University of London, U.K.
during 1995-1996 and a visiting research staff in Paul Drude Institute, Germany
in 2003. He is a guest professor in Tohoku University from 2006 and a directorof the Japanese Society of Applied Physics in 2008 and 2009. He is currently
an executive manager of Physical Science Laboratory and a group leader ofNanostructure Technology Research Group. He is a member of the Japan Societyof Applied Physics and the Physical Society of Japan.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)7

Yoshitaka Taniyasu was born in Toyama, Japan on June 10, 1973. He received
his B.E., M.E., and Dr. Eng. degrees in electrical engineering from Chiba
University, Chiba, Japan in 1996, 1998, and 2001, respectively. He joined NTT
Basic Research Laboratories in 2001. He has been engaged in wide bandgap
semiconductor research. His current interests are epitaxial growth and device
application of nitride semiconductors, especially aluminum nitride (AlN). He
received the Young Scientist Award for the Presentation of the Excellent Paper at
the Japan Society of Applied Physics (JSAP) in 2001, the Young Scientist Awardat the Semiconducting and Insulating Materials Conference in 2007, and theYoung Scientists’ Prize from the Minister of Education, Culture, Sports, Scienceand Technology in 2011. He is a member of the JSAP.

Norio Kumada was born in Gifu, Japan in 1975. He received his B.S., M.S.,
and Ph.D. degrees in physics from Tohoku University, Japan, in 1998, 2000,
and 2003, respectively. In 2003, he joined NTT Basic Research Laboratories,
Kanagawa, Japan. Since then, he has been engaged in the study of highly
correlated electronic states realized in semiconductor heterostructures. He
received Young Scientist Award of the Physical Society of Japan in 2008. He is amember of the Physical Society of Japan.

8

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Advisory Board (2010 Fiscal Year)
Name

Affiliation

Prof. Gerhard Abstreiter

Walter Schottky Institute, Germany

Prof. Boris L. Altshuler

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

Prof. Serge Haroche

Département de Physique,
De l'Ecole Normale Supérieure, France

Prof. Theodor W. Hänsch

Max-Planck-Institut für Quantenoptik, Germany

Prof. Mats Jonson

Department of Physics, Göteborg University, Sweden

Prof. Anthony J. Leggett

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

Prof. Johan E. Mooij

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

Prof. John F. Ryan

Clarendon Laboratory, University of Oxford, U.K.

Prof. Klaus von Klitzing

Max-Planck-Institut für Festkörperforschung, Germany

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)9

Invited / Guest Scientists (2010 Fiscal Year)

10

Name

Affiliation

PeriodDr. Hideomi Hashiba

Institute of Quantum Science,
Nihon University

Apr. 2010 – Mar. 2011

Dr. Lars Tiemann

Japan Science and Technology
Agency (JST)Apr. 2010 – Mar. 2011

Dr. Takasumi Tanabe

Dept. of Electronics and ElectricalEngineering, Keio University

Apr. 2010 – Mar. 2011

Prof. David Cox

University of Surrey, U.K.

Apr. 2010 – Jun. 2010

Prof. Tobias Nyberg

Royal Institute of Technology, Sweden

Jul. 2010 – Aug. 2010

Ms. Katherine Brown

University of Leeds, U. K.

Sep. 2010

Dr. Stefan Fölsch

Paul-Drud-Institute, Germany

Oct. 2010

Prof. Johan Elisa Mooij

Delft University of Technology,
The Netherlands

Oct. 2010 – Nov. 2010

Prof. Yuli V. Nazarov

Delft University of Technology,
The Netherlands

Nov. 2010

Prof. Amnon Aharony

Ben Gurion University of the Negev,
IsraelJan. 2011 – Feb. 2011

Prof. Ora Entin-Wohlman

Ben Gurion University of the Negev,
IsraelJan. 2011 – Feb. 2011

Dr. Daniel Paul Collins

University of Oxford, U. K.

Jan. 2011 – Feb. 2011

Dr. Akiko Ueda

Ben Gurion University, Israel

Jan. 2011 – Feb. 2011

Dr. Genki Odawara

Applied Physics Curriculum1,
Waseda University School of Advanced
Science and Engineering

Feb. 2011 – Mar. 2011

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Overseas Trainees (2010 Fiscal Year)
Name

Affiliation

PeriodOliver Johan Pirquet

University of Victoria, Canada

Sep. 2009 – Apr. 2010

Jessica Sparks

University of Waterloo, Canada

Sep. 2009 – Apr. 2010

Arianne McAllister

University of Ottawa, Canada

Sep. 2009 – Aug. 2010

Fabio Massimo Zennaro

Polytecnico di Milano, Italy

Jan. 2010 – Aug. 2010

Gary Wolfowicz

Ecole Normale Supérieure (ENS) de Cachan,FranceJan. 2010 – Aug. 2010David Framil Carpeno

Complutense Univeristy of Madrid, Spain

Jan. 2010 – Aug. 2010

Jan Fiala

Czech Techinical University in Prague,
Czech Republic

Jan. 2010 – Aug. 2010

Juan Manuel Agudo
Carrizo

Polytechnic University of Valencia (UPV),
Spain

Jan. 2010 – Aug. 2010

Romain Duval

INSA (Institut National des Sciences
Appliquées de Toulouse), France

Feb. 2010 – Aug. 2010

Kylie Ellis

The University of Adelaide, Australia

Mar. 2010 – Apr. 2010

Yuichiro Matsuzaki

University of Oxford, U.K.

Mar. 2010 – Apr. 2010

Shaun Lee

University of British Columbia, Canada

May. 2010 – Dec. 2010

Nadege KainaESPCI (Ecole Supérieure de Physiqueet de Chimie Industrielle), France

July. 2010 – Dec. 2010

Quentin Wilmart

ESPCI (Ecole Supérieure de Physiqueet de Chimie Industrielle), France

July. 2010 – Dec. 2010

Antoine GaumeESPCI (Ecole Supérieure de Physiqueet de Chimie Industrielle), France

July. 2010 – Dec. 2010

Mohamed Oudah

University of Ottawa, Canada

Sep. 2010 – Sep. 2011

Yasir Makhdoom

University of British Columbia, Canada

Sep. 2010 – Sep. 2011

Jessica Planade

ESPCI (Ecole Supérieure de Physiqueet de Chimie Industrielle), France

Sep. 2010 – Dec. 2010

Jelena Baranovic

University of Oxford, U.K.

Nov. 2010 – Dec. 2010

Roberto Lo Nardo

Palermo University, Italy

Jan. 2011 – Aug.2011

Diego Sabbagh

University of Studies "Roma Tre", Italy

Jan. 2011 – Aug.2011

Bas van den Broek

Delft University of Technology,
The Netherlands

Jan. 2011 – Mar. 2011

Yibo Fu

University of Toulouse, France

Feb. 2011 – Sep. 2011

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)11

Domestic Trainees (2010 Fiscal Year)

12

Name

Affiliation

PeriodKohei Morita

Kyushu University, Japan

Apr. 2010 – Mar. 2011

Shogo Aihara

Keio University, Japan

Apr. 2010 – Mar. 2011

Yasuhiko Oda

University of Tokyo, Japan

Apr. 2010 – Mar. 2011

Takayuki Watanabe

Tohoku University, Japan

Apr. 2010 – Mar. 2011

Tatsuki Takakura

University of Tokyo, Japan

Apr. 2010 – Mar. 2011

Hiroki Shioya

University of Tokyo, Japan

Apr. 2010 – Mar. 2011

Takashi Kobayashi

Tohoku University, Japan

Apr. 2010 – Mar. 2011

Yuma Okazaki

Tohoku University, Japan

Apr. 2010 – Mar. 2011

Ken-ichiro Kusudo

University of Tokyo, Japan

Apr. 2010 – Mar. 2011

Naoyuki Masumoto

University of Tokyo, Japan

Apr. 2010 – Mar. 2011

Hiroshi Kamata

Tokyo Institute of Technology, Japan

Apr. 2010 – Mar. 2011

Yu Morikawa

University of Tsukuba, Japan

Apr. 2010 – Mar. 2011

Hiroshi Takahashi

Tokyo Institute of Technology, Japan

Apr. 2010 – Mar. 2011

Yoji Kunihashi

Tohoku University, Japan

Apr. 2010 – Mar. 2011

Takumi Inaba

Tokyo University of Science, Japan

Apr. 2010 – Mar. 2011

Tatsuya Baba

Tokyo University of Science, Japan

May. 2010 – Mar. 2011

Yuta Toga

Tohoku University, Japan

Aug. 2010– Sep. 2010

Soichiro Suzuki

Hirosaki University, Japan

Aug. 2010– Sep. 2010

Takumi Kato

Tohoku University, Japan

Aug. 2010– Sep. 2010

Masaya Mitsuhashi

Nagaoka University of Technology, Japan

Oct. 2010 – Feb. 2011

Takashi Aiba

Nagaoka University of Technology, Japan

Oct. 2010 – Feb. 2011

Mitsugu Kiryu

Nagaoka University of Technology, Japan

Oct. 2010 – Feb. 2011

Yuji Ueda

Waseda University, Japan

Oct. 2010 – Dec. 2010

Yusuke Takei

Tokyo University of Science, Japan

Oct. 2010 – Mar. 2011

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Ⅰ．Research Topics

Overview of Research in Laboratories
Materials Science Laboratory
Toshiki Makimoto
The Materials Science Laboratory aims at producing new functional materials and designingof advanced device based on novel materials and biological function. Controlling theconfiguration and coupling of atoms and molecules is our approach to accomplish these goals.
We have three research groups covering from thin film materials, such as nitride
semiconductors, diamond, graphene, and superconductors, to biological molecules, suchas receptor proteins and lipid bilayers. The distinctive characteristic of our laboratory is its
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 future information technology.
In this year, the significant progresses have been made in the researches on the opticalcharacteristics of AlN, the transport characteristics of graphene, and the structural observationof a receptor protein molecule.

Physical Science Laboratory
Hiroshi Yamaguchi
We are studying semiconductor and superconductor-based solid-state devices, which will
have a revolutionary impact on communication and information technologies in the 21st
century. In particular, we promote research of nanoscale devices fabricated using high-quality
crystal growth and fine lithographic techniques.
The five groups in our laboratory are working in the following areas: precise and dynamical
control of single electrons, nanodevices operating with ultra low power consumption, novel
nanomechanical systems utilizing mechanical degrees of freedom in solid-state architechtures,
coherent quantum control of semiconductor and superconductor systems, carrier interactions
in semiconductor hetero- and nanostructures, spintronics manipulating both electron andnuclear spins. We also promote the studies of cutting-edge nanolithography techniques, highquality crystal growth, and theoretical studies including first-principle calculations.

Optical Science Laboratory
Yasuhiro Tokura
This laboratory aims for the development of core-technologies that will innovate on opticalcommunications and optical signal processing, and seeks fundamental scientific progresses.
The groups in our laboratory are working for the quantum state control by very weak light,
the search for intriguing phenomena using very intensive and short pulse light, and verysmall optical integrated circuits using two-dimensional photonic crystals, based on the opticalproperties of semiconductor nanostructures like a quantum dot.
In this year, we reported telecommunication-band singlet photon detection by MgB2 nanowire, field experiments of quantum key distribution, observation of coherent phonon in carbon
nanotubes, and first sub-femtojoule all-optical switch.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)13

Robust Superconductivity in Pr2CuO4 Prepared by MBE
Hideki Yamamoto, Yoshiharu Krockenberger, Osamu Matsumoto*, Keitaro Yamagami,
Masaya Mitsuhashi, and Michio Naito*
Materials Science Laboratory, *Tokyo Univ. of Agricul. & Technol.
Commonly, high-Tc cuprates are considered as doped-Mott insulators (charge transfer
insulators). We have shown that the parent compounds of electron-doped superconductors,
T’-RE2-xCexCuO4 (RE: rare-earth ion) at x = 0 are not insulators but superconductors [1, 2]. A
complex oxygen diffusion process lies beneath the contradiction of earlier reported and ourpresent results. Superconducting parent compounds are a novelty in solid state physics andthe physical origin of the superconducting state requires clarification. We have prepared highquality Pr2CuO4 thin films by MBE.
Superconductivity is induced after a specially designed two-step post-annealing process
is applied. Systematic optimization of the annealing conditions resulted in Pr2CuO4 thinfilms with a Tc of 26 K (Δ Tc < 0.5 K) and metallic conduction [ρ RT = 400 μΩcm, RRR = 10](Fig. 1). The resistivity value is lowest [ρ (30 K) ~ 40 μΩcm] for Tred = 475 - 500°C whereas
Tc is highest (Tc ~ 26 K) for Tred = 500°C. A strong diamagnetic signal was observed (Fig. 2)
in parallel configuration with an onset at 23 K, confirming a robust superconducting responseof Pr2CuO4. A nearly ideal oxygen sub-lattice and therefore intrinsic properties of the parent
compounds are unveiled after applying an optimal post-annealing process. Our observations
are supported by recent theoretical considerations where the parent compounds of T’-structure
cuprates are not exclusively Mott insulators (charge-transfer insulators) [3, 4].
[1] O. Matsumoto et al., Phys. Rev. B 79 (2009) 100508R.
[2] H. Yamamoto et al., Solid State Commun. 151 (2011) 771.
[3] C. Weber et al., Nature Phys. 6 (2010) 574; Phys. Rev. B 82 (2010) 125107.
[4] H. Das and T. Saha-Dasgupta, Phys. Rev. B 79 (2009) 134522.

Fig. 1. Influence of the annealing temperature (Tred)during step II in the two-step annealing sequenceon the ρ (T) characteristics of the Pr2CuO4 films.
The films were first annealed at Ta = 750°C andP aO2 = 1 x 10-4 Torr (step I).

14

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Fig. 2. Plot of Magnetization M(T) curves of
Pr2CuO4 film having the highest Tc intransport measurement. Thickness of thefilm is 1000 Å.

