Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K
Resonance Raman spectra of DNA-wrapped single-walled carbon nanotubes films were studied at 5 and 295 K in the range of radial-breathing (175–320 cm⁻¹) and tangential (1520–1625 cm⁻¹) modes. The spectra were compared with those of nanotubes in bundles. At 5 K in the spectrum of film an upshift of ba...
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irk-123456789-1170362017-05-20T03:02:55Z Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K Karachevtsev, V.A. Glamazda, A.Yu. Nanostructures and Impurity Centers in Cryogenic Environment Resonance Raman spectra of DNA-wrapped single-walled carbon nanotubes films were studied at 5 and 295 K in the range of radial-breathing (175–320 cm⁻¹) and tangential (1520–1625 cm⁻¹) modes. The spectra were compared with those of nanotubes in bundles. At 5 K in the spectrum of film an upshift of bands regard to their spectrum at high temperature and the intensity redistribution among bands of two samples were observed. The magnitude of this upshift depends on the nanotube type. The influence of temperature lowering, the environment and the electron–phonon coupling on the Raman spectrum of nanotubes are discussed. 2010 Article Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K / V.A. Karachevtsev, A.Yu. Glamazda // Физика низких температур. — 2010. — Т. 36, № 5. — С. 474-483. — Бібліогр.: 51 назв. — англ. 0132-6414 PACS: 78.67.Ch http://dspace.nbuv.gov.ua/handle/123456789/117036 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Nanostructures and Impurity Centers in Cryogenic Environment Nanostructures and Impurity Centers in Cryogenic Environment |
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Nanostructures and Impurity Centers in Cryogenic Environment Nanostructures and Impurity Centers in Cryogenic Environment Karachevtsev, V.A. Glamazda, A.Yu. Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K Физика низких температур |
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Resonance Raman spectra of DNA-wrapped single-walled carbon nanotubes films were studied at 5 and 295 K in the range of radial-breathing (175–320 cm⁻¹) and tangential (1520–1625 cm⁻¹) modes. The spectra were compared with those of nanotubes in bundles. At 5 K in the spectrum of film an upshift of bands regard to their spectrum at high temperature and the intensity redistribution among bands of two samples were observed. The magnitude of this upshift depends on the nanotube type. The influence of temperature lowering, the environment and the electron–phonon coupling on the Raman spectrum of nanotubes are discussed. |
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Karachevtsev, V.A. Glamazda, A.Yu. |
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Karachevtsev, V.A. Glamazda, A.Yu. |
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Karachevtsev, V.A. |
| title |
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K |
| title_short |
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K |
| title_full |
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K |
| title_fullStr |
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K |
| title_full_unstemmed |
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K |
| title_sort |
raman spectroscopy of dna-wrapped single-walled carbon nanotube films at 295 and 5 k |
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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2010 |
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Nanostructures and Impurity Centers in Cryogenic Environment |
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| citation_txt |
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K / V.A. Karachevtsev, A.Yu. Glamazda // Физика низких температур. — 2010. — Т. 36, № 5. — С. 474-483. — Бібліогр.: 51 назв. — англ. |
| series |
Физика низких температур |
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AT karachevtsevva ramanspectroscopyofdnawrappedsinglewalledcarbonnanotubefilmsat295and5k AT glamazdaayu ramanspectroscopyofdnawrappedsinglewalledcarbonnanotubefilmsat295and5k |
| first_indexed |
2025-07-08T11:31:51Z |
| last_indexed |
2025-07-08T11:31:51Z |
| _version_ |
1837078219277205504 |
| fulltext |
© V.A. Karachevtsev and A.Yu. Glamazda, 2010
Fizika Nizkikh Temperatur, 2010, v. 36, No. 5, p. 474–483
Raman spectroscopy of DNA-wrapped single-walled
carbon nanotube films at 295 and 5 K
V.A. Karachevtsev and A.Yu. Glamazda
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine
47 Lenin Ave., Kharkov 61103, Ukraine
E-mail: karachevtsev@ilt.kharkov.ua
Received January 21, 2010
Resonance Raman spectra of DNA-wrapped single-walled carbon nanotubes films were studied at 5 and
295 K in the range of radial-breathing (175–320 cm–1) and tangential (1520–1625 cm–1) modes. The spectra
were compared with those of nanotubes in bundles. At 5 K in the spectrum of film an upshift of bands regard to
their spectrum at high temperature and the intensity redistribution among bands of two samples were observed.
The magnitude of this upshift depends on the nanotube type. The influence of temperature lowering, the envi-
ronment and the electron–phonon coupling on the Raman spectrum of nanotubes are discussed.
PACS: 78.67.Ch Nanotubes.
Keywords: single-walled carbon nanotubes, DNA, Raman scattering, electron-phonon coupling, low temperatures.
Introduction
A single-walled carbon nanotube (SWNT) is a quasi-
one-dimensional crystal characterized with unique physical
and chemical properties, which can be used in various
fields of nanotechnology [1,2]. Despite a rather rigid me-
chanical frame of nanotubes, the environment affects es-
sentially their physical properties. Therefore, study of this
environment influence is actual and important at present in
carbon nanotube science.
By volume synthesis, carbon nanotubes are obtained in
the form of bundles, which appeared due to the strong in-
ternanotube interaction caused mainly by van der Waals
forces. Splitting of these bundles into individual nanotubes
and the following hindrance of nanotube aggregation was
not turned out such a simple task as expected. Efforts ap-
plied to solve this problem leaded to nanotechnology based
on the ultrasonication of nanotubes in water with a surfac-
tant and the following ultracentrifugation. Stable aqueous
suspension of individual nanotubes is prepared with adding
of charged or neutral surfactants or water-soluble polymers
which are prevent nanotubes from sticking after ultrasoni-
cation treatment [3]. Besides the need for isolated SWNTs
in aqueous solutions, it is desirable to obtain them in the
film which extends of range for practical use, for example,
as sensors. In this respect, polymers are more promising.
