Density control of dodecamanganese clusters anchored on silicon(100)

A synthetic strategy to control the density of Mn12 clusters anchored on silicon(100) was investigated. Diluted monolayers suitable for Mn12 anchoring were prepared by Si-grafting mixtures of the methyl 10-undecylenoate precursor ligand with 1-decene spectator spacers. Different ratios of these mixtures were tested. The grafted surfaces were hydrolyzed to reveal the carboxylic groups available for the subsequent exchange with the [Mn12O12(OAc)16(H2O)4]4 H2O2 AcOH cluster. Modified surfaces were analyzed by attenuated total reflection (ATR)-FTIR spectroscopy, X-ray photoemission spectroscopy (XPS), and AFM imaging. Results of XPS and ATR-FTIR spectroscopy show that the surface mole ratio between grafted ester and decene is higher than in the source solution. The surface density of the Mn12 cluster is, in turn, strictly proportional to the ester mole fraction. Well-resolved and isolated clusters were observed by AFM, using a diluted ester/decene 1:1 solution.     

Grafting cavitands on the Si(100) surface

Cavitand molecules having double bond terminated alkyl chains and different bridging groups at the upper rim have been grafted on H-terminated Si(100) surface via photochemical hydrosilylation of the double bonds. Pure and mixed monolayers have been obtained from mesitylene solutions of either pure cavitand or cavitand/1-octene mixtures. Angle resolved high-resolution X-ray photoelectron spectroscopy has been used as the main tool for the monolayer characterization. The cavitand decorated surface consists of Si-C bonded layers with the upper rim at the top of the layer. Grafting of pure cavitands leads to not-well-packed layers, which are not able to efficiently passivate the Si(100) surface. By contrast, monolayers obtained from cavitand/1-octene mixtures consist of well-packed layers since they prevent silicon oxidation after aging. AFM measurements showed that these monolayers have a structured topography, with objects protruding from the Si(100) surface with average heights compatible with the expected ones for cavitand molecules.     

Group IV Organometallic Compounds Based on Dianionic “Pincer” Ligands: Synthesis,Characterization, and Catalytic Activity in Intramolecular Hydroamination Reactions

Neutral Zr^IV and Hf^IV diamido complexes stabilized by unsymmetrical dianionic N,C,N′ pincer ligands have been prepared through the simplest and convenient direct metal‐induced C_aryl? H bond activation. Simple ligand modification has contributed to highlight the non‐innocent role played by the donor atom set in the control of the cyclometallation kinetics. The as‐prepared bis‐amido catalysts were found to be good candidates for the intramolecular hydroamination/cyclization of primary aminoalkenes. The ability of these compounds to promote such a catalytic transformation efficiently (by providing, in some cases, fast and complete substrate conversion at room temperature) constitutes a remarkable step forward toward catalytic systems that can operate at relatively low catalyst loading and under milder reaction conditions. Kinetic studies and substrate‐scope investigations, in conjunction with preliminary DFT calculations on the real systems, were used to elucidate the effects of the substrate substitution on the catalyst performance and to support the most reliable mechanistic path operative in the hydroamination reaction.     

Spin-spin interaction sensitivity in the indirect MARF imaging of polymers

This paper is mostly devoted to the presentation of the main experimental characteristics of the MARF (Magic Angle in the Rotating Frame) solid state imaging technique, as refined after the first preliminary and initial phases, the results of which are also summarized. The recent progress has made easier the experimental set-up and increased the whole sensitivity of the method as well as it has developed new possibilities for the introduction of NMR parameters sensitivity on the image, especially of polymers.     

Nearly flat, terraced, hydrogen-terminated, 1×1 (100) silicon prepared by high-temperature exposure to H2

A method is described for the preparation of device-quality, nearly flat, terraced, hydrogen-terminated, (100) silicon. The method requires heating at high temperature (say, 1100 °C) in H₂, cooling to moderate temperature (670–700 °C) in the same ambient, and quenching to room temperature in N₂. Evidence that the process really results in the said surface is based on atomic force microscopy, infrared absorption spectroscopy in the attenuated total reflection mode, thermal programmed desorption, reflection high energy electron diffraction, and angle-resolved X-ray photoelectron spectroscopy. PACS 68.45.Da; 34.50.Dy; 82.30.Hk; 82.65.MyThis corrected version was published in January 2005 with a correction to the title.     

Role of patterning in islands nucleation on semiconductor surfaces

Quantum dots (QDs) grown on semiconductors surfaces are actually the main researchers' interest for applications in the forthcoming nanotechnology era. New frontiers in nanodevice technology rely on the precise positioning of the nucleation site and on controlling the shape and size of the dots. In this article we will review some recent studies regarding the control of the nucleation process on semiconductor surfaces. A few approaches to form ordered patterns on surfaces are described: natural patterning induced by surface instabilities (as step bunching or step meandering), in situ substrate patterning by Scanning Tunneling Microscopy (STM), high resolution patterning by Focused Ion Beam (FIB). Growth of epitaxial layers of semiconductors (Ge/Si(100) and InAs/GaAs(100)) on patterned surfaces has been studied by STM or Atomic Force Microscopy (AFM) unveiling the way in which the first atoms start to aggregate and identifying their exact nucleation site. Control of the dot size to match the patterning typical wavelength has been achieved by using surfactants on misoriented substrates. STM images acquired in real time allows one to identify the mechanism of Ge cluster formation on patterned Si(100), and to follow the island transition from pre-pyramid to pyramid. Nucleation of ordered Ge dots on SiO₂ substrates has been obtained thanks to FIB tight patterning, achieving island densities of 3.5×10¹⁰/cm². To cite this article: N. Motta et al., C. R. Physique 7 (2006).     

The solid‐state 2:1 molecular complex of 1,5:3,7‐dimethano‐1,3,5,7‐benzotetrazonine with hydroquinone

The title compound, 1,5:3,7‐dimethano‐1,3,5,7‐benzotetrazonine–hydroquinone (2/1), 2C₁₁H₁₄N₄·C₆H₆O₂, crystallizes with the hydroquinone molecule located on a center of inversion. In contrast to other hydroquinone–adamanzane adducts, which form extended hydrogen‐bonded networks, in the present case, one hydroquinone molecule is linked to two 1,5:3,7‐dimethano‐1,3,5,7‐benzotetrazonine molecules, forming a 2:1 cluster through O—H...N hydrogen bonds.     

Peagol and peagoldione, two new strigolactone-like metabolites isolated from pea root exudates

Two new strigolactone-like metabolites, named peagol and peagoldione, with germinative activity for root parasitic plants, were isolated from pea root exudates and were characterized by spectroscopic methods. Peagol was more active on Orobanche foetida and Phelipanche aegyptiaca seeds, while peagoldione was active on P. aegyptiaca only. Low activity was found on Orobanche crenata and Orobanche minor. Stimulatory activity of peagol on O. foetida seeds is most relevant as this species does not respond to the synthetic strigolactone analogue GR24, usually used as Orobanche germination standard.