The generation of mesostructured crystalline CeO2, ZrO2and CeO2–ZrO2films using evaporation-induced self-assembly

Brezesinski, Torsten; Antonietti, Markus; Groenewolt, Matthijs; Pinna, Nicola; Smarsly, Bernd M.

doi:10.1039/b412306a

Cited by 78 publications

(78 citation statements)

References 31 publications

(13 reference statements)

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“…8 nm. [14,17,18] XRD experiments revealed that the crystallographic orientation of the nanocrystals was maintained even in the presence of mesopores, and the degree of preferred orientation only slightly decreased in comparison to the nonporous films prepared with low amounts of surfactant. Such mesoporous metal oxides with the nanocrystals being highly oriented with respect to the substrate have not been reported to date.…”

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confidence: 87%

Surfactant‐Mediated Generation of Iso‐Oriented Dense and Mesoporous Crystalline Metal‐Oxide Layers

et al. 2006

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The fabrication of thin layers of a transition-metal oxide with 3D oriented crystallites has substantial importance for industrial applications, for example, semiconductor technology. [1,2] Chemical vapor deposition [3] and molecular beam epitaxy [4] onto single-crystalline substrates are widely used fabrication techniques but they suffer from elaborate preparation setups. Most of the currently applied concepts to generate layers of oriented crystals involve the deposition of molecular species from the gas phase [5] (pulsed laser deposition, molecular beam epitaxy) or the liquid phase [6] (liquid phase epitaxy)on suitable single-crystalline surfaces. In these processes the crystals grow in a direction that is dictated by the lattice planes of the substrate exposed to the surface, and the substrate has to match the lattice parameter of the oxide (epitaxy). Solution-processing (SP) routes have been proposed as a versatile and facile alternative, especially for transition-metal oxides applying sol-gel reactions, because of the evident advantages of "beaker" chemistry and liquid-coating processing. [7][8][9] However, up until now SP has required single-crystalline substrates to achieve oriented crystallization, which represents a substantial limitation and complication. Therefore, it is not commonly expected and it has not been reported yet that crack-free layers of transition-metal oxides with a high degree of crystallographic orientation can be formed from aqueous solutions on arbitrary substrates.[10] Furthermore, the recently introduced class of mesoporous metal oxides could solely be prepared with a random distribution of nanocrystals within the pore walls. Here, we report a general, straightforward surfactant-mediated methodology for the preparation of dense and even well-ordered mesoporous films of transition-metal oxides with crystallographically oriented crystals (MoO 3 , Nb 2 O 5 , Ta 2 O 5 , V 2 O 5 , perovskites etc.) on noncrystalline substrates such as glass. In order to understand the underlying principles for this surprising finding, we performed a systematic study on a broad series of metal oxides (TiO 2 , CeO 2 , SnO 2 , etc.) to understand the relationship between the crystallographic orientation and the unit-cell characteristics of the different oxides. Interestingly, our studies revealed that this effect generally occurs for metal oxides with certain anisotropic unit-cell features, which is exemplified here in detail for MoO 3 and Nb 2 O 5 . It is justified to term this new surfactantmediated crystallization phenomenon "soft epitaxy", following the previously introduced polymer-controlled nucleation and crystallization of different inorganic salts as powders with various macroscopic 3D crystal structures. [11] As key element, our straightforward soft-epitactic process uses a surfactantmediated oriented nucleation from surfaces, starting from aqueous-ethanolic or water-free solutions, depending on the respective oxide. In essence, the approach involves dip-coating polar, wettable substrates (e.g.,...

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confidence: 87%

Surfactant‐Mediated Generation of Iso‐Oriented Dense and Mesoporous Crystalline Metal‐Oxide Layers

et al. 2006

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“…With these improved templates, various metal oxides could be applied as highly crystalline coatings with high structural regularity of the mesopores (spherical, size larger than 12 nm). [34][35][36] Beside the technically highly relevant anatase, ZrO 2 , CeO 2 , and a variety of mixed intermediary ternary oxide mixtures of the two metals have also been synthesized (see Figure 8). [34] Figure 8.…”

Section: Synthesis Of Mesoporous Crystalline Metal Oxidesmentioning

confidence: 99%

Block Copolymer Assemblies as Templates for the Generation of Mesoporous Inorganic Materials and Crystalline Films

