P. Picozzi

Thin and ultra-thin films of nickel phthalocyanine grown on highly oriented pyrolitic graphite : an XPS, UHV-AFM and air tapping-mode AFM study

Abstract Thin and ultra-thin films of nickel phthalocyanine have been deposited in ultra-high vacuum on highly oriented pyrolitic graphite. The growth mode and the interaction with the substrate have been studied in situ by X-ray photoelectron spectroscopy, scanning tunneling microscopy and atomic force microscopy, and ex situ by means of tapping-mode atomic force microscopy. We present photoelectron spectroscopy measurements at various film thicknesses which show no detectable interaction of the adsorbed organic layers with the substrate, but, varying the deposited film thickness by in-situ annealing the substrate, we show desorption effects semiquantitatively described. The XPS spectrum of the C 1s multiplet structure of NiPC obtained using a monochromatized source is also presented. The scanning probe images presented address morphological issues like the growth mode at initial stages of deposition and at higher coverages. Moreover, upon annealing of the PC films, we show high-resolution measurements consistent with the low-size stable α crystalline phase of phthalocyanine molecules. The potential of tapping-mode atomic force microscopy in imaging soft adlayers deposited over soft substrates is addressed throughout the paper.

Size effects on the linewidths of the Auger spectra of Cu clusters

Abstract We discuss the role of the size distribution of Cu clusters deposited on graphite in determining the broadening and the shifting of the Auger L 3 VV Lineshapes observed when the average cluster size decreases. In our interpretation this broadening is only due to the superposition of various narrow Auger lines relative to the various cluster dimensional classes, each shifted towards lower kinetic energies because their small sizes. The Auger peak shifts are mainly due to the change in the valence band and core levels as the cluster size decreases. The model used to reproduce the Auger line broadening, following the Cini-Sawatzky approach, takes into account the broad distribution of the different diameters.

Copper hexadecafluoro phthalocyanine and naphthalocyanine: The role of shake up excitations in the interpretation and electronic distinction of high-resolution X-ray photoelectron spectroscopy measurements

We present the first high-resolution X-ray photoelectron core level spectra of bulk copper hexadecafluoro phthalocyanine (CuFPC) and naphthalocyanine (H NPC). The measurements have been performed in UHV onto samples grown in situ. A 2 shake-up satellite assigned to a monopole on-site HOMO-LUMO molecular excitation has been evidenced in the F, C and N core-level spectra measured. In the case of the CuFPC, the shake-up is characteristic of the F atoms, of the four N atoms that are Cu bonded, and of the F- and N-bonded C atoms. The shake-up to main peak relative binding energy has been estimated to be 1.6 eV. In the case of H NPC, the outer benzenic C atoms do not show a satellite excitation, which instead is 2 characteristic of the C and N atoms belonging to the inner porphyrin-like central ring of the molecule. The shake-up is less than 1 eV at higher binding energies from the main core line. The localisation of the HOMO level in the central structure of the molecule is confirmed by Hartree-Fock all-electron molecular orbital calculations performed on the metal-free phthalocyanine (H PC) and hexadecafluoro phthalocyanine (H FPC) molecules.

Characterisation of aerosol individual particles in a controlled underground area

The aim of this study is to determine the sources and provide a physico-chemical description of the airborne particulate present in two communicating underground areas: a highway tunnel with heavy vehicular traffic and a controlled underground laboratory. Individual particles were collected in the two zones and examined using scanning electron microscopy with EDS X-ray attachment. The principal components of the particulate were analysed using principal factor analysis and hierarchical cluster analysis. The data obtained suggest that three main factors determine airborne particulate pollution in the laboratory: the ventilation system for air replacement, the access of motor vehicles into the laboratory, and the metallic installations and structure of the laboratory itself.

Preparation and characterization of bulk ZnGa2O4

High-quality bulk ZnGa2O4 has been synthesized from equimolar mixtures of ZnO and Ga2O3 by the conventional solid-state method. For the first time, the sample has been characterized in detail to confirm the formation of pure single phase of spinel ZnGa2O4. The formation of ZnGa2O4 has been confirmed by sintering the mixtures of ZnO and Ga2O3 at different temperatures, ranging from 900–1200 °C. It is observed that the single phase of ZnGa2O4 has been formed at and above 1000 °C sintering temperature for 24 h. The crystallinity and phase formation of this single phase has been confirmed by X-ray diffraction. X-ray photoelectron spectroscopic studies have been carried out for bulk ZnGa2O4 sintered at 1000 °C for 24 h which showed 14% Zn, 28% Ga and 58% O, indicating stoichiometric ZnGa2O4. A new parameter, the energetic separation between the Zn 2p3/2 and Ga 2p3/2 peaks, has been used as a sensitive tool to distinguish between a complete formation of ZnGa2O4 compound and a mixture of ZnO and Ga2O3 powders. Surface morphology studies by scanning electron microscopy reveal that the formation of ZnGa2O4 takes place in mosaic rod-like structure. The purity of the compound has also been checked by the energy dispersive X-ray method, indicating the absence of foreign ions and the ratio of zinc to gallium has been calculated and found to be 1 : 2, indicating stoichiometric ZnGa2O4.

