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X-ray excited optical luminescence (XEOL) and x-ray absorption near-edge structure in total electron, x-ray fluorescence, and photoluminescence yields at Sn M5,4-, O K-, and Sn K-edges have been used to study the luminescence from SnO2 nanoribbons. The effect of the surface on the luminescence from SnO2 nanoribbons was studied by preferential excitation of the ions in the near-surface region and at the normal lattice positions, respectively. No noticeable change of luminescence from SnO2 nanoribbons was observed if the Sn ions in the near-surface region were excited selectively, while the luminescence intensity changes markedly when Sn or O ions at the normal lattice positions were excited across the corresponding edges. Based on the experimental results, we show that the luminescence from SnO2 nanoribbons is dominated by energy transfer from the excitation of the whole SnO2 lattice to the surface states. Surface site specificity is not observable due to its low concentration and weak absorption coefficient although the surface plays an important role in the emission as a luminescence center. The energy transfer and site specificity of the XEOL or the lack of the site specificity from a single-phase sample is discussed. [ABSTRACT FROM AUTHOR]

The interfaces of In[sub 2]O[sub 3], a model for indium-tin-oxide (ITO), with benzene, thiophene, and benzaldehyde, models for technologically important organic molecules, are studied using angle resolved ultraviolet photoemission and work function measurements. Band alignment diagrams for hypothetical Al/organic/ITO devices have been drawn, using values determined from this work and previously published studies of these molecules on Al(111). The similarity between the bonding of benzene and thiophene on Al(111) and In[sub 2]O[sub 3], i.e., largely electrostatic, leads to near identical alignment at both metal and oxide interfaces. This indicates that clean Al and ITO will make a very poor electron/hole injecting pair. We suggest that the apparent efficiency of Al as an electron injecting contact in real devices is due to the presence of oxygen at the Al/organic interface. For benzaldehyde the interaction with In[sub 2]O[sub 3] is largely electrostatic, in contrast to the covalent bonds formed on Al(111). This leads to very different alignment at the Al and oxide interfaces, showing the importance of the particular organic-inorganic interaction in determining band alignment. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Canadian Light Source (CLS) is Canada's national synchrotron radiation facility. The CLS mission statement includes a mandate to “participate actively in educational, social and cultural development of our communities.” Over 6,000 people annually, more than half of them school children, tour the CLS. This is facilitated by the design of the building, which has a mezzanine affording panoramic views of the accelerators and experimental floor (see Figure 1). CLS staff have presented to more than a thousand educators through various professional development sessions, and for these educators classroom resource material is made available for easy inclusion in daily lessons where possible. The CLS also hosts an annual workshop for teachers where, since 2006, more than one hundred teachers have spent several days at CLS becoming familiar with the facility. [ABSTRACT FROM AUTHOR]

The quantity and quality of soil organic N and C are strongly influenced by variations in landscape position and management practices such as cultivation. In this study, we used synchrotron-based C and N K-edge x-ray absorption near-edge structure (XANES) spectroscopy coupled with pyrolysis-field ionization mass spectrometry (Py-FIMS) to explore C and N chemistry among soils obtained from different landscape positions along a hummocky transect and from locations under different management practices. A distinct landscape pattern in soil organic matter (SOM) functionality was observed, but only a small effect of management (cultivated vs. uncultivated) was detected. We observed that both carbohydrates and low-molecular-weight aromatics, which are usually considered readily degradable, were apparently stabilized in divergent (i.e., water-shedding) slope positions, while lipids and high-molecular-weight lignins were enriched in depressional areas. We posit that tillage incorporation was probably responsible for the enrichment of older, microbially altered carbohydrates and lignins at divergent positions. Using novel application of nonmetric multidimensional scaling ordination to XANES data, we observed more heterocyclic N compounds in cultivated vs. uncultivated soils. The XANES data 'also showed the presence of unique, oxidized N-bonded aromatics, which predominated at calcareous divergent slope positions. These types of organic N compounds are rarely reported in the literature except for samples obtained in acidic or anaerobic environments. This study provides analytical evidence that C and N K-edge XANES and Py-FIMS differentiate SOM composition at the molecular level from soils obtained from diverse topographic positions and management regimes in a hummocky prairie landscape. Results provide complementary evidence that SOM comprises more stabilized compounds at divergent slope positions and more active compounds at depressional positions. [ABSTRACT FROM AUTHOR]

The rhizosphere is a region of complex interactions among plants, soil, and microbiota and by its very nature, it presents many technical challenges to the analyst. Whereas previous studies have generally focused on root exudation in artificial systems, we compared whole-soil samples from bulk and rhizosphere soils developed under field pea (Pisum sativa L.). Synchrotron-based C and N K-edge x-ray absorption near-edge structure (XANES) spectroscopy and pyrolysis field-ionization mass-spectrometry (Py-FIMS) were used to investigate plant effects on the organic chemistry of the rhizosphere in a growth chamber experiment. Soil type appeared to play a significant role in the development of the rhizosphere. Indeed, the C and N K-edge XANES analyses revealed patterns of rhizosphere development that were strongly influenced by soil type. Relative to the bulk soil, pea rhizospheres developed on a clay soil showed increases in hetcrocyclic N compounds, proteins, and carboxylates. Pea rhizospheres developed on a sandy clay loam soil showed increased nitroaromatic compounds and reduced aromatics, while proteins, carbohydrates, and carboxylic compounds remained unchanged relative to the bulk soils. Pyrolysis mass spectrometry results showed that rhizosphere processes promote selective enrichment of lipid compounds (alkanes, alkenes, alkylamides, alkylaromatics, and alkyl, benzoic, and phthalic esters) with a concomitant depletion of carbohydrates, proteins, phenols, and lignins. These results suggest enhanced decomposition of labile organic matter at a molecular level in the rhizosphere, presumably as a result of enhanced microbial activity. The presence of nitroaromatic and alkylamide compounds in the rhizosphere indicates a unique cycling of N in this region. Synchrotron-based analysis of whole soils offers useful, corroborating information regarding the organic chemistry of the rhizosphere when compared with established pyrolytic techniques. [ABSTRACT FROM AUTHOR]

