Nanoscience volume 1 nanostructures through chemistry

Specialist Periodical Reports

Edited by P O’Brien

Nanoscience
Volume 1: Nanostructures through Chemistry


Nanoscience
Volume 1: Nanostructures through Chemistry



A Specialist Periodical Report

Nanoscience
Volume 1: Nanostructures through
Chemistry
A Review of Recent Literature
Editor
Paul O’Brien, University of Manchester, UK

Authors
Victoria S Coker, University of Manchester, UK
Serena A. Corr, University of Kent, UK
Mark Green, King’s College London, UK
Sarah Haigh, University of Manchester, UK
Hiroaki Imai, Keio University, Japan
Ian A Kinloch, University of Manchester, UK
Gerrit van der Laan, University of Manchester, UK and Diamond Light
Source, UK

Jonathan R Lloyd, University of Manchester, UK
Mohammad Azad Malik, University of Manchester, UK
Ammu Mathew, Indian Institute of Technology Madras, India
Philip Moriarty, University of Nottingham, UK
Yuya Oaki, Keio University, Japan
Daniel Ortega, University College London, UK
Quentin A. Pankhurst, University College London, UK and The Royal
Institution of Great Britain
Arunkumar Panneerselvam, King’s College London, UK
Richard A D Pattrick, University of Manchester, UK
Carolyn I Pearce, Pacific and Northwest National Laboratory, USA
T. Pradeep, Indian Institute of Technology Madras, India
Karthik Ramasamy, University of Alabama, USA
Neerish Revaprasadu, University of Zululand, South Africa
Anirban Som, Indian Institute of Technology Madras, India
N. D. Telling, Keele University, UK
Paulrajpillai Lourdu Xavier, Indian Institute of Technology Madras, India
Robert J Young, University of Manchester, UK


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ISBN: 978-1-84973-435-6
DOI: 10.1039/9781849734844
ISSN: 2049-3541
A catalogue record for this book is available from the British Library
& The Royal Society of Chemistry 2013

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For further information see our web site at www.rsc.org


Preface
DOI: 10.1039/9781849734844-FP005

Welcome to the first Edition of a new RSC SPR Nanoscience. I would like to
begin by thanking all the authors for providing such interesting reading and
in time to meet our publication deadlines.
This SPR will try each year to feature different and topical issues. It
would frankly be impossible to cover this enormous area each year without
excessive length or condensation of the content. I hope some articles will
appear on an annual basis where there is sufficient activity and interest. A

new idea is to provide regional perspectives as in the chapter on India this
year. I am keen to commission an initial report on nanoscience in China as
well as other regional perspectives reflecting growth areas in contemporary
science and engineering.
I do hope that you enjoy the book and find it useful. I am happy to receive
suggestions for contributions over the next few months.
Paul O’Brien
Manchester

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CONTENTS
Cover
The cover image shows a model of
molecules of water being channelled
through a single-walled carbon
nanotube.

Preface
Paul O’Brien

v

Recent advances in mesocrystals and their related structures

Yuya Oaki and Hiroaki Imai
1 Introduction to mesocrystals and nonclassical
crystallization
2 Mesocrystals and their related structures
3 Recent development and application of mesocrystals
4 Conclusions and outlook
Acknowledgement
References

1

Nanomaterials for solar energy
Mohammad Azad Malik, Neerish Revaprasadu and
Karthik Ramasamy
1 Introduction
2 Ternary and quaternary materials
3 Binary materials
4 Conclusion
References

1
3
17
24
25
25

29

29

30
36
56
56

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Magnetic hyperthermia
Daniel Ortega and Quentin A. Pankhurst
1 Introduction
2 Physical principles of magnetic hyperthermia
3 Biocompatible magnetic colloids for hyperthermia
4 Clinical trials: recent case studies
5 Conclusions
References

