Induction of hormesis in plants by urban trace metal pollution

Hormesis is a dose–response phenomenon observed in numerous living organisms, caused by low levels of a large number of stressors, among which metal ions. In cities, metal levels are usually below toxicity limits for most plant species, however, it is of primary importance to understand whether urban metal pollution can threaten plant survival, or, conversely, be beneficial by triggering hormesis. The effects of Cd, Cr and Pb urban concentrations were tested in hydroponics on three annual plants, Cardamine hirsuta L., Poa annua L. and Stellaria media (L.) Vill., commonly growing in cities. Results highlighted for the first time that average urban trace metal concentrations do not hinder plant growth but cause instead hormesis, leading to a considerable increase in plant performance (e.g., two to five-fold higher shoot biomass with Cd and Cr). The present findings, show that city habitats are more suitable for plants than previously assumed, and that what is generally considered to be detrimental to plants, such as trace metals, could instead be exactly the plus factor allowing urban plants to thrive

Simbol-X Hard X-ray Focusing Mirrors: Results Obtained During the Phase A Study

Simbol-X will push grazing incidence imaging up to 80 keV, providing a strong improvement both in sensitivity and angular resolution compared to all instruments that have operated so far above 10 keV. The superb hard X-ray imaging capability will be guaranteed by a mirror module of 100 electroformed Nickel shells with a multilayer reflecting coating. Here we will describe the technogical development and solutions adopted for the fabrication of the mirror module, that must guarantee an Half Energy Width (HEW) better than 20 arcsec from 0.5 up to 30 keV and a goal of 40 arcsec at 60 keV. During the phase A, terminated at the end of 2008, we have developed three engineering models with two, two and three shells, respectively. The most critical aspects in the development of the Simbol-X mirrors are i) the production of the 100 mandrels with very good surface quality within the timeline of the mission; ii) the replication of shells that must be very thin (a factor of 2 thinner than those of XMM-Newton) and still have very good image quality up to 80 keV; iii) the development of an integration process that allows us to integrate these very thin mirrors maintaining their intrinsic good image quality. The Phase A study has shown that we can fabricate the mandrels with the needed quality and that we have developed a valid integration process. The shells that we have produced so far have a quite good image quality, e.g. HEW <~30 arcsec at 30 keV, and effective area. However, we still need to make some improvements to reach the requirements. We will briefly present these results and discuss the possible improvements that we will investigate during phase B.Comment: 6 pages, 3 figures, invited talk at the conference "2nd International Simbol-X Symposium", Paris, 2-5 december, 200

Interplay between magnetic anisotropies in CoAu and Co films and antidot arrays: Effects on the spin configuration and hysteretic behavior

We studied (i) a set of three Co:Au continuous films, grown by sputtering co-deposition (∼80 nm thick) with concentration ratios of 2:1, 1:1 and 1:0 (i.e., a pure Co film was also included), and (ii) a corresponding set of antidot arrays, produced by nanosphere lithography with the same hexagonal pattern (nominal lattice periodicity ∼520 nm). The samples were investigated by atomic and magnetic force microscopy and SQUID magnetometry. A twofold aim was fulfilled: to gain information on the magnetism of the CoAu compound (saturation magnetization, effective in-plane and out-of-plane anisotropy, exchange stiffness constant and magnetostrictive behavior) and to compare the magnetic behavior of the continuous and patterned samples. The continuous films exhibited a variety of hysteretic behaviours and magnetic configurations, ruled by the interplay between different magnetic anisotropy terms (magnetocrystalline, magnetoelastic and shape). The Co1Au1film was anisotropic in the plane, whereas Co2Au1and Co were isotropic and had an out-of-plane magnetization component; stripe domains were observed in Co2Au1, resulting in a transcritical hysteresis loop. A key role in determining these properties was ascribed to the magnetoelastic anisotropy term. Unlike the continuous films, the antidot arrays showed a similar hysteretic behavior and important similarities in the spin configuration were pointed out, despite the different compositions. We argue, also based on micromagnetic simulations, that this occurred because the nanopatterning enabled a local modification of the shape anisotropy, thus smoothing out the differences observed in the continuous films

Amorphous intermixing of noble and magnetic metals in thin film-based nanostructures

In nanostructures made of a mixture of bulk-immiscible metallic species, the alloy formation down to the atomic scale is a crucial and debated point. We report on the first experimental evidence of an amorphous metallic phase in Au-Co thin films and 2D array of nanostructures, that is constituted by a fine mixing of single-metal (sub)-nm domains, as shown by experiments coupling short- and long range- order characterization techniques, as X-ray Absorption Spectroscopy-XAS, X-ray Diffraction-XRD, Diffraction Anomalous Fine Structure-DAFS. Despite the mixing does not reach the atomic scale, the extended Au-Co interface can entail about half of atoms, and is responsible for the previously measured magnetic moment of Au in these systems. This amorphous nanomixed phase coexists with a minor fraction of fcc AuxCo1-x nanocrystals, preferentially oriented with the 111 crystallographic planes parallel to the film surface. 2D patterned Au-Co films with very similar structure can be easily obtained, but with smaller and randomly oriented nanocrystals. The thermal stability of the system (amorphous and crystalline) is limited to below 250 \ub0C. At higher temperatures an extended decomposition occurs and Au and fcc Co nanocrystals coexist

