Optical limiting properties of metal nanowires

Article abstract of DOI:10.1063/1.2208549

Metal (Cu, Co, Ni, Pd, Pt, and Ag) nanowires (MNWs) have been produced using anodic aluminum oxide as template. The grown MNWs are characterized by scanning electron microscopy, x-ray diffraction, transmission electron microscopy, and electron diffraction

Full text of DOI:10.1063/1.2208549

Optical limiting properties of metal nanowires
Hui Pan, Weizhe Chen, Yuan Ping Feng, Wei Ji, and Jianyi Lin
Citation: Applied Physics Letters 88, 223106 (2006); doi: 10.1063/1.2208549
View online: http://dx.doi.org/10.1063/1.2208549
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APPLIED PHYSICS LETTERS 88, 223106 ͑2006͒
Optical limiting properties of metal nanowires
a͒
Hui Pan, Weizhe Chen, Yuan Ping Feng, and Wei Ji
Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore
b͒
Jianyi Lin
Institute of Chemical and Engineering Sciences, 1 Pesek Road, Jurong Island, Singapore 627833, Singapore
͑
Received 27 November 2005; accepted 4 May 2006; published online 31 May 2006͒
Metal ͑Cu, Co, Ni, Pd, Pt, and Ag͒ nanowires ͑MNWs͒ have been produced using anodic aluminum
oxide as template. The grown MNWs are characterized by scanning electron microscopy, x-ray
diffraction, transmission electron microscopy, and electron diffraction. The optical limiting
properties of the MNWs are also studied and results obtained at 532 and 1064 nm indicate that
MNWs have broadband optical limiting capability and the optical limiting performances of some
MNWs are comparable to or better than that of carbon nanotubes. It was found that the nonlinear
response of MNWs is dominated by nonlinear scattering. © 2006 American Institute of Physics.
͓
DOI: 10.1063/1.2208549͔
One-dimensional nanostructured metals have attracted
great attention because of their potential applications in
ultrahigh-density magnetic recording, ultrafast optical
doubled Q-switched Nd:YAG ͑yttrium aluminum garnet͒ la-
ser ͑Spectra Physics DCR3͒, at two different wavelengths
͑532 and 1064 nm͒. The laser pulses were produced at 10 Hz
repetition rate and were focused on the central point of the
quartz cell with a spot radius of 30 ␮m. The nonlinear scat-
tering measurements were conducted with the detector set at
various angles from the propagation axis of the transmitted
laser pulses. An aperture was placed in front of the detector.
The radius of the aperture was adjusted so that a solid angle
for collecting the scattered light was 0.015 rad.
1
,2
switching, and microwave devices. In many of these appli-
cations, nonlinear optical effects may play an important role.
An optical limiter exhibits the following transmission behav-
ior, which is a function of the fluence. That is, the output
fluence is proportional to the input fluence at low input flu-
ence but approaches a constant after the input fluence be-
comes greater than the limiting threshold. Recently, strong
optical limiting effects were observed in carbon nanostruc-
All the MNWs tested were grown from identical AAO
template which was prepared following the modified two-
3
,4
5–7
tures, including C ,
carbon nanotubes,
and carbon
6
0
8
,9
10,11
1
5
black suspension ͑CBS͒. Semiconductor-doped glasses
and semiconductor nanoparticle solutions
step anodization. Briefly, the pure Al sheet ͑99.999%͒ was
anodized at 40 V in an oxalic acid solution of 3 wt % at
room temperature. After removing the alumina, the ordered
pore arrangement was achieved during the second anodiza-
tion. dc electrodeposition was performed at an applied volt-
age of 1.5 V and the temperature of 25 °C. For Ni nanowire
deposition, 240 g/l NiSO ·7H O with the pH value of 2.5
1
2–14
have also been
investigated for the nonlinear optical applications. On the
other hand, metal nanowires ͑MNWs͒ have been grown and
their applications in high-density storage devices have been
1
5,16
explored.
However, to the best of our knowledge, the
optical limiting property of the MNWs has not been studied.
Besides the scientific interest in mechanisms of nonlinear
optical properties in such nanosystems, study of optical lim-
iting properties of the MNWs may lead to cheap and efficient
optical limiters. In this work, the nonlinear optical properties
of the MNWs are studied and their potential applications as
optical limiters are explored.
