UV photopatterning, electron beam lithography and site-specific surface reactions of alkanethiolate self-assembled monolayers adsorbed on gold and gallium arsenide (001)

The reaction pathways involved in the UV photopatteming and electron beam lithography of functionalized alkanethiolate self-assembled monolayers (SAMs) adsorbed on Au and GaAs (001) surfaces have been investigated using time-of-flight secondary ion mass spectrometry (TOF SIMS). It is observed that the resolution of UV photopatterned alkanethiolate SAMs adsorbed on Au is dependent on the light source used, patterning time, terminal groups and the methylene chain lengths. The UV photopatterning of alkanethiolate SAMs adsorbed on GaAs (001) has been demonstrated. Upon UV exposure both the SAM and the substrate photooxidize. The kinetic analyses suggest that the photooxidation of SAMs adsorbed on GaAs (001) depends on the length of the SAM molecules, which is most likely due to the different SAM structure as the number of carbons in the methylene chain increases. The degradation of SAMs using electron beam irradiation involves the formation of C=C double bonds and polycyclic aromatic hydrocarbons as well as C--S bond scission. The rates of photooxidation and electron beam degradation of SAMs adsorbed on GaAs (001) are observed to be higher than those of SAMs on Au, which can be related to differences in the monolayer structure on these surfaces. It is demonstrated that for SAMs adsorbed on GaAs (001) UV photopatterning and electron beam lithography can be performed to produce well-defined multifunctional patterned surfaces without the complete damage of the SAM allowing greatly reduced UV irradiation times and electron doses to be used. Patterned SAM surfaces produced using UV photopatterning were then used to demonstrate the formation of 3D structures using layer-by-layer assembly and site-specific organic surface reactions.