Magnetic study of nanocomposite films consisting of ultrafine Co particles embedded in a ferromagnetic AuCo alloy

Nowadays, the search for innovative nanocomposite systems consisting of at least two different magnetic phases is attracting remarkable attention. Indeed, the intimate mixing of the different phases at the nanoscale level may give rise to new materials showing unique properties. In particular, a fine tuning of their overall magnetic anisotropy may be obtained and, accordingly, of their magnetic hysteretic properties. In this framework, we present an in-depth study of the magnetic properties of a set of three AuCo films, ~ 30 nm thick, with different Au:Co concentration ratio (2:1, 1:1, 1:2). The samples were grown by magnetron sputtering co-deposition technique on naturally oxidized (100)-Si substrates, and it turns out that this method allows the alloying of Au and Co and the production of a bimetallic compound is achieved to a good extent. The samples mainly consist of a structurally disordered ferromagnetic alloy in which segregated Co particles (~ 2 nm in size) are dispersed and the two phases are finely intermixed. Magnetization measurements, performed with a SQUID magnetometer in the 6 K - 300 K temperature range, have pointed out a peculiar hysteretic behavior, especially well visible in samples Au1Co1 and Au1Co2, characterized by in-plane anisotropy and crossed branches in the loops measured along the hard magnetization direction (Fig. 1(a)). To elucidate the origin of this behavior, micromagnetic calculations have been carried out using the object-oriented micromagnetic framework (OOMMF) code. The calculations have been performed for a simplified system made of two exchange-coupled ferromagnetic phases: an AuCo matrix surrounding a Co cluster, i.e. an aggregate of smaller Co particles. Indeed, our experimental results suggest that the exchange coupling of the Co particles with the surrounding matrix may result in the formation of magnetic clusters. So our model emphasizes both the nanocomposite nature of the investigated samples and the role of interparticle magnetic interactions. The main features of the hysteretic behavior are qualitatively well reproduced provided that the two phases have almost orthogonal magnetic anisotropy axes. We hypothesize a dominant magnetoelastic character of the anisotropy in both phases and we discuss how this requirement can be plausibly fulfilled

Thin film and multilayer coating development for the extreme ultraviolet spectral region

B4C optical coating represents, together with Ir, Pt, SiC, one of best choice for high reflectance in the extreme ultraviolet region. This material is also used combined with others materials in multilayer such as Si/B4C or as interlayer in Mo/Si multilayer to avoid interdiffusion. In this study we have performed optical, compositional and structural analyses for thin film of B4C deposited by means of magnetron sputtering and on preliminary samples deposited by e-beam evaporation. Here we report reflectivity measurements and the derived optical constants of B4C in the 400\u20131500 \uc5 region

Effects of ion bombardment and gas incorporation on the properties of Mo/a-Si:H multilayers for EUV applications

A study of Moya-Si:H multilayer for EUV mirrors produced by rf-magnetron sputtering in pure Ar, Xe and AryH2 gas mixtures is presented. The high reflectance mirrors are designed for solar space experiments at 17, 19 and 30.4 nm and for the lithography applications at 13 nm. The multilayers are grown in different ion bombardment conditions determined by different bias levels of the substrate. Plasma diagnostics are performed to correctly evaluate flux and energy of plasma ions bombardment. The a-Si:H layers have been obtained by introducing H2 gas in the sputtering chamber at different partial pressures during silicon deposition. The deposition rates as well as the composition of Mo and Si layers have been investigated by Ion Beam Analysis (RBS and ERDA). The coating microstructure has been characterised primarily by X-ray micro-diffraction (micro-XRD). X-Ray Reflection analysis (XRR) has been carried out to investigate the layer density and the multilayer structure. RBS analyses show that noble gas (Ar, Xe) incorporation is limited to the Si layers and depends on the sample bias. Noble gas concentration is correlated to the different ion bombardment growth conditions that influence also the (110) orientation of Mo nano-crystals. ERD analyses of Si layers show hydrogen incorporation up to 30 at.% as a function of the H2 partial pressure. Hydrogen incorporation leads to a decrease of the a-Si layer density. Hydrogen content in Mo layers is less than 0.5 at.% even at the highest H2 partial pressure. The optical properties of these mirrors have been characterised by EUV reflection measurements