Nuclear probes in the materials science of solar cells

We present background material about solar cells and the copper-indium-sulphur system and then discuss three important processes for the production of CuInS₂ solar-cell material. These include: sulphurization of metallic copper-indium precursors, physical vapour deposition of the elements, and three-source molecular beam deposition. Using perturbed angular correlations with the¹¹¹In-¹¹¹Cd probe, we are able to identify the indium-containing phases of the system and thus to characterize the cited production processes. The prospects of nuclear probe methods in the development of solar-cell materials are discussed.     

Far-infrared studies of ethanols and fluoroethanols trapped in low-temperature matrices

Ethanol, its deuterated derivatives (C₂H₅OD, C₂D₅OD) and fluoroethanols (CFH₂CH₂OH, CF₃CH₂OH) have been isolated in low temperature matrices and investigated in the far-infrared region. From the concentration dependency of the observed bands and from studies of the pure alcohols in the gaseous, liquid, and solid phase it was found that the hydrogen bond stretching frequencies ν_σ associated with the hydrogen bonded system OH?O appear in the 100 – 160 cm^?1 range. At higher M/A ratios the OD(OD) torsion modes τ_OH are dominating and were identified in the 200 – 300 cm^?1 region. The influence of various matrix materials like argon, krypton, xenon, nitrogen and methane on the low frequency spectra of ethanol have also been studied. It was found, that nitrogen and methane matrices produce significant changes in the far infrared spectra.     

A Model of Simple Liquids

The intuitively clear hole defect model can be used for quantitative estimates and for understanding the properties of liquids. An ideal liquid is defined in analogy with an ideal gas and corrected for real liquids with hole defects. The good agreement permits an application of this approximation process to the understanding of some important material properties. The effective model fills a gap in the area of applied chemistry and of chemical teaching. It also leads to a correction factor for the failure of the theorem of corresponding states. The reasons for the applicability of such a simple model are demonstrated on the basis of the Lennard-Jones potential.     

Spectral Properties of Zero Temperature Dynamics in a Model of a Compacting Granular Column

The compacting of a column of grains has been studied using a one-dimensional Ising model with long range directed interactions in which down and up spins represent orientations of the grain having or not having an associated void. When the column is not shaken (zero “temperature”) the motion becomes highly constrained and under most circumstances we find that the generator of the stochastic dynamics assumes an unusual form: many eigenvalues become degenerate, but the associated multi-dimensional invariant spaces have but a single eigenvector. There is no spectral expansion and a Jordan form must be used. Many properties of the dynamics are established here analytically; some are not. General issues associated with the Jordan form are also taken up.     

Cyclooctene epoxidation with H2O2 and single crystal X-ray determined crystal structures of new molybdenum and tungsten catalysts bearing the hydrophilic ligand hydroxymethyldiphenylphosphine oxide

The dioxo molybdenum and tungsten complexes MoO₂Cl₂(OPPh₂CH₂OH)₂ and WO₂Cl₂(OPPh₂CH₂OH)₂ have been synthesized and characterized by FT-IR, ¹H and ³¹P NMR. Their structures, as determined by single crystal X-ray diffraction analysis, reveal distorted octahedral geometries with cis terminal oxygen atoms, trans Cl ligands and that the hydroxymethyldiphenylphosphine oxide ligands coordinate through the oxygen atom bonded to the P atom. Both of the compounds are studied as catalysts for the epoxidation of cis-cyclooctene in the presence of hydrogen peroxide as a source of oxygen. Both complexes showed good activity and very high selectivity for the formation of cyclooctene oxide.     

meso-1,2-Bis­(methyl­azo)-1,2-di­phenyl­ethane

The title compound, meso-1,2-bis­(methyl­diazenyl)-1,2-di­phenyl­ethane, C₁₆H₁₈N₄, is arranged in a disordered manner around an inversion point. The N—N atom distances in the azo group of 1.192 (8) and 1.195 (8) Å, and the C—C atom distances in the ethyl­ene moiety at 1.512 (8) and 1.503 (8) Å in the two models [refined to 51.7 (6) and 48.3 (6)% occupancies] were not significantly different.     

Preparation and crystal structure of a quadruply bonded dimolybdenum complex with trans-crotonate ligands

A quadruply bonded dimolybdenum complex with trans-crotonate ligands, Mo₂(O₂CC₃H₅)₄, was synthesized and characterized by UV–VIS, IR, and NMR spectra. The crystal structure was determined by an X-ray single crystal diffraction analysis. The title complex (C₁₆H₂₀O₈Mo₂, M _w = 532.2) crystallized in the triclinic space group P-1 with the following crystallographic parameters: a = 10.236(2) ?, b = 10.393(2) ?, c = 10.524(2) ?, α = 89.59(1)°, β = 73.34(1)°, γ = 70.78(2)°, V = 1008.1(3) ?³, Z = 2, D _c = 1.753 Mg m⁻³, μ(Mo Kα = 0.71073 ?, F(000) = 528, and final R ₁ = 0.041, wR ₂ = 0.114 for observed reflections 2889 (I > 2σ(I)). The Mo₂ ⁴⁺ unit was surrounded by four trans-crotonate ligands resulting in a paddle wheel structure with one disordered trans-crotonate ligand. Molecules are bonded together by means of interactions consisting of the donation of lone pairs of electron on carboxylate O atoms on one molecule to the Mo atom on an adjacent complex. A new pattern of intermolecular bonding is observed.     

Water desorption isotherms of cellulose-acetate membranes

 The water desorption isotherms are determined in three cellulose acetate membranes with different acetyl content as a function of p/p ₀ at 10–40 °C. The partition coefficients (adsorbed water over water pressure) show a minimum at p/p ₀=0.5–0.6. This indicates a two energy mechanism. The agreement of our results with the BET adsorption isotherms only till p/p ₀<0.3 shows that a two energy adsorption mechanism is valid only for small water contents, probably one hydrate layer and a second more liquid-like water layer. At large p/p ₀, the adsorbed water becomes more and more liquid like by polarization of the hydrogen bonds. The heat of desorption is larger than the vaporization heat of water ΔH _vap(H₂O). It decreases with increasing water content asymptotically to ΔH _vap(H₂O). The cause may be a larger van der Waals interaction of the hydrate layer due to coordination numbers larger than 4.4 as in liquid water. Additionally, we found a hole adsorption process by sorbing unpolar solvents. The water and methonal adsorption are 100 times larger due to a swelling mechanism depending on the number of acetyl groups in the membranes. The amounts of n-alcohols sorbed decrease with their chain length. Received: 25 April 1997 Accepted: 10 June 1997