Micropatterning of self-assembled monolayers using vacuum ultraviolet light
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A micropatterning technique was applied to an n-octadecyltrimethoxysilane self-assembled monolayer (ODS-SAM) formed on Si substrates covered with a 2 nm thick layer oxide using excimer lamps to radiate vacuum ultraviolet (VUV) light at 172 nm in wavelength. The results of Kelvin-probe force microscopy (KFM) and lateral force microscopy (LFM) analyses showed that the second monolayer was stacked to the VUV-modified area of the ODS-SAM. Oxides, i.e., –COOH groups, were formed before the ODS-SAM completely decomposed and was removed from the substrate. Coplanar binary alkylsilane SAM microstructures were successfully fabricated by adopting the response between –OCH3 functional groups with –COOH groups on the ODS-SAM modified using VUV light. Furthermore, as shown in the KFM image, the region covered with the FAS had a surface potential ~60 mV lower than that of the region covered with ODS. The origin of the image contrasts between the ODS- and FAS-SAMs was the significant difference in the electronic states between the ODS and FAS owing to the electron negativity of fluorine atoms. The difference in the surface chemical composition of the SAMs could be clearly and sensitively measured through KFM based on the difference in the surface potential between the ODS and FAS.
Abstract
A micropatterning technique was applied to an n-octadecyltrimethoxysilane self-assembled monolayer (ODS-SAM) formed on Si substrates covered with a 2 nm thick layer oxide using excimer lamps to radiate vacuum ultraviolet (VUV) light at 172 nm in wavelength. The results of Kelvin-probe force microscopy (KFM) and lateral force microscopy (LFM) analyses showed that the second monolayer was stacked to the VUV-modified area of the ODS-SAM. Oxides, i.e., –COOH groups, were formed before the ODS-SAM completely decomposed and was removed from the substrate. Coplanar binary alkylsilane SAM microstructures were successfully fabricated by adopting the response between –OCH3 functional groups with –COOH groups on the ODS-SAM modified using VUV light. Furthermore, as shown in the KFM image, the region covered with the FAS had a surface potential ~60 mV lower than that of the region covered with ODS. The origin of the image contrasts between the ODS- and FAS-SAMs was the significant difference in the electronic states between the ODS and FAS owing to the electron negativity of fluorine atoms. The difference in the surface chemical composition of the SAMs could be clearly and sensitively measured through KFM based on the difference in the surface potential between the ODS and FAS.
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