Molecular Multilayer Films: The Quest for Order ... - ACS Publications

Chapter 30

Downloaded by UNIV MASSACHUSETTS AMHERST on October 8, 2012 | http://pubs.acs.org Publication Date: September 1, 1997 | doi: 10.1021/bk-1997-0672.ch030

Molecular Multilayer Films: The Quest for Order, Orientation, and Optical Properties Gero Decher Centre de Recherches sur les Macromolécules (UPR 022), Institut Charles Sadron, Université Louis Pasteur and Centre National de la Recherche Scientifique, 6 rue Boussingault, F-67083 Strasbourg Cedex, France

Organic thin film coatings of surfaces show potential for various applica tions including integrated optics. However, the unique characteristics of organic chromophores are exploited best if the films possess suitable architecture (layering), in-plane order and a fixed orientation of molecules with respect to the substrate. Good control over defects is required in order to avoid light scattering and to allow for optical waveguiding. This report describes three techniques which are used for the fabrication of molecular multilayer films and compares their properties: Langmuir-Blodgett films, transferred freely-suspended films, and layer-by-layer adsorbed polyelectrolyte films. Ultrathin films composed of polymers or small organic molecules have attracted consid erable attention in the last decades (1-5). The possibility of tailoring their architecture and thus their optical properties has prompted research towards potential applications in the areas of integrated optics, frequency doubling, light emitting devices or even sensors based partially on optical effects. After everything started out with Langmuir-Blodgett films in the 1930s (6,7), different approaches have been taken to fabricate molecular multilayer structures as films on solid supports (8-17). However, for potential applications several prerequisites have to be met and this is still a tremendous challenge for any such system. The major demands are clearly the optical quality of the film and an architecture with appropriate optical properties, but last not least also thermal and mechanical stability and the possibility for automated manufacturing. Just the first part of these tasks, expressed in other words, could be the quest for order, orientation and optical properties. Techniques for the fabrication of molecular films. The existing techniques for multi layer fabrication address these requirements to a different extent. Langmuir-Blodgett films allow for excellent control of film architecture but typically lack stability. Selfassembled multilayers are extremely stable since they generally represent covalently crosslinked networks, but it seems to be difficult to obtain μ-thick films of high quality. Freely-suspended liquid crystalline films can be obtained as optical monodomains, but are © 1997 American Chemical Society

In Photonic and Optoelectronic Polymers; Jenekhe, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

445

446

PHOTONIC AND OPTOELECTRONIC P O L Y M E R S

extremely fragile. They can be transferred onto solid supports or, if prepared from poly meric liquid crystals, covalently cross-linked and thus tremendously stabilized, but the maximum areas of suchfilmsare restricted to a few cm or even mm . A relatively new approach is the consecutive adsorption of oppositely charged poly mers or colloids onto solid supports, which yields films that possess internal structure on the nm scale and thesefilmscan also be homogenous over large areas. The control over the layer architecture is as straightforward as in the case of LB-films, but there seems to be limits with respect to control of molecular order and orientation. On the other hand, the process can easily be automated since it simply consists of multiple adsorption from solu tion. The resultingfilmshave in some cases been observed to be stable for seven days at temperatures around 200 °C and at least for more than one year at ambient conditions. Another advantage of the latter type offilmsis that the materials that can be incorpo rated into such films are not restricted to synthetic molecules, biopolymers such as proteins (18-26), DNA (19,27 and Sukhorukov, G. B.; Môhwald, H.; Decher, G.; Lvov, Y. M. Thin Solid Films 1996, in the press) or inorganic colloids (20,28-33 and Schmitt, J.; Decher, G.; Dressik, W. J.; Brandow, S. L.; Geer, R. E.; Shashidhar, R.; Calvert, J. M. Adv. Mater., accepted for publication) have been employed for the fabrication of multi layer nanoheterostructures as well. It is even possible to carry out chemical reactions (thermal eliminations) in such films, thus allowing for the manipulation of chemical structures by using precursor materials for the film fabrication. The last possibility has prompted the preparation of polyelectrolyte multilayers incorporating precursors to elec troluminescent polymers (34-38) which are typically intractable substances (39). For such applications the technique offers the promising possibility to construct film architectures composed of an electron injecting layer, an electroluminescent layer and a hole injecting layer with a total thickness of a few hundred Angstroms or less and thefirststeps in this direction have already been taken. The following paragraphs describe selected examples of Langmuir-Blodgett films, freely-suspended liquid crystal films, transferred freely-suspended films and layer-bylayer adsorbedfilmswith respect to some of the desired properties described above.


