Capillary nanostamping with spongy mesoporous silica stamps

Many lithographic methods to pattern surfaces both by a mechanical manipulation of the surface or by printing functionalities in the form of particles or molecules have been developed and used in research. Examples for contact-lithographic methods are soft lithography and polymer-pen lithography. One of the main drawbacks of the these methods is the lateral dimension of the obtained pattern. Due to limitations of stamps, materials and the methods themselves, feature sizes of arrays consisting of discrete spots in the sub-micrometer range remain challenging. Another factor in the state-of-the-art contact-lithographic methods is the ex situ adsorption of ink prior to the stamping procedure and thus, an uninterrupted flow of ink cannot be guaranteed. As the variety of imaginable inks is wide and the appropriate solvent often appears to be of organic nature, state-of-the-art contact-lithographic methods are unable to print these inks. The elastomeric polymer stamps used within contact-lithographic methods swell or dissolve in contact with organic solvents. Often, contact-lithographic methods require expensive equipment or defined conditions, e.g. high vacuum or a solvent-enriched humidity, and cannot be carried out in a simple and efficient way under ambient conditions. In this work, a new approach to generate patterned structures with feature sizes in the sub-micrometer range and spot-to-spot distances in the one-micron range is presented. Stamps with an integrated, continuous pore system generate the patterns while the ink is supplied through the capillaries of the stamp. The method of capillary nanostamping provides a simple and low-cost stamping procedure by the synthesis of spongy mesoporous silica stamps. Due to a continuous pore system within the stamp, the ink can be supplied continuously and even without a refilling system, the stamp itself serves as ink reservoir. This provides a continuous or intermittently ink supply for a stamping process with several stamping cycles without the need to refill the stamp. A new stamp or re-inking after one stamping cycle is not necessary. The stamping process is carried out manually by hand under ambient conditions. Due to the silica network, the stamps can be infiltrated with organic solvents. The development of spongy mesoporous silica stamps for capillary nanostamping is presented in this work by demonstrating the progress from pure silica stamps in a typical well-known sol-gel synthesis to spongy and flexible silica stamps with a reduced network bonding and hydrophobic internal residues. For the proof of concept of capillary nanostamping with spongy mesoporous silica stamps, several different inks are stamped. All inks are chosen with respect to a potential application and consist of a volatile organic solvent to proof the stability of the stamps against these solvents, and a non-volatile component, which remains on the substrate surface after precipitation and drying of the solvent. As ink, a dispersion of C60 fullerenes in toluene is stamped onto perfluorinated glass slides. A solution of 1-dodecanethiol in ethanol is stamped onto a gold-coated glass with the outcome of a heterogeneous surface. As a model for nanoparticles, nanodiamonds dispersed in isopropanol are stamped and subsequently functionalized with a fluorescent dye in a click-reaction. A polymer and two different block copolymers dissolved in toluene/chloroform are stamped onto differently functionalized substrate surfaces to analyze the dependency of the nature of the substrate on the stamping results. In a final experiment, a solution of 17α-ethinylestradiol in acetonitrile is stamped as a model for an active pharmaceutical ingredient and subsequently detached from the substrate surface to obtain a defined nanodispersion