Communications
[16] J. P. Dismukes, J. W. Johnson, E. W. Corcoran, J. Vallone, J. J. Pizzuli,
M. P. Anderson, US Patent 5 643 987, 1997.
[17] J. P. Dismukes, J. S. Bradley, J. W. Johnson, E. W. Corcoran, US Patent
5 696 217, 1997.
[18] J. P. Dismukes, J. W. Johnson, J. S. Bradley, J. M. Millar, Chem. Mater.
1997, 9, 699.
[19] J. Lipowitz, J. A. Rabe, L. K. Frevel, R. L. Miller, J. Mater. Sci. 1990,
25, 2118.
[20] N. R. Dando, A. J. Perrotta, C. Strohmann, R. M. Stewart, D. Seyferth, Chem. Mater. 1993, 5, 1624.
[21] J. Desmaison, D. Giraud, M. Billy, Rev. Chim. Miner. 1972, 9, 417.
[22] E. A. Leone, S. Curran, M. E. Kotun, G. Carrasquillo, R. van Weeren,
S. C. Danforth, J. Am. Ceram. Soc. 1996, 79, 513.
[23] G. Horvath, K. Kawazo, J. Chem. Eng. Jpn. 1983, 16, 470.
[24] A. F. Venero, J. N. Chiou, Mater. Res. Soc. Symp. Proc. 1988, 111, 235.
[25] Argon adsorption isotherms were measured at 87 K on an Omnisorp
360 instrument (Coulter). Surface areas were determined derived from
BET analysis of the low pressure part of the isotherm. Micropore size
distribution was determined by the Horvath±Kawazoe model using
ADP software, version 3.03 (Porotec GmbH, Frankfurt), using a nitrogen on carbon potential at 77 K.
[26] Laser Synthesized Silicon Nitride Powder: Chemical and Physical
Characteristics (Eds: B. W. Sheldon, S. C. Danforth), American
Ceramic Society, Westerville, OH 1994, Vol. 42, p. 47.
[27] Gmelin: Handbook of Inorganic and Organometallic Chemistry, Si
Suppl., Vol. B4, Springer, Berlin 1989, p. 134.
[28] O. Glemser, P. Neumann, Z. Anorg. Allg. Chem. 1959, 298, 134.
[29] D. Peters, H. Jacobs, J. Less-Common Met. 1989, 146, 241.
[30] W. F. Maier, I.-C. Tilgner, M. Wiedhorn, H. C. Ko, Adv. Mater. 1993, 5,
726.
[31] W. F. Maier, J. A. Martens, S. Klein, J. Heilmann, R. Parton, K. Vercruysse, P. A. Jacobs, Angew. Chem., Int. Ed. Engl. 1996, 35, 180;
Angew. Chem. 1996, 108, 222.
[32] New Solid Acids and Bases: Their Catalytic Properties (Eds: K. Tanabe,
M. Misono, Y. Ono, H. Hattori), Elsevier, Amsterdam 1989 Vol. 51.
[33] W. F. Hölderich, in Proc. of the 10th Int. Congress on Catalysis (Eds: L.
Guczi, F. Solymosi, P. TØtØnyi), Elsevier, Amsterdam 1992, p. 127.
[34] Y. Ono, T. Baba, T. Catal. Today 1997, 38, 321.
[35] H. Hattori, Chem. Rev. 1995, 95, 537.
range,[2] while the synthesis of replicas of the L3 sponge
phase[5] and phase-separated block copolymers[6] has taken
the mesopore range upwards by about a factor of three. Inorganic mesostructures are beginning to spread throughout
the whole periodic table; phosphate, oxide, sulfide, and platinate mesophases have produced insulating, semiconducting, and metallic mesostructures.[3,4]
The synthesis of inorganic analogues of lyotropic hexagonal, cubic, and lamellar mesophases suggests that it may
be possible to replicate inorganic versions of the less well
known intermediate tetragonal, rhombohedral, and monoclinic mesh mesophases.[7] The morphological description
of the mesh stems from the mathematical topology of hyperbolic surfaces.[8,9] Some square mesh surfaces of different mean curvature are illustrated in Figure 1. The simplest
description of a mesh is a two-periodic hyperbolic surface
confined between two parallel bounding planes with a regular network of pores joining the two parallel sheets. Thus
an amphiphilic mesh phase contains a two-dimensional array of pores embedded within a bilayer. Holes in the bilayer are considered to be puncture defects and the parallel
stacking of mesh surfaces leads to a network of tunnels.[8,9]
Although lyotropic mesh phases are rather rare, their existence raises the possibility that they may be utilized to template an inorganic mesh.
