Alkanethiolate self-assembled monolayers (SAMs) have been formed on zinc selenide through adsorption from solution. Zinc selenide as a SAM-supporting substrate is of particular interest due to its transparency in the infrared region of the electromagnetic spectrum, enabling interfacial interactions at the substrate surface to be studied through transmission IR spectroscopy. In the past, mechanically polished, optical quality ZnSe surfaces have been used to support SAM formation. This surface, however, typically has an rms roughness around 40 nm, meaning it cannot support highly-ordered SAMs. In order to characterize the system, a more ordered system is required. A significantly smoother ZnSe surface has be produced through physical vapor deposition (PVD) onto silicon substrates. The PVD-generated zinc selenide exhibits the same IR transparency as the mechanically polished substrate, but with an rms roughness in the range of 2.7 ± 0.9 nm, which is over an order of magnitude improvement in surface roughness. The ZnSe-SAM system was further characterized through Fourier Transform Infrared (FTIR) spectroscopy, contact angle goniometry, atomic force microscopy (AFM), and angle resolved x-ray photoelectron spectroscopy (AR-XPS). In the XPS spectrum, the shifts and relative intensities of Zn2p, Se3d, S2p, and C1s peaks when SAMs are applied show whether the SAM is physiosorbed or chemisorbed. The thickness of the SAM and the tilt angle of the molecules could be estimated by the relative intensities of the C1s peak to the Se 3d and Zn 2p intensities, as a function of emission angle. The XPS analysis was done with a Mg Kα x-ray source, in order to avoid overlap of the C1s peak and the Se LMM auger peaks.<br/>

XPS characterization of alkanethiolate self-assembled monolayers in zinc selenide thin films

2019 Spring National Meeting

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