2006

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This Microreview presents the synthesis of mesoporous, crystalline inorganic materials using self‐assembled block copolymer mesostructures as templates. The advances in this field are discussed in light of the progress in the development of suitable polymer templates. Particular emphasis is placed on the special conditions and demands to transform the primary sol–gel films into mesoporous, aligned crystalline films for functional applications. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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“…First, a time-consuming pretreatment of films at moderate temperatures is not required to solidify or stabilize the mesostructured, amorphous network prior to crystallization, as recently reported for the generation of diverse mesoporous, crystalline films with intricate sol-gel behavior. [10,12,13,22] Second, at least for TiO 2 , the layers possess a better thermal stability than corresponding 3D-mesoporous films synthesized with the same polymer template, i.e., the mesostructural collapse due to mass transport in the pore walls takes place at higher temperatures (ca. 750°C compared to ca.…”

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confidence: 99%

“…This has been beyond the reach of common lithography techniques to date. Furthermore, in contrast to physical methods such as molecular-beam epitaxy, pulsed laser deposition, and chemical vapor deposition, which are often used in combination with lithography and are known to suffer from elaborate preparation techniques, the present sol-gel approach also allows one to address more complex metal oxides (e.g., BaTiO 3 ) by the ease of "beaker" chemistry and liquid-coating processing.For the generation of ultrathin, mesoporous metal oxide layers with periodicities in two dimensions and one dimension, respectively, we used two different types of structure-directing agents, namely a novel block copolymer of the "KLE" family (poly(ethylene-co-butylene)-block-poly(ethylene oxide)), [9] which has already enabled the synthesis of various mesoporous, crystalline metal oxide thin films (e.g., CeO 2 , [10] TiO 2 , [11] …”

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confidence: 99%

Evaporation‐Induced Self‐Assembly (EISA) at Its Limit: Ultrathin, Crystalline Patterns by Templating of Micellar Monolayers

Brezesinski

Groenewolt²,

Gibaud

et al. 2006

Advanced Materials

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Patterning of surfaces at the nanoscale is important in many fields of application, e.g., for electronic devices, storage media, and as a starting base for the generation of more complex structures. To exemplify the latter subject, it has been shown that a periodic surface structure with periodicity of surface energy and topology allows for the alignment of liquid crystals [1] or the consecutive construction of channels or pillars being vertically aligned with respect to the substrate, [2] thus making the application of strong external fields redundant. [3,4] Structures in the range of 45-300 nm are predominantly fabricated by either optical-or electron-beam lithography. To reach the sub-45 nm range, self-assembled block-copolymer mesophases are employed as templates within lithographic processes. For instance, Adamson and co-workers reported on the use of block copolymers in a lithography etching process to generate dense periodic arrays of holes and dots in a silicon nitride coated silicon wafer.[5] However, this process deals only with the structuring of a given surface, i.e., the physical properties of the final material are limited by the choice of the starting material and the restrictions of lithography.Herein, we present a straightforward approach towards a whole range of ultrathin, mesostructured metal oxide layers by sol-gel processing via a modified evaporation-induced selfassembly (EISA) approach introduced by Ogawa et al. and Brinker et al. several years ago.[6] EISA usually provides mesostructured films with a thickness of 50-1000 nm, which therefore consist of several stacked layers (multilayers of micellar aggregates). [7] However, it is challenging to use this well-established procedure to generate corresponding ultrathin films with ordered mesoporosity, although it is usually assumed that such fine control can only be achieved by Langmuir-Blodgett (LB) techniques. Kunitake and co-workers reported the successful preparation of ultrathin, self-supporting films of different oxides by sequential sol-gel processing using polymer underlayers and spin-coating, but the porosity was disordered and the metal oxides amorphous.[8]In the present study, it is shown that a modified EISA procedure allows for the preparation of crack-free, ultrathin, crystalline metal oxide films with highly ordered in-plane mesostructure and a tunable film thickness on the scale of only several nanometers, even achieving the sequential formation of mesostructured metal oxides with exactly one micellar monolayer in height. Different structures (e.g., circular pores or line patterns) of the final surface layer material can be simply adjusted by varying the assembly structure of the template, and by using sufficiently small templates, the periodicity of the patterns can be downsized to about 4-5 nm. In addition, the structure is instantaneously generated on macroscopic length scales (i.e., not serial/slow). This has been beyond the reach of common lithography techniques to date. Furthermore, in contrast to physical methods suc...

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The generation of mesostructured crystalline CeO₂, ZrO₂and CeO₂–ZrO₂films using evaporation-induced self-assembly

Cited by 78 publications

References 31 publications

Surfactant‐Mediated Generation of Iso‐Oriented Dense and Mesoporous Crystalline Metal‐Oxide Layers

Surfactant‐Mediated Generation of Iso‐Oriented Dense and Mesoporous Crystalline Metal‐Oxide Layers

Block Copolymer Assemblies as Templates for the Generation of Mesoporous Inorganic Materials and Crystalline Films

Evaporation‐Induced Self‐Assembly (EISA) at Its Limit: Ultrathin, Crystalline Patterns by Templating of Micellar Monolayers

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