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Core hole screening effects at organic/metal interfaces were studied by core level X-ray photoemission spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), and valence band ultraviolet photoemission spectroscopy (UPS). The comparison of energetic shifts in XPS and XAES enables the estimation of electronic relaxation energy (screening ability). Magnesium phthalocyanine (MgPc) and zinc phthalocyanine (ZnPc) evaporated on single crystalline Au(100) were used as model molecules. Two different features in the Mg KLL spectra can be clearly separated for (sub-)monolayer coverages, while only minor changes of the shape of Mg 1s are observed. Applying a dielectric continuum model, the major screening mechanism cannot be described sufficiently by polarization screening due to mirror charges, significant contributions by charge transfer screening have to be considered. In contrast, small screening effects in the bulk material can be explained by surface polarization. [ABSTRACT FROM AUTHOR]

The electronic structure of the interface between cobalt phthalocyanine (CoPc) and epitaxially grown manganese oxide (MnO) thin films is studied by means of photoemission (PES) and X-ray absorption spectroscopy (XAS). Our results reveal a flat-lying adsorption geometry of the molecules on the oxide surface which allows a maximal interaction between the p-system and the substrate. A charge transfer from MnO, in particular, to the central metal atom of CoPc is observed by both PES and XAS. The change of the shape of N-K XAS spectra at the interface points, however, to the involvement of the Pc macrocycle in the charge transfer process. As a consequence of the charge transfer, energetic shifts of MnO related core levels were observed, which are discussed in terms of a Fermi level shift in the semiconducting MnO films due to interface charge redistribution. [ABSTRACT FROM AUTHOR]

The influence of graphene interlayers on electronic interface properties of cobalt phthalocyanine on Ni(111) is studied using both photoemission and X-ray absorption spectroscopy. A charge transfer associated with a redistribution of the d-electrons at the Co-atom of the phthalocyanine occurs at the interface to Ni(111). Even a graphene buffer layer cannot prevent the charge transfer at the interface to Ni(111); however, the detailed electronic situation is different. [ABSTRACT FROM AUTHOR]

The μ-(oxo)bis[phthalocyaninato] aluminum(III) (AlPc)2O films, with the crystallites oriented preferably in one direction, were obtained via chemical transformation of chloroaluminum(III) phthalocyanine AlClPc film upon its annealing in magnetic field. A comparative analysis of the influence of postdeposition annealing without and under applied magnetic field of 1 T on composition and morphology of AlClPc films has been carried out. The chemical transformation of AlClPc to (AlPc)2O on the substrate surface is studied by the methods of UV-vis and infrared spectroscopies, Raman, x-ray photoelectron spectroscopy as well as atomic force microscopy. Two interesting effects were observed upon heating the AlClPc films in magnetic field of 1 T. First, the temperature of the chemical transformation of AlClPc to (AlPc)2O decreased from 300 °C to 200 °C when magnetic field was applied during postdeposition annealing. Second, the formation of (AlPc)2O films with elongated crystallites with a preferential orientation was observed. The heating of (AlPc)2O films in a magnetic field at the same conditions did not demonstrate any effect on the structure and morphology of these films. [ABSTRACT FROM AUTHOR]

We compare the interface properties of various 1,4,8,11,15,18,22,25 octa-alkyl-substituted zinc phthalocyanines [(But)8PcZn, (Hep)8PcZn, (Dec)8PcZn] with those of unsubstituted zinc phthalocyanine (PcZn) on gold using x-ray photoemission spectroscopy and valence band ultraviolet photoemission spectroscopy. Although the separation between the aromatic cores in the evaporated thin films depends clearly on the alkyl-chain length, it is found that the nature of the substituents causes only minor changes of electronic properties, such as optical gap and ionization potential. It is shown that the observed small energetic shifts for film thicknesses larger than the molecule size cannot be understood in terms of a band bending like mechanism. [ABSTRACT FROM AUTHOR]

We have studied the molecular orientation of well-known representatives of organic semiconductors from the family of the phthalocyanines [copper phthalocyanine (CuPc) and its perfluorinated relative sCuPcF16)] on a conducting polymer thin film using polarization-dependent x-ray absorption spectroscopy. As a polymer substrate PEDOT:PSS [a mixture of poly-3,4-ethylenedioxy-thiophene (PEDOT) and polystyrenesulfonate (PSS), which is often applied as an electrode material in (all-)organic semiconductor devices] was spin coated onto indium-tin-oxide substrates. Even if the interfaces themselves are relatively ill defined (we found recently a mixing of the two organic materials and charge-transfer processes), a very high degree of molecular ordering is observed in the 20—50 nm thick phthalocyanine films. [ABSTRACT FROM AUTHOR]

