Apertureless cantilever-free pen arrays for scanning photochemical printing

There are two categorically different approaches for defining patterns on surfaces, those based on the delivery of energy and those based on the delivery of materials. [1-4] The delivery of energy is the mainstay of the microelectronics community while the delivery of materials is commonly used in biological contexts where the materials of interest are chemically diverse and sensitive to harsh processing conditions. One recently developed set of techniques that spans this divide is cantilever-free scanning probe lithography (SPL) wherein materials or energy are deposited from an array of pens that rest on an elastomeric film on a rigid support. [5-12] This architecture affords the high resolution commonly observed in SPL in combination with high throughput by virtue of the simultaneous operation of as many as millions of pens. Given the widespread usage of energy delivery techniques, beam pen lithography (BPL), in which cantileverfree pens can be used as near-field probes to direct light onto surfaces in a massively parallel and multiplexed fashion, has aroused broad interest in low cost desktop nanofabrication and site-selective photochemistry. [7,13,14] However, the need for rigid opaque materials and apertures at the tips of the pens in BPL constrains this technique from fully leveraging the advantages inherent to elastomeric pens with respect to molecular printing and necessitates a complicated nanofabrication step to open uniform sub-wavelength apertures at the tip of each probe. Here, we explore the optical implications of not having opaque films or apertures at the tip of pens in a cantilever-free pen array and find that by blocking the flat backing layer between pens, the optical interaction with the surface is dominated by the light at the tip of the pen, allowing one to serially write sub-wavelength features. Furthermore, in the absence of a rigid metal film coating the pens, we find that they can be reversibly deformed to tune the illumination region from the submicrometer to micrometer scale and used to simultaneously deliver materials and optical energy in a single experiment. This approach provides a route to multiplexing with respect to length scales and materials.