REVIEW

Block Copolymers as a Tool

for Nanomaterial Fabrication**
By Massimo Lazzari*
and M. Arturo López-Quintela*

In this review the latest developments regarding the use of self-assembled copolymers
for the fabrication of nanomaterials will be presented and their real potential evalu-
ated. Most of the strategies reported so far are herewith classified under two main
approaches: a) use of block copolymers as nanostructured materials, either ªas they
areº or through a selective isolation of one or more component blocks, and b) as tem-
plates for the synthesis of metallic or semiconducting nanomaterials. The problems of
the orientation and large-scale order of self-organizing block copolymer mesophases
will be also introduced, due to their importance as a route towards further improve-
ments of the nanofabrication means.

1. Introduction mand of the microelectronic industries, ranging from milling

techniques to non-traditional photolitographic and chemical
The fabrication of systems having characteristic dimensions methods, with a strong prevalence of methods based on tem-
smaller than 100 nm requires the ability to obtain, control, plate synthesis.[1] However, their main weakness still remain
manipulate, and modify structures at the nanometer length in the difficult and poor control of the final morphology of the
scale, a step beyond microtechnology. It is well established produced nanostructures. In such a sense polymers represent
that microstructured materials may be industrially prepared, ideal nanoscale tools,[2] not only due to their intrinsic dimen-
e.g., by photolithography, but as the demand for smaller and sions, ease of synthesis and processing, strict control of archi-
smaller feature sizes always impose to lower the current state- tecture and chemical functionality, but also because of their
of-the-art limits, further steps towards miniaturization have peculiar mesophase separation both in bulk and in solution,
been raised in the last decade, focusing on different and more particularly in the case of block copolymers (BCs).[3±5]
suitable strategies, which are based on both ªtop±downº and BCs may be considered as two or more chemically homoge-
ªbottom±upº approaches. Many methods for the fabrication neous polymer fragments, i.e., homopolymer chains, joined to-
of nanomaterials have been proposed, mainly to meet the de- gether by covalent bonds to form more complex macromole-
cules such as linear di-, tri-, or multiblock copolymers, and
± nonlinear architectures such as multiarm, starblock, or graft
[*] Dr. M. Lazzari[+]
Dept. of Chemistry IPM
copolymers. In the frequent case of immiscibility among the
University of Torino constituent polymers, the competing thermodynamic effects
Via P. Giuria 7, I-10125 Torino (Italy) give rise to different kind of self-assembled morphologies, de-
E-mail: massimo.lazzari@unito.it
pending both in structural and dimensional terms on composi-
Prof. M. A. López-Quintela
Dept. of Physical Chemistry tion, segmental interaction, and molecular weights, and hav-
University of Santiago de Compostela ing periodicity suitable for application in nanotechnology.[6]
E-15782 Santiago de Compostela (Spain)
E-mail: qfarturo@usc.es
The existence of some morphologies can be theoretically pre-
[+] Current address: Magnetism and Nanotechnology Laboratory, Institute dicted within the self-consistent field theory,[7] on the basis of
of Technological Investigations, University of Santiago de Compostela, the volume fraction of the components, the number of seg-
E-15782 Santiago de Compostela, Spain. E-mail: qflzzmsm@usc.es ments in the copolymer, and the Flory±Huggins interaction
[**] Our own activities in the field are financed by the Ministerio de Ciencia y
Tecnologia. (MAT2002-00824: Synthesis and properties of 1D, 2D, and 3D
parameter, as is the case for the spherical, cylindrical, gyroid,
magnetic nanomaterials). M. L. also acknowledges the financial support and lamellar phases, which have been observed in the simplest
from the European Union for his stay at the University of Santiago amorphous diblock copolymers. Particularly in the case of
(MCFI-2001-0837: Polymeric membranes with tunable nanochannels for
the electrodeposition of metal nanowires) and the University of Torino more complex systems, differences from the theoretical pre-
for conceding research leave. dictions can, however, be expected, mainly because of chain

Adv. Mater. 2003, 15, No. 19, October 2 DOI: 10.1002/adma.200300382 Ó 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1583
 M. Lazzari, M. A. López-Quintela/Block Copolymers for Nanomaterial Fabrication
REVIEW

fluctuations and conformational block asymmetries. Also for

this reason, more recent efforts have focused on ordered
structures obtained from BCs having both rigid and flexible
segments,[8] and also from triblock and even tetrablock co-
polymers, with the observation of a series of novel and uncon-
ventional morphologies such as zig±zag,[9] core±shell double
gyroid,[10] spheres or rods between lamellae,[11] helices around
cylinders,[12] and hexagonal double[10] or triple[13] coaxial cy-
linder structures. A few of these morphologies, the ones most
frequently used for nanofabrication, are illustrated schemati-
cally in Figure 1.
Moreover, separation and orientation of domains are also
influenced, especially in thin films, by surface±interfacial in-
teractions as well as by the interplay between structural peri-
odicity and film thickness.[14] Such molecular self-assembly of Fig. 1. Sketches of equilibrium morphologies from BC self-assembly, among the
block copolymers therefore allows one to obtain in a simple most frequently used for nanofabrication. For diblock copolymers in bulk:
manner a large variety of highly regular mesostructures with- body-centered cubic-packed spheres (1), hexagonally ordered cylinders (2),
lamellae (3). For triblock copolymers: lamellae (4), hexagonal coaxial cylinders
out any direct human intervention, in a way similar to pro- (5), spheres between lamellae (6). For amphiphilic BCs in solution: spherical
cesses occurring commonly throughout nature.[15] micelles (7), and cylindrical micelles (8). Periodicities, or micellar dimensions,
are in the range 10±100 nm.
The potential technological application of such variety of
mesostructures, and particularly of those formed in the case
of thin films, can be easily appreciated by non-specialists alike use of BCs as a tool for the fabrication of nanomaterials are
and has been widely recognized, e.g., since the first successful presented, paying also attention to the possible application of
attempts to use self-assembly strategy for the preparation of amphiphilic BCs (Fig. 1), i.e., copolymers having both hydro-
membranes with tunable nanochannels[16] and the early block philic and hydrophobic blocks.[18] Nanomaterial synthesis is
copolymer-based nanolithography,[17] but only partially ex- herewith considered in its broader sense with the aim to in-
plored. In this review, the recent developments regarding the clude the most diverse aspects, from the direct use of self-as-

Massimo Lazzari studied Chemistry at the University of Torino (Italy) from 1986 to 1990. Dur-
ing the following years, his research focused on the characterization of copolymers (EnichemÐ
Research Centre of Mantova, Italy). He did his Ph.D. with Prof. O. Chiantore. After two years
postdoctoral work with Prof. K. Hatada at the Osaka University (Osaka, Japan), where he
learned the secrets of anionic polymerization, he joined the Group of Polymeric Materials at the
University of Torino in 1998, working on the characterization and degradation of complex
polymer systems. He is currently at the University of Santiago, Laboratory of Magnetism and
Nanotechnology (Santiago de Compostela, Spain) as visiting Professor. His current research
interests are focused on the synthesis and controlled degradation of self-assembling copolymers,
with special attention on their use as templates for the fabrication of metal nanomaterials.

M. Arturo Lopez-Quintela studied Chemistry at the University of Santiago de Compostela

(Spain) from 1970 to 1975. After finishing his PhD in chemical kinetics, his research focused on
chemical reactions in non-homogenous media. After postdoctoral work in Germany at the Max-
Planck-Institut für Biophysikalische Chemie, Göttingen, and at University of Bielefeld (1980-84)
he came back to the University of Santiago de Compostela as Professor of Physical Chemistry.
In collaboration with Prof. J. Rivas from the Applied Physics Department, he created a Labora-
tory of Nanotechnology in 1988. In 1990 and 1991 he spent several months at the Max-Planck-
Institut für Metallforschung, Stuttgart, and at the Centre for Magnetic Recording Research,
UCLA, USA, working in hard and soft magnetic nanomaterials. In 2001±2002 he spent a sab-
batical year in Japan at the Yokohama National University (Prof. Kunieda) and at the Research
Center for Materials Science (Prof. Imae) working in phase diagrams and microstructure of
diblock copolymers and surfactants, and incorporation of nanoparticles into dendrimers. His
current research interests are focused on the synthesis of magnetic nanomaterials, using different
kinds of templates, by chemical and electrochemical methods.

