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Interface properties of cobalt(II) phthalocyanine (CoPc) and cobalt(II) hexadecafluoro-phthalocyanine (CoPcF16) to gold are investigated by photo-excited electron spectroscopies (X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and X-ray excited Auger electron spectroscopy (XAES)). It is shown that a bidirectional charge transfer determines the interface energetics for CoPc and CoPcF16 on Au. Combined XPS and XAES measurements allow for the separation of chemical shifts based on different local charges at the considered atom caused by polarization effects. This facilitates a detailed discussion of energetic shifts of core level spectra. The data allow the discussion of site-specific charge-transfer processes.

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]

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]

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]

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: 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]