Observation of self-assembled monolayer using the lateral resonance of the cantilever in the contact and noncontact regions

A new imaging method utilizing the lateral resonance vibration of a cantilever in atomic force microscopy was applied to evaluate microcontact printed patterns of self-assembled monolayers. The lateral resonance vibration of a cantilever was excited by the feedback of the torsional signal detected optically to a shear piezo set at the base of the cantilever. The amplitude and frequency shift of the vibration were mapped as images in air and in vacuum. The phase-separated patterns of octadecanethiol and 16-mercaptohexadecanoic acid on gold substrates were observed in air using a contact-mode cantilever and -CH ₃-terminated cantilever, respectively. In most cases, amplitude mapping showed a similar contrast to friction force microscopy but with a better lateral resolution and contrast. In the case where the vibration amplitude was smaller than 3 nm, adhesive force was dominant on the image contrast. The observation using a noncontact-mode cantilever in vacuum gave a good contrast, where the tip-sample distance was controlled by maintaining a set lateral amplitude.