Spectroscopic characterization of Al2O3-Ni selective absorbers for solar collectors

Cataloged from PDF version of article.Optical spectroscopy of electrochemically prepared Ni-pigmented aluminum oxide selective absorbers have been determined in the 200—20000 nm range. It was found that samples anodized under the same conditions and pigmented using nickel acetate resulted in better thermal emittance values when compared with nickel sulfate although both have comparable solar absorbance values. Electron spectroscopic investigation revealed that only a small fraction of Ni is present on the surface with an oxidation state of *#2. The O/Al ratio determined by XPS is larger than 1.5. This information together with the measured Al 2p Auger parameter indicated that the surfaces contain additional OH groups which was also confirmed by the presence of a broad hyrogen-bonded band in the region 3000—3400 cm~1 observed in the reflection—absorption IR spectra of these samples. ( 1998 Elsevier Science B.V. All rights reserved

Elliptic flow in a strongly interacting normal Bose gas

We study the anisotropic, elliptic expansion of a thermal atomic Bose gas released from an anisotropic trapping potential, for a wide range of interaction strengths across a Feshbach resonance. We show that in our system this hydrodynamic phenomenon is for all interaction strengths fully described by a microscopic kinetic model with no free parameters. The success of this description crucially relies on taking into account the reduced thermalising power of elastic collisions in a strongly interacting gas, for which we derive an analytical theory. We also perform time-resolved measurements that directly reveal the dynamics of the energy transfer between the different expansion axes

Diffraction of complex molecules by structures made of light

We demonstrate that structures made of light can be used to coherently control the motion of complex molecules. In particular, we show diffraction of the fullerenes C60 and C70 at a thin grating based on a standing light wave. We prove experimentally that the principles of this effect, well known from atom optics, can be successfully extended to massive and large molecules which are internally in a thermodynamic mixed state and which do not exhibit narrow optical resonances. Our results will be important for the observation of quantum interference with even larger and more complex objects.Comment: 4 pages, 3 figure

Renormalization Group Approach to the Coulomb Pseudopotential for C_{60}

A numerical renormalization group technique recently developed by one of us is used to analyse the Coulomb pseudopotential (${\mu^*}$) in ${{\rm C}_{60}}$ for a variety of bare potentials. We find a large reduction in ${\mu^*}$ due to intraball screening alone, leading to an interesting non-monotonic dependence of ${\mu^*}$ on the bare interaction strength. We find that ${\mu^*}$ is positive for physically reasonable bare parameters, but small enough to make the electron-phonon coupling a viable mechanism for superconductivity in alkali-doped fullerides. We end with some open problems.Comment: 12 pages, latex, 7 figures available from [email protected]