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M. Lazzari, M. A. López-Quintela/Block Copolymers for Nanomaterial Fabrication

REVIEW
sembled nanostructures, to processes based on BCs either in 2.1. Polymeric Nano-objects
solution or as thin films for the fabrication of nanodevices or
of metallic or semiconducting nanostructures, through the Different types of self-assembling BCs have been used to
more general preparation of polymeric nano-objects as prepare individual polymeric nano-objects, with each method
spheres, rods, or tubes. All of them are suitable for technologi- having its advantages and limitations. In principle any of the
cal application or of remarkable interest as model objects, mesostructures in bulk so far reported, and even those still
which can have fascinating properties or are simply intended not discovered, could be used to create well-defined objects
as an academic exercise. with predetermined shapes, sizes, and compositions. For ex-
Most of the strategies developed so far may be classified ample, polymeric spheres, rods, or fibers are obtainable by
into two different main approaches to nanomaterial fabrica- some direct chemical isolation from the simplest spherical and
tion, which are schematically discussed in the paper as fol- cylindrical morphologies (Fig. 1, items 1 and 2, respectively).
lows: a) use of self-assembled copolymers as nanostructured The most complete investigation focused on this concept
materials, either ªas they areº or through selective chemical has been carried out by Liu et al., and is based on block co-
isolation or processing of one or more components; b) via polymers, which contain crosslinkable moieties.[24] Nanofibers
template formation, including both the use of copolymer films can be easily prepared from poly(styrene)-block-poly(2-cinna-
directly as the template and the fabrication techniques, which moethyl methacrylate) (PS-b-PCEMA)[25] and poly(styrene)-
rely on the preliminary formation of the template through a block-poly(isoprene) (PS-b-PI)[26] diblock copolymers, prop-
first processing, followed by a nanoscale synthesis. Methods erly selecting samples which allow a hexagonally packed cy-
presenting original approaches or requiring innovative manip- linder morphology (Fig. 1, 2) of the non-styrenic block dis-
ulation will be especially emphasized, also taking into account persed in the continuous matrix of the PS block. Following
their potential for large scale applications. Liu's strategy, the cylindrical domains of the minority block
As the scope of the review is limited by space, although also are locked in by crosslinking, either photoinduced or through
BC/ceramic hybrid materials[19] and, more generally, BC chemical processes, on PCEMA and PI chains, respectively.
nanocomposites[20] are extensively researched subjects, their After fixing the structure, nanofibers with PS hairs on their
potential for the preparation of novel materials and nano-ob- surface are easily separated via solvent dispersion in tetrahy-
jects is not discussed here. However, it is possible to extend drofurane (THF), i.e., a good solvent for PS, but they can re-
the applicability of the methodologies of fabrication herewith tain their structural integrity in many other organic solvents.
shown to any other BC-based material. From the structural point of view, such BC nanofibers may be
considered as the macroscopic counterparts of polymeric
chains (suprapolymer chains) and, in principle, are suitable
2. Block Copolymers as Nanomaterials for characterization and fractionation through the techniques
that have been developed for polymers. Among their peculiar
Direct use of the self-assembled BC morphologies without solution properties[27] it is worth mentioning the formation of
any further manipulation or processing appears quite intrigu- lyotropic liquid-crystalline phases.[25]
ing, but so far only a few potential applications have been se- A similar but more complex procedure which applies a
riously explored, mainly taking advantage of the BC optical triblock copolymer is also suitable for the preparation of
properties or of the electrical conductivity of at least one nanotubes having inner hydrophilic walls,[28] as it is schema-
block. Fink et al.[21] introduced the idea of using one-, two-, tized in Figure 2. Self-assembly in thin films of poly(butyl
and three-dimensional (1D, 2D, and 3D, respectively) BC pe- methacrylate)-block-poly(2-cinnamoethyl methacrylate)-block-
riodic structures (e.g., morphologies 2±5 in Fig. 1) as photonic poly-(tert-butyl acrylate) (PBMA-b-PCEMA-b-PtBA) triblock
crystals, namely materials in which the refractive index is a copolymers with higher content in PBMA formed hexagonally
periodic function of space. For a rigorous analysis of the real packed concentric cylinders of PtBA surrounded by PCEMA
promise that BC thin films can offer to photonic
applications, as well as for the illustration of the
major technological challenges still to overcome in
order to achieve the desired photonic properties,
the reading of two recently published reviews is
suggested.[22] Another potential direct application
of BC nanostructures deals with the preparation of
BCs containing conducting polymers or oligomer
units. In particular, McCullough and co-workers
have focused their investigation on a series of poly-
thiophene-based BCs,[23] which pave the way to uti-
Fig. 2. Schematic representation of the process for the preparation of nanotubes from a PBMA-
lize conjugated polymers for molecular level elec- b-PCEMA-b-PtBA triblock copolymer (reprinted with permission from Yian et al. [28], copy-
tronic devices. right 2001 American Chemical Society).

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REVIEW

and dispersed in the PBMA matrix (Fig. 1, 5). Once more the Fig. 1, 2-like). Subsequent removal of PDP with ethanol,
PCEMA shells are photo-crosslinked by UV irradiation, and which is a good solvent for the P4VP block as well, yields PS
the cylindrical domains separated from one another in THF, nanofibers. The straightforward merit of this proposal is that
yielding nanofiber dispersions. Due to their core±shell struc- the simple choice of different alkylphenols or other amphi-
ture these nanofibers may be further processed through a se- philic additives would allow tuning of the supramolecular BC
lective hydrolysis of tert-butyl groups of PtBA to yield poly self-organization and therefore controlling the shape of the
(acrylic acid) (PAA)-lined nanotubes of PBMA-b-PCEMA. isolable objects, without the requirement of a time consuming
The location of acid groups inside the cores was elegantly new BC synthesis. Moreover, countless many BC±amphiphile
demonstrated by reporting the production of c-Fe2O3-impreg- pairs with different morphologies can easily be envisaged,
nated nanotubes (Fig. 3) through a method based on the hy- thus illustrating a facile concept of fabrication aimed to intro-
drophilic interaction with ferrous ions. This shows, at the same duce novel design principles for the prediction of nanostruc-
time, the potential offered by this synthetic route to prepare tures.
hollow nanostructures with an inner diameter of about 40 nm. A further type of processing, which can in principle be con-
sidered as specular to the isolation of polymeric nano-objects
from thin films, is that leading to porous nanostructures. It is
well known that commercially available membranes for ultra-
filtration purposes can easily be prepared by track-etching
from polymeric sheets.[34] However, the resulting nanopores
(diameter as small as 10 nm) are not regularly packed and
their density is low, whereas in the case of BC thin films, the
selective degradation of e.g., cylindrical domains in morphol-
ogy 2 (Fig. 1), may result in the formation of more homoge-
neous membranes. For example, membranes with regularly
spaced nanochannels with diameters of 20±30 nm and period-
icities of around 50 nm have been prepared from PCEMA-b-
PtBA (through hydrolysis of the PtBA minor block),[35] and
bicontinuous nanoporous networks from PS-b-PI (via ozone
Fig. 3. Transmission electron micrograph of c-Fe2O3-impregnated PBMA-b-
PCEMA nanotubes with PAA-lined inner walls (reprinted with permission degradation of the PI minor block).[16] 3D nanostructured
from Yian et al. [28], copyright 2001 American Chemical Society). films have also been produced from silicon-containing tri-
block copolymers films through the selective removal of the
Other complex objects have been created via the synthetic hydrocarbon block and the conversion of the silicon-contain-
detour through the bulk phase of triblock copolymer films ing block to a highly stable silicon oxycarbide ceramic.[36] As
which exhibit the so-called lamellae±sphere morphology, with these highly ordered nanoporous membranes have also been
spheres narrowly distributed at the interface of the lamellae extensively investigated as templates, the last developments
(Fig. 1, item 6). Crosslinking in the bulk of the block that regarding their preparation and the solution of the non-trivial
forms spherical domains leads to the conservation of the com- problem of the orientation of the domains will be discussed in
partmentalization of the other blocks after dissolution in a detail in Section 3.
selective solvent. Janus-type[29] nanoparticles consisting of an Another general approach for the preparation of nano-ob-
interlocked core about 10 nm in radius and a corona with two jects is based on amphiphilic BCs.[18] In a solvent that prefer-
well-separated hemispheres were synthesized from poly(sty- entially dissolves one block, often an aqueous media or a po-
rene)-block-poly(2-vinylpyridine)-block-poly(butyl methacry- lar solvent, these copolymers form well-defined micelles with
late) (PS-b-PVP-b-PBMA)[30] and poly(styrene)-block-poly a core consisting of the less soluble block(s) and a highly swol-
(butadiene)-block-poly(methyl methacrylate) (PS-b-PB-b- len corona of the more soluble block.[37] Depending on the de-
PMMA)[31] of tailored compositions through crosslinking of gree of swelling of the corona and the relative composition of
the PVP and PB blocks, respectively. the copolymer, spherical (Fig. 1, 7) and worm- or rod-like
It is finally worth mentioning that polymeric nanofibers (Fig. 1, 8) micelles are formed, as well as more complex poly-
have also been prepared from self-organizing supramolecules mer vesicles[38] and compound micelles.[39] A specific case is
(also called supramolecular BCs).[32] Poly(4-vinylpyridine)- that of the so-called crew-cut aggregates, which are formed by
block-poly(styrene) (P4VP-b-PS) diblock copolymers were amphiphilic BCs having a short hydrophilic block.[40] Aggre-
stoichiometrically (with respect to the number of pyridine gates are prepared by first dissolving the BC in a good solvent
groups that act as hydrogen bonding acceptors) combined for both blocks, and subsequently adding water or decreasing
with a low molecular weight amphiphile, namely pentadecyl- the temperature to cause aggregation of the hydrophobic
phenol (PDP), to yield P4VP(PDP)-b-PS supramolecules.[33] block into a variety of morphologies, which resemble those of
Proper selection of the volume ratio between the P4VP(PDP) typical micelles.
complex and the PS block allowed the formation of a mor- Although only crew-cut micelle-like aggregates directly re-
phology of PS cylinders inside a P4VP(PDP) matrix (see fer to objects existing under non-equilibrium conditions, also

