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. As a consequence of this effect, care has to be taken when extracting chemical information from the XP spectra of ordered organic adsorbate layers. Our results, furthermore, imply that XPS is a powerful tool for probing local variations in the electrostatic energy in nanoscopic systems, especially in SAMs.

The presence of dipolar layers determines the functionality of most technologically relevant interfaces. The present contribution reviews how periodic dipole assemblies modify the properties of such interfaces through so‐called collective electrostatic effects. They impact the ionization energies and electron affinities of thin films, change the work function of metallic and semiconducting substrates, and determine the alignment of electronic states at interfaces. Dipolar layers originate either from the assembly of polar molecules or they arise from interfacial charge rearrangements triggered by the deposition of an adsorbate layer. Such charge rearrangements result from the omnipresent Pauli pushback caused by exchange interaction, from covalent bonds, or from charge transfer following the deposition of particularly electron rich (donors) or electron poor molecules (acceptors). A peculiarity of charge‐transfer interfaces is that they enter the realm of Fermi‐level pinning, where the sample work function becomes independent of the substrate and is solely determined by the electronic properties of the adsorbate. Beyond changing work functions and injection barriers, the presence of polar layers also modifies various other physical observables, like core‐level binding energies or tunneling currents in monolayer junctions. All these aspects suggest that polar layers can also be exploited for electrostatically designing the electronic properties of materials.

This work, first published in 1995, presents developments in understanding the subdominant exponential terms of asymptotic expansions which have previously been neglected. By considering special exponential series arising in number theory, the authors derive the generalised Euler-Jacobi series, expressed in terms of hypergeometric series. Dingle's theory of terminants is then employed to show how the divergences in both dominant and subdominant series of a complete asymptotic expansion can be tamed. Numerical results are used to illustrate that a complete asymptotic expansion can be made to agree with exact results for the generalised Euler-Jacobi series to any desired degree of accuracy. All researchers interested in the fascinating area of exponential asymptotics will find this a most valuable book.

Core-level energies are frequently calculated to explain the X-ray photoelectron spectra of metal-organic hybrid interfaces. The current paper describes how such simulations can be flawed when modeling interfaces between physisorbed organic molecules and metals. The problem occurs when applying periodic boundary conditions to correctly describe extended interfaces and simultaneously considering core hole excitations in the framework of a final-state approach to account for screening effects. Since the core hole is generated in every unit cell, an artificial dipole layer is formed. In this work, we study methane on an Al(100) surface as a deliberately chosen model system for hybrid interfaces to evaluate the impact of this computational artifact. We show that changing the supercell size leads to artificial shifts in the calculated core-level energies that can be well beyond 1 eV for small cells. The same applies to atoms at comparably large distances from the substrate, encountered, for example, in extended, upright-standing adsorbate molecules. We also argue that the calculated work function change due to a core-level excitation can serve as an indication for the occurrence of such an artifact and discuss possible remedies for the problem.

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