Patterning enhanced tetragonality in BiFeO3 thin films with effective negative pressure by helium implantation

Helium implantation in epitaxial thin films is a way to control the out-of-plane deformation independentlyfrom the in-plane strain controlled by epitaxy. In particular, implantation by means of a helium microscopeallows for local implantation and patterning down to the nanometer resolution, which is of interest for deviceapplications. We present here a study of bismuth ferrite (BiFeO3) films where strain was patterned locally byhelium implantation. Our combined Raman, x-ray diffraction, and transmission electron microscopy (TEM)study shows that the implantation causes an elongation of the BiFeO3unit cell and ultimately a transition towardsthe so-called supertetragonal polymorph via states with mixed phases. In addition, TEM reveals the onset ofamorphization at a threshold dose that does not seem to impede the overall increase in tetragonality. The phasetransition from the R-like to T-like BiFeO3appears as first-order in character, with regions of phase coexistenceand abrupt changes in lattice parameters

Fullerene-grafted block copolymers used as compatibilizer in P3HT/PCBM bulk heterojunctions: morphology and photovoltaic performances

International audienceThe nanostructure of the active layer in polymer/fullerene bulk heterojunction solar cells is known to have a strong impact on the device performances. Controlling the polymer/fullerene blend morphology is therefore particularly important. In this work, a rod-coil block copolymer, based on a regioregular poly(3-hexylthiophene) electron-donor rod block and a C-60-grafted coil block, is used as compatibilizer and its influences on the thin film morphology as well as the photovoltaic performances are investigated. It is shown that a small fraction of compatibilizer can enhance the device performances in an otherwise non-optimized process. At higher fractions or long annealing times however, the fullerene-grafted copolymer is found to behave as a nucleation center and triggers the formation of fullerene crystals

Recent Updates on the Melanin-Concentrating Hormone (MCH) and Its Receptor System: Lessons from MCH1R Antagonists

Melanin-concentrating hormone (MCH) is a 19-amino-acid cyclic peptide which was originally found to lighten skin color in fish that is highly conserved among many species. MCH interacts with two G-protein-coupled receptors, MCH1R and MCH2R, but only MCH1R is expressed in rodents. MCH is mainly synthesized in the lateral hypothalamus and zona incerta, while MCH1R is widely expressed throughout the brain. Thus, MCH signaling is implicated in the regulation of many physiological functions. The identification of MCH1R has led to the development of small-molecule MCH1R antagonists that can block MCH signaling. MCH1R antagonists are useful not only for their potential therapeutic value, but also for understanding the physiological functions of the endogenous MCH system. Here, we review the physiological functions of the MCH system which have been investigated using MCH1R antagonists such as food intake, anxiety, depression, reward, and sleep. This will help us understand the physiological functions of the MCH system and suggest some of the potential applications of MCH1R antagonists in human disorders

Visualisation of thyroid hormone synthesis by ion imaging

The main function of the thyroid gland is to make hormones, T4 and T3, which are essential for the regulation of metabolic processes throughout the body. Caveolae harbour is the key enzymes involved in this iodide organification. The analyses of thyroids from normal mice and caveolin-1 Knockout mice (mice deficient in caveolin) have been performed using the SIMS imaging. In the thyroid of control mice, the epithelium is homogeneous and iodine (I-127) is observed in the follicle lumen. In Knockout mice, we observe an accumulation of intracellular vesicles and apoptotic nuclei resulting from oxidative stress due to H2O2 overproduction also inducing apical lesions of the thyrocytes, at the site of iodine organification and H2O2 generation. We also observe in the Knockout mice an accumulation of I-127 in the cellular cytoplasm and an absence of the iodine in some follicular lumina, indicating a problem at the level of iodine organification. Crown Copyright (C) 2008 Published by Elsevier B. V. All rights reserved

Multitechnique characterization of thin films of immiscible polymer systems: PS-b-PMMA diblock copolymers and PS-PMMA symmetric blends