2

2

Langmuir-Blodgett Films: Thermal Relaxation of Non-Centrosymmetric Structure, a Typical Case for Non-Polymeric Amphiphiles? Whereas Langmuir-Blodgett (LB) films, which have dominated the area for over 50 years, allow for excellent initial control over the film architecture and partial control over molecular orientations, they typically lack thermal stability and undergo different struc tural relaxations with time (3,40-42). This is not unexpected since they are prepared as monomolecular layers on the surface of water and then transferred onto solid supports (Figure 1). Thus the environment of the molecules changes dramatically during deposition and the transfer is typically too fast to allow for complete equilibration. Furthermore, post-transfer structural changes cannot be compensated by 2-dimensional mass transport and thus lead always either to hole or island formation in the cases of contraction or expansion. As a result, LB-films often contain a considerable amount of trapped defects (43). Since the structure of the molecular crystal is typically the thermodynamically most stable one, there is a high tendency for multilayers to "recrystallize" to the bulk structure. Nevertheless, there exist cases where even non-centrosymmetric multilayers with a thick ness in the μ-range can be prepare by the LB-Technique and suchfilmseven appear to be stable over a few years.


30.

DECHER

Molecular Multilayer Films

447


An interesting example for second harmonic generation is the case of a non-centrosymmetric LB-film of a single amphiphile (2-docosylamino-5-nitropyridine, DCANP) which possesses a non-alternating head-to-head and tail-to-tail structure (Y-type) and a polar axis in the layer plane parallel to the dipping direction (44,45). DCANP is also an interesting material, because it allows the detection of monolayer collapse due to its unique spectroscopic properties, even when the pressure/area isotherms indicate that the monolayer seems to be stable at a certain surface pressure (46). It is clear that control of monolayer stability is a prerequisite for the fabrication of high quality films.

°

2N

^ - N

V^-Η 2-docosylamino-5-nitropyridine (DCANP)

The in-plane polarity arises from the combination of two effects: a) strongly tilted alkyl chains allow for a chromophore orientation within the layer plain and b) the crystalline domains are aligned preferentially along the dipping direction during transfer (47). The nonlinear optical coefficient d33 of LB-multilayers of DCANP is 7.8 ± 1.0 pm/V (at 1064 nm). In Cerenkov-type waveguiding setup it is possible to achieve phase matching conditions and values of d33 of 27 pm/V were reported for wavelengths of 820 nm (48,49). Although it is possible to fabricate transparent films thick enough for optical waveguiding, investigation by atomic force microscopy (AFM) shows that LB-films of DCANP are not molecularly smooth. Instead they exhibit mostly sub-micron size surface defects in the form of holes with a depth of one or several bilayers (50), which is not uncommon in LB-films as discussed below. The observation of holes with a depth of more than a bilayer shows that subsequent layers are not able to completely cover holes in the previous layers. On the other hand the average surface roughness of a 15-bilayer film, as estimated by x-ray reflectometry, is only 0.7 ± 0.5 nm (50). It should be mentioned that even "high quality" LB-films that can be transferred easily exhibit large numbers of bilayer defects (51). Despite these defects, it was demonstrated that LB-films of DCANP are in principle to guide visible light and a loss of about 12 dB/cm was determined at 632.8 nm (52,53). Although this seems to be a relatively large number, it should be emphasized that it is very difficult to fabricate LB-film waveguides with a loss of 1 -2 dB/cm or less. It was mentioned above that LB-films are often prone to thermal rearrangements and multilayers of DCANP are a case in which this can be studied in full detail. When LBfilms of DCANP are heated up, they rearrange to 2 new phases depending on the age of the film and the annealing conditions. The structural changes are verified independently by X-ray reflectometry, UV/Vis-spectroscopy and optical microscopy. Although the structural rearrangements are drastic, from an original bilayer spacing of 4.42 nm to layer spacings of either 3.80 nm (by annealing at about 60 °C) or 3.09 nm (by annealing at about 75 °C), a large number of well resolved Kiessig fringes are observed in all 3 phases, indicating that the films remain intact and smooth throughout the phase transition. The thermally induced phase transition proceeds so slowly that it can be followed by X-ray with time and a kinetic analysis yields that the nucleation of the 3.80-nm phase is sponta neous and occurs via the edge of a half-sphere. This is in good agreement with the fact that the films rearrange, but are not destroyed. Interestingly the 3.80-nm phase cannot be further converted to the 3.09-nm phase by a second annealing step at 75 °C (50).



448


Spreading (A)

Compression (B)

Transfer (Downstroke) (C)

Transfer (Upstroke) (D)

Figure 1. Schematic of the LB-transfer process. (A) After spreading, the monolayer is usually expanded at low surface pressures. (B) Compression with a movable bar rier leads typically to a condensed state. (C,D) The condensed monolayer is trans ferred onto a hydrophobic solid substrate by repeated downstroke/upstroke cycles which result in a head-to-head and tail-to-tail (Y-type) structure.