Some of them are able to wrap around the tube and to be
adsorbed to the tube surface after deposition on the sub-
strate and drying. Investigations performed in this direction
for last ten years have shown that the most effective poly-
mer is DNA as it has hydrophobic and hydrophilic parts in
the polymer structure simultaneously and, due to its helical
form, the polymer can wrap around the nanotube [4]. This
model proposes that hydrophobic nitrogen bases are ad-
sorbed to the nanotube surface via π–π stacking and the
hydrophilic sugar-phosphate backbone is directed to water
[3,4]. It should keep in mind that DNA is a negatively
charged polymer and that charged groups effect on its inte-
raction with the nanotube as well. This process takes place
not only during ultrasonication but after this treatment too,
due to self-ordering to find its optimal energetic position
on the nanotube surface in water. As experiments revealed,
the process can proceed for weeks and even months [5,6].
Upon the preparation of nanotube films from water sus-
pension with DNA, a composite is formed in which indi-
vidual nanotubes or small bundles are separated with the
polymer [7,8]. This conclusion is confirmed with the ob-
servation of the luminescence of SWNT:DNA film, which
suggests the presence of individual tubes as in nanotube
bundles a luminescence is quenched because of the semi-
conducting SWNT contact with metallic ones [7].
Raman spectroscopy has been used extensively to cha-
racterize carbon nanotubes since it can probe both the pho-
non spectrum and the electronic structure through the reso-
nant effect. Resonance Raman (RR) spectroscopy is cha-
racterized by the strong enhancement in the intensity of the
scattered light appeared in spectra. RR spectrum of carbon
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K
Fizika Nizkikh Temperatur, 2010, v. 36, No. 5 475
nanotubes is observed when the energy of the incident la-
ser matches the energy separation Eii between the peaks of
van Hove singularities in the valence and conduction bands
(see, for example, [9–13]). Since Eii depends on the nano-
tube structure, nanotubes of different chiralities or conduc-
tivity will be in resonance with laser energies. The sensi-
tivity of this informative method is sufficiently high and
researchers have opportunity to observe the spectrum of
the individual nanotube (see, for example, [10]). This
comparatively low cost method permits to determine di-
ameters, chirality, metallic or semiconducting types of
conductivity and to study the effect of temperature and the
environment on nanotube properties.
The intensity of bands in the RR spectrum can weaken
(even disappear) or, on the contrary, the intensity of other
bands may enhance, depending on the position of the elec-
tron energy transition relatively to the laser energy (the
resonance condition). Thus, there is a small range of laser
energy (resonance window) in which intensity of SWNT
band in the RR spectrum can attain a maximal value. It is
known that the width and shape of this resonance window
depends on the nanotube index chirality (n,m), environ-
ment, bundling or individual form, nanotubes are in solu-
tion or in film, type of surfactant (see, for example, [12]).
It should be added that, due to changes of the sample tem-
perature or environment, a shift of electronic levels occurs
and, as a result, these levels leave the resonance window or
enter it. Thus, even weak interaction between the nanotube
and molecule/polymer can be followed not only with the
band shift but with a rather strong transformation of the
spectrum intensity. Under study of the temperature influ-
ence on RR spectra of carbon nanotubes, a priori, such an
important factor as the electron-phonon interaction should
be accounted too [14]. It should be added that recent Ra-
man scattering experiments on metallic SWNTs revealed a
very strong electron-phonon coupling in these nanotubes
while applying an electrochemical gate voltage [15–17] or
combining Rayleigh scattering with RR spectroscopy [18].
This coupling is caused by the predicted Kohn anomaly
(KA) in their phonon dispersion [19–23].
Earlier, RR spectra of carbon nanotubes in bundles [24–
27] or of isolated SWNT [28–30] were investigated at low
temperatures in order to get information on thermal charac-
teristics of this nanomaterial and to study low temperature
effects on nanotube structural and energy parameters. It
was shown that the temperature dependence of Raman
frequencies of SWNT is mainly determined by the anhar-
monic terms in the bond potential energy.
This work presents results of the experimental study in
which effects of low temperature on RR spectrum in the
range of radial-breathing (RBM) (175–320 cm–1) and tan-
gential (1520–1625 cm–1) modes (G mode) of SWNT film
in DNA environment were elucidated as well as this nano-
tube film thermal properties were compared with those of
nanotubes in bundles.
Experimental details
SWNTs produced by HiPCO method were purified by
controlled thermal oxidation followed by HCl treatment
[31]. An aqueous suspension of SWNTs was prepared us-
ing single-stranded DNA. A single-stranded polymer was
obtained from a double-stranded one (extracted from
chicken erythrocytes, Reanal, Budapest, Hungary) by melt-
ing at 90 °C and quick cooling to ice temperature. SWNT
aqueous suspension with DNA was prepared by 30 min
ultrasonication of nanotubes and centrifugation (1 hour,
120000 g). Our electrophoresis estimation of the DNA
fragmentation after sonication gave the mean length of the
fragment within 200–300 base pairs. The SWNT:DNA
concentration ratio was 1:2. Nanotube films for Raman
experiments were obtained by dropping DNA-wrapped
SWNT suspension onto the quartz substrate, washing the
excess DNA and drying in warm air.
Our previous studies [7] and works of other authors [8]
showed that SWNTs covered with DNA aggregate into
small bundles as the film begins to dry but DNA precludes
the direct nanotube-nanotube aggregation in this film.
Thus, the bundles in SWNT:DNA film are different from
the usual SWNT bundles, and this is confirmed by obser-
vation of luminescence of SWNT:DNA in a film, which
suggests the presence of individual tubes (or small bun-
dles).
Raman experiments were performed in the 90° scat-
tering configuration relatively to the laser beam, using the
632.8 nm (1.96 eV) excitation from a He–Ne laser
(15 mW). The scattered light was analyzed with a double
monochromator (reverse dispersion 3.5 Å/mm) and de-
tected with a thermocooled CCD camera. In our spectral
measurements, the peak position of RBM bands and G+
band of SWNTs in films and in bundles was determined
with an accuracy no worse than 0.5 cm–1 . Such high accu-
racy was possible since the frequency positions of the
plasma lines from the He–Ne laser in the vicinity of these
bands were used for internal calibration of our spectrome-
ter. Low temperature studies were carried out with using
the optical cryostat (ILTPE, Ukraine) in helium vapors at
5 K.
Results and discussion
Resonance Raman spectra of SWNT bundles and
SWNT:DNA films at 295 K
Figure 1 presents two the most characteristic fragments
of RR spectrum of SWNT bundles and SWNT:DNA film
obtained upon deposition of individual nanotubes from
aqueous suspension (T = 295 K). Two spectral ranges are
shown which contain the low frequency region between
175–320 cm–1 (RBM bands) (Fig. 1,a) and the high fre-
quency range (Fig. 1,b) between 1520–1625 cm–1 attri-
buted to the tangential band (G band) frequency.
