5204
Langmuir 1997, 13, 5204-5207
Get a Certain Crystal Face Directly: Self-Organization of an Inorganic Ultrathin Crystal Film on an Organic Surface Ruikang Tang and Zihou Tai* State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute, Nanjing University, Nanjing 210093, People’s Republic of China Received March 12, 1997. In Final Form: May 19, 1997X Using a Langmuir-Blodgett film of 9-(hexadecylimino)-4,5-diazafluorene (L) as a template, we succeed in making an ultrathin film of CuSO4‚5H2O, which just is oriented in a (010) crystal face. Compared with the normal method, this route can get a certain crystal face directly and save both labor and time. The relationship between the ultrathin crystal film of CuSO4‚5H2O and the Langmuir-Blodgett films is also discussed, and it indicates that the quality of the CuSO4‚5H2O film depends on the structure and defects of the L Langmuir-Blodgett film.
Introduction Single crystals have lattice structure and are often anisotropic. As a result, some special functions of the crystals that are useful in various applications are not embodied in the block but in some of their crystal faces. At present, in order to get a useful crystal face, people have to grow a bulk crystal and cut it into thin slices before it can be used. Obviously, this is not an ideal way because it costs both time and labor. Can we obtain a certain crystal face directly? This is a very interesting topic. In fact, some natural phenomena have given us a perfect answer. In biological systems, there are various forms of laminated composites such as hydroxyapatite, CaCO3, SiO2, etc., and their nucleation and growth are specifically oriented.1-10 The minerals are of ultrathin (on a micron scale) structure, formed through an organized organic surface as a template. Since the organized organic surfaces, unlike inorganic ones, can be extensively tailored by specific chemical modifications, the potential scope for controlled, oriented inorganic crystallization is possible.6,10-12 Therefore, it prompts us to develop a new route to grow a certain crystal face directly as in nature. In the past, a different approach is the use of simplified organized surfaces, which are compressed monolayer surfactant films formed at air-water interfaces,6,13-17 and X
Abstract published in Advance ACS Abstracts, August 15, 1997.
(1) Mann, S. Struct. Bonding 1983, 54, 127. (2) Weiner, S. Curr. Rev. Biochem. 1986, 20, 365. (3) Lowenstam, H. A.; Weiner, S. On Biomineralization; Oxford University Press: Oxford, U.K., 1989. (4) Heuer, A. H.; Fink, D. J.; Laraia, V. J.; Arias, J. L.; Calvert, P. D.; Kendall, K.; Messing, G. L.; Blackwell, J.; Rieke, P. C.; Thompson, D. H.; Wheeler, A. P.; Veis, A.; Caplan, A. I. Science 1992, 255, 1098. (5) Aksay, I. A.; Tran, M.; Manne, S.; Honma, I.; Yao, N.; Zhou, L.; Fenter, P.; Eisenberger, P. M.; Grunner, S. M. Science 1996, 273, 892. (6) Addadi, L.; Weiner, S. Angew. Chem., Int. Ed. Engl. 1992, 31, 153. (7) Mann, S.; Archibald, D. D.; Didymus, J. M.; Douglas, T.; Heywood, B. R.; Meldrum, F. C.; Reeves, N. J. Science 1993, 261, 1286. (8) Mann, S. J. Chem. Soc., Dalton Trans. 1993, 1. (9) Mann, S. Nature 1988, 332, 119. (10) Mann, S.; Ozin, G. A. Nature 1996, 382, 313. (11) Mann, S.; Heywood, B. R.; Rajam, S.; Birchall, J. D. Nature 1988, 334, 692. (12) Berman, A.; Ahn, D. J.; Lio, A.; Salmerson, M.; Reichert, A.; Charych, D. Science 1995, 269, 515. (13) Mann, S.; Didymus, J. M.; Sanderson, N. P.; Heywood, B. R. J. Chem. Soc., Faraday Trans. 1990, 86, 1873. (14) Heywood, B. R.; Rajam, S.; Mann, S. J. Chem. Soc., Faraday Trans. 1991, 87, 735. (15) Kenn, R. M.; Bo¨hm, C.; Bibo, A. M.; Peterson, I. R.; Mo¨hwald, H.; Als-Nielsen, J.; Kjaer, K. J. Phys. Chem. 1991, 95, 2092. (16) Zhao, X. K.; Yang, J.; McCormick, L. D.; Fendler, J. H. J. Phys. Chem. 1992, 96, 9933.
