On the nature of the stretched exponential photoluminescence decay for silicon nanocrystals

The influence of hydrogen rate on optical properties of silicon nanocrystals deposited by sputtering method was studied by means of time-resolved photoluminescence spectroscopy as well as transmission and reflection measurements. It was found that photoluminescence decay is strongly non-single exponential and can be described by the stretched exponential function. It was also shown that effective decay rate probability density function may be recovered by means of Stehfest algorithm. Moreover, it was proposed that the observed broadening of obtained decay rate distributions reflects the disorder in the samples.     

Tripodal amido complexes: molecular "claws" in main group and transition metal chemistry

The chemistry of transition metal amides has received new impetus in recent years due to the systematic exploitation of the amido function [NR(2)](-) in ligand design. A class of 3-fold symmetrical tripodal amido ligands has proved to be a valuable tool in the stabilization of early transition metal and main group metal complexes and complex fragments. Moreover, promising strategies for their use as chemical reagents and homogeneous catalysts have been developed. An overwiew of the current state of this field is given and the potential for further development will be highlighted.     

On a correlation between the surface chemistry and the felting behavior of wool

The felting behavior of wool fibers is found to be correlated with their flocculation properties. The interaction between the fibers is suggested as the common factor responsible for this correlation. It is observed that in a felting medium there is attraction between natural wool fibers. Such attraction is observed to be greatly diminished, or absent, after the wool has been shrinkproffed by any one of several chemical modification treatments. Hydrophobic attraction and electrostatic repulsion are proposed as significant components of the interaction between fibers in aqueous media. These components are linked to the surface chemistry of natural and chemically modified wool. It is proposed that the hydrophobic nature of the fiber surface promotes the felting shrinkage of natural wool fabrics, that shrink-resist chemical treatments of wool top make the fiber surface more hydrophilic and may increase the electrostatic repulsion between fibers, and that the influence of surfactants on felting depends on the adsorption energy of the surfactant at the fiber surface. These ideas are presented as a guide for the development of further shrink-resist chemical modifications of wool. One of eight papers to be published from the Symposium “Surface Active Agents in the Textile Industry,” presented at the AOCS Meeting, New Orleans, April 1970. W. Utiliz. Res. Dev. Div., ARS, USDA.     

1,3-Bisdiphenylphosphinoferrocenes: the unexpected 2,5,-dilithiation of dibromoferrocene towards a new area of ferrocene-ligand chemistry

The synthesis and characterization of 1,3-bis-diphenylphosphinoferrocene is described for the first time. The ligand is obtained as a byproduct of the ortho-lithiation of 1,1′-dibromoferrocene, as a consequence of the dilithiation of one of the cyclopentadienyl rings. The intermediate compound 1,1′-dibromo-2,5-bis-(diphenylphosphino)ferrocene which is the precursor compound to the new ligand has been structurally characterized. Further reaction of 1,1′-dibromo-2,5-bis-(diphenylphosphino)ferrocene with n-butyllithium followed by quenching with chlorodiphenylphosphine affords the new 1,2,3,1′-tetrakis(diphenylphosphino)ferrocene, while the similar reaction of 1,1′-dibromo,2,2′-bis(diphenylphosphino)ferrocene gives 1,1′,2,2′-tetrakis(diphenylphosphino)ferrocene.     

Atomic force microscopy investigation of the kinetic growth mechanisms of sputtered nanostructured Au film on mica: towards a nanoscale morphology control

The study of surface morphology of Au deposited on mica is crucial for the fabrication of flat Au films for applications in biological, electronic, and optical devices. The understanding of the growth mechanisms of Au on mica allows to tune the process parameters to obtain ultra-flat film as suitable platform for anchoring self-assembling monolayers, molecules, nanotubes, and nanoparticles. Furthermore, atomically flat Au substrates are ideal for imaging adsorbate layers using scanning probe microscopy techniques. The control of these mechanisms is a prerequisite for control of the film nano- and micro-structure to obtain materials with desired morphological properties. We report on an atomic force microscopy (AFM) study of the morphology evolution of Au film deposited on mica by room-temperature sputtering as a function of subsequent annealing processes. Starting from an Au continuous film on the mica substrate, the AFM technique allowed us to observe nucleation and growth of Au clusters when annealing process is performed in the 573-773 K temperature range and 900-3600 s time range. The evolution of the clusters size was quantified allowing us to evaluate the growth exponent 〈z〉 = 1.88 ± 0.06. Furthermore, we observed that the late stage of cluster growth is accompanied by the formation of circular depletion zones around the largest clusters. From the quantification of the evolution of the size of these zones, the Au surface diffusion coefficient was evaluated in . These quantitative data and their correlation with existing theoretical models elucidate the kinetic growth mechanisms of the sputtered Au on mica. As a consequence we acquired a methodology to control the morphological characteristics of the Au film simply controlling the annealing temperature and time.     