Magneto-optical study of Mn ions implanted in Ge

Summary form only given. The synthesis of optimal materials for spin dependent electronics is the challenging goal of recent studies. Magnetic multilayers are the most popular solution, but a promising alternative is constituted by magnetic semiconductors. One of these is Mn:Ge which shows ferromagnetic properties and magnetoresistance phenomena below room temperature, attributed to Mn/sub x/Ge/sub 1-x/ clusters. In the present work, we investigate the properties of samples obtained by implanting Mn/sup +/ ions on Ge(100) at energy of 100 keV, with a dose of 2 x 10/sup 16/ at./cm/sup 2/. The temperature of the substrate was 300/spl deg/C. We report the results obtained in the as-prepared material, in the material annealed for 1 hour at 400/spl deg/C, and 600/spl deg/C.

RECTIFYING BEHAVIOR OF SILICON-PHTHALOCYANINE JUNCTIONS INVESTIGATED WITH SCANNING TUNNELING MICROSCOPY/SPECTROSCOPY

We present ultrahigh vacuum (UHV) scanning tunneling microscopy/spectroscopy (STM/STS) and ultraviolet photoemission spectroscopy (UPS) measurements on ultrathin films of nickel–phthalocyanine (Ni–PC) deposited onto clean Si(111)7×7 substrates. STS spectra refer to a sample with 5 A of Ni–PC nominal thickness. The current-voltage (I-V) measurements were taken at constant tip-sample separation showing high reproducibility at different nanometer size topographical features of the sample. In particular, three typical spectra have been repeatedly observed: (i) I-V curves with a slow increase of the current up to +1.9 eV (I 50 nA), (ii) highly noisy I-V curves symmetric with respect to the applied bias and, (iii) curves which show a marked rectifying behavior with negligible current (I 50 nA for V>0.5 V). We explain the different electronic behaviors in terms ...

Investigation on electronic structure of Cu clusters on graphite by EELS and XPS studies

Abstract We have applied electron energy loss (EELS) and X-ray photoemission (XPS) spectroscopies to study the electronic structure of copper clusters deposited in situ on clean graphite. The XPS results show an increase in the binding energy of both valence band and core levels when the cluster size decreases. Furthermore the EELS results show a sizeable increase in energy loss for the feature located at about 4 eV involving 3 d → E f states when the cluster size decreases. The observed shifts in the EELS spectrum are the same as those measured for the 3 d valence band shifts in the XPS spectra. Since the electrostatic charging effects, suggested in the past as the explanation for the variation in electronic properties occuring in the XPS of small clusters, cannot be invoked in EELS measurements we interpret the reported shifts as a genuine effect caused by band structure variation due to a redistribution of the states within the cluster d -band.

The interaction of Cu(100)Fe surfaces with oxygen studied by X-ray photoelectron spectroscopy

Abstract The oxidation of Cu(100)Fe surfaces was studied using XPS. Surfaces containing 0–10 ML of iron were oxidised at room temperature exposing 2 Pa · s of oxygen. For all surfaces evidence for Fe 2 O 3 was found. For surfaces containing more than 2 ML of iron, metallic Fe 2 p 3 2 and 2 p 1 2 signatures were observed. The analysis of the change of the 2p peak shape of a surface containing 1 ML of Fe as a function of different oxygen coverages showed that oxidation proceeds via an intermediate containing both Fe 2+ and Fe 3+ .

The use of the Auger parameter in the characterisation of some silicon compounds

Abstract The study of silicon and silicon compounds is of great interest for their technological applications. In particular the determination of the surface stoichiometry of thin silicon compounds is of fundamental importance when these films are used as coatings, chemical barriers, passivation layers. The modified Auger parameter has been used to calculate the surface composition of SiO x and SiO x N y thin films comparing the results with those obtained using other methods. The good agreement between these data indicates the validity of the modified Auger parameter as an easy and fast method, available in all electron spectroscopy laboratory, to study the surface stoichiometry of Si-based compounds.