Steps on Fe3O4(100): STM measurements and theoretical calculations

Scanning tunneling microscopy (STM) measurements of the step structure on natural single-crystal samples of Fe3O4(100) have been performed. Step edges are found to occur along both [110] and [1 (1) over bar0] directions. For step heights of 4.2 +/- 0.3 angstrom, the step edges are found to be straight, whereas for step heights of 2.1 +/- 0.2 angstrom, alternate step edges are straight and jagged. The straight (jagged) step edges are parallel (perpendicular) to the octahedral iron rows on the upper terrace. The concepts of coordinative unsaturation and excess surface charge are used to predict which atomic geometries are likely to be most stable along step edges. Our calculations show that steps parallel to the octahedral iron rows on the upper terrace are expected to be more stable than those perpendicular to them, in agreement with our STM observations. This step stability is found to be independent of both terrace structure and step height

Possible complete miscibility of (BN)x(C2)1−x(BN)_x(C_2)_{1-x} alloys

The stabilities of $(BN)_x(C_2)_{1-x}$ alloys and related superlattices are investigated by ab initio pseudopotential calculations. We find that the $(BN)_1/(C_2)_1$ superlattices in (111) orientations have the lowest formation energy among many short-range ordered $BNC_2$ structures due to the smallest number of B-C and C-N bonds. Based on the calculated formation energies at several compositions and for various ordered structures and assuming thermodynamic equilibrium, the solid solution phase diagram of $(BN)_x(C_2)_{1-x}$ alloys is constructed. We find that the complete miscibility of $(BN)_x(C_2)_{1-x}$ alloys is possible, which is in contrast with previous theoretical predictions but in agreement with experimental reports.Comment: 6 pages, 3 figure

Interfacial properties between CoO (100) and Fe(3)O(4) (100)

Using molecular beam epitaxy 1-20 ML thick CoO (100) films were grown monolayer by monolayer on Fe(3)O(4) (100) substrates. The stoichiometry of the films was verified by low-energy-electron diffraction and reflection-high-energy-electron diffraction patterns, as well as x-ray photoelectron spectroscopy. Auger measurements as a function of CoO film thickness indicated a layer-by-layer growth mode. Ultraviolet photoelectron spectroscopy (UPS) was used to monitor the thin film electronic properties. The evolution of the density of states in the O 2p/Fe 3d and O 2p/Co 3d bands exhibits a shift in the position of the CoO valence band for ultrathin films relative to bulklike thick films. The measured spectra (when aligned to cancel the band shift) are compared to models of the spectra that would be expected based on the bulk compounds, with and without additional interfacial electronic states. Electronic states at the Fe(3)O(4)-CoO interface have been identified, and their UPS spectrum has been determined

Measurement of electronic structure at nanoscale solid-solid interfaces by surface-sensitive electron spectroscopy

We explore the use of electron spectroscopy that samples the near-surface region of a crystal to study the electronic structure at the buried interfaces between two dissimilar transition-metal oxides. The interface is probed by comparing experimental ultraviolet photoelectron spectra to model spectra and by taking sequential differences between the experimental spectra as one oxide is grown on another. Using (100) Fe(3)O(4)-NiO and Fe(3)O(4)-CoO interfaces grown by molecular beam epitaxy, we show that there is a much higher density of electronic states at the Fe(3)O(4)-CoO interface than at the Fe(3)O(4)-NiO interface. The origin of this difference is discussed. (C) 2008 American Institute of Physics

Phase Segregation of ZnO/ZnMgO Superlattice Affected by Ⅱ-Ⅵ Ratio

在zn1-X Mg X O中,X=0.4~0.6仍为一个岩盐矿和纤锌矿共存的结构,影响了其晶格质量。本文利用等离子体辅助的分子束外延设备在C面蓝宝石衬底上外延生长了znO/znMgO超晶格,并改变其生长过程中的Ⅱ-Ⅵ比,利用原子力显微镜、X射线衍射、透射谱和X射线光电子能谱对样品进行了表征分析。发现在较低氧分压下制备的样品结构以岩盐矿为主导,而在较高氧分压下两相共存并以纤锌矿为主。这种相分离现象与裂解氧原子的密度有关。ZnMgO alloy allows for tunable optoelectronic devices.However,the compositional range between ZnO and MgO is interrupted by a crystalline miscibility gap where the wurtzite crystal structure of ZnO is structurally incompatible with the rocksalt structure of MgO.In this article,ten periods of ZnO / ZnMgO superlattice were produced by plasma-assistant molecular beam epitaxy on cplane sapphire substrate with different oxygen condition.It is found that the sample grown at lower oxygen flow and radio-frenquency( RF) plasma power tends to form rocksalt phase.With the increase of oxygen flow and RF plasma power,wurtzite phase tends to dominate and phase segregation is enhanced.The phase transform affected by the oxygen atoms density is reasoned by the formation enthalpies of ZnO and MgO.国家自然科学基金(61076084)资助项

Anti-inflammatoires non stéroïdiens (une vieille classe innovante pour le traitement du traumatisme crânien?)