Nucleus and Spiral Growth Mechanisms of GaN
Studied by Selective-Area MOVPE
Tetsuya Akasaka, Yasuyuki Kobayashi, and Makoto Kasu
Materials Science Laboratory
Crystal growth of semiconductor films generally proceeds under a combination of nucleus
and spiral growth modes. In this study, we tried to clarify the mechanisms of nucleus andspiral growth modes by using selective-area metalorganic vapor phase epitaxy (MOVPE) of
GaN.
First, a SiO2 mask was deposited on a GaN (0001) bulk substrate with low density of
threading dislocations. Then, the SiO2 mask was patterned by photolithography so that it
would have many hexagonal openings with the diameter of 16 μm. Finally, selective-area
MOVPE of GaN films was performed on the mask-patterned GaN substrate. Source gases
were ammonia and trimethylgallium. The surfaces of GaN were observed by atomic force
microscopy (AFM).
A step-free GaN surface (an atomically smooth surface without any monolayer step)
was formed by nucleus growth within a mask opening having no screw and mixed-type
dislocations [1]. On the other hand, growth spirals were observed on a GaN surface formed
within a mask opening having screw and mixed-type dislocations (Fig. 1) and the growthmode was spiral growth. The degree of supersaturation, σ, which is the driving force of crystal
growth, is generally estimated from the interstep distance of a growth spiral. Figure 2 shows
the nucleus and spiral growth rates plotted as a function of σ. The spiral growth rate increases
parabolically with increasing σ, while the nucleus growth rate has very low values in the σrange [2]. Solid and dotted lines in Fig. 2 are fitting results we obtained using a crystal growththeory [3]. It can be seen that our experimental results are well explained by the crystal growththeory.
In summary, selective-area MOVPE enables us not only to fabricate step-free GaN surfaces
but also to clarify the fundamental mechanisms of crystal growth including nucleus and spiralgrowth.
[1] T. Akasaka et al., Appl. Phys. Express 2 (2009) 191002.
[2] T. Akasaka et al., Appl. Phys. Lett. 97 (2010) 141902.
[3] W. K. Burton et al., Phil. Trans. Roy. Soc. A 243 (1951) 299.

Fig. 1. AFM image of a growth spiralcenter of GaN.

Fig. 2. Nucleus and spiral growth rates plotted as afunction of the degree of supersaturation.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)15

Emission Mechanism of AlN Deep-Ultraviolet Light-Emitting Diode
Yoshitaka Taniyasu and Makoto Kasu
Materials Science Laboratory
Aluminum nitride (AlN) is a direct-bandgap semiconductor with a bandgap energy of 6 eV,
the largest among semiconductors. Therefore, AlN is a promising material for deep-ultraviolet(deep-UV) light-emitting devices with an ultrashort wavelength. Previously, we achieved bothn-type and p-type doping in AlN and fabricated an AlN p-n junction light-emitting diode (LED)with near-band-edge electroluminescence (EL) at a wavelength of 210 nm, the shortest everreported for any kind of LED [1]. Here we identify the origin of the near-band-edge emission
and propose a high-efficiency LED structure based on the unique characteristic that theemission intensity largely changes depending on the crystal planes of its surface.
First, a C-plane AlN p-n junction LED structure was grown on C-plane SiC substrate bymetalorganic vapor phase epitaxy. By increasing the NH3 flow rate, the hole concentration in
the p-type AlN was increased because of the suppressed formation of N vacancies, which act
as compensating donors. As a result, the LED external quantum efficiency was increased from
–6
–4
8×10 to 1×10 % [2]. As shown in Fig. 1, the near-band-edge emission was dominated by an
exciton emission originating from the crystal-field split-off valence band (FXCH), but anotherexciton emission originating from heavy/light hole valence bands (FXHH/LH) was also observed.
From the emission energies, considering residual strain, the crystal-field splitting energy ΔCR
was determined to be –165 meV. Because of the negative ΔCR, the topmost valence band is the
crystal-field split off valence band with a pZ-like state and then the near-band-edge emission
polarizes for the electric field parallel to the c-axis (E||c). Consequently, the near-band-edge
emission is weak from the C-plane but strong from the A-plane for AlN.
For nitride semiconductors, like AlN and GaN, the C-plane is preferable for high-quality
growth and therefore a C-plane LED structure has been commonly fabricated. However, for
AlN, because of the E||c polarization, an A-plane LED structure is desirable for enhancing
the light extraction and improving the emission efficiency. We fabricated the A-plane LED
structure by using A-plane SiC substrate and observed a near-band-edge emission at 210 nm[3]. As shown in Fig. 2, the A-plane LED showed strong emission from the LED surface (θR =0°), while the conventional C-plane LED showed weak emission. Thus, the A-plane LED is apromising structure for high-efficiency AlN deep-UV LED.
[1] Y. Taniyasu, M. Kasu, and T. Makimoto, Nature 441 (2006) 325.
[2] Y. Taniyasu and M. Kasu, Appl. Phys. Lett. 98 (2011) 131910.
[3] Y. Taniyasu and M. Kasu, Appl. Phys. Lett. 96 (2010) 221110.

(a)

(b)

Fig. 1. (a) Emission spectrum of AlN LED and (b) opticaltransitions in AlN.

16

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Fig. 2. Radiation patterns of A-plane
and C-plane AlN LEDs.

AlGaN/GaN HEMTs Epitaxially Grown on Single-Crystal Diamond
Kazuyuki Hirama, Yoshitaka Taniyasu, and Makoto Kasu
Materials Science Laboratory
AlGaN/GaN high-electron mobility transistors (HEMTs) are being developed extensively
for RF high-power applications. However, the output power of AlGaN/GaN HEMTs is limitedby the thermal conductivities of the substrate materials. Among all materials, single-crystal
diamond has the highest thermal conductivity of ~ 22 W/cmK. Therefore, diamond is expected
to be the ideal substrate for high-power devices. However, due to the difference in the crystal
structures of nitride semiconductors and diamond, single-crystal nitride growth on diamondsubstrates is difficult. Recently, using (111) surface orientation, we have successfully grownsingle-crystal AlN (0001) layers on diamond substrates [1, 2].
Here, using the single-crystal AlN as a buffer layer, we epitaxially grew the AlGaN/GaN
HEMT structure on diamond (111) substrate. As shown in Fig. 1, first, a 180-nm-thick AlN
buffer layer was grown, followed by the growth of 20-period AlN(3 nm)/GaN(17 nm) multilayers, a 600-nm-thick GaN layer, a 1-nm-thick AlN spacer layer, a 30-nm-thick Al0.25Ga0.75N
barrier layer, and a 4-nm-thick GaN cap layer. From X-ray diffraction measurements, we
confirmed the single-crystal growth of the AlGaN/GaN HEMT structure. Next, we confirmed
the formation of two-dimensional electron gas (2DEG) in the AlGaN/GaN heterostructureby–2Hall-effect measurement. The sheet electron density at room temperature was 1×1013 cm . On
the other hand, the electron mobility at room temperature was 730 cm2/Vs.
A 3-μm-gate-length AlGaN/GaN HEMT on the diamond substrate showed the maximum
IDS of 220 mA/mm. Figure 1 shows the high-frequency small-signal characteristics. From thefrequency dependence of the current gain (|H21|2), maximum stable gain (MSG) and maximum
power gain (MAG), the cut-off frequency (fT) of 3 GHz and maximum frequency of oscillation(fmax) of 7 GHz were obtained. Then, we compared the device temperature of AlGaN/GaN
HEMTs on diamond and SiC substrates under high-DC-power operation. Figure 2(a) shows
the setup for measuring the device temperatures. Figures 2(b) and (c) show the temperature
distributions from the side of the AlGaN/GaN HEMTs on the diamond and SiC substrates
at a dissipated power of 2 W (3.2 W/mm). The device temperature at 2 W increased from 23
to 36°C (temperature rise ΔT = 13°C). On the other hand, on the SiC substrate, the device
temperature increased from 23 to 46 °C (ΔT = 23°C). From the dissipated power dependenceof the device temperature rise [Fig. 2(d)], we estimated the thermal resistance of the AlGaN/
GaN HEMT on the diamond substrate to be 4.1 Kmm/W, which is about half of that on a SiC
substrate (7.4 Kmm/W) [3]. The low thermal resistance for the AlGaN/GaN HEMT on the
diamond substrate is attributed to the high thermal conductivity of the single-crystal diamond.
These results show that AlGaN/GaN HEMTs on diamond are promising for high-frequency
and high-power applications.
[1] Y. Taniyasu and M. Kasu, J. Cryst. Growth 311 (2009) 2825.
[2] K. Hirama, Y. Taniyasu, and M. Kasu, J. Appl. Phys. 108 (2010) 013528.
[3] K. Hirama, Y. Taniyasu, and M. Kasu, Appl. Phys. Lett. 98 (2011) 162112.

Fig. 1. High-frequency smallsignal characteristics
of AlGaN/GaN HEMT
on diamond (111).

Fig. 2. (a) Setup for measuring the temperature distributions. Temperature
distribution of the AlGaN/GaN HEMTs on (b) diamond and (c) SiC substrates
at a dissipated power of 2 W (3.2 W/mm). (d) Dissipated-power dependence
of device temperature for AlGaN/GaN HEMTs on the diamond and SiC
substrates. Closed and open squares indicate the temperatures for diamondand SiC substrates, respectively.
Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)17

Highly Integrative Artificial Cell Membrane Microarray
Kazuaki Furukawa
Materials Science Laboratory
Microarrays of biological molecules such as DNA chips are widely used for high-throughput
bioanalysis. When developing new microarrays, it is essential to improve the technology for
fixing biomolecules without losing their biological functionality. A microarray consisting ofan artificial cell membrane supported on a solid surface is expected to provide an important
platform for the purpose. We have developed a new technique for fabricating an artificial cell
membrane microarray and demonstrated a biosensing application of the fabricated microarray.
We used the self-spreading phenomenon, which is a self-organizing process that forms a cell
membrane at a solid-liquid interface, to fabricate the artificial cell membrane microarray. Our
method is unique in that the position of the self-spreading is controlled with a hydrophilic/hydrophobic pattern [1]. According to the designed pattern, a self-spreading membrane
starting from a macroscopic area was guided to the microarray structure without mixing withmembranes in the different areas. We succeeded in fabricating 10-µm-width parallel lines,
each filled with an artificial cell membrane with a unique composition, at 5-µm intervals (color
frontispiece). Structures obtained with our new technique are in principle more than 100 times
more highly integrated than previously reported structures that employ the vesicle fusion
technique on patterned surfaces [2].
To demonstrate the validity of the microarray for biosensing applications, we fabricated
a composition microarray, part of which contained biotin-conjugated lipid. Figure 1 shows
fluorescence images of the array that were recorded (a) before and (b) after it was immersed
in Texas Red conjugated streptavidin solution. Red fluorescence, which originates from Texas
Red, was observed only in the lines containing biotin-conjugated lipids after 90 min, as shownin Fig. 1(b). This is due to the specific binding between biotin and streptavidin. Since the red
fluorescence from the lines without biotin is limited, the microarray is valuable for biosensing
applications.
This work was supported by KAKENHI.
[1] K. Furukawa et al., Lab Chip 6 (2006) 1001.
[2] K. Furukawa and T. Aiba, Langmuir 27 (2011) 7341.

(a):

green

(b) green & red

=

green

+

red

Fig. 1. Fluorescence images of artificial cell membrane microarray (a) before and (b) 90 min after the addition of
Texas Red conjugated streptavidin solution. The membranes are composed mainly of Egg-PC with top 3lines: 1 mol% NBD-conjugated lipid; middle 3: 1 mol% biotin-conjugated lipid; bottom 3: both lipids. The
green and red fluorescence is from NBD and Texas Red, respectively, and the green & red image in (b) is asuperimposition of two images, green and red.

18

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Evaluation of Carrier Density in Doped Single-Wall Carbon Nanotubes
Satoru Suzuki and Hiroki Hibino
Materials Science Laboratory
The thermal chemical vapor deposition (CVD) method has been widely used to grow singlewall carbon nanotubes (SWNTs). However, direct growth of doped SWNTs and tuning of
the impurity concentration in them are still a big challenge. Another very important issue for
doped SWNTs is their characterization. In particular, it is very difficult to evaluate carrier
concentrations in individual SWNTs. Thus, the carrier concentration has not been clarified inprevious studies of doped SWNTs. In this study, we grew boron (B)- and nitrogen (N)-doped
SWNTs from B- and N-containing feedstocks by the thermal CVD method. Raman spectral
shifts induced by carrier doping were clearly observed and the carrier densities were evaluatedfrom the shifts [1].
We used triisopropylborate (C9H21BO3) and benzylamine (C7H9N) as B- and N-containing
feedstocks. These chemicals also acted as a carbon source, and we did not use any othercarbon sources. B- or N-doped SWNTs were grown from either one or the other feedstock,with a Co thin film deposited on a SiO 2/Si substrate used as a catalyst. We were also able
to synthesize BN-doped SWNTs by supplying both triisopropylborate and benzylamine
simultaneously, as shown in Fig. 1. Transmission electron microscopy and Raman (radial
breathing mode) measurements indicated that the diameter of the doped SWNTs is mostly
1-2 nm, like that of undoped SWNTs grown using a similar catalyst. Figure 2 shows Raman(G band) spectra of B-, N-, and BN-doped SWNTs, and undoped SWNTs. As can be seen in
the figure, the G band position in the doped SWNTs is shifted to the high-wavenumber side–1by 3-6 cm , regardless of the choice of feedstock. The hardening of the G band regardless of
doping type (electron or hole doping) can be understood as renormalization of phonon energy
through electron-phonon coupling induced by a Fermi level shift in a semiconducting SWNT.
Originally, the energy of the G band phonon is softened by the electron-phonon interaction(Kohn anomaly). However, a Fermi level shift reduces the electron-phonon interaction andthus, reduces the effect of the Kohn anomaly. Consequently, the Fermi level shift induced byelectron or hole doping causes a hardening of the G band. The G band hardening is expected
to become prominent when the Fermi level reaches the valence or conduction band. Therefore,
the results shown in Fig. 2 indicate that the Fermi level in the doped SWNTs is located inside
the valence or conduction band. We can also estimate the carrier density. Assuming that the
SWNT diameter is 1.5 nm, the estimated carrier concentration reaches 0.4-0.8%, which is aconsiderably large value.
[1] S. Suzuki and H. Hibino, Carbon 49 (2011) 2264.

Fig. 1. SEM image of BN-doped SWNTs. Scalebar: 5 μm.

