José Roberto Tozoni

Sublattice magnetism in σ-phase Fe100-xVx (x=34.4, 39.9, and 47.9) studied via zero-field 51V NMR

The first successful measurements of a sub-lattice magnetism with 51V NMR techniques in the sigma-phase Fe(100-x)Vx alloys with x = 34.4, 39.9 and 47.9 are reported. Vanadium atoms present on all five crystallographic sites are magnetic. Their magnetic properties are characteristic of a given site, which strongly depend on the composition. The strongest magnetism exhibit sites A and the weakest one sites D. The estimated average magnetic moment per V atom decreases from 0.36 muB for x = 34.4 to 0.20 muB for x = 47.9. The magnetism revealed at V atoms is linearly correlated with the magnetic moment of Fe atoms, which implies that the former is induced by the latter.

PMMA/MEH-PPV Photoluminescent Polymer Blend as a Long Time Exposure Blue-light Dosimeter

In the present paper the photoemission intensity versus excitation exposure time of host/guest photoluminescent polymer blend has been investigated. The polymer blend was composed by poly(methyl methacrylate) (PMMA) as a host, and Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV) as a guest. The photoluminescent blend was characterized by optical absorbance and steady-state photoluminescence spectroscopy. The PMMA/MEH-PPV blend film presented high homogeneity and high photoemission intensity. Moreover, the PMMA/MEH-PPV blend film photodegradation in function of sample exposure time to the blue-light excitation curve presented long biexponential time decay. These results suggest that the PMMA/MEH-PPV blend film could be used as a long time exposure blue-light

Nanomolding the Surface of Polymer Films.

Slight changes in the experimental procedures of the micro contact printing (ACP) technique are introduced here, which allow for using polymers soluble in distinct solvents to fabricate submicrometric 2D periodic structures. Highly reproducible secondary and tertiary poly(dimethylsiloxane) (PDMS) molds could be produced, as demonstrated in atomic force microscopy images and light diffraction experiments. The replication of tertiary molds with no residues of PDMS demonstrates the feasibility of large-scale production with distinct polymers. The plane wave propagation along the tertiary poly(3,4-ethylenedioxythiophene) with poly(hydrogen 4-styrene sulfonate) molds was simulated with a finite-difference time-domain algorithm. A strong wave propagation was observed in the region containing the structures acting as a wave guide, in agreement with the results from the experimental absorption measurements. Furthermore, we show that the optical properties of the molds and their roughness can be tuned by choosing the polymers (including biopolymers) for printing pillars and tracks, thus bringing new possibilities for nanomolding of polymer surfaces for photonics, organic electronics and bioelectronics.