Analysis of Unbound Molecules Contained in Self-assembled Monolayer Membrane Formed by Amino-alkanethiol Molecules

Self-assembled monolayer membranes formed by amino-alkanethiol molecules have been widely used for modifying Au surfaces because the amino groups are useful for the immobilization of nanomaterials. However, the polarity of the amino group induces irregularity in the membrane; therefore, the structure needed to be analyzed. We analyzed the molecules contained in the membrane formed by amino-alkanethiols on the Au surface using X-ray photoelectron spectroscopy. The molecules that did not combine with the Au surface on the membrane consisted of unbound amino-alkanethiol molecules and the molecules containing sulfur oxide. The ratio depends on the length of the alkyl chain of the amino-alkanethiol molecule. Molecules containing oxidized sulfur were removed by rinsing with a buffer solution (pH 9.1) and ultra-pure water.