ΔΡ

(D)

Figure 2. Schematic of the transfer of freely-suspended liquid crystal films onto solid supports. (A) The freely-suspended film spans across an aperture of mm to cm size. (B) Withdrawing air from the inner compartment cause the film to bulge towards the substrate. Note that the drawing is not to scale, the thickness of the film is only a few nm and its actual distance from the substrate is less than a mm. (C) Further reduction of internal pressure brings the film into contact with the substrate. (D) After the transfer is complete the part of the film connecting the aperture and the substrate breaks and transferred FS-films of up to 1-2 cm are obtained. 2

2

2


30.

DECHER


449

Molecularly layered systems with built-in control of defects would therefore be highly interesting as an alternative to LB-films and we have developed 2 different approaches that are based on the self-organization of liquid crystals and on layer-by-layer adsorption from solution. Advantages and drawbacks of both techniques are briefly discussed below.


Freely-Suspended and Transferred Freely-Suspended Liquid Crystal Films: Candidates for Optically Homogenous Films This approach is based on the molecular self-organization of thermotropic liquid crystals in freely-suspended (FS) films, a highly ordered, but very fragile system which was reported for the first time in 1978 (54,55). Liquid crystals are interesting materials for low-defect molecular films, because they represent molecular stacks with liquid-like inplane order in the high temperature smectic A and smectic C phases. In the smectic A phase all molecules are oriented perpendicular to the layer normal (homeotropic align ment) and it is trivial that the absence of in-plane crystallinity automatically excludes the presence of grain boundaries, which are one of the reasons for light scattering. Even more interesting are films of the non-centrosymmetric chiral smectic C* phase which is polar and ferroelectric. Homogeneously oriented freely-suspended films of this phase are obtained by cooling from the smectic A phase in an electric field. We have tried to stabilize freely-suspended films in two ways: a) by transfer onto solid substrates and b) by using polymeric liquid crystals. Transferred Freely-Suspended Films. Transferred freely-suspended (TFS) films are prepared by a simple procedure: At first the freely-suspended film is spread across an aperture on the top of a small box which contains the desired substrate positioned directly below the aperture. The liquid crystalline FS-film is then transferred by lowering the air pressure in the box which causes the film to bulge towards the substrate. Additional reduction of internal pressure brings the FS-film into contact with the substrate after which further transfer occurs by wetting until the film finally ruptures in the vicinity of the edge of the aperture (Figure 2). This way one is able to fabricate supported liquid crystalline films of about 1-2 cm in size which would be large enough for potential opti cal applications (14,56). In the smectic A phase or in the electric field aligned chiral smectic C* phase, these transferred films represent optical monodomains, which are now stable over long times. When kept at the same temperature, the transferred films can be expected to remain homogenous and essentially free of defects, since they were annealed when freely-suspended and because the transfer does not cause a phase transition or require thermomechanical adaptation. 2

Freely-suspended Films of Polymeric Liquid Crystals. The stabilization of freelysuspended films by using polymeric liquid crystals is obviously interesting and has been attempted previously. Unfortunately it seems to be extremely difficult to polymerize films of liquid crystalline monomers as these films were reported to always break during poly merization. It seems to be equally difficult to fabricate FS-films of polymeric liquid crystals in their smectic A and smectic C phases, most likely due to their enhanced viscosities. However, if one heats slightly into the isotropic phase it is possible to spread a film across an aperture which thins out to form a truly freely-suspended liquid crystal film after cooling into the smectic phases (57). Films of this type are homeotropic in the smectic A phase and show birefringence when cooled to the ferroelectric smectic C*



450

PHOTONIC AND OPTOELECTRONIC POLYMERS

phase. The layer structure of these first polymeric films and their phase transition from the smectic A to the smectic C* phase was investigated in some detail by X-ray reflec tometry and some differences from the behavior of the bulk was found (57). Transmission electron diffraction after transfer onto electron microscope grids shows beautiful diffractograms of a higher ordered phase at lower temperature. Of course it is possible to further increase the stability of polymeric FS-films by transfer onto solid substrates as described above. Here polymeric materials offer a second advantage, namely the possibility to freeze order and orientation of the smectic phases by rapid cooling into the glassy state. With a different ferroelectric LC-polymer it was even possible to obtain very homo genous FS-films of thicknesses of only 6 to 16 layers as determined by both optical and X-ray reflectometry (58). Since these polymeric films contained a small fraction of polymerizable mesogenic side-groups, it was even possible to photocrosslink these systems. It should be mentioned that in this first case the crosslinking caused some changes in film morphology, but the resulting films are very stable and do not even break when small holes are formed by mechanical stress (58). Comparison of Transferred Freely-Suspended Films and Langmuir-Blodgett Films of the Same Liquid Crystalline Amphiphile. In order to compare structure, defects and stability of both Langmuir-Blodgett and trans ferred freely-suspended films, we have synthesized an amphiphilic liquid crystal which allows deposition in multilayer films by both techniques. The molecule employed for this purpose was ethyl-4'-n-octyloxybiphenyl-4-carboxylate (280BC) (40,59). Its LB-film forming properties are actually quite interesting since LB-transfer initially yields a depo sition enforced bilayer phase, which then rearranges, even at room temperature, to a more stable monolayer phase (40). This further underlines the fact that LB-films are not nec essarily equilibrium structures. X-ray-reflectivity measurements performed on both LBfilms and on the transferred FS-films reveal that the layer spacings are the same in both types of films (2.41 ± 0.01 nm and 2.38 ± 0.02 nm respectively) which is very close to the long spacing of the bulk (2.46 ± 0.01 nm), indicating that both films are very close if not identical to the stable bulk structure, given the differences in the experimental set-up for reflectivity and bulk-diffraction experiments.