Fig. 2. G band spectra of B-, N-, and BN-doped
SWNTs. The peak positions are denoted. The
excitation wave length was 785 nm.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)19

Transport Properties of Epitaxial Monolayer and Bilayer Graphene
Shinichi Tanabe1, Yoshiaki Sekine2, Hiroyuki Kageshima2, Masao Nagase3, and Hiroki Hibino1
1
Materials Science Laboratory, 2Physical Science Laboratory, 3The University of Tokushima
Monolayer and bilayer graphene have gained significant attention because of their potential
applications for high-frequency devices and for logic devices, respectively. The mechanicalexfoliation of graphite is a common way of making graphene because high-quality graphene
can be obtained. However, this technique is only good for making graphene flakes of only
a few tens micrometers in size. For wafer-scale synthesis of graphene, we employ thermal
decomposition of SiC, which enables epitaxial growth of graphene layers. By annealing
SiC(0001) in an Ar atmosphere and in an UHV environment, we have succeeded in growing
monolayer and bilayer graphene, respectively. To elucidate the transport properties of thesegraphene, we systematically studied the electrical properties of monolayer and bilayer
graphene in top-gate devices.
Figure 1 shows the magnetic-field dependences of longitudinal resistance and Hall
resistance of the monolayer-graphene device. The magnetic field was applied perpendicular
to the graphene plane. The Hall resistances become constant as a function of magnetic fieldat the resistances unique to monolayer graphene, where, at the same time, the longitudinal
resistances show minima. At high-magnetic field, the minimum resistance of the longitudinal
resistance becomes zero, which is a hallmark of the quantum Hall state. By decreasing thecarrier density with applying gate voltage (Vg), the mobility increases, and the mobility at 2
–1 –1
–2
K exceeded 10,000 cm2 V s at a carrier density of 3×1010 cm , which is comparable to thatof exfoliated graphene transferred onto SiO2 [1]. Figure 2 shows the gate-voltage dependenceof resistance of the bilayer-graphene device from 2 to 300 K. In all temperatures, resistanceat the charge neutrality point (CNP) shows maximum resistance [2]. The strong temperaturedependence of the resistance at the CNP results from band gap opening due to the interactionof the graphene with the substrate. The observed quantum Hall effect in the monolayergraphene device proves high quality of the monolayer graphene and the electrical detectionof the band gap in bilayer-graphene device is an important finding for its applications. These
results show that the thermal decomposition of SiC is an effective method to grow monolayer
and bilayer graphene.
This work was supported by KAKENHI.
[1] S. Tanabe et al., Appl. Phys. Express 3 (2010) 075102.
[2] S. Tanabe et al., Jpn. J. Appl. Phys. 50 (2011) 04DN04.

Fig. 1. Temperature dependence of longitudinal
resistance and Hall resistance of monolayer
graphene.

20

Fig. 2. Gate-voltage dependence of resistance of
bilayer graphene from 2 to 300 K.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Manipulation of Biomolecules on Solid Substrate
Using Artificial Cell Membrane
Hiroshi Nakashima and Kazuaki Furukawa
Materials Science Laboratory
The development of biofunctional devices requires a biointerface for maintaining
biomolecules on a substrate without interfering with their structure or biological functions.
By using an artificial membrane biointerface, we can control the position, density andarrangement of biomolecules, leading to the design of various bio devices such as highly
sensitive biosensors or implant-type biochips. Here we produced artificial cell membranes ona substrate that enable proteins to be adsorbed or transported to a desired position, and thus
realized a novel molecular manipulation technique for use at the biointerfaces [1].
A cell membrane is essentially composed of phospholipids (lipids). The fluidity of an
artificial cell membrane is controlled by the choice of lipid components. We selectively
fabricated artificial cell membranes with high/low fluidity that contained nickel-chelating
lipids (Ni-lipid). The Ni-lipid is capable of specific binding with terminal modified proteins.
Figure 1(a) and (b) shows AFM images of an artificial cell membrane consisting of DSPC
(low fluid lipid) and Ni-lipid. The image of a 50/50 mol% of DSPC/Ni-lipid reveals a heterogeneous membrane structure with round DSPC-rich domains distributed in a Ni-lipid-richfluid-phase domain. The DSPC domains were slightly thicker (1.0 nm) than the surrounding
Ni-lipid domain. The area of each domain was controlled by controlling the molar ratio of thelipid components. When histidine-tagged green fluorescent proteins (His-tagged GFPs) wereadded to the membrane, the fluorescent pattern was evidently based on the specific adsorptionof His-GFPs only in the Ni-lipid domain [Fig. 1 (c) and (d)]. While the membrane producedby DOPC (high fluid lipid) and Ni-lipid formed a homogeneous structure with high fluidity.
The membrane exhibited a self-spreading ability in buffer solution whereby a single lipid
membrane (5 nm high) grows on a substrate surface by self-organization [2]. By employing
the self-spreading nature, we demonstrated protein transport along the micro-pattern. Figure 2
shows the time evolution of the molecular transport of His-GFPs tethered on the membrane.
The transport property agreed well with the existing self-spreading model of an artificial
membrane [velocity (ν ) = (β /time (t))1/2] where the kinetic spreading coefficient (β ) was 10.4μm2/s.
The biointerface produced by lipids can also employ a cell membrane model to analyze
biomolecular interactions or signal transmission events. Therefore, the biointerface will bebeneficial for bioscience as well as providing a framework for building biofunctional devices.
[1] H. Nakashima et al., Langmuir 26 (2010) 12716.
[2] K. Furukawa et al., Lab Chip 6 (2006) 1001.

Fig. 1. Pattern formation of artificial cell membrane
and absorption of proteins at specific location
on membrane.

Fig. 2. Protein transport through self-spreadingof artificial cell membrane.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

21

AFM Observation of a Receptor Subunit Structure
Nahoko Kasai, Aya Tanaka, and Chandra S. Ramanujan*
Materials Science Laboratory，*University of Oxford
Membrane receptor proteins play the crucial role of transmitting signals in the central
nervous system. They are regulated by chemicals called ligands which bind to the extracellular
ligand binding domains. This binding either effects a change in the protein that forms a poreallowing movement of charged ions into the cell or modifies inside the cells chemically. As
such, receptor proteins are small but highly selective devices. Most of the receptor proteinsconsist of multiple subunit proteins. The structure of the receptor proteins has been examinedby mainly by X-ray crystallography and cryo-EM, however, these techniques do not allow
the examination of functioning receptors. Atomic force microscopy (AFM) enables the nanoscale observation of proteins in a liquid environment, offering a unique opportunity to observefunctional biological molecule such as single proteins under physiological conditions.
We have succeeded in observing the structure of single purified and ionotropic receptor
proteins in the solution using the AFM [1]. In this study, receptor proteins were purified fromover-expressed insect cells (Fig. 1), and then reconstituted into an artificial lipid bilayer by
dialysis because the receptors would function as in vivo when reconstituted into the lipid
bilayer. Receptor samples were settled on to mica substrate and rinsed thoroughly. We thenimaged the reconstituted receptor proteins on a substrate in a buffer solution using AFM. We
determined the orientation of the reconstituted receptor using antibody reaction, and then we
magnified and found four protrusions indicating tetrameric structure of the protein (Fig. 2),
which provides various different shapes of the single receptor. This result first demonstrated
that the structure of the functioning receptor proteins seems to change mainly by heatfluctuation.
This research was supported in part by Bio-nanotechnology IRC in UK and by KAKENHI .
[1] N. Kasai et al., BBA Gen. Subj. 1800 (2010) 655.

Fig. 1. Electrophoresis analysis of purified
ion-channel receptor protein.

22

Fig. 2. AFM images of subunit structured ion-channel
receptor protein reconstituted into artificial lipid
bilayer. (100x100 nm)

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Electrostatic Control of Artificial Cell Membrane Self-Spreading
Yoshiaki Kashimura and Kazuaki Furukawa
Materials Science Laboratory
A lipid bilayer, which is a fundamental component of a cell membrane, can be spread
artificially on a substrate by self-assembly. Using this self-spreading nature of an artificial
cell membrane (ACM), we have investigated the effect of a single nanogap structure on themolecular dynamics within an ACM [1, 2]. We report here the electrostatic control of ACM
self-spreading by the temporal switching of an electric field applied to a nanogap structure [3].
A pair of electrodes with a nanogap was fabricated using Au/Ti. A 10 μm wide microchannel
with wells at both ends was fabricated on this nanogap structure. A lipid mixture consisting of
Egg-PC and Egg-PG (molar ratio 7:3) containing 1 mol% Texas Red-DHPE was attached to
one of the wells. The self-spreading of an ACM was initiated by immersing the substrate in abuffer solution containing 0.1–100 mM NaCl.
Figure 1 shows a typical time evolution for a self-spreading ACM induced by the temporalswitching of the applied voltage when we used a 100 mM NaCl solution and a nanogap witha separation of <5 nm. Before the ACM passed through the nanogap, no voltage-dependentchanges in the self-spreading were observed [Fig. 1(a) and (b)]. However, when the ACM
reached the nanogap, the self-spreading was forcibly prevented by the voltage application[Fig. 1(c)]. This continued for ~300 s, corresponding to the interval of the voltage application[Fig. 1(d)]. Interestingly, the ACM started to develop again immediately after the applied
voltage was returned to 0 V [Fig. 1(e)-(g)]. Furthermore, we confirmed that this ON/OFF
switching of the self-spreading behavior could be repeatedly observed, corresponding to thetemporal switching of the applied voltage [Fig. 1(h)-(l)]. The electric double layer, which ischaracterized by the Debye length, plays a crucial role in this behavior. In a bulk condition,
the electric field is shielded by counterions in the electrolyte solution. In contrast, the sumof the Debye length (D) from both electrode surfaces (a few nanometers for a 100 mM NaClsolution) is close to the nanogap width (d ), the electric field can be effectively applied in the
nanogap spacing, leading to the electrostatic trapping of lipid molecules. A continuous supplyof lipid molecules is vital for the self-spreading. Therefore,
the electric field applied to a nanogap acted as a molecule gate
for the self-spreading (Fig. 2). The technique described here
constitutes the first demonstration of the temporal and spatial
control of biomembrane development in a nanometer-scale
device and can provide new opportunities for the realization of
nanobio devices.
This work was supported by KAKENHI.
[1] Y. Kashimura et al., Jpn. J. Appl. Phys. 47 (2008) 3248.
[2] Y. Kashimura et al., Jpn. J. Appl. Phys. 49 (2010) 04DL15.
[3] Y. Kashimura et al., J. Am. Chem. Soc. 133 (2011) 6118.
Fig. 1. (right). Time evolution of a self-spreading ACM.

Fig. 2. (upper). Mechanism of electrostatic trapping.
Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)23

Single-Electron Resonant Activation over an Oscillating Barrier
Satoru Miyamoto1, 2, Katsuhiko Nishiguchi1, Yukinori Ono1,
Kohei M. Itoh2, and Akira Fujiwara1
1
Physical Science Laboratory, 2Keio University
Single-electron (SE) transfer device has been investigated from the viewpoints of its
application to metrological current standards and low power circuits. At relatively hightemperatures the device is also a good platform to study the dynamics of Brownian particles.
In this work we address resonant activation of a particle over an oscillating barrier [1], which
is known as one of the resonant phenomena for classical particles. Such resonance is predicted
to occur when the oscillation frequency satisfies the condition of scale matching with theaverage rate of the particles crossing the barrier. Until now only the resonant activation ofmacroscopic variables has been observed in tunnel diodes and Josephson junctions.
The measured device consists of a silicon nanowire with multiple finger gates as shownin Fig. 1 (a). Figure 1 (b) describes how the SE transfer is performed using a SE ratchet [2]scheme, which enables clocked transfer of SEs from source to drain via a charge island.
Using proper gate voltages, we can create a situation where a SE in the island is thermally
activated over a potential barrier as shown in Fig. 1(c). Then we apply a small rf signal Arf witha frequency frf to introduce a modulation Um to the barrier. The SE transfer is performed at
16 K with the ratchet clock frequency of fRC=16.6 MHz. The average escape time τ avg isevaluated by measuring the transfer current by varying the ejection time tG1L during which
the electron is thermally activated over the barrier. Figure 2 shows τ avg as a function of frf at
different gate voltages VG1L which are used to change the order of τ avg. τ avg is found to manifest
a resonance at a frequency with the same order of 1/τ avg. Furthermore, the resonant frequency
fRES exhibits a shift to higher frequencies for a shorter τ avg. These behaviors are well explainedin the framework of the resonant activation which happens due to the synchronization between
the deterministic rf signal and the stochastic escape of a single electron as a Brownian particle[3].
[1] C. R. Doering and J. C. Gadoua, Phys. Rev. Lett. 69 (1992) 2318.
[2] A. Fujiwara, K. Nishiguchi, and Y. Ono, Appl. Phys. Lett. 92 (2008) 042102.
[3] S. Miyamoto et al., Phys. Rev. B 82 (2010) 033303.

Fig. 1. (a) Top-view scanning electron micrograph and(b) schematic potential diagram of the single-electron
ratchet. (c) Single-electron escape over an oscillating
barrier.
24

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Fig. 2. rf-frequency dependence of the average
escape time at different values of VG1L
which give different barrier heights.

Theoretical Study of Magnetoelectric and Thermoelectric Properties ofGraphene
Hiroyuki Kageshima1, Hiroki Hibino2, Masao Nagase3,
Yoshiaki Sekine1, and Hiroshi Yamaguchi1
1
Physical Science Laboratory, 2Materials Science Laboratory, 3The University of Tokusima
Graphene is atomically thin two-dimensional sheet. Because of this unique structure, it isexpected to show various novel properties. We theoretically study its potential [1-3].
Magnetoelectric effect controls magnetism by external electric field [1, 3]. Grapheneedge with the zigzag structure is theoretically predicted to show magnetism. However, themagnetism is difficult to be realized if the graphene is located on SiO2 substrate, because theedge should be appropriately terminated by H atoms. On the other hand, in case of epitaxial
graphene on SiC(0001) substrate, experiments show that islands of graphene are alreadyformed in the initial stage of the growth by the high-temperature annealing. In addition, it istheoretically revealed that the island edge is already connected seamlessly to the SiC substrate(Fig. 1). Therefore, the edge is not necessary to be terminated by H atoms. Since the epitaxial
graphene is also negatively charged due to the interaction with the substrate, and since theedge magnetism requires the charge neutrality, the island with the zigzag structure edge
shows magnetism, only when the application of external field by a gate electrode induces
positive charge to neutralize the epitaxial graphene. In this way, the magnetism appears by themagnetoelectric effect for the graphene islands on SiC (Fig. 1).
Thermoelectric effect induces the potential difference from the temperature difference. It isuseful for the electric power generation from wasted heat [2, 3]. The conventional graphene on–3
SiO2 substrate shows the thermoelectric figure of merit ZT0 of the order of 10 , which means
high difficulty for the practical use. However, if the density of ionic adsorbates on graphene
is reduced by 1/1000 times and the optical phonon scattering from the substrate is suppressedsignificantly, the graphene is expected to exhibit the figure of merit ZT0 over 1 around thecharge neutrality point, which means the strong possibility for the practical use (Fig. 2).
Graphene is plentiful, cheap, harmless, and low in specific gravity. Therefore, graphene is agood candidate for a practical thermoelectric conversion material.
This work is partly supported by KAKENHI.
[1] H. Kageshima et al., Appl. Phys. Express 3 (2010) 115103.
[2] H. Kageshima, Jpn. J. Appl. Phys. 49 (2010) 100207.
[3] H. Kageshima et al., Jpn. J. Appl. Phys., in press.

