We have investigated the interaction and orientation of a strongly dipolar zwitterionic p-benzoquinonemonoimine-type molecule, with a large intrinsic dipole of 10 Debye, on both conducting and on polar insulating substrates. Specifically, we deposited (6Z)-4-(butylamino)-6-(butyliminio)-3-oxocyclohexa-1,4-dien-1-olate C(6)H(2)([horiz bar, triple dot above]NHR)(2)([horiz bar, triple dot above]O)(2) where R = n-C(4)H(9), on both gold and ferroelectric lithium niobate surfaces. An influence of both transient and static electric dipoles on the zwitterionic adsorbate has been observed. For adsorption on gold, we find that the molecule bonds to the surface through the nitrogen atoms, forming films that remain fairly uniform down to thicknesses in the 1 nm range. Adsorption of this zwitterionic compound from solution on insulating, periodically poled ferroelectric lithium niobate substrates, showed preferential adsorption on one type of ferroelectric domain. For both gold and the lithium niobate substrates, the zwitterion adopts a preferential orientation with the plane of its "C(6) core" along the surface normal. This simplified geometry of strong dipole alignment provides a symmetry simplification allowing better identification of the vibrational modes responsible for Frank-Condon scattering revealed in the fine spectroscopic signature in the photoemission spectrum.
Environmentally persistent free radicals (EPFRs) are toxic organic/metal oxide composite particles that have been discovered to form from substituted benzenes chemisorbed to metal oxides. Here, we perform photoelectron spectroscopy, electron energy loss spectroscopy, and low energy electron diffraction of phenol chemisorbed to ZnO(1 0 1̱ 0) and (0 0 0 1̱)-Zn to observe electronic structure changes and charge transfer as a function adsorption temperature. We show direct evidence of charge transfer from the ZnO surfaces to the phenol. This evidence can help gain a better understanding of EPFRs and be used to develop possible future remediation strategies.
Brand, Jennifer I.; and Dowben, Peter A., "The local structure of transition metal doped semiconducting boron carbides" (2010 Abstract Transition metal doped boron carbides produced by plasma enhanced chemical vapour deposition of orthocarborane (closo-1,2-C 2 B 10 H 12 ) and 3d metal metallocenes were investigated by performing K-edge extended x-ray absorption fine structure and x-ray absorption near edge structure measurements. The 3d transition metal atom occupies one of the icosahedral boron or carbon atomic sites within the icosahedral cage. Good agreement was obtained between experiment and models for Mn, Fe and Co doping, based on the model structures of two adjoined vertex sharing carborane cages, each containing a transition metal. The local spin configurations of all the 3d transition metal doped boron carbides, Ti through Cu, are compared using cluster and/or icosahedral chain calculations, where the latter have periodic boundary conditions.
Transition-metal (TM)-doped solids are one of the most extensively studied compounds in the fields of catalysis, magnetism, solar cells, etc., due to their tunable optoelectronic properties that stem from TM energy-level hybridization. In this work, the hybridization of the Ni–O bond in TiO2:Ni films was controlled in a stable, reversible manner via surface functionalization with polarized molecules. The Ni-doped TiO2 surface was functionalized with para-benzoic acid groups to modify the electron density distribution within the film. The dopant distribution and elemental composition at the interface are probed via high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy mapping. The effect of the surface modification on the dopant, Ni2+, is studied via surface-sensitive electronic characterization techniques, such as X-ray photoelectron spectroscopy and soft X-ray absorption spectroscopy (XAS). The electron density in the valence orbitals of the dopant was observed to be a function of the dipole moment of the para-substituted benzoic acid. The resulting XAS spectra of the Ni2+ after surface modification of TiO2:Ni films were modeled (CTM4XAS) and indicated ligand-dependent symmetry breaking around the Ni2+ at the functionalized interface. Therefore, the modified electron density at the interface due to the polarized molecules is observed to impact the hybridization of the TM dopant energy levels in solid hosts. This phenomenon of adaptive dopant hybridization in a solid host (TiO2) can be exploited to obtain tunable optical responses from TM-doped inorganic phosphors, which have an impact in various fields, such as luminescent displays, solar cells, sensors, telecommunications, counterfeit technologies, and biodetection.
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