V.A. Karachevtsev and A.Yu. Glamazda
476 Fizika Nizkikh Temperatur, 2010, v. 36, No. 5
Radial-breathing mode of nanotubes
9 Lorentzians were fitted to the experimental spectrum
of SWNTs in RBM region (Fig. 1,a), parameters of which
are presented in Table 1. RR spectrum of SWNTs pro-
duced by HiPCO method was observed by some scientific
groups, so every band may be assigned to nanotubes of
certain chirality [26,32,33]. Low-frequency bands with
peaks at 198.9 and 221.0 cm–1 are attributed to metallic
tubes while those in the range of 250–300 cm–1 correspond
to semiconducting SWNTs at He–Ne laser excitation
(1.96 eV) [26]. Table 1 presents the band peak position
(ω), value of which gives nanotubes chirality and diame-
ters. In this Table for each RBM frequency of metallic and
semiconducting nanotubes corresponding electronic transi-
tions are also presented, values of which are close to the
laser energy (1.96 eV). In the case of metallic nanotubes,
11
mE denotes the electronic transition between the first
peaks of van Hove singularities in the valence and conduc-
tion bands, and 22
sE indicates the electronic transition be-
tween the second peaks of van Hove singularities of semi-
conducting nanotubes. Values of 11
mE , 22
sE and relative
intensity of lines (shown in brackets) presented in Table 1
were taken from Table in Ref. 32. These energies were
obtained for individual HiPCO SWNTs in aqueous suspen-
sion with SDS.
Table 1. Peak frequency (ω, cm–1) and area (normalized to G+
band) (in brackets) of Lorentzians used to fit the RBM band in
Raman spectra of SWNT bundles and SWNT:DNA film at
295 K; electronic transition between first pairs of van Hove sin-
gularities of metallic ( 11
mE ) and second ones semiconducting
22( )sE nanotubes (eV) and intensity (in brackets), chirality (n,m)
and diameters (d, nm) of nanotubes determined experimentally
from Raman spectrum of semiconducting and metallic HiPCO
SWNTs in SDS aqueous suspension [32] taken near with a laser
excitation energy (1.96 eV).
As was shown earlier, due to the strong van der
Waals tube–tube interaction in bundles, Eii lowers by
70–150 meV [11,12] (depending on nanotube chirality).
Thus, for our SWNTs in bundles, energy values are lower
by 80–100 meV (on average) than those presented in Ta-
ble 1. The integral intensity (area, indicated in brackets
near the frequency value) of every band (Table 1) was
normalized to that of the most intensive tangential band
(G+ band). As the bands corresponding to metallic nano-
tubes with the maximum at 198.9 and 221.0 cm–1 are ra-
ther broad and have an asymmetric form, therefore, each of
them was fitted with two Lorentzians. Thus, the band at
198.9 cm–1 was described with two lines with peaks at
195.2 and 201.6 cm–1, the first of them can be assigned to
three nanotubes with different chirality among them, the
most intensive line is attributed to (14.2) nanotube. 11
mE of
SWNT
(295 K)
SWNT:DNA
(295 K)
11
mE , 22
sE ,
eV [32]
(n,m) d, nm
ω, cm–1
(SRBM/SG+)
ω, cm–1
(SRBM/SG+)
195.2(4.3) 194.5(3.6)
1.93(2.5)
2.02(0.5)
1.94(3.6)
(13,4)
(9,9)
(14,2)
1.206
1.221
1.183
201.6(4.3) 200.9(4.6)
1.91(0.7)
2.07(0.9)
(15,0)
(10,7)
1.175
1.159
216.0(1.5) 215.8(0.4) 2.08(2.6) (12,3) 1.077
221.5(6.2) 221.4(6.2) 2.06(1.5) (13,1) 1.060
253.8(2) 254.3(6.2) 1.95(3.6) (10,3) 0.924
258.8(6.3) 258.9(2.7) 2.03(9.8) (11,1) 0.903
266.0(0.4) 266.5(1.0) 1.91(2.6) (7,6) 0.883
285.4(1.8) 285.5(2.8) 1.92(18.3) (7,5) 0.818
299.7(0.2) 299.8(0.2) 1.86(36) (8,3) 0.772
Fig. 1. Raman spectra in range of RBM (a) of SWNT bundles
(multiplied by 1.2) (bold line) and SWNT:DNA film (thin line)
and G mode (b) at 295 K. Each experimental spectrum obtained
at λexc = 632.8 nm laser excitation was fitted with curves de-
scribed with sum of Lorentzians (dashed line) and BWF (a low-
frequency band of G mode) functions. Value of band peak posi-
tion (cm–1) and its area (in brackets) is indicated in this Figure
close to the band location. Peaks labeled «*» correspond to the
plasma line of the laser.
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Raman shift, cmRaman shift, cm
––11
��������
��**** **
SWNTSWNT:DNA:DNA
TT = 295 K= 295 K
SWNTSWNT
aa
15201520 15401540 15601560 15801580 16001600 16201620
1559.61559.6
(14)(14)1546.21546.2
(13)(13)
Raman shift, cmRaman shift, cm
––11
��
��
1543.11543.1
(14)(14)
1557.01557.0
(16)(16)
1587.81587.8
(36)(36)
1591.31591.3
(34)(34)
**
**
SWNTSWNT
��**
��**
��
**
bb1592.21592.2
(32)(32)
1597.01597.0
(41)(41)
SWNTSWNT:DNA:DNA
TT = 295 K= 295 K
��
**
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K
Fizika Nizkikh Temperatur, 2010, v. 36, No. 5 477
this nanotube is located at 1.94 eV which is lower than the
laser energy (1.96 eV). A possible contribution of two oth-
er nanotubes with (13,4) and (9,9) chiralities into the inten-
sity of the line at 195.2 cm–1 should be taken into account
too. If to compare 11
mE with the laser energy, the first na-
notube has lower but the second one has higher transition
energies, respectively (see Table 1). The line with the peak
at 201.6 cm–1 can be assigned to (15,0) and (10,7) nano-
tubes with 11
mE located lower and higher than 1.96 eV,
respectively.
