Straining a heated metallic CNT led to a chi-
rality transition of an internal segment that
became a semiconductor, thus creating an in-
tramolecular nanotube transistor (Fig. 1A).
These transistors had a channel length as short
as 2.8 nm and exhibited coherent quantum
interference at room temperature.
The in situ TEM method combined nano-
manipulation, atomic characterization, and
transistor measurements. Step-by-step elec-
trical, thermal, and mechanical stimuli were
applied to suspended individual CNTs using
two piezo-controlled probes within the TEM.
The detailed fabrication process can be found
in the methods section of the supplementary
materials and fig. S1. In short, nanotubes were
attached to the edge of a metal wire or a TEM
grid by direct growth or transfer after growth.
Individual nanotubes protruding from the
metal edge were located and then approached
by the probes under TEM monitoring. Plastic
deformation of the nanotube was activated
and localized to the middle hot segment under
resistive (Joule) heating to induce a local chi-
rality change. The localized deformation is
related to the one-dimensional thermal trans-
port of the CNTs and good contacts with the
electrodes. We used a computer program (fig.
S1) to control the strain and voltage to keep a
near-transition condition with a temperature
high enough (>2000 K) to initiate the plastic
deformation and a relatively small strain step
(~1%) to localize the deformation region. A
bias ranging from 2.0 to 3.0 V was applied to
an individual CNT, resulting in a current of
tens of microamperes. The total duration of
the transformation process was ~10 s. The
electron beam current density was kept at
a low value (~0.5 pA/cm^2 at the fluorescent
TEM screen) to avoid irradiation damage.
After each processing cycle, changes in the
CNT chirality were determined by electron
diffraction patterns and spherical aberration
(Cs)–corrected TEM images with atomic reso-
lution. Electrical transport properties were
measured in a suspended transistor configura-
tion using a stationary electrode as the source
electrode, one probe as the drain electrode, and
another probe as the gate electrode (Fig. 1B).
As an example of these changes, TEM im-
ages of a double-wall carbon nanotube (DWCNT)
before and after a chirality transition show
distinct Moiré patterns from overlaid upper-
and lower-wall lattices (Fig. 1C). Analysis of
corresponding fast Fourier transform (FFT)
patterns showed that the chirality indices
changed from (23,16)@(18,10) to (21,16)@(17,7).
During the transition, local rotation and dis-
tortion of the lattice were observed, indicat-
ing the presence of dislocations (fig. S2).
After the transition, uniform graphitic lattices
showed that the channel was largely defect-
free. The electrical properties of a SWCNT
section stretched between two multiwall car-
bon nanotube sections were monitored as
the length was increased from ~1.1 to 7.7 nm
and the resistance increased from ~16.7 to
~22.9 kilohm (fig. S3). Both the initial re-
sistance and the small increase of resistance
after elongation indicated that the transport
was near the ballistic regime. Although defects
such as dislocations were generated during
chirality transformations, they were highly mo-
bile at the high temperature caused by Joule
heating. After the dislocation gliding, a junc-
tion was formed between the deformed and
undeformed regions, and the channel was large-
ly defect-free and therefore highly conductive.
The fabrication process of a SWCNT intra-
molecular transistor is shown in TEM images
(Fig. 2, A to C) and a schematic (Fig. 2D). The
initial diameter of the SWCNT was ~7.7 nm
(Fig. 2A). Because of the large diameter, the
nanotube was metallic (Fig. 2, E and F), as
confirmedbythegatevoltage(VG) independent
conductance and the nearly linear source-drain
(SD) current-voltage (ISD-VSD)curvewithacon-
ductance of ~3.73 × 10−^5 S, around half thequantum conductance (~7.75 × 10−^5 S, or near-
ballistic transport at room temperature). Ther-
momechanical processing was performed
under a bias of 3.0 V and a current of ~6.5mA
with a pulse duration of 0.1 ms. After eight
stretching cycles, the channel length increased
from ~15.2 to ~26.1 nm, and the diameter de-
creased from ~7.7 to 2.7 nm.
The resulting chirality transitions of the
SWCNT turned the stretched region into a
semiconductor with an on-off current (ION/
IOFF) ratio of ~4.3 × 10^3 (Fig. 2E) and a non-
linear current-voltage (I-V) curve (Fig. 2F).
The transfer curve indicated ambipolar trans-
port characteristics, with the electron and
hole branches being largely symmetric, which
is expected for a molecular junction between
a metallic nanotube and an intrinsic semicon-
ducting nanotube with the Fermi level at the
middle of the bandgap ( 19 ). After another
three stretching cycles, the tube diameter was
further reduced to ~1.7 nm, and the gate volt-
age required to turn on the current became
larger, confirming a widened bandgap inversely
proportional to the CNT diameter ( 1 ).
In addition, reversible transitions between
metallic and semiconducting behavior were
observed with consecutive cycles (fig. S4). By
monitoring the electrical properties as a feed-
back signal during repeated thermomechan-
ical processing (typically 10 cycles), the desired
transition to semiconducting CNTs could be
obtained in a controlled manner. The method
was used to alter the chirality of SWCNTs
grown by chemical vapor deposition (CVD).
Figure S5 shows a SWCNT in which the chiral
indices changed from (23,5) to (15,4) along
with a transition from metallic to semicon-
ducting behavior that was confirmed by a
VG-dependent conductance measurement.
We used this method to fabricate a SWCNT
transistor with a diameter of ~0.6 nm and a
channel length as short as ~2.8 nm (Fig. 2, G
to I). For such a narrow channel under a driveSCIENCEscience.org 24 DECEMBER 2021•VOL 374 ISSUE 6575 1617
Fig. 1. Fabrication and characterization of CNT intramolecular transistors.(A) Schematic of a CNT intramolecular transistor with local chirality altered by
mechanical strain and Joule heating. (B) TEM image of a SWCNT transistor with a fixed source electrode, a probe as drain electrode, and another probe as gate
electrode. (C) Lattice-resolved TEM images and corresponding FFT patterns of a DWCNT before and after the chirality transition.
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