Fig. 1. Atomic structure of graphene with zigzag edgeson SiC(0001) and the spin polarization distribution
when the induced charge is +8e. Large and small
circles are Si and C atoms, respectively.

Fig. 2. Thermoelectric figure of merit ZT0 ofgraphene as the function of the Fermi energy
position ε F. Conventional case (case 1) andsuppressed carrier scattering case (case 2).

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)25

Strong Stark Effect in Electroluminescence from Phosphorous-Doped
SOI-MOSFETs
Jin-ichiro Noborisaka, Katsuhiko Nishiguchi, Yukinori Ono,
Hiroyuki Kageshima, and Akira Fujiwara
Physical Science Laboratory
The electronic states of phosphorous atoms in silicon (Si) are now attracting much attention
because they could be useful for solid-state quantum computers. We report a strong Stark
effect in electroluminescence (EL) from phosphorous-doped silicon-on-insulator (SOI)MOSFETs when electrons are injected into the sub-10-nm-thick SOI channel by tunneling [1].
The devices were SOI-MOSFETs with an n-type polycrystalline Si (poly-Si) tunneling gate
[Fig. 1(a)]. Two SOI thicknesses (tSOI) of 8.5 and 25 nm were prepared. The thicknesses ofthe front-gate oxide (FOX), and the buried oxide (BOX) were approximately 2 and 400 nm,
respectively. The potential profiles for the device are shown in Fig. 1(b). Due to the thermal
treatment for the device fabrication, the SOI channel was phosphorous-doped on the order−3of 1017 cm . Electroluminescence spectra were taken at temperature (T) of 80 K. Electrons
are injected from the front gate into the SOI channel, while holes are injected from the boron
doped p+ contact. Figure 2(a) shows the VBG dependence of the EL spectrum for the device
with tSOI of 25 nm. The EL intensity decreased as VBG was positively increased, producing anelectric field in the SOI so that electrons distribute near BOX/SOI interface. Then electrons
and holes are strongly separated, which results in the decrease of the EL intensity. On theother hand, the V BG dependence of the EL spectra for tSOI of 8.5 nm showed complicatedbehavior [Fig. 2(b)]. The peak for a neutralized donor and free-hole recombination (D 0-h)
showed Stark shift of up to 50 meV at VBG of 136 V. The EL intensity kept a higher value evenwhen that for 25 nm became almost zero, and then suddenly decreased around VBG of 80 V [Fig.
2(c)]. The sudden change of the EL intensity can be explained by electron dissociation fromstrongly bound states. In contrast to the thicker QW, the ground state of triangular well at the
BOX interface in the QW for tSOI of 8.5 nm is higher than that of phosphorous-bound state at
low electric field. Therefore, electrons bound at phosphorous atoms hardly dissociate in thethin QW. This is the reason for the difference in the specific field needed to cause the sudden
decrease of the EL intensity.
[1] J. Noborisaka et al., Appl. Phys. Lett. 98 (2011) 033503.

Fig. 1. (a) Schematic cross section of the device
structure (top) and top view of the device(bottom). (b) Potential profile from source
to drain (top) and from top to bottom of thedevice (bottom).
26

Fig. 2. (a) The VBG dependence of EL for tSOI = 25 nm.
(b) That for tSOI = 8.5 nm. The arrows trace thepeak for D0-h. The voltage steps for VBG are 10 V
except for |VBG| of 136 V. (c) The VBG dependenceof the integrated EL intensity.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Parametric Frequency Conversion and
Logic Operations Using Electromechanical Resonators
Imran Mahboob, Emmanuel Flurin, Katsuhiko Nishiguchi,
Akira Fujiwara, and Hiroshi Yamaguchi
Physical Science Laboratory
The pioneering mechanical computer has been largely forgotten with the advent of Boolean
logic, the semiconductor transistor and integrated circuits which have given rise to logic
gates that underpin all modern computation [1]. However as conventional computers toil
to conserve Moore’s law, the nanoelectromechanical computer was proposed which has
acquired urgency as it offers the tantalizing prospect of low power consumption. In spite ofsome recent experimental effort, a universal electromechanical logic gate based on Boolean
algebra has remained beyond reach. To address this, we realise a practical logic device in anelectromechanical resonator operated in the non-degenerate parametric amplification regime[2, 3].
Widely used in optics, non-degenerate parametric amplifiers can enable the frequency of alaser to be tuned. Frequency conversion is realised by exploiting the interaction of an intensehigh frequency pump beam (fp) with a less intense lower frequency signal beam (fs) in a crystal
with a nonlinearity due for example to the Kerr effect which both amplifies the signal beam aswell as generating an idler beam (fi) where this process conserves energy i.e. hfp=hfs + hfi andh is Planck’s constant.
Here we exploit this concept in a tiny mechanical resonator (Fig. 1) where multiple channelsof binary information are encoded via the pump as nanometre scale oscillations at different
frequencies. The parametrically activated nonlinearity in the mechanical resonator can mix the
input binary channels resulting in a rich idler spectrum of output oscillation states that can beused to not only construct all the primary logic gates and multi-bit logic circuits (Fig. 2) but
also to execute Boolean logic functions in parallel all in just a single mechanical oscillator.
These results suggest that a nanomechanical computer based on these ground breaking
techniques could have potentially unrivalled data processing power.
[1] http://www.sciencemuseum.org.uk/onlinestuff/stories/babbage.aspx[2] I. Mahboob et al., Nature Commun. 2 (2011) 198.
[3] I. Mahboob et al., Appl. Phys. Lett. 97 (2010) 253105.

Fig. 1. An SEM image of the parametric amplifier consisting of adoubly clamped beam with an out-of-plane oscillation mode.
Application of a.c. bias to the resonator can piezoelectricallyinduce both harmonic and parametric resonances. Also
shown are the input pump and signal excitations and theoutput amplified signal and idler oscillations.

Fig. 2. Application of 3 pumps A, B and C
at different pump frequencies results
in a rich idler spectrum which canbe used to realise multi-bit logic
circuits in parallel.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)27

Carrier-Mediated Opto-Mechanical Coupling in GaAs Cantilevers
Hajime Okamoto, Koji Onomitsu, Haruki Sanada*, Hideki Gotoh*,
Tetsuomi Sogawa*, and Hiroshi Yamaguchi
Physical Science Laboratory, *Optical Science Laboratory
Optically induced dynamic backaction in micromechanical systems has recently become
the focus of research [1, 2]. Cavity-induced opto-mechanical coupling via radiation pressureor photothermal stress influences the thermal vibration of the mechanical system, leading to
amplification and de-amplification of the vibration modes [1, 2]. The vibration amplification isof great interest because it can lead to the self-oscillation of a micromechanical resonator [1, 2].
The de-amplification is of equal interest because it enables cooling of the vibration modes[1, 2]. In contrast, we have recently observed novel opto-mechanical coupling, which does not
require any cavities but is based on optical carrier excitation [3, 4]. Here, we report the carriermediated opto-mechanical coupling found in n-GaAs/i-GaAs bilayer cantilevers [Fig. 1(a)].
The carrier-mediated opto-mechanical coupling is based on the strain-assisted optopiezoelectric effect, which is associated with the separation of electron-hole pairs due to thebuilt-in electric field. Thermal vibration of the [110]-oriented cantilever is amplified by the
optical excitation with the near absorption-edge wavelength (λ ex = 840 nm at 50 K) and theself-oscillation is induced for the strong excitation (Pex > 10 μW) [Fig. 1(b)]. In contrast, for
the [–110]-oriented cantilever, the opto-piezoelectric backaction de-amplifies the vibration
because the piezoelectric effect is reversed in the 90-degree rotated orientation [Fig. 1(c)].
This opto-piezoelectric backaction is maximized when the laser wavelength matches the
optical absorption edge [4]. This is because the strain-induced change in the optical absorption
is maximized at the strain-sensitive absorption edge. This carrier-mediated opto-mechanicalcoupling has an advantage in compatibility with semiconductor opto-electronics and will
also provide a tool for studying the fundamental properties of semiconductors, such as carrier
dynamics, strain effects, and carrier-related energy relaxation.
[1] I. Favero and K. Karrai, Nature Photon. 3 (2009) 201.
[2] C. H. Metzger and K. Karrai, Nature 432 (2004) 1002.
[3] H. Okamoto et al., Appl. Phys. Express. 2 (2009) 035001.
[4] H. Okamoto et al., Phys. Rev. Lett. 106 (2011) 036801.
(a)

(b)

(c)

Fig. 1. (a) Scanning electron micrograph of the cantilever. The cantilever consists of 100-nm-thick n-GaAs and
200-nm-thick i-GaAs. The Ti:Sa cw laser beam is focused on the leg where the larger strain results. The
thermal vibration is detected with the He:Ne cw laser beam by laser interferometry. The measurements
were done in a vacuum at 50 K. The Ti:Sa laser power dependence of the displacement noise power
spectrum for λ ex = 840 nm in the (b) [110]-oriented cantilever and (c) [–110]-oriented cantilever.

28

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)Voltage-Controlled Group Velocity of Edge Magnetoplasmon
in the Quantum Hall Regime
Hiroshi Kamata1, 2, Takeshi Ota1, Koji Muraki1, and Toshimasa Fujisawa2
1
Physical Science Laboratory, 2Tokyo Institute of Technology
When a two-dimensional electron system is subjected to a strong perpendicular magnetic
field, the Lorentz force makes electrons to propagate along the edge of the sample. In thequantum Hall regime, as the Fermi level in the sample interior lies in the gap between theenergy levels discretized by the magnetic field, back scattering between channels at opposite
edges is prohibited, which makes these edge channels ideal coherent one dimensional
channels without dissipation. Electronic analogues of quantum optics experiments using
various interferometers defined with edge channels have been demonstrated, allowing one to
study coherent transport properties and quantum statistics of electrons. These experimentssuggest the possibility of using edge channels as quantum channels, through which quantum
states may be transmitted over a macroscopic distance comparable to the device size. To thisend, the group velocity of electrons is one important physical parameters to be controlled.
We investigate the group velocity of edge magnetoplasmons (EMPs) in the quantum Hall
regime by means of time-of-flight measurement [1]. EMPs generated at t = 0 by applying a
voltage pulse to the source electrode propagate along the sample edge toward the quantum
point contact (QPC). By temporarily opening the QPC at a delay time td with another voltage
pulse, we are able to selectively detect EMPs arriving at a given time delay td as a drain current
IDS (Fig. 1). We find that the group velocity of EMPs traveling along the edges defined by ametallic gate strongly depends on the voltage VG on the gate (Fig. 2). The observed variationof the velocity with VG can be understood as reflecting the degree of screening provided by themetallic gate, which damps the in-plane electric field andhence reduces the velocity. The degree of screening varies
as VG changes the distance between the gate and the edge
channel.
[1] H. Kamata, T. Ota, K. Muraki, and T. Fujisawa, Phys.
Rev. B 81 (2010) 085329.

Fig. 1. (a) Schematic illustration of device structure andexperimental setup for time-of-flight measurement. A
short voltage pulse VPS(t) is applied to the source contact
to inject a pulse of EMPs. Another voltage pulse VPG(t) is
applied to the QPC to probe the local potential. The timeinterval between the two voltage pulses is varied using
the mechanical delay line. Four delay gates between thesource contact and the QPC are used to add extra path
length.

Fig. 2. (a) IDS vs td for various VG. Data
are offset for clarity. (b) Groupvelocity ν g as a function of VG. (c)Schematic illustrating the crosssectional view of the sample
structure.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)29

Wide-Band Capacitance Measurement on a Semiconductor
Double Quantum Dot for Studying Tunneling Dynamics
Takeshi Ota, Toshiaki Hayashi, Koji Muraki, and Toshimasa Fujisawa*
Physical Science Laboratory, *Tokyo Institute of Technology
The electronic properties of a semiconductor quantum dot, that forms a basic for solid-state
qubits, can be often well described by a capacitance that characterizes the static and dynamic
response of a quantum dot to externally applied voltages. We propose and demonstrate
a new experimental technique to measure impedance (both resistance and capacitance)of semiconductor quantum dots in order to study tunneling dynamics [1]. Figure 1(a)schematically shows the experimental setup. A DQD and a nearby quantum point contact(QPC) are formed in a two-dimensional electron gas at the interface of a GaAs/AlGaAs
heterojunction by applying negative voltages to surface Schottky metal gates. A square wave
VDQD(t) applied to the DQD induces a single-electron tunneling both on and off and between
the dots and the resultant change in the charge state of the DQD QDQD(t) modulates the
conductance of the QPC. By applying another square wave VQPC(t) with a relative phase θ to
the QPC, we measure the averaged dc current <IQPC> through the QPC by a Lock-in detection.
<IQPC> is proportional to the capacitance (conductance) when θ = 0 (π/2). The capacitancesignal appears as a peak or a dip depending on the location of the DQD and the QPC. Figure1(b) shows the capacitance signal measured at 1 kHz as a function of the gate voltages VUR and
VUL. The data reveal a charge stability diagram which forms a honeycomb-shaped structure
characteristic of a weakly coupled DQD. In a strongly coupled DQD, the capacitanceundergoes a quantum mechanical correction due to the interdot tunnel coupling, and quantum
capacitance CQ is observed. Figure 1(c) shows the variation of CQ due to interdot tunnelingwith VUC. As the interdot coupling is weakened by making VUC more negative, the dip becomes
sharper. These results suggest that the size and the width of the dip reflect the strength of thequantum mechanical coupling. This CQ, given by the second derivative, or the curvature, of the22
energy band E with respect to the gate voltage VG, i.e., CQ ≡ d E/dVG , is therefore expected tobe capable of distinguishing the bonding and antibonding states of single-electron systems or
the singlet and triplet states of two-electron systems.
This work was partly supported by SCOPE from the Ministry of Internal Affairs andCommunications of Japan.
[1] T. Ota et al., Appl. Phys. Lett. 96 (2010) 032104.