4
2
was used. Other metal nanowires were prepared at the same
electrodeposition conditions as the Ni deposition, using a
corresponding sulfate or chloride electrolyte. A total of six
MNW samples were prepared and studied, which are Ni
nanowires ͑NiNWs͒, Pd nanowires ͑PdNWs͒, Pt nanowires
͑PtNWs͒, Ag nanowires ͑AgNWs͒, Cu nanowires ͑CuNWs͒,
Uniform-sized MNWs, i.e., Cu, Co, Ni, Pd, Pt, and Ag
nanowires, were produced by electrochemically depositing
the metal into the anodic aluminum oxide ͑AAO͒ template
that had the uniform pore structures. The morphology and
crystalline structure of the deposited MNWs were studied by
scanning electron microscopy ͑SEM͒ ͑JEOL JSM-6700F͒
and x-ray diffraction ͑XRD͒ ͑Brucker AXS D8͒. The optical
absorption spectra of the MNWs suspended in water and
contained by 1-cm-thick quartz cells were measured in the
UV-visible region between 200 and 1100 nm on Shimadzu
UV2101. The optical limiting properties of the MNWs sus-
pended in water and contained by 1-cm-thick quartz cells
were studied by fluence-dependent transmission measure-
ments, using 7-ns light pulses generated from a frequency-
and Co nanowires ͑CoNWs͒. For optical measurements, the
MNWs were totally liberated from AAO template ͑using 1M
NaOH solution͒, cleaned in distilled water till pH=7, and
suspended in distilled water. All six samples have similar
diameter and length because of identical AAO template and
deposition conditions.
Figure 1 shows the SEM image of a typical MNW
sample embedded in AAO template. The AAO template was
partly removed so that the embedded MNWs become ob-
servable. The diameter and length of nanowires are approxi-
mately 50 nm and 30 ␮m, respectively. Figure 2͑a͒ displays
the XRD patterns of the MNWs. The Ni, Co, and Ag nano-
wires each exhibits only one diffraction peak at the orienta-
tion along ͓220͔, ͓100͔, and ͓220͔, respectively. For Pd, Pt,
and Cu nanowires, the characteristic peaks are observable in
their XRD patterns. The high intensity and small peak width
indicate good crystallinity of the nanowires.
a͒Author to whom correspondence should be addressed; electronic mail:
phyjiwei@nus.edu.sg
b͒
Electronic mail: linគjianyi@ices.a-star.edu.sg
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003-6951/2006/88͑22͒/223106/3/$23.00 88, 223106-1 © 2006 American Institute of Physics
30.113.86.233 On: Wed, 10 Dec 2014 19:07:27
0
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223106-2
Pan et al.
Appl. Phys. Lett. 88, 223106 ͑2006͒
FIG. 1. The SEM images of MNWs grown on AAO template with the
alumina matrix partially removed. The inset shows the MNWs after the
AAO was totally removed. The scale bar in the inset is 1 ␮m.
In the optical absorption spectra shown in Fig. 2͑b͒, ab-
sorption bands around 250–600 nm are noticed, particularly
for Co, Cu, and Ag nanowires. There is a dip at 320 nm
͑
3.8 eV͒ in the absorption spectrum for Ag nanowire solu-
17
tion. According to Boyd et al., this is photon-induced Ag-
bulk-plasmon emission. The broadband of the absorption
around 430 nm ͑2.9 eV͒ in the Ag spectrum is therefore at-
1
8
tributed to surface plasmon resonance and its long-
wavelength tail is due to d-sp interband transitions. Similar
1
7
assignments can be applied to the absorption bands for Cu
1
8
and Co nanowires. The optical absorption is weak for Ni,
Pd, and Pt nanowire solutions in the entire range between
3
00 and 1100 nm. It seems that the latter group of metals has
1
9
higher values of work function and first ionization potential
FIG. 3. The optical limiting response of the MNWs measured with 7-ns
laser pulses at ͑a͒ 532 nm and ͑b͒ 1064 nm wavelengths.
and their plasmon resonance would be in the shorter wave-
length range.