Recent developments in transmission electron microscopy and their
application for nanoparticle characterisation
Sarah Haigh
1 Aberration corrected transmission electron microscopy
2 Exit wavefunction restoration
3 Chromatic aberration correction
4 Electron energy loss spectroscopy
5 Energy dispersive x-ray spectroscopy (EDXS)
6 Specimen preparation

7 Three dimensional TEM tomography
8 Conclusions
References

60
60
63
74
80
84
85

89

89
90
90
92
94
96
97
98
99

Extracellular bacterial production of doped magnetite nanoparticles

102

Richard A D Pattrick, Victoria S Coker, Carolyn I Pearce,
Neil D Telling, Gerrit van der Laan and Jonathan R Lloyd

1 Introduction
2 Exploiting extracellular biogenic magnetite
3 Metal doped magnetites
4 X-ray magnetic circular dichroism (XMCD)
5 Vanadium biomagnetite
6 Bionanomagnetite in textile wastewater treatment
7 Conclusions
Acknowledgements
References

102
105
105
107
108
110
112
112
113

Atom-technology and beyond: manipulating matter using scanning
probes
Philip Moriarty
1 Introduction
2 A potted history of advances in (ultra)high resolution SPM
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116

116

117


3

Plucking, positioning, and perturbing atoms at silicon
surfaces
4 Visualising (intra)molecular force-fields and submolecular
structure
5 ‘Dialling in’ dirac fermions and addressing atomic spins
6 The trouble with tips (reprise)
7 Conclusions
Acknowledgements
References

120
129
137
139
141
141
141

Graphene and graphene-based nanocomposites

145

Robert J Young and Ian A Kinloch
1 Introduction
2 Graphene

3 Graphene oxide
4 Nanocomposites
5 Functional nanocomposites
6 Conclusions and prospects
References

145
146
153
158
169
171
171

Metal oxide nanoparticles
Serena A Corr
1 Introduction
2 Recent synthetic developments
3 Case study of advances in characterisation: BaTiO3
nanoparticles
4 Concluding remarks
References

180
180
182
202

Recent advances in quantum dot synthesis

208

Arunkumar Panneerselvam and Mark Green
Introduction
II-VI chalcogenides
Transition metal chalcogenides
Copper chalcogenides
IV-VI chalcogenides
Ternary materials
Copper-based multicomponent chalcogenides

208
209
215
218
223
228
232

204
205

Nanoscience, 2013, 1, vii–x | ix


Phosphide and arsenide – containing quantum dots
Acknowledgements
References

235

239
239

Nanoscience in India: a perspective
Anirban Som, Ammu Mathew, Paulrajpillai Lourdu Xavier and
T. Pradeep
1 Introduction
2 Nanoscience research in India
3 Applications of nanomaterials
4 Nano-bio interface, nanomedicine and nanotoxicity
5 Nano and industry
6 Nano and education
7 Future of nano-research in India
8 Conclusions
Acknowledgement
References

244

x | Nanoscience, 2013, 1, vii–x

244
246
260
266
272
273
274
274
275

275


Recent advances in mesocrystals and their
related structures
Yuya Oaki and Hiroaki Imai*
DOI: 10.1039/9781849734844-00001

Noncalssical crystallization has attracted much interest in recent years. In classical
models, crystalline materials were classified into single crystal and polycrystal. A
variety of recent reports have showed mesocrystals as the intermediate states
between single crystal and polycrystal. The present report focuses on mesocrystals
and their related architectures consisting of the unit crystals. A variety of
mesocrystals and their related architectures were categorized by the ordered state
of the unit crystals. These new superstructures have potentials for a variety of
applications, such as electrode and catalyst materials.

