Laser-Induced generation of thin silicone layers with high chemical and spectral purity

Excimer lasers (ArF, λ = 193 nm, and KrF, λ = 248 nm) were used to generate polymers free of additives such as catalysts, initiators, or sensitizers. The layers obtained are of potential interest for medical applications and future molecular electronics. Dimethylpolysiloxanes and dimethylsiloxane copolymers that contain phenyl-, n-hexyl- or 3.3.3-trifluoropropyl groups or silicon-bound hydrogen atoms were crosslinked in the liquid phase, whereby layer thicknesses in the range from 1–300 μm were obtained. Disiloxanes and alkoxysilanes were deposited from the gas phase (LCVD, laser chemical vapor deposition) resulting in layer thicknesses below 1 μm. In almost all cases, organic layers with a smooth surface, transparency, and good adhesion were obtained on silicon as well as quartz substrates. © 1994 John Wiley & Sons, Inc.     

Phonon density-of-states for high-T c (Y,RE) Ba2Cu3O7 superconductors and non-superconducting reference systems

From inelastic neutron scattering experiments, we determined the generalized phonon density-of-states (PDOS) for the high-T _c superconductors MEBA₂Cu₃O₇ (ME=Y, Y_0.5Pr_0.5, Nd) and the non-superconducting references YBa₂Cu₃O₆ and PrBa₂Cu₃O₇. A detailed study of the Y-O₇ compound at temperatures between 300 K and 6 K gave no evidence of any pronounced soft-mode behaviour. Moderate changes only occur in the PDOS between Nd and Pr samples and Y and Y_0.5Pr_0.5 samples, respectively, but drastic differences show up in the Y-O₇ and Y-O₆ spectra. Thus, we could not find correlations betweenT _c -values and particular features in the PDOS although there is some evidence that electron-phonon coupling is strong in this class of materials.     

First observation of a negative elastic constant in intermediate valent TmSe

The sound velocities v_L, v_T1 and v_T2 have been measured at 15 MHz on Tm³⁺_0.87Se and Tm^2.8+_0.99Se between 300 K and 4.2 K and the elastic constants c_ij have been derived. In intermediate valent Tm^2.8+_0.99Se c₁₂ turned out to be negative. This sign is interpreted as being typical for intermediate valent compounds. Also for the first time experimental evidence is given for crystal field effects in Tm³⁺_0.87Se. Strong elastic nonlinearities are observed in intermediate valent Tm^2.8+_0.99Se with uniaxial pressure.     

The Wickbold combustion method for the determination of mercury under statistical aspects

The combination of the Wickbold combustion apparatus with a mercury/hydride atomic absorption spectrometer for the routine determination of mercury is investigated. A flow injection system is used to introduce the solution from the decomposition into the spectrometer. The data obtained are treated by several statistical tests which have been recommended for quality control purposes. Simplicity of the statistical treatment is emphasized. The mercury content of certified reference materials is determined using the Wickbold combustion unit, and the resulting data are analyzed statistically.     

Conductivity study of stretch-oriented new polyacetylene

Oriented polyacetylene samples were synthetized and doped with iodine and FeCl₃. Their electric conductivity and anisotropy were measured within the temperature range 4-300 K. The results were described using the Ping Sheng model. It is concluded that the factors limiting the conductivity parallel and perpendicular to the stretching direction are the same and thus no interfibrillar conduction occurs. Some processes related to the mechanical stretching are discussed. © 1994 John Wiley & Sons, Inc.