ethyl-4'-n-octyloxybiphenyl-4-carboxylate (280BC) But what about defects? The TFS-films certainly will possess defects arising from the fact that they were transferred at elevated temperature, but then cooled down to the crystalline bulk phase. Since the thermal expansion coefficients of the substrate and the film should be different, the formation of some defects, even besides the occurrence of grain bound aries due to crystallization, is to be expected. In fact cracks have been observed between very smooth areas from which molecular resolution could be obtained (57). However, these films appear perfectly transparent to the naked eye and macroscopic defects (besides dust particles) are not even visible under an optical microscope. LB-films of the same material are also initially transparent but already show some defects visible to the naked eye. After rearrangement to the monolayer phase, the defects become even more pronounced. Nevertheless, comparison of the rearranged LB-films with LB-films of



30. DECHER

451 Molecular Multilayer Films

several tens of other materials clearly shows that the LB-films of 280BC are certainly of low-end quality, but do not really represent a particular poor case. The structural similarities and expected defect dissimilarities in both kinds of films (TFS- and LB-films), made it interesting to look at both their respective thermal stabili ties. When slowly heated the LB-film underwent an irreversible phase transition at 64 °C and started to melt under droplet formation at approximately 80 °C, which is 30 °C below the melting point of the bulk material. At 100 °C the LB-film has almost entirely dewetted the substrate and formed a large number of islands that are clearly visible to the naked eye. As seen for example in the section on LB-films, thermal rearrangements are not uncommon in Langmuir-Blodgett multilayers and melting below the melting point of the bulk is also frequently observed. This further underlines the fact, that ethyl-4'-n-octyloxybiphenyl-4-carboxylate is not a particularly bad LB-film forming material. In contrast TFS-films of 280BC can reversibly be heated to 108 °C and cooled back to ambient without noticeable changes in film morphology (59). The fact that TFS-films can be heated to 2 degrees below the bulk melting temperature clearly points towards a much lower defect density, even of crystallized transferred freely-suspended films as compared to LB-films of the same material. Layer-by-Layer Adsorbed Films of Oppositely Charged Synthetic or Biological Polymers or Colloids: Control of Layer Architecture Over Large Surface Areas Multilayer fabrication by multiple consecutive electrostatically driven adsorption of oppositely charged polyions (17) (Figure 3) or colloidal particles (28) overcomes two problems: a) the use of charge reduces the steric requirements in comparison to covalent bond formation and b) the use of polyions allows for compensation of defects or small charge densities in underlying layers. The resulting films are, with the exception of very few cases, of high optical quality, but optical loss measurements on films in waveguide configuration have not yet been performed. The reason for the good film quality is prob ably the fact that poly electrolyte complexes are generally not crystalline. This means that the films should be rather homogeneous since domain boundaries on the submicron length scale are not present and therefore cannot contribute to light scattering. A conse quence of this is, however, that multilayer structural resolution is limited, since it is only defined on the molecular but not on the atomic scale. The key to a successful multilayer deposition is the surface refunctionalization in each adsorption step (17). Each adsorption step is self-regulating and thus leading to a defined thickness of individual layers. In this case the build-up of heterofunctional film architectures in a layer-by-layer fashion is straightforward and easily achieved (Figure 3), since one has complete control of layer sequence (19,60). Depending on the application, the multilayers may be fabricated on planar surfaces (e. g. for basic research, optical or sensing applications), on large custom shape surfaces or even on colloidal particles. For strong polyelectrolytes adsorption times may be as fast as 10 seconds, however, such conditions do not always lead to transparent films or to a linear film growth over many layers. For the simplest case of a (AB) two-component film in which A is a polyanion and Β is a polycation and η is the number of repetitions of this sequence, linear film growth is observed over several tens to hundreds of layers, when adsorption times are in the minute range. n

Multilayer Film Structure and Properties. Although the resulting films loose or take up water when heated to different temperatures and re-cooled, they are thermally quite



452

PHOTONIC AND

OPTOELECTRONIC POLYMERS

Figure 3. Schematic of the electrostatically driven layer-by-layer adsorption pro cess. It describes the case of the adsorption of a polyanion to a positively charged substrate (A), followed by washing (B), the adsorption of a polycation (C) and an other washing step (D). Multilayer films are prepared by repeating steps (A) through (D) in a cyclic fashion. More complicated film architectures are obtained by using additional adsorption/washing steps and applying more than two polyelectrolytes. Note that the drawing is oversimplified with respect to polyion conformation and interpénétration of adjacent layers. Furthermore, any counterions that might be pre sent in the films were omitted for reasons of clarity.



