Lucyna Grządziel

Photoemission study of the electronic properties of in situ prepared copper phthalocyanine (CuPc) thin films exposed to oxygen and hydrogen

Abstract The electronic properties of space charge layer of the copper phthalocyanine (CuPc) thin films in situ prepared by an UHV evaporation method and, subsequently, exposed to molecular oxygen (O 2 ) and molecular hydrogen (H 2 ) have been studied using the high resolution photoemission yield spectroscopy (PYS) technique. The influence of interaction of these active gases on the work function ϕ and ionisation energy Φ was determined, together with the changes of effective density of filled electronic states localised in the band gap below the Fermi level and in the upper part of the valence band. In order to direct comparison to the commonly used procedure for UPS and XPS techniques, the changes of macroscopic parameters of the space charge layer were expressed by the surface Fermi level position in the band gap E F – E v . The observed changes of surface Fermi level position upon adsorption/desorption of molecular oxygen O 2 and hydrogen H 2 were attributed to decrease/increase of the induced charge in near surface region.

On the correlation between morphology and electronic properties of copper phthalocyanine (CuPc) thin films

Abstract The morphology of vacuum deposited copper phthalocyanine (CuPc) thin films surface deposited on Si(111) have been studied using the contact mode Atomic Force Microscope (AFM). The influence of substrate temperature during deposition and of the post-deposition UHV annealing on surface roughness as well as on the average and maximum grain height was determined. The observed changes of surface morphology were in a good correlation with the shift of surface Fermi level position in the band gap after O 2 exposure determined in our recent photoemission studies.

Zinc oxide as a defect-dominated material in thin films for photovoltaic applications – experimental determination of defect levels, quantification of composition, and construction of band diagram

In the present work, thin ZnO layers were synthesized by the sol-gel method with subsequent spin-coating on Si(100). We show that the detailed analysis of lab-recorded photoemission spectra in combination with Kelvin probe data yielded the work function, ionization energy, and valence band - Fermi level separation - and hence enabled the construction of band diagrams of the examined layers. With small modifications in preparation, very different films can be obtained. One set shows a homogeneous depth-dependent n carrier distribution, and another a significant carrier concentration gradient from n-type conductivity to almost metal-like n(+) character. Likewise, the surface morphology can be tuned from a uniform, compact surface with spherical single-nm sized grain-like features to a structured surface with 5-10 nm tall crystallites with (002) dominating crystal orientation. Based on the band-bending and the energy levels observed, defects of contradictory nature, i.e. acceptor-donor-trap (ADT) properties, were identified. These defects may be groups of point defects, with opposite character. The ADT states affect the energy levels of the oxide layers and due to their nature cannot be considered in the photoemission experiment as mutually independent. The versatile nature of the synthesis provides us with the opportunity to tune the properties with a high degree of freedom, at low processing costs, yielding layers with an exotic electronic structure. Such layers are interesting candidates for applications in photovoltaic and nanoelectronic devices.

Electronic properties of the space charge layer of in situ prepared copper phthalocyanine thin films exposed to oxygen

Abstract The electronic properties of the space charge layer of copper phthalocyanine (CuPc) prepared under ultrahigh vacuum (UHV) conditions were in situ studied by photoemission yield spectroscopy (PYS). Depending on the oxygen exposure, as well as subsequent UHV annealing the variation of the work function ϕ, ionization energy Φ and the surface Fermi level position in the band gap E F − E v were analyzed, together with the effective density of filled electronic states localized in the band gap below the Fermi level E F . Moreover, the obtained results were compared to the recently determined ex situ studied CuPc thin films.

Correlation between morphology and local thermal properties of iron (II) phthalocyanine thin layers

The effect of substrate temperature and post-deposition annealing temperature on the surface morphology, topography and local thermal properties of iron(II) phthalocyanine (FePc) 500 nm thick films was investigated. The investigations were conducted by a combination of scanning probe microscopies (atomic force microscopy, scanning thermal microscopy) and scanning electron microscopy with structural (x-ray diffraction) and chemical (energy-dispersive x-ray spectroscopy) analysis. FePc is always obtained in its α-form. While for heated substrates, FePc crystallites lie flat on the surface, so post-deposition annealing leads to vertically oriented crystallites. The total surface area obtained does not depend significantly on the substrate temperature, while it is strongly dependent on the annealing temperature. For both groups of samples, the increase of roughness was accompanied by a decrease of the samples thermal resistivity, which is in agreement with the picture of a decreased number of grain boundaries resulting in higher heat transport. The results obtained here show that the exposed surface area of an organic film strongly depends on the thermal treatments; hence surface morphology can be tailored to particular needs.