Search results for "X-ray"

Synthesis of Uvarovite Garnet

1989

A garnet with interesting optical properties is synthesized by means of the ceramic method and the formation of gels. Colloidal silica or tetraethoxysilane (TEOS) is used as a starting reagent in the latter method of synthesis, together with nitrate and chloride salts of the remaining components. Use is made of ultraviolet-visible and infrared spectroscopy techniques and X-ray diffraction in studying the evolution of the system. Formation of the garnet phase at lower temperatures is observed when using the gel methods, as well as the absence of chromates during the process in the samples which contained chlorides.

Study of interface diffusion of Ti and TiN PVD layers by Bremsstrahlung-induced AES

1992

The influence of heat treatment in ultrahigh vacuum (UHV) on Ti and TiN layers coated by physical vapour deposition (PVD) has been studied by AES, XPS and bremsstrahlung-induced AES. It could be concluded that up to 500 o C (1 h) the Ti layer does not change significantly. At the TiN/steel substrate interface, however, a counter-diffusion of nitrogen and adventitious oxygen takes place, resulting in partial nitridation of the steel substrate and oxidation of the coating

Thermal behaviour and electrochemical properties of bis(trifluoromethanesulfonyl)amide and dodecatungstosilicate viologen dimers

2012

We report the synthesis and characterization of dimeric viologen salts (1',1''-(alkane-1,n-diyl)bis(1-ethyl-4,4'-bipyridinium) with n = 4-10) with bis(trifluoromethanesulfonyl)amide (bistriflimide, Tf(2)N(-)) as a counteranion. For n = 4, 5 and 6, and for the nonylviologen cation (1,1'-dinonyl-4,4'-bipyridinium) we also prepared salts with the totally inorganic dodecatungstosilicate anion, SiW(12)O(40)(4-), featuring a poly-charged surface and nanosized dimensions. The materials have been characterized by means of calorimetric techniques, X-ray diffraction and solid state NMR and a comparison is made with analogous monomeric viologen salts exhibiting smectic mesophases. A strong odd-even ef…

Characterization of [Cu]-MCM-41 by XPS and CO or NO adsorption heat measurements

2002

We report the characterization of copper doped MCM-41 prepared by original direct synthesis by XPS and adsorption calorimetry of CO and NO, which are selective molecular probes for Cu(I) and Cu(II) respectively. Investigation of the nature of the copper ions in this particular calcined Cu-MCM-41 by NO adsorption calorimetry shows that two types of energetically distinct adsorption sites exist, meaning the presence of two populations of Cu(II) species differently coordinated to the silica surface in quasi-equimolar concentration, as ascertained by XPS data. A small amount of Cu(I) was also detected, probably stemming from a partial reduction upon the successive vacuum treatments. The respect…

Unexpected Formation of a 1,2-Dichloroacenaphthylene in a Friedel-Crafts Reaction with Chloral Hydrate

2012

An unprecedented rearrangement was encountered during an attempted alkylation of an electron-rich naphthalene with chloral hydrate. The reaction produced a dichlorinated acenaphthylene and presumably involves the intermediate formation of a chloronium ion which is opened to produce the five-membered ring of the final product.

Radiation-induced defects and their recombination processes in the x-ray storage phosphor BaBr2:Eu2 

2003

The recombination processes in the x-ray storage phosphor BaBr2:Eu2+ were investigated by optical and magneto-optical methods. A structure-sensitive investigation of the defects involved in the recombination processes was performed by detecting the microwave-induced changes in the recombination luminescence in a high magnetic field. F centres as well as VK hole centres are created after x-irradiation at low temperatures. The low-energy recombination band peaking at about 460 nm is due to F–VK centre recombinations, whereas the two high energy bands at 282 and 315 nm are probably due to recombinations of self-trapped excitons.

Cover Feature: Controlling the Formation of Sodium/Black Phosphorus IntercalationCompounds Towards High Sodium Content (8/2021)

2021

Tuning the Magnetic Properties of Carbon by Nitrogen Doping of Its Graphene Domains

2015

Here we present the formation of predominantly sp-coordinate carbon with magnetic- and heteroatom-induced structural defects in a graphene lattice by a stoichiometric dehalogenation of perchlorinated (hetero)aromatic precursors [hexachlorobenzene, CCl (HCB), and pentachloropyridine, NCCl (PCP)] with transition metals such as copper in a combustion synthesis. This route allows the build-up of a carbon lattice by a chemistry free of hydrogen and oxygen compared to other pyrolytic approaches and yields either nitrogen-doped or -undoped graphene domains depending on the precursor. The resulting carbon was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM…

Binding Modes of Nonspherical Anions to N-Alkylammonium Resorcinarenes in the Solid State

2012

A series of hydrogen bond stabilized N-alkylammonium resorcinarene salts with nitrate, triflate, and picrate as the counteranions were synthesized and characterized with 1H NMR and electrospray ionization (ESI) mass spectrometry. Together with electrostatic interactions, the binding of the anions with several hydrogen bond donor sites proceeds through a complex array of intra- and intermolecular hydrogen bonds, evidenced by single crystal X-ray diffraction analysis. These N-alkyl ammonium resorcinarenes bind the larger nonspherical anions into deformed cavitand-like structures and enforce a transformation of the resorcinarene conformation from almost symmetrical to extremely distorted.

Synthesis, characterization and X-ray crystal structures of cyclam derivatives. 7. Hydrogen-bond induced allosteric effects and protonation cooperati…

2005

The unprecedented cooperative protonation properties displayed by a barrel-shaped macrotricyclic tetraamine incorporating two 14-membered bisamide rings maintained in a face-to-face arrangement is rationalized in terms of allosteric effects upon binding of the first and third protons.