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M. Lazzari, M. A. López-Quintela/Block Copolymers for Nanomaterial Fabrication

REVIEW
the stability of micellar associates in thermodynamic equilibri- ferent PI-b-PCEMA-b-PtBA.[46] The PCEMA shell of the
um depends on phenomena that involve basic molecular inter- cylindrical micelle was photo-crosslinked, in this case fol-
actions, as such ªsoftº assemblies are held together essentially lowed by the complete degradation of the PI core through
by weak undirected forces (van der Waals forces, hydrophobic ozonolysis. The dispersion medium for the whole structure
effects). As a consequence, all the structures constructed with was provided by the high molecular weight PtBA corona.
these macromolecular amphiphiles are not only non-perma- Fixation of non-spherical micelles to get individual macro-
nent, but even a relatively slight change in the physical condi- molecular objects with molar masses several orders of magni-
tions that resulted in the original self-assembly can completely tude greater than those of conventional polymers has been
disrupt them. For this reason, notwithstanding micelles and mainly investigated by Bates and co-workers, around 20 years
crew-cut aggregates have been a popular subject of research later the first impressive images of collapsed BC worm-like
activity, the impossibility to fractionate these nano-objects micelles.[37b,c] Self-assembly of a low molecular weight poly-
make them far from the philosophy of nanomaterial fabrica- (ethylene oxide)-block-poly(butadiene) (PEO-b-PB) contain-
tion that this review aims to highlight. Only the development ing 50 wt.-% of PEO gave rise to the formation of worm-like
of tailored amphiphile-based materials that are less sensible micelles at low concentration in water (< 5 wt.-%), while the
to environmental perturbation will therefore be documented presence of reactive double bonds in the PB cores allowed the
in detail. use of a conventional water-based crosslinker without disrup-
Successful approaches for the preparation of stable micelles tion of the cylindrical morphology (Fig. 5).[47] The authors
consist of the use of amphiphilic BCs that either have reactive also pointed out the irreplaceable utilization of these cova-
functional groups or a block which can crystallize, in both lently bonded giant macromolecules as model nano-objects,
cases with the final aim to fix the micellar structures.[41] Since thus investigating their peculiar rheological properties.[48] In
the first systematic works on crosslinked micelles,[42] increas- our opinion, such results represent the best example of a di-
ing interest has been focused on the chemical fixation of more rect comparison between the properties of ªlivingº, less
and more complex structures,[43] up to triblock micelles with stable, micellar systems and those of ªpermanentº micelles.
surprising characteristics such as tunable hydrophilic or hol-
low cores. For example, Armes and co-workers[44] has devel-
oped an efficient synthesis of micelles with pH-responsive
cores from a series of poly(ethylene oxide)-block-poly[2-(di-
methylamino)ethyl methacrylate]-block-poly[2-(diethylami-
no) methacrylate] (PEO-b-PDMA-b-PDEA) triblock copoly-
mers (Fig. 4). The micelles formed in aqueous solution at
> pH 7.3 consist of a PEO corona, a PDMA innershell, and a

Fig. 4. Schematic illustration of the formation of ªhardº micelles from PEO-b-

PDMA-b-PDEA triblock copolymers by crosslinking of the PDMA inner shells
with 1,2-bis(2-iodoethyloxy)ethane (BIEE) [44]. Fig. 5. Cryo-transmission electron micrograph of a 0.05 wt.- % solution in water
of crosslinked worm-like micelles of PEO-b-PB (reprinted with permission
from Won et al. [47], copyright 1999 American Association for the Advance-
PDEA core, and show a degree of (de)swelling strictly depen- ment of Science).
dent on the degree of inner-shell crosslinking, PDEA block
length, and solution pH. Furthermore, Underhill and Liu Also the intrinsic properties of amphiphilic rod±coil diblock
reported the preparation of hollow triblock nanospheres[45] copolymers have been exploited for the fabrication of ªhardº
following an approach based on the methodology already pre- micelles. These polymers, consisting of a flexible block at-
sented in Figure 2. A PI-b-PCEMA-b-PtBA, with 370 iso- tached to a rigid or semi-rigid second block, present morphol-
prene, 420 CEMA, and 350 tBA units, was used to form three ogies that result from the competition between microphase
layer ªonion-likeº micelles in THF comprising PI-hydroxylat- separation of the immiscible blocks and aggregation of the
ed coronas, solvent insoluble PCEMA shells, and PtBA cores. rod-segments into crystalline domains. Those polymers, in
The structures were locked by photo-crosslinking the which the crystalline blocks are also insoluble, may self-as-
PCEMA shell to yield ªhardº nanospheres. The core was cavi- semble into micelles, whose core structure depends on the
tated and made compatible with inorganic species by removal strong crystal packing forces. Manners and Winnik have inves-
of the tert-butyl groups through controlled hydrolysis. A simi- tigated the structures formed from poly(ferrocenylsilane)-
lar approach has also been used for the preparation of nano- block-poly(dimethylsiloxane) (PFS-b-PDMS) in hydrocarbon
tubes, i.e., hollow cylindrical micelles, in methanol from a dif- solvents in which the PFS block is insoluble. Some of these co-

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REVIEW

polymers formed long, thin, relatively flexible cylindrical mi- the use of 2D-ordered morphologies from diblock copolymer
celles having a crystalline PFS core,[49] while in the case of the films, which are processed through the eventual removal of
highly asymmetric PFS-b-PDMS with a block ratio of 1:12 the one of the blocks, and using the film as a mask for subsequent
samples generated a tubular morphology.[50] In the latter case, deposition steps or etching through the film to transfer the
when aggregation occurs, the short PFS block crystallizes to BC motif pattern to a substrate. This part will be followed by
form a shell with a central cavity, surrounded by a solvent an overview on the potential of amphiphilic BCs in solution
swollen PDMS corona. These equilibrium structures are as templates.
stable in a wide range of temperatures, and their structure was
confirmed by the encapsulation of Pb(n-Bu)4. The tubes
formed are up to 100 lm long and have both wall thickness 3.1. Nanolithography
and interior cavity of ca. 10 nm (Fig. 6). As the authors sug-
gested, the potential of these copolymers is intriguing, not A prime satisfactory example of the utilization of BC thin
only for encapsulation purposes but particularly because PFS films as templates for lithography under conventional reactive
is a red±ox material with semiconducting properties, which ion etching (RIE) techniques was provided by Park et al.,[17b]
can also serve as ceramic precursor.[36] who managed to transfer the spherical microdomain pattern
of a PS-b-PB monolayer to the underlying silicon nitride. Not-
withstanding, further refinement of this technique, the two
processing approaches reproduced in Figure 7 still exemplify
the potential offered by nanolithography well. In general, as
the etching rates of different organic polymers are almost
identical, it is first necessary to resort to some manipulation
for enhancing the etching selectivity between the different re-
gions. One approach involves the selective removal of one

Fig. 6. Chemical structure of PFS-b-PDMS and transmission electron microsco-

py image of its assemblies formed in n-decane (reprinted with permission from
Raez et al. [50], copyright 2002 American Chemical Society).