We review the interaction mechanism of transition metal phthalocyanines (TMPcs, TM = Mn, Fe, Co) on different metal substrates (Au, Ag, Ni). The interface to Ni is further modified by the introduction of a graphene intermediate layer. Although TMPcs are representatives for flat, π-conjugated carbon systems, their electronic properties are determined to a large extent by the central metal atom. We focus on the role of the central metal atom in interfacial charge transfer processes. On single crystalline metal substrates the molecules grow highly ordered with flat lying adsorption geometry. We focus on studies using photoexcited electron spectroscopies: photoemission and X-ray absorption spectroscopy (XAS or NEXAFS). The highly ordered growth of TMPcs supports the assignment of polarization dependent XAS features. Depending on both the substrate and the TMPc, the strength of the interaction reaches from weak physisorption to strong chemical interactions. The introduction of graphene buffer layers seems to be a promising route for the tuning of interface properties. [ABSTRACT FROM AUTHOR]

The chemical transformation of the polar chloroaluminum phthalocyanine, AlClPc, to μ-(oxo)bis(phthalocyaninato)aluminum(III), (PcAl)O, in thin films on indium tin oxide is studied and its influence on the molecular orientation is discussed. The studies were conducted using complementary spectroscopic techniques: Raman spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. In addition, density functional theory calculations were performed in order to identify specific vibrations and to monitor the product formation. The thin films of AlClPc were annealed in controlled environmental conditions to obtain (PcAl)O. It is shown that the chemical transformation in the thin films can proceed only in the presence of water. The influence of the reaction and the annealing on the molecular orientation was studied with Raman spectroscopy and NEXAFS spectroscopy in total electron yield and partial electron yield modes. The comparison of the results obtained from these techniques allows the determination of the molecular orientation of the film as a function of the probing depth. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: The Ultraviolet and X-ray Photoemission Spectroscopy (UPS, XPS) investigation was done to examine the interface formation between deposited copper phthalocyanine (CuPc) thin films and covered with native oxide n- and p-type silicon Si(111) substrates. The UPS results indicated the existence of small interface dipole effect for very first layer of CuPc deposited on both types of substrates. The dipoles were oriented differently depending on silicon conductivity type. In this paper we present that near the inorganic/organic interface the phthalocyanine’s molecular orbital levels shift downwards 0.20±0.05eV in the case of n-Si substrate and upwards 0.25±0.05eV for p-Si indicating the different displacement of the negative charge within the interface region. This tendency was also confirmed by conducted XPS study of the core levels. It is highly probable that band bending-like shift is provoked by the continuous change of CuPc molecule orientation induced by interface polarization layer. [Copyright &y& Elsevier]

This work presents an investigation of films prepared by doctor blade casting, the formation of self-assembled microstructures of a liquid crystalline phthalocyanine with highly oriented molecules. Raman Spectroscopy in combination with atomic force microscopy is applied to study the structures within the films. By keeping the substrate at room temperature or at 353 K during coating, different geometric structures namely rods and islands form. Rod-like structures are growing in coating direction, whereas directional growth of the islands is not observed. The distribution of the rod lengths varies widely, whereas the width appears more uniform. Annealing of the samples shows a different behavior of the two textures. Islands tend to melt, and rods smooth their structural form, which is extracted from Raman imaging in combination with atomic force microscopy. Additionally, Raman imaging gives insight into laterally different relative crystallinity. These observations are discussed in the context of the molecular orientation as probed by polarized Raman spectroscopy. These polarized Raman spectra indicate azimuthal alignment of the molecules within the rods (edge on alignment). This alignment occurs along and also perpendicular to the growth direction. In contrast to the alignment in the rods, the molecules inside the islands occurring at higher temperature do not show preferential molecular orientation. After annealing, no preferential molecular orientation is observed in rods because of the loss of anisotropy, too. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we present photoemission studies of the influence of 12-hour exposure to the ambient air on the chemical and electronic properties of thin 16-nm copper phthalocyanine (CuPc) sensing layers deposited on n- and p-type silicon Si(111) substrates covered with the native oxide. The surface chemistry and electronic parameters of organic thin film including surface band bending, work function, electron affinity and their variations upon the exposure have been monitored with X-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy techniques. We found that after the exposure, the surface chemistry of CuPc remained unaffected, however the work function and surface band bending increased by 0.55eV and 0.45eV for the layers on n-Si and by 0.25eV and 0.30eV for those on p-Si. Additionally, we detected a slight surface dipole at CuPc on n-Si manifested by a small shift in electron affinity of 0.10eV. In order to explain these changes we developed a model basing on the interaction of ionic species with the phthalocyanine surface. [ABSTRACT FROM AUTHOR]

Abstract: Herein investigation of the effects of substrate temperature on the structural and morphological features of both cobalt(II) phthalocyanine (CoPc) and cobalt(II) hexadecafluorophthalocyanine (CoPcF16) thin films is presented. For these purposes thin films of CoPc and CoPcF16 prepared by organic molecular beam deposition were investigated by means of optical absorption spectroscopy, X-ray diffraction, Raman spectroscopy, and atomic force microscopy. Concerning the degree of crystallinity, the morphology, the phase composition and the preferential molecular orientation of both CoPc and CoPcF16 thin films, we found out that the increase of substrate temperature during growth influences these properties of the above-mentioned thin film systems (CoPc vs. CoPcF16) in a different way. [ABSTRACT FROM AUTHOR]

