X-ray reflectivity measurements of layer-by-layer films at the solid/liquid interface

In this Letter, we present a method for the decoration of layer-by-layer (LbL) structures by heavy metal ions, which allows X-ray reflectivity (XRR) measurements at the solid/water interface. The improved contrast has allowed us to obtain well-structured X-ray reflectivity curves from samples at the liquid/solid interface that can be used for the film structure modeling. The developed technique was also used to follow the formation of complexes between DNA and the LbL multilayer. The XRR data are confirmed by independent null-ellipsometric measurements at the solid/liquid interface on the very same architectures.     

Interaction of DNA oligomers with cationic lipidic monolayers: complexation and splitting

Interactions of native DNA with octadecylamine (ODA) and hexadecymdimethylammonium bromide (HTAB) monolayers at the air/water interface were studied by pi-A isotherms, ellipsometry, and X-ray reflectivity. We show that the microscopic structure of ODA-DNA complexes is definitely consistent with a single-stranded form for DNA. On the contrary, with HTAB, DNA complexes in its native form. The crucial difference in the behavior of these two fairly similar lipids is due to the presence of the amine group in ODA. These results should be relevant to applications such as DNA chips and sensors.     

A μ+SR study of the magnetic properties of ferritin

We present a study of the magnetic properties of the superparamagnetic ferritin system by employing zero‐field (ZF) and longitudinal‐field (LF) μ⁺SR measurements. Two μ⁺ fractions with different depolarisation behaviour are detected, one arising from muons stopped in the organic shell and one from muons stopped in the mineral core. The freezing of the superparamagnetic moments is evident in the temperature evolution of the ZF relaxation rates of both fractions. It occurs gradually below \approx 60\ K and is essentially complete at \approx 11\ K. The results are consistent with a distribution of blocking temperatures which in turn reflects the distribution of core sizes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnetism and superconductivity in La1.875Ba0.125-ySryCuO4+\delta and La1.6-yNd0.4SryCuO4

μ+SR and neutron diffraction measurements show that at low temperatures in La_1.875 Ba_0.125 CuO₄, there is phase separation into a long range ordered magnetic component of SDW‐like nature, identified with the LTT phase and a superconducting component, identified with the LTO phase. Partial substitution of Ba by Sr at a fixed doping level of 1/8 leads to gradual decrease of the magnetic freezing temperature, accompanied by a decrease in the fraction of the magnetic component. The La_1.875 Ba_0.025 Sr_0.100 CuO_4 composition exhibits freezing of the Cu electronic moments into a disordered arrangement. Excess interstitial oxygen leads to a rapid recovery of superconductivity and a marked depression of the magnetic volume fraction. Study of the LTT phase – after stabilisation with partial substitution of La by Nd – away from the 1/8 doping level, reveals no evidence of long range magnetic ordering with magnetic fluctuations surviving down to 3 K. This revised version was published online in August 2006 with corrections to the Cover Date.