Rational fabrication of nanostructures on surfaces using Dip-Pen nanolithography

Dip-Pen Nanolithography (DPN), an atomic force microscope (AFM) based lithography technique, has been used to create rationally-patterned nanostructures on surfaces from a variety of materials. In DPN, a molecule is coated onto an AFM tip and directly transferred from the tip to an appropriate surface, where it is immobilized on the surface through ink-substrate chemical or physical interactions. Because the AFM tip is a nanosized instrument, DPN is capable of easily producing sub-100 nm nanostructures of molecules that are pre-coated onto the tip. Prior to this work, it had been demonstrated that DPN patterning requires immobilization of a compound on a surface, such as through gold-thiol or silicon-oxygen covalent bonds. In this work, DPN patterning has been extended to other systems by expanding the range of chemical interactions that can be used to immobilize compounds onto surfaces. Covalent chemical interactions between alkylphosphonic acid monolayers and alumina and titania have been used to facilitate patterning on these surfaces and specific oxidation-reduction chemistry has been used to pattern gold nanostructures on silicon surfaces. A related AFM lithography process, Electrochemical Dip-Pen Nanolithography (E-DPN), has been developed that is capable of fabricating nanostructures on conducting and insulating surfaces. E-DPN is unique because it does not require a specific molecule-surface chemical reaction to immobilize the nanostructures; instead, E-DPN uses an external bias voltage to chemically change tip-applied precursors to immobile surface-adsorbed nanostructures. This process is conceptually similar to the well-known processes of electrodeposition or electropolymerization. E-DPN has been used to fabricate metallic, semiconducting, and conducting polymer nanostructures on semiconducting, insulating, and metallic surfaces. E-DPN has also been used for the site-specific fabrication of conducting polymer nanodevices. The properties of these devices have been measured and they have been used to fabricate an HCl-responsive nanodevice. E-DPN has also been used for the repair of electromigration-induced break junctions. Finally, novel DPN and E-DPN chemistries have been used to locally modify prefabricated nanodevices, demonstrating that E-DPN can be a useful technique for the rational construction of electronic devices.