Materials Literature
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ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA heteropolyanion with fivefold molecular symmetry that contains a nonlabile encapsulated sodium ion. The structure and chemistry of [NaP5W30O110]14-Mohammed H. Alizadeh, Subhash P. Harmalker, Yves Jeannin, Jeanne Martin-Frere, and Michael T. PopeCite this: J. Am. Chem. Soc.…
Abstract Amorphous silica phases (opal-A) precipitate in nature due to the formation of dense colloids in supersaturated alkaline aqueous solutions with low relative concentrations of other ions. Opal-A dissolves and yields solutions of still relatively high silica content. In pore waters containing abundant cations,…
A general approach to diffusion-limited crystal growth is proposed. It consists of a modified (nonequilibrium) Cahn-Hilliard representation of the interface coupled to a diffusion equation. Arguments are given as to its superiority over previous models. These are illlustrated in a one-dimensional solution which shows…
Abstract The diagenetic sequence of silica is examined in terms of several thermodynamic and kinetic concepts. The relationship between solubility and surface area or particle size is sufficient to explain simple opal-A --> opal-CT --> quartz transformations, suggesting that the role of temperature and o…
Mechanisms of failure in a unidirectional Sic‐fibe/glass‐ceramic composite are investigated using in situ observations during tensile and flexural loading. These experiments show that failure in tension occurs in several stages (similar to certain other brittle fiber composites): multiple matrix cracking, followed by…
The ultraviolet (UV)/ozone surface cleaning method is reviewed. The UV/ozone cleaning procedure is an effective method of removing a variety of contaminants from surfaces. It is a simple-to-use dry process which is inexpensive to set up and operate. It can rapidly produce clean surfaces, in air or in a vacuum system,…
Electroactive polyaniline coatings have been deposited on ferritic stainless steels. The coatings appear to be deposited over the passive metal oxide film but can undergo electron transfer with the metal. Polyaniline immobilized on the alloys imparts a form of anodic protection which stabilizes the materials in minera…
The results of structural and theoretical studies on cluster compounds with a framework in the form of a triangle made up of metal atoms are examined, a systematic account is given of the types of three-membered metallocycles in which the number of electrons is different from the magic number, and the causes of their…
Raman spectra are reported for single Se and Te chains stabilised in the regular system of parallel channels of a mordenite dielectric matrix. The symmetric bond-stretching mode frequency is determined for Se chains (260 cm -1 ) and for Te chains (164 cm -1 ). The distinct bond-bending mode bands associated with ring-…
We develop a model for the recrystallization of Si films that are traversed by a molten zone. The model simulates the branching behavior of low-angle grain-boundary defects in these films to a remarkable degree. The simulated subboundary patterns scale approximately as the square root of the scan velocity, in excellen…
A well-resolved core exciton at the bulk diamond C-$1s$ absorption edge has been observed using high-resolution partial-yield spectroscopy with synchrotron radiation. The obtained excitonic binding energy, 0.19\ifmmode\pm\else\textpm\fi{}0.015 eV, agrees well with a first-principles effective-mass approximation (EMA).…
The optical modulation technique is used for direct determination of energy levels and the effective correlation energy ${U}_{\mathrm{eff}}$ of dangling-bond defects. With an accuracy of 0.1 eV we found for the dangling-bond defect in $a$-Si: H, ${U}_{\mathrm{eff}}=0.5$ eV; in $a$-${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$…
Resistivity measurements on epitaxial, single-crystal films of Co${\mathrm{Si}}_{2}$ grown on Si show little dependence on film thickness down to \ensuremath{\sim}60 \AA{}. This dimension is much less than the bulk transport scattering length of \ensuremath{\sim} 1000 \AA{} as determined from magnetoresistance measure…
The electronic and vibrational properties of group IVB transition-metal dichalcogenides are investigated by near-normal-incidence reflectivity measurements. The experimental spectra are discussed in terms of a dielectric function expressed as epsilon ( omega )=1+ chi VE + chi PH + chi FC , where chi VE represents the…
Five absorption bands of the allowed 5d←4f transitions of Ce3+ were detected in the ultraviolet region between 37 and 51 × 103 cm-1 by σ- and π-polarized absorption, luminescence excitation, and MCD spectra with the single crystals of Ce3+ doped lanthanum ethylsulphate enneahydrate. In the crystal, Ce3+ is in a D 3h l…
A general theoretical treatment is developed for NMR spin-lattice (T 1 and T 1 rho ) and spin-spin (T 2 ) times for relaxation due to modulation for dipolar interactions by diffusion of atoms on inequivalent lattice sites. This extends previous calculations of T 2 to the other relaxation parameters and gives rate equa…
A model of the superionic conductor Ag 2 S is proposed and studies by the molecular dynamics technique using effective pair potentials. The self-diffusion for silver, D Ag (T), is in good agreement with experiment. The Ag density map and its temperature dependence is calculated. The authors also calculate the X-ray an…
The Raman spectra of the symmetric stretching v 1(A′1) mode of NO3 - ions have been measured in a series of molten nitrates, LiNO3, NaNO3, KNO3, RbNO3, CsNO3, AgNO3, TlNO3, at a temperature 10–20 K above each melting point. Temperature dependence of the Raman spectrum was also measured in molten NaNO3. Reorientation o…
The phase transformations and magnetic properties of single crystals of a MnAlC alloy are investigated. Using optical microscopy and X-ray diffraction method it is found that the morphology and the number of orientations of the τ-phases formed at 500 and 600 °C are different. This leads to a considerable difference i…
On the basis that metal films possess the properties of high reflection for infrared and induced transmission for visible bands, the authors have designed a broadband dichroic filter capable of transmitting visible and reflecting infrared bands through stacking to form a combined dielectric–metal–dielectric thin-film…