1

Introduction to mesocrystals and nonclassical crystallization

1.1 Crystalline materials – Two categories: classical and nonclassical
In classical models, crystalline materials have been classified into single
crystal and polycrystal. In nonclassical models, mesocrystals are defined as
the intermediate states between single crystal and polycrystal (Fig. 1). Single
crystal can be regarded as the regular continuous packing of unit cells. For
example, hexagonal prisms of quarts and cubes of table salt are typical single
crystals. The macroscopic faceted morphologies consist of a continuous
arrangement of unit cells. We cannot observe any intermediate ordered structures between the macroscopic shape and the atomic arrangements (Fig. 1a).
The crystallographic direction is the same throughout the macroscopic

shapes. In contrast, polycrystals are a random aggregate of small single crystals.
The crystallographic direction of each single crystal is not the same in the
aggregate (Fig. 1i). In a classical category of crystalline materials, researchers
can classify the crystalline materials only into single crystals and polycrystals.
Many researchers have observed ordered arrangements of unit crystals that
are not simply assigned to a polycrystal.1–8 The presence of a segmentalized unit
is not ascribed to a perfect single crystal. The oriented architectures of
unit single crystals can be regarded as an intermediate structures between
single crystals and polycrystals (Fig. 1c–e). Based on these facts, Co¨lfen and
Antonietti proposed mesocrystal as a new category of crystalline materials
consisting of oriented nanocrystals.1–3 The colloidal crystallization of faceted
nanocrystals leads to the formation of mesocrystals. The term of mesocrystal
spread rapidly since the proposal of the concept. A variety of review articles
related to mesocrystals have been published.4–8 In recent years, Zhou and
O’Brien extended the concept of mesocrystals by addition of related structures.5,8
Recent studies suggest nonclassical crystallization processes as well as
the structures and applications of mesocrystals. The appearance of
Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1
Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan. E-mail: ,


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Fig. 1 Schematic illustrations of single crystal (a), polycrystal (i), and intermediate structures
(b–h).

prenucleation clusters is one of the most important findings in nonclassical
crystallization behavior.9–13 In addition, the presence of precursor phases
and their roles for the subsequent crystallization have been studied in an
attempt to understand nonclassical crystallization behavior.14,15
In the present article, we focus on the structures and applications of
mesocrystals. In Section 1.2, the structure is reviewed using biominerals as a
typical model of mesocrystal. In Section 2, mesocrystals and their related
structures are summarized with recent papers. In Section 3, the applications
of mesocrystals are introduced on the basis of recent reports.
1.2 Biominerals – A model of mesocrystals
Mesocrystal is found in biominerals, such as the nacreous layer, sea urchin
spine, and eggshell (Fig. 2).16–20 In previous work, researchers tried to
determine whether or not the crystal structures of these biominerals are
single crystal.21–30 Our group reported that carbonate-based biominerals
possess mesocrystal structures.16–19 At approximately the same time,
Sethmann and coworkers reported on the presence of nanostructures in
biominerals.20 We analyzed the nanoscopic structures of biominerals, such
as the nacreous layers, corals, echinoderms, foraminifers, and eggshells.
These biominerals have unique macroscopic and micrometer-scale
morphologies (Fig. 2a). Nanocrystals 20–100 nm in size are observed on
magnified scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) images regardless of the polymorphs, such as calcite and
aragonite of calcium carbonate (CaCO3) (Fig. 2b–e). The spotted electron
diffraction patterns are observed on these biominerals (Fig. 3a,b). The peak
broadening originating from the miniaturization of the crystallites is not
recognized on the XRD pattern (Fig. 3c). In addition, each unit crystal
is found to be arranged in the same direction in TEM images (Fig. 3d,e).
These facts indicate that the nanocrystals, as the building blocks, are
oriented in the same crystallographic directions. Since the diffraction

behavior is the same as that of the single crystals, these biominerals were
recognized as single crystals in previous studies. Based on electron
microscopy and diffraction analyses, the biominerals form mesocrystal
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Fig. 2 Summarized SEM (a,b) and TEM (c–e) images of the biominerals investigated in this
report. (a) the macroscopic appearance (inset) and the SEM images of the characteristic
morphologies. (b) the magnified SEM images on the fractured surface, indicating the presence
of nanoscopic structures. (c) the corresponding TEM images in the same scale as panel b.
(d) the TEM images of each nanocrystal exhibiting a specified facet. (e) the high-resolution
TEM images of the nanocrystals, showing that a nanocrystal is a single crystal. Reprinted with
permission from Wiley-VCH.17–19

structures consisting of oriented nanocrystals with biological macromolecules. The nanocrystals and the biological macromolecules can be
regarded as the nanoscale bricks and mortar, respectively. Since the nanocrystals are the building blocks for morphogenesis, living organisms can
make up a variety of macroscopic shapes with single crystalline orientation
through biomineralization. the first line in either of the columns and press the
required button.
2

