Ab initio molecular dynamics using density based energy functionals: application to ground state geometries of some small clusters

The ground state geometries of some small clusters have been obtained via ab initio molecular dynamical simulations by employing density based energy functionals. The approximate kinetic energy functionals that have been employed are the standard Thomas-Fermi $(T_{TF})$ along with the Weizsacker correction $T_W$ and a combination $F(N_e)T_{TF} + T_W$. It is shown that the functional involving $F(N_e)$ gives superior charge densities and bondlengths over the standard functional. Apart from dimers and trimers of Na, Mg, Al, Li, Si, equilibrium geometries for $Li_nAl, n=1,8$ and $Al_{13}$ clusters have also been reported. For all the clusters investigated, the method yields the ground state geometries with the correct symmetries with bondlengths within 5\% when compared with the corresponding results obtained via full orbital based Kohn-Sham method. The method is fast and a promising one to study the ground state geometries of large clusters.Comment: 15 pages, 3 PS figure

Pathological study of experimentally induced bovine respiratory syncytial viral infection in lambs

An experimental model was designed to characterize lesions in the lung of limbs inoculated with bovine respiratory syncytial virus (BRSV). Twenty-five Merino lambs of both sexes, with a live weight of 17 ± 3 kg, received an intratracheal inoculation of 20 ml saline solution containing 1.26 × 106 TCID50 BRSV (strain NMK-7) per ml. Lambs were slaughtered 1, 3, 7, 11 and 15 days postinoculation (DPI), and samples were taken for analysis using light-microscopic and immunohistochemical techniques. The results reflected the effect of the virus on airway epithelia. The presence of BRSV in ciliated bronchial and bronchiolar epithelial cells gave rise to cytopathological changes, including loss of cilia and cell necrosis; these changes might be expected to decrease the efficiency of mucociliary clearance, favouring the development of secondary bacterial bronchopneumonia. These results suggest a reduction in BRSV tropism for alveolar epithelia compared to bronchial and bronchiolar epithelia. Light-microscopic analysis revealed a narrowing of alveolar and airway lumina and a considerable interstitial inflammatory reaction

Soft-Chemistry-Based Routes to Epitaxial alpha-Quartz Thin Films with Tunable Textures

International audiencePiezoelectric nanostructured quartz films of high resonance frequencies are needed for microelectronic devices; however, synthesis methods have been frustrated by the inhomogeneous crystal growth, crystal twinning, and loss of nanofeatures upon crystallization. We report the epitaxial growth of nanostructured polycrystalline quartz films on silicon [Si(100)] substrates via the solution deposition and gelation of amorphous silica thin films, followed by thermal treatment. Key to the process is the combined use of either a strontium (Sr2+) or barium (Ba2+) catalyst with an amphiphilic molecular template. The silica nanostructure constructed by cooperative self-assembly permits homogeneous distribution of the cations, which are responsible for the crystallization of quartz. The low mismatch between the silicon and a-quartz cell parameters selects this particular polymorph, inducing epitaxial growth

Thin epitaxial quartz films with tunable textures on silicon.

9-13 March 2015International audienceThe integration of quartz on silicon in thin film form is appealing for its prospective applications in sensing and electronics. For instance, this could be used to make oscillators with higher resonance frequencies, in new electromechanical devices or mass sensors showing improved detection limits. We have recently reported the epitaxial growth of quartz films on silicon following a soft-chemistry approach1. The aim of this contribution is to discuss in detail the mechanisms of this synthesis. The films are obtained by the crystallization of amorphous silica films prepared by chemical solution deposition. Two key components of the solution are Sr2+, acting as catalyst for the crystallization of silica, and amphipilic templates playing the role of structuring agents and assisting in the crucial phase separation of the catalyst. The good matching between the quartz and silicon cell parameters is also essential in the stabilization of quartz over other SiO2 polymorphs and is at the origin of the epitaxial growth. The films are piezoelectric and can be tailored to be dense or to present an ordered porosity with pore diameters ranging from a few tenths of nanometer to the micron scale