30. DECHER


453

stable. Films were heated to 200 °C in dry air for one week but no significant changes in X-ray reflectivity were observed after re-equilibration at ambient conditions. When heated directly in the X-ray reflectometer the film thickness shrinks, but the surface roughness stays constant. The conformation of polyelectrolytes in solution depends strongly on the concentra tion of added electrolyte. At low salt concentrations the polyelectrolytes are rather extended due to the repulsion of charges along the polymer backbone. At high salt concentrations the polyions coil up because the added salt screens this repulsion. Accord ingly, layers adsorbed from solutions containing no salt are thin and layers adsorbed from solutions containing large amounts of salt are thick. The control of the average incremen tal film growth is remarkable. In the case of films composed of poly(styrene sulfonate) (PSS) and poly(allylamine) (PAH), the thickness of a polyanion/polycation layer pair increases from 1.77 nm to 1.94 nm and to 2.26 nm when the PSS is adsorbed from a solution of NaCl with concentrations of 1.0 M to 1.5 M and to 2.0 M respectively and the PAH is adsorbed from pure water (67). PSS/PAH films were also thefirston which the spatial confinement of individual polymer layers (= multilayer superlattice architecture) was demonstrated (62,63). A film composed of 48 layers of PSS and PAH in which every sixth layer (= every third layer of PSS) was deuterated has a total thickness of 121 nm and a distance of 15.9 nm between the deuterated layers, as determined by neutron reflec tivity (62). A detailed neutron reflectivity study on the effects of salt and molecular weight on the average layer thicknesses and interfacial roughnesses has been carried out, its results will be published elsewhere (Schmitt, J.; Decher, G.; Bouwman, W.; Kjaer, K.; Lôsche, M. manuscript in preparation). It is now clear that the overlap of adjacent polyion layers is considerable, but many details such as charge stoichiometry and its relation to the film structure are not yet understood. Potential Applications. Currently, the technique of consecutive electrostatically driven adsorption of polyanions and polycations has not yet been developed to the point of commercially available devices, but the prospects for future use are quite promising. An advantage over other molecular deposition techniques is, that no dedicated and sensitive equipment (e. g. ultrahigh vacuum apparatus or Langmuir troughs) is needed and that the adsorption is carried out from aqueous solutions, which makes the technique also envi ronmentally attractive and allows incorporation of natural or modified biological materi als. This has already prompted considerable research from several groups (e.g. refs. (20,22,29,30,34-37,64-76). An overview of the different polyions used in these studies is given in scheme 1. Certainly one of the most interesting applications lies in the control of architecture (control of hole and electron injecting and active layers) in very thin electroluminescent devices. The existence of a precursor polyelectrolyte Pre-PPV (39,90,91) of the electro luminescent material poly(p-phenylene-vinylene) (PPV) (92) makes it possible to fabri cate polyion multilayer film architectures, in which the Pre-PPV can subsequently be converted to PPV by thermal annealing (19,34-38,87,88,93). Thefirstelectroluminescent devices have been prepared and it was found that devices as thin as 13 nm emit light (88). Turn-on voltages of less than 2 V are required to generate light (35) and even an influence of the film architecture on the luminescent properties has been observed (88). However, the structural details of these films are presently not understood and it is not clear how device properties are influenced by film composition and architecture. We have recently shown that the thermal conversion of Pre-PPV to PPV can be carried out with preser vation of a layered structure. These results were obtained by neutron reflectometry on






Pre-PPV

PDDA

PMPyA

R-PHPyV

Scheme 1: Chemical structures of synthetic polyelectrolytes used up to now for the fabrication of multilayers. There are considerably more polyelectrolytes whose ad sorption onto solid surfaces has been studied previously. Counter-ions are omitted in some cases, most of the abbreviations of the substances follow the original literature. The compounds are referenced as follows: PSS (17,21,24,61-63,71,75,77-79); PVS (80,81); PAZO (77); PAPSA (24); SPAN (35,65); PTAA (65); PAMPSA (82); PSMDEMA (16,17); P A H (77,20,24,27,61-63,65,68,71,73-75,79,80,83-86); PrePPV (19,34,35,38,87,88); PDDA (24,29); PMPyA (65); R-PHpyV (36); PEI (24, 79,81,89)

PAH


456


multilayer films in which selected layers were deuterated and will be published separately (Lehr, B.; Oeser, R.; Decher, G. manuscript in preparation). However, the fact that just within 4 years of the first report on polyelectrolyte multi layer films, homogeneous large area light emitting diodes have been described, has pro duced considerable enthusiasm towards applications (especially in the field of light emit ting diodes) of these layered polymeric nanoheterostructures.