Tin Sulfide Mesh: AFM Imaging of Lamellae
and Mesopores**
By Igor Sokolov, Tong Jiang, and Geoffrey A. Ozin*
Synthesis of inorganic copies of lyotropic mesophases
represents a paradigm shift in materials chemistry.[1] Since
researchers from Mobil[2] announced their discovery of liquid crystal templating of mesostructured silica in 1992, such
replica chemistry has leapt into the realm of hierarchical
inorganic materials, in which morphology and structure are
controlled over three length scales and spatial dimensions.[3,4] Since this breakthrough, a diversity of amphiphilic
assemblies and inorganic precursors have been combined
to create a myriad of composite mesostructures. Using surfactant templates and organic additives, mesopore dimensions have been finely tuned over the 20±100 Š size
±
[*] Prof. G. A. Ozin, Dr. I. Sokolov, Dr. T. Jiang
Lash Miller Chemical Laboratories
University of Toronto
80 St. George Street, Toronto, Ontario M5S 3H6 (Canada)
[**] Financial support for this research from the Natural Sciences and Engineering Research Council of Canada (NSERC) and Universal Oil
Products (UOP) is deeply appreciated.
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Fig. 1. Illustration of some two-periodic square mesh surfaces of different
mean curvature [7±9].
Recently we reported the synthesis of a novel tin sulfide±
alkylamine composite mesostructure, denoted Meso-SnS-1,
with stoichiometry Sn1.00S2.07(HDA)2.34(H2O)2.23, where
HDA represents hexadecylamine.[10] Powder X-ray diffraction (PXRD), transmission electron microscopy (TEM),
119
Sn NMR and 119Sn Mössbauer studies indicated that the
structure of the as-synthesized crystalline material is based
upon parallel-stacked mesoporous tin(IV) sulfide layers
sandwiched between a mixed bilayer of neutral and protonated hexadecylamine. Because of the unique combination
of electrical, optical, and thermotropic liquid-crystalline
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properties revealed for Meso-SnS-1, it is important to learn
as much as possible about the structure of the material.
This is especially important because the material is electron
beam sensitive, which renders the recording of TEM
images somewhat problematical.[10] In an effort to provide
reliable high resolution structural information about the lamellae and mesopores in such a soft and flexible material,
in this study we have resorted to gentle imaging atomic
force microscopy (AFM) techniques, which have recently
proved successful for imaging the mesostructure of a 500 Š
thick lyotropic liquid-crystalline film on a graphite substrate.[11]
As-synthesized Meso-SnS-1 was initially tested to see
how it stood up to AFM scanning when the flaky micrometer-sized crystals were simply deposited onto a layer of
epoxy. The pristine material supported in this way is extremely soft and not at all suitable for obtaining high resolution images of the mesostructure. An approach that
yielded acceptable quality AFM images involved initially
annealing the material, at around the liquid crystal transition temperature of 85 C for about 2 h,[10] between two
glass slides. To facilitate both homeotropic and planar organization of the director field of the tin sulfide mesophase
with respect to the contacting surfaces of the glass slides,
either transverse compression or lateral shear forces were
applied to the Meso-SnS-1 liquid crystal film for a period
of 1 min. The material was allowed to crystallize slowly
over a period of a few days at room temperature to optimize the degree of orientational order in the film and to
provide the smoothest possible surfaces for AFM imaging
of the mesostructure. Images were recorded immediately
after one of the confining glass plates had been removed
from the film. Flat areas that were found after this cleavage
process were scanned with the atomic force microscope.