Integrating functional oxide nanomaterials in silicon technology by chemical solution deposition

24-28 Janvier 2014International audienceIn the past years, great efforts have been devoted to combine the functionality of oxides with the performances of semiconductor platforms for the development of novel and more efficient device applications. However, further incorporation of functional oxide nanostructures as active materials in electronics critically depends on the ability to integrate crystalline metal oxides into silicon structures. In this regard, the presented work takes advantage of all the benefits of soft chemistry to overcome the main challenges for the monolithic integration of novel nanostructured functional oxide materials on silicon including (i) epitaxial piezoelectric α-quartz thin films with tunable textures on silicon wafers [1] and (ii) 1D single crystalline phases of manganese oxide based nanostructures with enhanced ferromagnetic properties on silicon wafers that share common growth mechanisms [2]. Importantly, these mechanisms are governed by a thermally activated devitrification of the native amorphous silica surface layer assisted by a heterogeneous catalysis under atmospheric conditions driven by alkaline earth cations present in the precursor solution. Quartz films are made of perfectly oriented individual crystallites epitaxially grown on (100) face of Si substrate with a controlled porosity after using templating agents. Moreover, a quantitative study of the converse piezoelectric effect of quartz thin films through piezoresponse force microscopy shows that the piezoelectric coefficient d33 is between 1.5 and 3.5 pm/V which is in agreement with the 2.3 pm/V of the quartz single crystal d11. Manganese based molecular sieve nanowires growth mechanism, involves the use of track-etched nanoporous polymer templates combined with the controlled growth of quartz thin films at the silicon surface, which allowed OMS nanowires to stabilize and crystallize. All together, the methodology presented here exhibits a great potential and offers a pathway to design novel oxide compounds on silicon substrates by chemical routes with unique optical, electric, or magnetic properties. [1] A.Carretero-Genevrier et al. Science 340, (2013) 827 [2] A.Carretero-Genevrier et al. Chem.Soc.Rev. (2014) DOI: 10.1039/C3CS60288E

Integrating functional oxide nanomaterials in silicon technology by chemical solution deposition

24-28 Janvier 2014International audienceIn the past years, great efforts have been devoted to combine the functionality of oxides with the performances of semiconductor platforms for the development of novel and more efficient device applications. However, further incorporation of functional oxide nanostructures as active materials in electronics critically depends on the ability to integrate crystalline metal oxides into silicon structures. In this regard, the presented work takes advantage of all the benefits of soft chemistry to overcome the main challenges for the monolithic integration of novel nanostructured functional oxide materials on silicon including (i) epitaxial piezoelectric α-quartz thin films with tunable textures on silicon wafers [1] and (ii) 1D single crystalline phases of manganese oxide based nanostructures with enhanced ferromagnetic properties on silicon wafers that share common growth mechanisms [2]. Importantly, these mechanisms are governed by a thermally activated devitrification of the native amorphous silica surface layer assisted by a heterogeneous catalysis under atmospheric conditions driven by alkaline earth cations present in the precursor solution. Quartz films are made of perfectly oriented individual crystallites epitaxially grown on (100) face of Si substrate with a controlled porosity after using templating agents. Moreover, a quantitative study of the converse piezoelectric effect of quartz thin films through piezoresponse force microscopy shows that the piezoelectric coefficient d33 is between 1.5 and 3.5 pm/V which is in agreement with the 2.3 pm/V of the quartz single crystal d11. Manganese based molecular sieve nanowires growth mechanism, involves the use of track-etched nanoporous polymer templates combined with the controlled growth of quartz thin films at the silicon surface, which allowed OMS nanowires to stabilize and crystallize. All together, the methodology presented here exhibits a great potential and offers a pathway to design novel oxide compounds on silicon substrates by chemical routes with unique optical, electric, or magnetic properties. [1] A.Carretero-Genevrier et al. Science 340, (2013) 827 [2] A.Carretero-Genevrier et al. Chem.Soc.Rev. (2014) DOI: 10.1039/C3CS60288E