Two Lorentzian functions with peaks at 216.0 and
221.5 cm–1 were fitted to the band with the maximum at
221.0 cm–1, that can be attributed to nanotubes with chira-
lities (12,3) and (13,1), respectively. 11
mE of these nano-
tubes is located somewhat higher than the laser energy
(Table 1).
The situation with the assignment of bands of semicon-
ducting nanotubes to the certain chirality is simpler than
for metallic nanotubes (Table 1), because these bands are
narrow and their peaks are separated in the spectrum. It
should be noted that among these SWNTs only one band
(at 258.8 cm–1) is assigned to the tube with (11,1) chirality,
the electronic transition of which is located higher than the
laser energy. The electronic transition of other nanotubes is
lower than 1.96 eV.
Energies of electronic transitions of individual nano-
tubes covered with DNA in aqueous suspension are about
10–80 meV lower than Eii of nanotubes in SDS surround-
ing [7,34–36]. This is caused by a stronger polymer inte-
raction with the nanotube surface or by an incomplete cov-
ering of the nanotube surface with the polymer. As a result,
polymer free surface will be in contact with water mole-
cules, and this, in part, lowers the electronic level [37]. In
comparison with aqueous suspension of SWNT:DNA,
the magnitude of Eii in film decreases further by about
10–20 meV [7]. Evidently, such energy lowering is a result
of increasing the interaction energy between the polymer
and the nanotube in the solid state as well as of the forma-
tion of bundles in which, however, nanotubes are separated
with the polymer. One confirmation of this statement that
the interaction between the nanotube and DNA in the solid
state is stronger is based on the enhancement of the elec-
trostatic interaction in the solid state because: i) the dielec-
tric constant of water is much higher than that of air and
ii) the distance between charges in the film is decreased in
comparison with solution where water molecules reduces
interaction between the nanotube and DNA. It should be
noted that this energy lowering is weaker than at the nano-
tube bundle formation. At the same time, the nanotube
interaction with the substrate should decrease Eii too, and
this fact must be taken into account. Thus, electronic levels
of nanotubes in the film with DNA are energetically higher
than those in bundles (by about 50–100 meV). This energy
analysis needs to consider the influence of the resonance
conditions on the band intensity. It is known that the width
of the resonance window is wider for nanotubes in bundles
than for isolated SWNTs [11,12].
RR spectrum of SWNT:DNA films in the range of
RBM is of common similarity with the spectrum of nano-
tubes in bundles (Fig. 1,a). We note 25% enhancement of
the semiconducting nanotube intensity in comparison with
metallic SWNTs. Thus, the M:S (metallic:semiconducting)
ratio of integrated intensities for RBM associated with me-
tallic tubes to those of semiconducting ones in bundles and
film with DNA are 1.52 and 1.15, respectively. Such an
enhancement can be explained both by changes in reson-
ance conditions and DNA selectivity to interact preferably
with nanotubes of the certain diameter [38,39].
For metallic nanotubes in film with DNA, the intensi-
ty of the band with a maximum at 198.8 cm–1 frequency
increased in comparison with the band intensity at
221.4 cm–1. In semiconducting nanotubes an essential rise
of the band intensity at 254.3 cm–1 and the intensity drop
of the band at 258.9 cm–1 are observed. Such a redistribu-
tion of band intensities can be attributed to changes in re-
sonance conditions for different nanotubes in bundles and
film with DNA. Some insight into the manifestation of
these conditions in Raman spectra may be got from Fig. 2
which presents the energetic scheme of resonant windows
for two semiconducting SWNTs (in various environments)
with regard to the laser energy (1.96 eV). The vertical line
denotes the laser energy and shapes of the window for in-
dividual SWNTs in aqueous solutions with SDS (bold line)
or with DNA (dashed line) and in bundles (thin line). To
describe this window, a Lorentzian function was used.
Two nanotubes with index chirality (10,3) (Fig. 2,a) and
(11,1) (Fig. 2,b) were selected for this scheme. These na-
notubes have RBM frequencies at 254.3 and 258.9 cm–1 in
the SWNT:DNA film, respectively. For the first nanotube
22
ssE is lower (1.95 eV) and for the second one is higher
(2.03 eV) than the laser energy. 22
ssE for these nanotubes
in bundles was taken by 80 meV (on average) lower than
obtained for individual SWNTs. Average values of the
resonance window width (at half of height) were taken as
80 meV for nanotubes in bundles [12], 40 meV for
SWNT:DNA film [35,36] and 30 meV for individual nano-
tubes in aqueous solutions with SDS [32]. If to proceed
from bundles to film with DNA, the integral intensity of
the line at 254.3 cm–1 must increase due to better reson-
ance conditions and, on the contrary, the integral intensity
of the line at 258.9 cm–1 must decrease because of 22
ssE of
this tube escapes from the resonance. Just the same intensi-
ty behavior of selected bands has been observed in experi-
mental spectra.
Detailed analysis provided for two semiconducting na-
notubes, with 22
ssE being lower or higher than the laser
energy, can be applied to other nanotubes. Thus, integral
intensity of bands at 266.5, 285.4 and 299.8 cm–1 will in-
crease if to proceed from bundles to the film with DNA
that is well seen in RR nanotubes spectra (Fig. 1,a).