3. Block Copolymers as Templates

Many polymer systems have been successfully employed as

templates for nanofabrication,[1c,d,g,h] and among them, all the
above mentioned self-organizing BC systems may play a cru-
cial role, mainly because of the variety of tunable matrixes at
nanoscale level that they offer, ranging from micelles to 3D
structures. Since the remarkable number of related works
published in journals of many different fields, e.g., chemistry,
physics, materials science, and engineering, and the possibility
Fig. 7. Fabrication processes of silicon nitride dot (B) and hole (C) arrays via a
of scale-up for industrial applications, a special emphasis will nanolithography template consisting of a uniform monolayer of hexagonally or-
first be placed on the sophisticated procedures to arrive at dered PB spheres in a PS matrix (cross-sectional view in A). PB wets the inter-
faces with the air and the silicon nitride substrate due to preferential inter-
continuous arrays of metallic or semiconducting objects from actions (reprinted with permission from Park et al. [17b], copyright 1997
BC thin films. The most common methods are those based on American Association for the Advancement of Science).

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M. Lazzari, M. A. López-Quintela/Block Copolymers for Nanomaterial Fabrication

REVIEW
block component before etching. For example, in Figure 7 A
(processing flow B) the spherical PB domains ordered in a 2D
D
hexagonal lattice are ozone degraded, leading to regular voids
in the PS matrix and hence to a variation in the thickness of
the mask. Once exposed to the etchings, the thinner parts of
the mask underneath the removed domains yield holes on the
substrate. Other procedures achieve etching contrast by load-
ing one of the microphase separated blocks. In the case that
one block contains double bonds, it can selectively incorpo- B
rate compounds containing transition metals possessing reac-
tivity for unsaturated double bonds. In the processing shown
in Figure 7C, OsO4 staining PB reduces the etching rate of E
such domains, producing an etching selectivity under CF4/O2±
RIE of PS to stained PB of approximately 2:1. When the plas-
ma is applied, the regions below PB domains are partially
masked, resulting in the production of dots. Similar proce-
dures have also been performed on PS-b-PI monolayers, in
both cases with the production of etched features on silicon, C
silicon nitride, and germanium with a periodicity of 30±40 nm,
corresponding to a density of around 1011 cm±2, and an aspect
ratio of about one.[17b,51] More recently, the combination with F
other microfabrication techniques has permitted the creation
of dense arrays of GaAs nanocrystals[52] and gold dots.[53] The
first were made through selective growing of GaAs into or-
Fig. 8. Nanolithography fabrication of a cobalt dot array from PS-b-PFS.
dered holes patterned as reported above on a silicon nitride± A) Cross-sectional view of the spherical microdomain monolayer consisting of
GaAs bilayer, while the latter where produced by combining PFS spheres ordered in a 2D hexagonal lattice on a multilayer of silica, tungsten
and cobalt. B) Formation of the mask through the O2±RIE process. C) Silica
BC nanolithography with a trilayer resist technique, hence patterning using CHF3±RIE. D) Tungsten patterning using CF4/O2±RIE.
transferring the pattern by different etching techniques from E) Removal of silica and residual polymer by further CF4/O2±RIE at high pres-
the BC film to the underlying layers, down to the gold layer. sure. F) Final formation of cobalt dots by ion beam etching [56].

The real advantage this trilayer pattern-transfer method of-

fers, despite its apparent complexity, is a viable route of gener- der of the features fabricated by such monolayer masks. A
al applicability for nanoscale patterning of different materials practical difficulty for the creation of higher (or deeper) fea-
on arbitrary surfaces. Moreover, the high aspect ratio holes tures arises from the necessity to use thicker BC films with
that are generated can be used for other applications, e.g., suitable patterns, as might be the case with surface-perpendic-
electroplating and elastomer molding.[54] ular lamellae or cylinder morphologies (e.g., Fig. 1, items 2±
A simplification of the nanolithography process has con- 5). As mentioned in the introduction, the orientation of
sisted in approaches where ªimageableº BCs are used, in domains is not at all a trivial problem, since their disposition
which one of the blocks already contains components that and long-range order are dependent upon the interaction with
provide a barrier to etching, thus eliminating the preliminary the surfaces (usually a substrate and a free surface). Notewor-
step, consisting of either the loading with inorganics or the se- thy efforts to understand and control the domain alignment in
lective removal of one block. Silicon-containing polymers, BC morphologies have been carried out by several groups
and in particular BCs based on PFS (chemical structure in through the investigation of the effect of external fields and
Fig. 6),[55] have been proposed as good candidates, since they surface energy boundary conditions on the self-assembly pro-
can form a thin SixOyFez layer on the surface when exposed cess. These include the use of applied mechanical or electrical
to an oxygen plasma (O2±RIE). This results in a lower etching fields,[57,58] applied temperature gradients,[59] solvent evapora-
rate and therefore in an etching selectivity that is as high as tion or crystallization,[60,61] and patterned or neutral sur-
50:1, in comparison with organic polymers. As an example, faces.[62,63] The best results obtained so far, in terms of large-
Figure 8 shows the fabrication of a cobalt magnetic dot array area ordering of domains and efficiency of orientation in
by lithography using a PS-b-PFS monolayer.[56] The first O2± thicker films (up to few micrometers), were achieved from
RIE step removes the organic part of the polymer and con- directional crystallization of a solvent[61a] and application of
verts the PFS into the non-volatile iron±silicon oxides. The an electric field,[58a±c] respectively.
spherical features of the template are transferred sequentially Despite of these promising results, the use of highly ordered
through the silica, then the tungsten, and finally the cobalt, BC templates for nanolithography application is so far limited
with the formation of patterns A±D shown in Figure 9. to a surprisingly low number of cases, essentially based on
The main restriction for a wider use of all the above lithog- very thin films (< 50 nm thickness). In most investigations, PS-
raphy processes is the limited aspect ratio and long-range or- b-PMMA films with PMMA cylinders normal to the surface

Adv. Mater. 2003, 15, No. 19, October 2 http://www.advmat.de Ó 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1589
 M. Lazzari, M. A. López-Quintela/Block Copolymers for Nanomaterial Fabrication
REVIEW

3.2. Membrane-Based Synthesis

A B

At the same time, the tuning of the pro-

cedure for the preparation of nanoporous
films with controlled spatial orientation (es-
sentially carried out by Russell and co-
workers)[66] has also constituted a decisive
step forward in membrane-based nanofab-
rication.[1d,i] Synthesis of nano-objects via
chemical- or electrodeposition[67,68] into
particle track-etched polymeric membranes
C D are performed with well established proce-
dures, and the introduction of a versatile
and robust route to the fabrication of
densely packed nanoporous arrays (as those
shown in Fig. 10) certainly opened up novel
unprecedented developments.[69] Two
groundbreaking papers have recently re-
ported the electrodeposition of ferromag-
netic cobalt nanowires,[70] and the chemical
deposition of nanoscopic SiO2 posts[71] into
Fig. 9. Tilted scanning electron microscopy image of the intermediate stages of the PS-b-PFS nanolithog- nanoporous films used as scaffolds. In both
raphy. A±D) Images correspond to the different patterns after the stages B,C,E,F as schematized in cases, a template was used, which was gen-
Figure 8 [56]. erated by selective removal of PMMA do-
mains from PS-b-PMMA films with hexag-
and dispersed in the PS matrix were obtained by deposition onally packed cylinder morphology and oriented normal to
onto a neutral surface,[63a] and subsequently transformed into the surface either by application of an electric field[58b] or de-
a nanoporous template by elimination of PMMA domains via position onto a neutral substrate.[63a] The corresponding pro-
UV degradation. Such masks have found applications for cessing flows are shown in Figures 11,12 (the steps are de-
transferring the pattern (Fig. 10) over full silicon wafers and scribed in detail in the captions), while images of the arrays of
into various substrate materials[64] including antiferromagnet±
ferromagnet bilayers, such as a FeF2±Fe bilayer.[65]

Fig. 10. Scanning electron microscopy images of a nanoporous template formed

from a 40 nm thick film of PS-b-PMMA self-assembled in a hexagonally or-
dered cylinder morphology normal to the surface. Dark regions correspond to
the pores (< 20 nm diameter) from which PMMA microdomains were removed
by UV degradation (reprinted with permission from Guarini et al. [64a], copy-
right 2001 AVSÐThe Science & Technology Society).

