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Chemical Reaction of Polar Phthalocyanines on Silver: Chloroaluminum Phthalocyanine and Fluoroaluminum Phthalocyanine Małgorzata Polek,† Florian Latteyer,† Tamara V. Basova,§,∥ Fotini Petraki,† Umut Aygül,† Johannes Uihlein,† Peter Nagel,⊥ Michael Merz,⊥ Stefan Schuppler,⊥ Thomas Chassé,†,‡ and Heiko Peisert*,† †

Institute of Physical and Theoretical Chemistry and ‡Center for Light-Matter Interaction, Sensors & Analytics (LISA+), University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany § Nikolaev Institute of Inorganic Chemistry SB RAS, 3 Lavrentiev Avenue, 630090 Novosibirsk, Russia ∥ Novosibirsk State University, Pirogova Street 2, 630090 Novosibirsk, Russia ⊥ Karlsruher Institut für Technologie, Institut für Festkörperphysik, 76021 Karlsruhe, Germany S Supporting Information *

ABSTRACT: Interface properties of chloroaluminum(III) phthalocyanine (AlClPc) and fluoroaluminum(III) phthalocyanine (AlFPc) on different silver surfaces have been studied using X-ray and ultraviolet photoemission spectroscopy (XPS and UPS) and X-ray absorption spectroscopy (XAS). Both polycrystalline silver foil and silver single crystals were used as a substrate. In all cases a chemical reaction was detected by XPS, visible as additional species in chlorine or fluorine core level spectra. However, UPS spectra show additional intensity in vicinity of the Fermi edge only for monolayer coverages of AlClPc and AlFPc on silver foil. Possible scenarios for the different interaction on polycrystalline and single-crystalline silver surfaces are discussed. The roughness of the substrate may influence the strength of the interaction significantly.

1. INTRODUCTION Highly delocalized π-conjugated organic systems such as metal phthalocyanines (MPcs) represent one of the most promising candidates for various applications. Among other novel properties, MPcs show a high stability under diverse environmental conditions and excellent film-forming properties. In addition, porphyrins and phthalocyanines exhibit a very complex surface chemistry,1 which could further boost future applications. An engineering of atomic and molecular nanostructures at surfaces by autonomous ordering and assembly of atoms and molecules, as already described in 2005,2 becomes more and more real. The most common representatives of MPcs are planar molecules with D4h symmetry, but nonplanar complexes with a perpendicular component of the permanent electric dipole moment are also known. Such axially substituted, polar MPcs may open further fields of applications; one example is the tuning of the interface energetics. The possible dipole-up and dipole-down adsorption configurations of polar phthalocyanines allow tuning of the energy level alignment for the respective interface, e.g., as recently demonstrated for VOPc.3,4 It was reported that chloroindium phthalocyanine (ClInPc) and titanyl phthalocyanine (TiOPc) can improve the energetics of organic solar cells (OSCs).5 In addition, such molecules can even act as an active layer in OSCs.6−8 As example, ClInPc:C60 © 2016 American Chemical Society

OSCs are shown to be capable of near-IR absorption, promising power conversion efficiencies and show comparably high open-circuit voltages.8 Furthermore, applications in memory devices were proposed based on the reversible switching of single AlClPc molecules.9 Thus, both interface properties and the molecular organization in thin films may significantly affect properties of possible devices. Due to the additional axial dipole moment, the growth- and temperaturedependent polymorphism can differ significantly from those of planar nonpolar phthalocyanines.10−12 The aim of this article is the investigation of interface properties of chloroaluminum phthalocyanine (AlClPc) and fluoroaluminum phthalocyanine (AlFPc) on different silver surfaces. Chemical structures of the molecules are shown in Figure 1. A motivation for the chosen system was also the application of silver electrodes in several optoelectronic devices. The role of the substrate surface (single-crystalline or polycrystalline) on the molecular orientation is studied, and the results are compared to the relatively (chemically) inert gold interface. Received: July 14, 2016 Revised: October 10, 2016 Published: October 10, 2016 24715

DOI: 10.1021/acs.jpcc.6b07052 J. Phys. Chem. C 2016, 120, 24715−24723

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The Journal of Physical Chemistry C

Figure 1. Chemical structure of studied molecules: (a) chloroaluminum phthalocyanine; (b) fluoroaluminum phthalocyanine.

