RESUMEN
An electrochemical microcantilever (EMC) was used to study the intermolecular interaction of self-assembly monolayers (SAMs) with different n-alkanethiols chain lengths (n = 0, 4, 6, 8, 12, 16) on a Au-coated microcantilever surface. Comparing potential cycling and steps in NaClO(4) solution within the same potential range, the deflection rate of bare microcantilevers is much smaller for the former which revealed that potential excitation, i.e. the surface charge, played the dominant role in driving the instant and large deflection of the bare microcantilever, while the smaller deflection amplitude of the former implied that adsorption of ClO(4)( - ) had an adverse effect on the potential-induced stress. Upon adsorption of SAMs, the deflection amplitude of the microcantilever under the potential step was much smaller than that of a bare microcantilever, and linearly decreased with the chain length increasing for n ≤ 8 (the linear correlation coefficient and the slope are 0.98 and about - 10.4 nm per CH(2) unit, respectively), following a transition (8 ≤ n ≤ 12) to a stable state (n ≥ 12). The decrease of deflection amplitude and faster decay of deflection rate of the SAMs modified microcantilever under the potential step implyed increasing compactness of the SAMs with longer chains.
RESUMEN
The replacement of coronene monolayer on Au (111) by 6-mercapto-1-hexanol (MHO) was studied by in situ scanning tunneling microscopy (STM) in solutions. It was found that the rate of replacement depends strongly on the concentration of MHO. The replacement finished within a second at a higher concentration of MHO. At a lower concentration, the slow replacement could be followed by in situ STM. The replacement occurred initially near the elbow position of reconstructed Au (111) with the formation of pits in a single or several missing molecules. With the proceeding of replacement, these small pits expanded, and the surrounding coronene molecules were gradually substituted by MHO, which developed into ordered domains within a spatial confined environment. Meanwhile, the reconstruction of Au (111) was lifted. The replacement expanded fast along the reconstruction lines in the domain. For the fast replacement, a ( radical3 x radical3) R30 degrees adlattice was observed, while a c(4 x 2) superlattice was observed for the slow replacement. The close-packed phase of MHO self-assembled monolayers (SAMs) appeared directly instead of a flat-lying phase, which implied that the coronene molecules resist the direct contact of hydrocarbon chain of MHO with Au (111) surface. The replacing rate of the overall process exhibited a signoidal shape with time.
RESUMEN
The adsorption of dopamine (DA) molecules on gold and their interactions with Fe3+ were studied by a microcantilever in a flow cell. The microcantilever bent toward the Au side with the adsorption of DA due to the change of surface stress induced by the intermolecular hydrogen bonds of DA or the charge transfer effect between adsorbates and the substrate. The interaction process between DA adsorbates and Fe3+ was revealed by the deflection curves of microcantilever. As indicated by the appearance of a variation during the decline of curves, two steps were observed in the curve at relative high concentrations of Fe3+. In this case, Fe3+ reacted with DA molecules only in the outer layers and the complexes removed with solution. Then Fe3+ reacted further with DA molecules forming the surface complex in the first layer next to the gold. At this stage, the stability of surface complexes was time dependent, i.e., unstable initially and stable finally. This may be due to the surface complexes change from mono-dentate to bi-dentate complexes. In another case, i.e., at relative low concentration of Fe3+, only the first step was observed as indicated by the absence of a variation. X-ray photoelectron spectroscopy (XPS) and cycling voltammetry (CV) results provided complementary evidence for the result of microcantilever and proposal. As low as 5 x 10(-10) M Fe3+ was detected by DA modified microcantilever with a good selectivity over other common metal ions.