Confined micro-explosion induced by ultrashort laser pulse at SiO2/Si interface

Ultrashort laser pulses tightly focused inside a transparent material present an example of laser interaction with matter where all the laser-affected material remains inside the bulk, thus the mass is conserved. In this paper, we present the case where the high intensity of a laser pulse is above the threshold for optical breakdown, and the material is ionised in the focal area. We consider in detail a special case where a micro-explosion is formed at the boundary of a silicon surface buried under a 10-micron-thick oxidised layer, providing the opportunity to affect the silicon crystal by a strong shock wave and creating new material phases from the plasma state. We summarise the main conclusions on ultrafast laser-induced material modifications in confined geometry and discuss the prospects of confined micro-explosion for forming new silicon phases.     

Functionalization of Non‐activated C?H Bonds of Alkanes: An Effective and Recyclable Catalytic System Based on Fluorinated Silver Catalysts and Solvents

The complexes F_n‐TpAg(L) (F_n‐Tp=a perfluorinated hydrotris(indazolyl) borate ligand; L=acetone or tetrahydrofuran) efficiently catalyze the functionalization of non‐activated alkanes such as hexane, 2,3‐dimethylbutane, or 2‐methylpentane by insertion of CHCO₂Et units (from N₂CHCO₂Et, ethyl diazoacetate, EDA) into their C? H bonds. The reactions are quantitative (EDA‐based), with no byproducts derived from diazo coupling being formed. In the case of hexane, the functionalization of the methyl C? H bonds has been achieved with the highest regioselectivity known to date with this diazo compound. This catalytic system also operates under biphasic conditions by using fluorous solvents such as Fomblin or perfluorophenanthrene. Several cycles of catalyst recovery and reuse have been performed, with identical chemo‐ and regioselectivities.     

2,6,9-Trioxabicyclo[3.3.1]nona-3,7-dienes and 2,4,6,8-Tetraoxaadamantanes: Novel Chiral Spacer Units in Macrocyclic Polyethers

The unusual chiral heterocyclic systems, trioxabicyclo[3.3.1]nona-3,7-dienes ("bridged bisdioxines"), are incorporated as novel spacer molecules into macrocyclic polyether ring systems of various sizes (8, 9 as well as 11-15) by cyclocondensation reaction of the bisacid chloride 4b or bisesters 6,7 and 10, with several ethylene glycols. The 2:2 macrocycles 12-14 are obtained in approximately 50:50 mixtures of diastereomers. These conclusions are mainly based on HPLC data presented in Table I as well as X-ray analyses of (1R,5R)-8c (space group Pbca, a =10.163(3) Å, b =18.999(4) Å, c =36.187(10) Å, V =6987(3) ų , Z =8, d _calc =1.218 g cm^{m 3}, 6974 reflections, R =0.0553), meso/rac-11 (space group P1 ¥ , a =10.472(5) Å, b=16.390(5) Å, c =17.211(5) Å, f =98.69(2)°, g =93.04(2)°, n =98.52(2)°, V =2879.3(18) Å 3 , Z =2, d _calc =1.173 g cm m 3 , 11,162 reflections, R =0.0945) and meso-12 (space group P2₁/c, a =9.927(2), b =18.166(3), c =17.820(3) Å, g =96.590(10)°, V =3192.3(10) Å 3 , Z =4, D _c =1.109 g cm^{m 3}, 3490 reflections, R =0.0646). The 1:1 macrocycles 8b,c are also formed by intramolecular transesterification of the open-chain bisesters 7b,c and their formation is favored by the use of metal ions as templates. The bridged bisdioxine moieties in 8b and 12 are converted into the corresponding chiral tetraoxaadamantane spacers to afford macrocycles 16 and 17. Preliminary metal ion complexation studies with selected species (8c, 11-14) were also performed.     

Divalent metal vinylphosphonate layered materials: compositional variability, structural peculiarities, dehydration behavior, and photoluminescent properties

A family of M-VP (M = Ni, Co, Cd, Mn, Zn, Fe, Cu, Pb; VP = vinylphosphonate) and M-PVP (M = Co, Cd; PVP = phenylvinylphosphonate) materials have been synthesized by hydrothermal methods and characterized by FT-IR, elemental analysis, and thermogravimetric analysis (TGA). Their structures were determined either by single crystal X-ray crystallography or from laboratory X-ray powder diffraction data. The crystal structure of some M-VP and M-PVP materials is two-dimensional (2D) layered, with the organic groups (vinyl or phenylvinyl) protruding into the interlamellar space. However, the Pb-VP and Cu-VP materials show dramatically different structural features. The porous, three-dimensional (3D) structure of Pb-VP contains the Pb center in a pentagonal pyramid. A Cu-VP variant of the common 2D layered structure shows a very peculiar structure. The structure of the material is 2D with the layers based upon three crystallographically distinct Cu atoms; an octahedrally coordinated Cu(2+) atom, a square planar Cu(2+) atom and a Cu(+) atom. The latter has an unusual co-ordination environment as it is 3-coordinated to two oxygen atoms with the third bond across the double bond of the vinyl group. Metal-coordinated water loss was studied by TGA and thermodiffractometry. The rehydration of the anhydrous phases to give the initial phase takes place rapidly for Cd-PVP but it takes several days for Co-PVP. The M-VP materials exhibit variable dehydration-rehydration behavior, with most of them losing crystallinity during the process.     

Polymeric porphyrin and metalloporphyrin assemblies in bulk solution

Some water-soluble porphyrins aggregate in aqueous media to form fibrous assemblies. When polynucleotides are used as matrices, porphyrin monomers are aligned at the periphery or intercalated. Porphyrin-porphyrin interactions hardly occur. Metal-metal or metal-ligand-metal interactions have been observed in oxo-oligomers, pyrazine-bridged dimers and radical dimers. β-Substituted metallo-porphyrins, however, form no polymers. The only linear polymerization, which has so far been observed in molecular asemblies, occurs with amphiphilic porphyrin amides, amines and carboxylates and their metal complexes in water and of bacteriochlorophyll in DMF/water. These compounds form long-lived high molecular weight micellar, inverse micellar and vesicular fibers spontaneously in aqueous media. The porphyrin fibers in water are about 4-6 nm thick and up to several of μm long.     

Modelling of Wave Propagation using Spectral Finite Elements

For the analysis of wave propagation at high frequencies, the spectral finite element method (SFEM) is under investigation. In contrast to the conventional finite element method high-order shape functions are used. They are composed of Lagrange polynomials with nodes at the Gauß-Lobatto-Legendre points. The Gauß-Lobatto-Legendre integration scheme is applied in order to obtain a diagonal mass matrix. So, the resulting system equations can be solved efficiently. In the numerical examples, spectral finite elements with shape functions of different order are applied to a plane strain problem. The numerical examples cover structures without and with stiffness discontinuities. It is shown that the results agree well with analytical solutions. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)