V.A. Karachevtsev and A.Yu. Glamazda
478 Fizika Nizkikh Temperatur, 2010, v. 36, No. 5
In the case of metallic nanotubes the similar analysis is
complicated as two lines are taken to fit to the experimen-
tal band and each line can be assigned to 2–3 nanotubes of
different chirality, 11
mE value of which is lower or higher
than the laser energy. The ratio of integral intensities of
low- and high-frequency bands are 1.12 in RR spectra of
metallic nanotubes in bundles and 1.24 in spectra of
SWNT:DNA film. Table 1 demonstrates that this ratio
change is mainly caused by the intensity decrease of the
high-frequency band. As 11
mE of nanotubes attributed to
this band has a higher value than the laser energy, such an
intensity decrease (proceeding from bundles to the film
with DNA) is expected. The integral intensity of the band
at 198.9 cm–1 is somewhat weaker for SWNT:DNA films
too in comparison with that of bundles though (14,2) nano-
tube has a lower value of 11
mE than the laser energy, and in
this case the intensity rise could be expected. However,
this has not occurred, possibly, because the contribution of
other nanotubes into the integral intensity of this band must
be taken into account.
Comparing the band position in RBM spectra of nano-
tubes in bundles and in the film with DNA reveals that the
spectral shift does not exceed 0.7 cm–1. It should be noted
that for metallic nanotubes in the film with DNA the
downshift is observed, and in the case of semiconducting
SWNTs the band is upshifted or the band position is not
changed practically. A small shift of peaks of RBM bands
of SWNT:DNA film versus bands of nanotube bundles
into different sides for semiconducting and metallic nano-
tubes indicates that DNA interactions with various types of
SWNTs are different. In recent article of Prof. S. Iijima
with coworkers [40] it was concluded that ssDNA selec-
tively interacts with the metallic nanotubes and modifies
the electronic structure.
Is it possible to explain the evolution in the intensity of
RBM bands proceeding from nanotubes in the bundle to a
SWNT:DNA film, considering only changes in resonance
conditions? Let us to compare changes in the intensity of
the band at 221.4 cm–1, attributed to two metallic nano-
tubes with 11
mE that is higher than 1.96 eV, and in the in-
tensity of the semiconducting nanotube at 258.9 cm–1 with
the similar value of energy transition ( 22
sE ). The decrease
of the last band integral intensity going from bundles to
film with DNA is 57% but the band intensity of metallic
nanotubes weakens only by 14%. In part, such a difference
in the intensity weakness can be explained with the differ-
ent resonance window the width of which depends on the
tube chirality [11,12]. But it seems to us that the main rea-
son of this different intensity weakening is caused by vari-
ous DNA interactions with metallic and semiconducting
nanotubes. As for one type of SWNTs, this interaction
depends on the diameter/chirality too [38,39].
Tangential mode of nanotubes
The tangential mode of nanotubes (Fig. 1,b) consists of
two components: a narrow band near 1590 cm–1 and a
broadened low-frequency 1520–1570 cm–1 band (G+ and
G– bands, respectively). These bands are due to C–C vib-
ration along the nanotube axis (LO phonon) and with
the carbon atom vibration in the tangential direction with
regard to the tube axis (TO phonon). The high-frequency
component (1560–1620 cm–1) is observed not only in
SWNTs spectrum but in the Raman spectra of multi-
walled carbon nanotubes and of graphite and graphene as
well. The presence of the low-frequency component G–
which appears due to curvature and confinement is a fea-
ture of SWNTs only. It should be noted that the observed
spectrum is a result of the spectrum superposition of both
semiconducting and metallic type nanotubes with different
diameters. To describe the two components of the tangen-
tial mode, the nanotube spectrum was fitted with the mi-
nimal number of approximation functions: two curves for
each nanotubes type.
Fig. 2. Scheme of resonant windows of semiconducting nano-
tubes with different chirality (10,3) (a) and (11,1) (b): arranged in
bundles (thin curve), aqueous suspension of individual nanotubes
in SDS (bold curve) and DNA surrounding (dashed curve) lo-
cated close to energy excitation (1.96 eV) of He–Ne laser
(straight line). Lorentzian curves were used to describe a contour
of resonant windows.
1,71,7 1,81,8 1,91,9 2,02,0 2,12,1 2,22,2
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EnerEnergygy, eV, eV
(10,3) SWNT(10,3) SWNT
aa
295 K295 K 5 K5 K
15 meV15 meV
1,71,7 1,81,8 1,91,9 2,02,0 2,12,1 2,22,2
EnerEnergygy, eV, eV
(1(11,1) SWNT1,1) SWNT
bb
295 K295 K 5 K5 K
15 meV15 meV
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K
Fizika Nizkikh Temperatur, 2010, v. 36, No. 5 479
The low-frequency component of the G– band is wide
with an asymmetric form, which is strongly broadened in
the range of lower frequencies. As was shown, the sloping
lower-frequency front of the band is conditioned with me-
tallic nanotubes. The shape of such a band is well de-
scribed by Breit–Wigner–Fano (BWF) function [41]:
I(ω) = I0{1 + (ω – ω0)/qΓ}2/{1 + [(ω – ω0)/Γ]2}, where I0,
ω0, Γ and q are intensity, the BWF peak frequency, broa-
dening parameter, and the asymmetry parameter, respec-
tively. The asymmetric line shape of the G– band has been
attributed to interference scattering between an electronic
continuum present in metallic tubes and the G– Raman
active band. This BWF band is of a weak intensity in indi-
vidual nanotubes [42] and is practically absent in
SWNT:DNA aqueous suspensions after ultracentrifugation
[7,43]. The intensity of G– band rises significantly in bun-
dles as it was supposed earlier due to the strong influence
of the tube–tube interaction on coupling of phonons with
plasmons in metallic nanotubes [42].
However, recent detailed theoretical models showed
that the G–
peak in metallic nanotubes is caused by the LO
mode, but not the TO mode as in semiconducting SWNTs
[19–23]. The LO mode is softened by a Kohn anomaly at
the point Γ in the phonon dispersion. This model predicates
that the G– band in metallic SWNTs is due to coupling
between phonons and electron-hole pairs, contrary to the
earlier theory of plasmon-phonon coupling. The KA occurs
in the LO phonon branch because the LO phonon distorts
the lattice such so that a dynamic band gap is induced in
the electronic band structure. This accompanies with the
energy decrease of the electrons near the Fermi point, and
the energy required to distort the lattice is reduced too,
leading to phonon softening. Thus, LO phonon in RR spec-
trum of metallic nanotubes has a lower frequency than TO
phonon. In the spectrum of semiconducting nanotubes the
assignment of bands is opposite: the frequency for LO-
phonons is higher than for TO ones. This model was sup-
ported by the experimental study [15–18].
