Probing dynamic covalent chemistry in a 2D boroxine framework by in situ near-ambient pressure X-ray photoelectron spectroscopy

peer reviewedDynamic covalent chemistry is a powerful approach to design covalent organic frameworks, where high crystallinity is achieved through reversible bond formation. Here, we exploit near-ambient pressure X-ray photoelectron spectroscopy to elucidate the reversible formation of a two-dimensional boroxine framework. By in situ mapping the pressure–temperature parameter space, we identify the regions where the rates of the condensation and hydrolysis reactions become dominant, being the key to enable the thermodynamically controlled growth of crystalline frameworks

The new FAST module: A portable and transparent add-on module for time-resolved investigations with commercial scanning probe microscopes

peer reviewedTime resolution is one of the most severe limitations of scanning probe microscopies (SPMs), since the typical image acquisition times are in the order of several seconds or even few minutes. As a consequence, the characterization of dynamical processes occurring at surfaces (e.g. surface diffusion, film growth, self-assembly and chemical reactions) cannot be thoroughly addressed by conventional SPMs. To overcome this limitation, several years ago we developed a first prototype of the FAST module, an add-on instrument capable of driving a commercial scanning tunneling microscope (STM) at and beyond video rate frequencies. Here we report on a fully redesigned version of the FAST module, featuring improved performance and user experience, which can be used both with STMs and atomic force microscopes (AFMs), and offers additional capabilities such as an atom tracking mode. All the new features of the FAST module, including portability between different commercial instruments, are described in detail and practically demonstrated

Anchoring and bending of pentacene on aluminum (001)

We study the structural, electronic, and spectroscopic properties of pentacene adsorbed on Al(001) surface, combining density functional theory (DFT) methods including van der Waals interactions with X-ray photoemission (XPS), near-edge X-ray absorption fine structure (NEXAFS), and scanning tunneling microscopy (STM). We find a major change of the molecular backbone resulting in a peculiar V-shape bending, due to the direct anchoring of the two central carbons atop two Al atoms underneath. In the most stable adsorption configuration, pentacene is oriented with the long axis parallel to the substrate [110] direction, where such anchoring is favored by optimally matched interatomic distances. Remarkably, due to the generally low degree of order, we measure by STM a significant portion of molecules oriented along the [100] direction, which also display the same V-shape conformation, as driven by the bond of the central carbon atoms of pentacene to a pair of slightly displaced Al atoms

Anchoring and Bending of Pentacene on Aluminum

The adsorption of the first layer of organic molecules at the metal 12organic interface in electronic devices is critical as it influences the carrier injection across the interface and also forms the foundation for the growth of the subsequent layers, which in turn affects the overall performance of these devices. Pentacene (C22H14) has shown temperature-independent highest hole and electron mobility among the various organic small molecules. Aluminum is also a metal of potential interest for Si-free electronic devices. Pentacene coupled to aluminum could be used to fabricate devices like Schottky diodes and organic thin film transistors, and the interaction between pentacene and aluminum is also important in organic solar cells and memory devices. In our study of pentacene/Al(001), we combined ab initio simulations, based on density functional theory (DFT) corrected for the van der Waals interaction, with techniques to determine the structure of the system, such as reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) and core-level spectroscopies, namely X-ray photoemission spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) [1]. We find a major change of the molecular backbone resulting into a peculiar V-shape bending, due to the direct anchoring of the two central carbons atop two Al atoms underneath. In the most stable adsorption configuration, pentacene is oriented with the long axis parallel to the substrate [110] direction, where such anchoring is favored by optimally matched interatomic distances. Remarkably, due to the generally low degree of order, we measure by STM a significant portion of molecules oriented along the [100] direction, which also display the same V-shape conformation, as driven by the bond of the central carbon atoms of pentacene to a pair of slightly displaced Al atoms. Even in absence of long-range order, the substrate thus favors a specific structural and electronic molecular conformation, which can be representative of a real interface layer of pentacene at an Al electrode. [1] J. Phys. Chem. C, 2015, 119 (7), pp 3624\u2013363