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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)2S 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)2S 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)2S 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 ALD did not lead to any detectable changes of the AlPO4/InP interface and suggested simple overgrowth with Al2O3.
In this contribution we report on investigations of the electronic structure and composition of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) based films by using Near Edge X-Ray Absorption Fine Structure (NEXAFS). The measurements were done at the U49/2-PGM2 beam line of BESSY II, Berlin using TEY (total electron yield) and TFY (total fluorescence yield) detection. The samples were produced by spin casting a mixture of P3HT (dissolved in chloroform) and PCBM (dissolved in chlorobenzene) on ITO (indium tin oxide) coated glass slides. Measurements of pure P3HT and PCBM show all typical excitations, whereas the blended system is a weighted superposition of the related peaks. Analyzing these weighted superposition, we observe in the surface sensitive TEY data an accumulation of P3HT, whereas in the bulk sensitive TFY signal an as expected mixture is found. We also show angular dependent NEXAFS measurements of the P3HT/PCBM blend in order to measure the orientation and distribution of the P3HT polymer. Additionally, we will show a new approach for organic solar cell application by introducing ferroelectric nanoparticles into the mixture.
We present the complete genome of Stenotrophomonas indicatrix DAIF1, which was isolated from an oligotrophic pond in a water protection area. Whole-genome alignments indicated that strain DAIF1 belongs to the species Stenotrophomonas indicatrix. The whole genome (4,639,375 bp) harbors 4,108 protein-encoding genes, including 3,029 genes with assigned functions.
We present the first two complete genomes of the Janthinobacterium lividum species, namely strains EIF1 and EIF2, which both possess the ability to synthesize violacein. The violet pigment violacein is a secondary metabolite with antibacterial, antifungal, antiviral, and antitumoral properties. Both strains were isolated from environmental oligotrophic water ponds in Göttingen. The strains were phylogenetically classified by ANI analysis and showed a species assignment to Janthinobacterium lividum with 97.72% (EIF1) and 97.66% (EIF2) identity. These are the first complete genome sequences of strains belonging to the species Janthinobacterium lividum. The genome of strain EIF1 consists of one circular chromosome (6,373,589 bp) with a GC-content of 61.98%. The genome contains 5,551 coding sequences, 122 rRNAs, 93 tRNAs, and 1 tm-RNA. The genome of EIF2 comprises one circular chromosome (6,399,352 bp) with a GC-content of 61.63% and a circular plasmid p356839 (356,839 bp) with a GC-content of 57.21%. The chromosome encodes 5,691 coding sequences, 122 rRNAs, 93 tRNAs, and 1 tm-RNA and the plasmid harbors 245 coding sequences. In addition to the highly conserved chromosomally encoded violacein operon, the plasmid comprises a non-ribosomal peptide synthetase cluster (NRPS) with similarity to xenoamicin, which is a bioactive compound effective against protozoan parasites.
Resonant photoemission spectroscopy(resPES) is used to probe the occupied pi- and unoccupied pi*-bands of
carbon thin films with particular focus on the Auger decay. Highly Oriented Pyrolytic Graphite (HOPG) is
studied at the C1s edge. We find strong resonant features at 285.5 eV and 292 eV in the resPES diagram. The normal two-hole Auger decay proceeds under constant kinetic energy (451)only in the sigma*-region. In the pi*-region, however, it proceeds under 67.5° in terms of a Ebind(w) diagram. We attribute this to a multiple Auger decay with a net three hole final state. For this novel decay process we propose a model.We discuss
the long lifetime of the first resonant excitation and conclude that it arises from the strong excitonic character
of the first resonant state. We use HOPG as a reference system and suggest that this novel process is a tool to
identify interlayer–substrate interaction of the carbon layers involved.
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 π*-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.
Spectroscopic characterization of Cobalt–Phthalocyanine electrocatalysts for fuel cell applications
(2012)
For polymer–electrolyte–membrane fuel cells (PEM-FC), platinumcatalysts 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 X-ray 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 °C show graphite-like, formally pyrrolic and pyridinic like features, without any significant contri-bution 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 par-ticles become oxidized upon contact with air.
We show recent results of our in-situ investigations where the role of substrate chemistry in ALD is outlined. While the usual strategy to develop new properties of ALD films is to find new precursors or new procedures, the influence of substrate chemistry on the growth properties of ALD films has been often underestimated. This has principally a technical reason, as the usual characterization methods (QMS, FTIR, ellipsometry) are only weakly sensitive to the substrate, and a characterization of substrates before ALD is often not possible. Thanks to the use of in-situ characterization methods, including photoemission and X-ray absorption spectroscopy with synchrotron radiation, we are able to determine chemical properties of substrates before ALD and after either half or complete ALD cycles. The substrate chemistry influences the standard Al2O3 ALD with TMA and water [1,2], as well as the TiO2 ALD with TTIP and either water, O2 or O2-plasma.