For two investigated samples the low-frequency com-
ponent of G mode was approximated with one BWF and
one Lorentzian functions. Unlike aqueous suspension of
SWNT:DNA, in its film the band intensity described with
BWF function increases [7,44] but its intensity is lower
than that of nanotubes in bundles. The second band de-
scribed with Lorentzian function was assigned to semicon-
ducting nanotubes with the maximum at 1557.0 cm–1, in
SWNT:DNA film this band is by 2.6 cm–1 is upshifted
versus this band in SWNT bundles. The similar evolution
with the G+ band was observed too: its peak is upshifted by
4.3 cm–1. Two Lorentzians were fitted to this band, the
low-frequency line was attributed to nanotubes with metal-
lic conductivity and the line of higher frequency is related
to semiconducting ones [45]. The value of the band peak
position and its area are indicated (in brackets) near the
bands in Fig. 1,b. The area of each line was normalized to
the total area of all bands of G mode, being taken as 100%.
It should be noted that the width of G+ band increased in
SWNT:DNA films. Most likely, the possible reason of
such an increasing is the nanotube interaction with the po-
lymer which structure includes the charged group, or other
reason can be caused by the inhomogeneous broadening
because of the disordering arrangement of nanotubes in the
film. The important parameter characterizing the bundle
formation is the ratio of areas of high- and low-frequency
components of G mode, upon the bundle splitting, this
ratio increases [42]. In SWNT:DNA film the integral in-
tensity of the band, described with BWF function, lowers
by about 30%.
One possible reason of G+ band upshift in SWNT:DNA
film may be caused by the transfer of the charge between
the nanotube and adsorbed molecule. Upon the charge
transfer from the nanotube to the molecule, the G+ band
is upshifted, and, when the electron transfer occurs in
the opposite direction, this band is downshifted [41,46].
A single-stranded DNA chain forms a helically wrapped
hybrid structure around the nanotube, in which the nitrogen
bases are extended from the backbone and stacked onto the
nanotube surface [3,4]. The interaction between bases and
the nanotube surface is accompanied by the weak charge
transfer. However, as recent ab initio calculations were
demonstrated, a weak charge transfer takes place from
bases to the nanotube and the G+ mode softening is ob-
served in RR spectrum of nanotubes covered with bases
[47].
The other possible reason of G+ band upshift in
SWNT:DNA film may be connected with the polymer
pressure onto the nanotube. Such an assumption is reason-
able as the polymer wraps around the nanotube and this
adsorption is very strong both in water and in film but the
interaction between the nanotube and DNA in the solid
state is stronger. According to results of investigations on
the external pressure effect on RR spectra of carbon nano-
tubes [48,49], the G+ band is shifted to the high-frequency
region upon pressure onto the nanotube. In any case, the
upshift of G mode frequency indicates that C–C bond force
constant of nanotubes in film with DNA becomes stronger
relatively to this constant in bundles.
Effect of temperature lowering on Raman spectra of
carbon nanotubes in bundles and in film with DNA
Figure 3 presents spectral evolution observed in nano-
tube bundles upon the temperature lowering from 295 to
5 K. As with RR spectra of these nanotubes at room tem-
perature, the low-temperature spectrum was fitted by the
same number of Lorentzian and BWF functions too.
In RR spectrum of nanotubes in bundles at T = 5 K the
intensities of RBM bands corresponding to metallic nano-
tubes decrease relatively to those of semiconducting nano-
tubes, for example, M:S ratio is equal to 0.6 but at 295 K it
is 1.52. At the same time the intensity of the metallic nano-
V.A. Karachevtsev and A.Yu. Glamazda
480 Fizika Nizkikh Temperatur, 2010, v. 36, No. 5
tube band with the maximum at 222.5 cm–1 lowers more
significantly in comparison with the band at 200.7 cm–1,
and, as a result, the ratio of integral intensities of low- and
high-frequency bands increased from 1.12 at 295 K to 1.55
(Table 2).
As with the temperature lowering the population of
phonon states in nanotubes decreases, this results in the
increase in the energy of electronic transitions (see,
for example, [14,50]). The value of Eii increase with tem-
perature about 10–20 meV (this value is different for me-
tallic and semiconducting nanotubes). This energetic evo-
lution changes resonance conditions for nanotubes. So,
SWNT with Eii more than the laser excitation energy will
leave the resonance window, and the intensity of RBM
bands of such nanotubes will weaken, and, to the contrary,
the intensity of RBM bands of nanotubes with Eii lower
than 1.96 eV will strengthen.
The temperature drop results in an upshift of RBM
bands. The shift value for metallic nanotubes is 1.1–3.5 cm–1,
for semiconducting nanotubes this upshift is lower (about
1 cm–1). It should be noted that similar spectral upshift
upon the temperature decrease was observed for isolated
nanotubes too [28]. At low temperature the RBM bands
became narrow, for some nanotubes this width value (at
half of height) reaches 3 cm–1.
Table 2. Peak frequency (ω, cm–1) and area (normalized to G+
band) (in brackets) of Lorentzian lines used to fit the RBM band
in Raman spectra of SWNT bundles and SWNT:DNA film at
5 K; difference (Δ(295–5 K), cm–1) between peaks of Lorentzians
determined from the fitting to RBM band in Raman spectra ob-
tained at 5 and 295 K.
As well, the decrease in T effects on the RR spectrum
of nanotubes in bundles in the region of the tangential
mode. G+ band fitted by two Lorentzian functions which
demonstrate 2.5 and 2 cm–1 upshifts, for the low- and high-
frequency bands, respectively. When T is lowered, an av-
erage upshift is 2.5 cm–1, this gives an estimated average
temperature coefficient dω/dT – 0.0083 cm–1/K for the
G+ peak of semiconducting tubes in bundles. This value is
close to the temperature coefficient in isolated nanotubes,
being determined as –0.011 cm–1/K [28]. It should be
noted that, for graphene, this coefficient is twice higher
[28]. The upshift of the band fitted by BWF does not ex-
ceed 3.6 cm–1. The integral intensity of the last band de-
creases at low temperature (Fig. 3).
