Characterization of nanocluster formation in Cu-implanted silica: Influence of the annealing atmosphere and the ion fluence

High-purity silica plates were implanted with 2 MeV Cu⁺ ions at various ion fluences: 0.7 × 10¹⁶, 3 × 10¹⁶ and 6 × 10¹⁶ ions/cm². After implantation, thermal treatments were performed at 400 °C and 900 °C in either an oxidizing (air) or a reducing (50% H₂ + 50% N₂) atmosphere for 1 h. All the samples were studied by electron paramagnetic resonance, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy (HRTEM), Rutherford backscattering spectrometry and optical absorption. The advantages of the reducing atmosphere (RA) over the oxidizing atmosphere (OA) are clearly observed. When annealed in a RA, the surface plasmon resonance is more intense and a narrower size distribution of the Cu nanoparticles is obtained. The existence of CuO nanoparticles was confirmed by HRTEM, and while both annealing atmospheres favor the formation of CuO nanoparticles, this process is strengthened when the sample is annealed in an OA.     

S4NR (R=Methyl,n-Octyl) as Novel Chelating Ligands in Titanocene Complexes and First Synthesis of Small Sulfurimide Heterocycles SnNR (n=5, 6)

Not the expected insertion into a S−S bond but rather substitution of one NR unit takes place in the reaction of [Cp₂Ti(CO)₂] with cyclic tetrasulfurdiimides 1,4-S₄(NR)₂. The product obtained contains the novel ligand S₄NR and serves as precursor in the synthesis of small SN heterocycles not accessible before (see below).     

New Developments in the Pauson–Khand Reaction

Catalytic and asymmetric variations , enones, enynes, and allene as other starting materials, and numerous applications in natural product synthesis are all evidence of the diversity of the Pauson–Khand reaction [Eq. (a)], which now definitely counts among the standard tools of organic synthesis.     

Models for the Carbonyl–ene Cyclization Reaction: Open and Closed Transition States

Different cyclization products are formed with different Lewis acids in the ene cyclization of 5-hexenals (see scheme on the right; a: methylaluminum bisphenoxide, b: Me₂AlCl, c: Sc(OSO₂CF₃)₃). This is not surprising, but it is gratifying that these result can be rationalized with an internally consistent model.     

Colorings generated by monotone properties

Given a graph G of order n containing no C₄, color an edge e of the complement of G red if G+e contains a C₄, and blue otherwise. Among other results, we answer a question of Erdős, de la Vina, and Fajtlowicz by showing that neither the red nor the blue graph obtained need contain a large complete subgraph. © 1998 John Wiley & Sons, Inc. Random Struct. Alg., 12 : 1–25, 1998