And finally, BC nanolithographic techniques certainly offer Fig. 11. Process of fabrication of cobalt nanowire arrays with densities in excess
unprecedented feature dimensions and densities well below of 1.9 ” 1011 wires cm±2. A 1 lm thick film of PS-b-PMMA is annealed above
the glass-transition temperature of both blocks between an electric field, in
the photolithographic resolution limits, but this may not be order to form a hexagonally ordered cylinder morphology normal to the elec-
the only key advantage of BCs in the near future. At least as trodes (A). After removal of PMMA microdomains by UV degradation a nano-
important is that the feature sizes may be realized over porous film (B) is left, which is used for the controlled electrodeposition of
nanowires (approximate diameter 15 nm, C), thus forming an array of nano-
macroscopically larger areas than by standard top±down ap- wires within the PS matrix (reprinted with permission from Thurn-Albrecht et
proaches. al. [70], copyright 2000 American Association for the Advancement of Science).

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M. Lazzari, M. A. López-Quintela/Block Copolymers for Nanomaterial Fabrication

REVIEW
laterally ordered hexagonal array of spherical micelles (Fig. 1,
item 7, with dimensions falling in the approximate 10±100 nm
range) deposited into a monolayer film. Furthermore, long-
range positional order and orientation of these BC domains
can be efficiently controlled by the application of graphoepi-
taxy,[75] in which the surface-relief structure of the substrate
directs epitaxial growth of the overlying micelles.[76]
Micellar cores offer unique microenvironments (ªnanoreac-
torsº) in which inorganic precursors are loaded and then pro-
cessed by wet chemical methods to produce comparatively
uniform nanoparticles, in a similar way as it is usually done
with microemulsions.[1 l] BC±nanoparticle hybrids present pe-
culiar magnetic, electro-optical, and catalytic properties aris-
ing primarily from single inorganic colloids,[19a] but even more
fascinating are the possibilities, offered by their self-assembly,
as templates. Synthesis of different single-metal nanoclusters
within microphase separated domains of amphiphilic diblock
copolymers has been already reviewed,[19a] and need not to be
repeated here. Further developments that have been reported
are, for example, the ordered deposition of gold and silver
Fig. 12. Process of fabrication of SiO2 nanoposts. A PS-b-PMMA thin film (A)
is selectively degraded to form a nanoporous template like that in Figure 10.
nanoclusters from micellar PS-b-PVP[77] and PS-b-PAA
SiO2 is grown within the nanoporous (B) by SiCl4 hydrolysis with atmospheric (Fig. 14)[78] films, respectively. The versatility of this procedure
water, then SiO2 nanoposts are left after removing PS matrix with CF4±RIE is such that it allows the use of various different amphiphilic
(C, Kim et al. [71]).
BC, with the only requirement to form reverse micelles in a

SiO2 are presented in Figure 13. In any case, the impact of

these highly ordered templates might be much broader, as
they offer different practical means of producing tailored
nanostructures. More recent publications demonstrated few
other likely routes, such as processing to high-density arrays
of chromium, and layered gold±chromium nanodots and
nanoholes by evaporation onto nanoporous templates.[72] In
addition, such nanoporous membranes have been proposed
for the creation of nanoelectrode arrays.[73]

Fig. 14. Transmission electron microscopy image of a PS-b-PAA monolayer

(film thickness 22 nm) containing silver nanoclusters. Silver was loaded as silver
A B acetate in aqueous solution and reduced in a hydrogen atmosphere (reprinted
with permission from Boontongkong and Cohen [78], copyright 2002 American
Chemical Society).

non-polar solvent. A large variety of inorganic compounds can

be loaded in the micellar polar cores and, in principle, their
chemical transformation can be performed either before or
after film deposition. At the same time, a large number of sub-
strates can be used. It is also worth mentioning that the poly-
mer can be removed after deposition, leaving on the substrate
an inorganic nanopattern suitable for other applications, such
Fig. 13. Atomic force microscopy height (A) and phase (B) images of the SiO2 as nanolithographic masks. Möller and co-workers reported
nanoposts fabricated as schematized in Figure 12 (adapted from H.-C. Kim et
al. [71]). The size of the images is approximately 1 lm ” 1 lm. the application of this approach for the fabrication of quantum
structures with a very high aspect ratio of 1:10 and dimensions
down to 10 nm.[79] The metal cluster mask resulting from a
monolayer of Au-loaded PS-b-PVP micelles has been used in
3.3. Amphiphilic Block Copolymer Templates a chlorine dry etching process to etch free-standing cylinders
in GaAs and its alloys on In and Al. This combination of stan-
The formation of ordered patterns is also possible by assem- dard and bottom±up lithography can be applied on virtually
bling BC micelles upon casting,[74] with a major interest in any semiconductor material and could widen the possibility of
terms of potential applications in nanotechnology placed on technological application of quantum dot devices.

Adv. Mater. 2003, 15, No. 19, October 2 http://www.advmat.de Ó 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1591
 M. Lazzari, M. A. López-Quintela/Block Copolymers for Nanomaterial Fabrication
REVIEW

4. Summary and Outlook require long-range order, e.g., preparation of individual nano-
objects or direct use of nanoporous films as membranes, only
Self-assembly of block copolymers into highly regular the tuning of a reproducible orientation procedure applicable
morphologies has been investigated by chemists for several with different BCs will permit more flexible fabrication of
decades[57a] but it is only in the last ten years that multidisci- very sharp, highly dense features, independently from the pro-
plinary groups have focused their research efforts on the use duction either by nanolithography or via a templated synthe-
of BCs as a tool for nanomaterial fabrication, following a sis, thereby pointing towards a route for further technological
wider scientific and technological trend towards miniaturiza- developments of applications such as in addressable ultra-high
tion. Diverse methods of fabrication have been presented density recording media. If one could template through a
throughout the review, with the final aim to provide an over- reproducible and robust process with those nanostructures
view of the potential applications offered by BC mesostruc- arrangements of single grain magnetic bits, storage densities
tures (Table 1 summarizes the main research reported so far). of more than 5 Tbit cm±2 could be achieved, which are two
It has been shown that relatively simple processing of self-as- orders of magnitude larger than the actual and most recent
sembled BCs in bulk or in solution permits the creation of indi- developments of announced storage densities.
vidual polymeric nano-objects with different shapes, such as In addition, amphiphilic BC templates have demonstrated
spheres, hollow spheres, fibres, and tubes. A better tailoring of their potential through the preparation of dense metal nano-
intrinsic properties and control of dimensions of such objects, clusters from as-cast monolayers of loaded micelles. Thus
as well as optimization of fabrication methods currently avail- following a procedure that could become an alternative, at
able do not appear as too difficult challenges. However their least in terms of ease of processing and reproducibility, to the
use for practical applications, as chemical or biological sensors fabrication from nanoporous templates.
or for encapsulation purposes, e.g., as carriers, is possibly hin- And finally, although polymer synthesis did not represent a
dered by the limited efforts so far focused on the development priori the limiting factor for further growth of interest in the
of efficient and reliable fractionation techniques.[26,27] More- use of BCs for the fabrication of nanomaterials, it is worth
over, a tremendous, almost unexplored potential is likely to pointing out that a new field has been opened by the availabil-
reside in the development of processes based on the controlled ity of mesostructures through reactive blending of homopoly-
pyrolysis of polymeric nano-objects, as well as of self-assembled mers.[83]
BC films as a whole,[80] to yield nanostructured carbons. Received: February 5, 2003
The preparation of templates from BC thin films has al- Final version: June 9, 2003
ready been performed by a relatively large number of re-
search groups through similar approaches, even though the
key point for a wider application of these films is still repre-
±
[1] For early papers see: a) G. M. Whitesides, J. P. Mathias, C. T. Seto, Science
sented by issues such as long-range order and control of do- 1991, 254, 1312. b) G. A. Ozin, Adv. Mater. 1992, 4, 612. c) C. R. Martin,
main orientation. Just few works have reported the applica- Science 1994, 266, 1961. d) C. R. Martin, Chem. Mater. 1996, 8, 1739. For
more recent reviews or books on nanomaterial synthesis see, e.g.:
tion of large-area, highly oriented thin films as templates, e) Y. Xia, J. A. Rogers, K. E. Paul, G. M. Whitesides, Chem. Rev. 1999,
using methodologies that only apply to PS-b-PMMA, while 99, 1823. f) Special issue on Nanoscale Materials, Acc. Chem. Res. 1999,
32, Issue 5. g) A. Huczko, Appl. Phys. A 2000, 70, 365. h) M. M. Alkaisi,
promising results can be also obtained from the use of order- R. J. Blaikie, S. J. McNab, Adv. Mater. 2001, 13, 877. i) T. Liu, C. Burger,
ing procedures, based on the deposition onto substrates B. Chu, Prog. Polym. Sci. 2003, 28, 5. l) M. A. López-Quintela, Curr.
neutralized with substances that do not present preferential Opin. Colloid Interface Sci. 2003, 8, 137. m) H. S. Nalwa, Handbook of
Nanostructured Materials and Technology, Vol. 1±5, Academic Press, San
interactions with any hydrocarbon polymers, such as carbon- Diego 2000. n) K. J. Klabunde, Nanoscale Materials in Chemistry, Wiley,
coated surfaces.[82] Notwithstanding many applications do not New York 2001.

