Preparation of gold nanoparticles (GNP) aqueous suspensions by a new method involving Tiron

A new method is proposed to produce gold nanoparticles (GNP) by in situ reduction of a gold salt dissolved in water. The reducing agent used is Tiron instead of the citrate anion most often mentioned in literature. The influence of various parameters has been investigated, such as the content of Tiron with respect to that of the precursor of gold HAuCl₄, or the initial pH of the solution after mixing of reactants. It is shown that Tiron also exerts a positive influence as a dispersant, which impedes agglomeration of gold nanoparticles. The typical average size of GNP synthesized in the present work is close to 7 nm.     

Repulsive Flux Pinning Force in NbTi/Nb Superconductor/Superconductor Multilayers

Flux pinning characteristics have been investigated for the Nb _x Ti_100-x /Nb(x = 65, 50 and 28) and Nb ₂₈ Ti ₇₂/Nb ₆₅ Ti ₃₅ superconductor(S)/superconductor(S^′) multilayers. The maximum of the pinning force F _{p⊥ max} perpendicular to the layer plane as a function of the structure modulation length λ has a peak in the quasi-two-dimensional region (λ～20 nm). The maximum. values of the F _{p⊥ max} versus λ curve are proportional to the difference of the GL coherence length (ξ _GL ) between the superconductive sublayers S and S^′. The results suggest that the large F _{p⊥ max} in the S/S^′ multilayer is caused by the repulsive pinning force due to Nb layers with larger ξ _GL .