Figure 2. N K edge X-ray absorption spectra for AlClPc on (a) Ag(111), (b) Ag-foil, (c) Ag-foil, (d) Au-foil, and (e) Au-foil. In f, the normalized N 1s−π* intensities with respect to the angle of incidence of the p-polarized synchrotron radiation for all films are summarized. Although the film thickness ranges from 0.5 to 4.1 nm, the trend of the angular dependence is similar in all cases.

2. EXPERIMENTAL SECTION

Synchrotron radiation based X-ray absorption spectroscopy (XAS) and photoemission (PES) measurements have been performed at BESSY II (Berlin, Germany) using the endstation SurICat at the Optics-beamline as well as at the WERA beamline of ANKA (Karlsruhe, Germany). The energy resolution for PES and XAS was set to about 100 meV at a photon energy of 400 eV. The absorption was monitored indirectly by measuring the total electron yield (sample current). For the calibration of the photon energy, the binding energies (BE) of the Au 4f7/2 peak excited by first- and secondorder light have been compared. The XAS spectra have been normalized to the same step height well above the ionization threshold. Measurements in our lab were performed using multichamber UHV systems (base pressure of 2 × 10−10 mbar). AlFPc on Ag foil was measured using a spectrometer equipped

Ag(100) and Ag(111) single crystals were cleaned by cycles of argon ion sputtering and annealing. The sputtering was carried out at a voltage of 800 V for typically 30 min; subsequently, the annealing was performed for 30 min at a temperature 900 K. The foil was cleaned by argon ion sputtering without an additional annealing step. AlClPc was prepared via reaction of 1,2-dicyanobenzene and anhydrous aluminum(III) chloride in quinoline media at a temperature of 230 °C.13 AlClPc was evaporated at rates of about 1−2 Å/min determined by a quartz microbalance. All values of the film thickness were obtained by the comparison of photoemission intensities of substrate and overlayer related peaks assuming layer-by-layer growth. Atomic cross sections were taken from ref 14. 24716


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Figure 3. C 1s (left) core level spectra of AlClPc on (a) Ag(100) and (b) Ag foil as a function of the nominal film thickness. All C 1s spectra can be described by the same model, implying that carbon is not involved in chemical reactions at the interface.

The measurement geometry is shown as an inset of Figure 2f: θ = 10° corresponds to grazing incidence, and θ = 90° corresponds to normal incidence. The spectra can be separated into two spectral regions: Spectral features at photon energies 402 eV are determined by in plane N 1s−σ* transitions.20,21 We note that weak in-plane polarized transitions appear in the same energy range as the π* resonances.20,23,24 For the evaluation of the intensity of the π* resonances in Figure 2f, the two prominent lowest lying features at photon energies below 402 eV were taken. In all cases in Figure 2a−e, the maxima of the N 1s−π* intensities are found at grazing incidence, while the maxima of the N 1s−σ* transitions are observed at normal incidence. Assuming 100% linear polarization of the synchrotron radiation, the intensity should be described by a simple cos2 θ function for molecules with their plane oriented parallel to the sample surface (flat-lying) and by a sin2 θ function for molecules perpendicular to the sample surface.25 The quantitative analysis of the N 1s−π* resonance intensities in Figure 2f follows well the cos2 θ function for flat-lying molecules for all systems. The absence of intensity in the range of π* transitions for AlClPc on Ag(111) at normal incidence indicates an almost perfect lying adsorption geometry. On the foils, a certain degree of disorder induced by the substrate morphology might be expected. For axially substituted phthalocyanines like AlClPc, the adsorption geometry can be in either dipole-up or dipole-down adsorption configuration of the first layer. For AlClPc on surfaces with comparably strong interactions such as Cu or ITO, often randomly distributed dipole moments were observed, whereas on graphite or graphene layers, it was reported that AlClPc is spontaneously aligned in the Cl-up configuration.9,26−28 In the case of AlClPc on Cu(111), DFT calculations indicate a strong charge accumulation at the interface region between Cu surface and the Cl atom in Cl-down adsorbed AlClPc due to the electron transfer from the bonded Cu atoms.28 We will discuss a

with a Phoibos 150 Hemispherical Energy Analyzer (SPECS) and an X-ray source with monochromator (XR 50 M, SPECS). For studies of AlClPc on Ag foil, a system consisting of a nonmonochromatic X-ray source (DAR 400) and a hemispherical Energy Analyzer (EA 125, Omicron) was used. Finally, measurements of AlClPc on Ag(100) were done using a spectrometer equipped with a nonmonochromatic X-ray source (XR 50 SPECS) with a hemispherical energy analyzer (Phoibos 100, SPECS). All UHV systems had also UV sources and the opportunity for low-energy electron diffraction (LEED) measurements. Excitation energies were 1486.6 and 21.2 eV for XPS and UPS, respectively. Peak fitting of XPS spectra was performed using the program Unifit.15 A Nanoscope IIIa atomic force microscope (AFM) from Veeco Instruments was used for surface topography measurements. Images were obtained using tapping mode.