No significant differences were found for the samples prepared with the application of transverse compression or lateral shear forces. With these sample preparation protocols
it proved possible to create exposed patches of the MesoSnS-1 film in which the lamellae and mesopores were
more-or-less correctly aligned for AFM soft imaging of the
mesostructure.
All AFM images of Meso-SnS-1 films were obtained
using the tapping mode technique on a Digital Instruments
NanoScope III with a phase extender module.[11] The extreme softness of the material does not allow the use of the
contact mode, as previously found in the imaging of lyotropic liquid-crystalline films.[11] The A+B feedback signal was
about 3 V while the root mean square (RMS) signal was
set as small as possible to record images at around 0.1±
0.2 V. Feedback gain parameters were set between 0.2 and
1 for both integral and proportional gains. A Digital Instruments Nanoprobe SPM TESP silicon tip (resonance frequency 250±300 kHz) for tapping mode in air and NTMDT UltraSharp silicon cantilevers SCS11 (resonance frequency 300±380 kHz) were used for this imaging study. The
drive amplitude was set between 10 and 30 mV (<10 nm).
Adv. Mater. 1998, 10, No. 12
Use of such a small amplitude to minimize the tip±sample
interaction has been reported previously.[11] The D scan
head (maximum scan area 12.5 ´ 12.5 mm2, z-sensitivity
9 nm/V) was employed throughout this study. Scan rates
were chosen in the range of 0.5±1.5 Hz.
Large-area unfiltered AFM images of Meso-SnS-1 are
shown in Figures 2A±C. The layered structure is quite apparent. In particular, the orientation of lamellae tends to
be upright in the first two images and more-or-less lying
flat in the third, with respect to the surface of the glass substrate. It seems from systematic studies of many images of
this kind that shear and compression forces applied to the
sample held between the glass plates tend to favor respectively planar and homeotropic alignment of the director
fields of the tin sulfide mesophase. Typically, the interlayer
distance was found to be about 5 nm, which is essentially
the same as the interlamellar spacing observed by PXRD
and TEM imaging of Meso-SnS-1.[10]
Higher resolution AFM scans support and amplify these
observations. Note that small inclines in the area being imaged are removed by the planefit option in the NanoScope
software package. Furthermore, artifacts were excluded
from the recorded images by decreasing the scanning tapping force, varying the feedback parameters, and changing
the scan direction and scan speed. Typical high resolution
raw AFM images of Meso-SnS-1 are displayed in Figures 3A and B, which show mostly uniaxial striations,
corresponding to the layered mesostructure. The parallelstacked layers are clearly observed and consistently emerge
with an interlayer spacing of around 5 nm.
It is more challenging to observe the surface mesostructure of a sheet. This necessitated exploration of the film
surface for flat areas such as the one indicated by the white
arrow in Figure 2C. A high magnification raw AFM image
of such an area, recorded in height mode, is displayed in
Figure 2D. Vertical distances between the layers in Figure 2D are about 5±8 nm, which corresponds to the expected interlayer distance. Figures 3C and 3D present raw
AFM images of the surface of a sheet. The pore structure is
clearly revealed after noise filtering by applying a twodimensional fast Fourier transform (2D-FFT), Figure 4.
Some raw AFM images of the most regular surface structure that has been observed for Meso-SnS-1 are presented
in Figures 5A and B. Numerous regions of this type have
been imaged and typically reveal patches of a regular mesostructure with lattice constants that lie in the range between ca. 3 and 10 nm, implying either that the mesopores
have a range of sizes or that they are being imaged in different orientations, or both (Figs. 4,5). The images also depict the existence of what appear to be topological defects
associated with the organization of the mesopores in the lamellae of Meso-SnS-1. This may explain the presence of
many orders of PXRD reflections originating from the
layers but not the mesopores.[10] Further studies will be
needed to define the subtleties of mesostructure and defects in meso-SnS-1 in greater depth.
