Localised Electrochemical Desorption of Gold Alkanethiolate Monolayers by Means of Scanning Electrochemical Microscopy (SECM)

Abstract.

 Lateral structures of bare gold within self-assembled monolayers (SAMs) of gold alkanethiolates were created by electrochemical desorption in the direct mode of the scanning electrochemical microscope (SECM). The ultramicroelectrode (UME) of the SECM was positioned 10–20 μm above the surface and used as the auxiliary electrode in a three electrode cell with the SAM-coated Au electrode as working electrode. The microscopic auxiliary electrode causes an inhomogeneous electric field above the macroscopic gold electrode and limits the total current. As a consequence only thiols located directly beneath the UME are affected by the desorption procedure. Sample regions from which the SAM had been removed were imaged in the SECM feedback mode or, after galvanic Cu deposition, by scanning electron microscopy (SEM) and optical microscopy (after sulfidisation of Cu). The influence of hydrocarbon chain length, protection of the SAM by an additional layer of n-octanol and the use of alternating current were investigated in order to decrease the size of the bare surface areas and to enhance their edge definition. In particular the use of alternating current led to feature sizes of 1.2 times the UME diameter which represents an advance with regard to 2–3 UME diameters reported earlier.