In situ nanoscale wet imaging of the heterogeneous catalyzationof nitriles in a solution phase: novel hydrogenation chemistry through nanocatalysts on nanosupports

Wet-environmental transmission electron microscopy studies of heterogeneous hydrogenation of complex nitriles in a liquid phase over new mesoporous cobalt-promoted ruthenium nanocatalysts on reducible nanotitania supports are presented. The desorbed organic products in the dynamic liquid phase hydrogenation are imaged situ on the nanoscale. The direct studies on the “nanocomposite” catalysts are correlated with parallel reaction chemistry measurements. They demonstrate high hydrogenation activity at low operating temperatures in the presence of atomic scale anion vacancy defects associated with Lewis acid sites at the nanosupport surface and an electronic and synergistic contribution to the promoter mechanism. The combined synergistic effect between the two metals and the interaction with the reduced nanosupport leading to an electronic modification lead to highly reactive site for the hydrogenation catalysis. The results illustrate novel selective hydrogenation chemistry with mesoporous nanocatalyst systems on nanosupports.     

Solvothermal in situ metal/ligand reactions: a new bridge between coordination chemistry and organic synthetic chemistry

Several important solvothermal (including hydrothermal) in situ metal/ligand reactions and their mechanisms, including dehydrogenative carbon-carbon coupling, hydroxylation of aromatic rings, cycloaddition of organic nitriles with azide and ammonia, transformation of inorganic and organic sulfur, as well as the CuII to CuI reduction, are outlined in this Account. The current progress clearly demonstrates the important potential of such reactions in the crystal engineering of functional coordination compounds and one-pot synthesis of some unusual organic ligands that are inaccessible or not easily obtainable via conventional methods, thereby substantiating our expectation that a new bridge has been created between coordination chemistry and synthetic organic chemistry.     

Revisit the adhesive contact between a nanoscale rigid sphere and an elastic half-space: considering the effect of sphere size

The current paper revisits the adhesive contact between a rigid nanoscale sphere and an elastic half-space. Using analytical solution for traction and a modified numerical scheme, a new simulation is proposed. The adhesive contact is simulated faster and more easily than previous researches. The effect of sphere size is investigated. A modified spherical JKR model and spherical DMT model are proposed. The results are compared with spherical JKR, spherical DMT, and rigid sphere model. The load–approach and contact radius–load relations can be predicted by the modified spherical JKR model for sphere radius larger than 50?. Finally, approximation equations for pull-off force vs. Tabor parameter and jump-in distance vs. Tabor parameter are proposed.     

On the nature of polymer interfacesd and interphases

An abbreviated review of the current state of knowledge of polymer interfacial phenomena is given. Classical thermodynamics treats the interfacial zone (the interphase) as a “black box” and yields rigorous relationships among interfacial quantities. A recent reformulation of interphase thermodynamics, which eliminates the use of a Gibbs dividing surface, is shown to be an invaluable tool for investigating interfacial properties. Microscopic theories, such as the gradient theory, yield more details about what is in the black box, but the information is only approximate. The gradient theory has been used to: (1) relate the surface tension of a polymer liquid to its isothermal compressibility, (2) develop a quantitative theory of polymer liquid surface tension, and (3) determine the interfacial tension between two immiscible polymer liquids. The gradient theory will be shown to be in harmony with the microscopic theory of Helfand and co-workers although the latter treats polymer interfaces from a completely different point of view.     

The chemistry and electrochemistry associated with the electroplating of group VIA transition metals

An overview of the requirements for the electroplating of refractory metals from molten salts is presented, followed by a discussion of recent electrochemical studies which have been carried out to delineate the solution chemistry of alkali metal halide plating baths. New results for halide baths involving chromium and molybdenum are presented and considered from the view of both solution chemistry and the electrocrystallization processes of these metals. Advantages and disadvantages of these electrolytes are discussed in the context of plating cell development and pulse modulated plating techniques.This paper was presented at a workshop on the electrodeposition of refractory metals, held at Imperial College, London, in July 1985.     