3. RESULTS AND DISCUSSION 3.1. Molecular Orientation of AlClPc in Thin Films. The orientation and the kind of interaction of the first molecular layer(s) on surfaces can affect properties of devices significantly. One of the reasons is that the adsorption geometry may affect distinctly complex charge transfer processes, involving both the central metal atom and the macrocycle of the MPc.16−19 We will therefore first discuss the molecular orientation of AlClPc (ultra)thin films on Ag and Au substrates studied by XAS. In order to probe the molecular orientation of the MPc macrocycle polarization-dependent N K edge, absorption spectra were measured for AlClPc on Ag(111) (at BESSY), Ag-foil (at ANKA), and Au-foil (at ANKA). Although AlClPc exhibits C4v symmetry, both carbon and nitrogen atoms are almost located in one plane; thus, C 1s−π* and N 1s−π* excitations can be used to analyze the molecular orientation in a similar manner, analogous to related phthalocyanines.20−22 In Figure 2a−e, we summarize selected angular-dependent N K edge absorption spectra of AlClPc on all substrates together with the analysis of the peak area of the N 1s−π* transitions. 24717


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Figure 4. Comparison of thickness-dependent Cl 2p spectra of AlClPc on (a) Ag(100) and (b) Ag foil. The analysis by a peak fitting routine reveals two Cl species: a bulk signal at higher binding energy (blue) and an interface species at 1.1 eV lower binding energy (green).

In order to gain information about a possible chemical interaction at AlClPc/Ag interfaces, we will discuss in the following core level spectra as a function of the layer thickness. In Figure 3, C 1s spectra are compared for AlClPc on Ag(100) and Ag foil. Additional spectra for AlClPc on Ag(111) can be found in the Figure S1. The C 1s spectra were fitted using a Voigt function, i.e., a convolution of a Lorentzian and Gaussian line profile. The Lorentzian peak width is related to the (core− hole) lifetime broadening, while the Gaussian width is usually attributed to the experimental resolution of the spectrometer. Further experimental artifacts, such as an unequal environment of the considered atom, different adsorption sites, or small layer-dependent energy shifts, are assumed to contribute to the Gaussian line width. From the fit of the thickest film we obtain a Lorentzian peak width of 0.31 eV; this value was kept constant for all spectra. For the fit of the C 1s spectrum, we assume four components, which are attributed to the aromatic carbon of the benzene rings (C-1), pyrrole carbon linked to nitrogen (C-2), and the corresponding π−π* satellites (SC‑1, SC‑2) as described in the literature for related phthalocyanines.32 A first inspection of the spectra in Figure 3 reveals a thicknessdependent broadening of the spectra, with a maximum at the lowest film thickness. However, the peak fit analysis shows that all spectra can be described by a similar peak shape, assuming the same intensity ratio of C-1 and C-2 allowing a variation of the Gaussian peak width. The intensity ratio between the two carbon types matches the stoichiometric value of 0.33 (cf. insert of Figure 3a). In agreement to the literature,22 the energetic separation between the main peaks and the corresponding satellites was set to 1.9 eV. Within this model, we obtain an increase of the Gaussian peak width from 0.9 eV for the 2.6 nm film to 1.3 eV for monolayer coverages on Ag foil (Ag(100): 1.1/1.2 eV). Also, the energetic distance between C-1 and C-2 is changed from 1.4 eV (thin film) to 1.0 and 1.2 eV at the interface for Ag foil and Ag(100), respectively. In addition, the intensity of the satellite SC‑2 is suppressed at the interface. All fitting parameters can be found in the Table S1. The similar peak shape may indicate that the macrocycle is not directly

