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Lead halide perovskitesolar cells have reached power conversionefficiencies during the past few years that rival those of crystallinesilicon solar cells, and there is a concentrated effort to commercializethem. The use of gold electrodes, the current standard, is prohibitivelycostly for commercial application. Copper is a promising low-costelectrode material that has shown good stability in perovskite solarcells with selective contacts. Furthermore, it has the potential tobe self-passivating through the formation of CuI, a copper salt whichis also used as a hole selective material. Based on these opportunities,we investigated the interface reactions between lead halide perovskitesand copper in this work. Specifically, copper was deposited on theperovskite surface, and the reactions were followed in detail usingsynchrotron-based and in-house photoelectron spectroscopy. The resultsshow a rich interfacial chemistry with reactions starting upon depositionand, with the exposure to oxygen and moisture, progress over manyweeks, resulting in significant degradation of both the copper andthe perovskite. The degradation results not only in the formationof CuI, as expected, but also in the formation of two previously unreporteddegradation products. The hope is that a deeper understanding of theseprocesses will aid in the design of corrosion-resistant copper-basedelectrodes.

The oxygen on Ag(111) system has been investigated with Auger electron–photoelectron coincidence spectroscopy (APECS). The coincidence spectra between O 1s core level photoelectrons and O KLL Auger electrons have been studied together with Ag3d/AgM4,5NN coincidences. We also describe the electron–electron coincidence spectrometer setup, CoESCA, consisting of two angle resolved time-of-flight spectrometers at a synchrotron light source. Contributions from molecular oxygen and chemisorbed oxygen are assigned using the coincidence data, conclusions are drawn primarily from the O 1s/O KLL data. The data acquisition and treatment procedure are also outlined. The chemisorbed oxygen species observed are relevant for the catalytic ethylene oxidation.

Auger-photoelectron coincidence spectroscopy (APECS) has been used to examine the electron correlation and itinerance effects in transition metals Cu, Ni and Co. It is shown that the LVV Auger, in coincidence with 2p photoelectrons, spectra can be represented using atomic multiplet positions if the 3d-shell is localized (atomic-like) and with a self-convoluted valence band for band-like (itinerant) materials as explained using the Cini-Sawatzky model. For transition metals, the 3d band changes from band-like to localized with increasing atomic number, with the possibility of a mixed behavior. Our result shows that the LVV spectra of Cu can be represented by atomic multiplet calculations, those of Co resemble the self-convolution of the valence band and those of Ni are a mixture of both, consistent with the Cini-Sawatzky model.

In this work, we present the CoESCA station for electron-electron coincidence spectroscopy from surfaces, built in a close collaboration between Uppsala University and Helmholtz-Zentrum Berlin at the BESSY II synchrotron facility in Berlin, Germany. We start with a detailed overview of previous work in the field of electron-electron coincidences, before we describe the CoESCA setup and its design parameters. The system is capable of recording shot-to-shot resolved 6D coincidence datasets, i.e. the kinetic energy and the two take off angles for both coincident electrons. The mathematics behind extracting and analysing these multi-dimensional coincidence datasets is introduced, with a focus on coincidence statistics, resulting in fundamental limits of the signal-to-noise ratio and its implications for acquisition times and the size of the raw data stream. The functionality of the CoESCA station is demonstrated for the example of Auger electron-photoelectron coincidences from silver surfaces for photoelectrons from the Ag 3d core levels and their corresponding MNN Auger electrons. The Auger spectra originating from the different core levels, 3d3/2 and 3d5/2 could be separated and further, the two-hole state energy distributions were determined for these Auger decay channels.

Unveiling the interplay of semiconducting organic molecules with their environment, such as inorganic materials or atmospheric gas, is the first step to designing hybrid devices with tailored optical, electronic or magnetic properties. The present article focuses on a double-decker lutetium phthalocyanine known as an intrinsic semiconducting molecule, holding a Lu ion in its center, sandwiched between two phthalocyanine rings. Carrying out experimental investigations by means of electron spectroscopies, X-ray diffraction and scanning probe microscopies together with advanced ab initio computations, allows us to unveil how this molecule interacts with weakly or highly reactive surfaces. Our studies reveal that a molecule-surface interaction is evidenced when molecules arc deposited on bare silicon or on gold surfaces together with a charge transferred from the substrate to the molecule, affecting to a higher extent the lower ring of the molecule. A new packing of the molecules on gold surfaces is proposed: an eclipse configuration in which molecules are flat and parallel to the surface, even for thick films of several hundreds of nanometers. Surprisingly, a robust tolerance of the double-decker phthalocyanine toward oxygen molecules is demonstrated, leading to weak chemisorption of oxygen below 100 K.

Unveiling the self-organization mechanism of semiconducting organic molecules onto metallic surfaces is the first step to design hybrid devices in which the self-assembling is exploited to tailor magnetic properties. In this study, double-decker rare-earth phthalocyanines, namely, lutetium phthalocyanine (LuPc2), are deposited on Au(111) gold surface forming large-scale self-assemblies. Global and local experimental techniques, namely, grazing incidence X-ray diffraction and scanning tunneling microscopy, supplemented by density functional theory calculations with van der Waals corrections, give insight into the molecular structural arrangement of the thin film and the self organization at the surface. Our results show unambiguously that the two plateaus of the double-decker phthalocyanine present a different rotation than the isolated molecule. This is evidenced by density functional theory simulations of optimized LuPc2 monolayer showing a perfect agreement with experimental findings. Moreover, the stabilized structure of double layers reveals an eclipsed configuration of the molecules in the stacking, having the ligand plateaus parallel to the gold surface. The high crystallinity of the molecular assembly and its weak electronic coupling with the metallic substrate is expected to open new perspective in magnetic devices.