Literature Cited. (1) Swalen, J. D.; Allara, D. L.; Andrade, J. D.; Chandross, Ε. Α.; Garoff, S.; Israelachvili, J.; McCarthy, T. J.; Murray, R.; Pease, R. F.; Rabolt, J. F.; Wynne, K. J.; Yu, H. Langmuir 1987, 3, 932-950. (2) Special Issue: Organic Thin Films Adv. Mater. 1991, 3, 3-180. (3) Ulman, A. An Introduction to Ultrathin Organic Films: From Langmuir-Blodgett to Self-Assembly; Academic Press: Boston, 1991; pp 442. (4) Ulman, A. Organic Thin Films and Surfaces: Directions for the Nineties; Ulman, Α., Ed.; Academic Press: San Diego, 1995; Vol. 20, pp 392. (5) Knoll, W. Curr. Opinion in Coll. & InterfaceSci.1996,1,137-143. (6) Langmuir, I.; Blodgett, Κ. B. Kolloid-Z. 1935, 73, 257-263. (7) Blodgett, Κ. B.; Langmuir, I. Phys. Rev. 1937, 51, 964-982. (8) Netzer, L.; Iscovici, R.; Sagiv, J. Thin Solid Films 1983, 99, 235-241. (9) Maoz, R.; Netzer, L.; Gun, J.; Sagiv, J. J. de Chim. Phys. 1988, 85, 1059-1065. (10) Lee, H.; Kepley, L. J.; Hong, H.-G.; Mallouk, T. E. J. Am. Chem. Soc. 1987, 110, 618-620. (11) Cao, G.; Hong, H.-G.; Mallouk, T. E. Acc. Chem. Res. 1992, 25, 420-427. (12) Kunitake, T.; Shimomura, M.; Kajiyama, T.; Harada, Α.; Okuyama, K.; Takayanagi, M. Thin Solid Films 1984, 121, L89-L91. (13) Coulon, G.; Russel, T. P.; Deline, V. R.; Green, P. F. Macromolecules 1989, 22, 2581-2589. (14) Maclennan, J.; Decher, G.; Sohling, U. Appl. Phys. Lett. 1991, 59, 917-919. (15) Decher, G.; Hong, J.-D. Makromol. Chem., Macromol. Symp. 1991, 46, 321-327. (16) Decher, G.; Hong, J.-D. Ber. Bunsenges. Phys. Chem. 1991, 95, 1430-1434. (17) Decher, G.; Hong, J.-D.; Schmitt, J. Thin Solid Films 1992, 210/211, 831-835. (18) Hong, J.-D.; Lowack, K.; Schmitt, J.; Decher, G. Progr. Colloid Polym. Sci. 1993, 93, 98-102. (19) Decher, G.; Lehr, B.; Lowack, K.; Lvov, Y.; Schmitt, J. Biosensors and Bioelectronics 1994, 9, 677-684. (20) Keller, S. W.; Kim, H.-N.; Mallouk, T. E. J. Am. Chem. Soc. 1994, 116, 8817-8818. (21) Lvov, Y.; Ariga, K.; Kunitake, T. Chemistry Letters 1994, 2323-2326. (22) Kong, W.; Zhang, X.; Gao, M. L.; Zhou, H.; Li, W.; Shen, J. Makromol. Chem., Rapid Commun. 1994, 15, 405-409. (23) Kong, W.; Wang, L. P.; Gao, M. L.; Zhou, H.; Zhang, X.; Li, W.; Shen, J. C. J. Chem. Soc., Chem. Commun. 1994, 1297-1298. (24) Lvov, Y.; Ariga, K.; Kunitake, T. J. Am. Chem.Soc.1995, 117, 6117-6123. (25) Sun, Y.; Zhang, X.; Sun, C.; Wang, B.; Shen, J. Macromol. Chem. Phys. 1996, 197, 147-153. (26) Onda, M.; Lvov, Y.; Ariga, K.; Kunitake, T. Biotechn. and Bioengin. 1996, 51, 163167. (27) Lvov, Y.; Decher, G.; Sukhorukov, G. Macromolecules 1993, 26, 5396-5399.



30.

