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Physics of thin-film ferroelectric oxides

This review covers the important advances in recent years in the physics of thin film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin film form. We introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this we cover the enormous progress that has been made in the first principles computational approach to understanding ferroelectrics. We then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, we look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in non conventional nanoscale geometries.Comment: This is an invited review for Reviews of Modern Physics. We welcome feedback and will endeavour to incorporate comments received promptly into the final versio

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Functional characterisation of murine gammaherpesvirus 68 glycoprotein 150

Murine gammaherpesvirus 68 (MHV-68) is a B cell tropic pathogen of small rodents which shares genetic and pathobiological similarities with Epstein-Barr virus (EBV) and Kaposi's sarcoma associated herpesvirus (KSHV). Unlike EBV and KSHV, MHV-68 replicates well in vitro and infects inbred mice making it a valuable and amenable model for the study of gammaherpesvirus replication and their interaction with the host. Glycoprotein 150 (gpl50) is a virion membrane glycoprotein of MHV-68 that shares similarities with gp340/220 a membrane glycoprotein of EBV which facilitates EBV attachment to B cells. Antibodies against gpl50 have been reported to neutralise MHV-68 infection. The aim of this study was to determine the function of gpl50 and latterly to assess the potential of gpl50 as a vaccine antigen to prime and protect inbred mice against MHV-68 infection. For functional studies of gpl50 two main strategies were adopted; (i) the production of a recombinant virus in which the gene encoding gpl50 is made dysfunctional resulting in a gpl50 'knockout' (KO) virus and (ii) generation and use of purified gpl50 in cell binding studies to determine if gpl50 can bind to cells. Recombinant viruses were generated; virus induced plaques expressing the green fluorescent protein, used as a marker gene for identification of recombinant viruses, were observed. However, no viruses in which the required deletion of the gpl50 gene had occurred were isolated. A gpl50-His fusion protein (gpl50-His) consisting of the extracellular domain of gpl50 attached to a hexahistidine residue was successfully cloned, expressed in bacteria and purified. Similarly, a glutathione-S-transferase-His (GST-His) fusion protein was generated to be used as a control in binding studies. No significant binding of gpl50-His to murine epithelial cells was detected in an enzyme linked immunosorbent assay (ELISA) or by fluorescent associated cell sorting (FACS) analysis. In contrast, significant binding of gpl50-His to primary splenocytes was shown by FACS analysis. Gpl50-His also bound to purified splenic B cells and both CD19+ (B cells) and CD 19" splenocytes. Antibodies against gpl50 failed to block binding of MHV-68 to murine epithelial cells. Results indicate that gpl50-His binds the heterogeneous splenic cell population as a whole i.e. not a particular subset of lymphocytes. This suggests gpl50 may interact with a ubiquitous cell surface protein or perhaps a protein specific to leukocytes and could be involved in MHV-68 attachment to these cells. Gene gun nucleic acid immunisation of inbred mice with a plasmid encoding gpl50 under the control of a constitutive promoter, alone or in combination with a recombinant vaccinia virus expressing gpl50 (VVᵍᵖ¹⁵⁰) was undertaken followed by intranasal challenge with MHV-68. Virus specific antibody appeared earlier in the group that received gpl50 DNA plus VVᵍᵖ¹⁵⁰. The groups that received gpl50 DNA in conjunction with either VVᵍᵖ¹⁵⁰ or a control vaccinia virus (VVgpt) appeared to have reduced levels of latently infected cells in the spleen day 15 post infection and reduced splenomegaly (a phenomenon of MHV-68 infection) in comparison with control mice. This could indicate that vaccinia virus, in a non-specific manner, boosts the specific immune response to previously administered DNA and in this case was able to limit the level of MHV-68 reaching the spleen. However, this vaccine regimen failed to significantly alter the level of infectious virus in the lung or prevent the establishment of latent virus in the spleen

Statistical switching kinetics in ferroelectrics

By assuming a more realistic nucleation and polarization reversal scenario we build a new statistical switching model for ferroelectrics, which is different from either the Kolmogorov-Avrami-Ishibashi (KAI) model or the Nucleation-Limited-Switching (NLS) model. After incorporating a time-dependent depolarization field this model gives a good description about the retardation behavior in polycrystalline thin films at medium or low fields, which can not be described by the traditional KAI model. This model predicts correctly n=1 for polycrystalline thin films at high Eappl or ceramic bulks in the ideal case

Unusual behaviour of the ferroelectric polarization in PbTiO3_{3}/SrTiO3_{3} superlattices

Artificial PbTiO$_{3}$/SrTiO$_{3}$ superlattices were constructed using off-axis RF magnetron sputtering. X-ray diffraction and piezoelectric atomic force microscopy were used to study the evolution of the ferroelectric polarization as the ratio of PbTiO$_{3}$ to SrTiO$_{3}$ was changed. For PbTiO$_{3}$ layer thicknesses larger than the 3-unit cells SrTiO$_{3}$ thickness used in the structure, the polarization is found to be reduced as the PbTiO$_{3}$ thickness is decreased. This observation confirms the primary role of the depolarization field in the polarization reduction in thin films. For the samples with ratios of PbTiO$_{3}$ to SrTiO$_{3}$ of less than one a surprising recovery of ferroelectricity that cannot be explained by electrostatic considerations was observed