En raison de la complexité de sa pathogenèse, le traumatisme crânien (TC) entraîne de nombreuses lésions cérébrales pour lesquelles il n existe aucun traitement neuroprotecteur. Il est aujourd hui clairement établi que la neuro-inflammation est fortement impliquée dans les conséquences post-traumatiques. Cette neuro-inflammation se manifeste entre autres par l induction de la cyclo-oxygénase de type 2 (COX-2). Bien que plusieurs données soient en faveur d un rôle délétère de cette enzyme au cours de ce processus dévastateur, l implication de la COX-2 dans les lésions induites par le TC reste encore controversée. Dans un modèle du TC par percussion mécanique chez la souris, nous avons mis en évidence une augmentation précoce et transitoire du contenu cérébral en COX-2 à 6 et 12 heures après le trauma. Cette induction protéique était à l origine d une production accrue de la prostacycline. Cependant, l inhibition préférentielle de COX-2 était sans effet sur l œdème cérébral et le déficit neurologique, deux indicateurs de pertinence clinique. Ces données montrent que la COX-2 ne peut pas constituer à elle seule une cible intéressante pour le traitement des conséquences post-traumatiques malgré son induction et son activité après le trauma. Par ailleurs, nous avons montré un effet bénéfique induit par l indométacine au niveau fonctionnel, ce qui est en faveur d un rôle délétère des COXs dans le déficit neurologique post-traumatique. Cet effet bénéfique peut impliquer uniquement la COX-1 ou en association avec la COX-2. Ces données constituent un argument supplémentaire qui s ajoute à plusieurs preuves récentes fournies par la littérature en faveur d un rôle délétère de COX-1 dans la neuro-inflammation. Malheureusement, ce rôle ne pourra pas être confirmé dans notre modèle car les inhibiteurs sélectifs de COX-1 disponibles à ce jour sont inexploitables dans nos conditions expérimentales. Ce travail constitue une nouvelle piste pour évaluer l intérêt de l inhibition des COXs au cours de la phase précoce de la prise en charge du patient traumatisé crânien. La bonne tolérance de l usage à court terme des inhibiteurs de COX, leur disponibilité sur le marché, leur prix abordable, leur simplicité d administration, leurs caractéristiques pharmacocinétiques et pharmacodynamiques bien connus sont des facteurs suscitant un intérêt croissant d élargir le spectre de leurs utilisations en clinique et de la mise en place de nouveaux essais thérapeutiques dans les années à venir.Because of its complex pathology, Traumatic Brain Injury (TBI) leads to numerous cerebral lesions for which there is no neuroprotective treatment. It is clearly known nowadays that neuro-inflammation is highly involved in post-traumatic consequences. This devastating process is manifested among others by the induction of cyclo-oxygenase type 2 (COX-2). Although many data are in agreement with a deleterious role of COX-2 in neuro-inflammation, the implication of this isoform in the TBI-induced lesions is still controversial. In a mouse model of TBI induced by mechanical percussion, we have shown an early and a transitory increase in the cerebral content of COX-2 at 6 and 12 hours after trauma. This protein induction was the source of an increased production of prostacyclin. However, the preferential inhibition of COX-2 had no effect against cerebral œdema and neurological deficit, two indicators of high clinical relevance. These data show that COX-2 cannot be considered by itself as an interesting target for the treatment of post-traumatic consequences despite its induction and activity after trauma. Besides, we have shown a beneficial effect that was induced by indomethacin at the functional level. This effect highly suggests a deleterious role of COXs in the post-traumatic neurological deficit. This neuroprotection could solely involve COX-1 or both COX isoforms. In accordance with several proofs that were recently supplied by literature, our data constitute an additional argument suggesting a deleterious role of COX-1 in neuro-inflammation. Unfortunately, this hypothesis cannot be confirmed in our model of TBI because the selective inhibitors of COX-1 available this day cannot be exploited in our experimental conditions. This experimental work is a new indication to evaluate the potential interest of COXs inhibition during the early phase of clinical management of patients with TBI. The good tolerance of the short-term intake of COX inhibitors, their availability on the market, their affordable price, their simple way of administration, their well-known pharmacokinetic and pharmacodynamic characteristics increase the need to widen the spectrum of their therapeutic indications and to design new clinical trials during the upcoming years.PARIS5-Bibliotheque electronique (751069902) / SudocPARIS-BIUM-Bib. électronique (751069903) / SudocSudocFranceF

An evaluation of the tree preservation measures in Hong Kong

published_or_final_versionPublic AdministrationMasterMaster of Public Administratio

Trends in bonding configuration at SiC/III-V semiconductor interfaces

10.1063/1.1402162Applied Physics Letters79111643-1645APPL

Studies of the electronic structure at the Fe3O4-NiO interface

The interfacial electronic structure between the metallic ferrimagnet Fe3O4 and the insulating antiferromagnet NiO is investigated in the lattice matched heteroepitaxial system Fe3O4 (100)-NiO (100) by growing ultrathin NiO films on single-crystal Fe3O4 (100) substrates. The Fe3O4 (root2 X root2)R45degrees surface is characterized prior to growth by low-energy electron diffraction, reflection high-energy diffraction, scanning tunneling microscopy, ultraviolet photoelectron spectroscopy (UPS), x-ray photoemission spectroscopy (XPS) and Auger electron spectroscopy. UPS and XPS, which sample several monolayers in the substrate-overlayer structure, are used to monitor near-surface electronic properties versus NiO overlayer thickness. Comparison of experimental He II UPS spectra of the valence band electronic structure with a simple model of substrate-overlayer emission indicates that the electronic transition from Fe3O4 to NiO is nearly atomically sharp. (C) 2004 American Vacuum Society

Relaxation of Cu(100), (110) and (111) surfaces using AB initio pseudopotentials

10.1016/S0218-625X(01)00142-7Surface Review and Letters85541-547SRLE