Triphenylene-Derived Electron Acceptors and Donors on Ag(111):Formation of Intermolecular Charge-Transfer Complexes with Common Unoccupied Molecular States

Over the past years, ultrathin films consisting of electron donating and accepting molecules have attracted increasing attention due to their potential usage in optoelectronic devices. Key parameters for understanding and tuning their performance are intermolecular and molecule–substrate interactions. Here, the formation of a monolayer thick blend of triphenylene‐based organic donor and acceptor molecules from 2,3,6,7,10,11‐hexamethoxytriphenylene (HAT) and 1,4,5,8,9,12‐hexaazatriphenylenehexacarbonitrile (HATCN), respectively, on a silver (111) surface is reported. Scanning tunneling microscopy and spectroscopy, valence and core level photoelectron spectroscopy, as well as low‐energy electron diffraction measurements are used, complemented by density functional theory calculations, to investigate both the electronic and structural properties of the homomolecular as well as the intermixed layers. The donor molecules are weakly interacting with the Ag(111) surface, while the acceptor molecules show a strong interaction with the substrate leading to charge transfer and substantial buckling of the top silver layer and of the adsorbates. Upon mixing acceptor and donor molecules, strong hybridization occurs between the two different molecules leading to the emergence of a common unoccupied molecular orbital located at both the donor and acceptor molecules. The donor acceptor blend studied here is, therefore, a compelling candidate for organic electronics based on self‐assembled charge‐transfer complexes

Electrode Based on Oxyphosphates as Anode Materials for High Energy Density Lithium-ion Batteries

Lithium-ion batteries (Li-ion) are interesting devices for electrochemical energy storage for most emerging green technologies such as wind and solar technologies or hybrid and plug-in electric vehicles or for classical electrical devices such as laptops, phones or other electronic tools. Nevertheless, the oxygen release at high potentials in the present commercialized electrode materials (e.g. LiCoO2) leads to high thermal instability of these oxides and thus to many safety problems. This safety problem is more pronounced for stationary applications for which large size batteries were needed. Polyanionic materials in general, and particularly phosphates were well renowned by their high structural stability which are essential to overcome the above mentioned safety issue. Here, we present the structural and the electrochemical performances of three oxyphosphates M0.5TiOPO4 (M: Ni, Co, Fe). More than 300 mAh/g discharge capacity could be delivered by these phosphates under relatively high cycling rate. The lithium insertion/extraction mechanism is composed from an intercalation process for low lithium content to a conversion mechanism for higher lithium concentration leading to the extrusion of the transition metal M from the structure

A new type of lithium-ion cell built using Li4Ti5O12 as anode and LiCo2/3Ni1/6Mn1/6O2 as cathode synthesized by self-combustion method