Fig. 1. Schematic illustration of the experimental setup (a), <IQPC> as a function of VUL and VUR (b), <IQPC> as afunction of the bias offset ε at several VUC (c).

30

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Coherent Operation of a Gap-Tunable Flux Qubit
Xiaobo Zhu, Alexander Kemp, Shiro Saito, and Kouichi Semba
Physical Science Laboratory
The flux qubit is one of the most promising candidates for constructing quantum processors.
An upgraded flux qubit, whose gap can be tuned in situ by two high bandwidth control lines,
gives us two fundamental improvements: "gap control" and "σx coupling". Based on these two
fundamental improvements many possible applications can be realized, for example, realizing
scalable qubus type multi qubits coupling and gate operations with large ON/OFF ratio[1] andσx coupling toward demonstration of quantum nondemolition measurement (QND) in solidstate device [2].
Recently, we experimentally demonstrated the in situ tunability of the gap of asuperconducting flux qubit, which was achieved by replacing the smallest Josepshon junctionof the qubit with a DC-SQUID. By adding pulses via a local control line we can tune the gap
over a range of several GHz on a nanosecond time scale (Fig.1). The variation of the persistentcurrent and the gap with the control pulses is consistent with the simulation.
Rabi oscillations between the ground state and the first excited state are a primarydemonstration of a single qubit coherent operation. In Fig. 2(a), we show Rabi oscillations
obtained at the degeneracy point. We set the voltage level of the two control lines to thedegeneracy point of a dispersion relation, and varied the length of the microwave pulse
resonant with the qubit, i.e., the gap frequency. After above sequence, the qubit state ismeasured by applying a measurement pulse. We repeated the whole sequence 2000 times
to detect the relative occupation of the ground state and the excited state. We varied theamplitude of the microwave, and verified the linear dependence of the Rabi frequency on the
microwave amplitude as shown in Fig. 2(b), which is a signature of the Rabi process [3].
[1] Y. D. Wang, A. Kemp, K. Semba, Phys. Rev. B 79 (2009) 024502.
[2] Y. D. Wang, X. Zhu, and C. Bruder, Phys. Rev. B 83 (2011) 134504.
[3] X. Zhu, A. Kemp, S. Saito, and K. Semba, Appl. Phys. Lett. 97 (2010) 102503.

Fig. 1. Spectroscopies with different gap
value (a) 3GHz, (b) 5GHz, (c) 7GHz
by applying in situ pulse at fixedmagnetic field.

Fig. 2. (a) Rabi oscillations at one degeneracy point
for five different microwave powers. (b) Linear
dependence of the Rabi frequency on the
microwave amplitude.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)31

Generation of Non-Classical Microwave Photon States in an InductorCapacitor Resonator Coupled to a Superconducting Flux Qubit
Kosuke Kakuyanagi, Shiro Saito, Hayato Nakano, and Kouichi Semba
Physical Science Laboratory
To realize quantum memories for quantum computation, we need to establish quantum
information transfer and the generation of a photon number state (especially a one-photon
state). However it is difficult to generate a photon number state because the method, which
excites an LC resonator by using a resonant microwave, forms a classical coherent state.
So, we attempt to generate a non-classical photon state by transferring a photon from asuperconducting qubit to an LC resonator.
The LC resonator, which is constructed from a line inductor and a capacitor, surrounds asuperconducting flux qubit (Fig. 1). The magnetic coupling energy between the flux qubit
and the LC resonator is 360 MHz. A large coupling energy is one of the advantages of using
a superconducting qubit. In this LC resonator and flux qubit system, we shift the external
magnetic field non-adiabatically, after realizing the excited qubit state. By tuning the resonantcondition of the LC resonator and qubit, we generate a photon oscillation, which is called avacuum Rabi oscillation. Time domain control of this quantum oscillation makes it possible totransfer a photon from a qubit to an LC resonator. By repeating this process, we can transfer
photons one by one. The ideal photon state achieved using this method becomes the photon
number state. Period time of quantum oscillation of this system depends on the photon
number, so we can obtain information about the photon distribution of the LC resonator by
analyzing the time domain oscillation.
Figure 2 shows the photon distribution results when we transfer one and two photons to
the LC resonator. Energy relaxation and the imperfection of the control pulses mean that thisphoton distribution is different from the pure photon number state. However, we succeededin generating a non-classical photon distribution, which is clearly different from a classicalPoisson distribution [1]. This is the result of using the LC resonator’s quantum characteristics,
so we can expect the development of quantum memories by using high-Q resonators.
[1] K. Kakuyanagi et al., Appl. Phys. Express 3 (2010) 103101.

Fig. 1. Sample design of LC resonator andsuperconducting flux qubit.

32

Fig. 2. Corresponding Poisson distributions andresults of photon distributions of LC resonatorwhen we transfer one and two photons.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Quantum Zeno Effect with a Superconducting Qubit
Yuichiro Matsuzaki, Shiro Saito, Kosuke Kakuyanagi, and Kouichi Semba
Physical Science Laboratory
Quantum Zeno effect (QZE) is one of fascinating phenomena which quantum mechanics
predict. A sequence of projective measurements to an unstable system can suppress the decay
process of the state [1]. This phenomenon will be observed if the time interval of projective
measurements is sufficiently small and the decay behavior in the time interval is quadratic.
The difficulty for the experimental demonstration of QZE is to observe such quadratic decay
behavior experimentally. The time region to show such quadratic behavior is comparable withthe correlation time of the noise, which is usually much shorter than typical time resolutionof a measurement apparatus in the current technology. After showing the quadratic decay,
unstable system shows an exponential decay and QZE does not occur through projective
measurements to a system which decays exponentially. Due to such difficulty, there wasonly one experimental demonstration to suppress the decay process of an unstable state byprojective measurements [2].
We suggest a way to demonstrate QZE experimentally with a superconducting qubit [3] (seeFig. 1). For a superconducting qubit, the quadratic decay can be observed in an experiment
due to 1/f noise whose correlation time is infinite unlike the other typical noise sources wheref denotes a frequency. Although a relaxation process causes an exponential decay to thesuperconducting qubit, by solving a master equation, we have found that one can still increase
the success probability to project the state into a target subspace through frequent selective
measurements as long as the relaxation time is sufficiently longer than the dephasing time (seeFig. 2). Also, we have shown that, with experimentally realizable parameters, it is possible toobserve the suppression of the dephasing caused by 1/f noise by nonselective measurements.
Although these results are theoretical, they have been obtained with practical experimental
conditions and therefore there will soon be experimental demonstration.
[1] B. Misra et al., J. Math. Phys. 18 (1997) 756.
[2] M. C. Fischer et al., Phys. Rev. Lett. 87 (2001) 040402.
[3] Y. Matsuzaki et al., Phys. Rev. B. 82 (2010) 180518.

Fig. 1. A schematic of a quantum state toshow how QZE is observed with asuperconducting qubit.

Fig. 2. A success probability of projections under thedecoherence for time interval of 20 (top line), 25,
30, 35 ns (bottom line). N and P denote the numberof measurements for the time and a successprobability, respectively.
Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)33

Evaluation of Spin Polarization in p -In0.96Mn0.04As Using Andreev
Reflection Spectroscopy Including Inverse Proximity EffectTatsushi Akazaki1, Takehito Yokoyama2, Yukio Tanaka3,
Hiro Munekata2, and Hideaki Takayanagi4,51
Physical Science Laboratory, 2Tokyo Inst. Tech., 3Nagoya Univ.,
4Tokyo Univ. of Science, 5NIMS-MANA
In superconductor/ferromagnet (S-F) junctions, new quantum phenomena can be expectedfrom the interplay between the superconductivity and the spin polarization of the ferromagnet.
This interplay allows us to determine experimentally the spin polarization of carriers P in aferromagnet using Andreev reflection spectroscopy [1]. However, it is inferred that, in an S-Fjunction, the pair potential Δ in a superconductor is weakened as a result of the penetrationof the exchange field from a ferromagnet into a superconductor, which is called the inverse
proximity effect. This interesting deliberation has motivated us to study the influence of theinverse proximity effect on spin-polarized carrier transport across the S-F interface as well as
the estimation of the P value.
We fabricated Nb/ferromagnetic semiconductor p-In 0.96Mn0.04As junctions as shown in
Fig. 1. Below ~10 K, p-In0.96Mn0.04As becomes ferromagnetic, as evidenced by the hysteretictransverse resistance caused by the anomalous Hall effect. Figure 2 shows the dI/dV-V
characteristics of a Nb/p-In0.96Mn0.04As junction at various temperatures. Below the TC of Nb(~8.2 K), a conductance reduction occurs within the bias voltage that is comparable to the Nbsuperconducting energy gap. A rather moderate slope in the differential conductance curves
within the gap region indicates the partial suppression of the Andreev reflection caused byspin-polarized carriers in p-In0.96Mn0.04As. The P value in p-In0.96Mn0.04As has been extracted
by fitting the measured differential conductance curves with a newly modified BlonderTinkham-Klapwijk model [2] with both spin polarizationand the inverse proximity effect as shown in Fig. 3. The
extracted P value is P = 0.725 at 0.5 K, and it decreases
gradually with increasing temperature.
This work was supported in part by the "Topological
Quantum Phenomena" KAKENHI on Innovative Areas fromMEXT.
[1] R. J. Soulen Jr. et al., Science 282 (1998) 85.
[2] G. E. Blonder et al., Phys. Rev. B 25 (1982) 4515.

Fig. 2. Normalized dI/dV - V characteristics atvarious temperatures.

34

Fig. 1. Schematic diagram of a Nb/
p-In0.96Mn0.04As junction.

Fig. 3. Comparison of the normalized dI/dV - V
characteristics calculated from our model (opencircles) with experimental data (thick solid line)
at 0.5 K. The values used in the calculation are
Z = 0.25 and P = 0.725.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Photoluminescence Spectroscopy of the Low-Density Two-Dimensional
Electron System in Electric Fields
Masumi Yamaguchi, Shintaro Nomura*, Hiroyuki Tamura, and Tatsushi Akazaki
Physical Science Laboratory, *Univ. of Tsukuba
At low temperature, the photoluminescence (PL) spectrum of a two-dimensional electron
system (2DES) reflects the potential fluctuation. We have studied the random-potential
screening across the metal-insulator transition of the 2DES formed in a double-gated GaAs
quantum well [1]. Here, we investigated the PL spectra of 2DES-hole emission in various
perpendicular electric fields and found that the difference in the PL linewidth in electric fields
decreases with electron density [2].
As shown in Fig. 1, the emission energy of PL decreases with perpendicular electric fields
due to the quantum confined Stark effect (QCSE). In addition, the PL linewidth increases
with perpendicular electric fields due to the monolayer well-width fluctuation since the QCSE
–2energy shift depends on the well width. Below ne~4x1010 cm , 2DES is highly inhomogenous
because of the Coulomb random potential of remote charge. In this case, the PL linewidth,
which is the superposition of individual emission energies at different positions, increases
with perpendicular electric fields. On the other hand, when the electron state extends to anarea larger than the spatial range of the well-width fluctuation, the electric field dependence ofPL linewidth disappears because the electrons feel the spatially averaged potential.
Figure 2 shows the slopes of the PL linewidth against perpendicular electric fields as a–2function of electron density. Below 4x10 10 cm , the slope decreases with increasing electron–2
10
density and becomes almost zero above 6x10 cm . This reflects the spatial extension of the
2DES over the Coulomb disorder and the well-width fluctuation range as electron density
increased.
This work was supported by KAKENHI.
[1] M. Yamaguchi et al., Phys. Rev. Lett. 100 (2008) 207401.
[2] M. Yamaguchi et al., Physics Procedia 3 (2010) 1183.

Fig. 1. Photoluminescence spectrum at ne=2x1010 cm
for various perpendicular electric fields.

–2Fig. 2. Electron density dependence of theslope of the PL linewdith change against
perpendicular electric fields.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)35

Single-Photon Detection Using Magnesium Diboride Superconducting
Nanowire at Telecommunication Wavelength
Hiroyuki Shibata, Hiroki Takesue, Toshimori Honjo, Tatsushi Akazaki*, and Yasuhiro Tokura
Optical Science Laboratory, *Physical Science Laboratory
Magnesium diboride (MgB2) is a next generation superconducting material because of
its highest Tc=39 K among intermetallic compounds and of its simple crystal structure with
only two elements. We have reported that it is possible to grow MgB2 ultra-thin films using
molecular beam epitaxy (MBE) with a precise control of evaporation ratio of Mg and B
vapors [1]. We have also reported that it is possible to fabricate nano-patterns of MgB2 by theliftoff process using amorphous carbon as a resist, which can bear at high temperature during
MgB2 deposition [1]. Recently, we have fabricated an MgB2 nanowire with the dimension of
100-nm-width and 10-nm-thick and have demonstrated that the nanowire can detect singlephotons in the visible to infrared wavelength range [2].
Figure 1 shows the atomic force microscopy (AFM) image of MgB 2 nanowire. The
uniform shape of the nanowire demonstrates that the liftoff process works well. The transportmeasurement also showed that the nanowire has no damage during nano-fabrication process.
The single-photon detection capability can be confirmed by investigating the statistics
regarding the number of detected signals and the average number of photons illuminating the
nanowire. When the illumination is a weakly coherent light source with a Poisson distribution,
the probability of detecting one photon is proportional to the average number of photons
μ . Figure 2(a) shows the μ dependence of the number of detected signals at wavelength of
405 nm. The dependence is linear, confirming the single-photon detection capability of the
nanowire. At 1560 nm, quadratic dependence is observed in Fig. 2(b) in the low bias region.
This indicates that the energy of single-photon at 1560 nm is not enough to make electric
signals and more than two-photons are necessary to make signals. The dependence changes
linear as the bias increases higher, demonstrating the single-photon detection capability of the
nanowire even at 1560 nm. We will try to fabricate a single-photon detector for the quantum
information and quantum optics using MgB2 nanowire.
This work was supported by KAKENHI.
[1] H. Shibata et al., IEEE Trans. Appl. Supercond. 19 (2009) 358; H. Shibata et al., Physica C
470 (2010) S1005.
[2] H. Shibata et al., Appl. Phys. Lett. 97 (2010) 212504.