Mesocrystals and their related structures

Mesocrystals can be regarded as the intermediate state between single
crystals and polycrystals. In the present article, mesocrystal is defined as the
oriented nanocrystals in the same crystallographic direction. Recently, a
number of reports have shown a number of related structures to mesocrystals. In this section, five types of mesocrystals and their related structures are introduced. The classification is based on the degree of the
ordering and the orientation of the unit crystals, even though the size and
shape of the unit crystals are different.
2.1 Oriented nanocrystals

As reported in detail in the reviews and in the literature, mesocrystal in the
narrow sense of the term is the assembly of oriented nanocrystals with
organic molecules (Fig. 1d). A variety of oriented nanocrystals have been
Nanoscience, 2013, 1, 1–28 | 3


Fig. 3 TEM with SAED (a,b,d,e) and XRD (c) analyses of the nanostructures in biominerals.
(a,b) the TEM images of the assembly with the SAED spot pattern (insets) in the nacreous layer
and eggshell, respectively. (c) XRD profiles of the powdered samples to analyze the peak
broadening (A: calcite single crystal (reference), B: a sea urchin (Heterocentrotus mammillatus),
C: a sea urchin spine (Echinometra mathaei (Blainville)), D: the shell of a sea urchin (scientific
name unknown)). The slight differences of the 2y values are ascribed to the doping of magnesium ions in biogenic calcite. (d,e) TEM images of the assembled nanocrystals with a similar
morphology to the each unit crystal and the schematic model of the crystallographic direction
estimated from the dihedral angle (inset). Reprinted with permission from Wiley-VCH.17–19

reported in previous studies. The formation of oriented nanocrystals is
mediated by the assembly of the particles.
For example, a variety of mesocrystals, such as CaCO3, BaSO4, Fe2O3,
and TiO2, were synthesized in the presence of organic molecules.31–44
Unit crystals with the adsorption of organic molecules are arranged in the
same crystallographic orientation. Co¨lfen and co-workers reported on
the formation of the calcite CaCO3 mesocrystals in the presence of
polystyrene sulfonate and its block polymers (Fig. 4).31,32 The faceted
rhombohedral shapes of calcite were changed to the morphologies
exposing the unusual crystal faces with an increase in the PSS
concentration. Zhou and O’Brien reported the formation of the
NH4TiOF3 mesocrystal in the presence of a surfactant (Fig. 5).33,34 Based
on a time-dependent observation, the particle-mediated crystallization
leads to the formation of mesocrystals. Kato and co-workers reported on
4 | Nanoscience, 2013, 1, 1–28

Fig. 4 SEM images of calcite mesocrystals synthesized in the presence of PSS (a–c) and
poly(styrene-alt-maleic acid) (d,e). (a–c) morphological variations with an increase in the PSS
concentration. (d,e) trigonal calcite mesocrystals with triangular capped building blocks.
Reprinted with permission from Wiley-VCH.32

Fig. 5 (a) Top and (b) cross-sectional SEM images of an NH4TiOF3 mesocrystal particle.
(c) Low- and (f) high-magnification TEM images of an NH4TiOF3 mesocrystal, and (d)
corresponding SAED pattern. (e) Still images taken from the video, which show identical
diffraction from different parts of an NH4TiOF3 mesocrystal. Reprinted with permission from
the Royal Society of Chemistry.33

