Scanning probe lithography of chemically functionalised surfaces

Abstract

A facile route to the production of highly uniform, ultra-thin metal oxide films has-been demonstrated using a combination of self-assembly and Langmuir-Blodgett techniques. Initial modification of a Si/SiO(_2) substrate through self-assembly of an octadecylsiloxane monolayer provides a hydrophobic surface suitable for the "tail down" deposition of a Langmuir-Blodgett monolayer of octadecylphosphonic acid, giving. The resulting –PO(_3)H(_2) functionalised film provides a suitable surface for binding of metal ions (e.g. Zr(^4+), Hf(^4+), Mg(^2+)). The tendency of these metal species to form polymeric structures in aqueous solution allows for the assembly of nanometre thick inorganic metal layers upon the –PO(_3)H(_2) surface. Thermal treatment of the Langmuir-Blodgett films was used to decompose the organic film components, whilst simultaneously calcining the inorganic metal layer, resulting in the formation of highly uniform metal oxide films, typically ca. 1.3 - 1.9 nm thick. Nanoscale patterning of the metal-stabilised Langmuir-Blodgett monolayers has also been demonstrated, by using an AFM probe to apply sufficiently high vertical forces upon the Langmuir-Blodgett surface to selectively displace the monolayer film material within spatially defined surface regions. Pattern resolutions dowm to 30 nm were achieved using this AFM "nanodisplacement" lithographic process. Excellent levels of structural retention of the patterns were also observed upon decomposition of the organic film components to generate the final metal oxide. Similarly, nanodisplacement patterning of metal-stabilised Langmuir-Blodgett monolayers deposited upon amino-flinctionalised substrates has been used for the fabrication of amine patterned surfaces. Selective binding of Au nanoparticles within the amine regions was demonstrated, highlighting the potential of such patterned surfaces as chemical templates for directing the assembly and organisation of other materials