possible dipole-up or dipole-down adsorption configuration for AlClPc on silver below. In the case of planar metal phthalocyanines grown on singlecrystalline metal substrates, the molecules often adsorb in a flatlying geometry with respect to the substrate surface, whereas on polycrystalline substrates, larger tilt angles are observed, e.g., refs 1, 19, and 20. For copper phthalocyanine (CuPc) on gold foil, the molecules are flat-lying in ultrathin films up to a thickness of about 0.8 nm, and with growing film thickness, a change of the orientation is observed, resulting in a buried highly oriented interfacial layer.20 The free surface energy of the gold substrate is expected to be significantly higher compared to the AlClPc film. Microscopically, among others, a charge redistribution and polarization effects at the interface to gold have to be taken into account. Thus, the molecular orientation for the first few layers directly at the interface to gold can be understood by the strong molecule−substrate interaction.20 For higher coverages, this interaction becomes negligible resulting in a change of the molecular orientation. In contrast, for AlClPc on Au and Ag foil the flat-lying molecular orientation is maintained, at least up to a film thickness of about 4 nm. It seems therefore that the axial Cl substitution associated with the dipole moment out of plane supports the “lock-in” of the initial orientation also in thin films. The driving force might be the maximization of the dipole−dipole interaction. This was recently also discussed for polar subphthalocyanines on Cu(111), where binary systems could be created combining up and down intact species, and a discrete well-defined bilayer and trilayer triangular nanocrystallites were observed.29 Another example is the growth of titanyl-phthalocyanine (TiOPc)30 and vanadyl-phthalocyanine (VOPc).31 As a consequence of such a strong dipole−dipole interaction, also AlClPc molecules keep the lying orientation even at a film thickness when the interaction with gold is negligible, contrary to the nonpolar CuPc on Au foil.20 3.2. Interface Properties of AlClPc on Silver. Silver is known to be a comparably reactive substrate, for many related systems strong interactions were observed, e.g., refs 1 and 19. 24718


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Figure 5. UPS valence band spectra of AlClPc on (a) Ag(100) and (b) Ag foil (zoom into the HOMO region). Although the energetic position of the HOMO is similar in both cases, enhanced intensity near the Fermi energy is observed for AlClPc on Ag foil only.

foil and on the single-crystalline substrates Ag(100) and Ag(111). The percentage of reacted molecules together with corresponding layer thickness can be found in Table S2. However, the analysis of Cl 2p core level spectra by the fitting procedure reveal the presence of nonreacted chlorine also for coverages in the monolayer range for both silver surfaces. This might be related to a randomly distributed dipole-up and dipole-down configuration as recently observed for a related, strongly interacting interface: VOPc on Ni(111).4 A chemical interaction at the interface might be preferred if the molecules are initially oriented with the chlorine atom pointing to the silver surface. We note that interface signals in Cl 2p spectra were also observed for a related system, chloro[subphthalocyaninato]boron(III) on Ag(111).36 For the same molecule on Cu(111), a combined scanning tunneling microscopy (STM) and density functional theory (DFT) study has shown that either the molecules adsorb as Cl-up with the Cl-atom pointing toward the vacuum side of the interface or they dechlorinate. This is in good agreement to the discussed AlClPc on silver surfaces, where obviously only a part of the molecules react at the interface.37 In Figure 5, we compare UPS valence band spectra for AlClPc on Ag(100) and on Ag foil. AlClPc related features are fully developed at a film thickness of >2 nm, indicating that the metal substrate is completely covered at this thickness. The maximum of the HOMO is found at about 1.6 eV on both substrates, suggesting a similar energy level alignment. The energy level alignment for AlClPc on Ag(100) and on Ag foil as extracted from UPS spectra is compared in Figure S4. Only at very low coverages might the position of the HOMO be somewhat lower in the case of the Ag foil substrate (1.35 eV instead of 1.45 eV on Ag(100)); this difference lies however within the experimental error. Despite the similar behavior of AlClPc on single-crystalline Ag surfaces and Ag foil, differences can be detected. In contrast to AlClPc on Ag(100), valence band spectra for AlClPc on Ag