Li-ion batteries (LIBs) have become the power sources of choice for portable applications, such as, cellular phones, laptop computers … More recently, LIBs have been also selected to power the first-generation of electric vehicles (EVs). Especially for the former application, new LIBs with higher energy and power, safer and cheaper are needed. To achieve this goal, the search and development of new electrode materials is one of the most powerful ways [1-2]. Refer to positive electrode (cathode), layered LiCoO2 is widely used in the LIB for portable applications. Nevertheless, its elevated price and toxicity are serious drawback for to use this material in larger-size LIBs needed for EVs. One of the alternatives to improve the performances of layered LiCoO2-based cathodes is to substitute Co for other transition metal cations as Ni, Mn … Layered LiCo1-2yNi1yMnyO2 has high capacity, high working voltage, improved structural and thermal stability and lower cost compared with LiCoO2. In the present poster we will show several of the most remarkable results attained for preparation and study of layered LiCo2/3Ni1/6Co1/6O2 oxide [3]. Refer to negative electrode (anode), it should be indicated that the lithium titanate Li4Ti5O12 (hereafter named as LTO) is one of the most promising materials to replace the graphite at the negative electrode. LTO is of the most promising materials to replace the graphite as negative electrode (anode). It has a constant operating voltage at approximately 1.5V vs. Li+/Li, which is above the potential range where most electrolytes are reduced [2]. LTO can work under high current loads without risk of internal short circuits as is the case of graphite. This feature notably improves the safety of LIBs. The spinel-type Li4Ti5O12 anodic material and the layered LiCo2/3Ni1/6Co1/6O2 cathodic material were prepared by a self-combustion method assisted by sucrose. The advantages of this procedure are that it is rapid and cheap. In the case LiMn2O4-based cathodes, it has permitted to prepare single-phase spinel, with different dopant cations in a broad compositional range with high particles size homogeneity [4] In this work, the structural and morphological characterization of the electrodes materials will be present. The study by X-ray diffraction (XRD) shows that the sample has high purity. The particles size determined from the micrographics obtained by field emission scanning electron microscopy (FE-SEM) were 0.8 micrometre for LTO and 0.3micrometre for LiCo2/3Ni1/6Co1/6O2. The materials are characterized by a high homogeneity and faceted shape. The electrochemical properties of Li4Ti5O12 and LiCo2/3Ni1/6Co1/6O2 had been determined in Li half cell by galvanostatic cycling. Results concerning the studies of cyclability and rate capability will be done. A new design of lithium-ion cell has been assembled using spinel Li4Ti5O12 as anode and high voltage layered LiCo2/3Ni1/6Co1/6O2 as cathode. In Fig. 1a. a selection of charge/discharge curves registered during the cycling is shown. The average voltage of the LIB cell is ca. 2.1V, being high the capacity drained during the first discharge Q=158.74 mAh g-1. The evolution of the discharge capacity vs. cycle number recorded at 0.5C rate is presented in Fig. 1b. Acknowledgements: Financial support through the projects MAT 2011-22969 (MEC), MATERYENER Ref. P2009/PPQ-1626 (CAM) and the joint project CSIC/CNRST de Morocco Ref. 2009MA0007 is thankfully recognized. The authors would like to thank AECID and CNRST. References : [1] M. Armand and J.-M. Tarascon, Nature, 451 (2008) 652. [2] Ting-Feng Yi, Li-JuanJiang, J.Shu , Cai-BoYue , Rong-SunZhu , Hong-BinQiao, Journal of Physics and Chemistry of Solids 71 (2010) 1236–1242. [3] A. Mahmoud, Ismael Saadoune, José Manuel Amarilla , Rachid Hakkou. Electrochimica Acta 56 (2011) 4081–408 [4] J.M. Amarilla, R.M. Rojas, F. Pico, L. Pascual, K. Petrov, D. Kovachevav, M.G. Lazarraga, I. Ledjona, J.M. Rojo. J. Power Sources, 174(2) (2007) 1212

Effect of acupressure on agitation in the elderly with dementia who receive institutional care: A pilot study

Purpose This pilot study was carried out to determine the effect of acupressure on agitation in the elderly with dementia who receive institutional care. Methods The study sample consisted of 38 elderly individuals (acupressure group [AG] = 19, usual-care group = 19). Acupressure application was performed on four points. The results were measured at the beginning (T-0), the week after acupressure was completed (T-1), and 2 weeks after acupressure was completed (T-2). Findings The change in the total Cohen-Mansfield Agitation Inventory score across the groups at T-1, T-2, and T(3)was statistically significant in favor of AG. Practical Implications The acupressure used in this study can be used for managing agitation in the elderly with dementia.WOS:0005797720000012-s2.0-85092335574PubMed: 3304404

Atomic Structure Of Submonolayer Nacl Grown On Ag(110) Surface

We report results on the growth of an NaCl film on Ag(110) under ultrahigh vacuum conditions. At room temperature, low-energy electron diffraction and scanning tunneling microscopy show that the NaCl film forms a (4×1) superstructure. At RT, the film consists of small-sized islands that coalesce into larger islands at 410 K. These large islands preserve the (4×1) superstructure and cover the entire surface. The apparent heights obtained from the STM images show that the initial thickness of the NaCl islands is one atomic layer, and they present a very small height corrugation. The density functional theory calculations, with and without the inclusion of van der Waals effects, confirm the coexistence of two domains in agreement with the observed structure

New insights on the structural formation of polyanionic phosphate compounds revealed by new Mossbauer and XRD measurements

The exploration of optional electrode materials for lithium and sodium ion batteries, still an active field with continuous research efforts. Based on several advantages, polyanionic phosphate compounds M0.5TiOPO4 (M= Fe, Ni, Co, Cu), as negative electrode materials of Lithium-ion batteries, were the subject of a limited number of experimental studies. Motivated by these studies, intensive efforts have been devoted by our group to understand crystal and electronic structure changes, upon lithium ions insertion/extraction. As a result, the Iron-57 Mössbauer measurements of Fe0.5TiOPO4 (pristine material) report new findings revealing the presence of two iron distinct environments, in contradiction with previously reported structural observations [1]. In addition, based on an XRD study with a Rietveld refinement, the newly found crystal structure of Fe0.5TiOPO4 shows that the Fe2+ cations are located in two different triangular based antiprism crystallographic sites. More importantly, this finding is further supported by DFT calculations that have showed the possibility of co-existence of several host sites for Fe2+

Synthèse, mécanismes réactionnels et performances électrochimiques de Fe0.5TiOPO4 comme électrode négative pour les batteries lithium-ion.

