EPAPS Supporting Auxiliary Material: Representative G-peak spectrum for a) the
IMJ transition region, compared to b) combinations of the pure metallic plus pure
semiconductor G-peak spectra. The combination spectra of figure b were obtained by
first normalizing the intensity of the pure metallic and semiconductor elements. These
normalized spectra were then added together in the following ratios to produce figure b:
0.1M + 0.9S, 0.2M + 0.8S, 0.3M + 0.7S, … 0.8M + 0.2S, 0.9M + 0.1S. None of the
linear combination spectra reproduce G-peak spectra obtained at the IMJ transition,
supporting the claim that the observed spectra are from a single nanotube, and not from
two nanotubes lying side-by-side.
Intensity
2500
a
2000
1500
1000
500
1500
1.0
b
1550
1600
1650
Raman Shift (cm-1)
Intensity
0.8
0.6
0.4
0.2
1500
1550
1600
Raman Shift (cm-1)
1650
A
i
i
ii
iii
ii
iii
B
C
Tapping mode AFM images of nanotube IMJ transition region. A) 90 m
segment (combined images of 3 X 30 m images) including highlighted M-S IMJ
transition region. B) High resolution detail of IMJ transition region. C) Height profiles
of transition region, showing the nanotube image is consistent with a single nanotube
with unchanging diameter near 1.7 nm. Note the AFM image in Figure A is a small
segment from a total length of 240 m that was probed by AFM on this nanotube. Only
one nanotube is evident over the entire image. This is also consistent with AFM
measurements of other long nanotubes present on our sample. All nanotubes greater than
100 ms in length exist as individual nanotubes and not as small bundles.
Positioning overlap of the regions imaged in SEM, AFM, and Raman is made
possible because the substrate has a number of large defects visible via SEM and also in
white light images of the surface. Raman and AFM positioning can be correlated
accurately to the position of these defect features. Additionally, the observed AFM and
SEM features match exactly (compare figure 1 inset and above AFM image)—providing
additional confidence that the targeted area has been imaged accurately.
b
Semicond.
12
a
Position (m)
10
8
IMJ
6
4
2
0
144
145
146
147
148
RBM Frequency (cm-1)
Metallic
100
120
140
Raman Shift
160
180
(cm-1)
a) RBM frequency vs. position along the imaged nanotube for the data appearing
in Figure 3a. Metallic to semiconducting character goes from high to low on the position
axis. b) Plot of RBM spectra obtained from a second mapping scan of the IMJ region
performed on a separate day. Within the +/- 1 cm-1 error in frequency for RBM peak
position obtained from each individual spectrum (using a Lorentzian fitting routine to
obtain peak position) no significant change in RBM frequency can be observed on
moving from the metallic to semiconductor segment. Although the RBM weakens
significantly (adding additional uncertainty to the semiconductor RBM frequency
determination) on going to the semiconductor region of the nanotube, intensity does
consistently appear for this mode for spectra taken on different days.
100
100
a
b
c
50
Intensity
Intensity
0
Intensity
50
50
0
-50
-50
1300
1400
1500
1200
1300
-1
100
d
1500
1200
1300
-1
RamanShift (cm)
100
50
e
0
1400
1500
-1
RamanShift(cm)
100
f
RamanShift (cm)
50
50
Intensity
Intensity
1400
Intensity
-50
1200
0
0
0
-50
-50
1200
1300
1400
1500
-50
1200
1300
1400
1500
1200
1300
1400
1500
Raman Shift (cm-1)
Background subtracted D-peak region spectra from a,d) nanotube position
corresponding to semiconductor region point “a” of Figure 2, b,e) position
corresponding to the IMJ transition region point “d” of Figure 2, c,f) position
corresponding to metallic region point “e” of Figure 2. The two sets of spectra were
taken from different mapping scans on separate days. The weak peak at 1450 cm-1 is
from the Si substrate. Its absence in Figure c and f is reproducible and is likely due to a
minor defect occurring in the substrate at that point. The weak peak at 1308 cm-1 in
Figure b appears to be spurious and cannot be identified as a D band with confidence.