[1] M. Tallarida, K. Kukli, M. Michling, M. Ritala, M. Leskelä and D. Schmeisser, Chem. Mater. 23, 3159 (2011);
[2] M. Tallarida, C. Adelmann, A. Delabie, S. van Elshocht, M. Caymax, and D. Schmeisser, Appl. Phys. Lett. 92, 042906 (2011).
In this contribution we report on the electronic structure of highly oriented pyrolitic graphite (HOPG). HOPG is a model system because of the clear separation between π- and σ-bands in the valence band regime. X-ray based measurements were done at the U49/2-PGM2 beam line at BESSYII in Berlin. The resonant photoemission spectra (resPES) at the carbon K-edge give a complete picture of the occupied and unoccupied states in these sp2 hybridized system. Above the K-edge the resPES data are dominated by the Auger process causing a C2p4 final state. The Auger lines appear at constant kinetic energy (spectator, 2h) or constant binding energy (participator, 1h). For the features right at the resonance we observe a different Auger decay mechanism. We attribute it to the decay out of an excitonic intermediate state with a long lifetime. It involves three valence hole states. The original primary core hole is filled by a normal KLL Auger decay. The excited electron rests in the excitonic intermediate state and decays later. We discuss the spectral features of such combined spectator-participator decays in detail which are found only close to resonance and only in the localized valence states of excitonic excitation i.e.C1s - 1π* transitions [1, 2, 3]. [1] Richter et al. (2011) BioNanoScience, submitted. [2] Michling et al. (2011) IOP C Ser Mater Sci Eng, submitted. [3] Schmidt et al. (2011) Solid State Ionics, submitted.
The conductivity of polyimide layers can be modified by several orders of magnitude by ion beam radiation. In order to understand the electronic structure of the pure polyimide before ion beam modification we focus in our preliminary experiments on spectroscopic investigations of thin as prepared polyimide films. The films were made by spin coating from a PMDA/ODA solution with subsequent vacuum annealing at 350°C. The layer thickness can be controlled by changing the concentration of PMDA/ODA in the solution realizing a thickness down to 3.5nm. For the characterization of the as prepared thin polyimide films the techniques NEXAFS, ResPES, XPS and CIS were applied at the U49/2-PGM2 beam line of Bessy II, Berlin. Our data including the valence band, core levels and absorption spectrum were compared with theoretical LCAO calculations. Based on these results we are able to attribute all spectral features to the specific atomic bonds in the molecule.
We present a study of the initial growth of TiO2 on Si(111) by atomic layer deposition (ALD). The Si substrate was etched with NH4F before ALD to remove the native oxide film and to produce a Si-H termination. In−situ experiments by means of photoemission and X-ray absorption spectroscopy were conducted with synchrotron radiation on Ti-oxide films produced using Ti-tetra-iso-propoxide (TTIP) and water as precursors. O1s, Ti2p, C1s, and Si2p core level, and O1s and Ti2p absorption edges show the transition of the Ti-oxide properties during the first layers. The growth starts with a very small growth rate (0.03nm/cycle) due to the growth inhibition of the Si-H termination and proceeds with higher growth rate (0.1nm/cycle) after 1.5nm Ti-oxide has been deposited.
Investigations of the electronic structure and composition of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) based films using Near Edge X-Ray Absorption Fine Structure (NEXAFS) are presented. The measurements were performed at the U49/2-PGM2 beam line of BESSY II, Berlin recording TEY (total electron yield) and TFY (total fluorescence yield) data. Samples prepared by spin coating a mixture of P3HT dissolved in chloroform and PCBM dissolved in chlorobenzene onto ITO (indium tin oxide) coated glass slides were analyzed. Upon measuring the pure P3HT and PCBM, all reported excitations were observed, whereas the blended system is a weighted superposition of the related peaks. Analyzing the data we calculate the composition of the mixture. We also show angular dependent NEXAFS measurements of the P3HT/PCBM blend in order to measure the orientation and distribution of the P3HT polymer. Additionally, we show a new approach for organic solar cell application. BaTiO3 nanoparticles were incorporated as nanodispersion into the donor-acceptor blend or the ferroelectric copolymer poly(vinylidene fluoride trifluoroethylene) (P(VDF-TrFE)) was spincoated as an ultrathin film below the blend.