Fig. 1. AFM image of a MgB2 nanowire.

36

Fig. 2. Optical detection characteristics of MgB2 nanowire at(a) 405 and (b) 1560 nm. Ibias is a bias current and Ic is a
critical current. n=1 means linear dependence and n=2
means quadratic dependence.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Tokyo QKD Network
Kiyoshi Tamaki, Toshimori Honjo, Hiroki Takesue, and Yasuhiro Tokura
Optical Science Laboratory
NTT, NEC, and Mitsubishi electric, which are funded by NICT, developed each of their
Quantum Key Distribution (QKD) system, and connected in Tokyo these systems as well as
QKD systems brought by AIT, Id quantique, Toshiba Research Europe, which forms TokyoQKD Network.
QKD is a way to distribute the so-called key. The key is a random bit string whose
information is not leaked to unauthorized parties, and the key is used for authorized parties tocommunicate each other without leakage of its information. In order to prevent eavesdropping,
QKD employs the fact that no one can be against the law of nature, including the socalled quantum mechanics. More attentions have been paid to this cryptography which isunbreakable given the users' devices operate as the theory imposes.
Tokyo QKD network consists of six nodes over the optical communication testbed network,
JGN2plus (Fig. 1), and two of the nodes can generate the key being fast enough for the live
transfer of a video data. NTT was in charge of the longest link of 90 km between Koganei
and Otemachi and back, and we have successfully realized 2 kbps of the key generation rate.
We have developed a system for the Differential Phase Shift QKD (DPS-QKD) [1], which
was proposed jointly by NTT and Stanford University. This protocol features its simplicityof the system configuration, and thus it is easy to be implemented. We have used FieldProgrammable Gate Array for high-speed random number generation with 1GHz clock, fast
signal generation, and fast memory access, and also we have implemented polarization feedback controller to eliminate the polarization dependency of superconducting single photon
detectors developed by NICT. This system outputs the "sifted key", from which the key tobe used over the optical network is distilled via some data processing by the key distillationengine developed by NEC.
Thanks to these attempts for the stabilization and speeding-up, we have achieved stable
generation of the sifted key over 8 days with about 18 kbps of the generation rate as well as
2 kbps of the secure key generation rate (Fig. 2) [2].
This work was in part supported by NICT.
[1] K. Inoue et al., Phys. Rev. A 68 (2003) 022317.
[2] M. Sasaki et al., Opt. Express 19 (2011) 10387.

Fig. 1. Topology of the network.

Fig. 2. QBER, shifted and key generation rate.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)37

Kondo Effects and Current Shot Noise in a Double Quantum Dot
Toshihiro Kubo and Yasuhiro Tokura
Optical Science Laboratory
The various kinds of Kondo effect not seen in conventional metallic systems havebeen revealed in semiconductor quantum dot (QD) systems since the many parameters
are experimentally tunable [1]. In a double quantum dot (DQD), the pseudospin state isrepresented as a state with an electron in either of two capacitively coupled QDs. We havetheoretically investigated the pseudospin Kondo effect without spin degree of freedom [2].
In this work, we consider the spin degree of freedom and study the spin/pseudospin Kondo
effects in a laterally coupled DQD as shown in Fig. 1. at zero temperature using the slaveboson mean-field theory based on the nonequilibrium Green’s function method. The notation(N1,N2) in Figs. 2 and 3 indicates the number of electrons in two QDs. Figure 2 shows thelinear conductance on the charge stability diagram. In the pseudospin Kondo regime such as
the boundary between (1,0) and (0,1), we cannot observe the characteristic property. Thus,
it is difficult to capture the signature of the pseudospin Kondo effect by standard transportmeasurements. In contrast, we plot the zero-frequency current shot noise on the charge
stability diagram under low bias voltage condition (eVSD/ηΓ =0.1, where Γ is the couplingstrength between the reservoir and the QD) in Fig. 3. In contrast to the linear conductance,
the current shot noise can provide a clear signature of the pseudospin Kondo effect, namely
the current shot noise is maximal in the psuedospin Kondo regime [3]. So far we consider
the DQD without coherent indirect coupling [4], in the following, we examine effects of thecoherent indirect coupling on the spin Kondo effect. When each QD holds just one electron,
the fourth-order perturbation theory of the tunneling process between the reservoir and QDs
gives rise to the antiferromagnetic kinetic exchange coupling. Although the effect of coherent
indirect coupling had been discussed only on the orbital degree of freedom, we clarified
this antiferromagnetic exchange coupling on the spin degree of freedom for the first time.
Consequently we found that the spin Kondo effect in (1,1) region is suppressed by such an
antiferromagnetic exchange coupling.
This research was supported by ICORP of Japan Science and Technology Agency, FIRST of
Government of Japan, and KAKENHI.
[1] S. Sasaki et al., Nature 405 (2000) 764.
[2] T. Kubo et al., Phys. Rev. B 77 (2008) 041305(R).
[3] T. Kubo et al., Phys. Rev. B 83 (2011) 115310.
[4] T. Kubo et al., Phys. Rev. B 74 (2006) 205310.

Fig. 1. Schematic diagram ofthe laterally coupled
double quantum dot.

38

Fig. 2. Linear conductance on the
charge stability diagram.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Fig. 3. Zero-frequency current shotnoise on the charge stability
diagram (eVSD/ηΓ =0.1).

Cavity Quantum Electrodynamics Using Single Quantum Dot
Takehiko Tawara, Hidehiko Kamada, and Stephen Hughes*
Optical Science Laboratory, *Queen’s University
Cavity quantum electrodynamics (cQED) has been intensively studied using a solid-state
two-level system, and has found use for quantum information devices such as those employing
nonlinearities generated by single photons and the quantum state exchange between lightand matter. In solid-state cQED, however, the environment that surrounds a two-level system
is quite different from that of an atom trapped in a vacuum, and so the interpretation of its
optical response is abstruse [1]. In this study, we explore a novel optical response in solid-statecQED in weak and strong coupling regimes, and investigate the corresponding mechanisms.
We used a self-assembled semiconductor quantum dot (QD) as a two-level system that isembedded in a 2D photonic crystal nanocavity. Figure 1 shows a series of PL spectra of a QD
exciton (X) and the cavity mode (C) in a weak coupling regime. As the temperature increases,
these two peaks experience a continuous redshift thereby reducing the relative energy
separation. However, surprisingly, as the two peaks approach one another near the crossover,the cavity modes clearly undergo a blueshift toward the exciton resonance (mode attraction)[2]. In contrast, the PL spectrum in a strong coupling regime exhibits Rabi splitting with anticrossing dispersion (Fig. 2). When the excitation power is increased, we observe that the Rabi
splitting vanishes although anti-crossing is maintained. We analyzed both curious phenomena
theoretically in weak and strong coupling regimes. As the result, we proved that these peculiar
phenomena in solid-state cQED arise from the large exciton dephasing and the opticalradiation characteristics of a 2D photonic crystal cavity [3].
This work was partially supported by the Strategic Information and Communications R&D
Promotion Programme (SCOPE) of Japan.
[1] For example, K. Hennessy et al., Nature 445 (2007) 896.
[2] T. Tawara et al., Opt. Express 18 (2010) 2719.
[3] S. Hughes et al., Opt. Express 17 (2009) 3322.

Fig. 1. Series of PL spectra as a function oftemperature in weak coupling regime.

Fig. 2. PL color map and PL spectra at zero detuning withvarious excitation powers in strong coupling regime.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)39

Nanowires Laterally Grown on GaAs Substrates
in the Vapor-Liquid-Solid Mode
Guoqiang Zhang, Kouta Tateno, Hideki Gotoh, and Tetsuomi Sogawa
Optical Science Laboratory
Semiconductor nanowires (NWs) have attracted much attention because of their exceptionalversatility and potential for a wide range of applications, from electronics and photonics tobiochemistry and medicine [1]. There are two main approaches to the integration of NWbased devices: (1) using freestanding NWs epitaxially grown on a patterned substrate;(2) using an ex-situ assembly method designed to align NWs removed from the grown
substrate and dispersed on another substrate. The former approach is preferable because of
the contamination that occurs during the ex-situ assembly process with the latter approach.
However, a freestanding structure is very difficult to use as regards electrode formation. The
most attractive way to integrate and extend the applications of NW-based devices is to growthe NWs laterally on the substrates with an in-situ process. In the current work, we developed
a technique for growing lateral GaAs NWs on GaAs (311)B and (001) substrates in the vaporliquid-solid (VLS) growth mode and demonstrated its high controllability in terms of size,
site, and composition [2, 3].
We used Au nanoparticles to catalyze the NW growth in the VLS mode. First, weinvestigated lateral GaAs NWs grown on a (311)B substrate under optimized growth
conditions in a metalorganic vapor phase epitaxy system. Figure 1 shows a cross-sectionaltransmission electron microscopy (TEM) image of a lateral GaAs NW. There is a Au
nanoparticle at the tip of the NW, indicating that the NW is grown in the Au-catalyzed VLS
mode. This enables us to control their size and density by using size- and density-selective Au
colloidal nanoparticles. We grew the site-specific lateral NW array by using a lithographicallydefined Au dot array. Figure 2 shows an atomic force microscopy (AFM) image of the array.
To form heterostructures for bandgap engineering in the lateral NWs, we incorporated indium(In) during the growth and confirmed the realization of lateral InGaAs NWs [3]. We expectthat the planar NW structure will provide new opportunities and new functionalities for thedevelopment of electronic devices and highly efficient photonic devices.
[1] L. Samuelson, Mater. Today 6 (2003) 22.
[2] G. Zhang, K. Tateno, H. Gotoh, and H. Nakano, Nanotechnology 21 (2010) 095607.
[3] G. Zhang, K. Tateno, H. Gotoh, and T. Sogawa, Appl. Phys. Express 3 (2010) 105002.

Fig. 1. Cross-sectional TEM image of lateral GaAs NWs on (311)
B substrate. Note that there is a Au particle at the lateral NW
tip. The arrow in the inset, which is a top-view SEM imageof lateral NWs, indicates a Au particle at the NW tip.

40

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Fig. 2. AFM image of lateral GaAs
NWs. Note that the Au particles
moved from the initial position,
indicated by the white arrows, to
the NW tips after the growth.

Coherent Phonons in Metallic Single-Walled Carbon Nanotubes
Keiko Kato, Katsuya Oguri, and Tetsuomi Sogawa
Optical Science Laboratory
Single-walled carbon nanotubes (SWCNT) become either metallic or semiconducting
depending on their structure (i.e., chirality). Metallic SWCNTs exhibit ballistic transport due
to their quasi-one-dimensional structure. However, electron scattering by optical phonons
sets the ultimate limit for high field ballistic transport. To employ metallic SWCNTs as
future electronic devices, we must understand the phonon to allow us quantify the interaction
between carriers and phonons. Ultrashort laser pulses, whose pulse duration is shorter
than the lattice vibration period, make it possible to achieve the real-time observation oflattice oscillation, that is, coherent phonons. Most SWCNTs contain a broad distributionof chiralities. Thus, it is difficult to obtain detailed information or control SWCNTs with a
specific chirality because SWCNTs with different chiralities are excited simultaneously in amixed sample. By using a separation scheme [1], we are able to report ultrafast carrier andcoherent phonon dynamics in metallic SWCNTs [2].
Time-resolved reflectivity was measured with a sub-10-fs laser pulse, whose wavelength wascentered on 780 nm. Figure 1 shows the time-resolved reflectivity of metallic SWCNTs. At azero delay-time, a sharp response originating from the excitation of free carriers appears anddecays within 30 fs through carrier-carrier scattering. Then, an oscillatory signal, induced withcoherent phonons, follows the carrier response (inset in Fig. 1). A Fourier transform analysis
reveals that the oscillation originates from coherent phonons of (i) the radial breathingmode, (iii) the G mode, and (ii) even the D mode, which originates from defects in SWCNTs(Fig. 2). The G mode consists of several peaks corresponding to the transverse andlongitudinal optical phonon modes for the peaks with the higher and lower frequencies,
respectively. The longitudinal phonon exhibits an asymmetric shape due to the interaction
between coherent phonons and free carriers. With the separation of metallic SWCNTs fromthe mixed sample, we identified ultrafast dynamics of free carriers and the electron-phonon
coupling.
This work was partly supported by KAKENHI.
[1] K. Yanagi et al., Appl. Phys. Express 1 (2008) 034003.
[2] K. Kato et al., Appl. Phys. Lett. 97 (2010) 121910.

Fig. 1. Time-resolved reflectivity of metallic SWCNTs.
Inset shows enlarged graph.

