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[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 Patent5 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. Sey-ferth, 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 fromBET analysis of the low pressure part of the isotherm. Micropore sizedistribution was determined by the Horvath±Kawazoe model usingADP software, version 3.03 (Porotec GmbH, Frankfurt), using a nitro-gen on carbon potential at 77 K.

[26] Laser Synthesized Silicon Nitride Powder: Chemical and PhysicalCharacteristics (Eds: B. W. Sheldon, S. C. Danforth), AmericanCeramic Society, Westerville, OH 1994, Vol. 42, p. 47.

[27] Gmelin: Handbook of Inorganic and Organometallic Chemistry, SiSuppl., 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. Ver-

cruysse, 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.

Tin Sulfide Mesh: AFM Imaging of Lamellaeand Mesopores**

By Igor Sokolov, Tong Jiang, and Geoffrey A. Ozin*

Synthesis of inorganic copies of lyotropic mesophasesrepresents a paradigm shift in materials chemistry.[1] Sinceresearchers from Mobil[2] announced their discovery of liq-uid crystal templating of mesostructured silica in 1992, suchreplica chemistry has leapt into the realm of hierarchicalinorganic materials, in which morphology and structure arecontrolled over three length scales and spatial dimen-sions.[3,4] Since this breakthrough, a diversity of amphiphilicassemblies and inorganic precursors have been combinedto create a myriad of composite mesostructures. Using sur-factant templates and organic additives, mesopore dimen-sions have been finely tuned over the 20±100 � size

range,[2] while the synthesis of replicas of the L3 spongephase[5] and phase-separated block copolymers[6] has takenthe mesopore range upwards by about a factor of three. In-organic mesostructures are beginning to spread throughoutthe whole periodic table; phosphate, oxide, sulfide, and pla-tinate mesophases have produced insulating, semiconduct-ing, and metallic mesostructures.[3,4]

The synthesis of inorganic analogues of lyotropic hex-agonal, cubic, and lamellar mesophases suggests that it maybe possible to replicate inorganic versions of the less wellknown intermediate tetragonal, rhombohedral, and mono-clinic mesh mesophases.[7] The morphological descriptionof the mesh stems from the mathematical topology of hy-perbolic surfaces.[8,9] Some square mesh surfaces of differ-ent mean curvature are illustrated in Figure 1. The simplestdescription of a mesh is a two-periodic hyperbolic surfaceconfined between two parallel bounding planes with a reg-ular network of pores joining the two parallel sheets. Thusan amphiphilic mesh phase contains a two-dimensional ar-ray of pores embedded within a bilayer. Holes in the bi-layer are considered to be puncture defects and the parallelstacking of mesh surfaces leads to a network of tunnels.[8,9]

Although lyotropic mesh phases are rather rare, their exis-tence raises the possibility that they may be utilized to tem-plate an inorganic mesh.

Fig. 1. Illustration of some two-periodic square mesh surfaces of differentmean 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, whereHDA represents hexadecylamine.[10] Powder X-ray diffrac-tion (PXRD), transmission electron microscopy (TEM),119Sn NMR and 119Sn Mössbauer studies indicated that thestructure of the as-synthesized crystalline material is basedupon parallel-stacked mesoporous tin(IV) sulfide layerssandwiched between a mixed bilayer of neutral and proton-ated hexadecylamine. Because of the unique combinationof electrical, optical, and thermotropic liquid-crystalline

±

[*] Prof. G. A. Ozin, Dr. I. Sokolov, Dr. T. JiangLash Miller Chemical LaboratoriesUniversity of Toronto80 St. George Street, Toronto, Ontario M5S 3H6 (Canada)

[**] Financial support for this research from the Natural Sciences and En-gineering Research Council of Canada (NSERC) and Universal OilProducts (UOP) is deeply appreciated.

properties revealed for Meso-SnS-1, it is important to learnas much as possible about the structure of the material.This is especially important because the material is electronbeam sensitive, which renders the recording of TEMimages somewhat problematical.[10] In an effort to providereliable high resolution structural information about the la-mellae and mesopores in such a soft and flexible material,in this study we have resorted to gentle imaging atomicforce microscopy (AFM) techniques, which have recentlyproved successful for imaging the mesostructure of a 500 �thick lyotropic liquid-crystalline film on a graphite sub-strate.[11]

