Materials Literature
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We have studied the vibrational and electronic structure and the elementary charged excitations of poly(1,4-phenylene-vinylene) and a series of its (2,5-alkoxy) derivatives including poly(2,5-methoxy-PV), poly(2,5-hexoxy-PV), poly(2,5-octoxy-PV), and poly[2-methoxy,5-(2'ethyl-hexoxy)-PV] by absorption, photoinduced (P…
ZnO:Al films were deposited on (12̄10) oriented sapphire substrates heated up to 400 °C by rf magnetron sputtering from a ZnO target mixed with Al2O3 of 2 wt%. Films deposited on a substrate heated to a temperature in the range 50–350 °C were (0001) oriented single crystals but those grown at 400 °C consisted of cryst…
Molecular dynamics calculations are performed that simulate the diffusion of penetrant molecules through an amorphous polymer. For the polymer and the penetrant molecules, model potentials are chosen that approximate polyethylene and methane, respectively. The simulations extend over several hundred picoseconds. The r…
Phonon-dispersion curves, lattice mode Gr\"uneisen parameters, and the coefficients of thermal expansion are calculated for Si and C within a tight-binding model. The results are in good agreement with experimental data. The origin of the negative thermal expansion in Si is examined, and we find that the different the…
A molecular-dynamics simulation has been carried out for liquid and amorphous selenium in the temperature range 350--720 K. The simulation used 64 atoms in a constant-volume simple cubic cell, and the energy surfaces and forces were calculated using the density-functional formalism, with a local-density approximation…
Pseudomonas aeruginosa elastase (PAE) is a zinc metalloprotease with 301 amino acids. We have crystallized and solved the three-dimensional structure of PAE, using data to 1.5-A resolution, and have refined the native molecular structure to R = 0.188. The overall tertiary structure of the PAE molecule is similar to th…
First direct experimental evidence for clathrate structures of (H2O)nH+ (n=20,21) is reported based on a technique allowing the number of nonhydrogen-bonded surface hydrogens to be counted. Neutral clusters (H2O)n⋅((CH3)3N)m, prepared in a pulsed nozzle supersonic expansion, are ionized by multiphoton ionization and i…
The stress in diamond films prepared by microwave plasma CVD was investigated as a function of methane concentration (0.2%–3.0%) and deposition temperature (600–900 °C). Tensile and compressive total (thermal and intrinsic) stress were observed, depending on the deposition conditions. The thermal stress is compressive…
The electron localization is increased with increasing one dimensionality of a quasi-one-dimensional disordered system (quasi-1D-DS). This concept is tested by studying the electron localization in the methyl ring-substituted derivative of polyaniline (PAN), poly(o-toluidine) (POT). The studies include the measurement…
[Fe(ptz)6](BF4)2 (ptz=1-propyltetrazole) is an Fe(II) spin crossover system, which shows a light-induced low-spin (1A1)→high-spin (5T2) conversion below ∼50 K by irradiating into the spin allowed 1A1→1T1 d–d absorption band. This phenomenon, known as light-induced excited spin state trapping (LIESST), is reversible, a…
The electronic properties of hexagonal graphite have been studied in the framework of the density-functional technique, using nonlocal ionic pseudopotentials and a large number of plane waves. The valence charge density and the density of states are presented, as well as the band structure and the charge-density contr…
The soft-potential model (an extension of the well-known tunneling model for two-level states in glasses) has been formulated in terms of soft-mode eigenvectors in order to characterize the localization of these modes. The interaction with high-frequency modes explains the absence of very small restoring-force constan…
We have applied the theory of McCumber to the (4)4I(13/2) ? (4)I(15/2) transition of Er(3+) -doped glasses and confirmed its ability to provide both spectra and accurate values of cross sections. For an Al/P-silica fiber, the exact McCumber treatment is within 3% of the measured emission cross section, whereas an Eins…
The relationships between the molecular packing and the morphology of rubredoxin crystals, a metalloprotein, have been studied in detail through the periodic bond chains (PBC) method of Hartman and Perdok (1955). To carry out the PBC analysis the authors considered that the crystallizing particle consisted of the prot…
There have been many previous studies of the IV-III phase transition in ammonium nitrate and water is known to play a mechanistic role. This work examines the effect of other solvents and additives on the transition kinetics of single crystals and combines these data with structural information to examine the overall…
An account is given of the origins, in the molecular electronic properties and crystal structure, of the large quadratic optical nonlinearities found in some organic crystals. Particular cases, in which powerful second-harmonic generation or large Pockels effects have been found, chosen to illustrate the influence of…
The structural and stereochemical factors involved in the oriented nucleation of CaCO 3 under compressed Langmuir monolayers have been studied by optical and electron microscopy, and X-ray and electron diffraction. The effect of headgroup charge, stereochemistry and changes in supersaturation have been investigated. A…
Experiments were carried out to study the precipitation of calcium carbonate resulting from the mixing of aqueous solutions of calcium nitrate and sodium carbonate in a continuous-flow crystallizer at 25 degrees C in the pH range 8.5 to 10.5, reagent concentration 0.025 to 0.2 mol/l and solution residence times of 5 t…
The development of structural models for predicting the external morphology of crystalline materials is presented and discussed in terms of their applications to molecular crystals. The predicted crystal morphologies of a number of molecular materials including alpha -sulphur, naphthalene, benzoic acid and hexamine ar…
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