Nanoscience, 2013, 1, 1–28 | 5


Fig. 6 SEM (a,b,e,f), optical microscopy (d), TEM (c) images of a variety of CaCO3-based
thin-film composites. (a–c) the thin film formed on the chitin matrix in the presence of
calcification-associated peptide (CAP-1) extracted from the exoskeleton of a crayfish. (d–f) rodlike mesocrystals formed on the oriented chitin matrices in the presence of PAA. Reprinted with
permission from Wiley-VCH.37,38

CaCO3 thin films with a variety of morphologies. Since the architectures
consist of nanocrystals with the acidic macromolecules, a variety of
morphologies with a specific crystallographic orientation can be formed
(Fig. 6).35–38 Yu and Co¨lfen reported the helical morphologies of BaCO3
through polymer-mediated crystallization (Fig. 7).39 The oriented and
spiral assembly of the unit crystals made up the helical shapes, whereas the
twisted morphologies were formed by the periodic changes of the growth
direction of each unit in our reports (see 2.4). It is noteworthy that the achiral
nanocrystals form the chiral shapes through the formation of mesocrystals.

Our group has reported on bridged nanocrystals (Fig. 1c).16–19,45,46 We
found that nanocrystals less than 100 nm in size were arranged with the
same crystallographic orientation in a number of CaCO3-based biominerals, such as nacreous layers, coral, sea urchin spines, and eggshells
(Fig. 2). As shown in Fig. 8, these nanocrystals were connected via nanoscale bridges.17 The spotted SAED pattern suggests that the resultant
architectures had a single crystalline orientation (Fig. 3). The oriented
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Fig. 7 SEM image (a) of the helical BaCO3 crystals and its schematic illustration (b).
Reprinted with permission from Nature Publishing Group.39

Fig. 8 FETEM images of the oriented nanocrystals with the bridges. (a,b) the nanoscale
bridges observed on a sea urchin spine (a) and an eggshell (b), respectively. (c,d) the
connected nanocrystals of potassium sulfate (c) and potassium hydrogen phthalate (d),
respectively. Reprinted with permission from Wiley-VCH and the Chemical Society of
Japan.17,45

nanocrystals in biominerals can be interpreted as a bridged architecture
with the incorporation of biological macromolecules. We also observed that
nanocrystals as the building blocks of the biomimetic materials are connected with each other (Fig. 8c,d). Since the crystallographic orientation
gradually vary with nonconformity or twin formation with the bridges, a
variety of macroscopic morphologies can be generated from the nanocrystals, especially in terms of complex or curved shapes with a smooth surface.
Since the nanocrystals are the building blocks, versatile macroscopic
shapes can be formed with the assistance of organic molecules. For example,
the cone-shaped and hierarchical architectures of sulfates and chromates
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Fig. 9 Hierarchical architectures based on K2SO4 (a–d) and CaCO3 (e,f) mesocrystals formed
in the presence of PAA. Reprinted with permission from Wiley-VCH and Nature Publishing

Group.43,44

were reported in the earlier works.40–43 Our group has reported a variety of
hierarchically organized structures based on mesocrystals (Fig. 9).43,44 The
formation of mesocrystals from nanocrystals is ascribed to the models of
particle-mediated assembly and bridged growth. However, the formation
mechanisms of the complex macroscopic shapes remain unclear issues.
2.2 Supercrystals and superlattices – Ordered assembly of nanocrystals
An ordered arrangement of particles, colloidal crystals, is found in a wide
range of scales. Opal is a typical colloidal crystal with an ordered
arrangement of silica particles.47 Photonic crystals have been developed
for the control of optical properties.48 A variety of supercrystals and
superlattices consisting of nanoparticles are fabricated through selfassembly.49–64 When the unit particles are an amorphous material and the
crystal lattices of each unit particle are not oriented, the colloidal assembly
is not regarded as a mesocrystal (Fig. 1g). In contrast, colloidal crystals
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Fig. 10 TEM images of the oriented assembly of the nanomaterials. (a) BaCrO4 nanorods,57
(b) Y2O3 nanorods,58 (c) tungsten oxide nanorods,59 (d) Ag polyhedrons,60 (e) Ag cubes,61
(f) CdS hexagonal prisms,62 (g–i) CeO2.63 Reprinted with permission from Nature publishing
group, Royal Society of Chemistry, and the American Chemical Society.

