Reversible Nanopatterning on Self-Assembled Monolayers on Gold

The reversible fabrication of positive and negative nanopatterns on 1-hexadecanethiol (HDT) self-assembled monolayers (SAMs) on Au(111) was realized by bias-assisted atomic force microscopy (AFM) nanolithography using an ethanol-ink tip. The formation of positive and negative nanopatterns via the bias-assisted nanolithography depends solely on the polarity of the applied bias, and their writing speeds can reach 800 μm/s and go beyond 1000 μm/s, respectively. The composition of the positive nanopatterns is gold oxide and the nanometer-scale gold oxide can be reduced by ethanol to gold, as proved by X-ray photoelectron spectroscopy (XPS) analysis, forming the negative nanopatterns which can be refilled with HDT to recover the SAMs. The inked material of ethanol acts as a reductant which is transferred to the substrate for the local chemical reactions like that in dip-pen nanolithography (DPN). The negative nanopatterns can be used as templates, for example, for the immobilization of magnetic nanoparticles. Interestingly, we found that the nanometer-scale gold oxide was very stable on hydrophobic HDT/Au(111) in air, whereas on hydrophilic SAMs it decomposed soon and resulted in the formation of the negative nanopattern. In addition, the effect of bias on the nanolithography was investigated.