Imaging of patterned self-assembled monolayers by scanning photoelectron microscopy

We have applied soft X-ray scanning photoelectron microscopy (SPEM) to image and characterize molecular patterns produced by electron irradiation of various aliphatic and aromatic thiol-derived self-assembled monolayers (SAMs) through masks. The fabricated patterns can be clearly distinguished and the inverse contrasts for the Au 4f and C 1s images suggest that the goal of chemical imaging has been achieved. The thickness of the films in the irradiated areas appeared to be higher than that in the non-irradiated ones. This can be explained by the adsorption of airborne carbon-containing molecules on the irradiated areas. In addition, the N 1s images were acquired from the structured films of NO 2 (C 6 H 4 ) 2 SH on gold to monitor the electron irradiation-induced transformation of the nitro tail groups into amino moieties. However, no chemical contrast related to the nitro-amino transformation was observed. This can be explained by the small intensity of the nitrogen photoelectron emission with respect to the inelastic background originated from the substrate and by the X-ray induced modification of the lithographic pattern during the image acquisition. The modification of aromatic SAMs caused by the zone-plate-focused X-ray beam has been utilized for direct lithographic writing by the microprobe.