Abstract: We study the electronic structure of cobalt phthalocyanine (CoPc) thin films on Au(100) using resonant photoemission spectroscopy and X-ray absorption spectroscopy (XAS). From XAS we conclude that the molecules are highly ordered and oriented parallel to the substrate surface. Cobalt related valence band states are identified using resonant photoemission. A strong enhancement of particular features is observed at the resonance energies, depending on the angle of incidence. This behavior can be understood by participator decay processes, the (de-)localization of Co-related valence band states is discussed. [Copyright &y& Elsevier]

Abstract: In this paper native and RCA-treated n- and p-doped Si(111) substrates and ultra-thin 16-nm copper phthalocyanine (CuPc) layers deposited thereon were investigated using X-ray Photoemission Spectroscopy and Angle-Resolved X-ray Photoemission Spectroscopy. The oxide layer thickness was determined to be 1.3nm on the RCA-treated substrates and 0.8nm on the native ones. The analysis of substrate carbon contamination showed the existence of C–H, C–OH and COOH components on all substrates. The RCA clean removes more readily the carbon components with the OH group from the n-type Si and causes the segregation of the contaminants. The initial carbon species propagate in the evaporated CuPc layer up to a thickness of about 5nm affecting the shape of the C1s peak. Additionally, the behavior of the binding energy difference between N1s and Si2p peaks upon the CuPc growth shows that there may occur various CuPc molecule adsorption modes on investigated Si substrates. It could be a useful information, from the technological point of view, especially for low dimensional electronic device preparation. [Copyright &y& Elsevier]

Abstract: We compare the molecular orientation of differently alkyl-substituted metal phthalocyanines on polycrystalline gold and on single crystalline substrates (Au(100) and GeS(001)). In both cases we observe a high degree of molecular ordering for ultrathin films (1–3 monolayers), the molecules are oriented parallel to the substrate surface (lying). However, the molecular orientation can be different for 5–30nm thick films: we observe “standing” molecules on relatively ill defined polycrystalline substrate surfaces whereas almost disordered films were found on single crystalline surfaces. The growth mode is discussed in terms of different molecule–molecule and molecule–substrate interactions. [Copyright &y& Elsevier]

The molecular orientation of the first layers and thin films of differently substituted phthalocyanines on gold substrates is compared. Due to a relatively strong molecule-substrate interaction the orientation is parallel to the sample surface for all materials in the first layers. At higher film thickness the orientation is determined by the substituents. Materials with short substituents prefer standing orientation, implying the substituents do not inhibit the intermolecular interactions. Molecules with long substituents are not able to build up the same aggregates, they grow disordered in the upper layers. [ABSTRACT FROM AUTHOR]

Abstract: The molecular ordering and orientation of zinc phthalocyanine (ZnPc) on a ZnS film as well as the chemical properties of the interface were investigated by X-ray photoelectron and absorption spectroscopy with synchrotron radiation excitation. Core level photoelectron spectra of the substrate and the ZnPc film indicate a weak interaction at the interface. We observe a high molecular ordering, which is enhanced with increasing film thickness. A standing (or highly-tilted) molecular orientation in about 8nm-thick ZnPc films is deduced from the polarization dependence of the N K X-ray absorption spectra. The same result was obtained from excitation energy dependence of the intensity ratio of the two carbon species in C 1s core level spectra. The annealing of the sample up to about 400°C causes a desorption of ZnPc and a stronger interaction between remaining molecules and ZnS. [Copyright &y& Elsevier]

Abstract: We have studied the molecular orientation of different metal (Mg,Zn) phthalocyanines (Pcs) grown as ultra-thin films on a polycrystalline gold substrate. For 10–20 nm thick films of Pcs with small substituents, a high degree of molecular orientation was observed. Similar to unsubstituted PcCu, the orientation of the molecules is perpendicular to the sample surface. Importantly, however, the molecular orientation is different for low coverages, the molecules lie on the substrate surface. The growth mode is discussed in terms of different molecule–molecule and molecule–substrate interactions. [Copyright &y& Elsevier]

The initial growth and interfacial electronic structure of perfluorinated iron phthalocyanine (FePcF16) on Cu(111) has been studied using X‐ray photoelectron spectroscopy (XPS) and polarization dependent X‐ray absorption spectroscopy (XAS). The planar molecules are oriented preferred flat lying on the substrate surface during the growth of the first layers while the tilt angle is increased in thicker films. A clear interaction at the interface is observed, involving both the central metal ion and the macrocycle. At monolayer coverages, the Fe2p spectrum shows an interface signal at 707.1 eV, while the C‐N component of the C1s spectrum is distinctly shifted with respect to the thicker films. In addition, the nitrogen atom is involved in the complex interaction (including charge transfer), best visible in the change of the shape in the π* resonance of N K edge spectra recorded from molecules at the interface. The initial growth and interfacial electronic structure of perfluorinated iron phthalocyanine (FePcF16) on Cu(111) is studied using X‐ray photoelectron spectroscopy (XPS) and polarization dependent X‐ray absorption spectroscopy (XAS). The interaction at the interface involves both the macrocycle (carbon and nitrogen) and the central metal ion of FePcF16. At higher coverages most likely the spin multiplicity of the Fe ion changes. [ABSTRACT FROM AUTHOR]