Inkless Soft Lithography: Utilizing Immobilized Enzymes and Small Molecules to Pattern Self-Assembled Monolayers Via Catalytic Microcontact Printing

Abstract

<p>During the past two decades, soft lithographic techniques that circumvent the limitations of photolithography have emerged as important tools for the transfer of patterns with sub-micron dimensions. Among these techniques, microcontact printing (uCP) has shown special promise. In uCP, an elastomeric stamp is first inked with surface-reactive molecules and placed in contact with an ink-reactive surface, resulting in pattern transfer in the form of self-assembled monolayers in regions of conformal contact. The resolution in uCP is ultimately limited to the diffusion of ink and the elastomechanical properties of the bulk stamping material. </p> <p>One way to improve resolution is to eliminate diffusion by using inkless methods for pattern transfer. Inkless catalytic-uCP uses a chemical reaction between a stamp-immobilized catalyst and surface bearing cognate substrate to transfer pattern in the areas of conformal contact. By using pre-assembled cognate surfaces, the approach extends the range of surfaces readily amenable to patterning while obviating diffusive resolution limits imposed by traditional uCP. </p> <p>In this thesis, we report two methods using inkless catalytic uCP: biocatalytic-uCP utilizes an immobilized enzyme as a catalyst whereas catalytic-uCP utilizes an immobilized small molecule as a catalyst, such as an acid or base. Both catalytic techniques demonstrate pattern transfer at the microscale while using unconventional, acrylate-based stamp materials. Previous results produced with catalytic-uCP have shown pattern transfer with sub-50 nm edge resolution. In this demonstration of catalytic-uCP, we use the technique to demonstrate a bi-layered patterning technique for H-terminated silicon, the foremost material in semi-conductor fabrication. This technique simultaneously protects the underlying silicon surface from degradation while a highly-reactive organic overlayer remains patternable by acidic-functionalized PU stamps. Lines bearing widths as small as 150 nm were reproduced on the reactive SAM overlayer, which would not be possible without circumvention of diffusion. Before and after patterning, no oxidation of the underlying silicon was observed, preserving desired electronic properties throughout the whole process. This bi-patterning technique could be extended to other technologically-relevant surfaces for further application in organic-based electronic devices and other related technologies.</p>