Table 1. Summary of the nanomaterials that may be obtained from microphase separated block copolymers (BCs) [a].

BC tool As nanomaterials As templates

direct use through processing direct use after processing
BCs in bulk [b] photonic crystals [21,22] individual polymeric nano-objects: nanolithographically patterned nanolithographically patterned
spheres, fibers, tubes [24±28,30±32] materials: cobalt [56] materials: silicon, silicon nitride,
conducting BCs [23] hierarchically self-assembled gold, others [17,51±53,64,65]
nanoporous membranes metal nanowires [81]
[16,35,36,66,73] high density arrays of metallic or
nanostructured carbons [80] semiconductor materials: cobalt,
silica, chromium, others [70,72]

amphiphilic BCs individual polymeric nano-objects: metal nanoclusters [19a,77,78] nanolithographically patterned
spheres, hollow spheres, cylinders, materials [79]
tubes [44±50] inorganic colloids [19a]

[a] Applications of BC nanocomposites and more specifically of BC/ceramic hybrids are not included because they are beyond the scope of the present review.
[b] Mainly as amorphous thin films.

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M. Lazzari, M. A. López-Quintela/Block Copolymers for Nanomaterial Fabrication

REVIEW
[2] a) H. Li, W. T. S. Huck, Curr. Opin. Solid State Mater. Sci. 2002, 6, 3. [31] R. Erhardt, A. Böker, H. Zettl, H. Kaya, W. Pyckhout-Hintzen,
b) K. Ishizu, K. Tsubaki, A. Mori, S. Uchida, Prog. Polym. Sci. 2003, 28, 27. G. Krausch, V. Abetz, A. H. E. Müller, Macromolecules 2001, 34, 1069.
[3] For an overview on the last developments on polymer synthesis: a) K. Ha- [32] See for example: a) J. Ruokolainen, G. ten Brinkle, O. Ikkala, Adv. Mater.
tada, T. Kitayama, O. Vogl, Macromolecular Design of Polymeric Materi- 1999, 11, 777. b) O. Ikkala, G. ten Brinkle, Science 2002, 295, 2407.
als, Marcel Dekker, New York 1997. b) T. E. Patten, K. Matyjaszewski, [33] K. de Moel, G. O. R. A. Van Ekenstein, H. Nijiland, E. Plushkin, G. Ten
Adv. Mater. 1998, 10, 901. c) N. Hadjichristidis, M. Pitzikalis, S. Pispas, Brinkle, Chem. Mater. 2001, 13, 4580.
H. Iatrou, Chem. Rev. 2001, 101, 3747. d) K. Matyjaszewski, T. P. Davis, [34] P. Apel, Radiat. Meas. 2001, 34, 559.
Handbook of Radical Polymerization, Wiley, New York, 2002. For more [35] a) G. Liu, J. Ding, A. Guo, M. Hertfort, D. Bazett-Jones, Macromolecules
specific examples on the preparation of complex polymer structures see 1997, 30, 1851. b) G. Liu, J. Ding, Adv. Mater. 1998, 10, 69. c) G. Liu,
e.g.: e) M. Lazzari, K. Hatada, T. Kitayama, M. JancÏo, Macromolecules J. Ding, T. Hashimoto, K. Kimishima, F. M. Winnik, S. Nigam, Chem. Ma-
2001, 34, 5734. f) P. Dumas, C. Delaite, G. Hurtrez, Macromol. Symp. ter. 1999, 11, 2233.
2002, 183, 29. g) D. Charalabidis, M. Pitsikalis, N. Hadjichristidis, Macro- [36] V. Z.-H. Chan, J. Hoffman, V. Y. Lee, H. Iatrou, A. Avgeropoulos,
mol. Chem. Phys. 2002, 203, 2132. h) R. Francis, N. Lepoittevin, D. Taton, N. Hadjichristidis, R. D. Miller, E. L. Thomas, Science 1999, 286, 1716
Y. Gnanou, Macromolecules 2002, 35, 9001. [37] For an introductory view on the formation of micelles by BCs, see:
[4] a) I. W. Hamley, The Physics of Block Copolymers, Oxford University a) C. Price, D. Woods, Eur. Polym. J. 1973, 9, 827. b) C. Price, Pure Appl.
Press, Oxford 1998. b) D. Y. Ryu, U. Jeong, J. K. Kim, T. P. Russell, Nat. Chem. 1983, 55, 1563. c) C. Price, E. K. M. Chan, A. L. Hudd, R. B. Stub-
Mater. 2002, 1, 114. bersfield, Polym. Comm. 1986, 27, 196. For a recent comprehensive paper
[5] The potential of BCs for the preparation of supramolecular materials has see: d) J. S. Pedersen, C. Svaneborg, Curr. Opin. Colloid Interface Sci.
been discussed in a previous review: H.-A. Klok, S. Commandoux, Adv. 2002, 7, 158.
Mater. 2001, 13, 1217. [38] For recent investigations see: a) H. Shen, A. Eisenberg, Angew. Chem. Int.
[6] I. W. Hamley, J. Phys.: Condens. Matter 2001, 13, R643. Ed. 2002, 39, 3310. b) D. E. Discher, A. Eisenberg, Science 2002, 297, 967.
[7] M. W. Matsen, F. S. Bates, J. Chem. Phys. 1997, 106, 2436. [39] a) K. Yu, A. Eisenberg, Macromolecules 1998, 31, 3509. b) L. Zhang,
[8] For a recent example of non-predicted morphologies, formed by introduc- A. Eisenberg, Macromolecules 1999, 32, 2239. c) H. Y. Zhao, E. P. Dou-
ing highly flexible block segments into a BC, see: M. H. Uddin, C. Rodri- glas, B. S. Harrison, K. S. Schanze, Langmuir 2001, 17, 8428.
guez, M. A. Lopez-Quintela, D. Leisner, C. Solans, J. Esquena, H. Kuni- [40] a) L. Zhang, A. Eisenberg, Science 1995, 268, 1728. b) L. Zhang, K. Yu,
eda, Macromolecules 2003, 36, 1261. A. Eisenberg, Science 1996, 272, 1777. c) T. Imae, H. Tabuchi, K. Funaya-
[9] J. T. Chen, E. L. Thomas, C. K. Oberle, G.-P. Mao, Science 1996, 273, 343. ma, A. Sato, T. Nakamura, N. Amaya, Coll. Surf. A 2000, 167, 63. d) I. C.
[10] H. Elbs, C. Drummer, V. Abetz, G. Krausch, Macromolecules 2002, 35, Riegel, A. Eisenberg, C. L. Petzhold, D. Semios, Langmuir 2002, 18, 3358.
5570. [41] It should be noticed that stable aggregates can be synthesized with tradi-
[11] R. Stadler, C. Auschra, J. Beckman, U. Krappe, I. Voigt-Martin, L. Leib- tional surfactants replacing the alkyl chains by rigid skeletons or connect-
ner, H. Elbs, Macromolecules 1995, 28, 3080. ing the head groups through intermolecular interactions: G. Li, W. Fudick-
[12] H. Elbs, C. Drummer, V. Abetz,, G. Hadziioannou, G. Krausch, Macro- ar, M. Skupin, A. Klyszcz, C. Draeger, M. Lauer, J.-H. Fuhrhop, Angew.
molecules 2001, 34, 7917. Chem. Int. Ed. 2002, 41, 1828.
[13] K. Takahashi, H. Hasegawa, T. Hashimoto, V. Bellas, H. Iatrou, N. Hadji- [42] a) K. B. Thurmond, T. Kowalewski, K. L. Wooley, J. Am. Chem. Soc.
