R. Pizzoferrato

High‐resolution simultaneous photothermal measurements of thermal parameters at a phase transition with the photopyroelectric technique

Photothermal techniques allow, under particular experimental conditions, the simultaneous determination of specific heat, thermal conductivity, and thermal diffusivity. A comparison has been made between measurements performed with the gas‐microphone (P) configuration and the photopyroelectric (PPE) one at a liquid‐crystal second‐order phase transition. An increase in the sensitivity with respect to thermal parameter variation has been observed in the case of PPE.

Second-harmonic generation and absorption spectra of platinum organometallic complexes incorporated in PMMA films

Pt-acetylides with different end-side groups have been synthesized and incorporated in poly(methylmethacrylate) (PMMA) films for second-order nonlinear optics through high-temperature corona-poling. By using two complementary optical techniques, i.e. in-situ second-harmonic generation (SHG) and angle-resolved spectroscopy, the order parameter and the molecular hyperpolarizability β of the chromophores have been characterized inside the polymer matrix. The relaxation of orientational after order poling fits a bi-exponential equation in agreement with the Debye model for guest/host systems. A comparison with the azo-dye Disperse Red 1 (DR1) is discussed within the two-level model and the role of the platinum moiety for conjugated molecules.

Simultaneous absolute measurements of the thermal diffusivity and the thermal effusivity in solids and liquids using photopyroelectric calorimetry

We report on the simultaneous “absolute” measurements of the thermal diffusivity and of the thermal effusivity in solid and liquid samples by using only the phase of the so called self-normalized Photopyroelectric signal, performing no other normalization/calibration procedure than that carried out during the actual measurements. Measurements, performed as a function of temperature, are characterized by a temperature resolution adequate to study phase transitions. The obtained results are in excellent agreement with those obtained in the previous studies.

Optical investigation of infrared dyes in hybrid thin films

We report on steady-state absorption and emission measurements for two infrared (IR) dye molecules, IR5 and IR1051, incorporated in hybrid organic/inorganic zirconia-based thin films synthesized with a sol-gel technique. For comparison, measurements in liquid solutions have also been carried out, and an estimation of the relative quantum efficiency in solid glassy material with respect to liquid solution is reported. Absorption and emission spectra are discussed in terms of physical and chemical interactions with the host matrix. The present work provides the evidence of successful doping of solid films with dyes for planar waveguides emitting in the infrared region up to 1.3 μm.

Ion dose effect in subgap absorption spectra of defects in ion implanted GaAs and Si

Subgap optical absorption investigations have been used to study the influence of increasing ion dose on the properties of ion implanted layers of Si and GaAs. Beside the spectral region corresponding to the band edge region, a second region at lower energy, also exhibiting an exponential behavior but with a substantially larger value of the inverse logarithmic slope, has been observed in all the investigated samples. A common trend has been observed for ion implanted Si and GaAs in the dependence of the values of the lower energy region inverse logarithmic slope as a function of the implantation dose, and it depended on the presence or not of amorphous material in the implanted layer. The results are discussed in terms of a possible evolution of gap states responsible for the observed features.

Optically induced reorientational birefringence in an artificial anisotropic Kerr medium

Abstract A laser induced optical birefringence has been obtained for the first time in an anisotropic artificial Kerr medium. This consists of an aqueous suspension of dielectric microellipsoids which reorientate under electromagnetic and brownian torques. The measured effective optical Kerr coefficients, n 2 , is 4.0x10 -4 cm 2 /MW while the response time is 2.6 ms. These values agree with the ones obtained from a simple Debye model assuming rigid anisotropic rotors in a statistical environment.

DODCI molecules incorporated in sol-gel glasses: The interaction with the silica matrix

Abstract The optical properties of the dye DODCI (3,3′-diethyloxadicarbocyanine iodide) incorporated in sol–gel silica-glass matrices have been investigated with regard to interaction with the surrounding silica cage. The absorption and emission spectra have been measured in silica-glass samples with different pore sizes and compared with the spectra obtained in liquid solutions that simulate different environments for the dye molecule. Measurements of a DODCI-derivative molecular structure have been performed by NMR spectroscopy in dimethyl sulfoxide. The results suggest that new electronic states are produced in the trapped molecule, for glass-pore sizes in the range of 2.5–3.5 nm, as a result of the attack of Si–O − groups on the conjugate chain and the protonation to the dicationic form.

Surface states and buried interface states studies in semiconductors by photothermal deflection spectroscopy

A method is presented which, through the simultaneous analysis of the photothermal deflection spectroscopy (PDS) signal amplitude and phase spectra, enables to detect surface states and buried interface states and to measure their absorption. A theoretical model for the PDS signal suitable for the present approach has been developed and the measurements were performed on single crystalline GaAs wafers with ion‐implanted layers on the front surface or buried beneath the front surface.

Optical investigation of infrared dyes in sol–gel films

We report on absorption and emission measurements relative to four different infrared (IR) dye molecules (IR1051, IR26, IR5 and IR1100), incorporated in hybrid organic/inorganic zirconia-based thin films synthesised with sol-gel technique. For comparison, measurements in liquid solutions have also been carried out. An estimation of the relative quantum efficiency in solid glassy material with respect to liquid solution is reported for the IR1051 specie. Absorption and emission spectra are discussed in terms of physical and chemical interactions with the host matrix. To our knowledge, this is the first evidence of successful doping of solid films with dyes for planar waveguides emitting in the infrared region up to 1.3 μm.

Surface states studies in semiconductors by photothermal deflection spectroscopy

A method based on the analysis of both the amplitude and phase of the photothermal deflection spectroscopy signal which enables one to locate surface states on the front or rear surface of semiconductor wafers and to measure their absorption. The procedure also allows the determination of the sample thermal conductivity.