The temperature effect on Raman frequencies of a ma-
terial is conditioned with the anharmonic terms in the bond
potential energy of the nanotube lattice, induced by its
thermal expansion upon the temperature rise. Thus, the
temperature increase results in softening of the force con-
stant of C–C bond, and the phonon frequency becomes
lower [51]. Such a behavior of peaks of RBM and G bands
of SWNTs is observed, but the spectral shift of these bands
is different, depending on the type of the nanotube conduc-
tivity.
To consider the effect of the temperature lowering on
RR spectrum of metallic nanotubes, besides an inharmonic
term, the contribution of the phonon and electron coupling
must be taken into account. The population of the electro-
SWNT (5 K) SWNT:DNA(5 K)
ω, cm–1
(SRBM/SG+)
Δ(295–5 K),
cm–1
ω, cm–1
(SRBM/SG+)
Δ(295–5 K),
cm–1
197.8(1.4) –2.6 197.6(0.5) –3.1
202.7(2) –1.1 202.6(0.7) –1.7
219.5(1.1) –3.5 217.6(0.1) –1.8
224.2(1.1) –2.7 223.8(0.5) –2.4
254.6(2.3) –0.8 255.1(3.0) –0.8
259.8(4.3) –1.0 259.9(0.5) –1.0
266.7(0.6) –0.7 266.9(0.8) –0.4
285.9(2) –0.5 286.1(2.1) –0.6
300.1(0.2) –0.4 300.8(0.1) –1.0
180180 200200 220220 240240 260260 280280 300300 320320
�������� ****** **
SWNTSWNT
295 K295 K
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15201520 15401540 15601560 15801580 16001600 16201620
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1559.81559.8
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1589.81589.8
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1593.81593.8
(42)(42)
**
**
**
SWNTSWNT
295 K295 K
bb
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5 K5 K
��1.21.2
2.5 cm2.5 cm
––11
Raman shift, cmRaman shift, cm
––11
Raman shift, cmRaman shift, cm
––11
Fig. 3. Raman spectrum in range of RBM (a) and G mode (b) of
SWNT bundles at 5 K (bold curve). Curves described by Lorent-
zian and BWF (a low-frequency band of G mode) functions were
used for fitting to the experimental spectrum (dashed lines). Val-
ue of band peak position and its area (in brackets) is indicated in
this Figure close to the location of bands. For comparison the
Raman spectrum of this sample obtained at 295 K (bold curve)
was shown.
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K
Fizika Nizkikh Temperatur, 2010, v. 36, No. 5 481
nic states with the temperature increase is determined by
Fermi-Dirac distribution which influences the shape of
Kohn anomaly. With the temperature rise the significance
of this anomaly weakens. Thus, the effect of temperature
becomes apparent in modification of the electronic screen-
ing, as a consequence, LO phonon frequency is changed
that can be observed in RR spectrum [15–18]. The effect of
LO phonon softening with the temperature rising becomes
weaker resulting in the G– band frequency increase. How-
ever, as the theoretical model predicts [22], this occurs
above the 450–500 K but from helium till room tempera-
tures the G– band frequency will decrease. Thus, in our
temperature range the frequency downshift induced by
electrons will intensify the shift caused by the unharmonic
term. As a result, the downshift value of BWF band with
temperature is larger than for other bands.
The influence of electron–phonon coupling on RBM of
carbon nanotubes was studied recently [17], and the 2 cm–1
softening of the radial breathing mode of metallic nano-
tubes due to this coupling was observed, meanwhile, the
RBM peak for a semiconducting SWNT shows no appreci-
able change. By analogy with G mode, we suppose that a
larger upshift of RBM of metallic nanotubes versus semi-
conducting ones, observed at the temperature lowering, is
caused by larger electron-phonon coupling for first type of
nanotubes. Nevertheless, to understand details of the effect
of electron–phonon coupling on RBM, additional experi-
mental and theoretical investigations are necessary.
As at low temperature the intensity of the low frequen-
cy component of G– band becomes weaker (Fig. 4), there-
fore, to fit this band with BWF function correctly, we were
guided by some rules, namely, at temperature lowering the
band width and parameter 1/q increase (does not decrease,
at least). These rules were based on detailed temperature
analysis of this band in metallic nanotubes, which was ful-
filled in the reference [44]. As well, for G– bands of
SWNT:DNA films the temperature decrease from 295 to
5 K results in the 7.9 cm–1 upshift for the band fitted with
BWF function and for another band this shift is equal to
4.1 cm–1. Fitting to the G+ band gives the upshift by 1.9
and 2.3 cm–1 for low- and high-frequency Lorentzian
curves, respectively. At 5 K the area of the BWF band de-
creases relatively to room temperature. It should be noted
that the high-frequency spectral shift of G bands observed
at 295 K for SWNT:DNA film versus nanotube bundles is
retained at helium temperature too (Fig. 5). –0.01 cm–1/K
(5–295 K) value of the temperature coefficient of the
SWNT:DNA film is obtained after the determination of the
G+ band shift. The absolute value of the temperature coef-
ficient is slightly larger than the magnitude obtained for
nanotubes in bundles.
We try to determine the magnitude of the spectral split-
ting between two components of the tangential mode for
metallic and semiconducting nanotubes ∆(G+ – G–) and to
compare their temperature dependences. There are two
complications upon these estimations: the first one is
caused by the decrease in accuracy of determining the peak
position of the G– band at low temperature because of
weakening the BWF band intensity, the another results
from the fact that in our samples the peaks of G+ and G–
bands are attributed to an averaged nanotube, and this re-
duces slightly the correctness of these estimations. With
temperature rising from 5 K till 295 K the magnitude of
∆(G+ – G–) for metallic SWNTs increases by 1.9 and
6 cm–1 for nanotubes in bundles and in film with DNA,
respectively. Meanwhile, the magnitude of ∆(G+ – G–) for
semiconducting SWNTs increases by 1.4 cm–1 with the
temperature growth only for SWNT:DNA film, and other
sample shows no appreciable change in this splitting.
