Search

Ferroelectric polarization in thin films is stabilized by screening charges in the metal electrodes. Imperfect screening of the polarization charge strongly modifies the film's capacitance and should lead to a variation of the Schottky barrier height at the interface with polarization direction. An experimental approach based on photoelectron spectroscopy is introduced which allows us to quantitatively determine Schottky barrier heights at ferroelectric/metal interfaces in dependence on polarization. The procedure is exemplified for BaTiC>3 single crystals with Ru02 and Pt electrodes, revealing a variation of Schottky barrier height of 1.1 and 0.65 eV in dependence on polarization for Ru02 and Pt electrodes, respectively. Inhomogeneous barrier switching is observed for Pt electrodes, which may be related to defect formation during metal deposition. [ABSTRACT FROM AUTHOR]

The chemical and electronic properties of tin-doped indium oxide (ITO) surfaces and its interface with zinc phthalocyanine (ZnPc) were investigated using photoelectron spectroscopy partly excited by synchrotron radiation from the BESSY II storage ring. Preparation and analysis of ITO and ITO/ZnPc layer sequences were performed in-situ without breaking vacuum. The Fermi level position at the ITO surface varies strongly with oxygen content in the sputter gas, which is attributed to an increase of surface band bending as a consequence of the passivation of the metallic surface states of ITO. The shift of the Fermi level is accompanied by a parallel increase of the work function from 4.4 to ∼5.2 eV. No changes in the surface dipole are observed with an ionization potential of IP = 7.65 ± 0.1 eV. The barrier height for hole injection at the ITO/ZnPc interface does not vary with initial ITO work function, which can be related to different chemical reactivities at the interface. [ABSTRACT FROM AUTHOR]

In situ x-ray photoelectron spectroscopy was employed to examine the change in Schottky barrier height at BaTiO3/RuO2 interfaces upon polarisation reversal for [1 0 0], [1 1 0] and [1 1 1] oriented BaTiO3 single crystals. Compared to previous measurements on BaTiO3/RuO2 interfaces (Chen and Klein 2012 Phys. Rev. B 86 094105), the crystals exhibit a significantly reduced dependence of barrier height on polarisation direction. This is connected to a much higher polarisation of the present cystals, which is comparable to the accepted bulk polarisation of BaTiO3 of and which exhibit the expected dependence on crystal orientation. This indicates a much higher crystal quality in the present experiments, which is also confirmed by a Kolmogorov–Avrami–Ishibashi like polarisation switching dynamics. It is observed that is reduced for the [1 1 0] and [1 1 1] orientation and scales with polarisation as long as crystals from the same batch are used. The fact, that a poor polarisation hysteresis behaviour relates to a high polarisation dependence of Schottky barrier height, indicates that the electrode’s ability to screen ferroelectric polarisation charges depends sensitively on crystal and/or interface quality. [ABSTRACT FROM AUTHOR]

The current transport through (Ba,Sr)TiO3 (BST)/Al2O3 bilayer structures with Pt electrodes is studied using current–voltage measurements. Due to its low permittivity compared to BST the Al2O3 layer, which is deposited by atomic layer deposition (ALD), enables electron injection by tunneling at low thickness, such that transport becomes limited by the bulk conductivity of BST. A current rectification of up to 106 is observed at an Al2O3 thickness of 1.8 nm, indicating that hole transport does not contribute to the current. The measurements are complemented by the determination of the energy band alignment at the interface using photoelectron spectroscopy. A Fermi level pinning in the Al2O3 layer, which seems to be characteristic for ALD films, leads to a significant modification of the energy band alignment. This pinning does not prohibit electron injection, which relies on the potential drop across the Al2O3 layer. [ABSTRACT FROM AUTHOR]

Our studies provide direct evidence that O-glycosylation pathways play a role in the regulation of cell growth through apoptosis and proliferation pathways. A series of small molecular weight analogs of the GalNAc-α-1-O-serine/threonine structure based on 1-benzyl-2-acetamido-2-deoxy-α-O-d-galactopyranoside have been synthesized and tested in the human colorectal cancer cell lines PC/AA/C1/SB10C and HCA7/C29. Three inhibitors, 1-benzyl-2-acetamido-2-deoxy-α-O-d-galactopyranoside, and the corresponding 2-azido- and C-glycoside analogs were screened in these colorectal cancer cell lines at 0.5 mM and showed induction of apoptosis and downregulation of proliferation. Treatment of both cell lines with inhibitors led to changes in glycosylation detected with peanut lectin. The inhibition of glycosyltransferase activity in cell homogenates from human colorectal mucosal cells and cultured cell lines could be shown. The competitive action of the inhibitors resulted in the intracellular formation of 28 aryl-glycan products which were identified by MALDI and electrospray mass spectroscopy. The structures showed a differential pattern for each of the inhibitors in both cell lines. Gene array analysis of the glycogenes illustrated a pattern of glycosyltransferases that matched the glycan structures found in glycoproteins and aryl-glycans formed in the PC/AA/C1/SB10C cells; however, there was no action of the three inhibitors on glycogene transcript levels. The inhibitors act at both intermediary metabolic and genomic levels, resulting in altered protein glycosylation and aryl-glycan formation. These events may play a part in growth arrest. [ABSTRACT FROM AUTHOR]