Download Wavelength-scaling and length dependence of ultrafast optical

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LENGTH DEPENDENCE OF ULTRAFAST OPTICAL
NONLINEARITIES IN VERTICALLY ALIGNED MULTIWALLED
CARBON NANOTUBE FILMS
Hendry Izaac Elim (Elim Heaven),1#,2 Yanwu Zhu,3 and Chorng-Haur Sow4
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Nanomaterials for Photonics Nanotechnology Laboratory (Lab. N4PN),
Physics Department, Faculty of Mathematics and Natural Sciences,
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Research Center of Nanotechnology and Innovative Creation (PPNRI-LEMLIT),
Pattimura University, Ambon, Indonesia 97233
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Department of Materials Science and Engineering, University of Science and
Technology of China, 96 Jin Zhai Rd., Hefei 230026
4
Department of Physics, National University of Singapore
2 Science Drive 3, Singapore 117542, Republic of Singapore
#Email: [email protected]; [email protected]
Telp. (+62-81247524158)
Abstract
Tube-length-dependent optical nonlinearities of vertically aligned multiwalled
carbon nanotube (MWNT) films have been investigated by Z-scan and transient
absorption measurements with femtosecond laser pulses in the near-IR spectral range
from 780 to 1550 nm. Both saturable absorption and optical Kerr nonlinearity are found
to be dependent on excitation wavelength and tube length, indicating that band-filling in
semiconducting tubes and longitudinal surface plasmon resonance in metallic tubes play
an important role, respectively. The 1-ps relaxation time for the nonlinear response of the
MWNT films, however, is independent of tube length, as evidence from dissipation of
excited energy in the radial direction. Such ultrafast vertically length-dependent in CNT
can significantly contribute to fabricate vertically nanochip in various types of integrated
nanodevice just like a creation of living 3D fish bone (a kind of cowfish).
Keywords: Carbon nanotubes, Nonlinear Optics, Nanochip, Ultrafast
Introduction
Recently, ultrafast nonlinear-optical (NLO) responses of single-wall carbon
nanotubes (SWNTs) in suspensions and films have received increasing attention.1-6 At
resonant band (0.8-1.1 eV) of the lowest inter-band transitions of semiconducting
SWNTs, a strong transient photo-bleaching has been observed with femtosecond laser
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pulses. The strongest imaginary part of the third-order NLO susceptibility, (3) has been
determined as large as 10-7 to 10-6 esu.5,7 Moreover, at the second lowest inter-band
transitions (~1.6 eV) of semiconducting electronic structure in SWNTs, saturable
absorption has also been detected using femtosecond laser pulses. In contrast, photoinduced absorption has been measured under off-resonant conditions of SWNTs. The
band-filling effects have been identified as the mechanism responsible for the resonant
saturable absorption, while the off-resonant photo-induced absorption is attributed to a
global red-shift of the -plasmon resonance.3 These investigations have been so far
focused on the ultrafast NLO responses of SWNTs.
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Experimental Method
MWNTs studied in our experiment were grown on quartz substrate. The MWNTs
were prepared by a method of plasma-enhanced chemical vapor deposition. The details
on the preparation were reported elsewhere.10-11 Figures 1(a)-(c) show high magnification
scanning electron microscopy (SEM) images of the films with three different lengths of
MWNTs. As shown by these images, the nanotubes were grown mainly in the direction
perpendicular to the surface of the quartz substrate. As the MWNTs were grown longer,
the higher order in alignment could be evident. There was no significant difference in the
outer-layer diameter (~20 nm) of nanotubes for the three films. Both linear optical and
NLO properties of the MWNT films were examined as the light propagates in the axis
perpendicular to the quartz substrate (or normal incidence on the film) at room
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temperature. In Fig. 1(d), the near-IR spectra of the MWNT films with L = 4 m, 7 m
and 12 m show a feature centered at ~1100 nm, which is assigned to the second lowest
interband transitions in semiconducting MWNTs. It unambiguously indicates the
existence of semiconducting nanotubes in the films, though they are predominated by
metallic nanotubes. The feature decreases to a minimum at ~1400 nm, where the
appearance of complex transitions is noticeable, reflecting the complex interplay of
various chiral indices (n, m) for different sizes and structures of nanotubes. As the
wavelength increases further, the absorbance arises due to be resonant with the lowest
interband transitions.
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Results and Discussions
Figure 2(a) illustrates a relationship inspiration of a 3D bone of fish called as
“poro bibi” fish (a type of cowfish living in east Africa) in Ambon, Indonesia with an
interaction of elastically graphene like structure associated with man-made interaction
between 3D vertically aligned MWNTs and laser beams with two different beam waists.
We thought in our opinion as the aim of such good illustration was that the created 3D
structure of living creature had been there in nature before the MWCNT structure was
discovered by man (Ijima, ~1991 at NEC company, Japan). Moreover, this illustration is
necessary to open the insight of many different physicist or multidisciplinary scientists to
elaborate and extend their work in the near future as an integrated research.
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Conclusion
In summary, we have presented, for the first time, the wavelength and tube-length
dependence of NLO properties in vertically aligned MWNT films, determined with
femtosecond Z-scans and pump-probe measurements. The wavelength and tube-length
dependence are attributed to the semiconducting and metallic properties of MWNTs.
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Acknowledgement
We would like to thank the support of H.I. Elim current research works from a fund
granted by “Riset Unggulan Daerah” grant no. 1039/UN13/SK/2015, Pattimura
University,
Indonesia
about
superfibers
project.
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References
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Figure Captions:
Fig. 1 (Color online) SEM images of aligned MWNT films with average tube length of
(a) 4 m, (b) 7 m, and (c) 12 m. (d) Absorption spectra provided with the
whole UV-VIS-NIR spectra.
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Table Captions and Table
Table 1. Types of carbon nanotubes (CNT) and their nonlinear optical properties.
Types
Nonlinear
Ultrafast
Behavior
Response
Single Walled Carbon Nanotubes (SWCNT)
……..
……..
Multiwalled Carbon Nanotubes (MWCNT)
……..
……..
Hybrid Polymer CNT
……..
……..
Hybrid inorganic nanoparticles coated CNT
……..
……..