involved in a strong interaction between AlClPc and the silver substrates. The different distance between C-1 and C-2 can be explained, at least to some extent, by a different polarization screening for each atom at the metal interface. However, complex bidirectional charge transfer processes, as recently discussed for related systems,16−18,33 may also contribute to a different energetic shift of C-1 and C-2 features. In particular, the comparable large change for Ag foil may point to a different charge distribution via the macrocycle for AlClPc molecules in the bulk and directly in contact to the silver substrate. Further information about possible complex charge transfer processes might be obtained from thickness dependent N 1s core level spectra, but due to the superposition with substrate related features the unambiguous analysis of the peak shape in the monolayer range is hindered (see Figure S2). The Al−Cl bond in AlClPc is the weakest point in terms of stability, e.g., in thin films a reaction from AlClPc to (PcAl)2O μ-(oxo)dimers is known in the presence of water.22 We will therefore consider more in detail thickness-dependent chlorine related signals. In Figure 4 we compare Cl 2p core level spectra for AlClPc on Ag(100) and Ag foil. A clear change of the peak shape can be observed as a function of the film thickness on both substrates. The Cl 2p signal can be fitted by two doublets; the signal at lower binding energies (197.7 eV) is maximal for the lowest film thicknesses and consequently assigned to an interface species. The energetic separation of the interface species and the AlClPc related signal is 1.1 eV, indicating a distinct change of the chemical environment. The binding energy of the interface component of 197.7 eV is in good agreement to Cl 2p binding energies for chlorine reactively adsorbed on Ag(110)34 and for AgCl electrodes.35 We conclude therefore that the Cl atom is strongly interacting with the Ag substrate resulting in a break of the Al−Cl bond and in the formation of an Ag−Cl bond. As a consequence, bond formation may also occur between silver and the AlPc. This interaction seems to be independent from the Ag substrate surface since the interaction was observed on polycrystalline Ag 24719


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Figure 6. (a) UPS valence band spectra (zoom into the HOMO region) of AlClPc on a Ag (100) single crystal, the surface structure of which is damaged by annealing temperatures above 750 °C. (b) AFM image (1 × 1 μm2) of the surface of an Ag(100) single crystal annealed at the temperature above 750 °C. Similar to AlClPc on Ag foil, enhanced intensity near the Fermi energy is observed in UPS.

Figure 7. AlFPc on Ag foil: (a) C 1s and (b) F 1s core level spectra as a function of the nominal film thickness. The presence of an interface F 1s component reveals a chemical interaction at the interface.

foil in the monolayer range show clearly additional intensity in the energy range of the Fermi level (EF). Also for AlClPc on Ag(111), no additional intensity close to the EF is visible for low coverages (see Figure S4), pointing to the absence of such an interface state on both single-crystalline substrates. The question therefore arises if the substrate roughness affects the interaction mechanism for AlClPc at the interface to silver. Alternatively, the different preparation procedure of the foil and single-crystalline substrates may affect the interaction; the missing final annealing step in the preparation of the foil may result in an increased reactivity of this surface. We studied therefore interface properties of AlClPc on another substrate: An Ag(100) single crystal was annealed to temperatures above 750 °C, resulting in a partial damaging of the single-crystalline structure at the surface. The AFM image of Figure 6b shows that single-crystalline regions remain present (even spots were observed in low-energy electron diffraction measurements); the greatest part of the surface however is covered by Ag islands due to the high annealing temperature above the melting point of the surface in the final annealing step. The total root-mean-

square (rms) roughness of the area shown in Figure 6b is 1.9 nm. UPS valence band spectra for different coverages of AlClPc on the highly annealed Ag(100) substrate are shown in the Figure 6a. The spectra are normalized to the same height of the bands in the binding energy range between 0.8 and 1.0 eV. Clearly visible is the enhanced intensity in the vicinity of the Fermi level, possibly from molecules adsorbed on the polycrystalline islands between the single-crystalline terraces. The final annealing step of the substrate, however, seems not to affect the interaction mechanism at the interface. 3.3. Interactions of AlFPc on Silver Foil. The Al−F bond might be stronger compared to Al−Cl due to the higher difference of the electronegativity of the atoms involved in the bonding. Therefore, AlFPc might exhibit an increased chemical stability at the interface to silver. As an example, we studied AlFPc on Ag foil. The corresponding C 1s and F 1s spectra are shown in Figure 7. Similar to AlClPc on silver substrates, C 1s spectra in Figure 7a can be described by essentially the same shape; detailed fitting parameters for AlClPc can be found in 24720


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Figure 8. (a) Valence band spectra of AlFPc (zoom into the HOMO region). (b) Comparison of the energy range in vicinity of the Fermi energy for the clean substrate and 1−2 monolayers (0.6 nm) AlFPc on Ag foil. Additional intensity at Fermi edge is clearly visible at coverage of 0.6 nm.

