Vibrational - Electrical Properties Relationship in Donor Doped TiO2 by Raman Spectroscopy

Transparent conducting TiO2, obtained by Nb or Ta doping of the anatase structure, is gaining increasing attention for the development of transparent electrodes. Usually, regardless the deposition technique, a crystallization process in reducing atmosphere is necessary to achieve large mobility; in addition, electrical and optical properties are also strongly sensitive to the oxygen deposition pressure. These facts reveal that the defect chemistry of donor doped TiO2 is not trivial and involves a strict interplay among extrinsic dopant atoms, oxygen vacancies and ‘electron killer’ defects such as Ti vacancies and O interstitials. We here present a Raman characterization of donor-doped TiO2 films synthesized under several deposition and post-annealing conditions, employing different doping levels and dopant elements (i.e. Ta and Nb). Correlations between structure, crystallinity, shift and width of Raman peaks and electrical properties are shown and discussed. In particular, a clear relationship between the shift of the Eg(1) anatase Raman mode and the charge carrier density is found, while the B1g(1) mode connected to Ti-Ti vibrations is significantly affected by the extrinsic doping level. In this complex framework Raman spectroscopy can provide an invaluable contribution towards understanding the material structure and its influence on the functional properties

Quantum inelastic conductance through molecular wires

We calculate non-perturbatively the inelastic effects on the conductance through a conjugated molecular wire-metal heterojunction, including realistic electron-phonon coupling. We show that at sub-band-gap energies the current is dominated by quantum coherent transport of virtual polarons through the molecule. In this regime, the tunneling current is strongly increased relative to the case of elastic scattering. It is essential to describe the full quantum coherence of the polaron formation and transport in order to obtain correct physics. Our results are generally applicable to one-dimensional atomic or molecular wires.Comment: 4 pages, 4 figures, accepted for publication in Physical Review Letter

Tuning of Electrical and Optical Properties of Highly Conducting and Transparent Ta-Doped TiO2 Polycrystalline Films

We present a detailed study on polycrystalline transparent conducting Ta-doped TiO2 films, obtained by room temperature pulsed laser deposition followed by an annealing treatment at 550°C in vacuum. The effect of Ta as a dopant element and of different synthesis conditions are explored in order to assess the relationship between material structure and functional properties, i.e. electrical conductivity and optical transparency. We show that for the doped samples it is possible to achieve low resistivity (of the order of 5×10-4 Ωcm) coupled with transmittance values exceeding 80% in the visible range, showing the potential of polycrystalline Ta:TiO2 for application as a transparent electrode in novel photovoltaic devices. The presence of trends in the structural (crystalline domain size, anatase cell parameters), electrical (resistivity, charge carrier density and mobility) and optical (transmittance, optical band gap, effective mass) properties as a function of the oxygen background pressures and laser fluence used during the deposition process and of the annealing atmosphere is discussed, and points towards a complex defect chemistry ruling the material behavior. The large mobility values obtained in this work for Ta:TiO2 polycrystalline films (up to 13 cm2V-1s-1) could represent a definitive advantage with respect to the more studied Nb-doped TiO2

Soliton effects in dangling-bond wires on Si(001)

Dangling bond wires on Si(001) are prototypical one dimensional wires, which are expected to show polaronic and solitonic effects. We present electronic structure calculations, using the tight binding model, of solitons in dangling-bond wires, and demonstrate that these defects are stable in even-length wires, although approximately 0.1 eV higher in energy than a perfect wire. We also note that in contrast to conjugated polymer systems, there are two types of soliton and that the type of soliton has strong effects on the energetics of the bandgap edges, with formation of intra-gap states between 0.1 eV and 0.2 eV from the band edges. These intra-gap states are localised on the atoms comprising the soliton.Comment: 6 pages, 3 figures, 3 tables, submitted to Phys. Rev.

Coherent electron-phonon coupling and polaron-like transport in molecular wires

We present a technique to calculate the transport properties through one-dimensional models of molecular wires. The calculations include inelastic electron scattering due to electron-lattice interaction. The coupling between the electron and the lattice is crucial to determine the transport properties in one-dimensional systems subject to Peierls transition since it drives the transition itself. The electron-phonon coupling is treated as a quantum coherent process, in the sense that no random dephasing due to electron-phonon interactions is introduced in the scattering wave functions. We show that charge carrier injection, even in the tunneling regime, induces lattice distortions localized around the tunneling electron. The transport in the molecular wire is due to polaron-like propagation. We show typical examples of the lattice distortions induced by charge injection into the wire. In the tunneling regime, the electron transmission is strongly enhanced in comparison with the case of elastic scattering through the undistorted molecular wire. We also show that although lattice fluctuations modify the electron transmission through the wire, the modifications are qualitatively different from those obtained by the quantum electron-phonon inelastic scattering technique. Our results should hold in principle for other one-dimensional atomic-scale wires subject to Peierls transitions.Comment: 21 pages, 8 figures, accepted for publication in Phys. Rev. B (to appear march 2001

Lactate Regulates Metabolic and Proinflammatory Circuits in Control of T Cell Migration and Effector Functions

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Atomic-scale visualization of initial growth of homoepitaxial SrTiO3 thin film on an atomically ordered substrate

The initial homoepitaxial growth of SrTiO3 on a (\surd13\times\surd13) - R33.7{\deg}SrTiO3(001) substrate surface, which can be prepared under oxide growth conditions, is atomically resolved by scanning tunneling microscopy. The identical (\surd13\times\surd13) atomic structure is clearly visualized on the deposited SrTiO3 film surface as well as on the substrate. This result indicates the transfer of the topmost Ti-rich (\surd13\times\surd13) structure to the film surface and atomic-scale coherent epitaxy at the film/substrate interface. Such atomically ordered SrTiO3 substrates can be applied to the fabrication of atom-by-atom controlled oxide epitaxial films and heterostructures

MUC1-C Oncoprotein Regulates Glycolysis and Pyruvate Kinase m2 Activity in Cancer Cells

Aerobic glycolysis in cancer cells is regulated by multiple effectors that include Akt and pyruvate kinase M2 (PKM2). Mucin 1 (MUC1) is a heterodimeric glycoprotein that is aberrantly overexpressed by human breast and other carcinomas. Here we show that transformation of rat fibroblasts by the oncogenic MUC1-C subunit is associated with Akt-mediated increases in glucose uptake and lactate production, consistent with the stimulation of glycolysis. The results also demonstrate that the MUC1-C cytoplasmic domain binds directly to PKM2 at the B- and C-domains. Interaction between the MUC1-C cytoplasmic domain Cys-3 and the PKM2 C-domain Cys-474 was found to stimulate PKM2 activity. Conversely, epidermal growth factor receptor (EGFR)-mediated phosphorylation of the MUC1-C cytoplasmic domain on Tyr-46 conferred binding to PKM2 Lys-433 and inhibited PKM2 activity. In human breast cancer cells, silencing MUC1-C was associated with decreases in glucose uptake and lactate production, confirming involvement of MUC1-C in the regulation of glycolysis. In addition, EGFR-mediated phosphorylation of MUC1-C in breast cancer cells was associated with decreases in PKM2 activity. These findings indicate that the MUC1-C subunit regulates glycolysis and that this response is conferred in part by PKM2. Thus, the overexpression of MUC1-C oncoprotein in diverse human carcinomas could be of importance to the Warburg effect of aerobic glycolysis