Fabrication of Gold Micro- and Nanostructures by Photolithographic Exposure of Thiol-Stabilized Gold Nanoparticles Shuqing Sun, § Paula Mendes, ² Kevin Critchley, # Sara Diegoli, ² Marcus Hanwell, ‡ Stephen D. Evans, # Graham J. Leggett,* ,§ Jon A. Preece,* ,² and Tim H. Richardson ‡ Department of Chemistry, UniVersity of Sheffield, Brook Hill, Sheffield S3 7HF, U.K., School of Chemistry, UniVersity of Birmingham, Edgbaston, Birmingham B15 2TT, U.K., School of Physics and Astronomy, UniVersity of Leeds, Leeds, LS2 9JT, U.K., and Department of Physics and Astronomy, UniVersity of Sheffield, Brook Hill, Sheffield S3 7RH, U.K. Received October 28, 2005; Revised Manuscript Received January 12, 2006 ABSTRACT Exposure of thiol-stabilized gold nanoparticles supported on silicon wafers to UV light leads to oxidation of the thiol molecules and coagulation of the nanoparticles, forming densified structures that are resistant to removal by solvent exposure. Unoxidized particles may, in contrast, readily be removed leaving gold structures behind at the surface. This process provides a convenient and simple route for the fabrication of gold structures with dimensions ranging from micrometers to nanometers. The use of masks enables micrometer-scale structures to be fabricated rapidly. Exposure of nanoparticles to light from a near-field scanning optical microscope (NSOM) leads to the formation of gold nanowires. The dimensions of these nanowires depend on the method of preparation of the film: for spin-cast films, a width of 200 nm was achieved. However, this was reduced significantly, to 60 nm, for Langmuir-Schaeffer films. The spatial organization of nanometer-scale components (such as metal nanoparticles, carbon nanotubes, proteins, cells, organic molecules, polymers, etc.) onto surfaces to fabricate functional nanostructured systems for electronic, 1,2 optical, 3 biological, 4 or sensing applications, 5,6 is one of the most important challenges in nanoscale science and technol- ogy. Recently there has been a great deal of interest in the fabrication of nanoscale structures composed of nanopar- ticles. Such structures are attractive for a variety of reasons, including their potential utility as nanostructured conductors, novel resists, and templates for the attachment of molecules with specific electronic, sensing, or biological recognition characteristics. 7 A variety of methods have been reported for the patterning of nanoparticles. One approach is to fabricate a template by patterning a suitable substrate. For example, gold clusters have been attached to adhesive patches fabricated in alkyl- silane monolayers on silicon substrates 8 and phosphonic acid- functionalized nanoparticles have been attached to silicon surfaces in areas delineated by the selective photolithographic passivation of the substrate. 9 Such approaches are not restricted to metallic nanoparticles. Xia and Brueck have formed patterns in photoresist on silicon to control the immobilization of spin-coated silica nanoparticles, 10 whereas Minelli et al. used block copolymer films, which exhibited nanoscale phase separation in conjunction with plasma treatment to form regions that were adhesive to nanopar- ticles. 11 Electron beam lithography 12 and scanning probe lithography methods have been utilized to create nanopat- terned templates. For example, dip-pen nanolithography 13,14 and nanoshaving 15 have been used to pattern self-assembled monolayer (SAM) templates onto which gold nanoparticles may subsequently be immobilized, and aldehyde-function- alized polymer nanoparticles have been patterned by attach- ment via imide bond formation to amine-functionalized regions fabricated in carboxylic acid-terminated SAMs using scanning near-field photolithography. 16 Local oxidation on exposure of alkylsiloxane monolayers to a biased AFM tip has been used to introduce hydroxyl functionalities, to which * To whom correspondence should be addressed. Tel:+ 44 (0) 121 414 3528, fax:+ 44 (0) 121 414 4403, e-mail: j.a.preece@bham.ac.uk; or tel: +44 (0) 114 222 9556, fax: +44 (0) 114 222 9346, e-mail: Graham.Leggett@sheff.ac.uk. ² University of Birmingham. ‡ Department of Physics and Astronomy, University of Sheffield. § Department of Chemistry, University of Sheffield. # University of Leeds. NANO LETTERS 2006 Vol. 6, No. 3 345-350 10.1021/nl052130h CCC: $33.50 © 2006 American Chemical Society Published on Web 02/21/2006