Fig. 11 SEM images of magnetite (Fe3O4) colloidal crystals in the Tagish Lake meteorite.
The morphology is inset at the upper right in each image. (a) Colloidal crystal with the bct
structure composed of octahedral, crystalline nanoparticles of Fe3O4 bounded by {111} faces.
(b) Colloidal crystal with the fcc structure. The morphology of theconstituent particles is
rhombic-dodecahedral, bounded only by {110} faces. (c) Colloidal crystal with the fcc structure
composed of particles bounded by {100}, {110}, and {311} faces. Reprinted with permission
from the American Chemical Society.65

consisting of faceted nanocrystals have been reported (Fig. 1e). For
example, the ordered arrays of barium chromate, yttrium oxide, tungsten
oxide, silver, and cadmium sulfide nanomaterials were mediated by organic
molecules (Fig. 10).57–64 In nature, Tsukamoto and co-workers recently
found an ordered array of magnetite nanocrystals in a meteorite65 (Fig. 11).
Nanoscience, 2013, 1, 1–28 | 9


The crystallographic direction of the unit particles is oriented in these
colloidal crystals. Therefore, these supercrystals are one of mesocrystals
comprised of the isolated nanoscale units. These findings suggest that the
self-assembled oriented architectures are easily formed by the faceted
polyhedral units with the surface modification by the organic molecules.
The shapes of the unit crystals are involved in the geometrical packing
state.
2.3 Porous single crystal
Porous single crystal has a continuous single crystalline framework with a
porous interior or occluded organic domains (Fig. 1b). Meldrum and
coworkers have recently reported the calcite single crystal occluded with 13
wt% of copolymer micelles ca. 20 nm in size (Fig. 12).66 The resultant
sponge crystals showed the same mechanical strength as that of the biogenic
calcite. Li and Estroff reported that single crystalline calcite was formed
with the occlusion of agarose gel (Fig. 13).67–69 In addition, the network
structures of the occluded organic molecules were visualized using an
electron tomography technique. Qi and coworkers have shown the syntheses of porous calcite single crystals using ordered arrangement of polymer
latex.70 These architectures are classified into not a perfect dense single
crystal but a type of mesocrystals, namely porous single crystal. It is inferred
that these single-crystalline structures are formed by the growth with
exclusion of organic molecules.

2.4 Periodic changes of the crystallographic directions in unit crystals
The branched forms, dumbbell shapes, and curved and twisted morphologies are observed in a variety of materials through self-organization.70
In these architectures, the unit crystals are arranged with the periodic

Fig. 12 SEM images of calcite crystals precipitated in the presence of copolymer micelles (a,b)
and their schematic representations (c,d). Reprinted with permission from Nature Publishing
Group.69

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Fig. 13 SEM images of the calcite sponge crystals grown in an agarose gel (a–c) and in the
presence of polymer microparticles (d,e). (a,b) the calcite crystal grown in an agarose gel after
etching in water, (c) tomographic reconstructions of the agarose network inside of a section of
a-sprepared calcite. (d,e) the calcite crystals synthesized in the presence of polymer latex particles with 380 nm in size after the dissolution of the polymer. Reprinted with permission from
the Royal Society of Chemistry, National Academy of Science (USA), and the American
Chemical Society.67,69,70

changes of their crystallographic orientations (Fig. 1f). The ordered
architectures are neither a random assembly of the units nor single
crystalline materials. For example, Kniep and co-workers have reported
that fluoroapatite with branched and dumbbell shapes is formed in gelatin
matrices (Fig. 14).71,72 Since the growth of rod-shaped unit crystal
proceeds with three-dimensional regular branching, the dumbbell
morphologies are obtained. Yu and co-workers reported that dumbbell
shaped barium carbonate crystals were obtained not in the gel matrices
but in the presence of polymers (Fig. 15a,b).73 They also showed that the
branched growth with the periodic changes of the crystallographic
direction led to the formation of the dumbbell shapes (Fig. 15c–e). When
the unit crystals had the platy morphologies of calcium carbonate,