Fig. 2. Fourier power spectrum of time-resolved
reflectivity in metallic SWCNTs. Inset shows
enlarged graph for D and G modes.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)41

High-Q One-Dimensional Photonic Crystal Nanocavity in a Silicon/SOI
Platform
Eiichi Kuramochi, Takasumi Tanabe, Laurent-Daniel Haret,
Hideaki Taniyama, and Masaya Notomi
Optical Science Laboratory
It is well known that a suitably designed chain of submicron holes in a silicon submincron
wire-like waveguide fabricated on a silicon-on-insulator (SOI) substrate acts as a nanocavity.
It belongs to one-dimensional (1D) photonic crystal (PhC) nanocavities and has attracted
attention because it has the simplest design and smallest footprint. However, compared to
two-dimensional (2D) PhC nanocavities, which have been highly developed and widely used,the 1D nanocavity have a relatively poor quality factor (Q). In this study, applying the modegap confinement approach, which had achieved great success in 2D nanocavities, we foundsolutions for realizing an ultrahigh Q value in a 1D nanocavity [1].
We studied 1D nanocavities consisting of rectangular (R) and circular holes (C). The buriedoxide (BOX) layer underneath the nanocavity was removed in an air-bridge structure (AB) andpreserved in a SOI structure. The size of the holes was continuously modulated to generate a
mode-gap barrier. Electro-magnetic simulations using the 3D finite-domain time-difference(FDTD) method demonstrated that both structures held ultrahigh Q values exceeding 108 andthat the C nanocavities had a modal volume (V) smaller than 1(λ /n)3 (Fig. 1) [1, 2]. Note thateven in a SOI structure, our design allows an ultrahigh Q of ~108, which is a unique featureof the 1D nanocavity. These numerical predictions were experimentally demonstrated bymeasured Q of 3.6×105 in the SOI C and 7.2×105 in AB C nanocavities (Fig. 2) [2].
Since air acts as thermal insulator, a 1D AB nanocavity has a considerably large heat
resistance, which was demonstrated by numerical simulation. In such a nanocavity, thermooptic nonliniearity is enhanced greatly. We observed the lowest thermo-optic bistabilty onset
power of 1.6 μW in a AB R nanocavity (Fig. 3) which had a high optical Q of 2.2×105[3].
Considering the great structural difference between the 1D and the 2D nanocavities, we can
expect unique advantages and applications of the former.
This work was partly supported by CREST of Japan Science and Technology Agency.
[1] M. Notomi et al., Opt. Express 16 11095 (2008).
[2] E. Kuramochi et al., Opt. Express 18 15859 (2010).
[3] L. D. Haret et al., Opt. Express 17 21108 (2009).

Fig. 1. Calculated Q and V.

42

Fig. 2. Spectra of high-Q mode in
the nanocavities.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

Fig. 3. Thermo-optic bistability
onset of a nanocavity mode.

GPGPU Acceleration of the FDTD Calculation
Hideaki Taniyama, Takashi Shimokawabe*, Takayuki Aoki*, and Masaya Notomi
Optical Science Laboratory, *Tokyo Institute of Technology
Finite-Difference Time-Domain (FDTD) method of Maxwell equation is widely used andis recognized as a powerful tool in the study of optical nanostructures. Generally, FDTD
simulation requires large amount of memories and long computing time. Therefore, it cannot
be used for the calculation of large structures. Recently, the General-Purpose Graphics
Processing Unit (GPGPU) featuring massive parallelism and high memory bandwidth has
been used for the acceleration in some supercomputers. We try to use GPU as an acceleratorof FDTD calculation, to accelerate the FDTD computation and overcome their limitation.
The FDTD calculation requires large memory access in the time integration step ofelectromagnetic fields. The bottle-neck of FDTD calculation lies in slow memory transfer
between main-memory and CPU. On the other hand, a memory bandwidth between GPU and
VRAM is high. This suggests the possibility of greatly accelerating the speed of computationby using GPU. To take full advantage of the high memory bandwidth of GPU, we must
minimize data transfer between CPU and GPU, because their data transfer costs much of thecomputation time and counteracts speedup effect of GPU.
We use CUDA 3.1, which is an integrated development environment for NVIDIA’s GPGPU.
For GPUs, we use NVIDIA’s Tesla C1060 and GeForce GTX 480, and for CPU we use Xeon/
W3580 3.33 GHz. To estimate the acceleration effect of our code, we simulate the photonic
crystal slab cavity and calculate the confined electromagnetic field profile of resonant mode(see Fig.1) using three-dimensional FDTD program. All calculation is performed in doubleprecision [1]. Figure 2 shows the elapsed time of CPU and CPU with GPU for several amountof simulation size. With GPU, our program achieves about 18 times speedup over CPU code.
About 2.5 times speedup of GTX 480 over Tesla C1060 can be attributed to the difference inmemory band width and L1 cashe.
[1] H. Taniyama et al., PIERS 2011, 1A9-K-14, March (2011).

Fig. 1. (a) Photonic Crystal Slab Cavity and(b) field profile of resonant mode.

Fig. 2. Elapsed time of FDTD calculation for CPU and
CPU with GPU.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)43

Ⅱ．Data

Science Plaza 2010
"Science Plaza 2010," an open-house event of NTT Basic Research Laboratories (BRL),
was held at NTT Atsugi R&D Center on Thursday, November 25th, 2010. Under the banner"Frontier Science: Open Door to the Future", Science Plaza aimed to disseminate our latest
research accomplishments through various sections of people inside and outside of NTT andto gather diverse opinions.
Following an opening address from Dr. Itaru Yokohama, the director of BRL, one of
distinguished technical members of NTT BRL, Dr. Yoshitaka Taniyasu gave a lecture on"Nitride Semiconductor Deep-ultraviolet Light-emitting Diodes – Material Physics andDevice Applications". In the afternoon session, Prof. Tatsuo Izawa, Executive Vice President
for Research, Tokyo Institute of Technology, gave a special lecture entitled "Optical Fiber
Communication and Glass Science". Each lecture was well-attended and followed by heatedquestion-and-answer sessions.
As regards the poster exhibits, 45 posters, including 16 from Microsystem Integration
Laboratories, Photonics Laboratories and Communication Science Laboratories, presented ourlatest research accomplishments. While explaining the originality and impact―as well as the
future prospects―of our research accomplishments, these posters were intensively discussed,
and many meaningful opinions were heard. This year’s "Lab Tour"―a guided tour of researchfacilities at NTT BRL that has been receiving high reputation from visitors over the years―
took place at five different labs, so that as many people as possible could join the tour. This
time we also opened a booth to show the NTT R&D recruitment system for job-seeking
researchers and students. After all lectures, presentations, and exhibitions, a banquet was heldin Center’s dining room, where lively conversation among participants deepened their amity.
More than 240 people from research institutes, universities, and general industries, as well
as from NTT Group, attended Science Plaza 2010. Thanks to the efforts of all participants, theconference ended on a high note. We would thus like sincerely to express our gratitude to allof the participants.

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)45

International Symposium on
Nanoscale Transport and Technology (ISNTT2011)
The symposium was held at the NTT Atsugi R&D Center from January 11 to 14, 2011.
The carrier transport properties in nanoscale semiconductor and superconducting structures
are receiving strong interest due to the potential they offer for novel devices such as solidstate quantum computers, single-electron transistors, nanomechanical systems and spintronic
devices and are being extensively studied in many research institutes. To further enhance thesestudies, this symposium was organized by Dr. Hiroshi Yamaguchi, Dr. Kouichi Semba and Dr.
Tatsushi Akazaki of NTT Basic Research Laboratories. NTT Basic Research Laboratories is aleader in these fields and the symposium aspired to gather leading scientists in these fields todiscuss the most recent topics.
On the 11th, after opening and welcoming remarks by Dr. Itaru Yokohama (Director of NTT
Basic Research Laboratories), Prof. Charles Marcus (Harverd University) gave a plenary
lecture on spin manipulation of electrons and nuclei in semiconductor nanostructures. In
addition, there were 6 invited and 4 oral presentations on nanomechanics, single-electron
systems and superconducting qubits followed by 33 poster presentations in the evening.
On the 12th, 7 invited and 8 oral presentations discussed graphene, single atom devices,coherent transport and the quantum Hall effect, as well as mesoscopic superconductors. These
were followed by further 35 poster presentations.
On the 13th and 14th, there were 10 invited and 15 oral presentations on nanomechanics,
superconducting qubits, semiconductor quantum dots and qubits, nano-SQUID andspintronics, edge channel, as well as their optical properties.
In total there were 193 participants (including 82 from NTT) who all greatly enjoyed thehigh-quality presentations and discussions on carrier interactions and spintronics.

46

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

The 6th Advisory Board (Fiscal 2010)
The Advisory Board, an external committee whose role is to evaluate the work of NTT
Basic Research Laboratories (NTT-BRL), met from February 14 - 16, 2011. This was thesixth 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.
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 levelis generally high on an international scale, and that it is important for us to maintain this toplevel research and transmit information about our research achievements to the world. They
also raised several issues related to human resources, the research budget and internal andexternal collaboration. We plan to make improvements based on these valuable suggestions.
At this meeting, the NTT-BRL researchers had a lunch with the board members and aposter session, where they had chances to present their researches to the board members.
The poster session was followed by a dinner party where the board members and the NTTBRL researchers were able to interact in a casual atmosphere. For the NTT-BRL and NTT
executives, we organized 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 be held in two years.

Board Members
Prof. Abstreiter
Prof. Altshuler
Prof. Hänsch
Prof. Haroche
Prof. Jonson
Prof. Leggett
Prof. Mooij
Prof. Ryan
Prof. von Klitzing

Affiliation
Walter Shottky Inst.
Columbia Univ.
Max-Planck-Inst.
Ecole Normale
Göteborg Univ.
Univ. Illinois
Delft Univ. Tech.
Univ. Oxford
Max-Planck-Inst.

Research Field
Low-dim. physics
Condensed matter
Quantum optics
Quantum optics
Condensed matter
Quantum physics
Quantum computer
Nano-bio technology
Semiconductor physics

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)47

Award Winners’ List (Fiscal 2010)
The Science and Technology
Award, Commendation by
the Minister of Education,
Culture, Sports, Science andTechnology
The Commendation for
Science and Technology by
the Minister of Education,
Culture, Sports, Scienceand Technology, The Young
Scientists’ Prize

M. Notomi

Research on Novel Ways ofControlling Propagation andConfinement of Light by Photonic
Crystals

Apr. 13,
2010

H. Takesue

Research on High-speed, Longdistance Quantum Cryptography inTelecommunication Band

Apr. 13,
2010

Y. Shinozaki

Observation of Structural Dynamics
in Single Receptor Proteins with
Fast-scanning AFM

Aug. 4,2010

K. TakaseDensity-imbalance Stability
Diagram of the νT=1 Bilayer
Electron System at Full Spin
Polarization

Aug. 6,2010

The 27th Paper Award of
the Japanese Association for
Crystal Growth (JACG)

M. Kasu

Surface Growth Kinetics ofMetalorganic Vapor Phase Epitaxy
and its Applidation to High Efficient
Aluminum Nitride Devices

Aug. 8,2010

The Japan Society of Applied
Physics Outstanding Paper
Award 2010

H. Okamoto
D. ItoK. Onomitsu
T. Sogawa
H. Yamaguchi

Controlling Quality Factor in
Micromechanical Resonators by
Carrier Excitation

Sep. 14,2010

JSAP Outstanding Paper
Award ― 2010

Y. Hayashi
K. Tanaka
T. Akazaki
M. Jo
H. Kumano
I. Suemune

Superconductor-based Light
Emitting Diode: Demonstration ofRole of Cooper Pairs in Radiative
Recombination Processes

Sep. 14,2010

International Conference
on Solid State Devices andMaterials Paper Award

H. Okamoto
D. ItoK. Onomitsu
H. Sanada
H. Gotoh
T. Sogawa
H. Yamaguchi

Carrier-induced Dynamic
Backaction in GaAs
Micromechanical Resonators

Sep. 22,2010

The 24th Diamond
Symposium
Best Poster Award

K. Hirama

Single-crystal n-type AlN/p-type
Diamond Heterojunction Diodes

Nov. 18,
2010

JSPS Nanoprobetechnology
Encouraging Award
The 19th Internaltional
Conference on the
Application of High
Magnetic Fields in
Semiconductor Physics andNanotechnology(HMF-19): Best Poster
Award for Young Researchers

48

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

In-house Award Winners’ List (Fiscal 2010)

NTT Science and CoreTechnology Laboratory
Group Director Award

S. Matsuo
K. Nozaki
A. Shinya
T. SatoY. Kawaguchi
H. Taniyama
T. Tanabe
T. Kakitsuka
C. H. Chen
M. Notomi

Development of Extremely-low-power
Photonic-crystal Lasers and Switches

Jan.19,2011

NTT Science and CoreTechnology Laboratory
Group Director Award

M. Okamoto
K. Ebata
K. YamadaS. Itabashi
F. Maeda

Replacement of Facility in Clean Roomsof the Building 3 and Dismantlement of
the SORJan.19,2011

BRL Director Award
Award for Achievements

H. Hibino
H. Kageshima
S. Tanabe
M. Nagase

Growth and Characterization of
Epitaxial Graphene

Mar. 29,2011

BRL Director Award
Award for Achievements

S. Sasaki

Investigation of the Kondo Effect inQuantum Dots

Mar. 29,2011

BRL Director Award
Award for Achievements

T. Honjo
K. Tamaki
H. Takesue

Contribution to the Tokyo QKD
Network ExperimentMar. 29,2011

BRL Director Award
Award for DistinguishedService

K. Sumitomo
F. Maeda

Contribution to Extending Laboratory
Space by Scrapping Large Fixed Asset

Mar. 29,2011

BRL Director Award
Award for Excellent Papers

K. Nozaki
T. Tanabe
A. Shinya
S. Matsuo
T. SatoH. Taniyama
M. Notomi"Sub-femtojoule All-optical Switching
using a Photonic-crystal Nanocavity,"
Nature Photonics 4, 477 (2010).

Mar. 29,2011

BRL Director Award
Award for Excellent Papers

H. Nakano
S. Saito
K. Semba"Quantum Time Evolution in a Qubit
Readout Process with a Josephson
Bifurcation Amplifier," Phys. Rev. Lett.
102, 257003 (2009).

Mar. 29,2011

BRL Director Award
Award for Excellent Papers

K. Inaba
M. Yamashita"Time-of-Flight Imaging
Method to Observe Signatures ofAntiferromagnetically Ordered States of
Fermionic Atoms in an Optical Lattice,"
Phys. Rev. Lett. 105, 173002 (2010) .