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A
B
D
C
A
C
B
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Fig. 2. Large area raw AFM images of
Meso-SnS-1 depicting regions of lamellae
in both a standing-up and lying-down configuration with respect to the surface of the
glass substrate.
D
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Fig. 3. Typical high resolution raw AFM
images of lamellae and mesopores in MesoSnS-1.
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Communications
A
A
B
B
Fig. 5. Raw AFM images of one of the most regular surface structures observed for Meso-SnS-1.
some perturbation of the actual symmetry and dimensions
of the lamellae and mesopores in the proposed mesh phase.
Surface interactions, topological defects, and director fields
in organic and inorganic mesh phases are issues that need
to be addressed both experimentally and theoretically in
the future.
Received: December 8, 1997
Final version: March 12, 1998
C
Fig. 4. 2D-FFT filtered images of three regions of Meso-SnS-1, with the lamellae organized roughly parallel to the surface of the glass substrate, that
mostly reveal areas with periodic arrangements of the mesopores.
Overall, the AFM images of Meso-SnS-1 give the impression that the structure of the material may be described
as a tin sulfide mimic of a mesh phase with rhombohedral
or monoclinic space symmetry. Although the reported
images are highly reproducible, the structure is extremely
pliable and susceptible to plastic deformation. Therefore it
is conceivable that, even with the gentle imaging AFM recording procedures used in this study, there may have been
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±
[1] S. Mann, G. A. Ozin, Nature 1996, 382, 313.
[2] C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, J. S. Beck,
Nature 1992, 359, 710.
[3] E. Chomski, D. Khushalani, M. MacLachlan, G. A. Ozin, Curr. Opin.
Colloid Interface Sci. 1998, 3, 181.
[4] S. Oliver, H. Yang, D. Khushalani, G. A. Ozin, J. Chem. Soc., Dalton
Trans. 1997, 20, 3074.
[5] K. M. McGrath, D. M. Dabbs, N. Yao, I. A. Aksay, S. M. Gruner, Science 1997, 277, 552.
[6] D. Zhao, J. Feng, Q. Ho, N. Melosh, G. H. Fredrickson, B. F. Chmelka,
G. D. Stucky, Science 1998, 279, 548. M. Templin, A. Franck, A. Du
Chesne, H. Leist, Y. Zhang, R. Ulrich, V. Schädler, U. Wiesner, Science
1998, 278, 1795.
[7] S. T. Hyde, Curr. Opin. Colloid Interface Sci. 1996 , 1, 653.
[8] S. Hyde, S. Andersson, K. Larsson, Z. Blum, T. Landh, S. Lidin, B. W.
Ninham, The Language of Shape: The Role of Curvature in Condensed
Matter Physics, Chemistry and Biology, Elsevier, Amsterdam, 1997.
[9] Note that in the context of surfactant templating of inorganic mesostructures, the mesh structure usually occurs in composition±temperature phase space between the hexagonal and cubic phases. Mesh and
cubic phases are both constructed from hyperbolic surfaces of infinite
genus, two-periodic for the former and three-periodic for the latter.
The mean curvature of both surfaces is constant. Only in the case of
Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1998
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Communications
the three-periodic hyperbolic surface can the mean curvature be everywhere identically zero and this is the defining characteristic of an
infinite periodic minimal surface (IPMS, named by Alan Schoen) [7].
The cubic bicontinuous phase is a case in point, where three-periodic
hyperbolic surfaces divide space into two intertwined, continuous,
non-intersecting and geometrically identical subvolumes, each resembling a 3D network of adjoined tubes. These features distinguish the
cubic from the mesh phase, where the curvature of the latter can be
constant but never equal to zero. Inner and outer volumes on either
side of the mesh surfaces are now distinct, where the exterior volume
comprises two half spaces joined through a lattice of pores while the
interior volume is a 2D tubular network (Fig. 1) [7,8].
[10] T. Jiang, G. A. Ozin, J. Mater. Chem. 1997, 7, 2213.
