A Novel AFM Chip for Fountain Pen Nanolithography - Design and Microfabrication
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A Novel AFM Chip for Fountain Pen Nanolithography - Design and Microfabrication Keun-Ho Kim, Nicolaie Moldovan, Changhong Ke, Horacio D. Espinosa* Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, U.S.A. ABSTRACT A novel atomic force microscopy (AFM) probe has been developed to expand the capability and applications of dip-pen nanolithography (DPN) technology. This new probe has integrated microchannels and reservoirs for continuous ink feed, which allow “fountain-pen” writing called “Fountain Pen Nanolithography” (FPN). Ink is transported from the reservoirs through the microchannels and eventually dispensed onto substrates via a volcano-like dispensing tip. Numerical simulations have been performed to select optimal materials and suitable tip shapes providing a stable fluid-air interface in the tip. Microchannel and dispensing tip have been fabricated by surface micromachining, in particular employing 3 layers of thin films. Fluid flow through the microchannels has been experimentally examined. The probe was used to write on a gold substrate. *Corresponding author: [email protected]
INTRODUCTION Nanoscale patterning capabilities are important to construct functional nanostructures on surfaces via bottom-up approach. Among nanopatterning methodologies, dip-pen nanolithography (DPN) is a direct-write method to produce nanostructures with high resolution of less than 20 nm [1]. In this method, an atomic force microscope (AFM) tip is coated with molecules or “inks” and brought into contact with a surface or “paper” to deposit the coated molecules. A water meniscus formed between an AFM tip and a surface is proposed as the transfer mechanism that enables the delivery of molecules from the tip to the surface. DPN was originally demonstrated for patterning monolayers of alkanethiol on gold surfaces, and subsequently expanded to patterning biomolecules [2,3] and inorganic materials [4-8]. In DPN, molecules are coated either by dipping an AFM tip into a solution containing the molecules or by evaporation from a source. When patterning of large areas or complex structures is required, the tips need to be replenished periodically, leading to additional time-consuming steps and strongly limiting the versatility of the technique. In an effort to overcome this drawback, several studies have been reported on continuous ink feeding. A pulled micropipette with a small aperture was used to continuously deliver liquid substance to a substrate enabling a nanoscale control of the chemical reaction [9-11]. However, pulled micropipettes typically suffer from irregular aperture size and low reproducibility. Another approach was to microfabricate an aperture at the apex of a hollow pyramidal tip, utilizing the back side of the tip as a reservoir [12]. However, the resolution is not competitive with DPN since the feature size is dependent on the aperture size. Here we report a novel AFM probe, so-called nano-fountain probe, integrated with microchannels and an ink-dispe
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