a similar growth behavior was observed in the polymer-mediated
crystallization (Fig. 16).74
Kato and co-workers have developed thin-film composites of CaCO3 and
organic macromolecules.75–78 When CaCO3 crystals are grown on poly(vinyl alcohol) matrices with the addition of poly(acrylic acid), relief structures are obtained on the thin film. They prepared calcite thin-film crystals
with the periodic changes of crystallographic orientations in the first step
(Fig. 17).77 In the second step, the relief structures consisting of needlelike
Nanoscience, 2013, 1, 1–28 | 11


Fig. 14 SEM and TEM images of the fluorapatite–gelatin composites. (a–d) SEM images
illustrating subsequent states of the morphogeneses for fan-like (left frames) and fractal (right
frames) growth mechanisms. (e) SEM images of the half of a dumbbell aggregate viewed along
the central seed axis. Inset: Central seed exhibiting tendencies of splitting at both ends (small
dumbbell). (f) TEM images of a fluorapatite–gelatine nanocomposite individual showing first
states of branching in the fan-like growth series. Reprinted with permission from WileyVCH.71,72

Fig. 15 Morphological evolution of the BaCO3 crystals obtained in the presence of PEG-bPMAA on a glass slip. (a) the presence of quadrupolar structures as a defect event. The insert
shows a typical fragmented half of a dumbbell and a growing dumbbell. (b) enlarged picture
shows detailed structure of the dumbbells with a thin connecting bar. (c–e) the schematic
growth models. Reprinted with permission from the American Chemical Society.73

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Fig. 16 SEM image of the convex–concave calcite (a) and its proposed formation mechanisms
(b). The primary blocks assemble to give flat, pseudo-symmetric mesocrystal structures. When a
certain size is exceeded, not only primary platelets, but also amorphous intermediates (spheres)
are attracted. By recrystallization of those species, bent crystalline structures without translational order can develop. Reprinted with permission from Wiley-VCH.74

Fig. 17 SEM images (a–d) and their schematic representation (e,f) of the relief structures

consisting of the CaCO3 crystals grown on the PVA matrices in the presence of PAA
after incubation for 8 h s the first step (a,b) and (c,d) 16 h. (a,b) the first step providing the thinfilm composites with the flat surface, (c,d) the second step leading to the self-organization of the
relief structures. Reprinted with permission from the American Chemical Society.77

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crystals spontaneously formed on the thin-film crystals obtained in the first
step. Since the c-axis directions as the growth direction of the needle-shaped
units periodically change, unique relief architectures are formed through
self-organization (Fig. 17e,f).
Our group has prepared a variety of helical morphologies of unit crystals
with the twisted growth in a specific crystallographic direction (Fig. 18).79–86
The twisted morphologies of K2Cr2O7, H3BO3, K2SO4, CuSO4 Á 5H2O, and
aspartic acid are formed in gel matrices. Since the unit crystals are not
oriented in the same crystallographic directions, these architectures with the
periodic changes of the crystallographic direction can be defined as a related
structure of mesocrystals.
In general, the morphologies of crystals change with an increase in the
driving force for crystallization (Fig. 19).46,80 A faceted single crystal is

Fig. 18 SEM images of the twisted morphologies consisting of the unit crystals. (a) K2Cr2O7,
(b) H3BO3, (c) K2SO4, (d) aspartic acid, (e) CuSO4 Á 5H2O, (f) the schematic models of the
twisted assembly consisting of the unit crystals. The crystallographic orientations are periodically changed with the growth in the axis. Reprinted with permission from the American
Chemical Society and Wiley-VCH.81,84,85

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