Ce travail a pour but l’étude de matériaux phosphatés pour une application comme électrode négative dans des batteries rechargeables lithium ion. Les oxyphosphates de titane sont particulièrement intéressants en raison de leurs importantes capacités massique et volumique. Les oxyphosphates de titane à base de métaux de transition M0.5TiOPO4 (M = Ni, Co et Fe) possèdent des propriétés électrochimiques très intéressantes, impliquant à la fois des mécanismes réactionnels d'intercalation et de conversion. L’oxyphosphate Fe0.5TiOPO4 a été synthétisé par voie sol-gel et une phase pure a été obtenue. Celle-ci a été ensuite enrobée de carbone pour améliorer la conductivité électronique, puis caractérisée par diffraction de rayons X (DRX), spectroscopie Mössbauer (SM) et spectroscopie d’absorption X (SAX), analyse thermogravimétrique (ATG), et magnétométrie. Le comportement électrochimique vis-à-vis du lithium a été étudié à différents régimes dans deux fenêtres de potentiels, 1.4-3V et 0.01-3V. L’étude des courbes de potentiel montre l´existence de plusieurs régions avec des mécanismes réactionnels différents en fonction de la quantité de lithium inséré. L’analyse détaillée du mécanisme électrochimique a été effectuée grâce à la complémentarité des différentes techniques expérimentales en mode operando (SM, DRX et SAX). L’examen de l’ensemble des résultats nous a permis de distinguer deux types de réactions : un mécanisme d'intercalation réversible du lithium quand la batterie est cyclée entre 1.4 et 3V, et un mécanisme d´intercalation et de conversion lors du fonctionnement de la batterie entre 0.01V et 3V

Toward understanding the lithiation/delithiation process in Fe0.5TiOPO4/C electrode material for lithium-ion batteries

Fe0.5TiOPO4/C composite was used as anode material for LIB and exhibits excellent cycling performance when the electrode is cycled in two different voltage ranges [3.0–1.3 V] and [3.0–0.02 V] where different insertion mechanisms were involved. A detailed in situ XANES spectroscopy study coupled to the electrochemical analyses, clearly established that the structure of Fe0.5TiOPO4/C electrode materials is preserved when cycled between 3.0 and 1.3 V. Furthermore, a formation of new phase at the end of first discharge was evidenced, with a reversible capacity of 100 mA h g−1 after 50 cycles at C/5 rate. At highly lithiated states, [3.0–0.02 V] voltage range, a reduction-decomposition reaction highlights the Li-insertion/extraction behaviors, and low phase crystallinity is observed during cycling, in addition an excellent rate behavior and a reversible capacity of 250 mA h g−1 can still be maintained after 50 cycles at high cycling rate 5C

Unveiling the impact of embedding resins on the physicochemical traits of wood cell walls with subcellular functional probing

International audienceAs pressing needs for exploring molecular interactions in plants soar, conventional sample preparation methods come into question. Though resins used to embed plant tissues have long been assumed to bear no palpable effect on their properties, discrepancies in recent studies exploiting nanoscale microscopy suggest that their impact could be significant at small scales. By juxtaposing the traits of poplar sections prepared with and without embedding, we evaluate the diffusion (penetration depth) of acrylic and epoxy resins commonly used for embedding. Our results unveil critical quantitative differences when probing mechanical properties with a microscale nanoindentation indenter or a nanoscale tip. The latter resolves significant stiffness variations between the compound middle lamellae, the secondary cell wall layers S1 and S2, and the cell corner, not accessible with nanoindentation. Similar observations are drawn from comparing confocal Raman and nanoscale infrared spectroscopy. Our findings shed light on the effect of resin diffusion suggesting acrylic LR White to be the least diffusive for plant cell wall studies