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ACKNOWLEDGMENTS
We are grateful to B. Lipshutz, J. Read de Alaniz, A. Zakarian, and
L. Zhang (UCSB) for their advice and generous support. We thank
Y. Wang (University of Pittsburgh) for helpful discussions and
comments on the manuscript. L. Lu is acknowledged for assistance
with radical clock studies.Funding:This work is supported by
the start-up funds from the University of California Santa Barbara
(Y.Y.) and the National Institutes of Health (R35GM128779; P.L.).
We acknowledge the BioPACIFIC MIP (NSF Materials Innovation
Platform, DMR-1933487) at UCSB for access to instrumentation.
Q.Z. is an Otis Williams Postdoctoral Fellow in Bioengineering.
Calculations were performed at the Center for Research
Computing at the University of Pittsburgh.Author contributions:
Y.Y. designed the overall research. Y.Y. and Q.Z. performed
initial evaluation of metalloenzymes and reaction conditions. Q.Z.,
M.C., and Y.Y. performed directed evolution of the P450ATRCase
metalloenzymes. Q.Z. and M.C. performed substrate scope study.
Y.F. carried out the computational studies, with P.L. providing
guidance. Y.Y. wrote the manuscript, with input from all other
authors. M.C. and Y.F. contributed equally, and their names appear
alphabetically in the author list.Competing interests:Y.Y., Q.Z.,
and M.C. are inventors on a patent application (US provisional
patent application no. 63/228,562) submitted by the University of
California Santa Barbara that covers stereoselective biocatalytic
atom-transfer radical addition processes.Data and materials
availability:All data are available in the main text or the
supplementary materials. Solid-state structures of2band2oare

available from the Cambridge Crystallographic Data Centre under

reference numbers CCDC 2087196 and 2087196. Plasmids encoding

engineered enzymes are available from Y.Y. under a material

transfer agreement with the University of California Santa Barbara.

SUPPLEMENTARY MATERIALS

science.org/doi/10.1126/science.abk1603

Materials and Methods

Figs. S1 to S6

Tables S1 to S17

References ( 42 Ð 102 )

25 June 2021; accepted 15 October 2021

10.1126/science.abk1603

CARBON NANOTUBES

Semiconductor nanochannels in metallic carbon

nanotubes by thermomechanical chirality alteration

Dai-Ming Tang^1 *, Sergey V. Erohin^2 , Dmitry G. Kvashnin2,3, Victor A. Demin^3 , Ovidiu Cretu^4 ,

Song Jiang^5 , Lili Zhang^5 , Peng-Xiang Hou^5 , Guohai Chen^6 , Don N. Futaba^6 , Yongjia Zheng^7 ,

Rong Xiang^7 , Xin Zhou^1 , Feng-Chun Hsia^1 , Naoyuki Kawamoto^4 , Masanori Mitome^1 , Yoshihiro Nemoto^8 ,

Fumihiko Uesugi^8 , Masaki Takeguchi^8 , Shigeo Maruyama^7 , Hui-Ming Cheng5,9,10, Yoshio Bando11,12,

Chang Liu^5 *, Pavel B. Sorokin2,13*, Dmitri Golberg1,14*

Carbon nanotubes have a helical structure wherein the chirality determines whether they are metallic or

semiconducting. Using in situ transmission electron microscopy, we applied heating and mechanical

strain to alter the local chirality and thereby control the electronic properties of individual single-wall

carbon nanotubes. A transition trend toward a larger chiral angle region was observed and explained in

terms of orientation-dependent dislocation formation energy. A controlled metal-to-semiconductor

transition was realized to create nanotube transistors with a semiconducting nanotube channel

covalently bonded between a metallic nanotube source and drain. Additionally, quantum transport

at room temperature was demonstrated for the fabricated nanotube transistors with a channel length

as short as 2.8 nanometers.

S

ingle-wall carbon nanotubes (SWCNTs)

have a one-dimensional helical tubular

molecular structure made up of hexag-

onally bonded sp^2 carbon atoms. Con-

ceptually, a SWCNT could be formed by

rolling up a graphene sheet along a so-called

chiral vector. The chirality of a SWCNT unique-

ly determines its atomic geometry and elec-

tronic structure, that is, whether it is metallic

or semiconducting ( 1 ). Semiconducting CNTs

can be used to make energy-efficient nanotran-

sistors ( 2 – 4 ) and so are promising for building

beyond-silicon microprocessors ( 5 , 6 ). How-

ever, despite progress in selective growth and

separation ( 7 – 10 ), it remains a great challenge

to control the chirality of individual CNTs.

Molecular junctions between metallic and

semiconducting nanotubes can also be used

as the basis for nanoscale electronic devices

( 11 ), and intramolecular CNT junctions have

exhibited nonlinear transport characteristics

similar to rectifying diodes ( 12 , 13 ). The junc-

tions formed at randomly occurring defects

during the nanotube growth. Mechanical strain

can modify the electronic properties, and the-

oretically, a plastic strain can change CNT chi-

rality ( 14 , 15 ) to create intramolecular nanotube

junctions. Experimentally, modification of the

CNT chirality by plastic deformation has been

reported ( 16 , 17 ), but these transformations, as

well as the resulting electrical properties, were

not controlled but rather were considered ran-

dom jumps caused by small energy differences

between different chiral structures ( 18 ).

Herein, we report the design and fabrication

of a CNT intramolecular transistor where the

local chirality is altered by thermomechan-

ical processing in a controlled manner with-

in a transmission electron microscope (TEM).

1616 24 DECEMBER 2021¥VOL 374 ISSUE 6575 science.orgSCIENCE

(^1) International Center for Materials Nanoarchitectonics
(MANA), National Institute for Materials Science (NIMS),
Tsukuba 305-0044, Japan.^2 National University of Science
and Technology (MISIS), Moscow 119049, Russian
Federation.^3 Emanuel Institute of Biochemical Physics,
Moscow 119334, Russian Federation.^4 Research Center for
Advanced Measurement and Characterization, National
Institute for Materials Science (NIMS), Tsukuba 305-0044,
Japan.^5 Shenyang National Laboratory for Materials
Science, Institute of Metal Research, Chinese Academy of
Sciences, Shenyang 110016, China.^6 CNT-Application
Research Center, National Institute of Advanced Industrial
Science and Technology (AIST), Tsukuba 305-8565, Japan.
(^7) Department of Mechanical Engineering, The University of
Tokyo, Tokyo 113-8656, Japan.^8 Electron Microscopy Analysis
Station, National Institute for Materials Science (NIMS),
Tsukuba 305-0047, Japan.^9 Shenzhen Geim Graphene
Center, Tsinghua-Berkeley Shenzhen Institute, Tsinghua
University, Shenzhen 518055, China.^10 Faculty of Materials
Science and Engineering/Institute of Technology for Carbon
Neutrality, Shenzhen Institute of Advanced Technology,
Chinese Academy of Sciences, Shenzhen 518055, China.
(^11) Institute of Molecular Plus, Tianjin University, Tianjin 300072,
China.^12 Australian Institute for Innovative Materials, University
of Wollongong, North Wollongong NSW 2500, Australia.
(^13) Moscow Institute of Physics and Technology, Moscow Region
141701, Russian Federation.^14 Centre for Materials Science and
School of Chemistry and Physics, Queensland University of
Technology (QUT), Brisbane QLD 4000, Australia.
*Corresponding author. Email: [email protected]
(D.-M.T.); [email protected] (C.L.); [email protected] (P.B.S.);
[email protected] (D.G.)
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