These estimations confirm the significant electron-phonon
coupling in metallic nanotubes and coincide with tempera-
ture measurements provided by other authors [15–17].
However, additional experiments with more intensive
Fig. 4. Raman spectra in range of RBM (a) and G mode (b) of
SWNT:DNA film at 5 K (thin curve). Curves described by Lo-
rentzian and BWF (a low-frequency band of G mode) functions
were used to fit the experimental spectra (dashed lines) obtained
at this temperature. Numbers indicated in this Figure close to the
bands denote the value of band peak position and its area (in
brackets). For comparison the Raman spectra of this sample ob-
tained at 295 K were shown.
180180 200200 220220 240240 260260 280280 300300 320320
�������� ****** **
SWNTSWNT:DNA:DNA
295 K295 K
àà
5 K5 K
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Raman shift, cmRaman shift, cm
––11
Raman shift, cmRaman shift, cm
––11
15201520 15401540 15601560 15801580 16001600 16201620
5 K5 K
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1554.11554.1
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1563.71563.7
(1(11)1)
1594.11594.1
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**
**
1599.31599.3
(50)(50)
2.4 cm2.4 cm––11SWNTSWNT:DNA:DNA
295 K295 K
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**
bb
V.A. Karachevtsev and A.Yu. Glamazda
482 Fizika Nizkikh Temperatur, 2010, v. 36, No. 5
BWF band in RR spectra and with individual nanotubes
should be carried out.
Figure 5 presents RR spectra of SWNT:DNA film and
nanotube bundles at 5 K, which permits to compare the
spectra evolution of two samples helium and room temper-
atures (Fig. 1). It is seen that for RBM region the tempera-
ture lowering is accompanied by noticeable changes in the
intensity redistribution among bands of two samples rela-
tively to 295 K and can be mainly explained by transfor-
mation of resonance conditions. G mode region is charac-
terized with an decrease of BWF band intensity, however,
the value of the spectral shift between G+ band peaks of
two samples retains the same as it was observed at 295 K
(Fig. 1). In general, a substitution of the strong interaction
between tubes in bundles with a rather strong of the SWNT
interaction with the polymer does not result in crucial
changes of the nanotube RR spectrum.
Conclusions
The carbon nanotube-DNA interaction results in the fol-
lowing changes in Raman spectrum of this sample relative-
ly to the spectrum of nanotubes in bundles: increasing of
the integral intensity of RBM bands, redistribution of in-
tensities between the bands, which can be explained partly
by transformation of resonance conditions, G band is up-
shifted, and the intensity of the asymmetric band of the
low-frequency component of this band weakens in film.
The temperature lowering from 295 to 5 K is accompa-
nied by the upshift of RBM bands, the magnitude of which
is higher for metallic nanotubes than that for semiconduct-
ing ones. A larger upshift of RBM of metallic nanotubes is
most probably caused by stronger electron-phonon coupl-
ing in these nanotubes. With the temperature decrease the
band width becomes narrower, and some band width
reaches 3 cm–1 at 5 K. The similar spectral evolution is
observed for nanotubes in bundles. Noticeable changes
observed in the intensity redistribution among RBM bands
of two samples at the decrease in T can be mainly ex-
plained by transformation of resonance conditions.
Upon the temperature lowering from 295 to 5 K, the
upshift of bands attributed to G mode is observed for two
samples but its magnitude is different for metallic and se-
miconducting nanotubes. Provided estimations confirm the
significant coupling between electron and this high-fre-
quency phonon in metallic nanotubes. The temperature
coefficient dω/dТ determined by the temperature shift
of G+ band is equal to –0.01 cm–1/K for NT:DNA film and
–0.0083 cm–1/K for nanotubes in bundles. It should be
noted that the spectral shift value between of G+ band
peaks of two samples at 5 K retains the same as it was ob-
served at 295 K
In general, it can be concluded that temperature changes
observed in RR spectra of SWNT:DNA film and nano-
tubes in bundles are similar. It results from the fact that the
strong interaction between tubes in bundles is replaced
with a rather strong SWNT interaction with the polymer.
Acknowledgment
We are grateful to Dr. U. Dettlaff-Weglikowska (Max-
Planck-Institute for Solid State Research) for purified
SWNTs, to PhD. A. Peschanskii (ILTPE) for helpful dis-
cussions and to V. Leontiev for samples preparation. This
work was partially supported by Grants 4950 of the
Science and Technology Center in Ukraine and National
Academy of Sciences of Ukraine.
1. Nanomaterials for Biosensors, C. Kumar (ed.) Wiley-VCH
Verlag GmbH&Co./KGaA (2007).
2. Applied Physics of Carbon Nanotubes, S. Rotkin and S. Sub-
ramoney (eds.) Springer Berlin Heidelberg New York (2005).
3. M.J. O'Connell, P. Boul, L.M. Ericson, Ch. Huffman, Y.
Wang, E. Haros, C. Kuper, J. Tour, K.D. Ausman, and R.E.
Smalley, Chem. Phys. Lett. 342, 265 (2001).
4. M. Zheng, A. Jagota, E. Semke, B. Diner, R. Mclean, S. Lustig,
R. Richardson, and N. Tassi, Nature Mater. 2, 338 (2003).
5. H. Cathcart, S. Quinn, V. Nicolosi, J.M. Kelly, W.J. Blau,
and J.N. Coleman, J. Phys. Chem. C111, 66 (2007).
Fig. 5. Raman spectra of SWNT bundles (bold curve) and
SWNT:DNA film (thin curve) at 5 K: (a) range of RBM and (b)
G mode.
180180 200200 220220 240240 260260 280280 300300 320320
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SWNTSWNT:DNA:DNA
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TT = 5 K= 5 K aa
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Raman shift, cmRaman shift, cm
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SWNTSWNT:DNA:DNA
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––11
Raman spectroscopy of DNA-wrapped single-walled carbon nanotube films at 295 and 5 K
Fizika Nizkikh Temperatur, 2010, v. 36, No. 5 483
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