Though alkanethiolate self-assembled monolayers (SAMs) have successfully been synthesized and characterized on the surface of zinc selenide (ZnSe) substrates, the relative roughness of these bulk samples makes forming a technologically-relevant monolayer difficult due to the varying uniformity in the monolayer. In order to address this synthetic challenge, a smoother zinc selenide surface, produced by physical vapor deposition (PVD) onto silicon wafers, has been used as a substrate for SAMs. Zinc selenide is a substrate of interest due to its infrared transparency, which allows SAMs to be characterized using Fourier Transform Infrared Spectroscopy (FTIR). Silicon does not change the overall infrared transparency, but the Si-ZnSe-SAM system results in significant thin film interference, which makes accurate quantitative analysis of the SAM thickness difficult. In this work, we explore the possibility of using atomic force microscopy (AFM) to detect the presence of SAMs on ZnSe substrates. In particular, we have analyzed how the phase shift of the AFM cantilever, when operating in the tapping mode, varies depending on the AFM feedback parameters and whether SAMs are present or not. We demonstrate that under certain conditions, there is a significant difference in the phase shift between the bare ZnSe substrate and a SAM-covered surface, which provides for an alternative way of detecting SAMs.

AFM characterization of alkanethiolate self-assembled monolayers on zinc selenide thin films

2019 Spring National Meeting

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