Employing X-ray Photoelectron Spectroscopy for Determining Layer Homogeneity in Mixed Polar Self-Assembled Monolayers.

Self-assembled monolayers (SAMs) containing embedded dipolar groups offer the particular advantage of changing the electronic properties of a surface without affecting the SAM-ambient interface. Here we show that such systems can also be used for continuously tuning metal work functions by growing mixed monolayers consisting of molecules with different orientations of the embedded dipolar groups. To avoid injection hot-spots when using the SAM-modified electrodes in devices, a homogeneous mixing of the two components is crucial.

Understanding Chemical versus Electrostatic Shifts in X-ray Photoelectron Spectra of Organic Self-Assembled Monolayers.

The focus of the present article is on understanding the insight that X-ray photoelectron spectroscopy (XPS) measurements can provide when studying self-assembled monolayers. Comparing density functional theory calculations to experimental data on deliberately chosen model systems, we show that both the chemical environment and electrostatic effects arising from a superposition of molecular dipoles influence the measured core-level binding energies to a significant degree. The crucial role of the often overlooked electrostatic effects in polar self-assembled monolayers (SAMs) is unambiguously demonstrated by changing the dipole density through varying the SAM coverage.