[11] I. Sokolov, H. Yang, G. A. Ozin, G. S. Henderson, Adv. Mater. 1997, 9,
917.
Nanosized Zinc Sulfide Obtained in the
Presence of Cationic Surfactants
By Jianquan Li, Henri Kessler,* Michel Soulard,
Lahcen Khouchaf, and Marie-HØl›ne Tuilier
Ordered and disordered mesoporous molecular sieves
have been synthesized as potential materials for catalysis
and adsorption via the organization of organic micelles with
inorganic molecular species since 1991.[1±7] Thus, for example, silica-based MCM-41 exhibits an intraparticle hexagonal array of unidimensional pores with a narrow pore
size distribution and amorphous inorganic pore walls.[1±3]
Such a type of material was recently studied for environment remediation by the covalent grafting of thiol moieties
to the hydroxyl groups lining the pore walls.[7] In addition,
an extension to the synthesis of mesoporous transition metal oxide molecular sieves has aroused much interest.[5,6]
Compared with studies of mesostructured materials
based on oxides, less attention has been paid to mesostructured sulfides[8±13] although metal sulfides show a richer coordination chemistry than inorganic oxides,[14] and also
show semiconducting properties.[15] Recently, a nanostructured material based on cadmium sulfide was reported by
using amphiphilic mesophases as precursors.[9,10] An extensive study on mesostructured tin(IV) sulfides was performed by using cationic surfactants. Different coordinations of the tin(IV) atomsÐsix and fourÐwere observed for
the mesoporous and lamellar phases, respectively.[11±13]
Zinc sulfide has been used, for example, as a material for
thin-film electroluminescent structures and as a light emitter for color display systems for many years.[16,17] This communication describes the synthesis of nanosized blende-
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Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1998
type zinc sulfide showing a narrow textural mesopore size
distribution after surfactant removal. The synthesis was carried out at room temperature and in the presence of alkyltrimethylammonium bromide. After reaction, the surfactant was removed by treatment with NaCl in ethanol. The
material was characterized by X-ray diffraction (XRD),
chemical analysis, nitrogen sorption at 77 K, transmission
electron microscopy (TEM), Fourier transform infrared
(FTIR) spectroscopy, 13C crossed polarization/magic angle
spinning (CP/MAS) NMR spectroscopy, and extended Xray absorption fine structure (EXAFS) measurements at
the Zn K-edge.
Figure 1 shows the XRD diagram of the product formed
in the presence of cetyltrimethylammonium cations
(C16TMA). A high-intensity peak is observed at low reflection angle near 2y = 1.16 (d = 76 Š, Irel = 100) and two
very weak broad lines at 28.6 (d = 3.12 Š, Irel = 2) and
47.7 (d = 1.90 Š, Irel = 1). The surfactants with a shorter
chain length (C12 and C14) lead to low angle reflections
with the same 2y value; however, no low angle peak is observed when using octyltrimethylammonium bromide. A
single intense peak at high d-spacing in the XRD patterns
of mesoporous alumina[18] and hexagonal mesoporous silica
(HMS)-type materials[4] was considered as an indication of
randomly ordered pores.
Fig. 1. XRD (Cu Ka) pattern of the sample obtained with C16TMABr.
The two very weak and broad peaks (Fig. 1) at d =
3.12 Š and d = 1.90 Š can be assigned to blende-type zinc
sulfide, the d values match the reported ones well. According to the Scherrer formula D2y = l/L cos y, where D is the
width at half maximum [rad], l the X-ray radiation [Š],
and L the particle size [Š], the size of the blende particles
is 42 ± 5 Š. This value is in good agreement with the size
determined by TEM. Indeed, Figure 2a shows a regular arrangement of rounded squares of 35 to 50 Š in size. The
electron diffraction diagram (SAED) corresponds to that
of polycrystalline blende-type zinc sulfide (Fig. 2c). Considering all the observations, it can be assumed that the
low-angle XRD peak observed in Figure 1 is due to the
regular arrangement of the nanoparticles of blende with
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