Control of Spatially Localized Chemical Reactions Using a Scanning Probe Microscope

Control of spatially localized chemical reactions such as site-selective reversible chemical conversion of functional groups and metal deposition on nano and/or micro areas is important to fabricate new devices in the next generation. In this study, the reaction controls were attempted with a nano probe. In the reversible chemical conversion, amino-terminated self-assembled monolayers (SAMs), which were prepared on Si substrates from (p-aminophenyl)trimethoxysilane (APhS) through chemical vapor deposition, were electrochemically converted into nitoroso-terminate ones using an atomic force microscope. The electrochemical reaction required the positive bias voltages of +0.5 to +3V. In order to define the chemical conversion, the sample substrates were immersed in a solution of pH=4 containing carboxylate-modified polystyrene (PS) spheres. The PS spheres were site-selectively adsorbed on the non-scanned regions. This indicates that non-scanned regions justifiably correspond to amino-terminated SAMs. On the other hand, the PS spheres were not adsorbed on the scanned regions at all, since the regions were oxidized and converted into nitoroso-terminated SAMs. Furthermore, the oxidized regions could also be reduced by a probe with negative bias voltage of −2V. The site-selective electroless deposition was actualized using a surface-induced reduction of gold ions combined with scanning probe lithography. Gold nano- or micro-structures on hydrogen-terminated Si surfaces were demonstrated. After fabrication of an Au nanostructure, 1-hexadecanethiol was immobilized on the Au surface. The result shows that we successfully controlled chemical reactions in nanometer-scale by the formation of metal patterns with the SPM.