Immiscible polymer systems are known to form various kinds of phase-separated structures capable of producing self-assembled patterns at the surface. In this study, different surface characterization methods were utilized to study the surface morphology and composition produced after annealing thin polymer films. Two different SIMS techniques - static time-of-flight secondary ion mass spectrometry (ToF-SIMS) and dynamic nano-SIMS - were used, complemented by x-ray photoelectron spectrometry (XPS) and atomic force microscopy (AFM). Thin films (spin-coated onto silicon wafers) of polystyrene (PS)-poly(methyl methacrylate) (PMMA) symmetric blends and diblock copolymers of similar molecular weight were investigated. Surface enrichment by PS was found on all as-cast samples. The samples were annealed at 160° C for different time periods, after which the blend and the copolymer films exhibited opposite behaviour as seen by ToF-SIMS and XPS. The annealed blend surface presented an increase in the PMMA concentration whereas that of copolymers showed a decrease in PMMA concentration compared with the as-cast sample. For blends, the nano-SIMS as well as AFM images revealed the formation of phase-separated domains at the surface. The composition information obtained from ToF-SIMS and XPS, as well as the surface mapping by nano-SIMS and AFM, allowed us to conclude that PS formed phase separated droplet-like domains on a thin PMMA matrix on annealing. The three-dimensional nano-SIMS images showed that the PS droplets were supported inside a rim of PMMA and that these droplets continued from the surface like columnar rods into the film until the substrate interface. In the case of annealed copolymer samples, the AFM images revealed topographical features resembling droplet-like domains on the surface but there was no phase difference between the domains and the matrix. In the case of copolymers, owing to the covalent bonding between the blocks, complete phase separation was not possible. The three-dimensional nano-SIMS images showed domain structures in the form of striations inside the film, which were not continuous until the substrate interface. Information from the different techniques was required to gain an accurate view of the surface composition and topographical changes that have occurred under the annealing conditions. Copyright © 2005 John Wiley & Sons, Ltd

Interaction of micro-discharges in heptane with metallic multi-layers

International audienceInteraction of discharges in heptane with magnetron-sputtered thin films made of aluminum, copper or iron is studied in a pin-to-plate configuration. The behavior of discharges on thin films can be used to better understand the interaction of discharges with given surfaces and it might also improve the reproducibility of the impacts in order to better control their shape. Single layers and bilayers of metals are characterized after impact by SEM, AFM, micro-EDX and nano-SIMS analyses. Discharges last typically for a few hundreds of nanoseconds and dissipated energies range between 1 and 100 mJ. We show that at low impact energy, copper and aluminum are heated and stretched by surface stress. At intermediate energy, melting occurs, leading to the synthesis of external beads by Marangoni's convection. At high energy, the shape of the impact is defined by the pressure release when the discharge stops. When iron is deposited onto silicon, dewetting is an important mechanism. The columnar structure of the deposit may have two distinct roles. On the one hand, gases trapped in intercolumnar boundaries can produce tiny holes. On the other hand, the shock wave can abrade the outermost and less cohesive part of the film if it is made of columns separated by large porosities

Photoluminescence of ZnO/ZnMgO heterostructure nanobelts grown by MBE

ZnO nanobelts grow with their polar axis perpendicular to growth direction. Heterostructure nanobelts may therefore contain hetero-interfaces along the polar axis of ZnO where polarization mismatch may induce electron confinement. We demonstrate the growth of such heterostructure nanobelts and investigate the effects of shell-growth temperature on nano-heterostructures using photoluminescence and secondary ion mass spectrometry in a focussed ion-beam microscope with a N+as the primary ion beam. We perform ow temperature photoluminescence on ensembles of such heterostructures and single nanostructure. We show how single nanobelts have photoluminescence spectra rich in features and attribute these to band misalignment at ZnO/ZnMgO interfaces embedded within nano-heterostructures