2
0
To study the nonlinear optical ͑NLO͒ response of the
MNWs, the fluence-dependent light transmission measure-
ments were conducted on the six samples under the same
conditions at two wavelengths, 532 nm ͓see Fig. 3͑a͔͒ and
decreases as the incident fluence increases, a typical limiting
property for all nanowires. The limiting threshold, defined as
the incident fluence at which the transmittance falls to 50%
1
064 nm ͓see Fig. 3͑b͔͒, respectively. Nevertheless the con-
5
of the normalized linear transmittance, is different for dif-
centration of the MNWs in the tested solutions could be
different, adjusted in such a way that their linear transmit-
tances are all 80%. In Fig. 3͑a͒ the energy transmittance at
ferent samples. The limiting threshold at 532 nm is 0.9, 1.2,
2
1
.3, 1.7, 2.5, and 4.2 J/cm for Pd, Ni, Pt, Ag, Cu, and Co
nanowires, respectively. The nonlinear optical limiting re-
sponses of Pd, Ni, Pt, and Ag nanowires are comparable to or
slightly better than those of single-wall and multiwall carbon
2
the light fluences less than 0.1 J/cm is constant for all the
2
samples. However, in excess of 0.1 J/cm , the transmittance
6
,21
nanotubes
͑MWCNTs͒ ͑Table I͒, whereas CuNWs and
CoNWs are slightly poorer. Figure 3͑b͒ shows similar optical
limiting properties of MNWs at 1064 nm. The optical limit-
ing of Pd, Pt, Ni, and Ag nanowires is better than or compa-
rable to those of carbon nanotubes at 1064 nm, whereas Cu
TABLE I. The limiting threshold of the MNWs at 532 and 1064 nm. The
limiting threshold of MWCNT is also listed for comparison.
Samples
Fth at 532 nm ͑J/cm2͒
Fth at 1064 nm ͑J/cm2͒
PdNW
NiNW
0.9
1.2
1.3
1.7
2.5
4.2
8
8
PtNW
8
AgNW
CuNW
CoNW
MWCNT
10.8
Ͼ30
Ͼ30
a
a
1.0
10.0
FIG. 2. ͑a͒ The XRD patterns of the MNWs and ͑b͒ the optical absorption
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a
spectra of the MNWs.
Reference 19.
30.113.86.233 On: Wed, 10 Dec 2014 19:07:27
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Pan et al.
Appl. Phys. Lett. 88, 223106 ͑2006͒
limiting observed in the MNWs. On the other hand, Pd and
Pt are expected to have optical absorption only at shorter
wavelengths ͑Ͻ200 nm͒ due to higher surface plasmon reso-
nance and their nonlinear limiting is more evident, slightly
better than carbon nanotubes. For the nonlinear limiting of
MNWs at 532 nm ͑2.32 eV͒ laser incidence, some d-sp in-
terband or near-Fermi-level intraband transitions may be-
come possible and other mechanisms than nonlinear scatter-
ing may also contribute to the nonlinear limiting.
Nevertheless the fact that MNW samples have similar trend
of the variation in optical limiting response in the two laser
energies ͑532 and 1064 nm͒ appears to indicate that nonlin-
ear scattering is the dominant mechanism.
In summary, we have grown high-quality MNWs, in-
cluding Ni, Co, Cu, Pt, Pd, and Ag nanowires, using AAO
template. XRD patterns illustrated that the Ni, Co, and Ag
nanowires are single crystals while Pt, Pd, and Cu nanowires
are polycrystalline. The optical limiting properties of Pt, Ni,
Pd, and Ag nanowires are better than those of Cu and Co
nanowires. With the observation of optical limiting both at
532 and 1064 nm, nonlinear scattering is believed to make a
dominant contribution to the limiting performance of
MNWs.
FIG. 4. Nonlinear scattering measured with 532-nm, 7-ns laser pulses at a
forward angle of 10° with a solid angle of 0.015 rad. The inset shows the
scattered energy of the NiNW and the MWCNT as a function of the input
fluence at various forward angles.
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2
at 1064 nm radiation is 8, 8, 8, and 10.8 J/cm for Pd, Ni, Pt,
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