Mar. 29,2011

BRL Director Award
Award for Encouragement

K. Kakuyanagi

Low-intrusion Quantum State
Measurement using Josephson
Bifurcation Amplifier

Mar. 29,2011

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)49

Numbers of Papers, Presentations and Patents (2010)
The numbers of papers published in international journals, presentations at international
conferences and applied patents in year 2010 amounted to 130, 187, and 58, respectively. The
numbers for each research area are as follows;
Papers Published in International Journals(Jan. – Dec. 2010)Materials Science

34

Physical Science

40

Optical Science

56
0

10

20

30

40

50

60

Number of Papers

Presentations at International Conferences(Jan. – Dec. 2010)Materials Science40

Physical Science

87

Optical Science

60

0

20

40

60

80

100

Number of Presentations

Applied Patents (Jan. – Dec. 2010)Materials Science28

Physical Science

21

Optical Science

9

0

5

10

15

Number of Applied Patents

50

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

20

25

30

The numbers of research papers published in the major journals are shown below.
Journals
Applied Physics Letters
Applied Physics Express
Japanese Journal of Applied Physics
Physical Review B
Physical Review Letters
Physical Review A
Optics Express
Nature Photonics
Optics Letters
Reviews of Modern Physics
Reports on Progress in Physics
CarbonJournal of Physical Chemistry C
Langmuir
Nanotechnology
IEEE Journal of Selected Topics in Quantum Electronics
Biochimica et Biophysica Acta, General Subjects
Nature Communications(IF2009*)
3.554
2.223
1.138
3.475
7.328
2.866
3.278
22.8693.059
33.145
11.444
4.504
4.224
3.898
3.137
3.064
2.958
-

Numbers
15
13
13
10
9
5
3
2
2
1
1
1
1
1
1
1
1
1

*IF2009: Impact Factor 2009 (Journal Citation Reports,2009)

The average IF2009 for all research papers from NTT Basic Research laboratories is 3.13.

The numbers of presentations in the major conferences are shown below.
Conferences
2010 International Conference on Solid State Devices and Materials
The 37th International Symposium on Compound Semiconductors
30th International Conference on the Physics of Semiconductors
Quantum Nanostructures and Spin-related Phenomena
23rd International Microprocesses and Nanotechnology Conference
Updating Quantum Cryptography and Communications 2010
The 6th International Conference on the Physics and Applications of Spin Related
Phenomena in Semiconductors
16th Internatinal Conference on Molecular Beam Epitaxy
CLEO/QELSInternational Symposium on Physics of Quantum Technology
Materials Research Society Meeting
Gordon Research Conference
The 19th International Conference on High Magnetic Fields in Semiconductor Physics andNanotechnology
10th International Conference on Quantum Communication
Adv. Func. 3D control. Quantum Structures
European Materials Research Society
Photonic and Electromagnetic Crystal Structures 2010
The 6th International Workshop on Nano-scale Spectroscopy and Nanotechnology
International Symposium on Graphene Devices 2010

Numbers
13
12
11
9
8
8
6
5
5
5
4
4
4
3
3
3
3
3
3

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)51

List of Invited Talks at International Conferences (2010)
I. Materials Science Laboratory

52

(1)

K. Torimitsu, "Nanobiodevice architecture using receptor protein", International Conference on
Nanoscience and Nanotechnology (ICONN 2010), Sydney, Australia (Feb. 2010). (Plenary)(2)

K. Torimitsu, Y. Shinozaki, N. Kasai, A. Shimada, K. Sumitomo, C. Ramanujan, and J. F. Ryan,"Understanding the structure and functions of receptor proteins", International Conference on Nanoscienceand Nanotechnology (ICONN 2010), Sydney, Australia (Feb. 2010).

(3)

H. Hibino, H. Kageshima, and M. Nagase, "In-situ surface electron microscopy observations of growthand etching of epitaxial few-layer graphene on SiC", International Workshop on in situ characterization ofnear surface processes 2010, Eisenerz, Austria (May 2010).

(4)

K. Torimitsu, Y. Shinozaki, N. Kasai, A. Shimada, and K. Sumitomo, "Receptor protein based nanobiointerface", Asia-Pacific Symposium on Nanobionics, Wollongong, Australia (June 2010).

(5)

K. Torimitsu, Y. Shinozaki, N. Kasai, A. Shimada, K. Sumitomo, and Y. Furukawa, "Analysis of receptor
conformation and its functional relations for biomimetic device", International Conferences on Modern
Materials & Technologies 2010, Montecatini Terme, Italy (June 2010).

(6)

K. Hirama, Y. Taniyasu, and M. Kasu, "N-type conduction of single-crystal Si-doped AlN (0001) layergrown on diamond (111) substrate", The 37th International Symposium on Compound Semiconductors,
Takamatsu, Japan (June 2010).

(7)

K. Torimitsu, Y. Shinozaki, Y. Furukawa, N. Kasai, and K. Sumitomo, "Conformational nanostructure
analysis of receptor protein and its application for biomimetic device formation", Gordon Research
Conferences, Tilton, U.S.A. (July 2010).

(8)

T. Akasaka, Y. Kobayashi, and M. Kasu, "Step-free GaN hexagons grown by selective-area MOVPE",The 3rd International Symposium on Growth of III-Nitrides, Montpellier, France (July 2010).

(9)

M. Kasu, "Surface kinetics and growth modes in metalorganic chemical vapor deposition (MOCVD) andtheir applications to aluminum nitride (AlN)", 16th International Conference on Crystal Growth (ICCG16)/14th International Conference on Vapor Phase Epitaxy (ICVGE-14), Beijing, China (Aug. 2010).

(10)

H. Hibino, "Dynamics of Si surface morphology/Epitaxial graphene growth on SiC surfaces", The 14th
International Summer School on Crystal Growth (ISSCG-14), Dalian, China (Aug. 2010).

(11)

Y. Shinozaki, "Dynamic structural changes in single receptor protein observed with fast-scanning atomic
force microscopy", 9th International Conference on Non-Contact Atomic Force Microscopy, Ishikawa,Japan (Aug. 2010).

(12)

H. Hibino, "Surface electron microscopy of epitaxial graphene", 2nd International Symposuim on the
Science and Technology of Epitaxial Graphene, Amelia Island, U.S.A. (Sep. 2010).

(13)

H. Hibino, H. Kageshima, S. Tanabe, and M. Nagase, "Growth, structure, and transport properties of
epitaxial graphene on SiC", International Symposium on Graphene Devices 2010, Sendai, Japan (Oct. 2010).

(14)

K. Torimitsu, "Functional analysis of receptor protein for biomimetic device formation - structure andfunction -", 4th International Symposium on Nanomedicine (ISNM2010), Okazaki, Japan (Nov. 2010).

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

II. Physical Science Laboratory(1)

H. Yamaguchi, I. Mahboob, H. Okamoto, and K. Onomitsu, "Micro/nanoelectromechanical systems foradvanced semiconductor devices", 2010 International RCIQE/CREST Joint Workshop, Sapporo, Japan (Mar.
2010).

(2)

Y. Ono, A. H. Khalafalla, K. Nishiguchi, and A. Fujiwara, "Single dopant effects in silicon nanotransistors", Single Dopant Control (SDC2010), Leiden, Netherlands (Mar. 2010).

(3)

Y. Ono, M. A. H. Khalafalla, K. Nishiguchi, and A. Fujiwara, "Single dopant effects in silicon nanotransistors", The 2010 International Symposium on Atom-scale Silicon Hybrid Nanotechnologies for 'Morethan-Moore' & 'Beyond CMOS' Era, Southampton, U.K. (Mar. 2010).

(4)

A. Fujiwara, K. Nishiguchi, and Y. Ono, "Single-electron transfer technology using Si nanowire
MOSFETs", The 2010 International Symposium on Atom-scale Silicon Hybrid Nanotechnologies for 'Morethan-Moore' & 'Beyond CMOS' Era, Southampton, U.K. (Mar. 2010).

(5)

K. Semba, "Manipulation of entanglement in the heterogeneous quantum system", 5th International
Workshop on "Advances in Foundations of Quantum Mechanics and Quantum Information with Atoms andPhotons" ad memoriam of Carlo Novero & the 3rd Italian Quantum Information Science Conference (VQuantum 2010 & 3rd IQIS2010), Torino, Italy (May 2010).

(6)

H. Yamaguchi, I. Mahboob, H. Okamoto, and K. Onomitsu, "Challenge for electromechanical logic
systems using compound semiconductor heterostructure", 2010 Asia-Pacific Workshop on Fundamentals
and Applications of Advanced Semiconductor Devices (AWAD2010), Tokyo, Japan (June 2010). (Plenary)(7)

Y. Okazaki, S. Sasaki, and K. Muraki, "Spin/pseudospin Kondo effect in a capacitively coupled parallel
double quantum dot", 30th International Conference on the Physics of Semiconductors (ICPS2010), Seoul,
Korea (July 2010).

(8)

H. Yamaguchi, H. Okamoto, Y. Maruta, S. Ishihara, and Y. Hirayama, "Mechanical to electrical energy
transduction using a micromechanical 2DES cantilever", 16th International Conference on Molecular Beam
Epitaxy (MBE2010), Berlin, Germany (Aug. 2010).

(9)

K. Kanisawa, "Structure of a single hydrogenic defect in a semiconductor quantum well", Gordon
Research Conference: Defects in Semiconductors (GRC), New London, U.S.A. (Aug. 2010).

(10)

H. Kageshima, H. Hibino, M. Nagase, Y. Sekine, and H. Yamaguchi, "Theoretical study on functions ofgraphene", The 2nd International Symposium on Graphene Devices: Technology, Physics, and Modeling(ISGD 2010), Sendai, Japan (Oct. 2010).

(11)

H. Kageshima, "Mechanism of nanochannel formation processes: thermal oxidation of Si nanostructuresand graphene formation on SiC", International Conference on Solid-State and Integrated Circuit Technology(ICSICT2010), Shanghai, China (Nov. 2010).

(12)

H. Kageshima, H. Hibino, M. Nagase, Y. Sekine, and H. Yamaguchi, "Theoretical study on growth,
structure, and physical properties of graphene on SiC", Japan-Korea Symposium on Surface andNanostructure 9th (JKSSN9), Sendai, Japan (Nov. 2010).

(13)

T. Yamaguchi, H. Yamaguchi, and T. Iyoda, "Graphoepitaxy of diblock copolymers for lithographic
application", 23rd International Microprocesses and Nanotechnology Conference (MNC2010), Fukuoka,
Japan (Nov. 2010).

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

53

(14)

H. Yamaguchi, "Quantum effects of motion", Japanese-American Frontiers of Science (JAFoS2010),
Chiba, Japan (Dec. 2010).

(15)

K. Nishiguchi and A. Fujiwara, "Single-electron applications using nano-wire MOSFETs", 2010
Workshop on Innovative Devices and Systems (WINDS2010), Hawaii, U.S.A. (Dec. 2010).

III. Optical Science Laboratory

54

(1)

H. Nakano, K. Oguri, and A. Ishizawa, "Dependence of the broadband spectrum of high-order harmonics
driven by a few-cycle laser pulse on carrier-envelope phase", 4th Asian Workshop on Generation andApplications of Coherent XUV and X-ray Radiation, Pohang, Korea (Jan. 2010).

(2)

M. Notomi, "Low-power nanophotonic components based on photonic crystals", SPIE Photonics West,San Francisco, U.S.A. (Jan. 2010).

(3)

M. Notomi, "Nonlinear and adiabatic control of light by photonic crystals", 2nd International Conference
on Metamaterials, Photonic Crystals and Plasmonics (META’10), Cairo, Egypt (Feb. 2010) (Plenary).

(4)

K. Oguri, T. Okano, T. Nishikawa, and H. Nakano, "Dynamics of femtosecond laser ablation plumestudied with ultarafast x-ray absorption fine structure imaging", The International High-Power Laser
Ablation Conference, Santa Fe, U.S.A. (Apr. 2010).

(5)

M. Notomi, E. Kuramochi, T. Tanabe, and H. Taniyama, "Manipulating light with photonic crystal
nanocavities and their coupled arrays", SPIE Photonics Europe, Brussels, Belgium (Apr. 2010).

(6)

T. Nishikawa, A. Ishizawa, A. Mizudori, H. Takara, H. Nakano, A. Takeda, and M. Koga, "Approachto achieving a wider mode spacing carrier-envelope phase-locked frequency comb at telecommunications
wavelength region", The 2th Shanghai Tokyo Advanced Research Symposium on Ultra Intense Laser
Science (STAR2), Xiamen, China (May 2010).

(7)

A. Shinya, S. Matsuo, T. Kakizuka, T. Segawa, G. Sato, E. Kawaguchi, and M. Notomi, "Low-powerand high-speed operation of ultra-small photonic crystal nanocavaty laser based on InGaAsP/InP buried
heterostructure", Conference on Lasers and Electro-Optics, San Jose, U.S.A. (May 2010).

(8)

K. Nozaki, T. Tanabe, A. Shinya, S. Matsuo, G. Sato, T. Kakizuka, E. Kuramochi, M. Notomi, and
H. Taniyama, "Extremely-low-power nanophotonic devices based on photonic crystals", Photonics in
Switching 2010, Monterey, U.S.A. (July 2010).

(9)

M. Notomi, "Photonic crystal for green ICT?", Photonics and Electromagnetic Crystal Structures (PECS
IX), Granada, Spain (Sep. 2010).

(10)

T. Honjo, H. Takesue, and Y. Tokura, "Quantum key distribution/communication research in NTT",
Updating Quantum Cryptography and Communication (UQCC) 2010, Tokyo, Japan (Oct. 2010).

(11)

W. Munro, "Scalable quantum repeaters and quantum networks", Updating Quantum Cryptography andCommunication (UQCC) 2010, Tokyo, Japan (Oct. 2010).

(12)

H. Nakano, K. Oguri, A. Ishizawa, and T. Nishikawa, "Ultrafast time-resolved spectroscopy using x-ray
pulses driven by femtosecond laser pulses", 6th Asian Symposium on Intense Laser Science (ASILS 6),
Beijing, China (Oct. 2010).

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)

(13)K. Tateno, G. Zhang, H. Gotoh, and T. Sogawa, "Characterization of quantum dots in III-V
semiconductor nanowires", 6th International Workshop on Nano-Scale Spectroscopy & Nanotechnology(NSS6), Kobe, Japan (Oct. 2010).

(14)

H. Takesue, "Single-photon frequency downconversion experiment", Photonics Global, Singapore,
Singapore (Dec. 2010).

(15)

H. Nakano, K. Oguri, A. Ishizawa, and T. Nishikawa, "High-order harmonics of carrier-envelope
phase controlled few-cycle laser pulse for probing dynamics of photo-excited solid surface", International
Symposium on Ultrafast Intense Laser Science, Hawaii, U.S.A. (Dec. 2010).

Research Activities in NTT Basic Research Laboratories Vol. 21 (2010)55

Research Activities in NTT-BRL
Editorial Committee
NTT Basic Research Laboratories
3-1 Morinosato Wakamiya, Atsugi
Kanagawa, 243-0198 Japan
URL: http://www.brl.ntt.co.jp/