S0743-7463(97)00278-3 CCC: $14.00
Figure 1. Structure of L monolayer and copper ions. The lattice structure is a ) 6.20 Å, b ) 6.00 Å, θ ) 73.0°, φ ) 20°, and τ ) 53°. The shadow part illustrates that the arrangement of the copper ions under the L monolayer is in close agreement with that on the (010) face of CuSO4‚5H2O.
their Langmuir-Blodgett films,18 as substrates for inorganic crystallization. Their results indicate that concepts such as morphogenesis, replication, self-organization, and metamorphosis could be useful for devising new synthetic strategies.6,10-12,19,20 We have also reported the oriented crystallization of CuSO4‚5H2O under a monolayer of 9-(hexadecylimino)-4,5-diazafluorene (L).21 The millimetersized CuSO4‚5H2O crystals form at the air-water interface, and the crystallization is oriented. Each crystal has a definite crystal face (010) induced by the monolayer. As we know, the monolayer is an organized assembly and has lattice structure with parameters a, b, and θ,22,23 like a crystal face. As L can interact with Cu2+, giving a 1:1 complex by a weak coordination bond, it preferentially (17) Lin, J.; Cater, E.; Bianconi, P. A. J. Am. Chem. Soc. 1994, 116, 4738. (18) Landau, E. M.; Grayer Wolf, S.; Levanon, M.; Leiserowitz, L.; Lahav, M.; Sagiv, J. J. Am. Chem. Soc. 1989, 111, 1436. (19) Meldrum, F. C.; Wade, V. J.; Nimma, D. L.; Heywood, B. R.; Mann, S. Nature 1991, 349, 684. (20) Weissbuch, I.; Frolow, F.; Addadi, L.; Lahav, M.; Leiserowitz, L. J. Am. Chem. Soc. 1990, 112, 7718. (21) Tang, R.; Tai, Z.; Chao, Y. J. Chem. Soc., Dalton Trans., in press. (22) Miao, Q.; Tang, R.; Tai, Z.; Qian, X. Langmuir 1995, 11, 1072. (23) Fendler, J. H. Membrane Mimetic Chemistry; John Wiley & Sons: New York, 1982.
© 1997 American Chemical Society
Get a Certain Crystal Face Directly
Langmuir, Vol. 13, No. 19, 1997 5205
Figure 2. Growth scheme of ultrathin crystal films (crystal face) by the Langmuir-Blodgett technique.
accumulates copper ions and their arrangement also becomes organized according to the monolayer. The parameters of the monolayer obtained are a ) 6.20 Å, b ) 6.00 Å, and θ ) 73.0°. The corresponding lattice parameters of the (010) crystal face of CuSO4‚5H2O are 6.12, 5.96, and 72.8°, which match the parameters of the L monolayer perfectly. As shown in Figure 1, the embryonic crystal face of (010) is formed under the monolayer easily and the further crystal growth is based on it. It is clear that, like the organic substrate in a biological system, organized amphiphilic films can choose certain crystal faces and make oriented crystallization also. Thus, should we use an ultrathin film as a reorganized template to make a crystal face directly? Recently, we developed Landau et al.’s Langmuir-Blodgett technique,18 succeeded in controlling epitaxial nucleation of a particular crystal face, and got the crystal face (an ultrathin crystal film) directly. Experimental Section Figure 2 is a scheme of the experimental process. By means of the MW-2 Langmuir trough system, the L monolayer was transferred onto a clean glass by up-down cycles at a speed of 1 mm‚min-1. As the surface of the glass slides for deposition of the L films were hydrophilic, two layers were deposited on the glass slides by Y-type stacking, so that the L’s headgroups of the second layer were directive to the outside.23 Then the LangmuirBlodgett film was immersed into a saturated CuSO4 solution and L would interact with the copper ions. Next, the glass was lifted from the solution at an even speed of 1 mm‚min-1; some CuSO4 solution as the attachment was lifted out of the solution also, and they covered the Langmuir-Blodgett film. When the adsorbed water had volatilized, an ultrathin film of CuSO4‚ 5H2O crystal was formed. All this work was carried out in a dust-free box at 25 °C. The ultrathin films of CuSO4‚5H2O covering the LangmuirBlodgett films were characterized by optical microscopy (Leitz, Germany) and rotating-anode X-ray diffractometry (D/Max-RA, Rigaku, Japan) with 2θ scans in reflection mode, respectively.