DECHER


457

(28) Iler, R. K. J. Colloid Interface Sci. 1966, 21, 569-594. (29) Kleinfeld, E. R.; Ferguson, G. S. Science 1994, 265, 370-373. (30) Gao, M.; Gao, M.; Zhang, X.; Yang, Y.; Yang, B.; Shen, J. J. Chem. Soc., Chem. Commun. 1994, 2777-2778. (31) Lvov, Y.; Ariga, K.; Ichinose, I.; Kunitake, T. Langmuir 1996, 12, 3038-3044. (32) Kleinfeld, E. R.; Ferguson, G. S. Chem. Mater. 1995, 7, 2327-2331. (33) Sano, M.; Lvov, Y.; Kunitake, T. Annu. Rev. Mater. Sci. 1996, 26, 153-187. (34) Ferreira, M.; Rubner, M. F.; Hsieh, B. R. Mat. Res. Soc. Symp. Proc. 1994, 328, 119-124. (35) Onoda, M.; Yoshino, K. Jpn. J. Appl. Phys. 1995, 34, L260-L263. (36) Tian, J.; Wu, C.-C.; Thompson, M. E.; Sturm, J. C.; Register, R. Α.; Marsella, M. J.; Swager, T. M. Adv. Mater. 1995, 7, 395-398. (37) Hong, H.; Davidov, D.; Avny, Y.; Chayet, H.; Faraggi, Ε. Z.; Neumann, R. Adv. Mater. 1995, 7, 846-849. (38) Lehr, B.; Seufert, M.; Wenz, G.; Decher, G. Supramolecular Science 1996, 2, 199207. (39) Hörhold, H.-H.; Helbig, M.; Raabe, D.; Opfermann, J.; Scherf, U.; Stockmann, R.; Weiß, D. Z. Chem. 1987, 27, 126-137. (40) Decher, G.; Sohling, U. Ber. Bunsenges. Phys. Chem. 1991, 95, 1538-1542. (41) Leuthe, Α.; Riegler, H. J. Phys. D: Appl. Phys. 1992, 25, 1786-1797. (42) Asmussen, Α.; Riegler, H. J. Chem. Phys. 1996, 104, 8151-8158. (43) Riegler, H.; Spratte, K. In Organic Thin Films and Surfaces: Directions for the Nineties; Ulman, Α., Ed.; Thin Films; Academic Press: San Diego, 1995, Vol. 20; pp 349364. (44) Decher, G.; Tieke, B.; Bosshard, C.; Günter, P. J. Chem. Soc., Chem. Commun. 1988, 933-934. (45) Decher, G.; Tieke, B.; Bosshard, C.; Gunter, P. Ferroelectrics 1989, 91, 193-207. (46) Decher, G.; Klinkhammer, F. Makromol. Chem.,Macromol.Symp. 1991, 46, 19-26. (47) Decher, G.; Klinkhammer, F.; Peterson, I. R.; Steitz, R. Thin Solid Films 1989, 178, 445-451. (48) Bosshard, C.; Flörsheimer, M.; Küpfer, M.; Günter, P. Opt. Commun. 1991, 85, 247253. (49) Flörsheimer, M.; Küpfer, M.; Bosshard, C.; Günter, P. In NONOLINEAR OPTICS: Fundamentals, Materials and Devices; Miyata, S., Ed.; Elsevier Science Publishers B.V.: 1992, pp 255-269. (50) Klinkhammer, F. Herstellung und Untersuchung von dünnenSchichten mit neuartigen Strukturprinzipien für die nichtlineare Optik; Edition Wissenschaft Reihe Chemie; Tectum Verlag: Marburg, 1995; Vol. 4, (ISBN 3-89608-504-2; printed from Klinkhammer, F. Dissertation, Johannes Gutenberg-Universität Mainz, Germany, 1994). (51) Overney, R. M.; Meyer, E.; Frommer, J.; Güntherodt, H.-J.; Decher, G.; Reibel, J.; Sohling, U. Langmuir 1993, 9, 341-346. (52) Decher, G.; Tieke, B.; Bosshard, C.; Günter, P. Organische Materialien mit nichtlinearen optischen Eigenschaflen; European Patent No. 89 81 108.4, 1989. (53) Bosshard, C.; Küpfer, M.; Günter, P.; Pasquier, C.; Zahir, S.; Seifert, M. Appl. Phys. Lett: 1990, 56, 1204. (54) Young, C. Y.; Pindak, R.; Clark, Ν. Α.; Meyer, R. B. Phys. Rev. Lett. 1978, 40, 773776. (55) Pindak, R.; Moncton, D. Physics Today 1982, 35, 57-62. (56) Decher, G.; Maclennan, J.; Reibel, J.; Sohling, U. Adv. Mater. 1991, 3, 617-619.



