Materials Literature
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The laser-induced deposition of high-purity aluminum metal has been achieved by pyrolytic decomposition of trimethylamine aluminum hydride. The chemical structure of the precursor affords a high ambient vapor pressure which results in rapid rates of aluminum film formation. In addition, the precursor is nonpyrophoric,…
We suggest that weak electron tunneling between layers is responsible for the experimentally observed dramatic deviations from two-dimensional behavior in the magnetoresistance in the metallic phase of the quasi-two-dimensional conductors (TMTSF${)}_{2}$${\mathrm{ClO}}_{4}$ and (TMTSF${)}_{2}$${\mathrm{PF}}_{6}$. We p…
The kinetics of electrochemical doping of polyaniline films has been studied using in situ ESR experiments. It has been found that the kinetics and the doping level achieved during a potential-reading step depend on the previous electrochemical events undergone by the sample. It is shown that slow relaxation process t…
(C3H7NH3)2PbCl4 is a new member of the family of perovskite-type layer compounds. Calorimetric, X-ray diffraction, and dieletric measurements show the occurrence of a structural phase transition at Tc ≈ 339 K, from an orthorhombic room temperature phase (ORT) with space group Pnma (Z = 4) to a monoclinic high temperat…
Frequency and temperature dependences of dielectric constant (ϵ′) and dielectric loss (ϵ″) are studied for glassy Se and Se100−xTex alloys where 2 ≦ x ≦ 25. The measurements are made in the audio-frequency range (120 Hz to 10 kHz) and in the temperature range 100 to 330 K. The results indicate that in glassy Se, ϵ′ an…
Needle crystal growth in the presence of kinetic effects and anisotropic surface energy is studied. Within the boundary layer model it is shown that at the dimensionless undercooling Δ > 1, instead of a parabolic dendrite, an “angular” dendrite, having planar sections far from the tip, grows. At Δ c > 1 needle crystal…
Electrical transport properties of a sintered yttrium aluminum garnet (YAG) doped with Ca or Mg have been investigated as a function of temperature and partial pressure of oxygen. Conductivity and ionic transport measurements show Ca- and Mg-doped YAG to be mixed ionic-electronic p-type conductors exhibiting an activa…
Room-temperature photoluminescence (PL) and electrolyte electroluminescence (EL) spectra of polycrystalline CdS samples, in air and in contact with aqueous electrolytes, have been studied as a function of the atmosphere and temperature of annealing, light excitation intensity and wavelength, applied bias, electrolyte…
Optical absorption (\ensuremath{\sim}1--5 eV) in rf-deposited hydrogenated (20--40 at. %) amorphous ``diamondlike'' carbon films has been studied as a function of heat treatment. For E\ensuremath{\gtrsim}2.5 eV a Tauc behavior is exhibited. Optical band gaps ${E}_{g}$ are \ensuremath{\lesssim}2.4 eV. At lower energies…
Deposition of Cu in ultrahigh vacuum on a clean Pd{001} surface leads to the growth of a new crystalline Cu phase with body-centered-tetragonal (bct) structure well ordered up to about 10 layers. A low-energy electron-diffraction (LEED) analysis of 6-layer films finds the bulk lattice parameters to be a=2.75 A\r{} and…
The bulk band structure of the IV-VI semiconductors PbSe and PbTe was determined experimentally through angle-resolved photoemission from cleaved PbSe(100) and PbTe(100) surfaces, using synchrotron radiation for photoexcitation. By analyzing spectra recorded in electron emission normal to the surface over a wide range…
Iron-bismuthate glassy semiconductors were prepared in a range of compositions and their electrical transport properties were measured in the temperature range of 100–500 K. The electrical data were analyzed in the light of the models of polaronic hopping conduction. The analysis showed that the high-temperature condu…
Accurate and explicitly electron-correlated wave functions have been used to determine the dynamic hyperpolarizability tensor (γ) and the dynamic field-gradient polarizabilities (B and C) for helium. The γ-tensor is related to nonlinear optical processes such as the Kerr effect, second- and third-harmonic generation a…
1,3-Bis(2-chloroethyl)-1-nitrosourea (BCNU) has been found to be an effective chemotherapeutic agent against brain tumors. However, because it has a very short half-life in plasma, the exposure of neoplastic cells to BCNU is very brief. The delivery of BCNU may be enhanced by using controlled release polymers. We meas…
The ultrafast photodynamics of four-coordinate nickel(II) porphyrins in noncoordinating solvents has been studied using femtosecond time resolved optical spectroscopy. Unambiguous evidence has been found for the formation of a metastable metal (d,d) excited state in less than 350 fs following excitation of the macrocy…
Thin films for optical second-harmonic generation (SHG) were prepared from a newly designed and synthesized amorphous polymer that incorporated a high density of active nonlinear optical groups (p-nitroaniline as attached side groups). For alignment of the nonlinear groups a very high electric field was applied by a c…
Observations of K -edges are made for solid targets compressed by laser-generated coalescing shocks. Using a short pulse blacklighter to avoid radiative pre-heating of the compressed solid, a blue-shifted chlorine K -edge is observed. Comparisons with simple theoretical models have indicated the relative magnitude of…
We have performed photoluminescence, photoexcitation, and transmission electron microscopy measurements on boron nitride films grown by chemical vapor deposition and later reacted with potassium. After reaction, the potassium atoms were found to intercalate the BN host and to form a (2×2)R0° in-plane structure which i…
By solving the full elastic equations on a two-dimensional lattice we grow cracks under various breaking conditions for a system that is submitted to external shear. We find that deterministic fracture patterns are in general branched and can be fractal. This effect is due to the competition between the direction of g…
We introduce a Ginzburg-Landau model for solid solutions to examine elastic effects near the phase separation. As a first application the spinodal curve is calculated when the elastic moduli depend on the concentration and an external stress is applied. The instability is triggered by fluctuations with wave vectors in…