ABSTRACT
The DC magnetron sputter grown Co/Ti multilayers, with ultra-low bi-layer thicknesses and with Co layers deposited under mixed ambience of argon and dry air, have been investigated for use in the water window soft x-ray regime of 23-44 Å. Initially, deposition parameters have been optimized for obtaining smooth and continuous low thickness Co and Ti single-layer films, and, then, multilayers with five bi-layers of various bi-layer thicknesses were deposited. The samples have been primarily characterized by the grazing incidence x-ray reflectivity (GIXR) measurements with a hard x-ray laboratory source. Subsequently, a set of multilayers with an increasing number of bi-layers has been deposited with a constant bi-layer thickness of 42 Å. GIXR results show that hard x-ray reflectivity at the first Bragg peak is maximum for the 20 bi-layer sample, beyond which the reflectivity decreases. Finally, the samples with the most promising hard x-ray GIXR have been used for soft x-ray reflectivity measurement with synchrotron radiation, and â¼2.5% peak reflectivity has been obtained in the multilayer sample at a 30.7 Å wavelength for a 21.5° grazing angle of incidence. The fitting results for both hard and soft x-ray reflectivities have been thoroughly investigated to find out the cause of the saturation of reflectivity with the increase in the number of bi-layers.
ABSTRACT
Brillouin scattering in liquids composed of optically and mechanically anisotropic molecules is affected by coupling between rotational and translational dynamics. While this effect has been extensively studied in depolarized (VH) scattering where it produces the "Rytov dip," recent theoretical analyses by Pick, Franosch show that it should also produce observable effects in polarized (VV) scattering [Eur. Phys. J. B 31, 217 (2003)]; 31, 229 (2003)]]. To test this theory, we carried out Brillouin scattering studies of the molecular glassformer salol in the temperature range 210-380 K, including VH-backscattering, VH-90 degrees, and VV-90 degrees spectra. The data were analyzed consistently to determine the effects of rotation-translation coupling on both the polarized and depolarized spectra. A previously unanticipated feature predicted by these authors was observed: a narrow negative region in the q -dependent part of the 90 degrees VV spectra, which we designate as the "VV dip." It is an analog of the Rytov dip observed at high temperatures in the 90 degrees VH spectra, which is also accurately described by this theory. Analysis of the 90 degrees VV spectra was carried out both with and without inclusion of translation-rotation coupling in order to determine quantitatively the role this coupling plays.
ABSTRACT
The "knee" found in the depolarized light scattering spectra of Ca0.4K0.6(NO3)(1.4) at low temperatures by G. Li, W.M. Du, X.K. Chen, H.Z. Cummins, and N.J. Tao [Phys. Rev. A 45, 3867 (1992)] appears to have been an experimental artifact. The origin of this feature is analyzed, and its implications for the mode coupling theory of the liquid-glass transition are considered.
