AVS 49th International Symposium
    Processing at the Nanoscale Thursday Sessions
       Session PN+SS-ThM

Paper PN+SS-ThM5
Covalent Nanopatterning of Liquid Phase Organic Molecules to Silicon Surfaces using Conductive Atomic Force Microscopy

Thursday, November 7, 2002, 9:40 am, Room C-109

Session: Patterning and Functionalization
Presenter: M.C. Hersam, Northwestern University
Authors: M.W. Such, Northwestern University
C.R. Kinser, Northwestern University
M.C. Hersam, Northwestern University
Correspondent: Click to Email
Electron stimulated desorption (ESD) with ultra-high vacuum (UHV) scanning tunneling microscopy (STM) is a well-established technique for creating reactive patterns of dangling bonds on predominantly hydrogen passivated silicon surfaces. Gas phase surface chemistry occurs selectively with these nanopatterns, allowing for controlled deposition of materials down to the single molecule level. Although this approach is effective in UHV, it has not yet been utilized for the patterning of non-UHV-compatible materials. This paper describes an analogous means of creating reactive nanopatterns on hydrogen passivated Si(111) surfaces using conductive atomic force microscopy (cAFM) in liquid environments. Unlike cAFM patterning in air that induces oxidation on silicon surfaces, this approach suppresses oxidation through encapsulation of the tip-sample junction in an anhydrous organic solvent (e.g., toluene or dimethyl sulfoxide). Following ESD induced with cAFM, olefinic organic molecules suspended in the organic solvent environment spontaneously bind to the dangling bond patterns. To demonstrate this technique, exo-5-norbornene-2-ol has been patterned with 50 nm resolution on Si(111):H. Lateral force microscopy and force-distance spectroscopy confirm the hydrophilic nature of this molecule compared to the hydrophobic Si(111):H surface. Following deposition, these nanopatterned molecules have been subjected to a subsequent nucleophilic acyl substitution reaction with Lauroyl Chloride at 50°C for 24 hours. Consistent with the expected dodecyl ester modification of the adsorbed norbornene molecule, the resulting nanopattern appears hydrophobic in LFM analysis. The stability of these nanopatterns to subsequent chemistry suggests that the adsorbed molecules are covalently bonded to the silicon substrate. Further applications of this lithography for covalently nanopatterning polymers and biological molecules to silicon surfaces will also be discussed.