The critical behavior of the specific heat, thermal conductivity, and thermal diffusivity at the smectic-A–nematic phase transition of aligned octylcyanobiphenyl (8CB) has been studied with the photopyroelectric technique. Though the values of the thermal transport parameters are substantially different for homeotropic and planar alignment, it has been shown that the thermal diffusivity critical behavior is characterized by the same critical exponent in the two cases. This result suggests that the mode couplings that govern the critical dynamics associated with the thermal parameters are isotropic. The thermal conductivity remains substantially flat, with only a minor increase close to the transition temperature. © 1996 The American Physical Society.

The dynamic as well as the static critical behavior associated with the thermal parameters was investigated over the smectic-A– nematic phase transiton of octyloxythiolbenzoate (8¯S5) through the simultaneous determination of the specific heat, thermal conductivity, and thermal diffusivity obtained by the photopyroelectric technique. The critical exponent of the specific heat is close to the one predicted for three-dimensional XY like (n=2,d=3) transitions, such as the superfluid transition in helium. A dip in the diffusivity was observed and the critical exponent results were consistent with a dynamic model, also with n=2 and d=3, which considered dissipative couplings between the order parameter and the conserved energy density in the free energy functional. A smooth thermal conductivity has been obtained over the transition temperature. © 1996 The American Physical Society.

We report on an approach for photopyroelectric calorimetry enabling a frequency dependence detection of the specific heat and of the latent heat exchanged over first order transitions. It has been applied to the nematic-isotropic transition of 4-$n$ -octyl-$4^{\prime }$ -cyanobiphenyl liquid crystal confined in a silica nanoparticles network, where the specific heat shows a double peak structure. The larger strain involved with the nematic nucleating over the low temperature peak induces a considerable lower latent heat than the one involved over the higher temperature peak. The frequency dependent measurements have shown a different dynamics of the nematic nucleating over the two peaks.

A detailed study of the implantation-induced damage in Si on sapphire, carried out by optical-absorption measurements extending from energies above the band gap down to energies far into the subgap region of Si, is presented. The changes induced in the optical band gap, band-edge slopes, and in the subgap features of the spectra are carefully described. The various stages of formation and quenching of divacancies were monitored as a function of implantation conditions and annealing cycles through their 1.8-μm absorption band. It is shown that the divacancies strongly affect the population of band-tail states and the annealing studies revealed that the progressive quenching of the divacancy band is followed by the appearance of another absorption band, characteristic of some intrinsic secondary defect, whose annealing behavior is similar to the one observed for the five-vacancy electron-paramagnetic-resonance spectrum. The study of the structural relaxation process in implanted a-Si gave indications that the process is indeed associated with annihilation of defects as well as average strain reduction in the material, in agreement with earlier indications. Finally, some common features, such as band-edge inverse-logarithmic slope values and subgap features, are found in annealed implanted crystalline and a-Si.

We report on the high-temperature resolution measurements of the optical and thermal parameters of a liquid-crystal–silica nanoparticle colloid, as well as its video inspection, simultaneously performed in an upgraded photopyroelectric calorimeter. Over the nematic-isotropic coexistence region, the determined nematic correlation length, obtained from turbidity measurements, showed the characteristic two-step nematic nucleation process previously reported only for the specific heat.