Microcontact Transfer Printing of Zeolite Monolayers

2009 WILEY-VCH Verlag Gmb Zeolites are aluminosilicates that are used in a broad field of applications. Because of their ion-exchange capabilities, presence of well-defined rigid cavities, and transparency in the UV–vis/NIR region, zeolites can act as water softeners, catalysts, and host systems for a variety of photoactive guests. In particular, zeolite L, which possesses unidirectional channels, has been shown to be a suitable material for supramolecular organization of different kinds of molecules. The size (30 nm to several micrometers) and aspect ratio of L-type zeolite can be controlled synthetically. Furthermore, it has been shown recently that they can be organized in monolayers on a silica substrate by chemical functionalization. Interestingly, the orientation of the channels is perpendicular to the surface so that they can be filled after their immobilization. However, reports on the formation of well-orderedmonolayers on other (conductive) substrates have been very limited and so far it has not yet been possible to transfer them from one surface to another without disruption of the monolayer. However, the preparation of an oriented monolayer of zeolite L crystals on certain substrates (silicon wafers, ITO, gold) represents an important prerequisite for achieving a controlled architecture of such microsized building blocks for possible optoelectronic applications. Many authors have reported several methods for pursuing this goal by chemical treatment of target surfaces via different kinds of molecular linkers, and in some cases perfect monolayers were achieved, especially for zeolite A. We report a strategy based on the microcontact printing technique (MCP) to obtain well-ordered and uniformly oriented zeolite L monolayers on conductive surfaces without any chemical modification of the zeolite or the substrate. MCP, which has been employed by many authors, represents an inexpensive tool for the formation of a wide variety of molecular assemblies, ranging from quantum dots and silicon particles to carbon nanotubes and nanowires, and it has been also applied to pattern materials allowing new applications in device fabrication. [21–26] We have successfully applied this technique to create particular patterns with L-type zeolites that were filled with fluorescent dyes. We have also demonstrated that it is possible not only to apply the method to cylindrical objects by transferring them and maintaining their orientation, but also to use the anisotropy of the systems to control the different color emissions of zeolites filled with two different dyes by exciting the materials with polarized light.