We use resonant photoemission at the C1s edge to study the electronic structure of HOPG, graphene flakes and monolayer graphene. We find remarkable differences in the profile of the Auger decay channels, which we attribute to an additional multiple-Auger with a three-hole final state. A prerequisite for the appearance of this decay mechanism is the existence of localized excitonic states, which cause the appearance of the multiple Auger decay. We use those effects to identify the existence and the quantity of such defect states within the p*-band regime in carbon thin films, because the intensity of the three-hole Auger decay is varying with the defect density of the carbon films. We find that the appearance of the multiple Auger decay is different for multilayer and monolayer graphene. In particular the interaction of impurities leads to broadening of the C1s core levels. The three-hole Auger decay spectroscopy is a new method to detect such contaminations with a high sensitivity.

The surface chemistry and the interface formation during the initial stages of the atomic layer deposition (ALD) of Al2O3 from trimethylaluminum (TMA) and H2O on InP(100) were studied by synchrotron radiation photoemission spectroscopy and scanning tunneling microscopy. The effect of the ex situ surface cleaning by either H2SO4 or (NH4)(2)S was examined. It is shown that the native oxide on the InP surface consisted mainly of indium hydrogen phosphates with a P enrichment at the interface with InP. After a (NH4)(2)S treatment, S was present on the surface as a sulfide in both surface and subsurface sites. Exposure to TMA led to the formation of a thin AlPO4 layer, irrespective of the surface cleaning. The surface Fermi level of p-type InP was found to be pinned close to midgap after H2SO4 cleaning and moved only slightly further toward the conduction band edge upon TMA exposure, indicating that the AlPO4/InP interface was rather defective. (NH4)(2)S passivation led to a Fermi level position of p-type InP close to the conduction band edge. Hence, the InP surface was weakly inverted, which can be attributed to surface doping by S donors. TMA exposure was found to remove surface S, which was accompanied by a shift of the Fermi level to midgap, consistent with the removal of (part of) the S donors in combination with a defective AlPO4/InP interface. Further TMA/H2O AID did not lead to any detectable changes of the AlPO4/InP interface and suggested simple overgrowth with Al2O3.

For polymer-electrolyte-membrane fuel cells (PEM-FC), platinum catalysts on carbon based substrates are state of the art, due to high electrochemical activity and chemical stability in acid electrolytes. High costs of platinum force investigations of alternative catalysts. With respect to the oxygen reduction reaction, possible candidates are transition metal (TM) complexes like TM-porphyrines or TM-phthalocyanines. Pyrolysis on carbon based substrates improves the catalytic activity. Highest activities were found for Fe or Co as transition metal centers. We present results of the pyrolysis of Co-phthalocyanine (CoPc) on carbon black. Besides an investigation of morphology by scanning electron microscopy (SEM) and chemical composition by energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) during pyrolysis, we present a near edge Xray absorption fine structure (NEXAFS) study of the chemical composition for the related annealing steps. This investigation is accompanied by an electrochemical characterization of the catalytic activity and selectivity. The XPS and NEXAFS data indicate a decomposition of the CoN4 (chelate-) complex during pyrolysis. The N1s data for 800 degrees C show graphite-like, formally pyrrolic and pyridinic like features, without any significant contribution of Co. The Co2p data for both, XPS and NEXAFS are dominated by CoO/Co2O3. It can be concluded that during the pyrolysis cobalt particles are formed by the disintegration of CoN4-centers, after pyrolysis these particles become oxidized upon contact with air. (C) 2012 Elsevier B.V. All rights reserved.

We have studied thin films of C60, [6,6]-phenyl-C61-butyric acid methyl ester, and fullerenol by Near-Edge X-ray Absorption Fine Structure Spectroscopy at the C1s edge. The advantage of this technique is the sensitivity to unoccupied π states within the sp2 chemical bond structure. In particular, we focus on the relative intensity of the C1s→π*(p-p) transitions. Upon adding functional groups to the C60 molecular frame, the intensity of these bands is reduced or almost vanished accompanied by increasing C1s→π*(s-p) transitions. This finding is confirmed by X-ray photoemission data in the valence band region where the peaks according to the occupied π states disappeared particularly in the fullerenol films. These data in combination with the quantitative analysis of the C1s core level data suggest that C=C double bonds are broken when binding two OH-groups correlated to a change of the carbon bonding state from sp2 to sp3.

We show a comparative study of the TiO2 ALD with TTIP and either O2 or O2-plasma on Si/SiO2 substrates. In particular we compare the surface morphology and crystalline phase by means of Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) for different O2-plasma procedures upon changing the time between cycles and the N2-purging pressure. The AFM images show that already these parameters may induce structural changes in the TiO2 films grown by ALD, with the formation of crystallites with average lateral width varying between 15 and 80 nm. By means of XAS we also found that the crystallites have mixed anatase and rutile crystalline phases and that smaller crystallites have a greater rutile component than the larger ones.

Conducting properties of several polymers after low-energy ion irradiation were investigated. The enhancement of conductance induced by the ions is discussed in terms of graphization. Field effect transistors (FET) on the graphitized polymer surfaces were studied. We found that the field effect mobility depends on the conductivity of the graphitized surfaces according to the power relation sigma similar to mu(182), Such behaviour is typical for disordered organic semiconductors with a variable range hopping mechanism of conductance. Incontrast, the graphitized surfaces with a semimetallic type of conductance demonstrate a high carrier mobility 1 cm(2)/Vs, which is almost independent on the conductance. These semimetallic materials consist of 2 and 3 nm graphene patches and are characterized by a significantly smaller disorder level. However, for a feasible FET application the carrier concentration in the graphitized surfaces must be reduced. Possibilities to improve the performance of the FETs are discussed.

Fullerene-based materials are considered to be a candidate for ultra-low-k material applications. We have incorporated fullerene C60 into a siloxane material by means of the sol-gel method. Thickness of obtained film was investigated by atomic force microscope, dielectric constant was measured by the capacitance-voltage characterization (CV). Interactions between the components within the films were investigated by using X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy. We found that the ratio of carbon, oxygen and silicon atoms within obtained film equals 2.7∶1.9∶1. The microscopic and CV investigations show that the sample's composition is inhomogenous although the fullerene's concentration within the material is low. However, dielectric constant is in the range of 2.3 to 2.5.

We present the first dynamic study of damage mechanisms in nanosized on-chip Cu interconnects caused by stress-induced voiding in advanced integrated circuits. Synchrotron-based transmission x-ray microscopy is applied to visualize the void evolution and conical dark-field analysis in the transmission electron microscopy to characterize the Cu microstructure. Our x-ray microscopy measurements showed, in contradiction to electromigration studies, no void movement over large dimensions during the stress-induced void evolution. We observed in via/line Cu interconnect structures that voids are formed directly beneath the via, i.e., in the Cu wide line at the edge of the via bottom. It is concluded that voids are originally formed at the site where eventually the catastrophic failure occurs. During stress migration tests, Cu atoms migrate from regions of low stress to regions of high tensile stress, and simultaneously, vacancies migrate along the stress gradient (within a limited range of some microns) in the opposite direction to the location where small vias connect wide Cu lines. The stress distribution and the driving forces for atomic transport depend strongly on the particular geometry of the tested structure but also on interface bonding and metal microstructure. Vacancies form agglomerates and subsequently voids that grow further. The void growth rate depends on the Cu thin film material and its microstructure, particularly the grain size and the grain orientations. The Cu microstructure in the surroundings of the formed void shows that Cu grains are predominantly (111) oriented relatively to the wafer surface. Interfaces and grain boundaries, and particularly their orientation, determine the void evolution dynamics.