As-synthesized Meso-SnS-1 was initially tested to seehow it stood up to AFM scanning when the flaky micro-meter-sized crystals were simply deposited onto a layer ofepoxy. The pristine material supported in this way is ex-tremely soft and not at all suitable for obtaining high res-olution images of the mesostructure. An approach thatyielded acceptable quality AFM images involved initiallyannealing the material, at around the liquid crystal transi-tion temperature of 85 �C for about 2 h,[10] between twoglass slides. To facilitate both homeotropic and planar orga-nization of the director field of the tin sulfide mesophasewith respect to the contacting surfaces of the glass slides,either transverse compression or lateral shear forces wereapplied to the Meso-SnS-1 liquid crystal film for a periodof 1 min. The material was allowed to crystallize slowlyover a period of a few days at room temperature to opti-mize the degree of orientational order in the film and toprovide the smoothest possible surfaces for AFM imagingof the mesostructure. Images were recorded immediatelyafter one of the confining glass plates had been removedfrom the film. Flat areas that were found after this cleavageprocess were scanned with the atomic force microscope.No significant differences were found for the samples pre-pared with the application of transverse compression or lat-eral shear forces. With these sample preparation protocolsit proved possible to create exposed patches of the Meso-SnS-1 film in which the lamellae and mesopores weremore-or-less correctly aligned for AFM soft imaging of themesostructure.

All AFM images of Meso-SnS-1 films were obtainedusing the tapping mode technique on a Digital InstrumentsNanoScope III with a phase extender module.[11] The ex-treme softness of the material does not allow the use of thecontact mode, as previously found in the imaging of lyotro-pic liquid-crystalline films.[11] The A+B feedback signal wasabout 3 V while the root mean square (RMS) signal wasset as small as possible to record images at around 0.1±0.2 V. Feedback gain parameters were set between 0.2 and1 for both integral and proportional gains. A Digital Instru-ments Nanoprobe SPM TESP silicon tip (resonance fre-quency 250±300 kHz) for tapping mode in air and NT-MDT UltraSharp silicon cantilevers SCS11 (resonance fre-quency 300±380 kHz) were used for this imaging study. Thedrive amplitude was set between 10 and 30 mV (<10 nm).

Use of such a small amplitude to minimize the tip±sampleinteraction has been reported previously.[11] The D scanhead (maximum scan area 12.5 ´ 12.5 mm2, z-sensitivity9 nm/V) was employed throughout this study. Scan rateswere chosen in the range of 0.5±1.5 Hz.

Large-area unfiltered AFM images of Meso-SnS-1 areshown in Figures 2A±C. The layered structure is quite ap-parent. In particular, the orientation of lamellae tends tobe upright in the first two images and more-or-less lyingflat in the third, with respect to the surface of the glass sub-strate. It seems from systematic studies of many images ofthis kind that shear and compression forces applied to thesample held between the glass plates tend to favor respec-tively planar and homeotropic alignment of the directorfields of the tin sulfide mesophase. Typically, the interlayerdistance was found to be about 5 nm, which is essentiallythe same as the interlamellar spacing observed by PXRDand TEM imaging of Meso-SnS-1.[10]

Higher resolution AFM scans support and amplify theseobservations. Note that small inclines in the area being im-aged are removed by the planefit option in the NanoScopesoftware package. Furthermore, artifacts were excludedfrom the recorded images by decreasing the scanning tap-ping force, varying the feedback parameters, and changingthe scan direction and scan speed. Typical high resolutionraw AFM images of Meso-SnS-1 are displayed in Fig-ures 3A and B, which show mostly uniaxial striations,corresponding to the layered mesostructure. The parallel-stacked layers are clearly observed and consistently emergewith an interlayer spacing of around 5 nm.

