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We studied by ESR the rotational motion of a paramagnetic tracer (a deuterated 15N-enriched nitroxide) in poly(vinyl acetate) (PVAc). The reorientation of the tracer occurs via jumps of about 50° with a heterogeneous distribution of correlation times. Depending on the temperature range, the average correlation time 〈τ〉 scales as the α, β, and γ relaxation times of PVAc, i.e., 〈τ〉 = C i 〈τ〉 i , i = α, β, γ. On cooling, 〈τ〉 tracks the α relaxation to about the α−β bifurcation temperature and then the β relaxation down to the glass transition. In glassy PVAc 〈τ〉/〈τ〉γ = C γ ≈ 1.

Ferroelectric domain kinetics on cleaved triglycine sulfate, quenched at different temperatures in the ferroelectric phase, is investigated in situ by scanning force microscopy in the dynamic contact mode. Thermally activated domain growth and dynamic scaling, in accordance with theoretical predictions for quenched disorder due to random-bond defects, is inferred from the temporal evolution of the spatial correlation functions and the related characteristic length scale.

Evidence of noise-induced effects in electron-paramagnetic-resonance (EPR) experiments is reported. The first observation of a stochastic resonance phenomenon in an EPR system operating in bistable conditions has been obtained. Experimental results indicate unambiguous effects on the frequency and phase of the response of the modulated bistable system in the presence of noise. Possible new progressions in the treatment of both theoretical and experimental stochastic resonance phenomenon are perceived. 05.40.+J

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Voltage-modulated scanning force microscopy has been employed to investigate the dynamics of ferroelectric domains as a function of time and temperature in triglycine sulfate ͑TGS͒ single crystals. Branching of the domain structure and nucleation of fine domain patterns by internal fields of thermal origin have been directly observed on the submicron scale. Domain coarsening after quenching TGS samples from the paraelectric phase into the ferroelectric one has been studied, revealing a nonlinear time dependence of the characteristic correlation domain length and supporting the validity of dynamical scaling law and the conservation of the total surface charge. Substantial differences in the evolution of the domain structure have been detected during cooling or heating treatment in the ferroelectric phase. Domain contrast is shown to monitor the ferroelectric phase transition through its temperature dependence, reflecting the competition between electrostatic and piezoelectric effects.

A couple of experimental techniques have been implemented to an aperture near-field scanning optical microscopy (NSOM) to obtain reliable measurement of sample dichroism on the local scale. First, a method to test NSOM tapered fiber probes toward polarization conservation into the near optical field is reported. The probes are characterized in terms of the in-plane polarization of the near field emerging from their aperture, by using a thin dichroic layer of chromophore molecules, structured along stretched polymeric chains, to probe such polarization when approached in the near-field region of the probe. Second, to assure that the light intensity coupled in the fiber is polarization independent, an active system operating in real time has been realized. Such combination of techniques allowed quantitative imaging of local dichroism degree and average orientation by means of dual-phase lock-in demodulation of the optical signal. Translation of the coupled light polarization state in the near field has been observed for one-half of the tested probes. For the others, the tip acts as a polarizer, and therefore showed it was not suitable for polarization modulation NSOM measurements