Metal sphere photonic crystals by nanomolding [16]

Full text of DOI:10.1021/ja005733y

J. Am. Chem. Soc. 2001, 123, 763-764
Metal Sphere Photonic Crystals by Nanomolding
763
Lianbin Xu,† Weilie Zhou, Mikhail E. Kozlov,
,‡
‡
§,|
Ilyas I. Khayrullin,§ Igor Udod, Anvar A. Zakhidov,
Ray H. Baughman,* and John B. Wiley*
,|
§
§
,§
,†,‡
Department of Chemistry and the
AdVanced Materials Research Institute
UniVersity of New Orleans
New Orleans, Louisiana 70148-2820
Honeywell Int., Materials Laboratory
Morristown, New Jersey 07962-1021
New Jersey Institute of Technology
Newark, New Jersey 07102-1982
Figure 1. Sequential methods for the preparation of metal nano-
sphere arrays (a) in a nonconductive matrix and (b) in a conductive carbon
matrix.
In the first method (Figure 1a), a sequence of electrochemical
and chemical steps was used to prepare metal sphere arrays within
a nonconductive matrix. Initially, an fcc porous opal slab
containing 290 nm diameter spheres was electrochemically
infiltrated11 with nickel. After removal of the opal template with
a 2% HF solution, the nickel mesh was slowly oxidized in air at
550 °C for 8 h (Figure 2a). The resulting poorly conducting nickel
oxide mesh was then used as a nanomold for the electrochemical
growth of a gold nanosphere array. Finally, the NiO template
was removed in dilute sulfuric acid to produce an ∼30 µm thick
array of gold nanospheres (Figure 2b,c).
ReceiVed October 25, 2000
Crystals of nanosize metal spheres have potential applications
1,2
as diverse as photonics, thermoelectrics, and magnetics. Though
methods exist for the chemical synthesis of metal nanospheres3
and the self-assembly of these spheres into submicron thick
1
crystals, the fabrication of large crystals has been illusive. In
contrast, centimeter-size face-centered-cubic (fcc) crystals of SiO
2
In the second approach (Figure 1b), periodic nanosphere arrays
were fabricated by the infiltration of molten metals into carbon
inverse opals made by the phenolic process (Figure 2d). This
nanospheres (porous opals) can be routinely fabricated by sphere
4
self-assembly. Since no methods are available for growing large
6
crystals of metal nanospheres, we have developed a different
melt infiltration (at close to the melting point and pressures of
5
-12
approach which builds upon recent success
cation of inVerse opals. Since these inverse opals replicate the
void space of ordinary porous SiO opals (Figure 1a), we can
in the fabri-
1
-2 kbar) resulted in nanosphere crystals for elemental metals
and semiconductors (Pb, Bi, Sb, and Te) and thermoelectric alloys
Bi-Sb, Bi-Te, and Bi-Te-Se). A typical SEM image of a
2
(
use them as nanomolds for “casting” crystals of metal nano-
spheres. Herein we present two methods based on this strategy
for the fabrication of large crystals of metal nanospheres, including
NaCl-type crystals based on two different size nanospheres. This
NaCl structure was previously obtainable only for metal sphere
sizes an order of magnitude smaller than the photonic crystal
range.13
fracture surface (Figure 2e) for centimeter dimension sample
shows that the melt-infiltration results in a high-fidelity inverse
replica of the carbon matrix, which is itself a high-fidelity inverse
2
replica of the original SiO opal. Since the minimum radius of
the infiltrated material decreases with pressure, the applied
pressure during solidification can be used to control the inter-
connections between spheres, and thereby the electrical and
thermal transport properties of the sphere array. Moreover, the
*
To whom correspondence should be addressed. E-mail: jwiley@uno.edu
and ray.baughman@honeywell.com.
†
carbon of the inverse replicas either substantially fills the void
Department of Chemistry, University of New Orleans.
‡
6
Advanced Materials Research Institute, University of New Orleans.
2
space of the original SiO opal or coats only the internal surfaces.
§
Honeywell Int.
In this latter case, the void space in the carbon replica comprises
two separate labyrinths (percolated spherical voids and a perco-
lated network of octahedral and tetrahedral void spaces). SEM
measurements (Figure 2f) show that both of these labyrinths can
be filled by melt infiltration at kilobar pressure to make the
nanosphere version of a NaCl-type structure.
|
New Jersey Institute of Technology.
(
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Since these metal sphere arrays are metallodielectric photonic
crystals, new properties should arise which are absent for dielectric
(
(
photonic crystalsslike the plasmon gap observed in the micro-
9
1
1
65.
14,15
wave or infrared
for metal meshes. These fabrication methods
(
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(
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antimony inverse opal (made by infiltrating antimony into a SiO
opal, and extracting the SiO ) with bismuth, we obtained a
999, 121, 7957-7958.
(
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1
0.1021/ja005733y CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/09/2001

764 J. Am. Chem. Soc., Vol. 123, No. 4, 2001
Communications to the Editor
Figure 2. (a) SEM of nickel oxide template used in electrochemical nanomolding, (d) fracture-surface image of a fcc phenolic inverse opal, which in
the carbonized state is used as a template for nanomolding by the melt process, (b, c, e, f) fracture-surface SEM images of fcc sphere arrays made by
replicating the void space of a porous SiO opal and then replicating the void space of the resulting replica. In panels b and c, arrays of gold spheres
2
were made using two electrochemical replication processes. In panels e and f, sphere arrays were made by replicating the void space of a carbon inverse
opal by melt infiltration of tellurium (e) and bismuth (f). In panel f, large metal spheres occupy the corners of the unit cell face (indicated by the square)
and smaller metal spheres occupy (or fractionally occupy) the sites between the large spheres, as in the NaCl structure. Stacking faults on close-packed
planes in the original SiO
2
opal are replicated in the fabricated sphere arrays, bringing (100) and (111) planes into near coincidence in panels b and e.
The length scales are 1 µm except for panels b and f, which are 5 µm and 100 nm, respectively.
thermoelectric “hyper alloy” in which a fcc array of Bi spheres
are in an antimony matrix. By applying similar methods to
optimally selected thermoelectrics and to combinations of hard
and soft ferromagnets, it may be possible to engineer high-
efficiency thermoelectrics and magnets with high-energy storage
capabilities.
(
16) Note Added in Proof: (a) In November 2000, a similar approach was
used for the preparation of ordered hollow titania spheres, see: Rengarajan,
Acknowledgment. Work supported by the Department of Defense
(DARPA MDA972-97-1-0003 and DAAB07-97-C-J036).
R.; Jiang, P.; Colvin, V.; Mittleman, D. Appl. Phys. Lett. 2000, 77, 3517-
3
519. (b) Analogous electrochemical strategies have been used for the
preparation of one-dimensional porous membranes, see: Hoyer, P.; Masuda,
H. J. Mater. Sci. Lett. 1996, 15, 1228-1230.
JA005733Y