It is more challenging to observe the surface mesostruc-ture of a sheet. This necessitated exploration of the filmsurface for flat areas such as the one indicated by the whitearrow in Figure 2C. A high magnification raw AFM imageof such an area, recorded in height mode, is displayed inFigure 2D. Vertical distances between the layers in Fig-ure 2D are about 5±8 nm, which corresponds to the ex-pected interlayer distance. Figures 3C and 3D present rawAFM images of the surface of a sheet. The pore structure isclearly revealed after noise filtering by applying a two-dimensional fast Fourier transform (2D-FFT), Figure 4.Some raw AFM images of the most regular surface struc-ture that has been observed for Meso-SnS-1 are presentedin Figures 5A and B. Numerous regions of this type havebeen imaged and typically reveal patches of a regular me-sostructure with lattice constants that lie in the range be-tween ca. 3 and 10 nm, implying either that the mesoporeshave a range of sizes or that they are being imaged in dif-ferent orientations, or both (Figs. 4,5). The images also de-pict the existence of what appear to be topological defectsassociated with the organization of the mesopores in the la-mellae of Meso-SnS-1. This may explain the presence ofmany orders of PXRD reflections originating from thelayers but not the mesopores.[10] Further studies will beneeded to define the subtleties of mesostructure and de-fects in meso-SnS-1 in greater depth.

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A B

C D

Fig. 2. Large area raw AFM images ofMeso-SnS-1 depicting regions of lamellaein both a standing-up and lying-down con-figuration with respect to the surface of theglass substrate.

A C

B DFig. 3. Typical high resolution raw AFMimages of lamellae and mesopores in Meso-SnS-1.

A

B

CFig. 4. 2D-FFT filtered images of three regions of Meso-SnS-1, with the la-mellae organized roughly parallel to the surface of the glass substrate, thatmostly reveal areas with periodic arrangements of the mesopores.

Overall, the AFM images of Meso-SnS-1 give the im-pression that the structure of the material may be describedas a tin sulfide mimic of a mesh phase with rhombohedralor monoclinic space symmetry. Although the reportedimages are highly reproducible, the structure is extremelypliable and susceptible to plastic deformation. Therefore itis conceivable that, even with the gentle imaging AFM re-cording procedures used in this study, there may have been

some perturbation of the actual symmetry and dimensionsof the lamellae and mesopores in the proposed mesh phase.Surface interactions, topological defects, and director fieldsin organic and inorganic mesh phases are issues that needto be addressed both experimentally and theoretically inthe future.

Received: December 8, 1997Final version: March 12, 1998

±[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, Sci-

ence 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. DuChesne, H. Leist, Y. Zhang, R. Ulrich, V. Schädler, U. Wiesner, Science1998, 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 CondensedMatter Physics, Chemistry and Biology, Elsevier, Amsterdam, 1997.

[9] Note that in the context of surfactant templating of inorganic meso-structures, the mesh structure usually occurs in composition±tempera-ture phase space between the hexagonal and cubic phases. Mesh andcubic phases are both constructed from hyperbolic surfaces of infinitegenus, two-periodic for the former and three-periodic for the latter.The mean curvature of both surfaces is constant. Only in the case of

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A

B

Fig. 5. Raw AFM images of one of the most regular surface structures ob-served for Meso-SnS-1.

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the three-periodic hyperbolic surface can the mean curvature be ev-erywhere identically zero and this is the defining characteristic of aninfinite periodic minimal surface (IPMS, named by Alan Schoen) [7].The cubic bicontinuous phase is a case in point, where three-periodichyperbolic surfaces divide space into two intertwined, continuous,non-intersecting and geometrically identical subvolumes, each resem-bling a 3D network of adjoined tubes. These features distinguish thecubic from the mesh phase, where the curvature of the latter can beconstant but never equal to zero. Inner and outer volumes on eitherside of the mesh surfaces are now distinct, where the exterior volumecomprises two half spaces joined through a lattice of pores while theinterior 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 thePresence of Cationic Surfactants

By Jianquan Li, Henri Kessler,* Michel Soulard,Lahcen Khouchaf, and Marie-HØl�ne Tuilier

