Electrochemical soft lithography of an 1,7-octadiene monolayer covalently linked to hydrogen-terminated silicon using scanning probe microscopy

Electrochemical scanning probe lithography (SPL) was carried out on a 1,7-octadiene (OD) monolayer directly attached to silicon. The chemical conversion of the OD-monolayer was investigated by Kelvin probe force microscopy (KPFM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and by an adsorption test of amino-modified fluorescent spheres. AFM and KPFM results indicated that the electrochemical reactions induced by SPL were governed by the bias voltage applied between the tip of the scanning probe microscope (SPM) and the substrate. XPS spectra indicated that the vinyl groups on the OD monolayer were oxidized and chemically converted into carboxyl groups at bias voltages of 1-2 V. At bias voltages of more than 3 V, OD molecules on the sample surface were decomposed and silicon oxide was formed on the surface. In addition, the formation of COOH groups was confirmed by the site-selective adsorption of amino-modified fluorescent spheres. However, XPS spectra for sample surfaces scanned at negative bias voltages showed no change since the peak was generally weak. However, KFM and AFM results indicated that at bias voltages of more than -1.5 V, cyclobutane rings formed.