christidis, Macromolecules 2002, 35, 4859. 1996, 118, 7239. b) J. Tao, G. Liu, J. Ding, M. Yang, Macromolecules 1997,
[14] a) M. J. Fasolka, A. M. Mays, Annu. Rev. Mater. Res. 2001, 31, 323. 30, 4084.
b) G. Krausch, R. Magerle, Adv. Mater. 2002, 14, 1579. [43] For other recent related examples not illustrated in this review see: a) S.
[15] G. M. Whitesides, B. Grzybowski, Science 2002, 295, 2418. Stewart, G. Liu, Chem. Mater. 1999, 11, 1048. b) Q. Zhang, E. E. Remsen,
[16] T. Hashimoto, K. Tsutsumi, Y. Funaki, Langmuir 1997, 13, 6869. K. L. Wooley, J. Am. Chem. Soc. 2000, 122, 651. c) Z. Zhang, G. Liu,
[17] a) P. Mansky, P. Chaikin, E. L. Thomas, J. Mater. Sci. 1995, 30, 1987. S. Bell, Macromolecules 2000, 33, 7877. d) Q. Ma, E. E. Remsen, T. Kowa-
b) M. Park, C. Harrison, P. M. Chaikin, R. A. Register, D. H. Adamson, lewski, J. Schaefer, K. L. Wooley, Nano Lett. 2001, 1, 651. e) M. L. Beck-
Science 1997, 276, 1401. er, E. E. Remsen, K. L. Wooley, J. Polym. Sci., Part A: Polym. Chem.
[18] P. Alexandridis, B. Lindman, Amphiphilic Block Copolymers, Elsevier, 2001, 39, 4152. f) J. Y. Zhou, Z. Li, G. J. Liu, Macromolecules 2002, 35,
Amsterdam 2000. 3690. g) G. J. Liu, J. Y. Zhou, Macromolecules 2002, 35, 8167.
[19] a) S. Förster, M. Antonietti, Adv. Mater. 1998, 10, 195. b) M. Breulmann, [44] S. Liu, J. V. M. Weaver, Y. Tang, N. C. Billingham, S. P. Armes, K. Tribe,
S. A. Davis, S. Mann, H. P. Hentze, M. Antonietti, Adv. Mater. 2000, 12, Macromolecules 2002, 35, 6121.
502. c) P. F. W. Simon, R. Ulrich, H. W. Spiess, U. Wiesner, Chem. Mater. [45] R. S. Underhill, G. Liu, Chem. Mater. 2000, 12, 2082.
2001, 13, 3464. d) R. Ulrich, J. W. Zwanziger, S. M. De Paul, A. Reiche, [46] S. Stewart, G. Liu, Angew. Chem. Int. Ed. 2000, 39, 340.
H. Leuninger, H. W. Spiess, U. Wiesner, Adv. Mater. 2002, 14, 1134. [47] Y.-Y. Won, H. T. Davis, F. S. Bates, Science 1999, 283, 960.
[20] a) R. B. Thompson, V. V. Ginzburg, M. W. Matsen, A. C. Balazs, Macro- [48] Y.-Y. Won, K. Paso, H. T. Davis, F. S. Bates, J. Phys. Chem. B 2001, 105,
molecules 2002, 35, 1060. b) K. A. Mauritz, R. F. Storey, D. A. Mountz, 8302.
D. A. Reuschle, Polymer 2002, 43, 4315. c) S. Yang, Y. Horibe, C.-H. [49] J. Massey, K. Temple, L. Cao, Y. Rharbi, J. Raez, M. A. Winnik, I. Man-
Chen, P. Mirau, T. Tatry, P. Evans, J. Grazul, E. M. Dufresne, Chem. Ma- ners, J. Am. Chem. Soc. 2000, 122, 11 577.
ter. 2002, 14, 5173. d) M. R. Bockstaller, Y. Lapetnikov, S. Margel, E. L. [50] J. Raez, I. Manners, M. A. Winnik, J. Am. Chem. Soc. 2002, 124, 10 381.
Thomas, J. Am. Chem. Soc. 2003, 125, 5276. [51] C. Harrison, M. Park, P. M. Chaikin, R. A. Register, D. H. Adamson,
[21] Y. Fink, A. M. Urbas, M. G. Bawendi, J. D. Joannopoulos, E. L. Thomas, J. Vac. Sci. Technol. B 1998, 16, 544.
J. Lightwave Technol. 1999, 17, 1963. [52] R. R. Li, P. D. Dapkus, M. E. Thompson, W. G. Jeong, C. Harrison, P. M.
[22] a) A. C. Endrington, A. M. Urbas, P. DeRege, C. X. Chen, T. M. Swager, Chaikin, R. A. Register, D. H. Adamson, Appl. Phys. Lett. 2000, 76, 1689.
N. Hadjichristidis, M. Xenidou, L. J. Fetters, J. D. Joannopoulos, Y. Fink, [53] M. Park, P. M. Chaikin, R. A. Register, D. H. Adamson, Appl. Phys. Lett.
E. L. Thomas, Adv. Mater. 2001, 13, 421. b) M. Maldovan, A. M. Urbas, 2001, 79, 257.
N. Yufa, W. C. Carter, E. L. Thomas, Phys. Rev. B 2002, 65, 165 123. [54] Y. Xia, G. M. Whitesides, Annu. Rev. Mater. Res. 1998, 28, 153.
[23] J. Liu, E. Sheina, T. Kowalewski, R. D. McCullough, Angew. Chem. Int. [55] a) R. G. H. Lammertink, M. A. Hempenius, J. E. van den Enk, V. Z.-H.
Ed. 2002, 41, 329. Chan, E. L. Thomas, G. J. Vancso, Adv. Mater. 2000, 12, 98. b) J. Y.
[24] For a general view of this approach, see also other examples not illustrat- Cheng, C. A. Ross, E. L. Thomas, H. I. Smith, G. J. Vancso, Appl. Phys.
ed in this review: a) G. Liu, L. Qiao, A. Guo, Macromolecules 1996, 29, Lett. 2002, 81, 3657.
5508. b) G. Liu, Adv. Mater. 1997, 9, 437. [56] J. Y. Cheng, C. A. Ross, V. Z.-H. Chan, E. L. Thomas, R. G. H. Lammer-
[25] G. Liu, J. Ding, L. Qiao, A. Guo, B. P. Dymov, J. T. Gleeson, T. Hashi- tink, G. J. Vancso, Adv. Mater. 2001, 13, 1174.
moto, K. Saijo, Chem. Eur. J. 1999, 5, 2740. [57] a) A. Keller, E. Pedemonte, F. M. Willmouth, Nature 1970, 225, 538.
[26] G. Liu, X. Yan, S. Duncan, Macromolecules 2002, 35, 9788. b) R. J. Albalak, E. L. Thomas, J. Polym. Sci., Part B: Polym. Phys. 1993,
[27] G. Liu, X. Yan, X. Qiu, Z. Li, Macromolecules 2002, 35, 7742. 31, 37. c) D. Maring, U. Wiesner, Macromolecules 1997, 30, 660. d) B. S.
[28] X. Yian, F. Liu, Z. Li, G. Liu, Macromolecules 2001, 34, 9112. Pinheiro, K. I. Winey, Macromolecules 1998, 31, 4447.
[29] The Roman mythological term ªJanusº describes the property of having [58] a) T. L. Morkved, M. Lu, A. M. Urbas, E. E. Ehrichs, H. M. Jaeger,
two faces and was first used in chemistry by C. Casagrande, M. VeyssiØ, P. Mansky, T. P. Russell, Science 1996, 273, 931. b) T. Thurn-Albrecht,
C. R. Acad. Sci., Ser. II: Mec., Phys., Chim., Sci. Terre Univers 1988, 306, J. DeRouchey, T. P. Russell, H. M. Jaeger, Macromolecules 2000, 33, 3250.
1423. c) A. Boker, A. Knoll, H. Elbs, V. Abetz, A. H. E. Muller, G. Krausch,
[30] R. Saito, A. Fujita, A. Ichimura, K. Ishizu, J. Polym. Sci., Part A: Polym. Macromolecules 2002, 35, 1319. For theoretical works: d) G. G. Pereira,
Chem. 2000, 38, 2091. D. R. M. Williams, Macromolecules 1999, 32, 8155. e) B. Ashok,

Adv. Mater. 2003, 15, No. 19, October 2 http://www.advmat.de Ó 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1593
 M. Lazzari, M. A. López-Quintela/Block Copolymers for Nanomaterial Fabrication
REVIEW