Ordered and disordered mesoporous molecular sieveshave been synthesized as potential materials for catalysisand adsorption via the organization of organic micelles withinorganic molecular species since 1991.[1±7] Thus, for exam-ple, silica-based MCM-41 exhibits an intraparticle hex-agonal array of unidimensional pores with a narrow poresize distribution and amorphous inorganic pore walls.[1±3]

Such a type of material was recently studied for environ-ment remediation by the covalent grafting of thiol moietiesto the hydroxyl groups lining the pore walls.[7] In addition,an extension to the synthesis of mesoporous transition met-al oxide molecular sieves has aroused much interest.[5,6]

Compared with studies of mesostructured materialsbased on oxides, less attention has been paid to mesostruc-tured sulfides[8±13] although metal sulfides show a richer co-ordination chemistry than inorganic oxides,[14] and alsoshow semiconducting properties.[15] Recently, a nanostruc-tured material based on cadmium sulfide was reported byusing amphiphilic mesophases as precursors.[9,10] An exten-sive study on mesostructured tin(IV) sulfides was per-formed by using cationic surfactants. Different coordina-tions of the tin(IV) atomsÐsix and fourÐwere observed forthe mesoporous and lamellar phases, respectively.[11±13]

Zinc sulfide has been used, for example, as a material forthin-film electroluminescent structures and as a light emit-ter for color display systems for many years.[16,17] This com-munication describes the synthesis of nanosized blende-

type zinc sulfide showing a narrow textural mesopore sizedistribution after surfactant removal. The synthesis was car-ried out at room temperature and in the presence of alkyl-trimethylammonium bromide. After reaction, the surfac-tant was removed by treatment with NaCl in ethanol. Thematerial was characterized by X-ray diffraction (XRD),chemical analysis, nitrogen sorption at 77 K, transmissionelectron microscopy (TEM), Fourier transform infrared(FTIR) spectroscopy, 13C crossed polarization/magic anglespinning (CP/MAS) NMR spectroscopy, and extended X-ray absorption fine structure (EXAFS) measurements atthe Zn K-edge.

Figure 1 shows the XRD diagram of the product formedin the presence of cetyltrimethylammonium cations(C16TMA). A high-intensity peak is observed at low reflec-tion angle near 2y = 1.16� (d = 76 �, Irel = 100) and twovery weak broad lines at 28.6� (d = 3.12 �, Irel = 2) and47.7� (d = 1.90 �, Irel = 1). The surfactants with a shorterchain length (C12 and C14) lead to low angle reflectionswith the same 2y value; however, no low angle peak is ob-served when using octyltrimethylammonium bromide. Asingle intense peak at high d-spacing in the XRD patternsof mesoporous alumina[18] and hexagonal mesoporous silica(HMS)-type materials[4] was considered as an indication ofrandomly 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 � and d = 1.90 � can be assigned to blende-type zincsulfide, the d values match the reported ones well. Accord-ing to the Scherrer formula D2y = l/L cos y, where D is thewidth at half maximum [rad], l the X-ray radiation [�],and L the particle size [�], the size of the blende particlesis 42 ± 5 �. This value is in good agreement with the sizedetermined by TEM. Indeed, Figure 2a shows a regular ar-rangement of rounded squares of 35 to 50 � in size. Theelectron diffraction diagram (SAED) corresponds to thatof polycrystalline blende-type zinc sulfide (Fig. 2c). Con-sidering all the observations, it can be assumed that thelow-angle XRD peak observed in Figure 1 is due to theregular arrangement of the nanoparticles of blende with

±

[*] Dr. H. Kessler, Dr. J. Li, Dr. M. SoulardLaboratoire de MatØriaux MinØraux, UPRES-A 7016Ecole Nationale SupØrieure de Chimie de MulhouseUniversitØ de Haute Alsace3, rue Alfred Werner, F-68093 Mulhouse Cedex (France)

Dr. L. Khouchaf, Dr. M.-H. TuilierLaboratoire de Physique et de Spectroscopoie ElectroniqueUPRES-A 7014, FacultØ des Sciences et TechniquesUniversitØ de Haute Alsace4, rue des Fr�res Lumi�re, F-68093 Mulhouse Cedex (France)