Opinion: On the Way towards the New Paradigm of Atherosclerosis

Atherosclerosis is a multicausal disease characterized by the formation of cholesterol-containing plaque in the pronounced intima nearest to the heart’s elastic-type arteries that have high levels of blood circulation. Plaques are formed due to arterial pressure-induced damage to the endothelium in areas of turbulent blood flow. It is found in the majority of the Western population, including young people. This denies the monogenic mechanism of atherogenesis. In 1988, Orekhov et al. and Kawai et al. discovered that the presence of atherogenic (modified, including oxidized ones) LDLs is necessary for atherogenesis. On the basis of our discovery, suggesting that the overloading of enterocytes with lipids could lead to the formation of modified LDLs, we proposed a new hypothesis explaining the main factors of atherogenesis. Indeed, when endothelial cells are damaged and then pass through the G2 phase of their cell cycle they secrete proteins into their basement membrane. This leads to thickening of the basement membrane and increases its affinity to LDL especially for modified ones. When the enterocyte transcytosis pathway is overloaded with fat, very large chylomicrons are formed, which have few sialic acids, circulate in the blood for a long time, undergo oxidation, and can induce the production of autoantibodies. It is the sialic acids that shield the short forks of the polysaccharide chains to which autoantibodies are produced. Here, these data are evaluated from the point of view of our new model.     

On the several molecules and nanostructures of water

This paper investigates the water molecule from a variety of viewpoints. Water can involve different isotopes of Hydrogen and Oxygen, it can form differently shaped isomer molecules, and, when frozen, it occupies space differently than most other substances do. The tool for conducting the investigation of all this is called 'Algebraic Chemistry'. This tool is a quantitative model for predicting the energy budget for all sorts of changes between different ionization states of atoms that are involved in chemical reactions and in changes of physical state. The model is based on consistent patterns seen in empirical data about ionization potentials, together with rational scaling laws that can interpolate and extrapolate for situations where no data are available. The results of the investigation of the water molecule include comments, both positive and negative, about technologies involving heavy water, poly water, Brown's gas, and cold fusion.     

Mechanical properties of porous ceramics in compression: On the transition between elastic,brittle, and cellular behavior

This paper deals with the uniaxial compression behavior of porous ceramics within a wide range of porosity, varying from 30 to 75 vol%. The load–displacement curves recorded on porous alumina samples showed a transition between a typical brittle behavior at porosity fractions below 60 vol% and a damageable, cellular-like behavior, at higher porosity fractions. This transition in fracture mode was confirmed by in situ compression tests in an X-ray tomograph. Based on a simple model taking into account the competition between the crack length initiating from spherical pores and the mean distance between pores, the porosity at which the transition took place was estimated. The influence of the pore size also depended on the volume fraction of pores: no size effect was noted at the lowest porosity whereas a statistical effect on the size of the solid walls was observed at higher porosity, with an increase in fracture strength with small pores.     

On the nature of turbulent and fast fluidized beds

Fluidization characteristics have been investigated over the range from bubbling to fast fluidization by using a circulating fluidized bed cold model (riser diameter: 50 mm i.d., riser height: 2 390 mm, powder: fluidized cracking catalyst (FCC) and silica sand). Special focus was placed on the concepts of turbulent and fast fluidization regimes. Based on careful measurements of flow structure and cluster behavior, it is demonstrated that the turbulent fluidization regime is a transition regime between bubbling and fast fluidization. Experimental evidence supports the postulate that in fast fluidization the clusters adjust their size so that the gas drag force acting on them compensates with their gravity.     

Palladium nanocrystals supported on photo-transformed C60 nanorods: Effect of crystal morphology and electron mobility on the electrocatalytic activity towards ethanol oxidation

We report on the synthesis and decoration of high-aspect-ratio crystalline C₆₀ nanorods (NRs) by functionalized palladium nanoparticles with an average size of 4.78 ± 0.66 nm. In their pristine form, C₆₀ NRs suffer from partial damage in the solution-based decoration process resulting in poor crystallinity. However, by modifying the NR surface via in situ photochemical transformation in the liquid state, we are able to prepare highly stable NRs that retain their crystalline structure during the decoration process. Our method thus opens up for the synthesis of highly crystalline nanocomposite hybrids comprising Pd nanoparticles and C₆₀ NRs. Bys measuring the electron mobility of different C₆₀ NRs, we relate both the effect of electron mobility and crystallinity to the final electrocatalytic performance of the synthesized hybrid structures. We show that the photo-transformed C₆₀ NRs exhibit highly advantageous properties for ethanol oxidation based on both a better crystallinity and a higher bulk conductivity. These findings give important information in the search for efficient catalyst support.