M. Muthukumar, T. P. Russell, J. Chem. Phys. 2001, 115, 1559. f) Y. Tsori, L. Piraux, J. Mater. Res. 1999, 14, 665. c) A. K. M. Bantu, J. Rivas,
D. Andelman, Macromolecules 2002, 35, 5161. G. Zaragoza, M. A. Lopez-Quintela, M. C. Blanco, J. Non-Cryst. Solids
[59] J. Bodycomb, Y. Funaki, K. Kimishima, T. Hashimoto, Macromolecules 2001, 287, 5. d) M. E. T. Molares, V. Buschmann, D. Dobrev, R. Neu-
1999, 32, 2075. mann, R. Scholz, I. U. Schuchert, J. Vetter, Adv. Mater. 2001, 13, 62.
[60] a) K. Fukunaga, H. Elbs, R. Magerle, G. Krausch, Macromolecules 2000, e) A. K. M. Bantu, J. Rivas, G. Zaragoza, M. A. Lopez-Quintela, M. C.
33, 947. b) Z. Lin, D. H. Kim, X. Wu, L. Boosahda, D. Stone, L. LaRose, Blanco, J. Appl. Phys. 2001, 89, 3393. f) J. Rivas, A. K. M. Bantu, G. Zar-
T. P. Russell, Adv. Mater. 2002, 12, 1373. agoza, M. C. Blanco, M. A. Lopez-Quintela, J. Magn. Magn. Mater.
[61] a) C. De Rosa, C. Park, B. Lodz, J.-C. Wittmann, L. J. Fetters, E. L. Tho- 2002, 249, 220.
mas, Macromolecules 2000, 33, 4871. b) C. De Rosa, C. Park, E. L. Tho- [69] a) U. Jeong, H.-C. Kim, R. L. Rodriguez, I. Y. Tsai, C. M. Stafford, J. K.
mas, B. Lodz, Nature 2000, 405, 433. c) C. Park, J. Y. Cheng, M. J. Fasolka, Kim, C. J. Hawker, T. P. Russell, Adv. Mater. 2002, 14, 274. b) K. W. Gua-
A. M. Mayes, C. A. Ross, E. L. Thomas, C. de Rosa, Appl. Phys. Lett. rini, C. T. Black, S. H. I. Yeung, Adv. Mater. 2002, 14, 1290.
2001, 79, 848. d) C. Park, C. de Rosa, L. J. Fetters, B. Lodz, E. L. Thomas, [70] T. Thurn-Albrecht, J. Schotter, G. A. Kästle, N. Emley, T. Shibauchi,
Adv. Mater. 2001, 13, 724. e) C. Park, C. de Rosa, E. L. Thomas, Macro- L. Krusin-Elbaum, K. Guarini, C. T. Black, M. T. Tuominen, T. P. Russell,
molecules 2001, 34, 2602. Science 2000, 290, 2126.
[62] a) J. Heier, J. Genzer, E. J. Kramer, F. S. Bates, S. Walheim, G. Krausch, [71] H.-C. Kim, X. Jia, C. M. Stafford, D. H. Kim, T. J. McCarthy, M. T. Tuo-
J. Chem. Phys. 1999, 111, 11 101. b) X. M. Yang, R. D. Peters, P. F. Nealey, minen, C. J. Hawker, T. P. Russell, Adv. Mater. 2001, 13, 795.
H. H. Solak, F. Cerrina, Macromolecules 2000, 33, 9575. c) L. Rockford, [72] K. Shin, K. A. Leach, J. T. Goldbach, D. H. Kim, J. Y. Jho, M. T. Tuomi-
S. G. J. Mochrie, T. P. Russell, Macromolecules 2001, 34, 1487. nen, C. J. Hawker, T. P. Russell, Nano Lett. 2002, 2, 933.
[63] a) E. Huang, T. P. Russell, C. Harrison, P. M. Chaikin, R. A. Register, [73] E. Jeoung, T. H. Galow, J. Schotter, M. Bal, A. Ursache, M. T. Tuominen,
C. J. Hawker, J. Mays, Macromolecules 1998, 31, 7641. b) R. G. H. Lam- C. M. Stafford, T. P. Russell, V. M. Rotello, Langmuir 2001, 17, 6396.
mertink, M. A. Hempenius, G. J. Vancso, K. Shin, M. H. Rafailovich, [74] M. Breulmann, S. Förster, M. Antonietti, Macromol. Chem. Phys. 2000,
J. Sokolov, Macromolecules 2001, 34, 942. c) B. Sundrani, S. J. Sibener, 201, 204.
Macromolecules 2002, 35, 8531. [75] H. I. Smith, D. C. Flanders, Appl. Phys. Lett. 1978, 32, 349.
[64] a) K. W. Guarini, C. T. Black, K. R. Milkove, R. L. Sandstrom, J. Vac. Sci. [76] a) R. A. Segalman, H. Yokoyama, E. J. Kramer, Adv. Mater. 2001, 13,
Technol. B 2001, 19, 2784. b) C. T. Black, K. W. Guarini, K. R. Milkove, 1152. b) J. Hahn, S. E. Webber, Langmuir 2003, 19, 3098.
S. M. Baker, T. P. Russell, M. T. Tuominen, Appl. Phys. Lett. 2001, 79, 409. [77] J. P. Spatz, S. Mössmer, C. Hartmann, M. Möller, T. Herzog, M. Krieger,
[65] K. Liu, S. M. Baker, M. T. Tuominen T. P. Russell, I. K. Schuller, Phys. H.-G. Boyen, P. Ziemann, B. Kabius, Langmuir 2000, 16, 407.
Rev. B. 2001, 63, 060 403(R). [78] Y. Boontongkong, R. E. Cohen, Macromolecules 2002, 35, 3647.
[66] a) T. Thurn-Albrecht, R. Steiner, J. DeRouchey, C. M. Stafford, E. Huang, [79] a) J. P. Spatz, T. Herzog, S. Möûmer, P. Ziemann, M. Möller, Adv. Mater.
M. Bal, M. T. Tuominen, C. J. Hawker, T. P. Russell, Adv. Mater. 2000, 12, 1999, 11, 149. b) M. Haupt, S. Miller, K. Bitzer, K. Thonke, R. Sauer, J. P.
787. b) T. P. Russell, T. Thurn-Albrecht, M. T. Tuominen, E. Huang, C. J. Spatz, S. Möûmer, C. Hartmann, M. Möller, Phys. Status Solidi B 2001,
Hawker, Macromol. Symp. 2000, 159, 77. 224, 867. c) M. Haupt, S. Miller, A. Ladenburger, R. Sauer, K. Thonke,
[67] a) C. J. Brumlik, V. P. Menon, C. R. Martin, J. Mater. Res. 1994, 9, 1174. J. P. Spatz, S. Riethmüller, M. Möller, F. Banhart, J. Appl. Phys. 2002, 91,
b) S. Demoustier-Champagne, M. Delvaux, Mater. Sci. Eng., C 2001, 15, 6057.
269. c) C. R. Martin, M. Nishizawa, K. Jirage, M. S. Kang, S. B. Lee, Adv. [80] a) T. Kowalewski, N. V. Tsarevsky, T. Matyjaszewski, J. Am. Chem. Soc.
Mater. 2001, 13, 1351. d) M. Barbic, J. J. Mock, D. R. Smith, S. Schultz, 2002, 124, 10 632. b) T. Kowalewski, R. D. McCullough, K. Matyjaszewski,
J. Appl. Phys. 2002, 91, 9341. e) M. Wirtz, M. Parker, Y. Kobayashi, C. R. Eur. Phys. J. E 2003, 10, 5.
Martin, Chem. Eur. J. 2002, 8, 3573. [81] a) W. A. Lopes, H. M. Jaeger, Nature 2001, 414, 735. b) W. A. Lopes,
[68] a) A. Blondel, J. Meier, B. Doudin, J.-P. Ansermet, K. Attenborough, Phys. Rev. E 2002, 65, 031 606.
P. Evans, R. Hart, G. Nabiyouni, W. Schwarzacher, J. Magn. Magn. Ma- [82] M. Lazzari, M. C. Blanco, J. Rivas, M. A. López-Quintela, unpublished.
ter. 1995, 148, 317. b) S. Dubois, A. Michel, J. P. Eymery, J. L. Duvail, [83] H. Pernot, M. Baumert, F. Court, L. Leibler, Nat. Mater. 2002, 1, 54.

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