The structure of two new non-centrosymmetric phases of oxygen deficient bismuth manganite

The structure of two new phases in the bismuth manganite system are reported. The phases were determined by electron diffraction studies of two oxygen-deficient bulk samples. The first phase, a minority component of bulk BiMnO2.94 forms a n=2 Ruddlesden-Popper phase with space group Cmc21 . The second phase, from bulk BiMnO2.99 , is an orthorhombic structure with spacegroup Pmn21 and a unit cell approximately equal to 4 × √ 2 × 2 √ 2 times the parent perovskite cell. Importantly both phases are non-centrosymmetric and offer further potential for multiferroic studies.The authors would like to thank EPSRC for financial support for this work through grant EP/H017712

Notícia de dues tesis doctorals llegides en 2016 sobre Curial e Güelfa, els lectors i els contextos de lectura del segle xv

Notícia de dues tesis doctorals llegides en 2016 sobre Curial e Güelfa, els lectors i els contextos de lectura del segle x

Rebels on trial! The configuration of the enemy in the Comentarios of Álvar Núñez Cabeza de Vaca

En 1545, el segundo gobernador de la provincia del Río de la Plata, Álvar Núñez Cabeza de Vaca, regresa a España engrillado y con catorce pliegos de acusaciones a sus espaldas. Tras un largo pleito, que acaba con la absolución del imputado, Cabeza de Vaca decide contar su versión de los hechos publicando sus Comentarios (1555). Este texto supone el punto final de su defensa, pero también un juicio público que vuelve las tornas y sienta en el banquillo de los acusados a sus enemigos capitales. En este artículo se analizará cómo se configura la imagen de los rebeldes desde una perspectiva que se presenta como única portadora de los valores civilizadores en aquellas lejanas tierras carentes de todo orden conocido.En 1545, el segundo gobernador de la provincia del Río de la Plata, Álvar Núñez Cabeza de Vaca, regresa a España engrillado y con catorce pliegos de acusaciones a sus espaldas. Tras un largo pleito, que acaba con la absolución del imputado, Cabeza de Vaca decide contar su versión de los hechos publicando sus Comentarios (1555). Este texto supone el punto final de su defensa, pero también un juicio público que vuelve las tornas y sienta en el banquillo de los acusados a sus enemigos capitales. En este artículo se analizará cómo se configura la imagen de los rebeldes desde una perspectiva que se presenta como única portadora de los valores civilizadores en aquellas lejanas tierras carentes de todo orden conocido.In 1545, the second governor of the province of the Rio de la Plata, Álvar Núñez Cabeza de Vaca, returns in shackles to Spain with fourteen sheets full of accusations. After a long litigation that finally ends with the absolution of the accused, Cabeza de Vaca decides to share his version publishing his Comentarios (1555). This text is the final point of his defense, but also a public process that turn the tables on his foremost enemies sending them to the bench of the accused. This paper will analyze how the rebels' image is set from the point of view that represents the only owner of civilizing powers in those far away lawless lands

Field Emission Properties and Fabrication of CdS Nanotube Arrays

A large area arrays (ca. 40 cm2) of CdS nanotube on silicon wafer are successfully fabricated by the method of layer-by-layer deposition cycle. The wall thicknesses of CdS nanotubes are tuned by controlling the times of layer-by-layer deposition cycle. The field emission (FE) properties of CdS nanotube arrays are investigated for the first time. The arrays of CdS nanotube with thin wall exhibit better FE properties, a lower turn-on field, and a higher field enhancement factor than that of the arrays of CdS nanotube with thick wall, for which the ratio of length to the wall thickness of the CdS nanotubes have played an important role. With increasing the wall thickness of CdS nanotube, the enhancement factorβdecreases and the values of turn-on field and threshold field increase

Annealing of gold nanostructures sputtered on polytetrafluoroethylene

Gold nanolayers sputtered on polytetrafluoroethylene (PTFE) surface and their changes induced by post-deposition annealing at 100°C to 300°C are studied. Changes in surface morphology and roughness are examined by atomic force microscopy, electrical sheet resistance by two point technique, zeta potential by electrokinetic analysis and chemical composition by X-ray photoelectron spectroscopy (XPS) in dependence on the gold layer thickness. Transition from discontinuous to continuous gold coverage takes place at the layer thicknesses 10 to 15 nm and this threshold remains practically unchanged after the annealing at the temperatures below 200°C. The annealing at 300°C, however, leads to significant rearrangement of the gold layer and the transition threshold increases to 70 nm. Significant carbon contamination and the presence of oxidized structures on gold-coated samples are observed in XPS spectra. Gold coating leads to a decrease in the sample surface roughness. Annealing at 300°C of pristine PTFE and gold-coated PTFE results in significant increase of the sample surface roughness

Chemically and thermally stable silica nanowires with a β-sheet peptide core for bionanotechnology

Background: A series of amyloidogenic peptides based on the sequence KFFEAAAKKFFE template the silica precursor, tetraethyl orthosilicate to form silica-nanowires containing a cross-β peptide core. Results: Investigation of the stability of these fibres reveals that the silica layers protect the silica-nanowires allowing them to maintain their shape and physical and chemical properties after incubation with organic solvents such as 2-propanol, ethanol, and acetonitrile, as well as in a strong acidic solution at pH 1.5. Furthermore, these nanowires were thermally stable in an aqueous solution when heated up to 70 °C, and upon autoclaving. They also preserved their conformation following incubation up to 4 weeks under these harsh conditions, and showed exceptionally high physical stability up to 1000 °C after ageing for 12 months. We show that they maintain their β-sheet peptide core even after harsh treatment by confirming the β-sheet content using Fourier transform infrared spectra. The silica nanowires show significantly higher chemical and thermal stability compared to the unsiliconised fibrils. Conclusions: The notable chemical and thermal stability of these silica nanowires points to their potential for use in microelectromechanics processes or fabrication for nanotechnological devices

Selective Deposition and Alignment of Single-Walled Carbon Nanotubes Assisted by Dielectrophoresis: From Thin Films to Individual Nanotubes

Dielectrophoresis has been used in the controlled deposition of single-walled carbon nanotubes (SWNTs) with the focus on the alignment of nanotube thin films and their applications in the last decade. In this paper, we extend the research from the selective deposition of SWNT thin films to the alignment of small nanotube bundles and individual nanotubes. Electrodes with “teeth”-like patterns are fabricated to study the influence of the electrode width on the deposition and alignment of SWNTs. The entire fabrication process is compatible with optical lithography-based techniques. Therefore, the fabrication cost is low, and the resulting devices are inexpensive. A series of SWNT solutions is prepared with concentrations ranging from 0.0125 to 0.2 mg/ml. The alignment of SWNT thin films, small bundles, and individual nanotubes is achieved under the optimized experimental conditions. The electrical properties of these samples are characterized; the linear current–voltage plots prove that the aligned SWNTs are mainly metallic nanotubes. The microscopy inspection of the samples demonstrates that the alignment of small nanotube bundles and individual nanotubes can only be achieved using narrow electrodes and low-concentration solutions. Our investigation shows that it is possible to deposit a controlled amount of SWNTs in desirable locations using dielectrophoresis