Supplementary information for “In-situ optical emission study on the role of C2 in
the synthesis of single-walled carbon nanotubes”
David Edmond Motaung
National Centre for Nano-Structured Materials, Council for Scientific and Industrial
Research, South Africa
Mathew Kisten Moodleya)
National Centre for Nano-Structured Materials, Council for Scientific and Industrial
Research and
School of Physics, University of the Witwatersrand
E Manikandan
National Centre for Nano-Structured Materials, Council for Scientific and Industrial
Research
Neil J Covilleb)
School of Chemistry, University of the Witwatersrand
S1.1 Target temperature calculations
The rise in the target temperature when it absorbs a pulsed nanosecond laser can be
estimated by :1
T  T0 
1  R  E
 C pVHAZ
(1.1)
and
VHAZ   w2  t pulse
(1.2)
and

K
C p
(1.3)
VHAZ in eqn. 1.3 gives an estimate of the heat volume. The meaning of the symbols and
their values are: w is the radius of the laser beam at the target surface in metres, ρ is the
density of graphite in kg.m-3, Cp is the heat capacity, t is the laser pulse width in seconds.
K is the thermal conductivity, E is the energy in joules, To is the initial temperature
which is equal to the furnace temperature and R is the reflectivity of the target. The
values for the density, heat capacity and thermal conductivity are those of graphite and
were taken from www.azonano.com2. Therefore, using w= 1.5 x 10-3 m, ρ =2000 kg/m3,
Cp=830 J/kg.K, t=15 x 10-9 s, K= 470 W/m.K, E= 1.07 J, T0= 1273 K, R=0.01. We get
VHAZ = 1.5 x 10-11 m3. The temperature rise of the target is T= 4.508 x104 K or about
45 000 K as indicated in the main article. The laser energy is absorbed within 15 ns. So
the heating rate would be 3 x 1012 K/s. We estimate that the volume of material ejected in
a
one laser shot equals VHAZ and from this we deduce for carbon, this equates to about 1.5
x1018 atoms. Hence our estimate is 1018-1019 atoms as stated in the main article.
S1.2 Plasma expansion velocity
We use the following equation to estimate the plasma expansion velocity in m.s-1 :3
v
2 kT
(1.4)
M
Where η is the number of internal degrees of freedom and can be between 2.53 and 3.28.
We use η =2.5. M is the mass of the species. T is the temperature in Kelvin and k is the
Boltzmann constant. For a single carbon atom, at T= 10000 K, v= 5.886 x 103 m.s-1≈5.9
km.s-1.
S1.3 Why do we neglect the effect of Doppler broadening?
The effect of Doppler broadening on the emission lines of CII was neglected. Doppler
broadening is estimated from:4
a
Corresponding authors a) MKMoodley@csir.co.za and b) Neil.Coville@wits.ac.za
 D 
V
c
(1.5)
Where c is the speed of light and  is the emission line of an atom or ion. In our case we
choose CII at 283.7 nm.
Using the velocities obtained from eqn. 1.4, we find that  is = 5.566 x 10-12 m. The
minimum resolving limit of the Andor spectrograph is:
 

5.104
(1.6)
Using the emission line of CII ion at 283.7 nm, we find that  = 5.674 x 10-12 m, which
is slightly larger than D . Therefore the effect of Doppler broadening would be not be
able to be resolved with the Andor ME5000 spectrograph used in this study.
S1.4 XRD of the target
XRD measurements were made on the target used in this study. A Panalytical X’pert
PRO PW 3040/60 x-ray diffractometer with a Cu K ( = 0.154 nm) monochromated
radiation source, operating at 45.0 kV and 40.0 mA were employed to characterize the
materials. XRD data were collected in the 2 ranging from 10 to 100 with a step size of
0.02.
The target was already subjected to a temperature of 1273 K in argon gas. It was allowed
to cool to room temperature. XRD pattern of Figure suppXRD identifies the presence of
Ni3C [JCDPS file: 00-06-0697], graphite [JCDPS file: 00-01-0646], YC2 [JCDPS file:
00-82-0628] and Y2O3 [JCDPS file: 00-41-1105]. Yttrium may have oxidized at room
temperature. No oxides of nickel were detected.
Figure S1. XRD pattern of the target used for the synthesis of SWCNTs.
1
C. P. Grigoropoulos, in Laser Ablation and Desorption, 1stth edition, edited by J. C.
Miller (Academic Press, San Diego, 1998), Vol. 30, Chap. 4, p.173.
2
http://www.azom.com/details.asp?articleid=1630
S.S. Harilal, R.C. Isaac, C.V. Bindhu, V.P.N. Nampoori, and C.P.G. Vallabhan, J. Appl.
Phys. 81, 3637 (1997).
3
S. S. Harilal, R. C. Isaac, C. V. Bindhu, V. P.N. Nampoori, and C.P.G. Vallabhan, J.
Appl. Phys. 81, 3637 (1996).
4
Andor ME 5000 Echelle Spectrograph Operating Manual (2007)