458


(57) Decher, G.; Honig, M.; Reibel, J.; Voigt-Martin, I.; Dittrich, Α.; Poths, H.; Ringsdorf, H.; Zentel, R. Ber. Bunsenges. Phys. Chem. 1993, 97, 1386-1394. (58) Reibel, J.; Brehmer, M.; Zentel, R.; Decher, G. Adv. Mater. 1995, 7, 849-852. (59) Decher, G.; Maclennan, J.; Sohling, U.; Reibel, J. Thin Solid Films 1992, 210/211, 504-507. (60) Decher, G. In Templating, Self-Assembly and Self-Organization; Sauvage, J.-P. and Hosseini, M. W., Eds.; Comprehensive Supramolecular Chemistry; Pergamon Press: Oxford, 1996, Vol. 9; pp 507-528. (61) Decher, G.; Schmitt, J. Progr. Colloid Polym. Sci. 1992, 89, 160-164. (62) Schmitt, J.; Grünewald, T.; Kjaer, K.; Pershan, P.; Decher, G.; Lösche, M. Macromolecules 1993, 26, 7058-7063. (63) Korneev, D.; Lvov, Y.; Decher, G.; Schmitt, J.; Yaradaikin, S. Physica Β 1995, 213&214, 954-956. (64) Cheung, J. H.; Fou, A. F.; Rubner, M. F. Thin Solid Films 1994, 244, 985-989. (65) Ferreira, M.; Cheung, J. H.; Rubner, M. F. Thin Solid Films 1994, 244, 806-809. (66) Pommersheim, R.; Schrenzenmeir, J.; Vogt, W. Macromol. Chem. Phys. 1994, 195, 1557-1567. (67) Cooper, T. M.; Campbell, A. L.; Crane, R. L. Langmuir 1995, 11, 2713-2718. (68) Ferreira, M.; Rubner, M. F. Macromolecules 1995, 28, 7107-7114. (69) Keller, S. W.; Johnson, S. Α.; Brigham, E. S.; Yonemoto, Ε. H.; Mallouk, T. E. J. Am. Chem. Soc. 1995, 117, 12879-12880. (70) Kotov, Ν. Α.; Dékány, I.; Fendler, J. H. J. Phys. Chem. 1995, 99, 13065. (71) Lowack, K.; Helm, C. A. Macromolecules 1995, 28, 2912-2921. (72) Mao, G.; Tsao, Y.-H.; Tirrell, M.; Davis, H. T.; Hessel, V.; Ringsdorf, H. Langmuir 1995,11,942-952. (73) Saremi, F.; Maassen, E.; Tieke, B.; Jordan, G.; Rammensee, W. Langmuir 1995, 11, 1068-1071. (74) Hammond, P. T.; Whitesides, G. M. Macromolecules 1995, 28, 7569-7571. (75) v. Klitzing, R.; Möhwald, H. Langmuir 1995,11,3554-3559. (76) Sellergren, B.; Swietlow, Α.; Amebrandt, T.; Unger, K. Anal. Chem. 1996, 68, 402407. (77) Decher, G.; Lvov, Y.; Schmitt, J. Thin Solid Films 1994, 244, 772-777. (78) Schlenoff, J. B.; Li, M. Ber. Bunsenges. Phys. Chem. 1996, 100, 943-947. (79) Sukhorukov, G. B.; Schmitt, J.; Decher, G. Ber. Bunsenges. Phys. Chem. 1996, 100, 948-953. (80) Lvov, Y.; Decher, G.; Möhwald, H. Langmuir 1993, 9, 481-486. (81) Laschewsky, Α.; Mayer, B.; Wischerhoff, E.; Arys, X.; Jonas, A. Ber. Bunsenges. Phys. Chem. 1996, 100, 1033-1038. (82) Mao, G.; Tsao, Y.; Tirrell, M.; Davis, H. T.; Hessel, V.; Ringsdorf, H. Langmuir 1993, 9, 3461-3470. (83) Lvov, Y.; Eßler, F.; Decher, G. J. Phys. Chem. 1993, 97, 13773-13777. (84) Lvov, Y.; Haas, H.; Decher, G.; Möhwald, H.; Kalachev, A. J. Phys. Chem. 1993, 97, 12835-12841. (85) Tronin, Α.; Lvov, Y.; Nicolini, C. Colloid Polym. Sci. 1994, 272, 1317-1321. (86) Ramsden, J. J.; Lvov, Y. M.; Decher, G. Thin Solid Films 1995, 254, 246-251 erratum: idem (1995), 261, 343-344. (87) Lehr, B. Ultradünne PPV-Filme - Herstellung und Charakterisierung-; Diploma Thesis; Johannes Gutenberg-Universität: Mainz, Germany, 1993.


30.

DECHER

459


(88) Fou, A. C.; Onitsuka, O.; Ferreira, M.; Rubner, M. F.; Hsieh, B. R. Mat. Res. Soc. Symp. Proc. 1995, 369, 575-580. (89) Decher, G. Nachr. Chem. Tech. Lab. 1993, 41, 793-800.

(90) Hörhold, H.-H.; Opfermann, J. Die

Makromolekulare Chemie

1970,

131,

105 - 132.

(91) Wessling, R. A. J. Polym. Sci.: Polym. Symp. 1985, 72, 55-66.


(92) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.; McMackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Nature 1990, 347, 539-541. (93) Tian, J.; Thompson, M. E.; Wu, C.-C.; Sturm, J. C.; Register, R. Α.; Marsella, M. J.; Swager, T. M. Polymer Preprints 1994, 35, 761-762.


Molecular Multilayer Films: The Quest for Order ... - ACS Publications

Recommend Documents