Eu doped rare-earth orthovanadates are known to be good red phosphor materials. In particular, LaVO4:Eu is a promising candidate due to the low Eu-site point symmetry, and thus high dipole transition probability within Judd-Ofelt theory. However, the low solubility limit (<3 mol %) of Eu in LaVO4 prevents its efficient use as a phosphor. We present optical evidence of enhanced Eu solubility as high as 10 mol % in LaVO4:Eu thin films grown by pulsed laser deposition and postannealing. The photoluminescent intensity exceeded that of YVO4:Eu thin films when excited below the host bandgap, indicating stronger direct emission of Eu in LaVO4. [ABSTRACT FROM AUTHOR]

We present an x-ray absorption study of the dependence of the V oxidation state on the thickness of LaVO3 (LVO) and capping LaAlO3 (LAO) layers in the multilayer structure of LVO sandwiched between LAO. We found that the change of the valence of V as a function of LAO layer thickness can be qualitatively explained by a transition between electronically reconstructed interfaces and a chemical reconstruction. The change as a function of LVO layer thickness is complicated by the presence of a considerable amount of V4+ in the bulk of the thicker LVO layers. [ABSTRACT FROM AUTHOR]

Time-resolved x-ray excited optical luminescence (XEOL) and x-ray absorption near edge structures have been employed to study the origin of the multicolor luminescence from SnO2 nanoribbons. The authors find that the yellow-green luminescence has a long lifetime while the blue luminescence a short one. The luminescence is attributed to the radiative decay of trapped electrons in oxygen vacancies just below the conduction band and electrons in the conduction band to intrinsic surface states in the band gap. [ABSTRACT FROM AUTHOR]

We report on white electroluminescence (EL) emission from a single-layer light-emitting diode based on a binary blend of organic soluble blue-emitting molecules, i.e., a diamine derivative and a substituted thiophene-1,1-dioxide. Weakly voltage-dependent white color, of coordinates (0.39, 0.40) according to the standard of the Commission Internationale de l'Eclairage, is obtained from the superposition of the blue emission from the donor and a low-energy peak due to a charge-transfer complex between the two molecules (exciplex). The EL spectrum is broader and more structured than the photoluminescence one: this could be due to the activation of exciplexes with different conformations as inferred from quantum-chemistry calculations. [ABSTRACT FROM AUTHOR]

The adsorption of thiophene and 2, 2′-bithiophene on Al(111) has been studied using thermal desorption spectroscopy (TDS), angle-resolved UV photoemission (ARUPS), and work function measurements. Ab initio density functional theory calculations have been performed for thiophene on Al(111). Both thiophene and bithiophene bond only very weakly to Al(111), as indicated by TDS and calculations of the thiophene absorption energy, which is found to be only 0.54 eV. There is no indication of π-bonding in either the ARUPS data or the calculations. The calculated S-Al distance, 3.7 Å, is much greater than either measured or calculated S-metal distances for covalent bonding. The bonding is shown to be almost entirely electrostatic, with a small contribution from the sulfur lone pair. This is in direct contrast to calculations for Al-thiophene complexes which show covalent bonds between the Al atoms and the thiophene α carbons. The calculations show the molecule to be essentially flat, with a tilt angle of only 2° of the molecular plane relative to the surface. There is some indication of self-assembly of bithiophene on Al(111). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We show that all possible binary combinations of molecules from four different families of organics—a diamine derivative, N,N′-bis(3methylphenyl)-N,N′-diphenylbenzidine, an oxidiazole derivative, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, a substituted thiophene dioxide, 2,5-bis(trimethylsilyl thiophene)-1,1-dioxide, and poly(9-vinylcarbazole)—produce white or near-white emission. We suggest that this is due to exciplex formation, and that this is likely to be a general phenomenon for blends of blue-emitting aromatic organics. This implies that films of spin-coated blends of blue-emitting organics represent a general, simple, and cheap route to white-emitting organic light-emitting diodes. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The presence of adventitious oxygen is inevitable when organic/metal interfaces are formed by evaporation in high vacuum (10[sup -6] mbar.). In this letter, we highlight the importance of this oxygen for band alignment, and hence, performance, in organic-based devices. The influence of controlled amounts of oxygen on band alignment in benzene/aluminum model cathode interfaces has been studied using ultraviolet photoemission in ultrahigh vacuum. We show that even small amounts of oxygen significantly lower the aluminum work function with concomitant improvement in band alignment. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The band alignment of the bithiophene interface with a diverse range of substrates has been determined by a combination of ultraviolet photoemission and work function measurements. Not only is vacuum level alignment clearly shown to be invalid but also any sort of linear relationship between band alignment and substrate work function is shown not to be the case. Rather, the alignment is determined by the interface dipole, which is specific to the interaction at the inorganic-organic interface. The interface dipoles, which always appear, while dominated by the first monolayer interaction, are completed after two to three monolayers. As the ionization potentials of the films are shown to be constant, it is argued that a simple work function measurement, for an organic film on a particular substrate, quantifies the band alignment. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]