Practical photoemission characterization of molecular films and related interfaces

TL;DR

This paper reviews photoemission techniques for characterizing the electronic properties of molecular films and interfaces in organic electronics, emphasizing growth, orientation, and energy level alignment insights.

Contribution

It highlights the importance of photoemission in analyzing molecular film properties, considering molecular orientation and interface effects, which are often overlooked in the field.

Findings

Photoemission effectively probes electronic and chemical structures.

Molecular orientation significantly influences electronic parameters.

Interfacial energy level alignment mechanisms are discussed.

Abstract

Even though the term `organic electronics' evokes rather organic devices, a significant part of its scope deals with physical properties of `active elements' such as organic films and interfaces. Examination of the film growth and the evolution of the interface formation are particularly needful for the understanding a mechanism controlling their final properties. Performing such experiments in an ultra-high vacuum allows both to `stretch' the time scale for pseudo real-time observations and to control properties of the probed systems on the atomic level. Photoemission technique probes directly electronic and chemical structure and it has thereby established among major tools employed in the field. This review primarily focuses to electronic properties of oligomeric molecular films and their interfaces examined by photoemission. Yet, it does not aspire after a complete overview on the topic; it rather aims to otherwise standard issues encountered at the photoemission characterization and analysis of the organic materials, though requiring to consider particularities of molecular films in terms of the growth, electronic properties, and their characterization and analysis. In particular, the fundamental electronic parameters of molecular films such as the work function, the ionization energy, and the interfacial energy level alignment, and their interplay, will be pursued with considering often neglected influence of the molecular orientation. Further, the implication on the band bending in molecular films based on photoemission characterization, and a model on the driving mechanism for the interfacial energy level alignment will be addressed.