Results When two-layer Langmuir-Blodgett films of L are prepared, they are examined by XRD. No peak appears in these spectra whose range is from 2θ ) 5° to 75° as their long spacing distances are always larger than 30 Å and the values of 2θ are much lower than 5° accordingly. Parts a-d of Figure 3 show the typical morphologies and XRD spectra of CuSO4‚5H2O ultrathin films on distinct Langmuir-Blodgett films, which are made at different area pressures, and some interesting phenomena are observed as follows: 1. When the Langmuir-Blodgett film of L is deposited at an area pressure of 0 mN‚m-1, it means there are almost no organic films on the glass. In this condition, the optical micrograph shows that the crystal film of CuSO4‚5H2O
consists of a lot of randomly aggregated microcrystals, which are distributed with heterogeneous size. The optical study also shows the thickness of the crystal film is about 1h µm. In the X-ray diffraction pattern, there are several sets of diffraction peaks and most of them belong to the habit crystal faces of CuSO4‚5H2O such as (100), (110), (11 h 0) etc. It is clear that, in the absence of the LangmuirBlodgett film, the crystallization is uncontrolled. 2. L Langmuir-Blodgett films are prepared at area pressures of 10, 20, and 30 mN‚m-1, respectively. Compared with the case 1 situation, although the films also have a great number of microcrystals, they are not as mixed and disordered. Its X-ray diffraction shows that some small peaks of case 1 vanish and a new crystal face (010) appears; this peak becomes stronger with increasing the area pressure. Meanwhile, the other peaks’ intensities are weakened. Figure 3b is a representative result of CuSO4‚5H2O ultrathin films on the Langmuir-Blodgett film of L prepared at an area pressure of 20 mN‚m-1. 3. An interesting result is obtained when the Langmuir-Blodgett film is made at an area pressure of 35 mN‚m-1. According to its isotherm curve, the monolayer is in a compressed solid state and at this pressure its structure is very similar to the (010) face of the CuSO4‚ 5H2O crystal as mentioned in Figure 1. This being the case, the X-ray diffraction pattern of the ultrathin film shows that there is only one set of peaks which is belong to the (010) crystal face of CuSO4‚5H2O; all other peaks disappear. This pattern is the same as that of the (010) crystal face we reported before,21 and this means they have the same characters (Figure 3c). The optical microscopy study illustrates that the ultrathin film has an organized domain structure24 instead of an assembly of randomly aggregated microcrystals. Under the control of a suitable template, it shows that the organized microcrystal of CuSO4‚5H2O can be aggregated to form an integrated crystal film, which can be seen just as a great (010) crystal face of the pentahydrate of copper sulfate. In addition, like cases 1 and 2, the thickness of the ultrathin film is of micron dimension. 4. Although a large (010) crystal face of CuSO4‚5H2O can be induced by the Langmuir-Blodgett film deposited at 35 mN‚m-1, on a few verges of the glass we find more than one kind of domain structure. The X-ray diffraction also shows there are two sets of peaks, which belong to the (010) and (11 h 0) crystal faces of CuSO4‚5H2O (Figure 3d). This is because some defects are formed in the Langmuir-Blodgett film. As Mann described9,10 the transcriptive synthesis involves reorganized, self-assembled, and relatively stable organic architecture searing as chemical and structural templates for patterned (24) The study is being continued to find out the meaning of the organized domain.
5206 Langmuir, Vol. 13, No. 19, 1997
Tang and Tai
Figure 3. Optical micrographs (×800) and X-ray diffraction patterns of the ultrathin films of CuSO4‚5H2O on the LangmuirBlodgett films, which are deposited at area pressures of (a) 0, (b) 20, and (c) 35 mN‚m-1, respectively. Part d is the situation on a few verges of part c and is due to some defects of the Langmuir-Blodgett film. In the diffraction patterns, the bulges are due to the amorphous halo resulting from diffraction of the X-rays by the glass.
materials deposition. These defects are replicated in an ultrathin film of CuSO4‚5H2O, and the different domain structure is observed.
As the case 3 shows, this method can succeed in making the crystal face directly by Langmuir-Blodgett technology. In comparison with the normal method which cuts faces
Get a Certain Crystal Face Directly
from crystals, the new one has some advantages. First, this method is different from the normal; a substrate refined by the Langmuir-Blodgett technique can act as a template. When both the crystal face of CuSO4‚5H2O and the organic film are in structural correspondence, the one-to-one geometrical matching between the functional group of the template and the crystallographic lattice dimensions of a special crystal face occurs and the controlled crystal face growth is induced. On the contrary, cases 1 and 2 cannot form the crystal face (010) in this experiment. This is because the structural correspondence between the template and CuSO4‚5H2O crystal is not complementary. Besides, the quality and defect of the Langmuir-Blodgett film can influence the quality of the ultrathin films of CuSO4‚5H2O just as case 4 shows. Second, this method can save both labor and time (usually, it only takes us less than 1 day to get the crystal face), and its size and shape also can be controlled by the LangmuirBlodgett technique easily. Besides, the micron thickness of the ultrathin film can suit many device applications, such as optical waveguides, and requires a patterned thin film. To some extent, this method is similar to molecular
Langmuir, Vol. 13, No. 19, 1997 5207
beam epitaxy;25,26 however, one no longer needs very much work or money to get an oriented crystal film that is wellordered and controlled. Conclusions In conclusion, like a biological system, we can grow a certain crystal face (oriented crystal film) directly with the help of the Langmuir-Blodgett technique. Although this method perhaps is not very mature now, a new scheme of crystal engineering will be developed and the scope of the biomineralization will be greatly extended in the future. The results also can be seen as a successful example for self-organization of an inorganic ultrathin crystal film occurring on an organic surface. Acknowledgment. We thank Prof. Kunji Chen and Prof. Yinqiu Liang for their useful suggestion and discussion about this project. The research work is granted by the National Natural Science Foundation of China. LA970278D (25) Lange, F. F. Science 1996, 273, 903. (26) Service, R. F. Science 1994, 265, 316.