A combined X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT) study has been performed to characterize the adsorbate interaction of lutetium biphthalocyanine (LuPc2) molecules on the Si(100)-2 × 1 surface. Large molecule–substrate adsorption energies are computed and are found to compete with the molecule–molecule interactions of the double decker molecules. A particularly good matching between STM images and computed ones confirms the deformation of the molecule upon the absorption process. The comparison between DFT calculations and XP spectra reveals that the electronic distribution in the two plateaus of the biphthalocyanine are not affected in the same manner upon the adsorption onto the silicon surface. This finding can be of particular importance in the implementation of organic molecules in hybrid devices.

The present work reports a photoelectron spectroscopy study of the low-energy region of the valence band of metal-free phthalocyanine (H2Pc) compared with those of iron phthalocyanine (FePc) and manganese phthalocyanine (MnPc). We have analysed in detail the atomic orbital composition of the valence band both experimentally, by making use of the variation in photoionization cross-sections with photon energy, and theoretically, by means of density functional theory. The atomic character of the Highest Occupied Molecular Orbital (HOMO), reflected on the outermost valence band binding energy region, is different for MnPc as compared to the other two molecules. The peaks related to the C 2p contributions, result in the HOMO for H2Pc and FePc and in the HOMO-1 for MnPc as described by the theoretical predictions, in very good agreement with the experimental results. The DFT simulations, discerning the atomic contribution to the density of states, indicate how the central metal atom interacts with the C and N atoms of the molecule, giving rise to different partial and total density of states for these three Pc molecules.

Despite the numerous studies dedicated to phthalocyanine molecules adsorbed on surfaces, in monolayer or thin film, very few works have been focused on the characterization of vapors of these molecules. In this article we present the C 1s, N 1s and Fe 2p photoemission results as well as N K-edge X-ray absorption data of iron phthalocyanine (FePc) in gas phase. Presented comparison of X-ray photoelectron spectroscopy and X-ray absorption spectroscopy spectra of FePc films show a great similarity with the gas phase results, confirming the molecular character of thick films. The Fe2p photoemission spectrum of the gas phase FePc, shown for the first time, can be considered as a fingerprint of the Fe(II) ionic state of the central metal of the iron phthalocyanine. The performed multiplet calculations for describing the Fe 2p XP spectrum indicate 3Eg (a1g2eg32g1) state as the most probable ground state for thick film of iron phthalocyanine.

The adsorption of monolayers and multilayers of metal-free phthalocyanine molecules on the Au(111) (root 3 x 22) reconstructed surface has been investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). Our results for the monolayer show that the molecules are arranged tightly onto the surface with their molecular plane parallel to it. In addition, the X-ray absorption spectra of the monolayer have been modeled by density functional theory, which could enlighten new aspect of the interaction between molecules and substrate. The XAS results evidence that also in the multilayer the molecules keep the orientation with the molecular plane parallel to the surface. These results are discussed in the framework of moleculemolecule/moleculeadsorbate interactions.

Using Near Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy, the thickness dependent formation of Lutetium Phthalocyanine (LuPc2) films on a stepped passivated Si(100)2x1 reconstructed surface was studied. Density functional theory (DFT) calculations were employed to gain detailed insights into the electronic structure. Photoelectron spectroscopy measurements have not revealed any noticeable interaction of LuPc2 with the H-passivated Si surface. The presented study can be considered to give a comprehensive description of the LuPc2 molecular electronic structure. The DFT calculations reveal the interaction of the two molecular rings with each other and with the metallic center forming new kinds of orbitals in between the phthalocyanine rings, which allows to better understand the experimentally obtained NEXAFS results.

We report an investigation of the initial growth and of the self-organization of lutetium biphthalocyanine LuPc2 on Si(001)-2 x 1 vicinal surfaces. Using surface-sensitive optical spectroscopies, namely, surface-difference-reflectance spectroscopy (SDRS) and reflectance-anisotropy spectroscopy (RAS), together with local-probe microscopies, we are able to propose a scenario for the growth mode up to about 20 nm. We demonstrate that the growth mode initially proceeds through the formation of a wetting layer, followed by the formation of clusters whose sizes increase while keeping a constant shape in which the molecules are inclined. Moreover, the LuPc2 molecules are self-organized along the step edges, and we are able to estimate that about 30% to 100% of the molecules are aligned when considering that the molecules are tilted by 45 degrees to 63 degrees with respect to the surface normal.

A combined photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) study has been performed to follow the change in adsorption geometry and to characterize the adsorbate interaction with the substrate for dierent thicknesses of lutetium biphthalocyanine (LuPc2) adlayers on pristine Si(100)-2x1 reconstructed stepped surface. A shift to lower binding energies with increasing thickness has been shown. The STM results showed clustering of LuPc2 starting from submonolayer coverages and two distinct adsorption types have been identied. The STM and PES results have been linked together to propose two dierent adsorption types involving a stronger and weaker interaction with the Si dangling bonds. A change in average angle of molecules with respect to the normal of the surface for increasing thicknesses has been seen from the XAS measurements, leading to disordered layers for thicker films.