the formation of such interface states. In this context, the roughness on the scale of the size of the molecule would be important. The presence of single-crystalline terraces in the order of the molecule size can be excluded for the foils and also for the predominant part of the highly annealed single crystal. Since the energetic distance between C-1 and C-2 components in the C 1s spectra of AlClPc is distinctly smaller at the interface to Ag foil (see above), we assume that the phthalocyanine macrocycle is involved in this interaction. However, for AlClPc on single-crystalline Ag substrates, the absence of gap states and the smaller change of the energetic distance between C-1 and C-2 at the interface indicates that the macrocycle of AlClPc on single-crystalline surfaces remains almost unaltered even if Cl reacts with Ag at the interface. In other words, AlClPc can be attached to the Ag substrate without a distinct change of the physical properties of the phthalocyanine. We note that states close to the Fermi level were also found for the related iron phthalocyanine (FePc) on single-crystalline Ag surfaces, e.g., refs 43 and 44; their nature however might be different. For FePc on Ag(111) it was shown that the interaction of the iron atom of FePc and the substrate results in the formation of such a gap state.44

the Supporting Information. Most remarkably, at the lowest film thickness, the energetic distance between the C-1 and C-2 components is 1.0 eV, i.e., significantly smaller than that observed for phthalocyanines in the bulk (1.4 eV). The behavior is similar to AlClPc and can be analogously understood by the presence of a charge transfer across the interface and/or a different charge distribution over the phthalocyanine macrocycle at the interface (see section 3.2). F 1s spectra of Figure 7b exhibit a distinct change of the peak shape as a function of the layer thickness. A single F 1s peak is found for the lowest film thickness of 0.6 nm (1−2 monolayers) at a binding energy of 684.6 eV, whereas the peak ascribed to AlFPc in the bulk at about 686.0 eV develops slowly with thickness. The species at lower binding energy can be assigned to an interface component. We conclude therefore that similar to AlClPc the Al−F bond breaks and Ag−F is formed at the interface. The F 1s binding energy for the Ag−F bond is expected to be significantly lower than 686.0 eV (measured for bulk AlFPc); reported values in the literature are about 683 eV.38−40 The shape of HOMO also changes with increasing coverage of AlFPc, as visible in Figure 8a. The comparison of the energy range in vicinity of the Fermi energy for the clean substrate and 0.6 nm of AlFPc on Ag (Figure 8b) reveals that beside the development of the AlFPc HOMO additional intensity at EF is detectable for low coverages. This behavior also reminds us of AlClPc on Ag foil. Such peaks close to the Fermi edge in photoemission can be understood by so-called “gap states”, in particular, those observed for reactive metal−organic interfaces. A possible mechanism for the formation of such interface states are interfacial doping effects caused by a charge transfer across the interface accompanied by a (partial) filling of the (former) LUMO, e.g., as discussed in detail for CuPcF4 on silver.41 As a result, a strong coupling to the metal states may occur for particular molecules, which may also lead to a surface-induced aromatic stabilization of substantially charged molecular monolayers and a metallic behavior.42 It seems that the roughness of polycrystalline silver substrate surfaces supports

4. SUMMARY We studied interface properties of AlClPc and AlFPc on different Ag substrates. AlClPc grows in thin film with preferred adsorption geometry of the molecular plane parallel to the substrate surface. In contrast to other phthalocyanines, the molecular orientation is almost not affected by the substrate roughness. Chemical reactions with Ag substrate were found for all systems studied, affecting the Al−Cl or Al−F bond, respectively. The formation of gap states was in particular observed on Ag foil, indicating that the roughness of the substrate surface significantly affects detailed interface properties. 24721


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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.6b07052. Additional XPS core level spectra and the energy level alignment of AlClPc on silver surfaces (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: (+49) 07071/ 29-76931. Fax: (+49) 07071/29-5490. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the German Research Council (PE 546/5-1 and CH 132/23-1). We acknowledge the Helmholtz Zentrum Berlin GmbH, Elektronenspeicherring BESSY II as well as ANKA and KNMF (both Karlsruhe, Germany) for the provision of beamtime. Financial travel support by Helmholtz Zentrum Berlin GmbH is gratefully acknowledged. We thank Antje Vollmer (BESSY Berlin) for helpful discussions and W. Neu for technical support.

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REFERENCES

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Chemical Reaction of Polar Phthalocyanines on ... - ACS Publications

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